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Variegation in Arum italicum leaves. A structural–functional study
Abstract
The presence of pale-green flecks on leaves (speckling) is a frequent character among herbaceous species from shady places and is usually due to local loosening of palisade tissue (air space type of variegation). In the winter-green Arum italicum L. (Araceae), dark-green areas of variegated leaf blades are ca. 400 μm thick with a chlorophyll content of 1080 mg m⁻² and a palisade parenchyma consisting of a double layer of oblong cells. Pale-green areas are 25% thinner, have 26% less chlorophyll and contain a single, loose layer of short palisade cells. Full-green leaves generally present only one compact layer of cylindrical palisade cells and the same pigment content as dark-green sectors, but the leaf blade is 13% thinner. A spongy parenchyma with extensive air space is present in all leaf types. Green cells of all tissues have normal chloroplasts. Assays of photosynthetic activities by chlorophyll fluorescence imaging and O₂ exchange measurements showed that variegated pale-green and dark-green sectors as well as full-green leaves have comparable photosynthetic activities on a leaf area basis at saturating illumination. However, full-green leaves require a higher saturating light with respect to variegated sectors, and pale-green sectors support relatively higher photosynthesis rates on a chlorophyll basis. We conclude that i) variegation in this species depends on number and organization of palisade cell layers and can be defined as a "variable palisade" type, and ii) the variegated habit has no limiting effects on the photosynthetic energy budget of A. italicum, consistent with the presence of variegated plants side by side to full-green ones in natural populations.
... Some studies have shown that leaf variegation plays important roles in plant adaptation to abiotic factors in the environment, predation prevention, and enhances reproduction. The high photosynthetic efficiency in the variegated leaves of Arum italicum was found to be closely related to the palisade tissue structure, which might be a result of the long-term adaptation of this plant to the low light environment under shade [7]. Stehlik et al. [8] suggested that various foliar patterns formed by structural variegation might provide protection against herbivores. ...
... Hara [1] indicated that many plant genera belong to the 'air space' variegation type, such as Arisaema, Begonia, Clematis, Cyclamen, Ornithogalum, Pyrola, Saxifraga and Viola. The location of the air spaces varies from plant to plant, with some found between the adaxial epidermal cells and the upper mesophyll, such as in Sonerila heterostemon [27], Begonia formosana [2] and Nervilia nipponica [28]; others surrounding spongy tissue [7]; and others located between the chlorenchyma and the water storage tissue, as in a Begonia cultivar [2]. In our study, air spaces were identified between the water storage tissue in the white type, which had not been observed in previous studies. ...
... In Begonia, the typical funnel-shaped chlorenchyma appears isodiametric in light areas [2]. In pale-green sectors of A. italicum leaf, the palisade tissue is reduced to a loose layer that is half the thickness of that in dark-green sectors and is composed of small, underdeveloped cells [7]. In the white area of leaves in Blastus cochinchinensis [6], the upper mesophyll is composed of three or four layers of colourless sponge-like cells, which contribute to the higher leaf thickness. ...
Background
Primulina pungentisepala is suitable for use as a potted plant because of its beautiful leaf variegation, which is significantly different in its selfed offspring. However, the mechanism of P. pungentisepala leaf variegation is unclear. In this study, two types of offspring showing the greatest differences were compared in terms of leaf structure, chlorophyll contents, chlorophyll fluorescence parameters and transcriptomes to provide a reference for studying the molecular mechanism of structural leaf variegation.
Results
Air spaces were found between water storage tissue, and the palisade tissue cells were spherical in the white type. The content of chlorophyll a and total chlorophyll (chlorophyll a + b) was significantly lower in the white type, but there were no significant differences in the content of chlorophyll b, chlorophyll a/b or chlorophyll fluorescence parameters between the white and green types. We performed transcriptomic sequencing to identify differentially expressed genes (DEGs) involved in cell division and differentiation, chlorophyll metabolism and photosynthesis. Among these genes, the expression of the cell division- and differentiation-related leucine-rich repeat receptor-like kinases (LRR-RLKs), xyloglucan endotransglycosylase/hydrolase ( XET/H ), pectinesterase ( PE ), expansin ( EXP ), cellulose synthase-like ( CSL ), VARIEGATED 3 ( VAR3 ), and ZAT10 genes were downregulated in the white type, which might have promoted the development air spaces and variant palisade cells. Chlorophyll biosynthesis-related hydroxymethylbilane synthase ( HEMC ) and the H subunit of magnesium chelatase ( CHLH ) were downregulated, while chlorophyll degradation-related chlorophyllase-2 ( CHL2 ) was upregulated in the white type, which might have led to lower chlorophyll accumulation.
Conclusion
Leaf variegation in P. pungentisepala was caused by a combination of mechanisms involving structural variegation and low chlorophyll levels. Our research provides significant insights into the molecular mechanisms of structural leaf variegation.
... Light-harvesting and photosynthetic capacity in white leaves is reported to decrease significantly only when the chlorophyll content decreases drastically (Rosso et al., 2009). However, little difference in photosynthetic capacity is indicated between white leaves and green leaves of Arum italicum and Begonia formosana (Rocca et al., 2011;Sheue et al., 2012). ...
... Thus, photosynthetic activity of the mesophyll also changes with the variation in composition of the photosynthetic apparatus (Borsuk and Brodersen, 2019). White leaves of Ranunculus ficaria and Arum italicum (Konoplyova et al., 2008;Rocca et al., 2011) possessed three or two palisade cell layers, which suggested that the leaf structure was altered. However, the authors considered that the change in leaf structure results in increased efficiency of light capture and electron transfer to a certain extent. ...
... Previous studies suggest that white areas of Begonia formosana leaves can maintain higher photosynthetic capacity (Sheue et al., 2012), which is the result of palisade mesophyll cells in white areas containing functional chloroplasts. In addition, in some plants, for example, Ranunculus ficaria and Arum italicum (Konoplyova et al., 2008;Rocca et al., 2011), white leaves possess two or three palisade cell layers, which effectively maintain the photosynthetic capacity of white leaves. However, for A. kolomikta, the specialized structure of white leaves suggested that the spongy mesophyll compensated for lower photosynthetic capacity of the palisade mesophyll and that the functioning of the spongy mesophyll as the main photosynthetic tissue plays a vital role in maintenance of the photosynthetic capacity of white leaves. ...
Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (Fv/Fm) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas Fv/Fm and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.
... On the basis of these observations in the breeding program, we have determined the trait as being sublethal, meaning variegation does not result in complete lethality and the plant is able to survive, but it has negative consequences on plant fitness and reduces the plant's chance of surviving in field conditions. Limited research has examined the effects or consequences of variegation in Vitis (Filler et al., 1994;Rathjen and Robinson, 1992), but several other variegated plant species have been investigated such as Arabidopsis thaliana (Aluru et al., 2001;Rosso et al., 2009;Wetzel et al., 1994), Silybum marianum (Shelef et al., 2019), Arum italicum (La Rocca et al., 2011), and Begonia spp. (Sheue et al., 2012). ...
... In two of the cultivars, the creamy-yellow sector's Chl a/b ratio was %5 times lower compared with green sectors. In variegated Arum italicum, pale-green variegated sectors had 26% less Chl than normal, dark-green sectors (La Rocca et al., 2011). In the Arum thaliana mutant immutans, variegated seedlings had a 4-to 5-fold decrease in Chl accumulation under exposure of continuous high light treatment (Rosso et al., 2009). ...
... Photosynthesis is another common parameter typically measured in studies comparing variegated to WT plants. Most studies found that variegated plants photosynthesized at a similar rate to WT plants which suggests that the variegated plants are able to compensate for a lack of pigments in some tissue of the leaf (Esteban et al., 2008;La Rocca et al., 2011;Shelef et al., 2019;Sheue et al., 2012). ...
