A high throughput protocol was established to preserve 140,000 mutants of a moss, Physcomitrella patens, a model plant for functional genomics studies, over liquid nitrogen. Regarding the reliable long-term storage of diverse mutant phenotypes, as well as time and cost effectiveness, each working step was optimized: 1) plant preparation, 2) freezing regime, cryogenic conditions, 3) regrowth after thawing. A prerequisite for maximum regrowth was a 1-week preculture of chopped plant material on a supplemented medium prior to freezing. Cryo vials as preculture vessels resulted in identical regrowth rates, compared to petri dishes. The cryo vial type had a significant influence on regrowth rates. A cooling rate of - 1 degrees C/min down to - 35 degrees C with a 10 min holding time before transferring plants to - 152 degrees C was the most suitable freezing regime. This protocol allows a cryopreservation of 1100 plants during a 5-day working week, practicable by one person. For more than 650 cryopreserved mutants a maximum regrowth rate of 100 % was obtained, independently of mutant phenotypes.
Plant cell wall modification is a critical component in stress responses. Endo-1,4-β-glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence-signalling network. A study of a set of Arabidopsis EG T-DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant-pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant-pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.
FUSARIUM SOLANI f. sp. GLYCINES (Fsg) has been reported to produce at least two phytotoxins. Cell-free FSG culture filtrates containing phytotoxins have been shown to develop foliar sudden death syndrome (SDS) in soybean. We have investigated the changes in protein profiles of diseased leaves caused by cell-free FSG culture filtrates prepared from FSG isolates. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) was conducted to investigate the protein profiles of diseased and healthy leaves. An approximately 55 kDa protein was found to be absent in diseased leaves. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometric analyses and a database search revealed that the missing protein is the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, which is involved in carbon assimilation and photorespiration. This result was confirmed by Western blot experiments. We have shown that light is essential for disappearance of the Rubisco large subunit initiated by cell-free FSG culture filtrates. The disappearance of the protein is fairly rapid and occurs within 24 h, presumably due to degradation. Cell-free, FSG culture-induced degradation of the Rubisco large subunit was accompanied by accumulation of reactive oxygen species under light conditions. Terminal deoxynucleotidyl transferase-mediated nick end labelling experiments suggested that programmed cell death was initiated in leaves of seedlings fed with cell-free FSG culture filtrates. These results suggest that, in the presence of light, FSG culture filtrates containing phytotoxins cause degradation of the Rubisco large subunit and accumulation of free radicals and, thereby, initiate programmed cell death leading to foliar SDS development in soybean.
The 4C DNA values of 112 species, belonging to 37 families have a range from 0.83 pg (Bixa orellana) to 15.54 pg (Thryallis angustifolia), showing a 18.72-fold variation. The genome size varies from 0.21 pg (Bixa orellana) to 3.32 (Thespesia populnea), with a 15.8-fold difference. The Bombacaceae has the minimum range (1.08-fold) of variation, while the maximum (5.0-fold) is shown by the Fabaceae. The Boraginaceae, Lauraceae, Malpighiaceae, and Malvaceae generally have higher 4C DNA values of > 10 pg, while the Bixaceae, Caricaceae, Oxalidaceae, and Santalaceae have lower values of < 2.0 pg. These data add further to our knowledge on variation in DNA amount in tropical hardwoods.
The pathways of currently fixed carbon in fruit bearing branchlets were investigated in two temperate forest tree species (CARPINUS BETULUS and FAGUS SYLVATICA), which differ in texture of their vegetative infructescence tissues (leaf-like in CARPINUS vs. woody in FAGUS). During late spring, (13)C pulse-labelling was conducted on girdled, defoliated, girdled plus defoliated and untreated fruiting branchlets of mature trees IN SITU, to assess changes in C relations in response to the introduced C source-sink imbalances. At harvest in early August, 75 - 100 % of the recovered (13)C label was bound to infructescences (either fruits or vegetative infructescence tissue), revealing them as the prime C sinks for current photoassimilates. Leaves on girdled branchlets were not stronger labelled than on ungirdled ones in both species, indicating no upregulation of the leaves' photosynthetic capacity in response to the prevention of phloemic transport, which was also supported by measurements of light saturated photosynthesis. In contrast, (13)C labels tended to be higher after complete defoliation in the vegetative infructescence tissues of CARPINUS, suggesting enhanced net photosynthesis of green infructescence parts as compensation for the loss of regular leaves. The total labelling-derived (13)C content of whole infructescences was very similar between foliated and defoliated CARPINUS branchlets. Cupulae of FAGUS, on the other hand, remained almost unlabelled on defoliated branchlets, indicating the photosynthetic inactivity of this woody infructescence tissue. Consequently, CARPINUS still produced relatively high fruit masses on girdled plus defoliated branchlets, while in FAGUS fruit development ceased almost completely at this most severe treatment. Our results highlight that green vegetative infructescence tissue assimilates substantial amounts of C and can partly substitute regular leaves as C sources for successful fruit development.
Contributions of C3 and C4 plants to respiration of C3-C4 ecosystems can be estimated on the basis of their contrasting 13C discrimination. But accurate partitioning requires accurate measurements of the isotope signature of whole system respiratory CO2 (δR), and of its members (δ3 and δ4). Unfortunately, experimental determination of representative δ3 and δ4 values is virtually impossible in nature, generating a need for proxies (surrogates) of δ3 and δ4 values (e.g., the δ of leaf biomass). However, recent evidence indicates that there may be systematic differences among the δ of respiratory and biomass components. Thus, partitioning may be biased depending on the proxy. We tested a wide range of biomass- and respiration-based δ proxies for the partitioning of respiration of mixed Lolium perenne (C3)-Paspalum dilatatum (C4) stands growing at two temperatures inside large 13CO 2/12CO2 gas exchange chambers. Proxy-based partitioning was compared with results of reference methods, including (i) the δ of whole plant respiratory CO2 (δ3 and δ4) or (ii) respiration rate of intact C3 and C4 plants. Results of the reference methods agreed near perfectly. Conversely, some proxies yielded erroneous partitioning results. Partitioning based on either the δ of shoot or root respiratory CO2 produced the worst bias, because shoot respiratory CO2 was enriched in 13C by several ‰ and root respiratory CO2 was depleted by several ‰ relative to whole plant respiratory CO2. Use of whole plant or whole shoot biomass δ gave satisfactory partitioning results under the constant conditions of the experiments, but their use in natural settings is cautioned if environmental conditions are variable and the time scales of respiration partitioning differ strongly from the residence time of C in biomass. Other biomass-based proxies with faster turnover (e.g., leaf growth zones) may be more useful in changing conditions.
