Chilling stress suppresses chloroplast development and nuclear gene expression in leaves of mung bean seedlings

Analysis of Complete Chloroplast Genome: Structure, Phylogenetic Relationships of Galega orientalis and Evolutionary Inference of Galegeae

Galega orientalis, a leguminous herb in the Fabaceae family, is an ecologically and economically important species widely cultivated for its strong stress resistance and high protein content. However, genomic information of Galega orientalis has not been reported, which limiting its evolutionary analysis. The small genome size makes chloroplast relatively easy to obtain genomic sequence for phylogenetic studies and molecular marker development. Here, the chloroplast genome of Galega orientalis was sequenced and annotated. The results showed that the chloroplast genome of G. orientalis is 125,280 bp in length with GC content of 34.11%. A total of 107 genes were identified, including 74 protein-coding genes, 29 tRNAs and four rRNAs. One inverted repeat (IR) region was lost in the chloroplast genome of G. orientalis. In addition, five genes (rpl22, ycf2, rps16, trnE-UUC and pbf1) were lost compared with the chloroplast genome of its related species G. officinalis. A total of 84 long repeats and 68 simple sequence repeats were detected, which could be used as potential markers in the genetic studies of G. orientalis and related species. We found that the Ka/Ks values of three genes petL, rpl20, and ycf4 were higher than one in the pairwise comparation of G. officinalis and other three Galegeae species (Calophaca sinica, Caragana jubata, Caragana korshinskii), which indicated those three genes were under positive selection. A comparative genomic analysis of 15 Galegeae species showed that most conserved non-coding sequence regions and two genic regions (ycf1 and clpP) were highly divergent, which could be used as DNA barcodes for rapid and accurate species identification. Phylogenetic trees constructed based on the ycf1 and clpP genes confirmed the evolutionary relationships among Galegeae species. In addition, among the 15 Galegeae species analyzed, Galega orientalis had a unique 30-bp intron in the ycf1 gene and Tibetia liangshanensis lacked two introns in the clpP gene, which is contrary to existing conclusion that only Glycyrrhiza species in the IR lacking clade (IRLC) lack two introns. In conclusion, for the first time, the complete chloroplast genome of G. orientalis was determined and annotated, which could provide insights into the unsolved evolutionary relationships within the genus Galegeae.

Physio-biochemical and molecular stress regulators and their crosstalk for low-temperature stress responses in fruit crops: A review

Low-temperature stress (LTS) drastically affects vegetative and reproductive growth in fruit crops leading to a gross reduction in the yield and loss in product quality. Among the fruit crops, temperate fruits, during the period of evolution, have developed the mechanism of tolerance, i.e., adaptive capability to chilling and freezing when exposed to LTS. However, tropical and sub-tropical fruit crops are most vulnerable to LTS. As a result, fruit crops respond to LTS by inducing the expression of LTS related genes, which is for climatic acclimatization. The activation of the stress-responsive gene leads to changes in physiological and biochemical mechanisms such as photosynthesis, chlorophyll biosynthesis, respiration, membrane composition changes, alteration in protein synthesis, increased antioxidant activity, altered levels of metabolites, and signaling pathways that enhance their tolerance/resistance and alleviate the damage caused due to LTS and chilling injury. The gene induction mechanism has been investigated extensively in the model crop Arabidopsis and several winter kinds of cereal. The ICE1 (inducer of C-repeat binding factor expression 1) and the CBF (C-repeat binding factor) transcriptional cascade are involved in transcriptional control. The functions of various CBFs and aquaporin genes were well studied in crop plants and their role in multiple stresses including cold stresses is deciphered. In addition, tissue nutrients and plant growth regulators like ABA, ethylene, jasmonic acid etc., also play a significant role in alleviating the LTS and chilling injury in fruit crops. However, these physiological, biochemical and molecular understanding of LTS tolerance/resistance are restricted to few of the temperate and tropical fruit crops. Therefore, a better understanding of cold tolerance's underlying physio-biochemical and molecular components in fruit crops is required under open and simulated LTS. The understanding of LTS tolerance/resistance mechanism will lay the foundation for tailoring the novel fruit genotypes for successful crop production under erratic weather conditions.