Variegation is a common trait in plants that characteristically displays white or off-colored plant tissue. In grapevine, leaf variegation is expressed as white and pale green leaf tissue resulting in plants that are stunted in growth and hindered in development. In this study, several experiments were performed to investigate the impact of this mutation has on the anatomy of grape leaves and physiology of the plant. Histological staining of variegated and nonvariegated leaf tissue transections showed alterations to the leaf palisade mesophyll structure that affected leaf tissue width. An assay quantifying leaf pigments was performed to compare chlorophyll and carotenoid concentrations in leaves between variegated and wild-type seedlings, which showed that variegated leaf samples had reduced chlorophyll and carotenoid concentration. Through fluorescence imaging, we determined that photochemical efficiency of photosystem II (PSII) is reduced in variegated seedlings. By growing variegated and wild-type plants under high, medium, and low light intensities that variegated plants exposed to higher light intensity reduces the phenotypic expression of the variegation trait. Also, we found variegated plants to have significant reductions in growth traits such as plant height, leaf number, branch number, and dry weight compared with wild-type phenotype plants. Overall, our experiments revealed the variegation mutation altered normal leaf development causing significant effects to grapevine physiology.
... Several studies have suggested that leaf variegation plays a significant role in adaptation to abiotic factors, as well as in the avoidance of predation, and in reproduction (Sheue et al., 2012;Pao et al., 2014;Shelef et al., 2019). For example, studies on the photosynthetic system of variegated leaves of Arum italicum (Araceae) have shown that photosystem II in discolored areas of leaves maintains high activity under low light conditions, and the high photosynthetic efficiency of the discolored areas of leaves is closely related to their 2-layered palisade tissue, which is likely the result of their long-term adaptation to low light environment under the forest canopy (La Rocca et al., 2011;Wang et al., 2016b). Leaf variegation can reduce the damage from herbivores to the leaves of Hydrophyllum virginianum (Campitelli et al., 2008) and can mimic plain leaves with infestation of leaf-mining moth larvae to prevent moth oviposition to the leaves of Caladium steudnerifolium (Soltau et al., 2009). ...
... However, Lee's argument is not entirely valid because the author did not consider the intercellular spaces around the palisade tissue cells of the main vein into account. La Rocca et al. (2011Rocca et al. ( : 1392 reported that there was only one layer of palisade cells in the white areas and two layers in the green areas of leaves of Arum italicum, and thus, he proposed the 'variable palisade' type. According to the location of the non-green parts and whether the veins were related, leaf variegations of begonias were divided into 'the vein' type and 'the non-vein' type (Cui and Guan, 2013). ...
... Additionally, considering the palisade cells and adjacent spongy tissue cells between the non-green and the green area, Chen et al. (2017) proposed that the 'variable palisade' type should be integrated into the 'upper mesophyll' type. Because the aforementioned studies on leaf variegation (Lee, 2007;La Rocca et al., 2011;Cui and Guan, 2013;Chen et al., 2017;Pao et al., 2020) only focused on a limited number of families and genera, the results do not suffice to improve Hara's (1957) classification system. ...
Variegated leaf plants are a group of plants with stable patterns of differently colored leaf areas. The variously colored patches on the surface of the leaves have important biological functions in plant reproduction and adaptation to the environment. Apart from that, these plants have attracted interest as valuable ornamental plants. In this study, 1710 species with variegated leaves belonging to 78 families were investigated based on field-collected samples and previous literature, including transverse sections of 117 species. The macroscopic patterns of variegated leaves are highly diverse and can be distinguished as fishbone-shaped, blotched, V-shaped, spotted, striped, reticulate, and pinnate, with varying levels of diversity across different families and genera. We classified variegated leaves into five types according to the location, shape, color, and cross-sectional structure of the differently colored leaf areas. These are: I, chlorophyll type; II, air space type; III, epidermis type; IV, pigment type; and V, appendages type. Type II is the most common type, which is found in approximately 56% of all variegated leaf species, whereas type V is newly defined to accommodate the variegated leaves with colored, unequally distributed, multicellular outgrowths on the epidermis. Relationships between the diverse macroscopic patterns and the five structural types are discussed.
... The upper mesophyll type embraces the 'variable palisade type' reported from Arum italicum L. (La Rocca et al. 2011), since the upper mesophyll cells may vary in form between diferent plant taxa, including palisade cells (for most of the dicots), funnel-shaped chlorenchyma cells (for many shade plants) (Sheue et al. 2007), and spongy-like cells as in Blastus (this study). In A. italicum, one layer of palisade tissue was found in the palepigmented area of the leaf, while two layers of palisade tissue were found in the dark-pigmented area (La Rocca et al. 2011). ...
... The upper mesophyll type embraces the 'variable palisade type' reported from Arum italicum L. (La Rocca et al. 2011), since the upper mesophyll cells may vary in form between diferent plant taxa, including palisade cells (for most of the dicots), funnel-shaped chlorenchyma cells (for many shade plants) (Sheue et al. 2007), and spongy-like cells as in Blastus (this study). In A. italicum, one layer of palisade tissue was found in the palepigmented area of the leaf, while two layers of palisade tissue were found in the dark-pigmented area (La Rocca et al. 2011). Table 1 Chlorophyll a, chl. ...
... The upper mesophyll type has not been shown generally to create variegation independently based on empirical information. However, in the form designated "palisade type" by La Rocca et al. (2011), diferent numbers of layers of palisade cells on diferent parts of a leaf were shown to create variegation. In Blastus, the upper mesophyll type consists of the diference between spongylike tissue and funnel-shaped chlorenchyma. ...
The presence of foliar variegation challenges perceptions of leaf form and functioning. But variegation is often incorrectly identified and misinterpreted. The striking variegation found in juvenile Blastus cochinchinensis
(Melastomataceae) provides an instructive case study of mechanisms and their ecophysiological implications. Variegated (white and green areas, vw and vg) and nonvariegated leaves (normal green leaves, ng) of seedlings of Blastus were compared structurally with microtechniques, and characterized for
chlorophyll content and fluorescence. More limited study of Sonerila heterostemon (Melastomataceae) and Kaempferia pulchra (Zingiberaceae) tested the generality of the findings. Variegation in Blastus combines five
mechanisms: epidermal, air space, upper mesophyll, chloroplast and crystal, the latter two being new mechanisms. All mesophyll cells (vw, vg, ng) have functional chloroplasts with dense thylakoids. Vw areas are distinguished by flatter adaxial epidermal cells and central trichomes containing crystals, the presence of air spaces between the adaxial epidermis and a colorless spongylike upper mesophyll containing smaller and fewer chloroplasts. The vw area is further distinguished by having the largest spongy tissue chloroplasts and
fewer stomata. Both leaf types have similar total chlorophyll content and similar F /F (maximum quantum yield of PSII), but vg has significantly higher F /F than ng. Variegation in Sonerila and Kaempferia is also caused by combined mechanisms, including the crystal type in Kaempferia. This finding of combined mechanisms in three different species suggests that combined mechanisms may occur more commonly in nature than current understanding. The combined mechanisms in Blastus variegated leaves represent intricate structural modifications that may compensate for and minimize photosynthetic loss, and reflect changing plant needs.
... For example, with Cyclamen persicum and Cyclamen hederifolium, the light-green sections of the leaf surface reflect more of the incoming radiation than the dark-green sections (Konoplyova et al., 2008), which has also been observed for Pulmonaria officinalis (Esteban et al., 2008) and Begonia rex (Zhang et al., 2009). This might have a photoprotective role against excessive radiation (Holmes and Keiller, 2002), as it has been shown that light-green leaf sections contain less photosynthetic pigments (Gaberščik et al., 2001;La Rocca et al., 2011). However, Esteban et al. (2008) observed that non-green sections of variegated leaves are more sensitive to excess light, which can result in greater decrease in the photochemical efficiency in comparison to the green sections of these leaves. ...
... However, Esteban et al. (2008) observed that non-green sections of variegated leaves are more sensitive to excess light, which can result in greater decrease in the photochemical efficiency in comparison to the green sections of these leaves. In contrast, La Rocca et al. (2011) showed that variegation has no limiting effects on the photosynthetic energy budget of Arum italicum leaves. Minor differences in photosynthetic CO 2 uptake between light-green and dark-green leaf sections have also been observed in Cyclamen leaves (Konoplyova et al., 2008). ...
... Therefore the light colouration of the leaf sections is also a consequence of the mesophyll structure. The palisade mesophyll cells of the light-green leaf sections are larger and more loosely arranged than those of the dark-green palisade mesophyll, with a greater percentage of intercellular air spaces (Konoplyova et al., 2008;Sheue et al., 2012;La Rocca et al., 2011). The more exposed cell surfaces in these intracellular spaces have larger areas, which potentially reflect and scatter the incoming radiation (Esteban et al., 2008). ...
