Abscisic acid is involved in brassinosteroids-induced chilling tolerance in the suspension cultured cells from Chorispora bungeana

Functional and Transcriptome Analysis Reveal Specific Roles of Dimocarpus longan DlRan3A and DlRan3B in Root Hair Development, Reproductive Growth, and Stress Tolerance

Ran GTPases play essential roles in plant growth and development. Our previous studies revealed the nuclear localization of DlRan3A and DlRan3B proteins and proposed their functional redundancy and distinction in Dimocarpus longan somatic embryogenesis, hormone, and abiotic stress responses. To further explore the possible roles of DlRan3A and DlRan3B, gene expression analysis by qPCR showed that their transcripts were both more abundant in the early embryo and pulp in longan. Heterologous expression of DlRan3A driven by its own previously cloned promoter led to stunted growth, increased root hair density, abnormal fruits, bigger seeds, and enhanced abiotic stress tolerance. Conversely, constitutive promoter CaMV 35S (35S)-driven expression of DlRan3A, 35S, or DlRan3B promoter-controlled expression of DlRan3B did not induce the alterations in growth phenotype, while they rendered different hypersensitivities to abiotic stresses. Based on the transcriptome profiling of longan Ran overexpression in tobacco plants, we propose new mechanisms of the Ran-mediated regulation of genes associated with cell wall biosynthesis and expansion. Also, the transgenic plants expressing DlRan3A or DlRan3B genes controlled by 35S or by their own promoter all exhibited altered mRNA levels of stress-related and transcription factor genes. Moreover, DlRan3A overexpressors were more tolerant to salinity, osmotic, and heat stresses, accompanied by upregulation of oxidation-related genes, possibly involving the Ran-RBOH-CIPK network. Analysis of a subset of selected genes from the Ran transcriptome identified possible cold stress-related roles of brassinosteroid (BR)-responsive genes. The marked presence of genes related to cell wall biosynthesis and expansion, hormone, and defense responses highlighted their close regulatory association with Ran.

Phytohormones regulate the non-redundant response of ω-3 fatty acid desaturases to low temperatures in Chorispora bungeana

To explore the contributions of ω-3 fatty acid desaturases (FADs) to cold stress response in a special cryophyte, Chorispora bungeana, two plastidial ω-3 desaturase genes (CbFAD7, CbFAD8) were cloned and verified in an Arabidopsis fad7fad8 mutant, before being compared with the microsomal ω-3 desaturase gene (CbFAD3). Though these genes were expressed in all tested tissues of C. bungeana, CbFAD7 and CbFAD8 have the highest expression in leaves, while CbFAD3 was mostly expressed in suspension-cultured cells. Low temperatures resulted in significant increases in trienoic fatty acids (TAs), corresponding to the cooperation of CbFAD3 and CbFAD8 in cultured cells, and the coordination of CbFAD7 and CbFAD8 in leaves. Furthermore, the cold induction of CbFAD8 in the two systems were increased with decreasing temperature and independently contributed to TAs accumulation at subfreezing temperature. A series of experiments revealed that jasmonie acid and brassinosteroids participated in the cold-responsive expression of ω-3 CbFAD genes in both C. bungeana cells and leaves, while the phytohormone regulation in leaves was complex with the participation of abscisic acid and gibberellin. These results point to the hormone-regulated non-redundant contributions of ω-3 CbFADs to maintain appropriate level of TAs under low temperatures, which help C. bungeana survive in cold environments.

Increased dehydrin level decreases leaf rolling grade by altering the reactive oxygen species homeostasis and abscisic acid content in maize subjected to osmotic stress

Dehydrins (DHNs) are stress proteins involved in the development of protective reactions in plants against dehydration. The relationship between DHNs and morphological responses such as leaf rolling in plants exposed to water deficit is not well known. In this study, we detected how variations in DHN levels affect the leaf rolling response in maize exposed to osmotic stress in relation to the antioxidant system and ABA level. In this context, we altered the DHN levels in maize seedlings by treatment with bio-regulators (salicylic acid and abscisic acid) under PEG6000-free and PEG6000-induced osmotic stress. When the DHN levels were increased by the bio-regulators (25 µM SA and 100 µM ABA), the relative expression level of the Zea mays dehydrin COR410 gene increased in the seedlings, while reactive oxygen species (ROS) and leaf rolling grade decreased. Moreover, induction of DHNs caused increases in the antioxidant enzyme activity and content of antioxidant substances, and very high amounts of endogenous abscisic acid. When DHN level was suppressed by a bio-regulator (200 µM SA) in the maize seedlings, dehydrin COR410 expression level decreased, while ROS and the leaf rolling grade increased. Moreover, the antioxidant enzyme activity and content of antioxidant substances decreased in the seedlings, while the amount of abscisic acid increased. Taken all together, an increase in DHN level by bio-regulator treatment can stimulate the antioxidant system, enable abscisic acid regulation, and thus reduce leaf rolling through decreased ROS levels. The results also indicated that DHNs may be involved in the signal pathways inducing expression of some genes related to leaf rolling response, possibly by modulating ROS levels, in maize seedlings exposed to osmotic stress.