To examine variation and taxonomic recognition of Pinus nigra (European black pine) at the intraspecific level, chromosomal distribution of 5S and 18S-5.8S-26S rDNA loci revealed by fluorescent in situ hybridisation (FISH) and fluorochrome banding with chromomycin A(3) and DAPI were analysed among allopatric populations belonging to different subspecies. Despite prevalent opinion on predominantly conserved and homogenous conifer karyotypes, several patterns were observed. Surprisingly, interstitial 18S rDNA loci and DAPI heterochromatin staining after FISH showed variations in distribution and localisation. Three subspecies shared a pattern with nine 18S rDNA loci (ssp. nigra, pallasiana and laricio) while ssp. dalmatica and salzmannii had eight rDNA loci. DAPI banding displayed two patterns, one with a high number of signals (ssp. nigra, pallasiana and dalmatica) and the other with a lower number of signals (ssp. salzmannii and laricio). We conclude that our results cannot provide proof for either classification scheme for the P. nigra complex, but rather demonstrate the variability of different heterochromatin fractions at the intraspecific level.
Proteins of the 14-3-3 family show a broad range of activities in plants, depending on their localisation in different cellular compartments. Different organelle membranes of pollen grains and pollen tubes of Lilium longiflorum Thunb. were separated simultaneously using optimised discontinuous sucrose density centrifugation. The obtained organelle-enriched fractions were identified as vacuolar, Golgi, endoplasmic reticulum and plasma membranes, according to their marker enzyme activities, and were assayed for membrane-bound 14-3-3 proteins by immunodetection. 14-3-3 proteins were detected in the cytoplasm as well as in all obtained organelle fractions but were also released into the extracellular medium. In pollen grains, much more plasma membrane-bound 14-3-3 proteins were detected than in the PM-enriched fraction of pollen tubes, whereas the level of Golgi- and ER-associated 14-3-3 proteins was similar in pollen grains and tubes. This shift in the localisation of membrane-associated 14-3-3 proteins is probably correlated with a change in the major function of 14-3-3 proteins, e.g., perhaps changing from initiating pollen grain germination by activation of the PM H +-ATPase to recruitment of membrane proteins via the secretory pathway during tube elongation.
Interaction of 14-3-3 proteins with their targets depends not only on the phosphorylation status of the target but also on that of 14-3-3 (Fu et al., 2000). In this work we demonstrated that the maize 14-3-3 isoform GF14-6 is a substrate of the tyrosine kinase insulin growth factor receptor 1. By means of site-directed mutants of GF14-6, we identified Tyr-137 as the specific tyrosine residue phosphorylated by the insulin growth factor receptor 1. Phosphorylation of GF14-6 on Tyr-137 lowered its affinity for a peptide mimicking the 14-3-3 binding site of the plant plasma membrane H+-ATPase. Moreover, phosphorylation in planta of 14-3-3 tyrosine residues, resulting from incubation with the tyrosine phosphatase inhibitor, phenylarsine oxide, decreased their association to the H+-ATPase.
Early view: http://onlinelibrary.wiley.com/doi/10.1111/plb.12048/pdf
In the dioecious genus Populus, sex determination has been located to chromosome 19. However, despite a high degree of genome collinearity, various Populus species seem to differ with regard to the location of the sex-determining region on the respective chromosome and the apparent heterogametic sex. In this study, the boundaries of the recombination-suppressed, sex-linked region of the male P. tremuloides clone Turesson 141 were localised by genetic mapping using new SNP and InDel markers. The respective region seems to be located in a pericentromeric position. The corresponding P. trichocarpa genome region spans about two million bp and comprises 65 gene loci, which were bioinformatically evaluated for their potential as candidate genes for sex determination. Three putative transcription factor genes and four genes that are potentially involved in flower development processes, e.g. meristem transition from the vegetative to the reproductive phase, were identified. Populus tremuloides sequence data of the sex-linked region is required for a final search for candidate genes.
delta(15)N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N(2)-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and delta(15)N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed delta(15)N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific delta(15)N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant-mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N(2)-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N(2)-fixing legumes.
Plants respond to environmental stimuli, such as heat shock, by re-programming cellular activity through differential gene expression, mainly controlled at the transcription level. The current study refers to two sunflower small heat shock protein (sHSP) genes arranged in tandem in head-to-head orientation and linked by a 3809 bp region. These genes exhibit only slight structural differences in the coding portion. They code for cytosolic class I sHSPs and are named HaHSP17.6a and HaHSP17.6b according to the molecular weight of the putative proteins. The genomic organization of these genes is consistent with the idea that many HSP genes originate from duplication events; in this case, probably an inversion and duplication occurred. The HaHSP17.6a and HaHSP17.6b genes are characterized by different expression levels under various heat stress conditions; moreover, their expression is differently induced by various elicitors. The differential regulation observed for HaHSP17.6a and HaHSP17.6b genes differs from previous observations on duplicated sHSP genes in plants.
Male and female flowering plants of the dioecious Urtica dioica occur in approximately equal numbers in our study area on the coastal sand dunes of Meijendel. The seed sex ratio (SSR, fraction of males) collected from female plants in the field varied between 0.05 and 0.76, and differed significantly between maternal parents. After one generation of selection for either high or low SSR, female plants produced seed batches with sex ratios as extreme as 0.08 and 0.73. Natural populations of U. dioica harbour considerable genetic variation in SSR.
Plants have evolved strategies of stimulating and supporting specific groups of antagonistic microorganisms in the rhizosphere as a defense against diseases caused by soilborne plant pathogens owing to a lack of genetic resistance to some of the most common and widespread soilborne pathogens. Some of the best examples of natural microbial defense of plant roots occur in disease suppressive soils. Soil suppressiveness against many different diseases has been described. Take-all is an important root disease of wheat, and soils become suppressive to take-all when wheat or barley is grown continuously in a field following a disease outbreak; this phenomenon is known as take-all decline (TAD). In Washington State, USA and The Netherlands, TAD results from the enrichment during monoculture of populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens to a density of 10 (5) CFU/g of root, the threshold required to suppress the take-all pathogen, Gaeumannomyces graminis var. tritici. 2,4-DAPG-producing P. fluorescens also are enriched by monoculture of other crops such as pea and flax, and evidence is accumulating that 2,4-DAPG producers contribute to the defense of plant roots in many different agroecosystems. At this time, 22 distinct genotypes of 2,4-DAPG producers (designated A - T, PfY and PfZ) have been defined by whole-cell repetitive sequence-based (rep)-PCR analysis, restriction fragment length polymorphism (RFLP) analysis of PHLD, and phylogenetic analysis of PHLD, but the number of genotypes is expected to increase. The genotype of an isolate is predictive of its rhizosphere competence on wheat and pea. Multiple genotypes often occur in a single soil and the crop species grown modulates the outcome of the competition among these genotypes in the rhizosphere. 2,4-DAPG producers are highly effective biocontrol agents against a variety of plant diseases and ideally suited for serving as vectors for expressing other biocontrol traits in the rhizosphere.