Cyclamen purpurascens originates from the forest understorey and has variegated leaves and red abaxial epidermis. We measured the morphological and biochemical traits, and reflectance and transmittance spectra of leaves of C. purpurascens sampled through the growing season. We determined the optical properties and differences between the light-green and dark-green sections of the variegated leaves, and investigated the role of the red abaxial epidermis. The light-green leaf sections contained lower contents of chlorophyll a and b, carotenoids (in all samples) and anthocyanins (in April only) per leaf area, compared to the dark-green leaf sections, although the ratios of chlorophyll a to b and carotenoids to total chlorophyll were the same, except in April. During the closing of the canopy, chlorophyll a and b contents increased, while contents of carotenoids and anthocyanins decreased, as did the chlorophyll a/b and carotenoid/total chlorophyll ratios. The optical properties of the leaves in February showed high reflectance for UV and violet radiation, and low reflectance for near infrared radiation, for both types of leaf sections. The transmittance spectra for leaves without the red anthocyanic epidermis showed a pronounced peak from 520 nm to 625 nm, and enhancement in the near infrared region. The relative reflectance spectra of the red and colourless abaxial epidermis alone differed only in the green and yellow range. The relative transmittance of the red abaxial epidermis was significantly lower than for the colourless epidermis over the entire spectral range. Decreased transmittance in the green and yellow was obtained only for the red coloured abaxial epidermis. The variability of transmittance spectra during the season is best explained by the levels of chlorophyll b, carotenoids and anthocyanins. Our data reveal the importance of these pigments in leaf variegation, and particularly of the red abaxial anthocyanic epidermis for absorbing light in the green, yellow and near infrared.
... The light green leaf parts also transmitted more radiation than the dark green leaf parts, wherein the most differences in transmission were seen for the green region . In spite of the differences in light management, the light green parts of the variegated leaves perform photosynthetic activities similar to those of the dark green leaf parts or of fully green leaves (Konoplyova et al. 2008, la Rocca et al. 2011, Sheue et al. 2012, la Rocca et al. 2014). The higher reflectance in the light green leaf parts is mainly a consequence of the morphological differences. ...
... This pattern is associated with air spaces between the epidermal and mesophyll cells (Zhang et al. 2009), and thus the light green colouration is also a consequence of leaf mesophyll structure (Sheue et al. 2012). The palisade mesophyll cells of these leaf parts are larger and loosely arranged, therefore having a greater volume of intercellular air spaces (Konoplyova et al. 2008, Sheue et al. 2012, la Rocca et al. 2011, which increase light reflection and the scattering of light (Esteban et al. 2008). In C. purpurascens the differences in tissue density between the light and dark green leaf parts were most pronounced in April under high light conditions, when tissue density was significantly higher in the dark green leaf sections . ...
This contribution discusses the optical properties of different structures of some herbaceous understorey plant species from temperate deciduous and mixed forests. These forests are marked by annual dynamics of radiation level that is related to the vegetation cycle of forest trees. During winter and early spring, the understorey is exposed to full solar radiation, while later in the growing season radiation is limited due to the closing of the tree storey. The plasticity of optical properties of photosynthetic structures of understorey plants is directly related to their structural and biochemical phenotypic plasticity that optimises harvesting and use of energy. The optimisation of energy harvesting is also achieved by specific adaptations of green leaves, such as variegation (Pulmonaria officinalis, Cyclamen sp.), anthocyanic lower epidermis (Cyclamen sp.), and by using structures other than green leaves for photosynthesis, such as bracts (Hacquetia epipactis) and sepals (Helleborus sp.). The optical properties of these structures are similar to those of green leaves. The understanding of optical responses of different structures contributes to the understanding of the forest understorey functioning.
... Furthermore, non-photosynthetic pigments compete with chlorophylls for photon capture, their presence entails a photosynthetic cost equal to the lost photons (Zeliou et al. 2009). In some plants, for example Begonia, Schismatoglottis calyptrata, and Arum italicum, a large proportion of leaves became white during development (Tsukaya et al. 2004, Zhang et al. 2009, Rocca et al. 2011). The photosynthesis is important physiological function of variegated leaves, especially of those appearing during juvenile stages (Solovchenko and Chivkunova 2011). ...
... The photosynthesis is important physiological function of variegated leaves, especially of those appearing during juvenile stages (Solovchenko and Chivkunova 2011). However, until now, few studies have paid attention to maintenance of the photosynthetic capacity of the variegated leaves (Rocca et al. 2011). ...
... Most studies have been developed in leaves of terrestrial plants (e.g. [10][11][12][13][14], and in phototrophic aquatic systems (e.g. [15][16][17], but this technique has been seldom used for photosynthetic measurements in fruits (18)(19)(20)(21)(22). ...
... SP intensities are as reported inFig. 2. F' m and Φ II means are plotted with respective AE SD (n =[13][14][15][16][17][18] ...
Grape berry development and ripening depends mainly on imported photosynthates from leaves, however fruit photosynthesis may also contribute to the carbon economy of the fruit. In the present study pulse amplitude modulated chlorophyll fluorescence imaging (imaging-PAM) was used to assess photosynthetic properties of tissues of green grape berries. In particular, the effect of the saturation pulse (SP) intensity was investigated. A clear tissue-specific distribution pattern of photosynthetic competence was observed. The exocarp revealed the highest photosynthetic capacity and the lowest susceptibility to photoinhibition, and the mesocarp exhibited very low fluorescence signals and photochemical competence. Remarkably, the seed outer integument revealed a photosynthetic ability similar to that of the exocarp. At a SP intensity of 5000 μmol m(-2) s(-1) several photochemical parameters were decreased, including maximum fluorescence in dark-adapted (F(m) ) and light-adapted (F'(m) ) samples and effective quantum yield of PSII (Φ(II) ), but the inner tissues were susceptible to a SP intensity as low as 3200 μmol m(-2) s(-1) under light-adapted conditions, indicating a photoinhibitory interaction between SP and actinic light intensities and repetitive exposure to SP. These results open the way to further studies concerning the involvement of tissue-specific photosynthesis in the highly compartmentalized production and accumulation of organic compounds during grape berry development. © 2013 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2013 The American Society of Photobiology.
... Especially the experimental work on variegation mutants in Arabidopsis thaliana helped us better understand the underlying mechanisms [1,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Other leaf variegation studies were carried out on tomato [23][24][25][26][27][28][29][30][31][32][33], and studies on Arum italicum [34], barley [35], Brassica napus [36], Camellia sinensis [37,38]; Grapevine [39], Ilex X altaclerensis [20,21], Lotus japonicus [20], Epipremnum aureum [40], tobacco [41], Hedera helix [42], Vigna radiata [43] and Zea mays [44]. ...
Background
Leaf variegation is an intriguing phenomenon observed in many plant species. However, questions remain on its mechanisms causing patterns of different colours. In this study, we describe a tomato plant detected in an M2 population of EMS mutagenised seeds, showing variegated leaves with sectors of dark green (DG), medium green (MG), light green (LG) hues, and white (WH). Cells and tissues of these classes, along with wild-type tomato plants, were studied by light, fluorescence, and transmission electron microscopy. We also measured chlorophyll a/b and carotene and quantified the variegation patterns with a machine-learning image analysis tool. We compared the genomes of pooled plants with wild-type-like and mutant phenotypes in a segregating F2 population to reveal candidate genes responsible for the variegation.
Results
A genetic test demonstrated a recessive nuclear mutation caused the variegated phenotype. Cross-sections displayed distinct anatomy of four-leaf phenotypes, suggesting a stepwise mesophyll degradation. DG sectors showed large spongy layers, MG presented intercellular spaces in palisade layers, and LG displayed deformed palisade cells. Electron photomicrographs of those mesophyll cells demonstrated a gradual breakdown of the chloroplasts. Chlorophyll a/b and carotene were proportionally reduced in the sectors with reduced green pigments, whereas white sectors have hardly any of these pigments. The colour segmentation system based on machine-learning image analysis was able to convert leaf variegation patterns into binary images for quantitative measurements. The bulk segregant analysis of pooled wild-type-like and variegated progeny enabled the identification of SNP and InDels via bioinformatic analysis. The mutation mapping bioinformatic pipeline revealed a region with three candidate genes in chromosome 4, of which the FtsH-like protein precursor (LOC100037730) carries an SNP that we consider the causal variegated phenotype mutation. Phylogenetic analysis shows the candidate is evolutionary closest to the Arabidopsis VAR1. The synonymous mutation created by the SNP generated a miRNA binding site, potentially disrupting the photoprotection mechanism and thylakoid development, resulting in leaf variegation.