Unveiling Molecular Mechanisms of Nitric Oxide-Induced Low-Temperature Tolerance in Cucumber by Transcriptome Profiling

Cucumber (Cucumis sativus L.) is one of the most popular cultivated vegetable crops but it is intrinsically sensitive to cold stress due to its thermophilic nature. To explore the molecular mechanism of plant response to low temperature (LT) and the mitigation effect of exogenous nitric oxide (NO) on LT stress in cucumber, transcriptome changes in cucumber leaves were compared. The results showed that LT stress regulated the transcript level of genes related to the cell cycle, photosynthesis, flavonoid accumulation, lignin synthesis, active gibberellin (GA), phenylalanine metabolism, phytohormone ethylene and salicylic acid (SA) signaling in cucumber seedlings. Exogenous NO improved the LT tolerance of cucumber as reflected by increased maximum photochemical efficiency (Fv/Fm) and decreased chilling damage index (CI), electrolyte leakage and malondialdehyde (MDA) content, and altered transcript levels of genes related to phenylalanine metabolism, lignin synthesis, plant hormone (SA and ethylene) signal transduction, and cell cycle. In addition, we found four differentially expressed transcription factors (MYB63, WRKY21, HD-ZIP, and b-ZIP) and their target genes such as the light-harvesting complex I chlorophyll a/b binding protein 1 gene (LHCA1), light-harvesting complex II chlorophyll a/b binding protein 1, 3, and 5 genes (LHCB1, LHCB3, and LHCB5), chalcone synthase gene (CSH), ethylene-insensitive protein 3 gene (EIN3), peroxidase, phenylalanine ammonia-lyase gene (PAL), DNA replication licensing factor gene (MCM5 and MCM6), gibberellin 3 beta-dioxygenase gene (GA3ox), and regulatory protein gene (NPRI), which are potentially associated with plant responses to NO and LT stress. Notably, HD-ZIP and b-ZIP specifically responded to exogenous NO under LT stress. Taken together, these results demonstrate that cucumber seedlings respond to LT stress and exogenous NO by modulating the transcription of some key transcription factors and their downstream genes, thereby regulating photosynthesis, lignin synthesis, plant hormone signal transduction, phenylalanine metabolism, cell cycle, and GA synthesis. Our study unveiled potential molecular mechanisms of plant response to LT stress and indicated the possibility of NO application in cucumber production under LT stress, particularly in winter and early spring.

Genome-wide identification and response stress expression analysis of the BES1 family in rubber tree (Hevea brasiliensis Muell. Arg.)

Brassinolide (BR) plays an important role in plant growth, development, and the adaptation adversity process. Moreover, BRI1-EMS-SUPPRESSOR 1 (BES1) genes are crucial transcription factors (TFs) in the BR signaling pathway. To realize the function of HbBES1 family is helpful to improve genetic resources for rubber tree breeding. Based on the rubber tree database, we used bioinformatics to characterize physicochemical properties, gene structure, cis-elements, and expression patterns. These results indicated that there were nine BES1 members in rubber tree, which we named HbBES1-1 to HbBES1-9 and divided into two groups (I and II) based on their genetic relationships. HbBES1 genes in the same group shared similar gene structures and motifs. Cis-acting element analysis showed that the promoter sequences of HbBES1 genes contained many regulator elements that were related to hormone and stress, indicating that HbBES1 genes might be involved in the regulation of hormone and stress signal pathways. Our analysis of tissue specificity revealed that all of the nine HbBES1 members expressed highly in branches. Gene expression profiles under different hormone treatments showed that the HbBES1 gene family was induced to varying degrees under different hormones, HbBES1-3 and HbBES1-9 were extremely induced by ethylene (ETH). These results lay the foundation for further exploration of the molecular mechanism of the BES1 gene family, especially HbBES1-3 and HbBES1-9, regulating plant stress tolerance in rubber tree.

Genome-Wide Identification and Expression Analysis of Chitinase-like Genes in Petunia axillaris

Chitinase (EC 3.2.1.14) is a kind of chitin-degrading glycosidase, which plays important roles in the abiotic and biotic defense of plants. In this study, we conducted whole-genome annotation, molecular evolution, and gene expression analyses on the chitinase-like (CTL) gene family members of Petunia axillaris. Thirty-three Petunia axillarischitinase-like genes (PaCTLs) were identified from the latest Petunia genome database. According to the phylogenetic analyses, these genes were divided into GH18 and GH19 subgroups and further subdivided into five classes (Class I to Class V). Conserved motif arrangements indicated their functional relevance within each group. The expansion and homeology analyses showed that gene replication events played an important role in the evolution of PaCTLs and the increase of the GH18 subgroup members was the main reason for the expansion of the PaCTL gene family in the evolution progress. By qRT-PCR analysis, we found that most of the PaCTLs showed a very low expression level in the normal growing plants. But lots of PaCTLs showed upregulated expression profiles when the plants suffered different abiotic stress conditions. Among them, five PaCTLs responded to high temperature and exhibited significantly upregulate expression level. Correspondingly, many hormone responses, as well as biotic and abiotic stress elements were found in the promoters of PaCTLs by using cis-acting element analysis. These results provide a foundation for the exploration of PaCTLs' function and enrich the evolutionary process of the CTL gene family.

