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... The hydraulic performance of trees is crucially affected by vessel diameter (Tyree and Zimmermann 2002;Lucas et al. 2013;Hacke et al. 2017;Williams et al. 2019;Olson et al. 2021;Aloni 2021), which also affects wood adaptation (Aloni 1987(Aloni , 2015 and xylem pathology (Aloni and Ullrich 2008;Ullrich et al. 2019). Therefore, it is important to understand and clarify the mechanisms that control the diameter of these vascular conduits in plants. ...
... When young trees are completely debudded in late winter, before any bud activity can be observed, new earlywood vessels differentiate in ring-porous trees, but are entirely absent in diffuse-porous species (Wareing 1951;Reines 1959). Young growing leaves are known to produce the auxin hormone that moves downward and induces cambial cell divisions and the differentiation of vessels along its pathway (Snow 1935;Jacobs 1952;Sachs 1981;Aloni 1987;Scarpella and Helariutta 2010). Therefore, it was difficult to explain the cambial reactivation and wide earlywood vessel differentiation in both normal and debudded ring-porous trees. ...
... In order to explain the adaptation of plants' vascular systems to the environment, Aloni (1987) proposed the vascular adaptation hypothesis suggesting that the environment controls the plant's vascular system through its control of plant's development, height, and shape. Limiting conditions suppress plant growth and shorten the active growth period, which restrict plant development resulting in small plants. ...
The chapter clarifies the hormonal mechanisms that regulate wood formation in plants focusing on hardwood trees. Uncovering the specific role of each of the hormones: auxin, gibberellin and cytokinin in controlling vascular differentiation. Explaining the hormonal control of vessels and fibers along the plant axis from leaves to roots, and during the growth season. Clarifying how the environment, by controlling plant growth and dimensions, regulates the internal hormonal mechanisms that shape the rate of vessel widening and their final size. How the environment has modified the sensitivity of the cambium to the auxin signal during the evolution of ring-porous trees, resulting in their typical very wide earlywood vessels, followed by latewood fibers with thick secondary walls.KeywordsAuxinCambium sensitivityCytokininEarlywood vessel differentiationEnvironmental adaptationGibberellinLatewood fibers
Pattern formation
Plant evolutionRing-porous wood
... The influence of various environmental factors on the anatomy of the xylem was extensively reviewed by Creber and Chaloner (1984), but the mechanisms whereby the vascular system of plants respond or adapt to their environment remained unknown. Therefore, in order to explain the adaptation of plants' vascular systems to the environment, Aloni (1987) suggested that the environment controls the plant's vascular system through its control of plant's development, height, and shape. To explain how the ecological conditions, control the size and frequency of vessels and fibers in plants, Aloni (1987) proposed the following tripartite vascular adaptation hypothesis: ...
... Therefore, in order to explain the adaptation of plants' vascular systems to the environment, Aloni (1987) suggested that the environment controls the plant's vascular system through its control of plant's development, height, and shape. To explain how the ecological conditions, control the size and frequency of vessels and fibers in plants, Aloni (1987) proposed the following tripartite vascular adaptation hypothesis: ...
... However, their statistical correlation between vessel diameter and plant size does not explain the biological causative factors regulating this relationship. Therefore, the picture presented by Olson and Rosell (2013) is incomplete, since they ignore the well-known adapting auxin gradient mechanism causing the correlation between plant size and vessel diameter that is shaped by the environment, which is already explained and predicted by the vascular adaption hypothesis (Aloni 1987). Likewise, the review of Rosell et al. (2017) clarifies that the main driver of vessel diameter is plant size, specifically the length of the stem, which are influenced by temperature and water availability that determine maximum plant height. ...
Plants grown in extreme suppressing habitats are characterized by very narrow vessels in high density. Such vascular systems are considered adaptive safety mechanisms against drought and freezing. Conversely, forest trees and lianas, which characterize the tropics and rain forests, have low density vessels of very wide diameter at the base of their stems, which afford maximal efficiency of water conduction. To understand the mechanism that controls these changes by the environment, the vascular adaptation hypothesis proposes that the environment controls the plants vascular system through its control of plant development, height, and shape. Limiting conditions suppress plant growth and restrict plant development resulting in small plants. Conversely, favorable conditions enable more growth and consequently well-developed plants and maximal height. The height of the plant and the degree of its branching determine gradients of auxin along the plant’s axis. In small shrubs, which are typical to extreme stressful environmental conditions, the distances from the young leaves to the roots are very short and no substantial decreasing gradient of auxin can be formed. Therefore, the concentrations of IAA along these small plants are relatively high and result in the differentiation of numerous very narrow vessels in the greatest densities. Conversely, in the large trees and in long lianas, the very great distances from the young auxin-producing leaves to the roots enable a substantial decrease in auxin concentrations in their lower parts, which leads to slow conduit differentiation that allows more cell expansion, resulting in very wide vessels in low density at their base. The hypothesis was confirmed by interesting experimental results and by a survey study on a large scale of collected species from a wide range of growth conditions.
... Die einzellschichtige abaxiale Epidermis erleichtert hierbei beispielsweise die Transpiration genau an den Stellen, die aufgrund starker Behaarung zu einer erhöhten Wasserdampfresorption fähig sind (Woolley, 1964). Die vaskulären Strukturen beider biologischer Vorbilder besitzen hingegen stark lignifizierte Zellwände (Aloni, 1987;Boudet, 2000), die neben ihrer Transport-und Stabilitätsfunktion zu ausgeprägten Quellungsund Schrumpfungsbewegungen in Längsrichtung aufgrund der helikalen Anordnung ihrer Gefäßwandverstärkungen in der Lage sind (vgl. Abb. 2 in Artikel A und Abb. 1 in Manuskript B). ...
... Drake et al., 1970;Grantz, 1990 Fahn et al., 1992;Mauseth, 2000;Ben-Yehoshua & Rodov, 2003). , 1987;Speck & Vogellehner, 1988;Niklas, 1989;Speck et al., 1990;Niklas, 1992;Speck & Vogellehner, 1994;Balsamo et al., 2006). Durch die Verknüpfung (Caliaro et al., 2013). ...
... Im Vergleich zur Epidermis und zum Leitgewebe ermöglichen ihre verhältnismäßig geringen Zellwanddicken während der Dehydration zudem einen schnelleren Wasseraustausch durch Osmose zwischen benachbarten Zellen (Cath et al., 2006). Im Gegensatz dazu zeigen epider- Aloni, 1987;Niklas, 1989;Boudet, 2000). Tyree & Jarvis, 1982;Augé et al., 1990;Lenz et al., 2006). ...
... In higher plants it is composed of two kinds of conducting tissues: the phloem, through which organic materials are transported and the xylem, which is the pathway for water and soil nutrients. In angiosperms, the functional conduits of the phloem are the sieve tubes, and the most specialized conduits of the xylem are the vessels (2). Vascular development in a plant is an open type of differentiation, continuing as long as the plant grows from apical and lateral meristems. ...
... Such evidence raises endless questions as to how this hormonal signal induces and controls complex patterns of xylem and phloem, and emphasizes the need to understand where and how the IAA signal is produced and transported, what are the mechanisms that control the formation of various cell types, their relationships, dimensions, differentiation and maturation patterns in the vascular system. Nevertheless, it should be emphasized that additional growth regulators may influence vascular differentiation, such as cytokinins which increase the sensitivity of the vascular cambium to auxin (3,4), gibberellin that induces fibers (2,47), and ethylene which reduces vessel diameter and retards fiber formation (12). These hormonal signals are beyond the scope of this article and the reader is directed to reviews on these topics (2,36,51,58). ...
... Nevertheless, it should be emphasized that additional growth regulators may influence vascular differentiation, such as cytokinins which increase the sensitivity of the vascular cambium to auxin (3,4), gibberellin that induces fibers (2,47), and ethylene which reduces vessel diameter and retards fiber formation (12). These hormonal signals are beyond the scope of this article and the reader is directed to reviews on these topics (2,36,51,58). ...
... These species flower early in the spring and have separate flower and leaf buds. Studies have shown that in these species during endodormancy the vascular system of the bud is undifferentiated or not completely differentiated, and the vascular tissue progressively differentiates during endo-and ecodormancy (Ashworth, 1984;Aloni, 1987;Ashworth et al., 1992;Bartolini & Giorgelli, 1994). At the beginning of floral bud differentiation, only elongated procambial cells are present (Ashworth, 1984), and xylem conduits differentiate while floral whorls develop (Faust et al., 1995). ...
... One hypothesis focuses on competition for carbohydrates remobilized from the reserves between the cambium and buds (Bonhomme et al., 2010). Another hypothesis argues that the greater length of vessels in ring-porous species (up to 18 m vs c. 1 m in diffuse-porous) would take longer to build up than shorter vessels in diffuse-porous species (Aloni, 1987). A third hypothesis ties this difference to whether or not species produce leaves continuously during a few months (like many diffuse-porous species) or over a shorter period (like many ring-porous species), which would require a higher flux of resources earlier in the season (Aloni & Peterson, 1997). ...
In seasonally cold climates, many woody plants tolerate chilling and freezing temperatures by ceasing growth, shedding leaves and entering dormancy. At the same time, transport within these plants often decreases as the vascular system exhibits reduced functionality. As spring growth requires water and nutrients, we ask the question: how much does bud, leaf and flower development depend on the vasculature in spring? In this review, we present what is known about leaf, flower and vascular phenology to sort out this question. In early stages of bud development, buds rely on internal resources and do not appear to require vascular support. The situation changes during organ expansion, after leaves and flowers reconnect to the stem vascular system. However, there are major gaps in our understanding of the timing of vascular development, especially regarding the phloem, as well as the synchronization among leaves, flowers, stem and root vasculature. We believe these gaps are mainly the outcome of research completed in silo and urge future work to take a more integrative approach. We highlight current challenges and propose future directions to make rapid progress on this important topic in upcoming years.
... Vascular connections may demand cytological peculiarities linked to the origins of the new vascular tissues: the procambium (Kraus et al. 2002), the vascular cambium (Ferreira and Isaias 2013), or the parenchyma cells (Aranda-Rickert et al. 2017). The activation of cytological programs toward the differentiation of the vascular cells demands the intermediation of auxins and cytokinins (Aloni 1987(Aloni , 2013Ye 2002;Matsumoto-Kitano et al. 2008;Schuetz et al. 2013). The neo-vascularization mediated by these hormones (Aloni et al. 1995;Ulrich and Aloni 2000) connects the vascular system of the gall with that of the host plant, and supply the hydraulic conductivity of the new organ. ...
... However, in the intralaminar fusiform galls, the galling herbivore disrupts the pattern of vascular development by stimulating alterations in cambium activity. Even though the differentiation of vascular tissues occurs in the apex-base direction (Sachs 1981;Aloni 1987;Fahn 1990), in the intralaminar galls on I. ingoides, the galling herbivore seems to disrupt this apex-based pattern, and stimulates the production of large vessels in gall portions proximal to the petiole. Alternatively, there may be a delay in the differentiation of vascular cells, and the vessel elements may enlarge prior to cell wall lignification (Aloni and Zimmermann 1983;Aloni 2015). ...
Key message
The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate hydraulic conductivity in galls.
AbstractGall position in its host organ may be determinant for the new patterns of xylem differentiation. Leaf galls may be attached to the host leaf by a peduncle, as the extralaminar galls, or may develop in a morphological continuum with their host organ, as the intralaminar galls. Due to these two distinct positions and the related patterns of cell differentiation, gall vascular cells and tissues may vary in area and size, which were investigated in the structural features of the vessel elements in galls and in their connections with their host leaflets in three gall morphotypes associated to Inga ingoides. Also, as phytohormones orchestrate the differentiation of vascular cells, the sites of accumulation of auxins and cytokinins were detected by histochemical techniques. Besides aspects of cell differentiation, cytometric and histometric xylem features, as well as the relative water content were evaluated looking for compensatory mechanisms related to hydraulic status of the galls and the gall constriction hypothesis. The detection of auxins was related with the differentiation of new vascular cells. The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate the hydraulic conductivity in galls. Extralaminar galls develop as appendages of adventitious origin, which theoretically imply in rupture with the host leaf ontogenetical pattern. Based on the fact that gall position influences xylem cell features, the gall-constriction hypothesis was revisited with leaflet galls as models of study, but was corroborated just for the intralaminar galls.
... Our result were in accord with Aloni (1987), Barcelo et al. (1988) and Vazquez et al. (1992) who reported that Cd reduces cell division and differentiation in vascular cylinder of Cd-treated bean plants, which seems essential for both production of cambium and cambium cells differentiation into vessels and fibers leading to poor development of vascular bundles. Moreover, the differentiation of cambium to these conducting elements depends on phytohormones like auxins and cytokinins (Aloni, 1987;Bhalerao et Bennett, 2003). ...