Cellulose is the major component of plant cell walls and is an important source of industrial raw material. Although cellulose biosynthesis is one of the most important biochemical processes in plant biology, the regulatory mechanisms of cellulose synthesis are still unclear. Here, we report that 2,6-dichlorobenzonitrile (DCB), an inhibitor of cellulose synthesis, inhibits Arabidopsis root development in a dose- and time-dependent manner. When treated with DCB, the plant cell wall showed altered cellulose distribution and intensity, as shown by calcofluor white and S4B staining. Moreover, pectin deposition was reduced in the presence of DCB when immunostained with the monoclonal antibody JIM5, which was raised against pectin epitopes. This result was confirmed using Fourier transform infrared (FTIR) analysis. Confocal microscopy revealed that the organisation of the microtubule cytoskeleton was significantly disrupted in the presence of low concentrations of DCB, whereas the actin cytoskeleton only showed changes with the application of high DCB concentrations. In addition, the subcellular dynamics of Golgi bodies labelled with N-ST-YFP and TGN labelled with VHA-a1-GFP were both partially blocked by DCB. Transmission electron microscopy indicated that the cell wall structure was affected by DCB, as were the Golgi bodies. Scanning electron microscopy showed changes in the organisation of cellulose microfibrils. These results suggest that the inhibition of cellulose synthesis by DCB not only induced changes in the chemical composition of the root cell wall and cytoskeleton structure, but also changed the distribution of cellulose microfibrils, implying that cellulose plays an important role in root development in Arabidopsis.
The 20S proteasome from wheat (Triticum aestivum L., Yangmai 158) endosperm was purified to apparent homogeneity by three sequential centrifugations and gradient PAGE (GPAGE). The purified 20S proteasome clearly cleaved peptidyl-arylamide bonds in the model synthetic substrates Z-GGL-AMC and Z-GGR-AMC, which are used to reflect chymotrypsin-like and trypsin-like activity, respectively. For both substrates, the optimum pH was 8.0, but the optimum temperatures for chymotrypsin-like and trypsin-like activity were 55 degrees C and 37 degrees C, respectively. Both enzyme activities were clearly inhibited by MG115 and PMSF. Polyubiquitinated proteins remained constant from 0 to 7 days after seed imbibition, but caseinolytic activity and the amount of the 20S proteasome associated with the aleurone layer decreased from 1 to 2 days after imbibition (DAI), then increased from 2 to 4 DAI, and reached a maximum at 4 DAI that was retained until 7 DAI. An increase was seen in the mRNA level of the beta5 subunit of the 20S proteasome from 2 DAI, and caseinolytic activity and the amount of the 20S proteasome increased from 3 DAI onwards. In addition, the main storage proteins of the wheat endosperm could not be hydrolyzed by the 20S proteasome. The evidence suggests that the main role of the 20S proteasome may not be to degrade massive proteins of the wheat endosperm after seed imbibition.
This study evaluated effects of foliar spraying 24-epibrassinoide (24-EBL) on the growth of salt-stressed canola. Seedlings at the four-leaf stage were treated with 150 mm NaCl and different concentrations of 24-EBL (10(-6) , 10(-8) , 10(-10) , 10(-12) m) for 15 days. A concentration of 10(-10) m 24-EBL was chosen as optimal and used in a subsequent experiment on plant biomass and leaf water potential parameters. The results showed that 24-EBL mainly promoted shoot growth of salt-stressed plants and also ameliorated leaf water status. Foliar spraying of salt-stressed canola with 24-EBL increased osmotic adjustment ability in all organs, especially in younger leaves and roots. This was mainly due to an increase of free amino acid content in upper leaves, soluble sugars in middle leaves, organic acids and proline in lower leaves, all of these compounds in roots, as well as essential inorganic ions. Na(+) and Cl(-) sharply increased in different organs under salt stress, and 24-EBL reduced their accumulation. 24-EBL improved the uptake of K(+) , Ca(2+) , Mg(2+) and NO3 (-) in roots, which were mainly transported to upper leaves, while NO3 (-) was mainly transported to middle leaves. Thus, 24-EBL improvements in ion homeostasis of K(+) /Na(+) , Ca(2+) /Na(+) , Mg(2+) /Na(+) and NO3 (-) /Cl(-) , especially in younger leaves and roots, could be explained. As most important parts, younger leaves and roots were the main organs protected by 24-EBL via improvement in osmotic adjustment ability and ion homeostasis. Further, physiological status of growth of salt-stressed canola was ameliorated after 24-EBL treatment.
Ectomycorrhizal (ECM) symbiosis is a mutualistic interaction between certain soil fungi and fine roots of perennial plants, mainly forest trees, by which both partners become capable of efficiently colonising nutrient-limited environments. The success of this interaction is reflected in the dominance of ECM forest ecosystems in the Northern hemisphere. Apart from their economic importance (wood production), forest ecosystems are essential for large-scale carbon sequestration, leading to substantial reductions in anthropogenic CO(2) release. The biological function of ECM symbiosis is the exchange of fungus-derived mineral nutrients for plant-derived carbohydrates. Improved plant nutrition as a result of this interaction, however, has a price. Together with their fungal partner, root systems of ECM plants can receive about half of the photosynthetically fixed carbon. To enable such a strong carbohydrate sink, the monosaccharide uptake capacity and carbohydrate flux through glycolysis and intermediate carbohydrate storage pools (trehalose and/or mannitol) of mycorrhizal fungi is strongly increased at the plant-fungus interface. Apart from their function as a carbohydrate store, trehalose/mannitol are additionally considered to be involved in carbon allocation within the fungal colony. Dependent on the fungal species involved in the symbiosis, regulation and fine-tuning of fungal carbohydrate uptake and metabolism seems to be controlled either by developmental mechanisms or by the apoplastic sugar content. As a consequence of the increased carbohydrate demand in symbiosis, trees increase their photosynthetic capacity. In addition, host plants control and restrict carbohydrate flux towards their partner to avoid fungal parasitism. The mechanisms behind this phenomenon are still largely unknown but rates of local sucrose hydrolysis and hexose uptake by rhizodermal cells are thought to restrict fungal carbohydrate nutrition under certain conditions (e.g., reduced fungal nutrient export).
The natural variability of wood formation in trees affords opportunities to correlate transcript profiles with the resulting wood properties. We have used cDNA microarrays to study transcript abundance in developing secondary xylem of loblolly pine (Pinus taeda) over a growing season. The cDNAs were selected from a collection of 75 000 ESTs that have been sequenced and annotated (http://web.ahc.umn.edu/biodata/nsfpine/). Cell wall thickness and climatic data were related to earlywood and latewood formation at different time points during the growing season. Seventy-one ESTs showed preferential expression in earlywood or latewood, including 23 genes with no significant similarity to genes in GenBank. Seven genes involved in lignin synthesis were preferentially expressed in latewood. The studies have provided initial insights into the variation of expression patterns of some of the genes related to the wood formation process.
Transcriptional gene silencing (TGS) is often associated with an increased level of cytosine methylation in the affected promoters. The effect of methylation of the cauliflower mosaic virus (CaMV) 35S promoter sequence on its binding to factors present in the nuclei was analyzed by electrophoretic mobility shift assays using extracts of petunia flowers. Specific DNA-protein interactions were detected in the region of the CaMV 35S promoter that contains the as-1 element and the region between - 345 and - 208. The binding of protein factor(s) to the as-1 element was influenced by cytosine methylation, whereas the binding to the region between - 345 and - 208 was unaffected. The results suggest that cytosine methylation of the as-1 element potentially affects the activity of the CaMV 35S promoter.