Improving Albino Tea Quality by Foliar Application of Glycinebetaine as a Green Regulator under Lower Temperature Conditions

White leaf No.1 (WL-1) is a low temperature-induced albino tea cultivar, which sticks out from tea plants with rich amino acids. Because harmonization of chloroplast ultrastructure integrity and lower chlorophyll contents during the albinism processes is much crucial for WL-1 production under extreme weather conditions, we carried out a field experiment to investigate the regulating effects of exogenous glycinebetaine (GB) on the chloroplast ultrastructure and quality constituents in young leaves of WL-1 at different albinism stages. The internal structure of chloroplasts degenerated at the albinistic stage, and chlorophyll contents were significantly lower than those at pre-albinistic and regreening stages. Spraying GB regulated etioplast-chloroplast transition, significantly increased epigallocatechin gallate, theanine, and caffeine contents, and lowered chlorophyll content in albinistic young leaves of WL-1, thus improving its quality in some aspects, maintaining special leaf color, exerting flavor and umami, and improving antioxidant and refreshing effects. Foliar application of GB is an efficient technical measure in practice.

Fine mapping of a candidate gene for cool-temperature-induced albinism in ornamental kale

BACKGROUND

The symptoms of cool-temperature-induced chlorosis (CTIC) are widely existed in higher plants. Although many studies have shown that the genetic mechanism of CTIC is generally controlled by recessive genes in model plants, the dominant inheritance of albinism has not been reported thus far. Here, two CTIC mutants, Red Kamome and White Kamome, were utilized to analyse the inheritance of the albino trait in ornamental kale. The objective of this investigation is to fine-map the target locus and identify the most likely candidate genes for albinism.

RESULTS

Genetic analysis revealed that the albinism in the inner leaves of ornamental kale followed semi-dominant inheritance and was controlled by a single locus in two segregating populations. BSR-seq in combination with linkage analysis was employed to fine-map the causal gene, named AK (Albino Kale), to an approximate 60 kb interval on chromosome C03. Transcriptome data from two extreme pools indicated that the differentially expressed gene of Bol015404, which encodes a cytochrome P450 protein, was the candidate gene. The Bol015404 gene was demonstrated to be upregulated in the albino leaves of ornamental kale by qPCR. Additionally, the critical temperature for the albinism was determined between 10 °C and 16 °C by gradient test.

CONCLUSIONS

Using two independent segregating populations, the albino mutants were shown to be controlled by one semi-dominant gene, AK, in ornamental kale. The Bol015404 gene was co-segregated with albinism phenotypes, suggesting this unknown function P450 gene as the most likely candidate gene. The albino trait appeared caused by the low temperatures rather than photoperiod. Our results lay a solid foundation on the genetic control of albinism in ornamental kale.

Evidence that melatonin promotes soybean seedlings growth from low-temperature stress by mediating plant mineral elements and genes involved in the antioxidant pathway

Melatonin (MT) regulates several physiological activities in plants. However, information on how MT regulates soybean growth under low-temperature (LT) stress is lacking. To better understand how MT promotes plant growth and development under LT stress, we designed this study to evaluate the role of MT pretreatment on soybean seedlings exposed to LT stress. Our results showed that LT stress increased oxidative damage by increasing reactive oxygen species (ROS) accumulation, which affected the growth and development of soybean seedlings. However, the application of 5 µmol L-1 MT significantly decreased the oxidative damage by increasing plant mineral element concentrations and the transcript abundance of antioxidant related genes, which enhanced the decrease in ROS accumulation. These results collectively suggest the involvement of MT in improving LT stress tolerance of soybean seedlings by mediating plant mineral elements and the expression of genes involved in the antioxidant pathway.

Ascorbic Acid Priming Enhances Seed Germination and Seedling Growth of Winter Wheat under Low Temperature Due to Late Sowing in Pakistan

Poor seed germination is a crucial yield-limiting factor when winter wheat is sown under low temperature. The objective of this study was to evaluate the role of ascorbic acid (AsA) in the extenuation of the harmful effects of low temperature at early and reproductive stages of wheat during 2016–2017 (15 November to 15 December). A two-year experiment was conducted using a randomized complete block design with split plot arrangement and with three replicates. Sowing dates (15 November and 15 December) were allotted to the main plot while seed priming (control, hydro-priming, and AsA priming) were allotted to the sub-plot. Results demonstrated that AsA priming significantly boosted different yield characteristics including chlorophyll content, tillers per unit area, number of grains per spike, and 1000-grain weight, contributing higher productivity and biomass during 2016–2017. The results further revealed that AsA could induce the up-regulation of diverse antioxidants (super oxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), thus offsetting the adverse effects of sub-supra optimum temperatures of late sowing wheat. It is therefore concluded in this work that AsA priming enhances stand establishment, yield and yield-related traits, antioxidant enzyme activities, and chlorophyll contents when wheat is sown under low temperature.