Conclusion
We described the histology, anatomy, physiology, and image analysis of four classes of cell layers and chloroplast degradation in a tomato plant with a variegated phenotype. The genomics and bioinformatics pipeline revealed a VAR1-related FtsH mutant, the first of its kind in tomato variegation phenotypes. The miRNA binding site of the mutated SNP opens the way to future studies on its epigenetic mechanism underlying the variegation.
... Variegata merupakan bagian tanaman yang mengalami mutasi sebagai contoh daun yang menjadi berwarna putih belang, berbeda dengan warna daun aslinya (La Rocca et al., 2011). Variegata pada daun disebabkan oleh penghambatan fotosintesis yang mengganggu produksi klorofil (Khouri et al, 2010;Jabeen and Mirza, 2013). ...
Monstera merupakan salah satu tanaman hias yang saat ini banyak diminati oleh pecinta tanaman karena memiliki nilai estetika tersendiri. Ditengah pandemi covid19 melanda dunia termasuk Indonesia, tanaman yang dijadikan primadona oleh pebisnis tanaman hias adalah genus Monstera, salah satunya Monstera adansonii. M. adansonii yang diminati saat ini adalah jenis variegata. Salah satu teknik untuk menghasilkan variegata pada M. adansonii adalah dengan melakukan mutasi pada bagian daun sehingga menghasilkan daun berwarna putih belang berbeda dari warna aslinya. Pada penelitian ini dilakukan mutasi pada M. adansonii menggunakan empat zat kimia yaitu streptomisin, strepson, etil metil sulfonat (EMS), dan ekstrak rokok kretek dengan tujuan untuk mengetahui mutagen yang paling efektif membentuk variegata pada M. adansonii. Setelah perlakuan diberikan, kemudian dilakukan pengamatan terhadap jumlah tunas, warna dan jumlah daun. M. adansonii dengan perlakuan streptomisin menghasilkan warna hijau bercorak putih pada daun, sedangkan zat mutagen lainnya strepson, EMS dan ekstrak rokok kretek tidak dapat menghasilkan variegata pada M. adansonii.
... Although physical color is easily observed in many animals, few cases of physical color are well known from plants ( Gould and Lee, 1996;Pao et al., 2018). Nevertheless, there have been recent reports of unusual structures creating foliar variegation patterns in plants (Fooshee and Henny, 1990;Tsukaya et al., 2004;Konoplyova et al., 2008;La Rocca et al., 2011;Sheue et al., 2012;Zheng et al., 2016;Chen et al., 2017). From these reports, it appears that variegation patterns caused by diffuse reflection of light from intercellular space are a common case of physical color in plants. ...
In nature, foliar variegation has varied origins, and can be ascribed to two major mechanisms: pigment-related variegation and structural variegation caused by the optical properties of leaf structure. However, understanding of these mechanisms is still lacking, and structural mechanisms are often misinterpreted. In this study, six variegated plants native to Taiwan and two ornamental plants, with novel and unusual foliar variegation patterns, are studied to reveal their mechanisms of variegation. Two newly understood variegation patterns, the silvery white leaf surface of Begonia aptera and the varnish on basal leaflets of Oxalis corymbosa, are reported here. White to light green patches on leaf surfaces characterize the foliar variegation in the other six study species, Nervilia nipponica, O. acetosella subsp. griffithii var. formosana, Paphiopedilum concolor, Selaginella picta, Smilax bracteata subsp. verruculosa and Valeriana hsuii. All six Taiwan native plants exhibit structural variegation, five of which have air space type variegation. Surprisingly the silvery white leaf surface of B. aptera results from numerous sand-like white spots caused by intercellular space. The varnish on leaves of O. corymbosa is the epidermis type of variegation comprised of two newly identified subtypes, larger epidermal cells and thicker outer cell walls. The two ornamental plants have variegation caused by pigments: the chloroplast type from fewer chloroplasts in P. concolor and the chlorophyll type, from absence of chloroplasts in S. picta. This study extends understanding of the mechanisms of natural foliar variegation, illustrating the diversity of mechanisms by which plants may change the appearance of their leaves.
... Lower contents of chlorophyll a and b, carotenoids, and anthocyanins were detected in the light-green leaf sections compared with the dark-green leaf sections of Cyclamen purpurascens (Klančnik et al., 2016). In Pulmonaria officinalis L. and Arum italicum, the amounts of chlorophylls and carotenoids in the variegated pale-green sectors were appreciably lower than in full-green sectors (Esteban et al., 2008;Rocca et al., 2011). Total chlorophyll in the yellow sectors of the variegated A. japonica 'Variegata' leaves was obviously lower than in the green areas (Table 2). ...
Aucuba japonica ‘Variegata’ is a widely used ornamental shrub with green-yellow variegated leaves. In this study, the formation of leaf variegation and photosynthetic characteristics in green and yellow sectors were investigated. There were no marked anatomical differences in tissue organization between the green and yellow sectors. At the cellular level, it was observed that the chloroplasts in the yellow leaf tissue were vacuolated. Besides, the pigment contents of the yellow leaf tissue were obviously lower than those in the green areas, and a very low intensity of chlorophyll auto-fluorescence was generated from the yellow areas. Furthermore, significantly lower values of F0, Fm, Fv/Fm, ФPSII and non-photochemical quenching (NPQ) were noticed in yellow sectors compared to the green ones, indicating that the yellow leaf tissue was less photoprotected than the green area. In addition, the yellow sectors showed lower net photosynthesis and dark respiration rates compared to the green leaf tissue. Immunofluorescence showed large amounts of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) in green leaf tissue, while only faint fluorescence was detected in the yellow sectors. As a whole, the results of this study suggest that the leaf variegation of A. japonica ‘Variegata’ is “pigment type” and that this pigment-related leaf variegation affects photosynthetic light use in the variegated leaves. These findings also shed light on the coloration mechanism of ornamental plant foliage.
... The PEBH Index, in so far as it is generated by experimental measurements, is totally unbiased, and is more sensitive than Ellenberg's empirical shade tolerance scale ( Ellenberg, 1979) of widespread use ( Humbert et al., 2007;Murchie and Horton, 1997;Niinemets and Valladares, 2006). Other recent photosynthesis data for ephemerals (Crocus, Badri et al., 2007;Corydalis, Kudo et al., 2008;Erythronium, La Rocca et al., 2014;Gagea, Sunmonu and Kudo, 2014) and long-cycle herbs (Arum italicum, La Rocca et al., 2011;Cyclamen hederifolium, Konoplyova et al., 2008;Helleborus viridis, Aschan et al., 2005;Pulmonaria officinalis, Esteban et al., 2008) are mainly in line with our findings. Records of photosynthesis of woody plants also compare favorably with present ones, e.g. for Hedera ( Oberhuber and Bauer, 1991), Laurus ( Arena et al., 2008), Metasequoia ( Equiza et al., 2005), and Sequoia ( Mullin et al., 2009), though there are scattered reports of higher photosynthetic rates for some trees ( Naidu and De Lucia, 1998;Kikuzawa, 2003;Turnbull et al., 1993). ...