In order to test the stress hypothesis of allelopathy of Reigosa et al. (1999, 2002), the combined action of a well-established allelochemical compound (2-3H-benzoxazolinone, BOA) and a common abiotic stress (salt stress) were investigated in lettuce (Lactuca sativa L.). In a previous study (Baerson et al. 2005), we demonstrated that the primary effects of BOA are related to the expression of genes involved in detoxification and stress responses, which might serve to simultaneously alleviate biotic and abiotic stresses. Through analysis of the same physiological and biochemical parameters previously studied for BOA alone (Sánchez-Moreiras & Reigosa 2005), we observed specific effects of salt stress alone, as well as for the two stresses together (BOA and salt). This paper demonstrates that plants showing tolerance to salt stress (reduced stomatal density, increased proline content, higher K(+) concentration, etc.) become salt sensitive (markedly low Psiw values, high putrescine content, increased lipid peroxidation, etc.) when simultaneously treated with the allelochemical BOA. We also report additional information on the mechanisms of action of BOA, and general stress responses in this plant species.
Inositol-containing phospholipids (phosphoinositides, PIs) control numerous cellular processes in eukaryotic cells. For plants, a key involvement of PIs has been demonstrated in the regulation of membrane trafficking, cytoskeletal dynamics and in processes mediating the adaptation to changing environmental conditions. Phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2 ) mediates its cellular functions via binding to various alternative target proteins. Such downstream targets of PtdIns(4,5)P2 are characterised by the possession of specific lipid-binding domains, and binding of the PtdIns(4,5)P2 ligand exerts effects on their activity or localisation. The large number of potential alternative binding partners - and associated cellular processes - raises the question how alternative or even contrapuntal effects of PtdIns(4,5)P2 are orchestrated to enable cellular function. This article aims to provide an overview of recent insights and new views on how distinct functional pools of PtdIns(4,5)P2 are generated and maintained. The emerging picture suggests that PtdIns(4,5)P2 species containing different fatty acids influence the lateral mobility of the lipids in the membrane, possibly enabling specific interactions of PtdIns(4,5)P2 pools with certain downstream targets. PtdIns(4,5)P2 pools with certain functions might also be defined by protein-protein interactions of PI4P 5-kinases, which pass PtdIns(4,5)P2 only to certain downstream partners. Individually or in combination, PtdIns(4,5)P2 species and specific protein-protein interactions of PI4P 5-kinases might contribute to the channelling of PtdIns(4,5)P2 signals towards specific functional effects. The dynamic nature of PI-dependent signalling complexes with specific functions is an added challenge for future studies of plant PI signalling.
Using a combined set of sequences of SSU and ITS regions of nuclear-encoded ribosomal DNA, the concept of the experimental algal genus Chlorella was evaluated. Conventionally in the genus Chlorella, only coccoid, solitary algae with spherical morphology that do not possess any mucilaginous envelope were included. All Chlorella species reproduce asexually by autospores. However, phylogenetic analyses showed that within the clade of 'true'Chlorella species (Chlorella vulgaris, C. lobophora, and C. sorokiniana), taxa with a mucilaginous envelope and colonial lifeform have also evolved. These algae, formerly designated as Dictyosphaerium, are considered as members of the genus Chlorella. In close relationship to Chlorella, five different genera were supported by the phylogenetic analyses: Micractinium (spherical cells, colonial, with bristles), Didymogenes (ellipsoidal cells, two-celled coenobia, with or without two spines per cell), Actinastrum (ellipsoidal cells within star-shaped coenobia), Meyerella (spherical cells, solitary, without pyrenoids), and Hegewaldia (spherical cells, colonial, with or without bristles, oogamous propagation). Based on the secondary structures of SSU and ITS rDNA sequences, molecular signatures are provided for each genus of the Chlorella clade.
Histone modifications occur during DNA damage and repair in eukaryotes. These modifications were analysed in wheat seedlings exposed to (60) Co-γ radiation. Seedling height was not significantly affected in the first 2 days after irradiation up to 150 Gy. Subsequently, in the next 2 weeks, there was 30-40% reduction in seedling height, indicating that there were late effects of irradiation. The histones isolated from irradiated seedlings were analysed in the initial stages for modifications of H3 and H4 using antibodies. Global acetylation of H3 decreased and H4 increased in a dose-dependent manner till 100 Gy. The time course of individual modifications showed that for H3K4 and H3K9, acetylation decreased, whereas for H3S10 phosphorylation increased. There were fluctuations in acetylation of H4K5, H4K12 and H4K16, whereas H4K8 showed hyper-acetylation. The results indicate that γ radiation induced DNA damage and repair in wheat seedlings and initiated differential acetylation of H3 and H4. This is the first report in plants on site-specific H3 and H4 modifications in response to exposure to ionizing radiation.
In order to investigate the metabolic importance of glycine decarboxylase (GDC) in cyanobacteria, mutants were generated defective in the genes encoding GDC subunits and the serine hydroxymethyl-transferase (SHMT). It was possible to mutate the genes for GDC subunits P, T, or H protein in the cyanobacterial model strain Synechocystis sp. PCC 6803, indicating that GDC is not necessary for cell viability under standard conditions. In contrast, the SHMT coding gene was found to be essential. Almost no changes in growth, pigmentation, or photosynthesis were detected in the GDC subunit mutants, regardless of whether or not they were cultivated at ambient or high CO2 concentrations. The mutation of GDC led to an increased glycine/serine ratio in the mutant cells. Furthermore, supplementation of the medium with low glycine concentrations was toxic for the mutants but not for wild type cells. Conditions stimulating photorespiration in plants, such as low CO2 concentrations, did not induce but decrease the expression of the GDC and SHMT genes in Synechocystis. It appears that, in contrast to heterotrophic bacteria and plants, GDC is dispensable for Synechocystis and possibly other cyanobacteria.
Disruption of the ccmM gene in the cyanobacterium Synechocystis sp. PCC 6803 causes a deficiency of carboxysomes and impairs growth in ambient CO2. The effect of this gene defect on cellular metabolism was investigated using electron microscopy, biochemical and fluorescence analysis. Mutant cells were devoid of the characteristic dense polyhedral bodies called carboxysomes. The photosynthetic oxygen evolution was considerably lower in mutant cells compared to wild type, while Rubisco activity in cell extracts was similar. During photosynthetic CO2-dependent oxygen evolution, Rubisco Vmax dropped from 142 micromol mg-1 chlorophyll h-1 (WT) to 77 micromol mg-1 chlorophyll h-1 in the mutant cells, and the Km for Ci (inorganic carbon) increased from 0.5 mM (WT) to 40 mM. The fluorescent indicator, acridine yellow, was used for non-invasive measurements of cytoplasmic pH changes in whole cells induced by addition of Ci, making use of the decrease in fluorescence yield that accompanies cytoplasmic acidification. The experimental results indicate that control of the cytoplasmic pH is linked to the internal carbon pool (Ci). Both wild-type and ccmM-deficient cells showed a linear response of acridine yellow fluorescence quenching and, thus, of internal acidification, with respect to externally added inorganic carbon. However, the fluorescence analysis of mutant (carboxysome-free) cells indicated slower kinetics of Ci accumulation.