... Our result were in accord with Aloni (1987), Barcelo et al. (1988) and Vazquez et al. (1992) who reported that Cd reduces cell division and differentiation in vascular cylinder of Cd-treated bean plants, which seems essential for both production of cambium and cambium cells differentiation into vessels and fibers leading to poor development of vascular bundles. Moreover, the differentiation of cambium to these conducting elements depends on phytohormones like auxins and cytokinins (Aloni, 1987;Bhalerao et Bennett, 2003). Lower auxin concentrations, result in slower differentiation and therefore fewer (Aloni, 1988). ...
Cadmium (Cd) is one of the most notable heavy metals because of its high mobility and toxicity towards plants. In the present study, we aimed to evaluate the effect of cadmium on growth, physiological parameters, anatomical changes and phenolic compounds content in Phaseolus vulgaris L plant. Seedlings were exposed to cadmium at 0.25; 0.5 and 1 g.l⁻¹ for 21 days. Results indicated that cadmium significantly decreased percent seed germination, embryonic radical elongation, plant dry weight, stem/root length and numbers of leaves and lateral roots. Cadmium also induced a decrease in chlorophyll and protein content with all treatments; however, sugar and proline increased significantly with 1 g.l⁻¹. Total phenolic content increased by around 43% and 32% in the above ground part and roots respectively. Flavonoids, flavonols, hydrolysable tannins and condensed tannins showed a significant increase with higher cadmium concentration. Cadmium also changed plant root and stem anatomy; a decrease in both number and size of xylem vessels and a delay in xylem differentiation were observed.
... Using the SEM method, we classified all leaves within a bud into Stages P1, P2, P3 and P4. In Arabidopsis, to achieve the final leaf morphology, leaf development is followed by the progression of trichomes [37], the provascular strand [38], enlarged epidermal cells [39], modified cellular morphology, and differentiating guard ...
... Using the SEM method, we classified all leaves within a bud into Stages P1, P2, P3 and P4. In Arabidopsis, to achieve the final leaf morphology, leaf development is followed by the progression of trichomes [37], the provascular strand [38], enlarged epidermal cells [39], modified cellular morphology, and differentiating guard cells [40]. We captured the image of tissue-like leaf primordium with only 50 µm size at Stage P1. ...
The leaf, a photosynthetic organ that plays an indispensable role in plant development and growth, has a certain ability to adapt to the environment and exhibits tremendous diversity among angiosperms. Liriodendron chinense, an ancestral angiosperm species, is very popular in landscaping. The leaf of this species has two lobes and resembles a Qing Dynasty Chinese robe; thus, leaf shape is the most valuable ornamental trait of the tree. In this work, to determine the candidate genes associated with leaf development in L. chinense, scanning electron microscopy (SEM) was employed to distinguish the developmental stages of tender leaves. Four stages were clearly separated, and transcriptome sequencing was performed for two special leaf stages. Altogether, there were 48.23 G clean reads in the libraries of the two leaf developmental stages, and 48,107 assembled unigenes were annotated with five databases. Among four libraries, 3118 differentially expressed genes (DEGs) were enriched in expression profiles. We selected ten DEGs associated with leaf development and validated their expression patterns via quantitative real-time PCR (qRT-PCR) assays. Most validation results were closely correlated with the RNA-sequencing data. Taken together, we examined the dynamic process of leaf development and indicated that several transcription factors and phytohormone metabolism genes may participate in leaf shape development. The transcriptome data analysis presented in this work aims to provide basic insights into the mechanisms mediating leaf development, and the results serve as a reference for the genetic breeding of ornamental traits in L. chinense.
... It is important when assessing sieve tube conductivity to consider that geometries are not anatomically similar throughout the plant. Auxin gradients result in cell differentiation patterns that yield increasingly wider xylem cells at increasing distances from new leaves (Aloni 1987). ...
... For vessel elements, an increasing diameter of cells has been reported to continue to increase into the roots (Aloni 1987). The six point hypothesis based on decreasing auxin concentrations, and therefore longer differentiation times, resulting in increasing cell diameter as a function of distance from the apical meristem (Aloni and Zimmerman 1983) appears to also be supported in phloem of trees in the data presented here. ...
... Autophagy thus plays a dual role: it is essential for both cell survival and cell death. In contrast, phloem sieve elements (SEs), which are living cells devoid of most organelles at maturity, present a unique case (Aloni, 1987). These elongated tubes are adapted for long-distance transport, containing only minimal cytoplasm and lacking a nucleus, Golgi apparatus, vacuoles and other organelles. ...
Background and Aims
The transformation of sieve elements (SEs) from meristematic cells, equipped with a full complement of organelles, to specialized transport tubes devoid of a nucleus, has long been enigmatic. We hypothesized a strong involvement of various degradation pathways, particularly macroautophagy in this context, emphasizing the importance of autophagic selectivity in the remaining viability of these cells.
Methods
Experiments were performed on pioneer roots of Populus trichocarpa cultivated in rhizotrons under field conditions. Through anatomical, ultrastructural and molecular analyses, we delineate the stages of phloemogenesis and the concurrent alterations in the cytoplasmic composition of SEs.
Key Results
Notably, we observed not only macroautophagic structures, but also the formation of autophagic plastids, the selective degradation of specific organelles, vacuole disruption and the release of vacuolar contents. These events initially lead to localized reductions in cytoplasm density, but organelle-rich cytoplasmic phase is safeguarded from the extensive damage by a membrane system derived from the endoplasmic reticulum. SE ultimately develops into a conduit containing electron-translucent cytoplasm. Eventually, mature SE is a tube filled only by the translucent cytoplasm, with sparse organelles tethered to the cell wall.
Conclusions
Although the activation of programmed cell death pathways was postulated, the persistence of SEs indicates that protoplast depletion is meticulously regulated by hitherto unidentified mechanisms. This research elucidates the sequential processes occurring in these cells during phloemogenesis and unveils novel insights into the mechanisms of selective autophagy.
... The decreasing polar flow of auxin, from the cauline apex, induces the differentiation of tracheal elements, promoting more cell division and an increase in the diameter of elements (Aloni, 1987;Aloni and Peterson, 1997;Evert, 2013). However, this gradient is also responsible for the decrease in element density, in the direction of leaves to roots (Aloni and Zimmermann, 1983). ...
The fundamental chemical components of wood (cellulose, hemicellulose and lignin) are anatomically inherent and vary along the trunks of each individual tree. The aim of this study was to analyse the formation and concentration gradient of lignin and cellulose intensity signals between knotless wood, the knot-to-wood transition zone and knots in the species Pinus elliottii var. elliottii Engelm. Wood samples in knotted and knotless regions of Pinus elliottii var. elliotti trees from a plant shop in Agudos-SP, were analysed in the laboratory of the Federal University of Rio de Janeiro. Based on the degradative methods of Klason Lignin, 13C spectroscopy and nuclear magnetic resonance and Fourier transforminfrared and histochemical tests in histological sections, differentiated patterns in the development dynamics between the anatomical elements of knotless wood and knotted wood were verified. The structure of lignin in knotted and knotless wood was different, despite the proximity of these regions to one another. Crystalline cellulose signals were more intense in the middle knot and top knot regions. It is possible to conjecture that these characteristics interfere with wood resistance in these regions along the trunk.
... These observations suggest the existence of genetic control of their differentiation, which will most probably involve transcription factors responsible for the xylem cell type differentiation together with hormone regulation (Schuetz et al., 2012). Nonetheless, since sugars have also been shown to affect xylem development (Aloni, 1987), we hypothesize that changes in sugar availability, mediated by SWEET transporters, could be at play in the VB type differentiation. In line with this hypothesis, a lower number of VBs, mainly due to fewer M-type VBs, was found only in swt16 swt17 mutant, along with a modified cellular morphology in the VBs involved in the connexion with the cauline leaves (Ltype VB) and those responsible for long-distance transport of water and nutrients (M-type VB) (Park et al., 2015). ...
Carbon (C) and nitrogen (N) metabolisms have long been known to be coupled, and this is required for adjusting nitrogen use efficiency. Despite this intricate relationship, it is still unclear how a deregulation of sugar transport impacts N allocation. Here, we investigated in Arabidopsis, the consequences of the simultaneous downregulation of the genes coding for the sugar transporters SWEET11, SWEET12, SWEET16, and SWEET17 on various anatomical and physiological traits ranging from the stem's vascular system development, plant biomass production, seed yield, and N remobilisation and use efficiency. Our results show that intracellular sugar exchanges mediated by SWEET16 and SWEET17 proteins specifically impact the vascular development but do not play a significant role in the distribution of N. Most importantly, we showed that the double mutant swt11 swt12, which has an impacted vascular development, displays an improved nitrogen use efficiency and nitrogen remobilisation to the seeds. In addition, a significant negative correlation between sugar and amino acids contents and the inflorescence stem radial growth exists, highlighting the complex interaction between the maintenance of C/N homeostasis and the inflorescence stem development. Our results thus deepen the link between sugar transport, C/N allocation and vascular system development.
... This result suggests that root diameter is a key factor moderating the effect of soil or water content on root properties. This phenomenon may be due to the fact that larger roots contain larger proportions of vascular tissues for water conductance and transport (Aloni, 1987), and therefore may be more susceptible to soil moisture. ...
Plant roots can protect soil against shallow landslides. The mechanics of rooted soil failure under varying soil water content remain poorly understood. The aim of our study was to characterize the impact of soil water content on root mechanical traits and reinforcement to soil. One-year-old Symplocos setchuensis trees were replanted in shear boxes (0.4 × 0.4 × 0.5 m³), which were placed in a canopy gap on Jinyun Mountain, Chongqing, China. After three years of vegetation growth, root mechanical measurements and soil direct shear tests were performed at five levels of volumetric soil water content varying from 14.9 to 44.4 %, by either wetting or drying the soil. For each shear box, we measured soil shear strength, root area ratio, root tensile force, root water content, and root failure mode (slippage versus breakage) during or after the shearing process. Root area ratio and root failure modes were examined for different root diameter classes. With increasing volumetric soil water content, we found a persistent decrease in root tensile strength (ca. 15 %) and an increase in root water content (ca. 11 %), although the dependence on volumetric soil water content was not statistically significant for certain soil water content levels. We found that both additional shear strength of rooted soil and proportion of root failure in breakage increased first and then decreased, with peak values occurring at a soil water content of ca. 22 %. Altered root tensile force (68.0 % contribution to root reinforcement variation) and the change in proportion of root failure modes (breakage or slippage; 8.4 % contribution to root reinforcement variation) jointly contribute to the negative impact of soil water on observed root reinforcement. Soil shear strength was positively correlated with root area ratio and their relationship was linear. At high soil water content (>28 %), the slope of the linear relationship decreased rapidly with increasing soil water content, suggesting that increasing root biomass is not effective for enhancing root reinforcement in very wet soil conditions. Regarding hysteresis, root reinforcement magnitude and efficiency were higher in the drying process than in the wetting process when soil moisture was low. Our results highlight the vital role of soil water features in affecting soil-root mechanical interactions and such effects should be taken into account in future root reinforcement modelling and assessment
... One proposed explanation for differences between ring-and diffuse-porous species is their sensitivity to auxin, a hormone that appears important in vessel production and expansion (Aloni, 1987;Johnson et al., 2018). Some evidence suggests that diffuseporous species require higher levels of auxin to initiate xylogenesis than ring-porous species, causing them to produce vessels only after new leaves become a major auxin source (Aloni et al., 1991;Aloni & Peterson, 1997). ...
There is a long‐standing idea that the timing of leaf production in seasonally cold climates is linked to xylem anatomy, specifically vessel diameter because of the hydraulic requirements of expanding leaves.
We tested for a relationship between the timing of leaf out and vessel diameter in 220 plants in three common gardens accounting for species’ phylogenetic relationships. We investigated how vessel diameter related to wood porosity, plant height and leaf length. We also used dye perfusion tests to determine whether plants relied on xylem produced during the previous growing season at the time of leaf out.
In all three gardens, there was later leaf out in species with wider vessels. Ring‐porous species had the widest vessels, exhibited latest leaf out and relied less on xylem made during the previous growing season than diffuse‐porous species. Wood anatomy and leaf phenology did not exhibit a phylogenetic signal.
The timing of leaf out is correlated with wood anatomy across species regardless of species’ geographic origin and phylogenetic relationships. This correlation could be a result of developmental and physiological links between leaves and wood or tied to a larger safety efficiency trade‐off.