Since spring ephemerals are credited to be all “sun” species with unusually elevate photosynthesis, in contrast to shade-tolerant trees and understory geophytes with a long aboveground cycle, we examined the photosynthetic efficiency of 6 woody species, 9 long-cycle geophytes, and 8 spring ephemeral geophytes using blue flashes of increasing energy with the Imaging PAM fluorometer. Several parameters were obtained: quantum yield of electron transport (ΦETR) or of PSII (ΦPSII), maximum measured photosynthesis rate (ETRhv), maximum extrapolated rate of photosynthesis (ETRem), half-saturating photon flux density (KPAR), and in some cases photochemical (qP) and non-photochemical quenching (NPQ). Results confirm the ecological consistency of the three plant groups, with internal differences. Woody species have low ETRem and KPAR values with good ΦETR; long-cycle herbs have low ETRem and ΦETR and moderate KPAR values; spring ephemerals have elevate ΦETR, ETRem and KPAR values. The mean ETRem of ephemerals of 91 μmol m⁻² s⁻¹ exceeds that of long-cycle herbs 2.9-fold and woody species 4.8-fold, and corresponds to 19 μmol CO2 m⁻² s⁻¹ by assuming an ETR/ΦCO2 ratio of 4.7. Highest photosynthesis rates and KPAR were exhibited by five ephemerals (Eranthis, Erythronium, Narcissus, Scilla, Tulipa) with peak ETRem values equivalent to ∼40 μmol CO2 m⁻² s⁻¹ or ∼60 μmol CO2 (g Chl)⁻¹ s⁻¹ (“sun” species). According to a new, fluorescence based heliophily index, all trees and five long-cycle herbs were definitely “shade” species, while four long-cycle herbs and three ephemerals were intermediate shade-tolerant.
... In this case the white color does not result in loss of photosynthetic ability, and the air spaces may even have various physiological functions (e.g., Konoplyova et al. 2008). The second and related type of white variegation is formed by the formation of a single loose layer of short palisade cells instead of a compact layer or two of long palisade cells in the green sectors of variegated leaves (La Rocca et al. 2011). The third type of variegation is formed by regulated lack of expression of chlorophyll in certain cell groups (Lev-Yadun et al. 2004b;Lee 2007). ...
It has been suggested that white variegation, the outcome of various developmental, genetic, and physiological processes, may defend leaves and other plant organs from herbivory by several proposed mechanisms: camouflage, aposematism (including Müllerian and Batesian mimicry), mimicry of insect damage and fungal attacks, dazzle effects that make it hard for large herbivores to decide where to bite the leaves and for insects to land on them, and by visual repellence of insects from landing as well as by unknown mechanisms. Very few cases of these suggested leaf defenses by variegation have been examined in depth. Some such studied cases were indeed found to actually operate as defense from herbivory either in nature or in experiments, suggesting the potential defensive function of others. However, the specific operating defensive mechanism by white variegation was not always identified or even proposed, even when variegation was found to be associated with reduced herbivory. Studying white variegation has a significant advantage over studying other types of plant defensive coloration because even bi-chromatic vision is sufficient to see these patterns. Moreover, white variegation is probably visible under most types of natural light conditions, including strong moonlight. While in this essay I wish to stimulate an effort for a broader and deeper understanding of the defensive roles of white variegation, the possible simultaneous physiological roles of white leaf variegation that will not be reviewed here should not be ignored.
... australis are little or no spotted, similarly to the new subspecies. A sensible explanation of spot reduction in these 'dark' plants would need a full understanding of spot functions in the genus Pulmonaria, which unfortunately is not yet available, contrarily e.g. to Arum, Araceae (La Rocca et al. 2011) and Erythronium, Liliaceae (La Rocca et al. 2013). ...
Populations of Pulmonaria with unique features and associated with shady and dry conditions were found in high beech woods on the west side of Mt. Marzola and in other dolomitic sites of Trentino (southern Alps). Morpho-statistical and karyological analyses suggest that these populations represent a new subspecies of P. officinalis, Pulmonaria officinalis subsp. marzolae. The change of the basal leaves shape during the year, the peculiar traits of foliar spots and hairs as well as a divergence of the karyotype asymmetry indices are distinct from the typical form of P. officinalis, whereas the general form, the major hair types, inflorescence morphology and the chromosome number 2n = 16 reveal their affinity to this species.
... In most cases, e.g. Pulmonaria officinalis (Esteban et al., 2008), Arum italicum (La Rocca et al., 2011), or Cyclamen species (Konoplyova et al., 2008), the variegation depends on different shades of green. The lighter spots are persistent and are possibly related to strategies of light exploitation in the limiting woodland habitat (Lee, 1986), but deception of herbivores is another possibility (Givnish, 1990;Campitelli et al., 2008). ...
Erythronium dens-canis is an early-flowering understory lily of southern Europe with two leaves and a single flower, although a number of plants have only one leaf and do not flower. The leaves are mottled with silvery flecks and brown patches, that gradually vanish turning to a lively green color. The nature and function of this striking variegation pattern were investigated in differently colored leaf parts following the springtime color change. Tissue organization was examined by light and electron microscopy; photosynthetic pigments were analyzed by spectrophotometry and HPLC; chlorophyll fluorescence parameters were evaluated by MINI-PAM. The results showed that brown patches originated in vacuolar anthocyanins in the subepidermal cell layer while air spaces between the upper epidermis and underlying chlorenchyma resulted in silvery flecks. The two leaf areas did not differ in photosynthetic pigments, chloroplast organization and photosynthetic parameters (Fv/Fm, NPQ, rETR). Greening of brown patches due to anthocyanin resorption was faster in non-flowering plants than in flowering ones, occurring only when young fruits were developing. Anthocyanin disappearance did not change the structural-functional features of photosynthetic tissues. As a whole the results suggest that the anthocyanin pigmentation of E. dens-canis leaves does not affect the photosynthetic light use and has no photoprotective function. It is proposed that the complex leaf color pattern may act as a camouflage to escape herbivores, while the reflective silvery spots may have a role in attracting pollinators of this early-flowering species.
Foliar variegation not only enhances the ornamental and economic value of plants but also challenges people's perceptions of leaf form and function. We studied four species of Zingiberaceae plants with both medicinal and ornamental values in southern China; and found that different Zingiberaceae plants had different variegation mechanisms. The variegated mechanism types of Curcuma phaeocaulis Valeton, Kaempferia rotunda L., Alpinia pumila Hook. f., and Alpinia zerumbet Burtt. et Smith were: (1) pigment and epidermal type, (2) epidermal type, (3) air space type, and (4) chloroplast type, respectively. C. phaeocaulis, K. rotunda, and A. zerumbet showed a positive correlation between their total chlorophyll content and the change of light-response curves, whereas A. pumila showed a negative correlation at a light intensity of 1500 or 2000 μmol m−2 s−1. Although C. phaeocaulis, K. rotunda and A. pumila exhibited high enzymatic antioxidant activity in the non-variegated area, we found POD was widely distributed in the variegated area of A. zerumbet. This is the first study that explored the physical and chemical attributes in variegated and non-variegated areas of four Zingiberaceae plants, while also supplementing the existing research on variegated leaves of Zingiberaceae plants. Therefore, our findings will provide a reference for studying the foliar variegation of Zingiberaceae.
The photosynthetic performance of variegated leaves can be very important in the cultivation and management of variegated plants. Actinidia kolomikta (Rupr. & Maxim.) Maxim. leaves have striking color variation. To clarify the variegated leaf type and photosynthetic cost, we measured leaf structure and ultrastructure, spectral properties, chlorophyll fluorescence and net photosynthetic rate (Pn). The study was conducted in Jilin during spring, summer, and fall in 2013. Leaf anatomy and ultrastructure were observed with light and electron microscopy. Leaf reflectance and pigment content were measured with a Unispec spectrometer and high performance liquid chromatography. Photosynthetic characterization was performed with a photosynthesis system and plant efficiency analyzer. In the palisade tissue of variegated areas, intercellular spaces were found, and cells contained fewer and abnormally developed chloroplasts. Normal chloroplasts were distributed mostly in spongy tissue. The reflectance of the adaxial surface was higher in variegated leaves than in green leaves. The Pn of variegated leaves was 80 to 94% of green leaves, the maximum photosystem II efficiency of the adaxial and abaxial surfaces in variegated leaves was similar to green leaves, and the quantum use efficiency of the abaxial surface was higher than the adaxial surface in variegated leaves. These results show that the photosynthetic performance of variegated leaves was retained well. Thus, variegated leaves are not a limiting factor for cultivation and application in A. kolomikta, and do not need to be removed as parasitic leaves during cultivation and management.