Brassinosteroid-mediated apoplastic H2 O2 -glutaredoxin 12/14 cascade regulates antioxidant capacity in response to chilling in tomato

Brassinosteroids (BRs) regulate plant development and stress response. Although much has been learned about their roles in plant development, the mechanisms by which BRs regulate plant stress tolerance remain unclear. Chilling is a major stress that adversely affects plant growth. Here, we report that BR positively regulates chilling tolerance in tomato. BR partial deficiency aggravated chilling-induced oxidized protein accumulation, membrane lipid peroxidation, and decrease of maximum quantum efficiency of photosystem II (Fv/Fm). By contrast, overexpression of BR biosynthetic gene Dwarf or treatment with 24-epibrassinolide (EBR) attenuated chilling-induced oxidative damages and resulted in an increase of Fv/Fm. BR increased transcripts of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1) and GLUTAREDOXIN (GRX) genes, and BR-induced chilling tolerance was associated with an increase in the ratio of reduced/oxidized 2-cysteine peroxiredoxin (2-Cys Prx) and activation of antioxidant enzymes. However, RBOH1-RNAi plants failed to respond to EBR as regards to the induction of GRX genes, activation of antioxidant capacity, and attenuation of chilling-induced oxidative damages. Furthermore, silencing of GRXS12 and S14 compromised EBR-induced increases in the ratio of reduced/oxidized 2-Cys Prx and activities of antioxidant enzymes. Our study suggests that BR enhances chilling tolerance through a signalling cascade involving RBOH1, GRXs, and 2-Cys Prx in tomato.

Cold and Heat Stress Diversely Alter Both Cauliflower Respiration and Distinct Mitochondrial Proteins Including OXPHOS Components and Matrix Enzymes

Complex proteomic and physiological approaches for studying cold and heat stress responses in plant mitochondria are still limited. Variations in the mitochondrial proteome of cauliflower (Brassica oleracea var. botrytis) curds after cold and heat and after stress recovery were assayed by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) in relation to mRNA abundance and respiratory parameters. Quantitative analysis of the mitochondrial proteome revealed numerous stress-affected protein spots. In cold, major downregulations in the level of photorespiratory enzymes, porine isoforms, oxidative phosphorylation (OXPHOS) and some low-abundant proteins were observed. In contrast, carbohydrate metabolism enzymes, heat-shock proteins, translation, protein import, and OXPHOS components were involved in heat response and recovery. Several transcriptomic and metabolic regulation mechanisms are also suggested. Cauliflower plants appeared less susceptible to heat; closed stomata in heat stress resulted in moderate photosynthetic, but only minor respiratory impairments, however, photosystem II performance was unaffected. Decreased photorespiration corresponded with proteomic alterations in cold. Our results show that cold and heat stress not only operate in diverse modes (exemplified by cold-specific accumulation of some heat shock proteins), but exert some associations at molecular and physiological levels. This implies a more complex model of action of investigated stresses on plant mitochondria.

Chilling susceptibility in mungbean varieties is associated with their differentially expressed genes

BACKGROUND

Mungbean (Vigna radiata L. Wilczek) is an economically important legume of high nutritional value, however, its cultivation is limited by susceptibility to chilling. Varieties NM94 and VC1973A, with differential susceptibility to stress, serve as good materials for uncovering how they differ in chilling tolerance. This study aimed to identify the ultrastructural, physiological and molecular changes to provide new insights on the differential susceptibility to chilling between varieties VC1973A and NM94.

RESULTS

Chilling stress caused a greater reduction in relative growth rate, a more significant decrease in maximum photochemical efficiency of PSII and DPPH scavenging activity and more-pronounced ultrastructural changes in VC1973A than in NM94 seedlings. Comparative analyses of transcriptional profiles in NM94 and VC1973A revealed that the higher expression of chilling regulated genes (CORs) in NM94. The transcript levels of lipid transfer protein (LTP), dehydrin (DHN) and plant defensin (PDF) in NM94 seedlings after 72 h at 4 °C was higher than that in its parental lines VC1973A, 6601 and VC2768A.

CONCLUSIONS

Our results suggested that LTP, DHN and PDF may mediate chilling tolerance in NM94 seedlings.