... The mechanisms driving these difference have been studied for a long time (Wareing, 1951), but are still debated (Frankenstein et al., 2005). Auxin (indole-3-acetic acid) is an important promoter of cambium reactivation and has long been thought to originate from developing leaves (Larson, 1962;Aloni, 1987). This assertion is supported by the high correlation values recorded here between spring leaf and diameter growth phenology in all eight diffuse-porous species studied here, but does not match with the capacity of ring-porous species to form new xylem and phloem before bud break (Prislan et al., 2013;Lavrič et al., 2017). ...
Climate models project warmer summer temperatures will increase the frequency and heat severity of droughts in temperate forests of Eastern North America. Hotter droughts are increasingly documented to affect tree growth and forest dynamics, with critical impacts on tree mortality, carbon sequestration, and timber provision. The growing acknowledgement of the dominant role of drought timing on tree vulnerability to water deficit raises the issue of our limited understanding of radial growth phenology for most temperate tree species. Here, we use well-replicated dendrometer band data sampled frequently during the growing season to assess the growth phenology of 610 trees from 15 temperate species over six years. Patterns of diameter growth follow a typical logistic shape, with growth rates reaching a maximum in June, and then decreasing until process termination. On average, we find that diffuse-porous species take 16–18 days less than other wood-structure types to put on 50% of their annual diameter growth. However, their peak growth rate occurs almost a full month later than ring-porous and conifer species (ca. 24 ± 4 days; mean ± 95% credible interval). Unlike other species, the growth phenology of diffuse-porous species in our dataset is highly correlated with their spring foliar phenology. We also find that the later window of growth in diffuse-porous species, coinciding with peak evapotranspiration and lower water availability, exposes them to a higher water deficit of 88 ± 19 mm (mean ± SE) during their peak growth than ring-porous and coniferous species (15 ± 35 mm and 30 ± 30 mm, respectively). Given the high climatic sensitivity of wood formation, our findings highlight the importance of wood porosity as one predictor of species climatic sensitivity to the projected intensification of the drought regime in the coming decades.
... In the AHS, tracheary elements formed in the haustorial structure in contact with host-derived auxin (NAA) and cytokinin (BA), sugar (glucose) and other nutrients in the media, suggesting that these are sufficient to induce differentiation in at least some cells (Fig. 5). This agrees with the crucial role for auxin and cytokinin in vascular differentiation (Wetmore & Rier, 1963;Aloni, 1987) and vascular reconnection during formation of grafting unions (Melnyk et al., 2015). Additionally, our observation of xylem elements is supported by transcriptional data that show an enrichment in xylem development and lignin biosynthetic process in haustorial regions compared to stems 15 dpi (Fig. 8a). ...
Cuscuta campestris is an obligate parasitic plant that requires a host to complete its lifecycle. Parasite-host connections occur via an haustorium, a unique organ that acts as a bridge for the uptake of water, nutrients and macromolecules. Research on Cuscuta is often complicated by host influences, but comparable systems for growing the parasite in the absence of a host do not exist. We developed an axenic method to grow C. campestris on an Artificial Host System (AHS). We evaluated the effects of nutrients and phytohormones on parasite haustoria development and growth. Haustorium morphology and gene expression were characterized. The AHS consists of an inert, fibrous stick that mimics a host stem, wicking water and nutrients to the parasite. It enables C. campestris to exhibit a parasitic habit and develop through all stages of its lifecycle, including production of new shoots and viable seeds. Phytohormones NAA and BA affect haustoria morphology, and increase parasite fresh weight and biomass. Gene expression in AHS haustoria reflect process similar to those in haustoria on actual host plants. The AHS is a methodological improvement for studying Cuscuta biology by avoiding specific host effects on parasite and giving researchers full control of the parasite environment.
... In general, trees respond to the higher water demand of an expanding crown, increasing flow resistances and a larger gravitational force when growing tall by increasing conduit diameters at the stem base (Lachenbruch et al. 2011). This increase in conduit size, especially during juvenile wood formation, is thought to be a function of cambial ageing (Gartner 1995;Kirfel et al. 2017;Li et al. 2019) and resulting changes in auxin concentration during vascular differentiation (Aloni 1987). While conduit size might increase constantly with age in some species, several studies observed that conduit size remained either constant or that the radial increase in conduit size slowed down after approximately 30 years, which agrees with our results (Leal et al. 2006(Leal et al. , 2011Fan et al. 2009). ...
Key message
By combining dendrochronological time-series analysis with radial vessel features, we show that the reconstruction of hydraulic properties improves our understanding of tree species’ acclimation potential to climate change.
Abstract
The vascular architecture plays a crucial role in the productivity and drought tolerance of broadleaf trees, but it is not yet fully understood how the hydraulic system is acclimating to a warmer and drier climate. Because vessel features may record temporal and spatial variability in climatic signals of the past better than tree-ring width, we combined dendrochronological time-series analysis with the calculation of stem hydraulic properties derived from radial vessel features. We aimed to reconstruct the development and sensitivity of the hydraulic system over six decades and to identify climatic control of xylem anatomy for five co-existing broad-leaved diffuse- and ring-porous tree species (genera Acer , Fagus , Fraxinus and Quercus ) across three sites covering a precipitation gradient from 548 to 793 mm. We observed a significant influence of the climatic water balance (CWB) on the vessel features of all species, but the time lag, magnitude and direction of the response was highly species-specific. All diffuse-porous species suffered a decline in vessel diameter in dry years, and increase in vessel density in dry years and the year following. However, F. sylvatica was the only species with a significant long-term change in anatomical traits and a significant reduction in potential hydraulic conductivity ( K p ) after dry winters and in dry summers, accompanied with the largest long-term decline in tree-ring width and the largest growth reduction in and after years with a more negative CWB. In contrast, the comparison across the precipitation gradient did not reveal any significant vessel-climate relationships. Our results revealed considerable plasticity in the hydraulic system especially of F. sylvatica , but also evidence of the drought-sensitivity of this species in accordance with earlier dendroecological and physiological studies. We conclude that the long-term reconstruction of hydraulic properties can add substantially to the understanding of the acclimation potential of different tree species to climate change.
... These results suggested that plants could undergo stigma exsertion by increasing the IAA content to promote style growth. IAA also regulates the differentiation of vascular bundles (Aloni 1987). In this study, by morphological observations, we found that there were more vascular bundles in T431 than in DL5. ...
Key message
Anatomical changes in and hormone roles of the exserted stigma were investigated, and localization and functional analysis of SlLst for the exserted stigma were performed using SLAF-BSA-seq, parental resequencing and overexpression of SlLst in tomato.
Abstract
Tomato accession T431 produces stigmas under relatively high temperatures (> 27 °C, the average temperature in Harbin, China, in June–August), so pollen can rarely reach the stigma properly. This allows the percentage of male sterility exceed 95%, making the use of this accession practical for hybrid seed production. To investigate the mechanism underlying the exserted stigma male sterility, the morphological changes of, anatomical changes of, and comparative endogenous hormone (IAA, ABA, GA3, ZT, SA) changes in flowers during flower development of tomato accessions DL5 and T431 were measured. The location and function of genes controlling exserted stigma sterility were analyzed using super SLAF-BSA-seq, parental resequencing, comparative genomics and the overexpression of SlLst in tomato. The results showed that an increase in cell number mainly caused stigma exsertion. IAA played a major role, while ABA had an opposite effect on stigma exertion. Moreover, 26 candidate genes related to the exserted stigma were found, located on chromosome 12. The Solyc12g027610.1 (SlLst) gene was identified as the key candidate gene by functional analysis. A subcellular localization assay revealed that SlLst is targeted to the nucleus and cell membrane. Phenotypic analysis of SlLst-overexpressing tomato showed that SlLst plays a crucial role during stigma exsertion.
... From young shoot organs polar transport of indole acetic acid (Aloni 2004 ) downward via the cambium to the root tips (Aloni et al. 2006 ) induces and controls wood formation. The vascular tissues continuity along the plant axis is a result of the steady polar fl ow of indole acetic acid from leaves to roots (Aloni 1987 ). Indole acetic acid plays a key role on regulating plant growth. ...
Climate represent the earth’s atmosphere over a given region, defined by certain factors viz. temperature, air pressure, humidity, precipitation, sunlight, cloudiness, and winds. While, climate change is the earth’s climate periodic modification brought as a result of atmospheric changes as well as atmosphere and other various geological, biological, geographic factors interaction between them within earth system. The atmosphere is like the dynamic fluid which is always in the continuous motion. The direction of motion and physical properties and its rate are stimulated by different factors, including the geographic position, solar radiation, ocean current, chemistry of atmosphere, continents geographic position, the location and orientation of mountain ranges, and vegetation growing on the land surface. Global sea-level rise is one of the major outcomes of global warming (12–22 cm occurred during the twentieth century), and several other climate models project an accelerated rate of about 0.18–0.59 m rise in global sea-level in coming decades. Such climatic changes have altered the marine ecosystem greatly.
... These patterns might be quite complex in fruit trees, in which the apical dominance has been perturbed by extensive training and pruning. On the other hand, dwarfing rootstocks are known to have lower capacity for basipetal auxin transport (Somelidou et al., 1994), which would be consistent with the development of narrower vessels (Aloni 1987). ...
• Excess vegetative growth and irregular fruit‐bearing are often undesirable in horticultural practice. However, the biological mechanisms underlying these traits in fruit trees are not fully understood. Here, we tested if growth vigour and susceptibility of apple and pear trees to alternate fruit‐bearing are associated with vascular anatomy.
• We examined anatomical traits related to water transport and nutrient storage in young woody shoots and roots of 15 different scion/rootstock cultivars of apple and pear trees. In addition, soil and leaf water potentials were measured across a drought period.
• We found a positive correlation between the mean vessel diameter of roots and the annual shoot length. Vigorously growing trees also maintained less negative midday leaf water potential during drought. Furthermore, we observed a close negative correlation between the proportions of total parenchyma in the shoots and the alternate bearing index.
• Based on anatomical proxies, our results suggest that xylem transport efficiency of rootstocks is linked to growth vigour of both apple and pear trees, while limited carbohydrate storage capacity of scions may be associated with increased susceptibility to alternate bearing. These findings can be useful for the breeding of new cultivars of commercially important fruit trees.
... The scion buds are effective in inducing differentiation of vascular elements in the tissues onto which they are grafted. It is mostly due to the phytohormone auxins especially in induction of wound repair xylem, induce cambial formation, and then auxins and carbohydrates can induce wound repair phloem in callus tissue (Aloni, 1987). ...
EFFECT OF GRAFTING DATES AND METHODS ON SUCCESS AND GROWTH
OF MANDARIN (Citrus reticulata Blanco) SAPLING
... Anatomically, the temporary reduction of endogenous gibberellin levels may have changed the meristematic cambial cells activity. Higher auxin concentration favors formation of xylem vessels, and higher gibberellin levels favor production of phloem vessels (Aloni, 1987). Other potential consequence may be an accelerated elongation of metaxylem, epidermal and cortical cells, with consequent increase of vacuolization of cells (Spitzer et al., 2015). ...
High nitrogen rates favor maize vegetative growth and grain yield losses due to stem lodging. The use of growth regulators can mitigate such effect. This work was carried out aiming to evaluate the effect of trinexapac ethyl on maize hybrids response to side-dress nitrogen rates. The experiment was carried out in Lages, Santa Catarina State, South of Brazil, during two growing seasons with two hybrids (P1680 and P30F53), and four nitrogen rates (0, 150, 300 and 450 kg N ha-1) were tested, with and without the presence of trinexapac ethyl. The experimental design was in randomized blocks arranged in split-split plots, with three replications per treatment. The plants height and ear insertion height, plant lodging and breaking, grain yield and yield components were evaluated. Grain yield increased in a quadratic way with increased nitrogen rate. The highest grain yields were 15,784 and 15,257 kg ha-1, in 2014/15 and 2015/16, respectively. Application rates higher than 150 kg of N ha-1, regardless of the use of the plant growth regulator, promoted maximum grain yield increases, ranging from 14.7 to 18.1%. The application of trinexapac-ethyl reduced the upper stem internode length, 1000-grain dry weight and did not affect the percentage of lodged plants and grain yield of both hybrids. Therefore, the use of trinexapac-ethyl did not enhance the maize grain yield response to increased rates of side-dress nitrogen.
... This effect could make the plants more susceptible to an infection (Hahlbrock and Grisebach, 1979;Arheim et al, 1980;Duke et al, 1980;Hollander and Arheim, 1980;Lee, 1982;Rubin et al, 1984). The application of indolebutyric acid (IBA) and ethephon to plants causes an unbalance of these growth regulators, and also may interfere with the biosynthesis of lignin (Sequeira, 1973;Aloni, 1980;Pegg, 1981;Misaghi, 1982;Aloni, 1987;Ke and Saltveit, 1988). Other growth regulators (gibberellic acid, benzylaminopurine etc), calcium and nitrogen could also predispose plants to the attack by some microorganisms by interfering with the biosynthesis of lignin (Graham, 1983). ...