Actinidia kolomikta (Rupr. & Maxim.) Maxim. leaves showed dramatic colour changes during plant growth phases, and we studied structure and optical properties of variegated leaves. Leaf surface cells were smooth, and there were no surface appendages (wax or trichomes) observed in variegated leaves. Palisade tissue cells in white and pink leaves were looser and contained relatively fewer chloroplasts. White leaves contained many intercellular spaces between the epidermal and mesophyll cells or within the palisade cell layer. Variegated leaves had three distinct radiation reflection patterns: a bright white area, a spotted pattern, and a polygonal pattern. Reflectance at 450 - 1100 nm from the adaxial surface of white leaves was greater than that of green leaves, but anthocyanin accumulation in pink leaves decreased the reflectance at 500 - 600 nm. When variegated leaves turned green, the reflectance at 500 - 600 nm increased. On abaxial surfaces, the reflectance of variegated leaves was similar to green leaves at 450 - 700 nm. In conclusion, reflection patterns and the formation of variegated leaves of A. kolomikta were significantly correlated with the leaf anatomy. The white and pink colours of leaves were a result of an internal reflection between air spaces and cells in the leaves, chlorophyll deficiency in palisade tissue, and anthocyanin accumulation. Variegated leaves turned green when the chlorophyll content in palisade tissue increased.
Variegated mutants are spotted rare in wild, and especially in the high light (HL) conditions. In addition, these plants are cultivated by a growing number of horticulturists due to their high economic value. In this experiment, the antioxidative response of both albino and green tissues from a mutant plant Golden Agave, which possesses leaves with different degrees of variegation, was investigated under normal or HL exposure, respectively. Severe oxidative stress was observed in green tissues of high albinism leaves (30–40 % albino tissues, muy) over low albinism counterparts (less than 10 % albino tissues, mug). Compared with green tissues, low oxidative damage (relative electrolyte leakage and protein damage) and antioxidant enzyme (SOD, CAT, APX, and GR) activities were observed in the albino than in the adjacent green tissues. Photoinactivation of the CAT and the APX enzyme activities were observed in the albino tissues to a significantly level under HL exposure. In addition, lower redox values (ASC/DHA and GSH/GSSG) and higher levels of reactive oxygen species (ROS) were monitored in the green tissues of the muy over mug mutant even under normal light conditions. This work could help us to understand the HL sensitivity of variegated mutant plants better and allow us to improve variegated mutant plant cultivation skills. At last, the “oxidative stress hypothesis” was introduced to illustrate the reduced evolutionary advantage of plant variegation phenomenon in the discussion.
Twenty-one wild spiny or thorny plant species growing in Israel have been found so far that are conspicuous because of white stripes and spots found on their leaves. Twenty of these species occupy open habitats, and only one is a climber (Smilax aspera) that is found in both shady and open habitats. I propose that these spiny, thorny, or prickly conspicuous plants form a defensive Müllerian mimicry ring. The genus Launaea (Asteraceae) includes several species that are both white variegated and spiny or thorny (a defended Müllerian mimicry ring), and four non-thorny but variegated plants (a Batesian mimicry ring). I propose that these four species that form a non-defended Batesian mimicry ring enjoy the indirect protection of both their co-generic spiny and thorny species and also of defended plants from other taxa. The long history of the considerable impact of grazing in this arid region seems to have selected for this character.
Leaf variegation refers to local regions of the upper surface of a leaf having reduced or obstructed chlorophyll, which results in whitish spots. These lighter spots may compromise the photosynthetic efficiency of a leaf, and many competing hypotheses have been put forward to explain why this patterning may be adaptive. It has been suggested that variegation is either an adaptive response to environmental conditions or a defence mechanism against herbivore damage. To test whether leaf variegation reduces herbivore damage, we first assessed the frequency of variegated and nonvariegated leaves in natural populations of the plant Hydrophyllum virginianum L., and second, measured herbivore damage to both variegated and nonvariegated leaves. We found that variegated leaves were present at high frequencies within natural populations (6%-31%) and that nonvariegated leaves sustained nearly twice the amount of damage by comparison with variegated leaves. Therefore, leaf variegation appears to be beneficial by reducing herbivore damage to leaves. These data are consistent with the fundamental prediction of the herbivory hypothesis for the benefits of leaf variegation.
The pollination ecology of Arum italicum was studied in south-western France. This plant attracts olfactory dung-breeding flies through deceit. These insects are principally represented by Diptera, all belonging to saprophyte families. The volatilization of the odouriferous compounds, responsible for their attraction, is achieved through the production of heat by the appendix. The insects are trapped for 24 h in order to participate in both sexual phases of the protogynous inflorescence. The male flowers produce three heat events during flowering. These peaks of heat seem to be involved in the spathe movements, since they occur during the opening of the inflorescence and the liberation of the insects. The last male heat event may be linked with the liberation of pollen and its dispersion by stimulating trapped flies. According to their frequency and pollen-load, two Psychoda species appear to be the most efficient pollinators (P. crassipenis and P. pusilla). Nevertheless, each of the other attracted species could play a significant role under different spatio-temporal conditions. Experiments on self-pollination have shown that obligate cross-pollination is necessary for A. italicum to set seeds. Moreover, hand- and natural-pollinated plants showed similarly high abortion frequencies suggesting that seed set may be more constrained by resources rather than by pollination limitation. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 205–214.
Dynamic responses of understory plants to sunflecks have been extensively studied, but how much differences in dynamic light responses affect daily photosynthesis (A
day) is still the subject of active research. Recent models of dynamic photosynthesis have provided a quantitative tool that allows the critical assessment of the importance of these sunfleck responses on A
day. Here we used a dynamic photosynthesis model to assess differences in four species that were growing in ambient and elevated CO2. We hypothesized that Liriodendron tulipifera, a species with rapid photosynthetic induction gain and slow induction loss, would have the least limitations to sunfleck photosynthesis relative to the other three species (Acer rubrum, Cornus florida, Liquidambar styraciflua). As a consequence, L. tulipifera should have the highest A
day in an understory environment, despite being the least shade tolerant of the species tested. We further hypothesized that daily photosynthetic enhancement by elevated CO2 would differ from enhancement levels observed during light-saturated, steady-state measurements. Both hypotheses were supported by the model results under conditions of low daily photosynthetic photon flux density (PFD; <3% of the above-canopy PFD). However, under moderate PFD (10–20% of the above-canopy PFD), differences in dynamic sunfleck responses had no direct impact on A
day for any of the species, since stomatal and photosynthetic induction limitations to sunfleck photosynthesis were small. Thus, the relative species ranking in A
day under moderate PFD closely matched their rankings in steady-state measurements of light-saturated photosynthesis. Similarly, under elevated CO2, enhancement of modeled A
day over A
day at ambient CO2 matched the enhancement measured under light saturation. Thus, the effects of species-specific differences in dynamic sunfleck responses, and differences in elevated CO2 responses of daily photosynthesis, are most important in marginal light environments.
Free porphyrins and their magnesium complexes, including chlorophylls, are potent photo-sensitizers. Plants usually accumulate these compounds bound to proteins together with protective compounds like carotenoids. Besides their protective role, carotenoids can play a structural role in these complexes. To analyze the effect of impaired carotenogenesis on plastid membranes we applied to barley seedlings the bleaching herbicide 2-(4-chlorophenylthio)triethylamine (CPTA) as a specific inhibitor for the cyclization of lycopene. To avoid interference with photo-oxidation, the essential experiments were performed on seedlings grown in darkness. While the amount of total carotenoids decreased, we found accumulation of more 6-carotene than lycopene in darkness clearly showing that CPTA inhibits the lycopene beta-cyclase more effectively than the lycopene epsilon-cyclase. The CPTA treatment resulted in accumulation of non-photoactive protochlorophyllide a; the amount of photoactive protochlorophyllide and NADPH:protochlorophyllide oxidoreductase remained constant. Further, the level of Mg protophorphyrin and its monomethyl ester increased to an extent similar to that obtained by application of 5-aminolevulinic acid (ALA). The perturbation of the ultrastructure of etioplast inner membranes, observed after CPTA-treatment, was not found after ALA-treatment; this excluded the accumulated tetrapyrroles as responsible for the perturbation. By contrast, the down-regulation of Lhcb and RbcS genes found after CPTA-treatment was compatible with the presumed role of Mg protophorphyrin as "plastid signal" for regulation of nuclear gene expression. Possible mechanisms for enhancement of tetrapyrrole accumulation by non-cyclic carotenoids are discussed.