Screening on the Presence of Plant Growth Regulators in High Biomass Forming Seaweeds from the Ionian Sea (Mediterranean Sea)

The use of seaweed as plant biostimulants is a solution for sustainable agriculture. The present study aims to quantify and compare the presence of plant growth regulators (PGRs) in four genetically labeled macroalgae growing in the Ionian Sea. Species were selected because they produce abundant biomass, disturbing ecological equilibrium and anthropic activities. We measured the content of gibberellic acid (GA3), kinetin (KN), indoleacetic acid (IAA), abscisic acid (ABA) and indole butyric acid (IBA). The method applied was modified from the literature to obtain simultaneously different PGRs from seaweed biomass in a shorter period of time. Among results, it is notable that Hypnea corona Huisman et Petrocelli (Rhodophyta) showed higher GA3 concentration, while in Spyridia filamentosa (Wulfen) Harvey (Rhodophyta), higher KN, IBA, IAA and ABA contents were recorded. The latter species displayed an interesting profile of PGRs, with an IAA value comparable with that reported in Ascophyllum nodosum (Linnaeus) Le Jolis (Ochrophyta), which is currently used as a source of plant biostimulants in agriculture. Macroalgae thrive abundantly in nutrient-rich environments, such as anthropized coastal areas affecting human economic activities. Consequently, environmental agencies are forced to dredge algal thalli and discard them as waste. Any use of unwanted biomass as an economic product is highly desirable in the perspective of ecosustainable development.

Brassinosteroids and metalloids: Regulation of plant biology

Metalloid contamination in the environment is one of the serious concerns posing threat to our ecosystems. Excess of metalloid concentrations (including antimony, arsenic, boron, selenium etc.) in soil results in their over accumulation in plant tissues, which ultimately causes phytotoxicity and their bio-magnification. So, it is very important to find some ecofriendly approaches to counter negative impacts of above mentioned metalloids on plant system. Brassinosteroids (BRs) belong to family of plant steroidal hormones, and are considered as one of the ecofriendly way to counter metalloid phytotoxicity. This phytohormone regulates the plant biology in presence of metalloids by modulating various key biological processes like cell signaling, primary and secondary metabolism, bio-molecule crosstalk and redox homeostasis. The present review explains the in-depth mechanisms of BR regulated plant responses in presence of metalloids, and provides some biotechnological aspects towards ecofriendly management of metalloid contamination.

Combination of sodium alginate and nitric oxide reduces browning and retains the quality of fresh-cut peach during cold storage

Fresh-cut peaches are susceptible to browning when exposed to air. Reducing the browning is important to maintain the quality of the fresh-cut peaches. Nitric oxide (NO) as the signal factor can improve the antioxidant capacity of organisms; sodium alginate (SA) is a natural polysaccharide with good antibacterial and film-forming properties. The study aimed to investigate the antioxidant and anti-browning activities of combined application of sodium alginate and nitric oxide on peaches slices preservation. The activities of some browning-related enzymes and antioxidant enzymes and the content of reactive oxygen species (ROS) and some browning-related components in fresh-cut peaches were determined. Results showed that combined treatment of 1% SA  +  10 μmol L^-1 NO slowed down the decrease in firmness, L*, and SSC, restrained the increase in browning degree and the activities of polyphenol oxidase, phenylalanine ammonia-lyase, peroxidase, and lipoxygenase. At the same time, it reduced the accumulation of O₂^•-, ·OH, H₂O₂, malondialdehyde, and total phenolic, and increased the activities of catalase and superoxide dismutase in peach slices. Overall, it was concluded that treatment with 1% SA  +  10 μmol L^-1 NO maintained quality and extended storage life of fresh-cut peaches.

Plant Group II LEA Proteins: Intrinsically Disordered Structure for Multiple Functions in Response to Environmental Stresses

In response to various environmental stresses, plants have evolved a wide range of defense mechanisms, resulting in the overexpression of a series of stress-responsive genes. Among them, there is certain set of genes that encode for intrinsically disordered proteins (IDPs) that repair and protect the plants from damage caused by environmental stresses. Group II LEA (late embryogenesis abundant) proteins compose the most abundant and characterized group of IDPs; they accumulate in the late stages of seed development and are expressed in response to dehydration, salinity, low temperature, or abscisic acid (ABA) treatment. The physiological and biochemical characterization of group II LEA proteins has been carried out in a number of investigations because of their vital roles in protecting the integrity of biomolecules by preventing the crystallization of cellular components prior to multiple stresses. This review describes the distribution, structural architecture, and genomic diversification of group II LEA proteins, with some recent investigations on their regulation and molecular expression under various abiotic stresses. Novel aspects of group II LEA proteins in Phoenix dactylifera and in orthodox seeds are also presented. Genome-wide association studies (GWAS) indicated a ubiquitous distribution and expression of group II LEA genes in different plant cells. In vitro experimental evidence from biochemical assays has suggested that group II LEA proteins perform heterogenous functions in response to extreme stresses. Various investigations have indicated the participation of group II LEA proteins in the plant stress tolerance mechanism, spotlighting the molecular aspects of group II LEA genes and their potential role in biotechnological strategies to increase plants' survival in adverse environments.