El síndrome de arqueo foliar/pudrición común de la flecha (AF/PCF) es el desorden más común en plantaciones jóvenes de palma aceitera en todo el mundo. Se compararon plantas sanas y enfermas, en su contenido nutricional, potencial hídrico, y tipo de suelo en que se encontraban las plantas. Las curvas de progreso de la enfermedad se ajustaron a las ecuaciones de Gompertz y monomolecular. Los microorganismos que se aislaron con más frecuencia a partir de las lesiones necróticas de las hojas y del raquis, fueron especies de Erwinia spp. y Fusarium spp., los cuales son probablemente habitantes comunes del filoplano. Los intentos de reproducir los síntomas de PCF por medio de la inoculación de los microorganismos aislados, fallaron normalmente; los síntomas típicos de PCF solamente se pudieron reproducir una vez, con tres diferentes aislamientos de Erwinia spp., en plantas de vivero de 19 meses de edad. La ecuación de Gompertz fue adecuada para describir la curva de progreso de la enfermedad para muchas de las progenies más susceptibles. Sin embargo, el progreso de la enfermedad tendió a seguir la ecuación monomolecular en las progenies más resistentes. Las plantas con síntomas de AF/PCF normalmente tuvieron un mayor contenido de nutrientes en sus hojas jóvenes, en comparación con plantas sanas. El genotipo fue el factor principal en la determinación de la susceptibilidad de las plantas a este desorden. Sin embargo, las condiciones que favorecen un crecimiento vigoroso podrían hacer que las plantas sean más susceptibles, debido a que causan una lignificación anormal de los tejidos jóvenes, lo que permite la entrada de microorganismos oportunistas.
... The interfascicular fibers are composed of three to four layers of fiber cells, which are mainly responsible for the mechanical strength of mature stems [66,67]. Therefore, the size and number of vessels and fiber cells are important parameters for the study of long-distance water transport, plant mechanical support, xylem adaptations or pathology of the xylem [68]. ...
Arabidopsis thaliana MYB43 (AtMYB43) is suggested to be involved in cell wall lignification. PtrMYB152, the Populus orthologue of AtMYB43, is a transcriptional activator of lignin biosynthesis and vessel wall deposition. In this research, MYB43 genes from Brassica napus (rapeseed) and its parental species B. rapa and B. oleracea were molecularly characterized, which were dominantly expressed in stem and other vascular organs and showed responsiveness to Sclerotinia sclerotiorum infection. The BnMYB43 family was silenced by RNAi, and the transgenic rapeseed lines showed retardation in growth and development with smaller organs, reduced lodging resistance, fewer silique number and lower yield potential. The thickness of the xylem layer decreased by 28%; the numbers of sclerenchymatous cells, vessels, interfascicular fibers, sieve tubes and pith cells in the whole cross section of the stem decreased by 28%, 59%, 48%, 34% and 21% in these lines, respectively. The contents of cellulose and lignin decreased by 17.49% and 16.21% respectively, while the pectin content increased by 71.92% in stems of RNAi lines. When inoculated with S. sclerotiorum, the lesion length was drastically decreased by 52.10% in the stems of transgenic plants compared with WT, implying great increase in disease resistance. Correspondingly, changes in the gene expression patterns of lignin biosynthesis, cellulose biosynthesis, pectin biosynthesis, cell cycle, SA- and JA-signals, and defensive pathways were in accordance with above phenotypic modifications. These results show that BnMYB43, being a growth-defense trade-off participant, positively regulates vascular lignification, plant morphology and yield potential, but negatively affects resistance to S. sclerotiorum. Moreover, this lignification activator influences cell biogenesis of both lignified and non-lignified tissues of the whole vascular organ.
... Secondary or 'short' fibres are unwanted because these fibres are too short for spinning and their presence hampers the production of fine and homogeneous yarns from the primary or long fibres (Bredemann et al., 1961;Hoffmann, 1957;Mediavilla et al., 2001;Ranalli, 1999;Schäfer and Honermeier, 2003). Kundu (1942) stated that the presence of a few layers of parenchyma cells between the primary and secondary fibre bundles enables the isolation of the primary fibre bundles by a retting process, but although secondary fibres can easily be distinguished under a microscope, and methods are available to isolate these short fibres in the laboratory (Bredemann et al., 1961;Van der Werf et al., 1994), it is technically difficult to separate them from the primary fibres during Primary bast fibre cells develop in the primary phloem that is differentiated from the procambium (Aloni, 1987;Kundu, 1942). Cells are initiated before or during stem elongation and fibre cells mainly grow with the surrounding tissue; they elongate when stems elongate (Amaducci et al., 2005;Chernova and Gorshkova, 2007;Kundu, 1942;Van Dam and Gorshkova, 2003). ...
In fibre hemp (Cannabis sativa L.) grown for the production of high‒quality textile yarns the presence of secondary fibres is unwanted. These fibres are too short for spinning and their presence hampers the production of fine and homogeneous yarns from the primary or long fibres. Primary fibres are present along the stem from bottom to top and hemp for fibres is traditionally harvested around the time of flowering, when the cell walls of these fibres are sufficiently thickened with cellulose to be extracted. In literature indications are found that the height up to which secondary fibres are present, moves upwards along the stem during the growing season, and that this process accelerates around flowering. To optimise the length of the stem part with primary fibres, but without secondary fibres, the background of secondary fibre development should be elucidated. It can be hypothesised that either flowering or the increasing plant size accelerates the formation of secondary fibres. To investigate this, an indoor experiment was conducted in greenhouses with mobile covers in which the day–length sensitivity of hemp was used to create size ranges of flowering and non–flowering plants for a single cultivar, Futura 75. Secondary fibre formation was recorded using microscopic techniques. The height up to which secondary fibres were present, depended on plant weight. The higher secondary fibre front in flowering plants was most likely caused by the higher weight of these plants as compared with non–flowering plants of the same height. As seed carrying inflorescences contribute to plant weight, dual use of fibre hemp for seed and high–quality textile fibres is not an option. Results from a field experiment confirmed the correlation between plant size and the height of the secondary fibre front. Therefore, to optimise the length of the stem part with primary fibres, but without secondary fibres above stubble height, for Futura 75 a relatively short crop of around 1.3–1.4 m should be harvested before flowering. This ideal crop height is likely to differ between varieties.
... The early steps of grafting are supported by adhesion and cohesion between the adjacent cells, resulting from the secretion of insoluble carbohydrates and pectin polysaccharides [113]. The interactions between grafting partners during formation of a callus and the vascular connectivity are regulated and controlled by hormones such as auxin, which are released by both grafting partners and stimulate vascular tissue differentiation [107,[114][115][116]. Recent studies suggest that small RNA or DNA fragments and even complete chloroplast and nuclear genomes can be exchanged between the grafting partners, directing DNA methylation and allowing horizontal gene or even genome transfer between sexually incompatible species [117][118][119][120]. ...
... This effect could make the plants more susceptible to an infection (Hahlbrock and Grisebach, 1979;Arheim et al, 1980;Duke et al, 1980;Hollander and Arheim, 1980;Lee, 1982;Rubin et al, 1984). The application of indolebutyric acid (IBA) and ethephon to plants causes an unbalance of these growth regulators, and also may interfere with the biosynthesis of lignin (Sequeira, 1973;Aloni, 1980;Pegg, 1981;Misaghi, 1982;Aloni, 1987;Ke and Saltveit, 1988). Other growth regulators (gibberellic acid, benzylaminopurine etc), calcium and nitrogen could also predispose plants to the attack by some microorganisms by interfering with the biosynthesis of lignin (Graham, 1983). ...
The crown disease/common spear rot (CD/CSR) syndrome is the most common disorder in young oil palm plantations worldwide. Diseased and healthy plants were compared in their nutrient content, water status and type of soil in which they were growing. Disease progress curves were adjusted to either the monomolecular or Gompertz equations. The most frequently isolated microorganisms from necrotic lesions on leaves and rachises were species of Erwinia spp and Fusarium spp. These are probably common inhabitants of the phylloplane. Attempts to reproduce the CSR symptoms through the inoculation of isolated microorganisms normally failed. Typical CSR symptoms were reproduced only once, with at least three isolates of Erwinia sp. in 19 month-old nursery palms. The Gompertz equation was adequate to describe the disease progress curve for several of the most susceptible progenies. However, disease progress tended to follow the monomolecular equation for the more resistant progenies. Plants with the CD/CSR symptoms usually had higher nutrient contents in their younger leaves than healthy plants. The genotype showed to be the main determinant of susceptibility to the disorder. However, conditions that favor a vigorous growth could make more susceptible the plant by causing abnormal lignification of young tissues and allowing opportunistic microorganisms enter.
... In addition, the promotive effect of low salinity level on sweet pepper leaves thickness may be due to an increase in thickness of mesophyll tissue. In addition, Aloni (1987) suggested that increase or decrease in the vessel diameter might increase or decrease the efficiency of water conduction, owing to increase or decrease in the resistance to flow. ...
All salinity types at 2000 mg/L increased stem diameter due to an increase in pith diameter, cortex thickness, width of epidermis cell and vascular bundles dimensions (length as well as metaxylem vessel diameter). In addition, CaCl 2 and NaCl+CaCl 2 1:1 (w/w) were the most effective in this respect. In addition, high salinity level (4000 mg/L) decreased most of the studied anatomical parameters. While, the pith diameter and number of vascular bundles were decreased only under NaCl at 4000 mg/L. On the other hand, pre-soaking seeds in selected chemicals used, in most cases, showed a positive effect on the stem structure and AsA at 50 mg/L or SA at 75 mg/L was the most effective in this respect. Low level of all salinity types (2000 mg/L) increased midrib region thickness due to increasing the length of main vascular bundle. While, the highest salinity level (4000 mg/L) led to a decrease in this respect due to the decrease in length of main vascular bundle. In addition, NaCl was more effective in this respect followed by NaCl+CaCl 2 (1:1). On the other hand, the leaf blade (lamina) thickness was also decreased in plants grown under NaCl at 4000 mg/L followed by NaCl+CaCl 2 (1:1) due to a decrease in the thickness of palisade and spongy tissues as well as upper and lower epidermis width. Moreover, the application of chemicals used led to an increase in the thickness of midrib region as compared with untreated plants. In addition, SA (75 mg/L), AsA (50 mg/L) and α-tocopherol (100 mg/L) were more effective. In most cases, AsA at 50 mg/L or SA at 75 mg/L alleviated the harmful effect of salinity level (4000 mg/L) on midrib region and lamina thickness as well as the main vascular bundle dimensions when compared with untreated plants. Furthermore, AsA at 50 mg/L was more effective than the remaining treatments.
... w/w) induced xylem differentiation. Likewise, in grafting experiments, an important group of substance involved in development of compatible graft unions is the auxins released from the vascular strands of the stock and the scion, which induce the differentiation of vascular tissues, thus functioning as morphogenic substances (Aloni, 1987;Mattsson et al., 2003). Shimomura and Fujihara, 1977 observed translocation from the scion to the stock were found to accelerate the development of a successful graft union in Cactus. ...
The mechanism of graft incompatibility is not yet fully understood and many reports focus on this problem in order to understand the mechanisms of graft development. Graft incompatibility is reported due to the Structural or Anatomical reasons, physiological and biochemical reasons, nutritional deficiency and presence of viruses at an early phase in response to grafting, as well as the consequences of these events on the future graft
response. All these abnormalities result in mechanical weakening of the union, which may manifest the first year after grafting or may appear several years later, leading to major economic losses. Successful union of stock/scion involves lining up of vascular cambiums, subsequent wound healing response, callus bridge formation, wound repair xylem and phloem occur in the callus bridge just prior to initial cambium formation, the vascular cambium is completed across the callus bridge and is forming secondary xylem and
phloem. The phloem mobile proteins have been reported that cross the graft interface when
graft bridging is established and is functional. Commercial fruit trees are usually formed
by the combination of a rootstock and a scion to broaden the adaptability of scion cultivars
to soil and climatic conditions, facilitate agricultural management, and/or increase
productivity. Graft incompatibility is a problem in cherry, almond, and apricot than in
peach or plum, pear or quince. In general, closely related cultivars species unite readily
and grow as a composite plant and that of unrelated plant do not. Even sometimes
stock/scion of unrelated species unites initially and develops symptoms of incompatibility
later and die eventually. An early and accurate prediction of graft incompatibility has great
importance because incompatible combinations could be avoided while compatible ones
could be selected. The complexity of incompatibility and the mechanism behind the
reactions have been investigated in several ways. Moreover, research is needed to fully
understand the mechanism of graft incompatibility, particularly in woody plants. This
knowledge is essential to develop molecular markers useful in rootstock breeding
programs.