The method of measuring the rate of photosynthesis and respiration of leaf slices by an oxygen electrode was examined with an emphasis upon the size of leaf slices. The results obtained are as follows. 1. The optimum pH of the buffer solution was about 7.2. 2. The rate of apparent photosynthesis was saturated at 20 mM NaHCO3 or KHCO3 solution. 3. The rate of apparent photosynthesis was saturated at a light intensity of 50 klx. 4. The maximum rate of apparent photosynthesis was obtained by the leaf slices with 1 mm square in size. The rate of photosynthesis decreased according as the leaf sample was cut into slices larger or smaller than 1 mm square in size. 5. The rate of respiration remained almost unchanged with leaf slices from 0.8 mm square to 1.5 mm square in size.
Photosynthetic mechanisms have been compared in leaves and, separately, in stems of Egeria densa Planch. In order to correlate the structural and functional characteristics of the two organs (1) the ultrastructural features of leaves and stems have been studied and (2) their photosynthetic activity has been evaluated by measuring in vivo both oxygen evolution and the kinetics of chlorophyll fluorescence. The results confirm the aquatic behaviour of the leaf which is able to utilize inorganic C supplied both as CO2 and HCO
3−. In this respect, the different wall organization found in the two cell layers of the leaf is particularly interesting, since it could be related to the known polar mechanism of inorganic-C uptake. The stem, by contrast, behaves rather as an aerial organ, needing very high CO2 concentrations in the aquatic environment in order to carry out photosynthesis. In the stem, the aerenchyma plays a role in supplying the green cells with gaseous respiratory CO2, thus facilitating the photosynthetic activity of the submerged stems.
Proposes that mottling may serve to camouflage the foliage of certain groups of short-statured forest herbs, by disrupting their outline as perceived by colour-blind vertebrate herbivores in sun-dappled understoreys. Certain phenological groups are likely to be particularly vulnerable to herbivores, based on their high leaf N content (spring ephemerals, spring leaves of summer-active species), leaf activity when few other species possess foliage (evergreen species, wintergreen species, winter leaves of dimorphic species) and/or relative cost of replacing consumed foliage (evergreen species on sterile soils). These groups are also exposed to relatively high irradiance and so are less likely to suffer photosynthetic losses as a result of the reduced leaf absorptance that accompanies mottling. A survey of the incidence of leaf mottling in the native flora of the NE USA supports these ideas: mottled leaves occur almost exclusively among forest herbs and are substantially over-represented among evergreen, wintergreen, and spring ephemeral species, and among the winter leaves of dimorphic species and the spring leaves of summer-active species. -from Author
Leaf-mining insects produce conspicuous and distinct leaf mines on various types of plant leaves. The diversity of leaf-mine morphology has typically been explained by several factors, such as selective feeding on plant tissues, improvement of microclimate, faecal disposal, reduction in the efficiency of parasitoid search behaviour and leafminer phylogeny. Although these factors are certainly associated with mining patterns, masking the mines, rather than making them conspicuous, appears to be more advantageous for deterring parasitoids and predators of leafminers. However, here, I propose that prominent leaf mines may serve to signal or cue herbivores to avoid feeding on the mined leaves. Because most leafminers are sessile and complete their development within a single leaf, herbivory of mined leaves is detrimental to leafminer survival. Other herbivores appear to avoid consuming mined leaves for a variety of reasons: leaf mines mimic leaf variegation or mottling; mined leaves induce chemical and physical defences against herbivores; and leaf mines mimic fungal infection, animal excrement, and necrosed plant tissues. Hence, natural selection may have favoured leafminers that produce conspicuous mines because of the increased survival and fecundity of thereby reducing herbivory on mined leaves.
Chlorophyll fluorescence induction (at 20^circC and 77 K) and quenching were analysed in relation to effects of environmental stresses imposed by chilling in high light and by freezing and thawing of spinach (Spinacia oleracea L.) leaves. The data indicate that cold acclimation of spinach plants, which leads to increased frost tolerance of the leaves, results in decreased susceptibility to photoinhibition of photosynthesis at chilling temperatures. When plants acclimated to 18^circC and 260-300 mumol quanta m-2 s-1 were exposed to higher light (550 mumol quanta m-2 s-1) at 4circC, they developed strong photoinhibition, as characterized by decreased quantum yield of O_2 evolution and decreased ratio of variable: maximum fluorescence (F_v/F_M) of photosystem II. The decrease in F_v/F_M resulted from a decline in F_v and an increase in F_0. The F_v/F_M ratio was lowered to a significantly greater extent when induction was recorded at 20circC, as compared with 77 K. The effects related to photoinhibition were fully reversible at 18circC in dim light. Plants that had been cold-acclimated for 10 days exhibited slightly decreased quantum yield and lowered F_v/F_M ratio. However, they did not show further photoinhibition on exposure to 550 mumol quanta m{-2} s{-1} at 4circC. The reversible photoinhibition is discussed as a protective pathway serving for thermal dissipation of excessive light energy. It is hypothesized that such a mechanism prevents destruction of the photosynthetic apparatus, until other means of protection become effective during long-term acclimation to high light. Inhibition of photosynthetic carbon assimilation caused by freezing and thawing of leaves in the dark was closely correlated with inhibition of photochemical fluorescence quenching (q_Q). As a sensitive response of the thylakoid membranes to freezing stress, the energy-dependent quenching, q_E, was inhibited. Only more severe impact of freezing caused a significant decline in the F_v/F_M ratio. It is concluded that measurements of fluorescence induction signals (F_v/F_M ratios) provide a sensitive tool with which to investigate photoinhibition, whereas freezing damage to the photosynthetic system can be detected more readily by the quenching coefficients q_Q and q_E than by F_v/F_M ratios.
The leaves of Caladium steudneriifolium (Araceae) of the understorey of a submontane rainforest in the Podocarpus National Park (South East Ecuador, 1,060m a.s.l.)
are plain green or patterned with whitish variegation. Of the 3,413 individual leaves randomly chosen and examined in April
2003, two-thirds were plain green, whereas one third were variegated (i.e., whitish due to absence of chloroplasts). Leaves
of both morphs are frequently attacked by mining moth caterpillars. Our BLAST analysis based on Cytochrome-c-Oxidase-subunit-1 sequences suggests that the moth is possibly a member of the Pyraloidea or another microlepidopteran group.
It was observed that the variegated leaf zones strongly resemble recent damages caused by mining larvae and therefore may
mimic an attack by moth larvae. Infestation was significantly 4–12 times higher for green leaves than for variegated leaves.
To test the hypothesis that variegation can be interpreted as mimicry to deter ovipositing moths, we first ruled out the possibility
that variegation is a function of canopy density (i.e., that the moths might be attracted or deterred by factors unrelated
to the plant). Then plain green leaves were artificially variegated and the number of mining larvae counted after 3months.
The results on infestation rate (7.88% of green leaves, 1.61% of the variegated leaves, 0.41% of white manipulated leaves
and 9.12% of uncoloured manipulated leaves) suggest that ovipositing moths are deterred by the miner-infestation mimicry.
Thus, variegation might be beneficial for the plants despite the implicated loss of photosynthetically active surface.
The extinction coefficients for chlorophylls a and b in diethylether (Smith, J.H.C. and Benitez, A. (1955) in Modern Methods of Plant Analysis (Paech, K. and Tracey, M.V., eds.), Vol. 4, pp. 143–196, Springer-Verlag, Berlin), used in this paper as primary standards, were verified, to within an error of less than 1%, by magnesium determination using atomic absorbance spectrophotometry. We also report the determination of accurate extinction coefficients for chlorophylls a and b in N,N′-dimethylformamide, methanol or buffered 80% aqueous acetone. Highly purified chlorophylls were used and methods were employed which not only minimize errors due to evaporation of the volatile solvents employed in their estimation but also eliminate variable micro-contamination by chlorophyll degradation products, a potential source of inconsistency between the extinction coefficients obtained in each of these three solvents. Using these new coefficients, expressed as both millimolar and specific coefficients, we have derived new simultaneous equations to obtain chlorophyll concentrations as nmol/ml and μg/ml, respectively. These equations were applied to data obtained with leaf discs from spinach and Flindersia brayleyana extracted with the three specified solvents and to a concentrated solution (in N,N′ -dimethylformamide) of a chlorophyll a + b mixture added to the threesolvent systems. The validity of these equations is proven by the consistency of the chlorophyll determinations and of the chlorophyll a/b ratios. New simultaneous equations, compatible with the equations derived for the threesolvents, are presented for the assay of chlorophylls a and b converted to their cyclic hydroxylactone derivatives by extraction with alkaline pyridine reagent (2.1 M pyridine in 0.35 M NaOH). Most chlorophyll analyses in higher plants, including the chlorophyll content and chlorophyll a/b ratios of plant thylakoids and chlorophyll-protein complexes, have been obtained in 80% aqueous acetone with the much used simultaneous equations of Arnon (Arnon, D.I. (1949) Plant Physiol. 24, 1–15). For this reason we include conversion factors whichcorrect these earlier data and make it compatible with data calculated with the simultaneous equations presented in this paper. The importance of these corrections to the formulation of meaningful models of the photosynthetic apparatus is demonstrated. Our results also indicate that grinding leaf discs with N,N′-dimethylformamide is a more reliable method for extracting all chlorophylls than shaking with this solvent for 24 h.