Spartina densiflora Brongn. is found in coastal marshes of southwest Spain, growing over sediments containing 100-4800 ppm Zn. A glasshouse experiment was designed to investigate the effect of Zn from 0 to 100 mmol.l(-1) on the growth and photosynthetic apparatus of S. densiflora, by measuring relative growth rate, leaf elongation rate, number of tillers, height of tillers, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. We also determined total ash, Zn, calcium, magnesium and phosphorus concentrations, and the C/N ratio. At 100 mmol.l(-1) Zn, S. densiflora showed a 48% biomass reduction after 1 month of treatment. Long-term effects of Zn on growth of S. densiflora consisted mainly of variations in net photosynthesis. Modification of the Zn/Mg ratio was linked to a strong decrease in RuBP carboxylase (Zn was favoured in local competition with Mg, so that the affinity of RuBisCO for CO(2) decreased), oxygenase activity of RuBisCO acting as a substitute for the photosynthetic function. Also, Zn had a marked overall effect on the photochemical (PSII) apparatus and the synthesis of photosynthetic pigments. However, the results indicate that S. densiflora is capable of tolerating very high and continued exposure to Zn, as this species lowers the translocation of Zn from the nutrient solution to roots and controls Zn ion transport into leaves. Therefore, S. densiflora could be useful in the phytostabilization of soils.
Although most cyanobacterial cells contain prominent polyphosphate bodies in the central cytoplasmic area enclosed by the peripheral thylakoid membranes, their roles are not fully understood. Storing phosphate for nucleotide production might be one of their important roles in survival of the cells. As a step towards identifying a possible contribution of the polyphosphate bodies to DNA synthesis, the relationship between polyphosphate bodies and DNA throughout cell division cycle of Synechococcus elongatus PCC 7942 cells cultured under light/dark cycles was investigated with light and electron microscopy. During the dark period, the average size of polyphosphate bodies increased gradually without significant change in their number and distribution. However, during the light period, the number of polyphosphate bodies increased, while the size of each polyphosphate body decreased and cells elongated until the end of the light period, when most cells divided. The ratio of the content of polyphosphate bodies to cell length increased gradually during the dark period and decreased during the light period. Hoechst 33342-stained DNA appeared diffuse during the dark period, but in the light period it became condensed and eventually formed a wavy, rope-like structure prior to cell division. Close association between fibres containing DNA and polyphosphate bodies was demonstrated by TEM using DNA-specific staining and BrdU labelling. These regular coordinated changes of polyphosphate bodies and DNA shape during the cell division cycle, together with their intimate interaction, imply a role of polyphosphate bodies in supplying material for DNA.
Flavonoids are natural compounds found in many plants, including the important fruit crop, tomato. Prenylated flavonoids consist of a large group of compounds, which often exhibit antitumour, antibacterial and/or anti-androgen activities. In this study, we engineered the biosynthesis of prenylated flavonoids using a Streptomyces prenyltransferase HypSc (SCO7190) possessing broad-range substrate specificity, in tomato as a host plant. LC/MS/MS analysis demonstrated the generation of 3'-dimethylallyl naringenin in tomato fruits when recombinant HypSc protein was targeted to the plastids, whereas the recombinant protein hardly produced this compound in vitro. This is the first report confirming the accumulation of a prenylated flavonoid using a bacterial prenyltransferase in transgenic plants, and our results suggest that the product specificities of prenyltransferases can be significantly influenced by the host plant.
Methylglyoxal (MG) is a highly reactive metabolite derived from glycolysis. In this study, we examined the effect of MG on seed germination, root elongation, chlorosis and stress-responsive gene expression in Arabidopsis using an abscisic acid (ABA)-deficient mutant, aba2-2. In the wild type, 0.1 mm MG did not affect germination but delayed root elongation, whereas 1.0 mm MG inhibited germination and root elongation and induced chlorosis. MG increased transcription levels of RD29B and RAB18 in a dose-dependent manner but did not affect RD29A transcription level. In contrast, in the aba2-2 mutant, MG inhibition of seed germination at 1.0 mm and 10.0 mm and a delay of root elongation at 0.1 mm MG were mitigated, although there was no significant difference in chlorosis between the wild type and mutant. Moreover, the aba2-2 mutation impaired MG-induced RD29B and RAB18 gene expression. These observations suggest that MG not only directly inhibits germination and root elongation but also indirectly modulates these processes via endogenous ABA in Arabidopsis.
We investigated the interaction among abscisic acid (ABA), reactive oxygen species (ROS) and antioxidant defence system in the transduction of osmotic stress signalling using Arabidopsis thaliana WT (Columbia ecotype, WT) and an ABA-deficient mutant (aba2-1). For this, 50 μm ABA and osmotic stress, induced with 40% (w/v) polyethylene glycol (PEG8000; -0.7 MPa), were applied to WT and aba2-1 for 6, 12 or 24 h. Time course analysis was undertaken for determination of total/isoenzyme activity of the antioxidant enzymes, superoxide dismutase (SOD; EC 220.127.116.11), catalase (CAT; EC 18.104.22.168), ascorbate peroxidase (APX; EC 22.214.171.124), NADPH oxidase (NOX; EC 126.96.36.199) activity; scavenging activity of the hydroxyl radical (OH˙), hydrogen peroxide (H(2) O(2) ); endogenous ABA and malondialdehyde (MDA). The highest H(2) O(2) and MDA content was found in PEG-treated groups of both genotypes, but with more in aba2-1. ABA treatment under stress reduced the accumulation of H(2) O(2) and MDA, while it promoted activity of SOD, CAT and APX. APX activity was higher than CAT activity in ABA-treated WT and aba2-1, indicating a protective role of APX rather than CAT during osmotic stress-induced oxidative damage. Treatment with ABA also significantly induced increased NOX activity. Oxidative damage was lower in ABA-treated seedlings of both genotypes, which was associated with greater activity of SOD (Mn-SOD1 and 2 and Fe-SOD isoenzymes), CAT and APX in these seedlings after 24 h of stress. These results suggest that osmotic stress effects were overcome by ABA treatment because of increased SOD, CAT, APX and NOX.
We studied the effect of cessation of management on carbohydrate reserves of plants in meadows with different environmental characteristics and plant composition. We recorded storage carbohydrates and seasonal changes for 40 plant species. We asked whether there are differences in responses of carbohydrate reserves in forbs versus graminoids and in plants storing starch versus plants storing osmotically active carbohydrates. We analysed belowground organs before the meadows were mown and at the end of the vegetation season in mown versus recently abandoned plots. Whereas starch and fructans were widely distributed, raffinose family oligosaccharides were the main carbohydrate reserves of the Lamiaceae and Plantago lanceolata. Properties of carbohydrate reserves differed between forbs and graminoids but no difference was found between plants storing starch versus osmotically active carbohydrates. Graminoids had lower carbohydrate concentrations than forbs. We observed a positive effect of mowing on carbohydrate concentrations of graminoids in the dry, calcium-rich meadow and higher seasonal fluctuations of these values in the acid, wet meadow, suggesting that local factors and/or the species pool affect carbohydrate reserves. Despite local conditions, graminoids represent a distinct functional group in meadows from the point of view of their storage economy. We suggest that as well as growth, storage processes should also be considered for understanding the functioning of meadow plant communities.