... Speck et al., 1990;Caliaro et al., 2013b). On the other hand, the highly lignified cell walls of the vascular bundles (sVb, Vbr) further increase the mechanical stability in these structures, as generally shown by Aloni (1987), Niklas (1989) and Boudet (2000). Due to their large volumetric sizes and interposed spatial arrangement, we assume that the ground tissues (Pac, Par) probably function as a 'hydro-mechanical buffer' by keeping the primary supporting tissues (Ep, sVb, Vbr) in place and simultaneously 'buffering' the water loss at the beginning of dehydration (cf. ...
The anisocotyledonous one-leaf plant Monophyllaea horsfieldii (Gesneriaceae) experiences regular periods of low water availability in its natural habitat. However, it is not known whether this species is desiccation-intolerant or desiccation-tolerant (the latter like many of its close relatives) because neither the functional morphology of the M. horsfieldii hypocotyl and macrocotyledon nor the respective physiological and/or structural behaviour under water stress have been investigated. Using various imaging techniques and dehydration–rehydration experiments, we examined the life cycle, morphometry, anatomy, water stress behaviour and relative water content changes of M. horsfieldii plants cultivated in the greenhouse. We identified six developmental stages during the life cycle of M. horsfieldii and reveal allometric relationships and morphological aspects of adult plants by morphometric and anatomical investigations. Moreover, we demonstrate that the posture and mechanical stability of M. horsfieldii correlate directly with alterations in the water status and associated physical parameters, similar to those in other desiccation-tolerant Gesneriaceae, and that it is unable to recover from severe dehydration, unlike other desiccation-tolerant Gesneriaceae. However, its ability to withstand moderate water stress could possibly render M. horsfieldii an important model plant for studying the evolution of desiccation tolerance in Gesneriaceae.
... Strogonov (1964) suggested that the increase in blade thickness is a remarkable response to salinity and succulence involves development of large cells in the spongy mesophyll and sometimes multilayer palisade tissue. Furthermore, Aloni (1987) suggested that increase or decrease in the vessel diameter might increase or decrease the efficiency of water conduction, owing to increase or decrease in the resistance to flow. The inhibiting effects of high salinity level in leaf structure may be due to suppressed cell division and cell enlargement proportionally (Nieman, 1965), and inhibition the growth of vascular elements (Rashid et al, 2004), and/or correlation with an inhibition of the procambial activity which form, primary vascular tissues and/or decrease in the number and size of mesophyll cells. ...
... Physiologically, plant growth is sustained by meristems producing new cells which subsequently enlarge and increase in mass (Aloni, 1987). We suppose that for each type of meristem, growth is proportional to its volume, that is to say that the mass of carbon allocated to a meristematic region will depend proportionally on the volume of meristem, which determines the maximum potential production rate of new cells. ...
Increasing CO2 concentrations are strongly controlled by the behavior of established forests, which are believed to be a major current sink of atmospheric CO2. There are many models which predict forest responses to environmental changes but they are almost exclusively carbon source (i.e., photosynthesis) driven. Here we present a model for an individual tree that takes into account the intrinsic limits of meristems and cellular growth rates, as well as control mechanisms within the tree that influence its diameter and height growth over time. This new framework is built on process-based understanding combined with differential equations solved by numerical method. Our aim is to construct a model framework of tree growth for replacing current formulations in Dynamic Global Vegetation Models, and so address the issue of the terrestrial carbon sink. Our approach was successfully tested for stands of beech trees in two different sites representing part of a long-term forest yield experiment in Germany. This model provides new insights into tree growth and limits to tree height, and addresses limitations of previous models with respect to sink-limited growth.
... Both AHK2 and AHK4 function as positive regulators of CK signaling and play key roles in early vascular development (Nishimura et al., 2004;Riefler et al., 2006). Additionally, evidence also showed the function of auxin and CK in promoting tracheary element (TE) differentiation (Aloni, 1987;Fukuda et al., 1997). The fact that differentially expressed proteins identified in this study are known to be involved in the auxin and CK pathways indicates that these hormones play important roles during the transition from primary to secondary growth. ...
Wood is the most important natural source of energy and also provides fuel and fiber. Considering the significant role of wood, it is critical to understand how wood is formed. Integration of knowledge about wood development at the cellular and molecular levels will allow more comprehensive understanding of this complex process. In the present study, we used a comparative proteomic approach to investigate the differences in protein profiles between primary and secondary growth in young poplar stems using tandem mass tag (TMT)-labeling. More than 10,816 proteins were identified, and, among these, 3,106 proteins were differentially expressed during primary to secondary growth. Proteomic data were validated using a combination of histochemical staining, enzyme activity assays, and quantitative real-time PCR. Bioinformatics analysis revealed that these differentially expressed proteins are related to various metabolic pathways, mainly including signaling, phytohormones, cell cycle, cell wall, secondary metabolism, carbohydrate and energy metabolism, and protein metabolism as well as redox and stress pathways. This large proteomics dataset will be valuable for uncovering the molecular changes occurring during the transition from primary to secondary growth. Further, it provides new and accurate information for tree breeding to modify wood properties.
... Results agree with Kotsias and Roussos (2001) and Carimi and De Pasquale (2003) who reported that auxin and cytokinin are the important growth regulators in plant tissue culture and they are the responsible on cell division. Also, Moore (1984); Aloni (1987), Aloni et al. (2010) and Pina and Eraaea (2005) added that the relationships between scion and stock are affected by growth regulators. In grafting, auxin which is released from vascular strands of the stock and scion is an important substance involved in the development of compatible unions, and induces the differentiation of vascular tissues, also, auxin is functioning as morphogenic substances. ...
Balady mandarin (Citrus. reticulata), belongs to family Rutaceae, is one of the ancestral species of
citrus, widely grown in the tropical and subtropical areas. Virus and viroids have been recognized as serious
problem limiting the vigor, yield and quality of citrus. These diseases are graft transmissible through infected bud
sticks. So, obtained of disease-free plants is imperative to provide certified microscions to the growers and to
encourage the planting of grafts instead of seedlings. Micrografting is one of virus-free plant production methods,
but, it is complex and its successful percent is low especially it is followed by acclimatization stage. Our paper is the
first one to examine producing virus-free microscions via in vitro propagation of vegetative nucellar embryos and
examine in vitro treatments which may affect microshoots propagation and successful of grafting the in vitro
producing microscions on volkamariana rootstock in greenhouse. Firstly, the sexual nucellar embryo was
determined using RAPD marker. Genetic analysis proved that 5th nucellar embryo (the youngest) is differed than
the other four embryos. The similarity between them was 84%. Cytokinin types and concentrations affected
multiplication of asexual nucellar embryos of Balady mandarin, the highest significant shoot number/explant
through second subculture resulted from the explants cultured on MS medium supplemented with 0.75 and 1.00
mg/l BAP (8.80 and 5.60 shoots/explant, respectively). Concerning grafting of in vitro produced microscions in
greenhouse, after 45 days of grafting in greenhouse, Balady mandarin scions (microscions) derived from MS
medium supplemented with 1.0mg/l Kin or 0.75 mg/l AS maximized successful grafts percentage (37 and 33%
successful grafts, respectively). Also, auxin types and concentrations affected successful grafting, microscions
derived from MS supplemented with 0.5 mg/l IAA or 0.5 mg/l NAA gave the highest percentage of successful grafts
followed by 1.0 mg/l IBA and control (57, 57, 55 and 30% successful grafts, respectively). Microscions derived
from MS medium supplemented with 0.6 mg/l PP333 gave the highest percentage of successful grafts 88.77%.
Diameter of rootstock and method of grafting also affected grafting successful percent. Producing of microscions in
vitro is good tool for producing virus-free plantlet of Balady mandarin.
... The earlywood (or springwood) is formed during the initial growth and consists of larger cells with thinner walls, but as the season progresses resources are instead allocated towards thicker walls at the expense of cell diameter and thus the LW (or summerwood) is formed (Glock 1937;Zahner 1963;Larson 1969). The increase in density over the growing season and abrupt decrease in the next season usually allow for visual identification of annual growth rings in many conifers and in numerous hardwoods (Aloni 1987). In some species, the boundary between earlywood and latewood is also abrupt (Figure 1), and the width of these seasonal growth bands has attracted scientific interest since the earliest days of dendrochronology (Douglass 1919). ...
The relationship between earlywood width (EW) and latewood width (LW) is investigated using 197 tree-ring collections representing several tree species from across the North American continent. Chronologies of LW have limited paleoclimate value when they have low variance or very high correlation with EW from the same site. The correlation of LW and EW can be removed by taking the residuals from linear regression to provide a chronology of discrete latewood growth free from the carryover effects of prior EW (the so-called adjusted latewood chronology, LWa). The correlation between EW and LW, along with LWa variance, varies dramatically across North America. The lowest correlations between EW and LW chronologies can be found in Pseudotsuga menziesii in the summer monsoon region of northwestern Mexico. Low correlations between EW and LW chronologies are also noted for Pinus echinata and Quercus stellata in the south-central United States. Q. stellata also displays the highest LWa variance among any species in the dataset. For three conifer species, correlations between EW and LW appear to increase with the biological age of the tree. An age-related decline in LWa variance was also detected for Douglas-fir, bald cypress and ponderosa pine older than 200 years. These results imply that heavy sampling to produce "age-stratified" chronologies based on trees ≤ 200 years in age throughout the record may produce the best quality LW chronologies with the highest variance and most discrete growth signal independent from EW.
... Many reports have indicated that auxin plays a role in vascular bundle formation since early physiological studies showed that auxin transport originating from the shoot apex is necessary for the formation of vascular tissues (Aloni 1987;Sachs 1991). Other evidences also indicate the auxin response element (ARFAT), which consists of a TGTCTC sequence and its reverse element (GAGACA), is found to exist in the promoter regions of many auxin-induced genes (Goda et al. 2004). ...
A 2000-bp 5′-flanking region of VvPAL-like was isolated from ‘Summer Black’ grapevine by PCR amplification, named pVvPAL-like. To gain a better understanding of the expression and regulatory mechanism of VvPAL-like, a chimeric expression unit consisting of the β-glucuronidase (GUS) reporter gene under the control of a 2000-bp fragment of the VvPAL-like promoter was transformed into tobacco via Agrobacterium tumefaciens. Histochemical staining showed that the full-length promoter directs efficient expression of the reporter gene in cotyledons and hypocotyls, stigma, style, anthers, pollen, ovary, trichomes, and vascular bundles of transgenic plants. A series of 5′ progressive deletions of the promoter revealed the presence of a negative regulatory region (−424 to −292) in the VvPAL-like promoter. Exposure of the transgenic tobacco plants to various abiotic stresses demonstrated that the full-length construct could be induced by light, copper (Cu), abscisic acid (ABA), indole-3-acetic (IAA), methyl jasmonate (MeJA) (N-1-naphthylphthalamic acid), ethylene, and drought. Furthermore, the ethylene-responsive region was found to be located in the −1461/−930 fragment, while the element(s) for the MeJA-responsive expression may be present in the −424/−292 region in the VvPAL-like promoter. These findings will help us to better understand the molecular mechanisms by which VvPAL-like participates in biosynthesis of flavonoids and stress responses.
Development of plants and animals depends on the formation of complex vascular systems for the delivery of water, nutrients, and hormonal signals. This review clarifies major controlling mechanisms that regulate vascular differentiation, regeneration, adaptation, and evolution of plants, which were discovered during the past 50 years. Hypotheses and evidence on the hormonal mechanisms that regulate vascular differentiation are discussed, focusing on phloem and xylem relationships, control of vessel width, fiber differentiation, leaf and flower development, root initiation, evolution of ring-porous wood, parasitism, gall formation, cancer development and prevention.