The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e. Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i) epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass basis. The small size of the light-green spots in the rest of the test plants precluded CO2 assimilation measurements, yet maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants. Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition, dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.
The effect of exposure to increasing cadmium concentrations was analyzed in rice seedlings (cv. Vialone nano). The highest Cd accumulation was found in roots, mostly in the apoplastic environment. Cd taken up in cells led to an increase in sulfhydryl groups, the appearance of phytochelatins, and formation of electron-dense vacuolar inclusions. The metal-exposure inhibited root growth and also interfered with correct root morphogenesis, causing disordered division and abnormal and forward enlargement of epidermal and cortical cell layers in the apical region. Cd accumulation in shoots was lower than in roots. In leaf cells, there was neither a substantial increase in sulfhydryl groups nor the appearance of phytochelatins. Shoot growth was reduced and, differently from in roots, leaf cell enlargement was inhibited. Chloroplasts had lowered contents of chlorophyll and a reduced number of thylakoids, but underwent structural alterations only at the highest Cd concentration tested (250 μM). Photosynthetic activity was limited due to the curtailment of CO2 availability caused by the greater resistance of Cd-exposed leaves. The damage suffered by seedlings worsened with the increase in Cd concentration, but was already evident at the lowest concentration examined (50 μM), showing that the cv. Vialone nano has a Cd-sensitivity higher than other rice cultivars.
We report a novel feature of leaf variegation. As is often the case in tropical forest floor herbs, Schismatoglottis calyptrata leaves feature structural variegation. Examination of leaf anatomy in S. calyptrata revealed a novel feature of structural variegation, which was generated by variation in the spatial arrangement of the adaxial-most tip of the palisade cells. In fully green leaf parts, contact between the adaxial-most tip of the palisade cells and the cone-shaped base of the outer epidermis cells was tight, and palisade cells were arranged radially around each epidermal cell. In dull, grayish-green leaf parts, the contact was loose, and no particular spatial arrangement of palisade cells relative to epidermal cells was observed. This feature of structural variation could be disadvantageous for photosynthesis efficiency in view of the hypothesis that, for rainforest herbs, cone-shaped epidermal cells may function as lenses. However, the high frequency of leaf variegation of S. calyptrata in natural habits suggests that this structural variegation plays an unknown advantageous role.
The growth of plants under stable light quality induces long-term acclimation responses of the photosynthetic apparatus. Light can even cause variations depending on the tissue location, as in Arum italicum leaf, where chloroplasts are developed in the lamina and in the entire thickness of the petiole. We addressed the question whether differences in plastids can be characterised in terms of protein-protein interactions in the thylakoid membranes. Thylakoid assembly was studied in the palisade and spongy tissue of the lamina and in the outer parenchyma and inner aerenchyma of the petiole of the mature winter leaf of Arum italicum. The chlorophyll-protein complexes were analysed by means of blue-native-PAGE and fluorescence emission spectra. The petiole chloroplasts differ from those in the lamina in thylakoid composition: (1) reaction centres are scarce, especially photosystem (PS) I in the inner aerenchyma; (2) light-harvesting complex (LHC) II is abundant, (3) the relative amount of LHCII trimers increases, but this is not accompanied by increased levels of PSII-LHCII supercomplexes. Nevertheless, the intrinsic PSII functionality is comparable in all tissues. In Arum italicum leaf, the gradient in thylakoid organisation, which occurs from the palisade tissue to the inner aerenchyma of the petiole, is typical for photosynthetic acclimation to low-light intensity with a high enrichment of far-red light. The results obtained demonstrate a high plasticity of chloroplasts even in an individual plant. The mutual interaction of thylakoid protein complexes is discussed in relation to the photosynthetic efficiency of the leaf parts and to the ecodevelopmental role of light.
The main point of our hypothesis "coloration undermines camouflage" is that many color patterns in plants undermine the camouflage of invertebrate herbivores, especially insects, thus exposing them to predation and causing them to avoid plant organs with unsuitable coloration, to the benefit of the plants. This is a common case of "the enemy of my enemy is my friend" and a visual parallel of the chemical signals that plants emit to call wasps when attacked by caterpillars. Moreover, this is also a common natural version of the well-known case of industrial melanism, which illustrates the great importance of plant-based camouflage for herbivorous insects and can serve as an independent test for our hypothesis. We claim that the enormous variations in coloration of leaves, petioles and stems as well as of flowers and fruits undermine the camouflage of invertebrate herbivores, especially insects. We assume that the same principle might operate in certain animal-parasite interactions. Our hypothesis, however, does not contrast or exclude other previous or future explanations of specific types of plant coloration. Traits such as coloration that have more than one type of benefit may be selected for by several agents and evolve more rapidly than ones with a single type of advantage.
Plant variegations are characterized by the presence of white sectors in normally green tissues and organs. Whereas the white
sectors contain defective plastids that lack coloured pigments, the green sectors contain morphologically normal chloroplasts.
Variegation mutants are defective in chloroplast developmental processes and arise due to mutations in nuclear or organellar
genes. Despite their widespread occurrence in nature, only a few variegations have been studied at the molecular level. In
this review, recent progress toward understanding two Arabidopsis variegations, immutans (im) and var2 is summarized. Both im and var2 are caused by nuclear recessive mutations and the responsible genes have been cloned and characterized. IMMUTANS functions
as a chloroplast terminal oxidase that transfers electrons from the plastoquinol pool to oxygen. It appears to be a versatile
electron sink, especially early in chloroplast development, when its function is crucial for carotenoid biosynthesis, and
in excess light, when it serves as a ‘safety valve’. IM also probably functions in chlororespiration. VAR2 encodes a chloroplast FtsH metalloprotease (termed AtFtsH2). Along with other AtFtsH proteins (AtFtsH1, 5 and 8), it forms
complexes in the thylakoid membrane that are probably involved in the process of PSII repair during photoinhibition. A model
has been proposed to explain the mechanism of var2 variegation, which suggests that threshold levels of FtsH complexes are required for green sector formation. It is concluded
that studies on im and var2 have provided novel insights into nuclear–chloroplast interactions and, especially, into mechanisms of photoprotection.
Variegated plants typically have green- and white-sectored leaves. Cells in the green sectors contain normal-appearing chloroplasts, whereas cells in the white sectors lack pigments and appear to be blocked at various stages of chloroplast biogenesis. Variegations can be caused by mutations in nuclear, chloroplast or mitochondrial genes. In some plants, the green and white sectors have different genotypes, but in others they have the same (mutant) genotype. One advantage of variegations is that they provide a means of studying genes for proteins that are important for chloroplast development, but for which mutant analysis is difficult, either because mutations in a gene of interest are lethal or because they do not show a readily distinguishable phenotype. This paper focuses on Arabidopsis variegations, for which the most information is available at the molecular level. Perhaps the most interesting of these are variegations caused by defective nuclear gene products in which the cells of the mutant have a uniform genotype. Two questions are of paramount interest: (1) What is the gene product and how does it function in chloroplast biogenesis? (2) What is the mechanism of variegation and why do green sectors arise in plants with a uniform (mutant) genotype? Two paradigms of variegation mechanism are described: immutans (im) and variegated2 (var2). Both mechanisms emphasize compensating activities and the notion of plastid autonomy, but redundant gene products are proposed to play a role in var2, but not in im. It is hypothesized that threshold levels of certain activities are necessary for normal chloroplast development.
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