In contrast to animals, plant gametes form in distinct haploid generations, termed gametophytes. The female gametophyte of Arabidopsis consists of two gametic cells, the egg and central cell, which are flanked by accessory cells. The gametic cells differ with respect to morphology, molecular attributes and, importantly, their fate: whereas the egg cell, upon fertilisation, gives rise to the embryo, the central cell forms the endosperm. To ensure correct endosperm formation, not only the egg cell but also the central cell has to fuse with a sperm cell. The respective sperm cell pair is delivered by a single pollen tube. In some plant species, the two male gametes appear to express a different bias towards the female gametes. Such a preference consequently determines their respective contribution to either embryo or endosperm development. In Arabidopsis and many other species the sperm cells are indistinguishable and it has been discussed whether they possess an inherent preference for either of the female gametes. The recent isolation of mutants that form an aberrant number of either male or female gametes stimulates discussion, albeit with different results. Furthermore, some data indicate that the central cell is competent to initiate endosperm formation without a paternal contribution. These data support the theory that the endosperm is of gametophytic rather than sporophytic origin.
Genome size, karyotype structure, heterochromatin distribution, position and number of ribosomal genes, as well as the ITS2 sequence of the internal transcribed spacer (ITS) were analysed in silver fir (Abies alba Mill.). The analysis also included characterization of the Arabidopsis-type of telomeric repeats in silver fir and in related species. The results were compared with results from other species of the Pinaceae, to evaluate phylogeny and chromosomal and molecular evolution in the Pinaceae. Integrated chromosomal data provided insights into chromosome and karyotype evolution in the Pinaceae. The evolutionary trend for GC-rich heterochromatic blocks seems to involve loss of blocks that are not associated with rDNA. Similarly, numerous large blocks of interstitial plant telomeric repeats that are typical for all analysed species of the genus Pinus were not observed in the evolutionarily younger genera, such as Abies, Picea and Larix. On the contrary, the majority of telomeric sequences in these three genera appeared confined to the chromosome ends. We confirmed the current position of Abies and Tsuga in subfamily Abietoideae and the position of Pinus in the subfamily Pinoideae based on ITS2 sequences. Pseudotsuga is placed together with Larix into the subfamily Laricoideae. We conclude that the current position of the genus Picea in the subfamily Abietoideae should be reconsidered and, possibly, the genus Picea should be reclassified as a separate subfamily, Piceoideae, as recently proposed.
This study attempted to detect the impact of ozone on adult trees of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) in an experimental mixed stand in Southern Bavaria, Germany. The aim was to examine whether there is a decrease in growth when trees are exposed to higher than atmospheric concentrations of ozone. This exposure was put into effect using a free-air fumigation system at tree crown level. Growth analysis was carried out on a group of 47 spruce and 36 beech trees, where radial stem increment at breast height - a sensitive index for stress - was measured. The ozone monitoring system allowed values to be obtained for the accumulated ozone exposure (SUM00) of each individual tree, so that their radial increment over three years could be correlated with the corresponding ozone exposure for the same time period. Correlation and regression analysis were then carried out to test the influence of ozone on diameter increment. In both spruce and beech, the initial stem diameter was the most influential factor on radial increment in the following year. A linear model was applied, including the diameter of the preceding year and the ozone exposure of the current year as predicting factors. For spruce trees, a significant negative influence of ozone exposure was found. In contrast, no significant ozone effect on diameter increment of beech was detected. The effect of ozone stress on a large spruce tree can lead to a decrease in potential radial increment of 22 %. The results are discussed in relation to other stress factors such as drought and lack of light.
The influence of long-term free-air ozone fumigation and canopy position on leaf contents of total glutathione, its redox state, non-structural proteins (NSP), soluble amino compounds, and total soluble sugars in old-growth beech (FAGUS SYLVATICA) and spruce (PICEA ABIES) trees were determined over a period of five years. Ozone fumigation had weak effects on the analysed metabolites of both tree species and significant changes in the contents of total glutathione, NSP, and soluble sugars were observed only selectively. Beech leaves were affected by crown position to a higher extent than spruce needles and exhibited lower contents of total glutathione and NSP and total soluble sugars, but enhanced contents of oxidised glutathione and amino compounds in the shade compared to the sun crown. Contents of total soluble sugars generally were decreased in shade compared to sun needles of spruce trees. Interspecific differences between beech and spruce were more distinct in the sun compared to the shade crown. Contents of total glutathione were increased whilst contents of amino compounds and total soluble sugars were lower in spruce needles compared to beech leaves. The metabolites determined showed individual patterns in the course of the five measurement years. Contents of total glutathione and its redox state correlated with air temperature and global radiation, indicating an important role for the antioxidant at low temperatures. Correlations of glutathione with instantaneous ozone concentrations seem to be a secondary effect. Differences in proteins and/or amino compounds in the inter-annual course are assumed to be a consequence of alterations in specific N uptake rates.
In a two-year phytotron study, juvenile trees of European beech (Fagus sylvatica) and Norway spruce (Picea abies) were grown in mixture under ambient and twice ambient ozone (O3) and infected with the root pathogen Phytophthora citricola. We investigated the influence of O3 on the trees' susceptibility to the root pathogen and assessed, through a 15N-labelling experiment, the impact of both treatments (O3 exposure and infection) on belowground competitiveness. The hypotheses tested were that: (1) both P. citricola and O3 reduce the belowground competitiveness (in view of N acquisition), and (2) that susceptibility to P. citricola infection is reduced through acclimation to enhanced O3 exposure. Belowground competitiveness was quantified via cost/benefit relationships, i.e., the ratio of structural investment in roots relative to their uptake of 15N. Beech had a lower biomass acquisition and captured less 15N under enhanced O3 and P. citricola infection alone than spruce, whereas the latter species appeared to profit from the lower resource acquisition of beech in these treatments. Nevertheless, in the combined treatment, susceptibility to P. citricola of spruce was increased, while beech growth and 15N uptake were not further reduced below the levels found under the single treatments. Potential trade-offs between stress defence, growth performance, and associated nitrogen status are discussed for trees affected through O3 and/or pathogen infection. With respect to growth performance, it is concluded that O3 enhances susceptibility to the pathogen in spruce, but apparently raises the defence capacity in beech..