This research was conducted in the experimental field of the General Station of Hort. and Forestry Ministry of Agricalture / Al-Mahaweel, in the two season of 2014 and 2015 to investigate the influance of Salicylic acid (0 ,100 and 200 mg.L-1) , Tryptophan acid (0 ,100 and 200 mg.L-1) and Nutrient solution with King live (0, 1.5 and 3 g.L-1) and their interactions in growth of olive seedlings of Manzanello cultivar. The experiment conducted in arrangement factorial in a completely randomized block design with three replicates (five seedling in each experimental unit), So the number of treatment is 27 distributed randomly on 405 seedling age of 1 year. The data were analyzed by using the ANOVA table using Genstat software and the mean were compared by using the least significant different ( L.S.D.) at 0.05 significant level. Results can be summarized as following :
1. The treatment with Salicylic acid at a concentration of 200mg.L-1 caused a significant increases in all vegetative growth traits ( plant height, stem diameter, branches number, branches lenght, leaves number, leaf area, and vegetative dry weight percentage), and root growth characteristics (roots number, roots length, lateral roots diameter , and roots dry weight percentage ). Salicylic acid on the other hand effected significantly in chlorophyll and percentage of N , P , K ,Fe, Zn , Cu, carbohydrate, C/N ratio, proteins and endogenous plant hormones concentration (IAA, GA3, Cks) in leaves for two seasons of the study were : 90.09& 117.49cm , 9.06& 10.50mm , 11.24&12.63 branches/ seedling , 23.14& 26.51cm , 328.04 & 348.58 leave/ seedling ، 7.06 & 8.17 cm2 , 44.86 &60.22%, 28.87 & 31.86 root/ seedling , 29.83& 35.04 cm , 3.04&4.10mm , 41.96 &54.25 %, 69.15 &77.67 Spad unit , 1.79 & 1.68% , 0.215 & 0.212%, 1.432 &1.428% , 114.19 & 113.37 mg.Kg-1 , 24.03 & 19.78 mg.Kg-1, 15.25&14.77 mg.Kg-1 , 13.80 &13.47%, 7.66 &8.02 , 11.13&10.46 % , 2.147 & 2.042 m molar , 22.614 &21.845 m molar, 11.049 & 10.144 m molar .
2. Tryptophan acid at 200 mg.L-1 increased significantly in all vegetative growth characteristics.
3. Nutrient solution ( King live) at 3 g.L-1 lead to significant increase in most vegetative and root characteristics, also chemical characteristics : percentage of N , P , K ,Fe, Zn , Cu, carbohydrate, proteins, C/N ratio, chlorophyll and endogenous plant hormones concentration (IAA, GA3, Cks) in leaves.
4. Treating olive seedling with Salicylic acid and Tryptophan acid and Nutrient solution reduced significantly the activity of antioxidant enzymes SOD, CAT, and POD, as well as leaf prolene content and concentration of ABA in leaves.
5. The dual interaction of the study factors causes a significant increase in most characteristics under study,while The dual interaction reduced significantly the activity of anti-oxidants enzymes SOD, CAT and POD, as well as leaf proline content and concentration of ABA in leaves.
6. The triple interaction of the trial factors causes a significant increase in in most characteristics under study( plant height, stem diameter, branches number, branches lenght, leaves number, leaf area, and vegetative dry weight percentage), and root growth characteristics (roots lenght, roots number, lateral roots diameter and roots dry weight percentage ) and effected significantly in chlorophyll and percentage of N , P , K ,Fe, Zn , Cu, carbohydrate, C/N ratio, proteins and endogenous plant hormones concentration (IAA, GA3, Cks) in leaves,while The triple interaction significantly reduced the activity of anti-oxidants enzymes SOD, CAT and POD, as well as leaf proline content and concentration of ABA in leaves for two seasons of the study were : 99.15 & 135.26 cm , 12.15 & 13.55 mm , 14.17 & 15.07 branches/ seedling , 27.20 &30.18cm , 379.67& 423.73 leave/ seedling , 9.31 &11.45cm 2, 54.50 &64.32 %, 35.19 &38.15 root/ seedling , 34.81 & 39.42cm , 3.36 &4.48 mm , 49.17 &60.68 %, 88.32 90.83& Spad unit , 1.89& 1.78 % , 0.290 &0.283 %,1.554 1.535& %, 130.94&128.20 mg.Kg-1, 29.74 &22.97 mg.Kg-1, 17.84&17.20 mg.Kg-1 , 15.68 & 15.10 %, 8.47 & 8.86 , 11.66 &11.15% , 0.308 &0.278 micromole.gm-1 dray weight , 2.884 & 2.989m molar , 26.911 & 25.263m molar , 13.642 &13.014 m molar , 116.57 &105.90 m molar , 10.90 &11.28 Un.mol , 1.23 & 2.45 Un.mol , 82.17 &95.64 Un.gm-1 .
يتناول الكتاب بصورة مبسطة فسيولوجيا النمو والإزهار والتزهير والإثمار فى أشجار الفاكهة
BACKGROUND
Wheat floret development has been a focus of research due to a desire to improve spike fertility, which majorly influences grain yield. Sowing date plays a vital role on grain yield in wheat, and increase in the grain number per spike of winter wheat (Triticum aestivum L.) has been obtained by delayed sowing. During the 2014–2015 and 2015–2016 growing seasons, variation in these developmental patterns was explored involving two winter wheat cultivars (Jimai 22 and Tainong 18) and five sowing dates (24 September; 1, 8, 15 and 22 October).
RESULTS
We noticed clear differences in the grain number per spikelet; delayed sowing had a greater impact on the number of fertile florets at anthesis than grain set. Significant differences in the developmental patterns of florets among spikelet positions corresponded to variations in the floret developmental rate, with faster floret development associated with higher floret fertility. Delayed sowing did not affect the grain number near the rachis, but significantly promoted grain set on distal florets. Increased spike dry weight (SDW) did not compensate for floret size or grain weight, mainly due to enhanced assimilate partitioning to florets.
CONCLUSION
Delayed sowing significantly affects floret developmental dynamics, causing differences in winter wheat floret fertility. An increased SDW concomitant with improved intra‐spike partitioning before anthesis contributes to increase the distal floret numbers per spike and then optimize winter wheat spike fertility. © 2022 Society of Chemical Industry.
Xylem hydraulic safety and efficiency are key traits determining tree fitness in a warmer and drier world. While numerous plant hydraulic studies have focused on branches, our understanding of root hydraulic functioning remains limited, although roots control water uptake, influence stomatal regulation and have commonly been considered as the most vulnerable organ along the hydraulic pathway.
We investigated 11 traits related to xylem safety and efficiency along the hydraulic pathway in four temperate broad‐leaved tree species.
Continuous vessel tapering from coarse roots to stems and branches caused considerable reduction in hydraulic efficiency. Wood density was always lowest in roots, but did not decline linearly along the flow path. In contrast, xylem embolism resistance (P50) did not differ significantly between roots and branches, except for one species. The limited variation in xylem safety between organs did not adequately reflect the corresponding reductions in vessel diameter (by ~70%) and hydraulic efficiency (by ~85%). Although we did not observe any trade‐off between xylem safety and specific conductivity, vessel diameter, vessel lumen fraction and wood density were related to embolism resistance, both across and partly within organs.
We conclude that coarse roots are not highly vulnerable to xylem embolism as commonly believed, indicating that hydraulic failure during soil drying might be restricted to fine roots.
A free Plain Language Summary can be found within the Supporting Information of this article.
The hydraulic performance of plants is crucially affected by tracheid and vessel diameter; therefore, it is important to understand the mechanisms that control the diameter of these vascular conduits in plants. A well-documented phenomenon is the downward gradual and continuous increase in conduit size from leaves to roots. The chapter discusses the auxin gradient hypothesis which proposes that the auxin hormone flowing polarly from young leaves to root tips acts as a morphogenetic signal which forms a long-distance decreasing IAA concentration gradient that controls conduit width and density along the plant axis. Along the gradient, the distance from the auxin-producing young leaves to the differentiating cells correlates the amount of auxin flowing through the differentiating cells; consequently, the duration of the differentiation process increases along the decreasing auxin gradient from leaves to roots. The final size of a conduit is determined by the rate of cell differentiation. Since cell expansion ceases after the secondary wall is deposited, high-auxin concentrations near the young leaves induce narrow tracheids and vessels because of their rapid differentiation, allowing only limited time for cell widening. Conversely, slow differentiation further down permits more cell expansion before secondary wall deposition and therefore results in wide tracheary elements at the base of the stem. The hypothesis was confirmed by a few studies that are discussed.
The major signaling molecules that regulate vascular differentiation and plant development are the plant hormones, also called phytohormones. The word hormone is derived from Greek, meaning to set in motion, excite, and stimulate. Plant hormones regulate gene expression, cellular activity, cell and tissue polarity, and growth and differentiation of tissues, organs, and the whole plant. The hormones can be produced in any living plant cell at extremely low concentrations. They may act locally or at a distance from the producing cells. The primary phytohormones that regulate vascular differentiation, namely, auxin, cytokinin, gibberellin, and ethylene, are discussed, with additional hormonal signals needed for understanding vascular differentiation in plants.
This research was conducted in the experimental field of the General Station of Hort. and Forestry Ministry of Agricalture / Al-Mahaweel, in the two season of 2014 and 2015 to investigate the influance of Salicylic acid (0 ,100 and 200 mg.L-1) , Tryptophan acid (0 ,100 and 200 mg.L-1) and Nutrient solution with King live (0, 1.5 and 3 g.L-1) and their interactions in growth of olive seedlings of Manzanello cultivar. The experiment conducted in arrangment factorial in a completely randomized block design with three replicates (five seedling in each experimental unit), So the number of treatment is 27 distributed randomly on 405 seedling age of 1 year. The data were analyzed by using the ANOVA table using Genstat software and the mean were compared by using the least significant different ( L.S.D.) at 0.05
With the seasonal change from winter to spring, grapevine compound buds break dormancy and start a new annual developmental cycle. The rebuilding of vascular connections between buds and canes is vital to ensure normal development of the bud. We monitored the dynamic development of grapevine buds under natural field conditions, observed vascular connections using light microscopy, and investigated the uptake and transport of water in buds and canes from dormancy to bud break. During dormancy, the bud was isolated from the cane and no xylem was observed in the bud or the junction region between the bud and the cane. However, at the stage of bud swelling (stage II), xylem was observed at the cane to bud junction. The rate of water uptake through the xylem at the junction increased as bud development progressed. These results suggest that buds were hydraulically isolated from the cane during dormancy and the formation of xylem between bud and cane started with swelling of the bud. The velocity of water transport into the bud also increased with bud development. We discuss several factors that affect the formation and differentiation of xylem, including temperature, hormones and water. It is likely that the rebuilding of vascular connections between buds and canes is related to multiple factors rather than any one individual factor.
For more than two millennia, superior fruit tree genotypes have been grafted onto rootstocks to maintain the genetic identity of the desirable scions. Until the 20th century most fruit trees were grafted onto seedling rootstocks. Following the classification, evaluation, and propagation of clonal rootstocks during the early 1900s, dwarfing rootstocks became important to the commercial apple industries. Although trees on dwarfing rootstocks are more economical to maintain, and are more precocious and productive than trees on seedling rootstocks, there remains a need for dwarfing rootstocks to be adapted to different growing conditions. During the past 100 years, considerable effort has been made to understand the physiological changes in the scion induced by rootstocks. More recently, molecular techniques have been utilized to identify the genes that control interactions between scion and rootstock. Modern rootstock breeding programs are combining molecular and traditional techniques to develop rootstocks that are dwarfing, productive, and tolerant to biotic and abiotic stresses. In this chapter, the history, development and current use of apple rootstocks, the current understanding of rootstock–scion interactions, and current efforts to develop and evaluate superior rootstocks are discussed.
In its natural habitat, the one-leaf plant Monophyllaea horsfieldii (Gesneriaceae) shows striking postural changes and dramatic loss of stability in response to intermittently occurring droughts. As the morphological, anatomical and biomechanical bases of these alterations are as yet unclear, we examined the influence of varying water contents on M. horsfieldii by conducting dehydration–rehydration experiments together with various imaging techniques as well as quantitative bending and turgor pressure measurements. As long as only moderate water stress was applied, gradual reductions in hypocotyl diameters and structural bending moduli during dehydration were almost always rapidly recovered in acropetal direction upon rehydration. On an anatomical scale, M. horsfieldii hypocotyls revealed substantial water stressinduced alterations in parenchymatous tissues, whereas the cell form and structure of epidermal and vascular tissues hardly changed. In summary, the functional morphology and biomechanics of M. horsfieldii hypocotyls directly correlated with water status alterations and associated physiological parameters (i.e. turgor pressure). Moreover, M. horsfieldii showed only little passive structural–functional adaptations to dehydration in comparison with poikilohydrous Ramonda myconi.
In plants, differentiated somatic cells may dedifferentiate and subsequently redifferentiate into (adventitious) shoots, roots, or embryos. The formation of adventitious shoots (caulogenesis) and roots (rhizogenesis) is specified with the term adventitious organogenesis, whereas somatic embryogenesis refers to the formation of adventitious (somatic) embryos. Adventitious organogenesis occurs frequently during natural life but may be achieved at very high frequencies in tissue culture. It is one of the basic tools in vegetative plant propagation and plant breeding. In propagation, adventitious formation of shoots is important in micropropagation of many crops and adventitious formation of roots from (micro)cuttings is required to obtain complete plants from excised shoots. In breeding, adventitious organogenesis is essential among others in transformation and haploid production. This article reviews adventitious organogenesis from the point of view of developmental biology and deals with physiological, biochemical, molecular, and genetic aspects. It covers both practical and fundamental aspects.