Dark-chilling induces substantial structural changes and modifies galactolipid and carotenoid composition during chloroplast biogenesis in cucumber (Cucumis sativus L.) cotyledons

Plants in a temperate climate are often subject to different environmental factors, chilling stress among them, which influence the growth especially during early stages of plant development. Chloroplasts are one of the first organelles affected by the chilling stress. Therefore the proper biogenesis of chloroplasts in early stages of plant growth is crucial for undertaking the photosynthetic activity. In this paper, the analysis of the cotyledon chloroplast biogenesis at different levels of plastid organization was performed in cucumber, one of the most popular chilling sensitive crops. Influence of low temperature on the ultrastructure was manifested by partial recrystallization of the prolamellar body, the formation of elongated grana thylakoids and a change of the prolamellar body structure from the compacted "closed" type to a more loose "open" type. Structural changes are strongly correlated with galactolipid and carotenoid content. Substantial changes in the galactolipid and the carotenoid composition in dark-chilled plants, especially a decrease of the monogalactosyldiacylglycerol to digalactosyldiacylglycerol ratio (MGDG/DGDG) and an increased level of lutein, responsible for a decrease in membrane fluidity, were registered together with a slower adaptation to higher light intensity and an increased level of non-photochemical reactions. Changes in the grana thylakoid fluidity, of their structure and photosynthetic efficiency in developing chloroplasts of dark-chilled plants, without significant changes in the PSI/PSII ratio, could distort the balance of photosystem rearrangements and be one of the reasons of cucumber sensitivity to chilling.

Isolation and dynamic expression of four genes involving in shikimic acid pathway in Camellia sinensis 'Baicha 1' during periodic albinism

Flavonoids are the main flavor components and functional ingredients in tea, and the shikimic acid pathway is considered as one of the most important pathways in flavonoid biosynthesis, but little was known about the function of regulatory genes in the metabolism phenolic compounds in tea plant (Camellia sinensis), especially related genes in shikimic acid pathway. The dynamic changes of catechin (predominant flavonoid) contents were analyzed in this study, and four genes (CsPPT, CsDAHPS, CsSDH and CsCS) involving in shikimic acid pathway in C. sinensis albino cultivar 'Baicha 1' were cloned and characterized. The full-length cDNA sequences of these genes were obtained using reverse transcription-PCR and rapid amplification of cDNA ends. At the albinistic stage, the amounts of all catechins decreased to the lowest levels, when epigallocatechin gallate was the highest, whereas gallocatechin-3-O-gallate the lowest. Gene expression patterns analyzed by qRT-PCR showed that CsPPT and CsDAHPS were highly expressed in flowers and buds, while CsSDH and CsCS showed high expression levels in buds and leaves. It was also found that the transcript abundance of shikimic acid biosynthetic genes followed a tightly regulated biphasic pattern, and was affected by albinism. The transcript levels of CsPPT and CsDAHPS were decreased at albinistic stage followed elevated expression, whereas CsSDH and CsCS were increased only at re-greening stage. Taken together, these findings suggested that these four genes in C. sinensis may play different roles in shikimic acid biosynthesis and these genes may have divergent functions.

Phloem transcriptome signatures underpin the physiological differentiation of the pedicel, stalk and fruit of cucumber (Cucumis sativus L.)

Cucumber is one of the most important vegetables grown worldwide due to its important economic and nutritional value. The cucumber fruit consists morphologically of the undesirable stalk and the tasty fruit; however, physiological differentiation of these two parts and the underlying molecular basis remain largely unknown. Here we characterized the physiological differences among the pedicel, stalk and fruit, and compared the respective phloem transcriptomes using laser capture microdissection coupled with RNA sequencing (RNA-Seq). We found that the pedicel was characterized by minor cell expansion and a high concentration of stachyose, the stalk showed rapid cell expansion and high raffinose accumulation, and the fruit featured transition from cell division to cell expansion and high levels of monosaccharides. Analyses of transcriptome data indicated that cell wall- and calcium ion binding-related genes contributed to the cell expansion in the pedicel and stalk, whereas genes implicated in cell cycle and hormone actions regulated the transition from cell division to cell expansion in the fruit. Differential sugar distribution in these three phloem-connected tissues resulted from tissue-specific sugar metabolism and transport. Enrichment of transcription factors in the stalk and fruit may facilitate nutrient accumulation in these sink organs. As such, phloem-located gene expression partially orchestrated physiological differentiation of the pedicel, stalk and fruit in cucumber. In addition, we identified 432 cucumber-unique genes and five phloem markers guiding future functional studies.