In pure and mixed stands of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) we have analyzed crown allometry and growing space efficiency at the tree level and have scaled this from tree level to stand level production. Allometry is quantified by the ratio A between the relative growth rates of laterally and vertically oriented tree dimensions. Efficiency parameters, EOC for efficiency in space occupation, EEX for efficiency in space exploitation, and EBI for efficiency in biomass investment, were evaluated, based on quantity and quality of growing space and were measured using crown size and competition index. The evaluation reveals why pure stands of spruce are preferred by foresters, even though the natural vegetation would be dominated by beech. Spruce occupies its share of resources intensively by means of tightly packed pillar-like crowns, whereas beech seizes resources extensively by means of a multi-layered, veil-like canopy. With a given relative biomass increment, beech achieves a 57 % higher increment in crown projection area and a 127 % higher increment in height due to its particular capacity of lateral and vertical expansion. Beech trees are approximately 60 % more efficient in space occupation than spruce trees, however, on average, they are about 70 % less efficient in space exploitation. As a vertical fast growing tree, spruce is efficient in space exploitation under constant conditions, but far more susceptible to disturbances and less well equipped to overcome them when compared with beech. Beech is weaker in terms of space exploitation, while being superior in space occupation, where it encircles competitors and fills gaps after disturbances, which is a successful long-term strategy. A mixture of the two species reduces stand level production by 24 % in comparison to a pure spruce stand, however, when considering enhanced stabilization of the whole stand and risk distribution in the long term, the mixed stand may exceed the production level of pure spruce stands. EEX reflects a strong ontogenetic drift and competition effect that should be considered when scaling from tree to stand level production.
Several previous studies have observed that species and individuals with large seeds respond more positively to elevated CO (2) than those with small seeds. We explored the reasons for this pattern by examining the relationship between seed size and CO (2) response in Picea abies and P. rubens using growth analysis. The large seeded species (P. abies) responded more positively to elevated CO (2) than the small seeded species (P. rubens). At the intraspecific level, P. abies individuals from large seeds responded more positively to elevated CO (2) than individuals from small seeds, however, there was no significant intraspecific variation in CO (2) response in P. rubens. The greater CO (2) response of plants from large seeds was not simply the result of a larger starting capital compounded at the same rate as in plants from small seeds. Elevated CO (2) increased relative growth rate to a greater extent in individuals from large seeds. This effect appears to be related to differences in time of establishment, source to sink ratio and nutrient availability with seed size. These results are significant not only in understanding the potential effect of rising atmospheric CO (2) concentrations on plant populations, but also in understanding the factors affecting plant success at current atmospheric CO (2) levels due to the elevation of CO (2) within the litter layer that occurs at many germination sites.
Root respiration has been shown to increase with temperature, but less is known about how this relationship is affected by the fungal partner in mycorrhizal root systems. In order to test respiratory temperature dependence, in particular Q (10) of mycorrhizal and non-mycorrhizal root systems, seedlings of PICEA ABIES (L.) Karst. (Norway spruce) were inoculated with the ectomycorrhizal fungus PILODERMA CROCEUM (Eriksson and Hjortstam, SR430; synonym: PILODERMA FALLAX: [Libert] Stalpers) and planted in soil respiration cuvettes (mycocosms). Temperature dependence of hyphal respiration in sterile cultures was determined and compared with respiration of mycorrhizal roots. Respiration rates of mycorrhizal and non-mycorrhizal root systems as well as sterile cultures were sensitive to temperature. Q (10) of mycorrhizal root systems of 3.0 +/- 0.1 was significantly higher than that of non-mycorrhizal systems (2.5 +/- 0.2). Q (10) of P. CROCEUM in sterile cultures (older than 2 months) was similar to that of mycorrhizal root systems, suggesting that mycorrhizae may have a large influence on the temperature sensitivity of roots in spite of their small biomass. Our results stress the importance of considering mycorrhization when modeling the temperature sensitivity of spruce roots.
We studied the effects of phosphorus fertilisation on foliar terpene concentrations and foliar volatile terpene emission rates in six half-sib families of Pinus pinaster Ait. seedlings. Half of the seedlings were resistant to attack of the pine weevil Hylobius abietis L., a generalist phloem feeder, and the remaining seedlings were susceptible to this insect. We hypothesised that P stress could modify the terpene concentration in the needles and thus lead to altered terpene emission patterns relevant to plant-insect signalling. The total concentration and emission rate ranged between 5732 and 13,995 μg·g(-1) DW and between 2 and 22 μg·g(-1) DW·h(-1), respectively. Storage and emission were dominated by the isomers α- and β-pinene (77.2% and 84.2% of the total terpene amount amassed and released, respectively). In both resistant and susceptible families, P stress caused an increase of 31% in foliar terpene concentration with an associated 5-fold decrease in terpene emission rates. A higher terpene content in the leaves implies that the 'excess carbon', available under limiting growth conditions (P scarcity), is allocated to terpene production. Sensitive families showed a greater increase in terpene emission rates with increasing P concentrations, which could explain their susceptibility to H. abietis.
The effect of stress hormones and abiotic stress treatments on reactive oxygen species and on antioxidants was compared in two maize (Zea mays L.) lines (Penjalinan and Z7) having different stress tolerance. Following treatment with abscisic acid, salicylic acid or hydrogen peroxide, the amount of hydrogen peroxide and lipid peroxides increased, while after osmotic stress or cultivation in continuous darkness, the levels were unchanged or decreased. The higher amount of lipid peroxides in Penjalinan indicated its greater sensitivity compared to Z7. The level of the examined antioxidants was increased by nearly all treatments. Glutathione and cysteine contents were higher after salicylic acid, hydrogen peroxide and polyethylene glycol treatments and lower after application of abscisic acid, NaCl and growth in darkness in Z7 than in Penjalinan. The activity of glutathione reductase, ascorbate peroxidase, catalase and glutathione S-transferase was higher after almost all treatments in Z7. The expression of the glutathione synthetase (EC 188.8.131.52) gene was not affected by the treatments, while the level of gamma-glutamylcysteine synthetase (EC 184.108.40.206) and glutathione reductase (EC 220.127.116.11) transcripts increased after most treatments. The two stress hormones and the stress treatments resulted in different changes in antioxidant levels in the two maize lines, which indicates the specific, stress tolerance-dependent response of plants to the various growth regulators and adverse environmental effects that were examined.
The plant hormones auxin and abscisic acid may at first sight appear to be a conflicting pair of plant regulators. Abscisic acid content increases during stress and protects plant water status. The content of free auxin in the developing xylem of poplar declines during stress, while auxin conjugates increase. This indicates that specific down-regulation of a signal transduction chain is important in plant adaptation to stress. Diminished auxin content may be a factor that adapts growth and wood development of poplar during adverse environmental conditions. To allow integration of environmental signals, abscisic acid and auxin must interact. Data are accumulating that abscisic acid-auxin cross-talk exists in plants. However, knowledge of the role of plant hormones in the response of trees to stress is scarce. Our data show that differences in the localisation of ABA synthesis exist between the annual, herbaceous plant Arabidopsis and the perennial woody species, poplar.