Apical dominance, internode elongation, radial growth and xylem cell size in coppice and apical shoots of Betula pubescens B. Pendula were determined and related to endogenous indole-3-acetic acid (IAA) levels, measured by gas chromatography-selected ion monitoring in the apical bud and at three positions along the stem. The effects of defoliation and debudding on morphological and anatomical characters and endogenous IAA levels were also investigated. The coppice shoots displayed superior stem elongation and increased branching during the initial phase of growth, after which their growth pattern was similar to that of the seedlings; however, their radial growth was greater throughout the experiment. Both plant types produced smaller-sized xylem cells at the top of the shoot than at the bottom with coppice shoots tending to form larger tracheids and smaller vessels than the seedlings. There was no consistent difference in IAA concentration between the coppice shoots and the seedlings. Defoliation and debudding reduced the IAA level in the stem within 36 h and it was still low after 25 days. Although the extent of the IAA decrease was similar in both coppice shoots and seedlings, the treatments affected the morphological and anatomical characters differently in the two plant types. The results suggest that the observed differences between seedlings and coppice shoots were not mediated through a drastic change in IAA level.
It is clear from numerous and diverse observations that endogenous growth substances play a critical role in cambial activity and xylem differentiation in both herbaceous and woody plants. Nevertheless, the information reviewed in this chapter seems to raise more problems than it solves.
Seasonal cambial activity and xylem development were monitored anatomically at several main-stem positions in 20-year-old Pinuscontorta Dougl. Gas chromatography – mass spectrometry and electron-capture gas-chromatography quantifications of endogenous indol-3-yl-acetic acid (IAA) and (S)-abscisic acid (ABA), respectively, were made in these same tissues. In addition, IAA and ABA were measured in shoot apices, growing needles, and mature needles. Cambial reactivation occurred several weeks before budbreak at the base of the living crown, and it occurred only slightly before budbreak in younger cambia. Neither an acropetal nor a basipetal progression of reactivation were found. In contrast, early-wood development commenced in foliated stem locations well before commencing in nonfoliated regions. IAA and ABA levels in the cambial region increased, but little, immediately before cambial reactivation. IAA levels in extending apices, extending needle bases, and cambia reached maxima in midsummer. Cambial IAA levels remained high and ABA levels declined after both shoot and needle extension were complete. IAA levels in cambia were highest in the main stem near the crown base at all times; ABA levels varied little throughout the season. Following autumn inactivation of the cambium, IAA levels decreased and tracheids with narrow radial diameters differentiated at this time. ABA levels showed no significant increase as shoots, needles, and cambium ceased growing.
A comparison was made of the relative vulnerability of xylem conduits to cavitation and embolism in three species [Thuja occidentalis L., Tsuga canadensis (L.) Carr. and Acer saccharum Marsh.]. Waterlogged samples of wood were air dehydrated while measuring relative water loss, loss of hydraulic conductance, cumulative acoustic emissions (= cavitations) and xylem water potential. Most cavitation events and loss of hydraulic conductance occurred while water potential declined from – 1 to –6 MPa. There were differences in vulnerability between species. Other people have hypothesized that large xylem conduits (e.g. vessels) should be more vulnerable to cavitations than small conduits (e.g. tracheids). Our findings are contrary to this hypothesis. Under water stress, the vessel bearing wood retained water better than tracheid bearing wood. However, within a species large conduits were more prone to cavitation than small conduits.
IAA was essential for the occurrence of callus growth in stem explants. Callus growth was similar in appearance and extent in winter- and summer-explanted material. Tracheids differentiated in explants only when actively differentiating tracheids were already present at the moment of explanting, suggesting the absence of factors necessary for tracheid differentiation in over-wintering tissues. Experiments with single intact needles onPinus cembroides var.monophylla cuttings confirmed a previous interpretation that the mature pine needle, rather than the short-shoot apical meristem at its base, promotes tracheid differentiation in the stem.
Following cation and anion exchange chromatography, 1-aminocyclopropane-1-carboxylic acid (ACC) was converted to the 2,4-dinitrophenyl derivative and then purified by high-performance liquid chromatography (HPLC). After three HPLC steps, endogenous ACC was identified by GCMS in the vascular cambium on the lower side of Pinus contorta Dougl. ssp. latifolia branches in association with compressionwood differentiation, but ACC was not detected in the opposite wood cambial region on the upper sides of the same branches.The possibility that ACC and ethylene have physiological roles in cambial activity and compressionwood tracheid differentiation is discussed.
The regulatory effect of cytokinin on the formation of secondary xylem fibers was studied in the hypocotyl of young Helianthus annuus L. plants. Positive correlation was found between the kinetin supplied (0.25-0.5 micrograms/gram) to the growth medium and the rate of fiber formation within and between the vascular bundles. Reducing the root originated cytokinin supply, either by root removal or by lowering the transpiration rate, diminished the number of newly formed secondary xylem fibers. This decrease was considerably reversed in the presence of 0.5 microgram/gram kinetin. Early pulse exposure of kinetin had a temporary promoting effect on fiber differentiation at low concentrations and a permanent inhibitory effect at high concentration.
In Avicennia germinans, A. resinifera and A. marina no correlation was found between the number of successive anomalous rings in the internodes and sylleptic shoots and the number of leaves that developed above an internode. This suggests that leaf and lateral branch formation have no immediate effect on new cambium initiation. The results show that although there is some correlation between the internode location along the shoot (radial increment) and the number of rings, initiation of successive cambia might be regulated by the overall vigour of growth rather than by the simple sequence of leaf and lateral branch formation.
Roots of Khaya ivorensis andK senegalensis were studied with reference to the anatomical structure of the secondary xylem. Though growing in ecologically contrasting habitats and showing morphologically different root systems, the two species do not differ anato- mically. There are more vessels in the roots than in the stem. Compared with the vessels of the stem they are wider in the lateral roots, narrower in the vertical roots. The amount of parenchyma tissue does not vary greatly, but storage of starch is denser in the roots, especially in the septate fibres. In the very superficial lateral roots of K ivorensis no anatomical differences can be observed between aerial and underground portions. A comparison is made with a few other tropical woody plants.
The differentiation of primary and secondary tracheids was studied quantitatively in the hypocotyl ofPimis pineaL. seedlings. The number of primary and secondary tracheids decreases and their radial diameter increases from cotyledons to roots. Rapid differentiation immediately beneath the cotyledons results in narrow tracheids, while slow development at the root end yields wide tracheids. The metaxylem elements in the root direction are the widest tracheids as a result of the longer time of their cell expansion. Differentiation of secondary tracheids starts immediately below the cotyledons, where the highest auxin concentration is expected, and continues basipetally towards the roots. These results are in accordance with the hypothesis that high levels of auxin induce narrow tracheids, whereas low levels of auxin result in wide elements.
Treatment of plants of Cochorusoiltorius L., Hibiscus cannabinus L., and Cannabis sativa L. with gibberellic acid induced highly significant increases in cell diameter and wall thickness of problem fibres. This difference varies along the shoot and is maximal in the middle region, internodes 10–15.
The ratio The ratio cell wall thicknesscell breadth is higher in treated plants. is higher in treated plants. Gibberellic acid reduces the angle of orientation of the pits to the cell wall and also the pit frequency. Pits in treated plants are longer and narrower in surface view.
We report measurements of the number of vessels ending within the nodes in comparison with that in the internodes. Such measurements have been carried out during autumn 1982 and 1983 in 1-year-old twigs of three species with diffuse-porous wood (Vitis vinifera L., Populus deltoides Bartr. and Olea europaea L.) and three ring-porous trees (Juglans nigra L., Castanea sativa Mill., Sophora japonica L.). In all three species with diffuse-porous wood, a significantly higher percentage of vessels ending in the nodes (at the leaf gap) was recorded when compared with that in the internodes. No significant differences were found between nodes and internodes in this respect in ring-porous trees. Since vessel ends are capable of screening out gaseous emboli and/or particles bigger than 1 μm in diameter, we interpret the nodes of diffuse-porous trees as stem zones providing safety for the water conducting system. The reason why ring-porous trees are likely not to need such 'safety zones' is also discussed.
It is known that growing parts of the shoot induce the differentiation of vascular tissues below them and that this induction is due to the production of auxin. The problem dealt with here is why the formation of xylem proceeds in the growing roots. The redifferentiation of parenchyma to tracheary elements in grafts of pea plants was used in this study. It is proved that this is not due to stimuli coming from the root tip but rather to the movement of a stimulus coming from the shoot into the root. The polarity of movement is maintained even in thin sections, but it can be reversed by a strong shoot influence.
This work deals with those properties of plant tissues which are responsible for the organization of vascular cells in ordered strands. It is shown that auxin alone is sufficient to cause the differentiation of strands of xylem cells in the parenchyma of pea roots. An artificially induced strand, once it is formed, attracts towards itself newly induced vascular strands, and this attraction results in the union of old and new strands. It is also shown that the application of auxin to natural vascular tissues prevents their being joined by newly induced vascular strands. It is proved that this is dependent on a directional effect and not simply on a local accumulation of auxin.
To understand these results, it must be assumed that the polarity in terms of auxin transport is increased during the process of vascular tissue induction. The same polarity, once established, is maintained by the presence of auxin, so that the differentiation of strands perpendicular to the axis of this polarity is prevented. These characteristics of plant tissues concerning auxin transport explain the basic phenomena of the organization of vascular cells in defined and ordered strands.
Publisher Summary This chapter discusses the interactions and internal programmes that result in the patterned differentiation of vascular tissues. The term “pattern” is used to refer to the high degree of order, or predictability, of the system at all levels— the orientation and contacts of the strands forming a coherent system supplying all the organs of the plant, the organization of the transporting cells in files that are functional vessels and sieve tubes, and the relations among the different vascular tissues (phloem, cambium and xylem) and their component cells. The stress is, thus, on relations between cells of the same and of different types and not on the processes of differentiation and controlled gene expression. It is shown that all aspects of the development and maintenance of the vascular tissues might depend on one control system, which is at least partially hormonal. The way this control could operate is in the working hypothesis that together with the problems and possibilities it poses is the central conclusion of this work. A major characteristic of the hypothesis considered is that a gradual, feedback relation between differentiation and signal distribution creates a reliable pattern. Controls of this type may not result in very precise patterns, but they would be simple and dependable in avoiding mistakes of functional significance. They could, thus, account for the vascular patterns found in plants, where no two halves of the same leaf are exactly the same. These controls also have the virtue of depending on known signals and cellular responses. It is, thus, possible that the principles on which these controls are based have a wide relevance, both in plants and in other cases of biological development. The results considered in the chapter suggest that plant hormones, and especially auxin, play an essential role both in the relation among plant organs and in the relations among neighboring cells.
Summary Every part of the tree contains a range of vessel lengths, and always a much larger percen tage of short than long vessels. Vessel diameter and longest vessel length increase from twigs to branches, down along the stem, to the long, rope-like roots. The percentage of vessels in the shortest length class decreases in the same di rection. Although red maple is considered a dif fuse-porous species, vessels in latewood are nar rower and shorter than in the earlywood in any given part of the tree.
A B S T R A C T One mm-thick segments cut 10-11 mm proximal to the root tip of germinating seeds of garden pea Pisum sativum were cultured in sterile nutrient medium containing auxin in the presence and absence of kinetin. In the absence of added cytokinin, pericyclic proliferation occurred, the cortical tissues showed no proliferation and were sloughed off, and a callus tissue of diploid cells was formed. In the presence of kinetin concentrations from 0.1-1.0 ppm cortical cells of the segments were induced to divide, beginning at the third day. From experiments with 3H-thymidine incorporation at different times of culture, from cytological squash preparations and from histological sections it was shown that the cortical cells stimulated to divide by cytokinin underwent DNA synthesis prior to division, were polyploid, and following cell division rapidly underwent cytodifferentiation at 5-7 days to form mature tracheary elements. At 10 days, when over 300,000 new cells had been formed per segment about 16% of these cells had formed traeheary elements. It was concluded that cytokinin, together with auxin, was essential for the initiation of DNA synthesis in the cortical cells, for their subsequent division, and finally for their specific cytodifferentiation.
A Kontron MOP system (electromagnetic electronic image analyser with built-in microprocessor system) was used for the quantitative microscopic analysis of trunks from sycamore maple and elm. It was established that the radial sizes of the derivative cells (mainly wood fibres) from each single cambium mother cell occur in a wave pattern over time which is not identical with the growth ring changes. Trachea appear regularly in the troughs in the sycamore maple and in the peaks in the elm. The author traces the well-known diverse nature of cambial production back to the most simple and antagonistic basic characteristics of cambial activity. This enables the construction of an encompassing variation system using code words for the distinct characterization of all possible wood structures and classification according to dynamic-cambial combinations. Furthermore, the existence of function-determining factors which move along the cambium may be regarded as proven on the basis of the analysis. The appearance can be explained according to the so-called "rhythmic profactor theory," which enables the construction of all possible wood structures through the appropriate combination of only a few rhythmic (harmonic) oscillation components in model systems.