Lycopersicon esculentum under low temperature stress: an approach toward enhanced antioxidants and yield

Brassinosteroids (BRs) have been implicated to overcome various abiotic stresses, and low temperature stress poses a serious threat to productivity of various horticultural crops like tomato. Therefore, a study was conducted to unravel the possible role of BRs in conferring alleviation to low temperature stress in Lycopersicon esculentum. Twenty-day-old seedlings of tomato var. S-22 (chilling tolerant) and PKM-1 (chilling sensitive) were sown in earthen pots, and at 40 days stage of growth, plants were exposed to varied levels of low temperatures (10/3, 12/7, 20/14, or 25/18 °C) for 24 h in a growth chamber. At 50 days stage of growth, the foliage of plants were sprayed with 0 or 10(-8) M of BRs (28-homobrassinolide or 24-epibrassinolide), and 60-day-old plants were harvested to assess various physiological and biochemical parameters. Low temperatures induced a significant reduction in growth traits, chlorophyll content, and rate of photosynthesis in both the varieties differentially. Activities of antioxidant enzymes (catalase, peroxidase, and superoxide dismutase) and leaf proline content also increased substantially in both the varieties with decreasing temperature. On the other hand, treatment of BRs under stress and stress-free conditions significantly increased the aforesaid growth traits and biochemical parameters. Moreover, BRs further accelerated the antioxidative enzymes and proline content, which were already enhanced by the low temperature stress. Out of the two analogues of BRs tested, 24-epibrassinolide (EBL) was found more effective for both the varieties of tomato. EBL was found more potent stress alleviator against low temperature in both varieties of tomato.

Dynamic changes in catechin levels and catechin biosynthesis-related gene expression in albino tea plants (Camellia sinensis L.)

Tea (Camellia sinensis (L.) O. Kuntze) leaves are a major source of flavonoids that mainly belong to the flavan-3-ols or catechins and are implicated in a wide range of health benefits. Although the catechins in tea leaves were identified long ago, the regulatory mechanisms governing catechin biosynthesis remain unclear. In the present work, the dynamic changes of catechin levels and the expression profiles of catechin-related genes in albino tea plants were intensively examined. The amounts of most catechins decreased to their lowest levels in the albino phase, when epigallocatechingallate was the highest of the catechins compared to all catechins, and catechin the lowest. Enzyme assays indicated that phenylalanine ammonia-lyase (PAL) activity was positively correlated with the concentration of catechins (r = 0.673). Gene expression profiling by quantitative real-time reverse transcription-polymerase chain reaction showed that the transcript abundance of flavonoid biosynthetic genes followed a tightly regulated biphasic pattern, and was affected by albinism. These genes (PAL, C4H, 4CL, CHS, CHI, F3H, FLS, F3'H, F3'5'H, DFR, LAR, ANS and ANR) encode enzymes in flavonoid biosynthesis. The expression levels of PAL, F3H and FLS were correlated with the concentration of catechins and the correlation coefficients were -0.683, 0.687 and -0.602, respectively. Therefore, these results indicate that PAL might be a core regulator in the control of catechin biosynthesis in albino tea plants.

Proteomic analysis of young leaves at three developmental stages in an albino tea cultivar

Background

White leaf No.1 is a typical albino tea cultivar grown in China and it has received increased attention in recent years due to the fact that white leaves containing a high level of amino acids, which are very important components affecting the quality of tea drink. According to the color of its leaves, the development of this tea cultivar is divided into three stages: the pre-albinistic stage, the albinistic stage and the regreening stage. To understand the intricate mechanism of periodic albinism, a comparative proteomic approach based on two-dimensional electrophoresis (2-DE) and mass spectrometry was adopted first time to identify proteins that changed in abundance during the three developmental periods.

Results

The 2-DE results showed that the expression level of 61 protein spots varied markedly during the three developmental stages. To analyze the functions of the significantly differentially expressed protein spots, 30 spots were excised from gels and analyzed by matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry. Of these, 26 spots were successfully identified. All identified protein spots were involved in metabolism of carbon, nitrogen and sulfur, photosynthesis, protein processing, stress defense and RNA processing, indicating these physiological processes may play crucial roles in the periodic albinism. Quantitative real-time RT-PCR analysis was used to assess the transcriptional level of differentially expressed proteins. In addition, the ultrastructural studies revealed that the etioplast-chloroplast transition in the leaf cell of White leaf No. 1 was inhibited and the grana in the chloroplast was destroyed at the albinistic stage.