24-epibrassinolide improves differential cadmium tolerance of mung bean roots, stems, and leaves via amending antioxidative systems similar to that of abscisic acid

Cadmium (Cd) pollution has attracted global concern. In the present study, the biochemical mechanisms underlying the amelioration of 24-epibrassinolide (eBL) and abscisic acid (ABA) on Cd tolerance of roots, stems, and leaves in mung bean seedlings were comparatively analyzed. Foliar application of eBL markedly ameliorated the growth of mung bean seedling exposed to 100 μM Cd. eBL alone had no significant effects on the activities of antioxidative enzymes and the contents of glutathione (GSH) and polyphenols in the three organs whereas significantly increased the root, stem, and leaf proline contents on average by 54.9%, 39.9%, and 94.4%, respectively, and leaf malondialdehyde (MDA) content on average by 69.0% compared with the controls. When the plants were exposed to Cd, eBL significantly reversed the Cd-increased root ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, root polyphenol, proline, and GSH levels, leaf chlorophyll contents, and MDA levels in the three organs. eBL significantly restored the Cd-decreased leaf catalase (CAT) activity and leaf polyphenol levels. These results indicated that eBL played roles in maintaining cellular redox homeostasis and evidently alleviated Cd-caused membrane lipid peroxidation via controlling the activity of antioxidative systems. eBL mediated the differential responses of cellular biochemical processes in the three organs to Cd exposure. Furthermore, a comparative analysis revealed that, under Cd stress, the effects of eBL on the biochemical processes were very similar to those of ABA, suggesting that ABA and eBL improve plant Cd tolerance via some common downstream pathways.

StMBF1c positively regulates disease resistance to Ralstonia solanacearum via it's primary and secondary upregulation combining expression of StTPS5 and resistance marker genes in potato

Multiprotein bridging factor 1 (MBF1) is a transcription coactivator that has a general defense response to pathogens. However, the regulatory mechanisms of MBF1 resistance bacterial wilt remain largely unknown. Here, the role of StMBF1c in potato resistance to Ralstonia solanacearum infection was characterized. qRT-PCR assays indicated that StMBF1c could was elicited by SA, MJ and ABA and the time-course expression pattern of the StMBF1c gene induced by R. solanacearum was found to be twice significant upregulated expression during the early and middle stages of bacterial wilt. Combined with the co-expression analysis of disease-resistant marker genes, gain-of-function and loss-of-function assays demonstrated that StMBF1c was associated with defence priming. Overexpression or silencing the MBF1c could enhance plants resistance or sensitivity to R. solanacearum through inducing or reducing NPR and PR genes related to SA signal pathway. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) experiment results confirmed the interaction of StMBF1c with StTPS5 which played a key role in ABA signal pathway in potato. It is speculated that by combining StTPS5 and resistance marker genes, StMBF1c is activated twice to participate in potato bacterial wilt resistance, in which EPI, PTI involved.

Molecular cloning, characterization and expression analysis of CbPLDδ gene from Chorispora bungeana in low temperature

Chorispora bungeana (C. bungeana) is a rare alpine subnival species that is highly tolerant to low temperature stress. Phospholipase D (PLD) is a key enzyme involved in membrane phospholipid catabolism during plant growth and the stress response. In this study, one member of CbPLD gene family, CbPLDδ, was cloned from C. bungeana and was introduced into tobacco. This gene encodes an 864-amino acid protein with two catalytic HxKxxxxD motifs which are essential for phospholipase D activity. After the CbPLDδ gene is fused with the vector containing the GFP tag, subcellular localization showed that CbPLDδ was predominately located in the cell membrane. RT-qPCR and histochemical GUS assays showed that CbPLDδ gene was induced by low temperature and expressed predominantly in leaf and root. Compared with wild-type tobacco, CbPLDδ transgenic tobacco showed higher activities of antioxidant enzymes, and lower levels of malonidiadehyde and electrolyte leakage under low temperature stress. These results reflected that CbPLDδ is involved in the response to low temperature stress, and has the potential to improve the low temperature tolerance of plants.

Abscisic Acid-Enemy or Savior in the Response of Cereals to Abiotic and Biotic Stresses?

Abscisic acid (ABA) is well-known phytohormone involved in the control of plant natural developmental processes, as well as the stress response. Although in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) its role in mechanism of the tolerance to most common abiotic stresses, such as drought, salinity, or extreme temperatures seems to be fairly well recognized, not many authors considered that changes in ABA content may also influence the sensitivity of cereals to adverse environmental factors, e.g., by accelerating senescence, lowering pollen fertility, and inducing seed dormancy. Moreover, recently, ABA has also been regarded as an element of the biotic stress response; however, its role is still highly unclear. Many studies connect the susceptibility to various diseases with increased concentration of this phytohormone. Therefore, in contrast to the original assumptions, the role of ABA in response to biotic and abiotic stress does not always have to be associated with survival mechanisms; on the contrary, in some cases, abscisic acid can be one of the factors that increases the susceptibility of plants to adverse biotic and abiotic environmental factors.