The purpose of this chapter is to describe a conceptual framework for understanding how trees grow and how they and other perennial plants defend themselves. The concept of compartmentalization has developed over many years, a synthesis of ideas from a number of investigators. It is derived from detailed studies of the gross morphology and cellular anatomy of the wood and bark of roots and stems in healthy angiosperms and gymnosperms. It is based on research in tree physiology and the chemistry of wood and bark. It is founded on observations of trees injured in the field by wind, snow, ice, fire, animals, and insects, as well as during pruning, coppicing, sugaring, and other forest and orchard management practices. It is based on experimental studies of natural and artificial wounds with and without controlled inoculations with selected pathogenic and saprophytic microorganisms. These microbes have included wood-decaying Basidiomycetes and Ascomycetes, wood-staining Ascomycetes and Fungi Imperfecti, canker fungi, and a myriad of woodinhabiting bacteria. The end result of all these studies is an integrating concept that involves defenses laid down by trees prior to injury and defenses laid down by trees after injury.
The coleoptile curvature bioassay of agar diffusates from successive cambial‐region sections of Pinus silvestris L. stem tissue reveals the existence of a wave‐like pattern, possibly of auxin translocation. Spectrofluorometric determinations of indolyl‐3‐acetic acid (IAA) in these diffusates gave only a poor correlation. Probably another phytohormone, also an auxin, plays a more important role in the pattern.
The amplification in the amplitude of the pattern, brought about by apically applied IAA, cannot be induced by the synthetic auxin, 2,4‐dichlorophenoxyacetic acid.
Cambial activity and vessel differentiation of the Quercus robur stem were investigated in relation to concentration of growth regulators and sucrose, seasonal changes in the sensitivity of cambial cells, and axial polarity of the stem. Basipetal efflux of natural auxin was measured in the oak stem cambial region. IAA, GA3, kinetin and sucrose affected cambial activity and/or initiation of vessel differentiation differently, depending upon concentration. Depending upon the season, kinetin increased or reduced the stimulation of cambial activity caused by IAA and GA3, but it did not affect the differentiation of vessels. Supply of sucrose in higher concentrations reduced the number of differentiated vessels but did not decrease the stimulation of cambial divisions.Unlike stimulation of cambial activity by GA3, auxin stimulation of cambial divisions and differentiation of vessels were highly dependent upon stem polarity, 2,3,5-triiodobenzoic acid (TIBA) inhibited formation of vessels, but not cambial activity. The oscillations in basipetal efflux of natural auxin from the cambial stem region of successive 6 mm long sections substantiate the hypothesis that the histogenesis of xylem tissue in ring-porous species is under control of the vectoriat field that is associated with oscillatory phenomena in polar auxin transport.
S ummary
Vessel endings in various parts of the alfalfa ( Medicago sativa L.) shoot were mapped by an India ink movement method. Stems were excised at various locations between the fifth and sixth nodes below the apex and placed in vials of India ink. Vessel endings were determined by examining the distance to which ink penetrated in the transpiration stream; the particles of India ink are too large to pass from vessel to vessel through pit membranes. The highest frequencies of vessel endings were found (1) in the petiolules and blades of the leaflets, (2) in the pulvinus of the petiole where the leaf traces emerge from the stem and anastomose while traversing the abscission zone, and (3) in the stem nodes where leaf traces arise and vascular bundles anastomose. The frequency of vessel endings was low and uniformly distributed throughout both internodes and petioles. Vessels were longest in the internodes and shortest in the leaflets. The regions where vessel endings were grouped coincided with those determined in other studies to be particularly susceptible to vascular blocking by macromolecules such as those produced by vascular wilt pathogens.
Three-year-old active and dormant sycamore plants were treated with labelled auxin solution applied to the outer bark or the inner xylem in order to establish the rate of transport of radioactive materials in longitudinal and radial directions.
The velocity of auxin transport in the vertical direction within the bark was 0.4–0.6 cm/h in active plants and 0.1–0.2 cm/h in dormant plants. It was found that auxin can move from bark to xylem or vice versa. Autoradiography shows that radial transport takes place within the rays. Auxin is translocated from xylem to bark at a higher rate and in greater amounts than in the reverse direction both in active and dormant plants, but the radial transport from bark to xylem in dormant plants is greater than in active plants. The slower the vertical transport within the bark the faster the radial one in the centripetal direction. On the other hand, the rate of the transport in the centrifugal direction was found to be slower for dormant plants. A higher level of auxin may be maintained in the cambium of active plants because of the centrifugal movement of auxin within the xylem.
The occurrence of vessels in the form of rings is used as a critical example for a hypothesis about the control of the pattern of cells in vascular tissues. These vessels, rare in intact plants, are common in the basal or root side of tissues close to transverse wounds of bean seedlings, radish storage tissues, and other plant material. Their formation is promoted, as are normal vascular tissues, by developing parts of the shoot or by a source of the hormone auxin. They are also found in grafts where cells of opposite polarities are close together, and in cut plants where vascular induction occurs from the direction of the roots and is therefore opposite to the original polarity of the tissue. Circular vessels are found, therefore, where the flux of auxin and possibly other signals controlling vascular differentiation is expected to follow a circular route. They show that differentiation is a response of individual cells to the flux rather than the gradient or concentration of the hormonal signals a
Callus tissues in established maintenance culture lack morphological and physiological organization. Such callus consists of homogeneous parenchyma. Movement of auxin and sugar, therefore, must be along diffusion gradients. The only vascular tissues occurring in callus are induced. Experimental induction of vascular tissues has been successful in callus of 3 sp. of the Oleaceae: a tree, Fraxinus americana, and 2 shrubs, Syringa vulgaris and Ligustrum vulgare; another tree, Salix purpurea, var. lambertiana; a vine, Parthenocissus tricuspidata; and an herb, Helianthus tuberosus. In each of these species, an auxin (IAA or NAA in these studies) and a sugar (sucrose or glucose in these studies) prove necessary for the induction and complete differentiation of xylem and phloem in callus tissues. Varying concentrations of sugar alter the proportions of xylem to phloem: low concentrations, 1.5%-2.5%, favor xylem formation; high, 3%-4%, favor phloem. Middle concentrations, 2.5%-3.5%, favor the presence of xy
The mode of development of successive cambia and the differentiation of cambium derivatives are unique to Avicennia and do not follow the scheme proposed for members of other families possessing included phloem. The sequence of formation of cambial derivatives and their differentiation are: (1) There are few parenchyma cells toward the inside; (2) the xylem is toward the inside with continued production of up to 10 files of parenchyma cells toward the outside; (3) a ring of one to three sclereids thick develops, one to three cells from the outer limit of the secondary parenchyma files; the sclereids start to develop very early, sometimes when only four outer cambial derivatives have been produced; (4) the cambium gradually ceases to function and phloem strands are formed by cell divisions in the parenchyma files; only short fragmented cambium remnants are left on the inner side of the phloem; and (5) a new cambium develops in the most distal parenchyma file, immediately outside the sclereids. The new c
STEMS OF PERENNIAL PLANTS, particularly trees, represent a considerable investment in biomass. Trees can survive even under the most adverse conditions, but only if the hydraulic integrity of the stem is preserved. A very important and vulnerable part of the stem is the xylem. As water is pulled into the top of the tree, a period of excessive drought can drop xylem pressures to such low negative values that water columns break (cavitation). The tracheary elements in which this happens are permanently lost as functional parts unless positive pressures refill them within a very short time (perhaps hours?). Journal Article
The problem studied in this work was that of the internal control of the formation of strands of fibres in Pisum sativum . It is shown that fibre differentiation is dependent on stimuli originating in young leaf primordia. Removing these primordia early enough prevents fibre differentiation; changing the position of the leaves experimentally changes the position of the fibres as well. It was demonstrated that some stimuli for fibre differentiation must flow through the strands at the time they differentiate. The evidence for this flow is in experiments concerning the ability of very young fibre strands to regenerate after cuts as well as in experiments concerning their pattern of joining. The stimuli which originate in the leaves and control the differentiation of fibres and xylem are shown to differ in at least one component: auxin does not cause fibre differentiation and no surgical treatments, carried out on very young tissues, caused the replacement of part of a strand of fibres byor xylem or vice versa.
Cortical parenchyma of pea roots normally does not divide nor differentiate as tracheary elements. After excision from the root these cells can be induced to undergo cell division followed by differentiation of tracheary elements in the presence of cytokinin. 5-Fluorodeoxyuridine prevents cell replication and cytodifferentiation. The thymidine analog, 5-bromodeoxyuridine, specifically prevents cytodifferentiation with little or no effect on the rate of cell replication. Thymidine can also prevent cytodifferentiation with little effect on cell replication. Thymidine reverses the effect of 5-bromodeoxyuridine (BrdU) or 5-fluorodeoxyuridine (FdU) when given simultaneous with or subsequent to either BrdU or FdU. BrdU given with FdU allows up to one round of cell replication but no cytodifferentiation. Differentiation is rarely observed unless the entire cell population has undergone the equivalent of two cell generations. These results are combined with those of other investigators to present an hypothesis that implicates DNA replication but not cytokinesis in the regulation of certain types of differentiation.
THE formulation of a general model of gene regulation in eukaryotic organisms would be facilitated were it known when the molecular events responsible for reprogramming of genetic information occur during the cell cycle. Evidence from various systems in which animal cells differentiate in vivo and in vitro suggests that certain characteristics of the fully differentiated state are not manifest until the cells undergo DNA synthesis and nuclear division1. Similarly the differentiation of wound vessel members (WVM) in plant parenchyma tissue is thought to occur only after cells have replicated at least once in inductive conditions2.
A sycamore callus (S 4) has been isolated and grown on a medium containing salts, vitamins, a casein digest, 2% sucrose and 1 mg/l. NAA. The callus, which would not grow in the absence of the added auxin, was much firmer in texture than a sycamore callus (S 2) isolated in this laboratory in 1958 which has not been induced to differentiate. When kinetin over the range 0.05-0.5 mg/l. was included in the growth medium of S 4 nodules of xylem and phloem were induced within the tissue and roots frequently grew from the surface of the callus. Some roots developed geotropic sensitivity although the majority grew radially outwards from the callus surface. The roots also varied with respect to the number of root hairs they carried. No roots were produced at sucrose concentrations less than 2%, although histological examination revealed extensive xylem and phloem differentiation relative to the amount of growth which had taken place. When sugars other than sucrose were supplied in the medium at a concentration of 3% (w/v) roots were also induced in those calluses where the carbon source had supported good growth. Sucrose, glucose and fructose were identified in the ethanol-soluble extracts of all these calluses. Radioactivity was incorporated into sucrose when S 4 was incubated on a medium containing D-[U-14C]glucose for 24 h.
Any sugar which supported growth and differentiation was therefore one which was capable of entering the common metabolic pathway used by the plant for glucose and sucrose. The cells could undergo differentiation so long as the sugar they were supplied with supported active growth and division. The possibility of a physiological role for sucrose is discussed.
A technique is described for the processing of regenerated xylem and sieve tubes from the same wound area for microscopic and quantitative comparison.Regeneration was examined in internodes of 2 developmental stages in Coleus: internode 2, elongating, characteristic of primary growth; and internode 5, non-elongating, characteristic of secondary growth.Transport of indoleacetic acid (IAA) in excised number 5 internodes of Coleus is strictly polar, in a basipetal direction, judging by a regeneration bioassay involving both sieve tube strands and xylem cells. Similar results were obtained with tomato.If isolated number 5 Coleus internodes are not treated with hormone, they regenerate no xylem cells and a small number of sieve tube strands. With increasing concentrations of IAA added apically, the number of regenerated sieve tube strands (and, with higher concentrations, of xylem cells) increases progressively up to 1% IAA, the highest concentration applied.Internode 2 of Coleus regenerates fewer xylem cells or sieve tube strands than internode 5, whether on the otherwise intact plant or with a given concentration of IAA added apically. The amount of regenerated xylem increases with added apical IAA, except that the highest concentration gives no further increase. The number of xylem cells regenerated in intact plants occurs at the same interpolated IAA concentration as in number 5 internodes. No concentration of IAA tried provided replacement of intact number of sieve tube strands in internode 2.IAA can exert a regenerative stimulus on both xylem and sieve tubes in the area immediately adjacent to the site of its application.
Auxin waves and plant morphogenesis
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by Tel Aviv University on 05/05/12. For personal use only.
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differentiation in Xanthium by auxin and
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Differences in wood anatomy of Iianas and trees
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Initiation of radial polarity in the interfascicular cambium of Ricinus communis L
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