Conclusions

In this work, the proteomic analysis revealed that some proteins may have important roles in the molecular events involved in periodic albinism of White leaf No. 1 and identificated many attractive candidates for further investigation. In addition, the ultrastructural studies revealed that the change in leaf color of White leaf No. 1 might be a consequence of suppression of the etioplast-chloroplast transition and damage to grana in the chloroplast induced by temperature. These results provide much useful information to improve our understanding of the mechanism of albinism in the albino tea cultivar.

Early developmental and stress responsive ESTs from mungbean, Vigna radiata (L.) Wilczek, seedlings

Although mungbean (Vigna radiata (L.) Wilczek) is commonly used as human food; the genomic resources of this species available in databases are limited. This study aims to develop expressed sequence tag (EST) resources for mungbean genes informative to early seedling development and chilling response. Two mungbean varieties that differ in disease resistance were found to also differ in their susceptibility to chilling temperatures. A total of 1,198 ESTs were obtained from one cDNA library and four PCR-select cDNA subtraction libraries; among these 523 were clustered into 136 contigs and 675 were singletons. The 811 non-redundant uniESTs were compared to GenBank using the Basic Local Alignment Search Tool (BLAST) and WU-BLAST algorithms, of these only 489 uniESTs had significant sequence homology, which may be involved in resuming the metabolic activity of seedlings, switching on photomorphogenesis, fuelling photosynthesis and/or initiating the unique developmental programs. Their encoded proteins may associate with regulatory proteins to trigger a direct stress response or participate in acclimation to environmental stressors. The uniEST platform reported will enrich the genomic resources of mungbean for functional genomic research on seedling development and chilling response of tropical crops and provide targets for improving the chilling tolerance of the tropical crops.

Contrasting effect of dark-chilling on chloroplast structure and arrangement of chlorophyll-protein complexes in pea and tomato: plants with a different susceptibility to non-freezing temperature

The effect of dark-chilling and subsequent photoactivation on chloroplast structure and arrangements of chlorophyll-protein complexes in thylakoid membranes was studied in chilling-tolerant (CT) pea and in chilling-sensitive (CS) tomato. Dark-chilling did not influence chlorophyll content and Chl a/b ratio in thylakoids of both species. A decline of Chl a fluorescence intensity and an increase of the ratio of fluorescence intensities of PSI and PSII at 120 K was observed after dark-chilling in thylakoids isolated from tomato, but not from pea leaves. Chilling of pea leaves induced an increase of the relative contribution of LHCII and PSII fluorescence. A substantial decrease of the LHCII/PSII fluorescence accompanied by an increase of that from LHCI/PSI was observed in thylakoids from chilled tomato leaves; both were attenuated by photoactivation. Chlorophyll fluorescence of bright grana discs in chloroplasts from dark-chilled leaves, detected by confocal laser scanning microscopy, was more condensed in pea but significantly dispersed in tomato, compared with control samples. The chloroplast images from transmission-electron microscopy revealed that dark-chilling induced an increase of the degree of grana stacking only in pea chloroplasts. Analyses of O-J-D-I-P fluorescence induction curves in leaves of CS tomato before and after recovery from chilling indicate changes in electron transport rates at acceptor- and donor side of PS II and an increase in antenna size. In CT pea leaves these effects were absent, except for a small but irreversible effect on PSII activity and antenna size. Thus, the differences in chloroplast structure between CS and CT plants, induced by dark-chilling are a consequence of different thylakoid supercomplexes rearrangements.

A proteomics study of the mung bean epicotyl regulated by brassinosteroids under conditions of chilling stress

Mung bean CYP90A2 is a putative brassinosteroid (BR) synthetic gene that shares 77% identity with the Arabidopsis CPD gene. It was strongly suppressed by chilling stress. This implies that exogenous treatment with BR could allow the plant to recover from the inhibited growth caused by chilling. In this study, we used proteomics to investigate whether the mung bean epicotyl can be regulated by brassinosteroids under conditions of chilling stress. Mung bean epicotyls whose growth was initially suppressed by chilling partly recovered their ability to elongate after treatment with 24-epibrassinolde; 17 proteins down-regulated by this chilling were re-up-regulated. These up-regulated proteins are involved in methionine assimilation, ATP synthesis, cell wall construction and the stress response. This is consistent with the re-up-regulation of methionine synthase and S-adenosyl-L-methionine synthetase, since chilling-inhibited mung bean epicotyl elongation could be partially recovered by exogenous treatment with DL-methionine. This is the first proteome established for the mung bean species. The regulatory relationship between brassinosteroids and chilling conditions was investigated, and possible mechanisms are discussed herein.