Exogenous application of 24-epibrassinosteroid mitigates NaCl toxicity in flax by modifying free amino acids profile and antioxidant defence system

In the present study, we investigated the ameliorative effects of 24-epibrassinosteroid (24-epiBL) on antioxidant response and ion homeostasis in two NaCl-stressed Linum usitatissimum L. (flax) cultivars differing in salt tolerance. The content and profile of amino acids were also studied in the tolerant cultivar. Salt stress differently altered the activity of antioxidant enzymes, phenol and flavonoid contents, total antioxidant capacity and ion homeostasis in both cultivars, whereas H2O2 and malondialdehyde (MDA) contents were induced only in the TN-97-95 cultivar. Free amino acid concentrations showed variable patterns under salinity conditions compared with the control plants. 24-epiBL decreased the soluble protein content in NaCl-treated plants and also decreased stimulatory effects of salinity on the production and accumulation of phenol and flavonoid contents and antioxidant capacity with altered ion (Na+, K+, and Cl-) contents. The 24-epiBL reduced the chlorophylls (a, b) and carotenoid contents in salt-treated TN-97-95 cultivar while enhanced the activity of antioxidant enzymes and declined the H2O2 content and lipid peroxidation in both NaCl-stressed cultivars. The profile and content of amino acids were significantly changed by 24-epiBL application under salinity treatment. In summary, our findings demonstrate that 24-epiBL seed priming mitigates the deleterious effects of salt stress in flax plants.

Wheat germ agglutinin is involved in the protective action of 24-epibrassinolide on the roots of wheat seedlings under drought conditions

The involvement of wheat germ agglutinin (WGA) in the protective action of 24-epibrassinolide (EBR) against drought stress was studied in the seedling roots of two wheat cultivars differing in drought tolerance. Under dehydration conditions, the contents of ABA and WGA were shown to change significantly in the roots of either drought-tolerant cultivar Omskaya 35 or drought-sensitive cultivar Salavat Yulaev. Meanwhile, accumulation of either ABA or WGA started earlier and was two times greater in plants of drought-tolerant cultivar. Since WGA is an excreted protein, it is not surprising that the level of lectin in the roots gradually decreased by the 7th day of treatment due to its exudation into root environment. Pre-sowing treatment with EBR contributed to additional accumulation of lectin as compared to the control variants of either cultivar, while the hormone treatment did not change ABA content. Meanwhile, under conditions of drought, EBR-pretreated seedlings were characterized by lower level of accumulation of ABA and WGA in the roots. EBR application was found to prevent drought-induced inhibition of cell division in the root apical meristem, while WGA excreted into the root environment may contribute significantly to the effect.

Changes in content of steroid regulators during cold hardening of winter wheat - Steroid physiological/biochemical activity and impact on frost tolerance

The purpose of experiments was to describe the alterations of content of steroid regulators (brassinosteroids, progesterone) during cold hardening of winter wheat. Further we studied physiological and biochemical changes induced by these steroids in cold hardened winter wheat together with estimation of plant frost tolerance. The endogenous brassinosteroid content was elevated in winter wheat during cold hardening while level of progesterone was lowered. A higher content of brassinosteroids (but not progesterone) was connected to better frost tolerance of winter wheat cultivars. Plant supplementation with brassinosteroid (24-epibrassinolide) and progesterone before cold hardening reduced frost damage. Tests with the inhibitors of the biosynthesis of brassinosteroids and progesterone suggested that these steroids are one of players in regulating the antioxidant system in winter wheat during cold hardening. Their role in regulating the expression of Rubisco or the Rubisco activase gene was less clear. Steroid regulators did not affect the content of the stress hormone ABA. Model studies of the membranes, made on a Langmuir bath, showed an increase in the value of the parameter describing differences in membrane compressibility (resulting from stronger interactions among the molecules in the monolayers). This suggests that 24-epibrassinolide and progesterone enter into the lipid layer and - in a similar way to sterols - stabilise the interaction among lipids. It may be significant step for better frost tolerance. The use of steroid regulators (especially brassinosteroids) as agrochemicals improving frost tolerance of winter cereals will be discussed.

Interactive effects of abscisic acid and nitric oxide on chilling resistance and active oxygen metabolism in peach fruit during cold storage

BACKGROUND

Cold conditions can accelerate the production of reactive oxygen species (ROS), and excessive ROS may attack biological macromolecules, disrupt related signal pathways, induce oxidative stress and influence plant metabolism. The cross-talk between nitric oxide (NO) and abscisic acid (ABA) and the inhibitions by NO or ABA on oxidative damage have been reported in fruits. However, there are few reports about the roles of NO-ABA interactions in chilling stress and antioxidant defense in fruits during cold storage. This study was conducted to investigate the roles of NO, ABA and interactions between NO and ABA in response to chilling stress on peach fruit (Prunus persica (L.) Batsch, cv. 'Xintaihong').

RESULTS

Treatments with 15 µmol L^-1 NO, 100 µmol L^-1 ABA and 15 µmol L^-1 NO + 5 mmol L^-1 sodium tungstate solution could reduce ROS content, alleviate lipid peroxidation and enhance antioxidant enzyme activities and antioxidant capacities. However, treatments with 5 µmol L^-1 potassium 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), 5 mmol L^-1 sodium tungstate and 100 µmol L^-1 ABA + 5 µmol L^-1 c-PTIO differentially blocked these protective effects and significantly increased ROS content and lipid peroxidation of peaches under low-temperature conditions.