We have employed EST analysis in the resurrection moss Tortula ruralis to discover genes that control vegetative desiccation tolerance and describe the characterization of the EST-derived cDNA TrDr3 ( Tortula ruralis desiccation-stress related). The deduced polypeptide TRDR3 has a predicted molecular mass of 25.5 kDa, predicted pI of 6.7, and six transmembrane helical domains. Preliminary expression analyses demonstrate that the TrDr3 transcript ratio increases in response to slow desiccation relative to the hydrated control in both total and polysomal mRNA (mRNP fraction), which classifies TrDr3 as a rehydrin. Bioinformatic searches of the electronic databases reveal that Tortula TRDR3 shares significant similarities to the hdeD gene product ( HNS- dependent expression) from Escherichia coli. The function of the HdeD protein in E. coli is unknown, but it is postulated to be involved in a mechanism of acid stress defence. To establish the role of E. coli HdeD in abiotic stress tolerance, we determined the log survival percentage from shaking cultures of wild-type bacteria and the isogenic hdeD deletion strain (Delta hdeD) in the presence of low temperature (28 degrees C), elevated NaCl (5 % (w/v)), or decreased pH (4.5), or all treatments simultaneously. The Delta hdeD deletion strain was less sensitive, as compared to wild-type E. coli, in response to decreased pH ( p > 0.009), and the combination of all three stresses ( p > 0.0001).
The discovery of genes that can be used to increase plant tolerance to environmental stress has practical implications for agriculture, since knowledge at the molecular level can potentially be translated from model plants to crops or from tolerant to sensitive cultivars. For more than a decade, researchers have attempted to identify transcriptional and metabolic pathways involved in stress tolerance using functional genomics tools. In some cases, promising results were obtained when a clear causal link was found between transcripts and tolerance/sensitivity to stress. However, recent reports question the global translational power of functional genomics for biotechnological applications, as one of the main limitations seems to be the large variability in gene expression. Transcript-level variability under stress has not been considered of interest in the scientific literature because it is intuitively obvious, but most reports seem to naively overlook the consequences. Here, three case situations are reviewed (variability between genotypes, variability due to environmental interactions and variability between stressors) in support of the concept that inherent transcript-level variation in biological systems may limit our knowledge of environmental plant tolerance and of functional genomics in molecular stress physiology.
Sugars are important signals in the regulation of plant metabolism and development. During stress and in senescing leaves, sugars often accumulate. In addition, both sugar accumulation and stress can induce leaf senescence. Infection by bacterial and fungal pathogens and attack by herbivores and gall-forming insects may influence leaf senescence via modulation of the sugar status, either by directly affecting primary carbon metabolism or by regulating steady state levels of plant hormones. Many types of biotic interactions involve the induction of extracellular invertase as the key enzyme of an apoplasmic phloem unloading pathway, resulting in a source-sink transition and an increased hexose/sucrose ratio. Induction of the levels of the phytohormones ethylene and jasmonate in biotic interactions results in accelerated senescence, whereas an increase in plant- or pathogen-derived cytokinins delays senescence and results in the formation of green islands within senescing leaves. Interactions between sugar and hormone signalling also play a role in response to abiotic stress. For example, interactions between sugar and abscisic acid (ABA) signalling may be responsible for the induction of senescence during drought stress. Cold treatment, on the other hand, can result in delayed senescence, despite sugar and ABA accumulation. Moreover, natural variation can be found in senescence regulation by sugars and in response to stress: in response to drought stress, both drought escape and dehydration avoidance strategies have been described in different Arabidopsis accessions. The regulation of senescence by sugars may be key to these different strategies in response to stress.
Abiotic stresses resulting from water deficit, high salinity or periods of drought adversely affect plant growth and development and represent major selective forces during plant evolution. The raffinose family oligosaccharides (RFOs) are synthesised from sucrose by the subsequent addition of activated galactinol moieties donated by galactinol. RFOs are characterised as compatible solutes involved in stress tolerance defence mechanisms, although evidence also suggests that they act as antioxidants, are part of carbon partitioning strategies and may serve as signals in response to stress. The key enzyme and regulatory point in RFO biosynthesis is galactinol synthase (GolS), and an increase of GolS in expression and activity is often associated with abiotic stress. It has also been shown that different GolS isoforms are expressed in response to different types of abiotic stress, suggesting that the timing and accumulation of RFOs are controlled for each abiotic stress. However, the accumulation of RFOs in response to stress is not universal and other functional roles have been suggested for RFOs, such as being part of a carbon storage mechanism. Transgenic Arabidopsis plants with increased galactinol and raffinose concentrations had better ROS scavenging capacity, while many sugars have been shown in vitro to have antioxidant activity, suggesting that RFOs may also act as antioxidants. The RFO pathway also interacts with other carbohydrate pathways, such as that of O-methyl inositol (OMI), which shows that the functional relevance of RFOs must not be seen in isolation to overall carbon re-allocation during stress responses.
Population dynamics of the annual plant Arabidopsis thaliana (L.) Heynh. were studied in a natural habitat of this species on the coastal dunes of the Netherlands. The main objective was to elucidate factors controlling population dynamics and the relative importance of factors affecting final population density. Permanent plots were established and plants were mapped to obtain data on survival and reproductive performance of each individual, with special attention to herbivore damage. In experimental plots we studied how watering, addition of nutrients, artificial disturbance, and natural herbivores affected survival and growth. Mortality was low during autumn and early winter and high at the time of stem elongation, between February and April. A key factor analysis showed a high correlation between mortality from February to April and total mortality. The specialist weevils Ceutorhyncus atomus and C. contractus (Curculionidae) were identified as the major insect herbivores on A. thaliana, reducing seed production by more than 40 %. These herbivores acted in a plant size-dependent manner, attacking a greater fraction of the fruits on large plants. While mortality rates were not affected by density, fecundity decreased with density, although the effect was small. Adding water reduced mortality in rosette and flowering plant stages. Soil disturbance did not increase seed germination, but did have a significant positive effect on survival of rosette and flowering plants. Seed production of A. thaliana populations varied greatly between years, leading to population fluctuations, with a small role for density-dependent fecundity and plant size-dependent herbivory.
Enhanced resistance of barley (Hordeum vulgare L. cv. Ingrid) against barley powdery mildew (Blumeria graminis f. sp. hordei race A6) was induced by abiotic stress in a concentration-dependent manner. The papilla-mediated resistance was not only induced by osmotic stress, but also by proton stress. Resistance was directly correlated with increasing concentrations of various salts in the nutrient solution. Resistance induced by proton stress also depended on the stress intensity. Resistance induction occurred even at low stress intensities. Any specific ion toxicity affecting the fungal growth directly, and therefore leading to enhanced pathogen resistance, can be excluded because of the independence of resistance induction of the ion used and of the time course of sodium accumulation in the leaves. BCI-4, a marker for benzo[1,2,3]thiadiazolecarbothioic acid S-methyl ester (BTH)-induced resistance was not induced by these abiotic stresses. However, resistance was induced in the same concentration-dependent manner by the application of the stress hormone ABA to the root medium. During the relief of water stress, resistance did not decrease constantly. On the contrary, after a phase of decreasing resistance for 24 h the pathogen resistance increased again for 48 h before decreasing finally to control levels.