CONCLUSIONS

Application of exogenous ABA could increase the resistance to cold-induced oxidative stress by enhancing the efficiency of enzymatic and non-enzymatic systems, which were partially mediated by NO. © 2018 Society of Chemical Industry.

5-Aminolevulinic Acid Improves Nutrient Uptake and Endogenous Hormone Accumulation, Enhancing Low-Temperature Stress Tolerance in Cucumbers

5-aminolevulinic acid (ALA) increases plant tolerance to low-temperature stress, but the physiological and biochemical mechanisms that underlie its effects are not fully understood. To investigate them, cucumber seedlings were treated with different ALA concentrations (0, 15, 30 and 45 mg/L ALA) and subjected to low temperatures (12/8 °C day/night temperature). The another group (RT; regular temperature) was exposed to normal temperature (28/18 °C day/night temperature). Low-temperature stress decreased plant height, root length, leaf area, dry mass accumulation and the strong seedling index (SSI), chlorophyll contents, photosynthesis, leaf and root nutrient contents, antioxidant enzymatic activities, and hormone accumulation. Exogenous ALA application significantly alleviated the inhibition of seedling growth and increased plant height, root length, hypocotyl diameter, leaf area, and dry mass accumulation under low-temperature stress. Moreover, ALA increased chlorophyll content (Chl a, Chl b, Chl a+b, and Carotenoids) and photosynthetic capacity, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), and transpiration rate (Tr), as well as the activities of superoxide dismutase (SOD), peroxidase (POD, catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) enzymes, while decreasing hydrogen peroxide (H₂O₂), superoxide (O₂^•−), and malondialdehyde (MDA) contents under low-temperature stress. In addition, nutrient contents (N, P, K, Mg, Ca, Cu, Fe, Mn, and Zn) and endogenous hormones (JA, IAA, BR, iPA, and ZR) were enhanced in roots and leaves, and GA4 and ABA were decreased. Our results suggest the up-regulation of antioxidant enzyme activities, nutrient contents, and hormone accumulation with the application of ALA increases tolerance to low-temperature stress, leading to improved cucumber seedling performance.

24-Epibrassinolide Ameliorates Endogenous Hormone Levels to Enhance Low-Temperature Stress Tolerance in Cucumber Seedlings

Phytohormone biosynthesis and accumulation are essential for plant growth and development and stress responses. Here, we investigated the effects of 24-epibrassinolide (EBR) on physiological and biochemical mechanisms in cucumber leaves under low-temperature stress. The cucumber seedlings were exposed to treatments as follows: NT (normal temperature, 26 °C/18 °C day/night), and three low-temperature (12 °C/8 °C day/night) treatments: CK (low-temperature stress); EBR (low-temperature and 0.1 μM EBR); and BZR (low-temperature and 4 μM BZR, a specific EBR biosynthesis inhibitor). The results indicated that low-temperature stress proportionately decreased cucumber seedling growth and the strong seedling index, chlorophyll (Chl) content, photosynthetic capacity, and antioxidant enzyme activities, while increasing reactive oxygen species (ROS) and malondialdehyde (MDA) contents, hormone levels, and EBR biosynthesis gene expression level. However, EBR treatments significantly enhanced cucumber seedling growth and the strong seedling index, chlorophyll content, photosynthetic capacity, activities of antioxidant enzymes, the cell membrane stability, and endogenous hormones, and upregulated EBR biosynthesis gene expression level, while decreasing ROS and the MDA content. Based on these results, it can be concluded that exogenous EBR regulates endogenous hormones by activating at the transcript level EBR biosynthetic genes, which increases antioxidant enzyme capacity levels and reduces the overproduction of ROS and MDA, protecting chlorophyll and photosynthetic machinery, thus improving cucumber seedling growth.

Classification and Genome-Wide Analysis of Chitin-Binding Proteins Gene Family in Pepper (Capsicum annuum L.) and Transcriptional Regulation to Phytophthora capsici, Abiotic Stresses and Hormonal Applications

Chitin-binding proteins are pathogenesis-related gene family, which play a key role in the defense response of plants. However, thus far, little is known about the chitin-binding family genes in pepper (Capsicum annuum L.). In current study, 16 putative chitin genes (CaChi) were retrieved from the latest pepper genome database, and were classified into four distinct classes (I, III, IV and VI) based on their sequence structure and domain architectures. Furthermore, the structure of gene, genome location, gene duplication and phylogenetic relationship were examined to clarify a comprehensive background of the CaChi genes in pepper. The tissue-specific expression analysis of the CaChi showed the highest transcript levels in seed followed by stem, flower, leaf and root, whereas the lowest transcript levels were noted in red-fruit. Phytophthora capsici post inoculation, most of the CaChi (CaChiI3, CaChiIII1, CaChiIII2, CaChiIII4, CaChiIII6, CaChiIII7, CaChiIV1, CaChiVI1 and CaChiVI2) were induced by both strains (PC and HX-9). Under abiotic and exogenous hormonal treatments, the CaChiIII2, CaChiIII7, CaChiVI1 and CaChiVI2 were upregulated by abiotic stress, while CaChiI1, CaChiIII7, CaChiIV1 and CaChiIV2 responded to hormonal treatments. Furthermore, CaChiIV1-silenced plants display weakened defense by reducing (60%) root activity and increase susceptibility to NaCl stress. Gene ontology (GO) enrichment analysis revealed that CaChi genes primarily contribute in response to biotic, abiotic stresses and metabolic/catabolic process within the biological process category. These results exposed that CaChi genes are involved in defense response and signal transduction, suggesting their vital roles in growth regulation as well as response to stresses in pepper plant. In conclusion, these finding provide basic insights for functional validation of the CaChi genes in different biotic and abiotic stresses.

The beneficial role of potassium in Cd-induced stress alleviation and growth improvement in Gladiolus grandiflora L

Heavy metal contaminated agricultural soils are one of the most important constraints for successful cultivation of crops. The current research was conducted to evaluate the role of potassium (K) on plant growth and amelioration of cadmium (Cd) stress in Gladiolus grandiflora under greenhouse conditions. G. grandiflora corms were sown in media contaminated with 0 (C), 50 (Cd50) and 100 (Cd100) mg Cd kg^-1 soil. The plants growing in Cd-contaminated media exhibited reduced gas exchange attributes, chlorophyll (Chl) contents, vegetative and reproductive growth as compared to control. The plants raised in Cd contaminated media showed reduced nutrition yet higher Cd contents. However, supplementation of 60 mg Kg^-1 K in treated plants (C+K, Cd50+K and Cd100+K) improved quantity of total soluble protein and proline (Pro) along with activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) under Cd stress. Similarly, K supplementation reduced the level of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in treated plants. Potassium supplemented plants exhibited better vegetative and reproductive growth. The improved stress tolerance in K supplemented plants was attributed to the reduced quantity of MDA and H₂O₂, enhanced synthesis of protein, proline, phenols, flavonides and improved activity of antioxidant enzymes. The present research supports the application of K for alleviation of Cd stress in G. grandiflora.

Abscisic acid treatment alleviates cadmium toxicity in purple flowering stalk (Brassica campestris L. ssp. chinensis var. purpurea Hort.) seedlings

The aim of this research was to investigate how exogenous abscisic acid (ABA) alleviates cadmium (Cd) toxicity in purple flowering stalk (Brassica campestris L. ssp. chinensis) and evaluate whether it could be a potential choice for phytoremediation. Purple flowering stalk seedlings were cultivated in a hydroponic system with Cd at various concentrations (0-100 μmol L^-1) as controls and Cd plus ABA as the treatment in the growth media. The soluble proteins, chlorophyll contents and the activity of the antioxidant enzyme system were determined by previously established biochemical methods. The contents of soluble protein and chlorophyll, and the activities of superoxide dismutase (SOD, EC 1. 15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbic peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.8.1.7) and superoxide anion (O2^·-) increased with the increase of external Cd concentrations, and then decreased in both Cd and Cd+ABA treatments, with higher activities of enzymes but lower level of O2^·- in Cd+ABA than those in Cdonly treatments. It indicated that a stress adaptation mechanism was employed at lower Cd concentrations. The contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), increased with the increase of Cd concentrations in the growth medium, with the highest levels in the treatment of 100 μmol L^-1 Cd with lower levels in respective Cd+ABAtreatments than the Cd only treatmetns. Plants treated with 100 μmol L^-1 Cd plus ABA showed a 60% decrease in Cd content in the leaves but a 259% increase in Cd content in the roots. In summary, exogenous ABA might alleviate Cd toxicity in purple flowering stalk mainly by reducing the reactive oxygen species (ROS) though activing the antioxidant enzyme system and accumulating more Cd in roots.

Brassinosteroid Action in Plant Abiotic Stress Tolerance

Brassinosteroids (BRs) are a class of plant steroidal hormones that play essential roles in plant growth and development. Systematic studies had first been undertaken concomitantly to determine both the effects of exogenous BR on stress phenotypes of Arabidopsis thaliana and Brassica napus (rapeseed) seedlings and the expression of stress marker genes in BR-treated and untreated seedlings. When reproducible and convincing evidence of the role of BR in stress tolerance had been obtained, molecular mechanisms underlying the ability of BR to confer tolerance against heat, cold, drought, and salt stress, as well as pathogen resistance were studied with several molecular approaches and tools. The results of these studies have together provided valuable insights into how BRs, through their control of many basic cellular processes and stress responses, promote vigor in plants and prepare the plant to mount a dynamic response upon environmental challenges. Protocols to assess BR effects on abiotic stress tolerance in Arabidopsis and rapeseed seedlings are described here and they can be fine-tuned and adapted for other plant species.

Involvement of dehydrins in 24-epibrassinolide-induced protection of wheat plants against drought stress

In this study, we performed a comparative analysis of the physiological and biochemical parameters of wheat cultivars with contrasting drought resistance, drought-resistant Omskaya 35 (O-35) and less drought-resistant Salavat Yulaev (SYu), during 7-day germination under drought stress simulated by 5% mannitol. In addition, we evaluated the effectiveness of pre-sowing seed treatment with 0.4 μM 24-epibrassinolide (EBR) used to increase the resistance of plants of both cultivars to drought stress. It was revealed that mannitol has caused significant changes in the hormonal balance of the plants of both cultivars, associated with abscisic acid (ABA) accumulation and decrease in the contents of indoleacetic acid (IAA) and cytokinins (CKs). It should be noted that more dramatic changes in the content of phytohormones were characteristic for seedlings of SYu cultivar, which was reflected in a stronger growth inhibition of these plants. Pretreatment with EBR mitigated the negative effect of drought on the hormonal status and growth of seedlings during their germination. Furthermore, we found that drought caused accumulation of dehydrin (DHN) proteins, especially of low molecular weight DHNs, whose abundance was 2.5 times greater in O-35 cultivar than in SYu plants. EBR-pretreated plants of both cultivars were characterized by the additional accumulation of DHNs, indicating their involvement in the development of the EBR-induced wheat drought resistance. The use of fluridone allowed us to demonstrate ABA-dependent and ABA-independent pathways of regulation of low molecular mass dehydrins accumulation by EBR in wheat plants of both cultivars under drought conditions.

Molecular Characterization of LRB7 Gene and a Water Channel Protein TIP2 in Chorispora bungeana

Background. Water channel proteins, also called aquaporins, are integral membrane proteins from major intrinsic protein (MIP) family and involved in several pathways including not only water transport but also cell signaling, reproduction, and photosynthesis. The full cDNA and protein sequences of aquaporin in Chorispora bungeana Fisch. & C.A. Mey (C. bungeana) are still unknown. Results. In this study, PCR and rapid amplification of cDNA ends approaches were used to clone the full cDNA of LRB7 (GenBank accession number: EU636988) of C. bungeana. Sequence analysis indicated that it was 1235 bp, which had two introns and encoded a protein of 250 amino acids. Structure analysis revealed that the protein had two conserved NPA motifs, one of which is MIP signature sequence (SGxHxNPAVT), six membrane helix regions, and additional membrane-embedded domains. Phylogenetic analysis suggested that the protein was from TIP2 subgroup. Surprisingly, semiquantitative RT-PCR experiment and western blot analysis showed that LRB7 and TIP2 were only detectable in roots, unlike Arabidopsis and Raphanus. Connecting with our previous studies, LRB7 was supported to associate with chilling-tolerance in C. bungeana. Conclusion. This is the first time to characterize the full sequences of LRB7 gene and water channel protein in C. bungeana. Our findings contribute to understanding the water transports in plants under low temperatures.

Enhancement of trichothecene mycotoxins of Fusarium oxysporum by ferulic acid aggravates oxidative damage in Rehmannia glutinosa Libosch

Rehmannia glutinosa is an important medicinal herb that cannot be replanted in the same field due to the effects of autotoxic substances. The effects of these substances on R. glutinosa in continuous cropping systems are unknown. In the present study, bioassays revealed that R. glutinosa exhibited severe growth restriction and higher disease indices in the FO+FA (F.oxysporum pretreated with ferulic acid) treatment. The increases in the contents of MDA and H2O2 were greater in the FA+FO treatment than in the FA or FO only treatments, respectively. Consistent with this result, the enzyme activities in the seedlings increased with treatment time. To identify the main factor underlying the increased pathogenicity of FO, macroconidia and trichothecene mycotoxins coproduced by FO were separated and used to treat R. glutinosa seedlings. The MDA and H2O2 contents were similar in the seedlings treated with deoxynivalenol and in the FA+FO treatment. Quantification of the relative expression of certain genes involved in Ca2+ signal transduction pathways suggested that trichothecene mycotoxins play an important role in the increased pathogenicity of FO. In conclusion, FA not only directly enhances oxidative damage in R. glutinosa but also increases wilting symptom outbreaks by promoting the secretion of trichothecene mycotoxins by FO.

Chilling- and Freezing-Induced Alterations in Cytosine Methylation and Its Association with the Cold Tolerance of an Alpine Subnival Plant, Chorispora bungeana

Chilling (0–18°C) and freezing (<0°C) are two distinct types of cold stresses. Epigenetic regulation can play an important role in plant adaptation to abiotic stresses. However, it is not yet clear whether and how epigenetic modification (i.e., DNA methylation) mediates the adaptation to cold stresses in nature (e.g., in alpine regions). Especially, whether the adaptation to chilling and freezing is involved in differential epigenetic regulations in plants is largely unknown. Chorispora bungeana is an alpine subnival plant that is distributed in the freeze-thaw tundra in Asia, where chilling and freezing frequently fluctuate daily (24 h). To disentangle how C. bungeana copes with these intricate cold stresses through epigenetic modifications, plants of C. bungeana were treated at 4°C (chilling) and -4°C (freezing) over five periods of time (0–24 h). Methylation-sensitive amplified fragment-length polymorphism markers were used to investigate the variation in DNA methylation of C. bungeana in response to chilling and freezing. It was found that the alterations in DNA methylation of C. bungeana largely occurred over the period of chilling and freezing. Moreover, chilling and freezing appeared to gradually induce distinct DNA methylation variations, as the treatment went on (e.g., after 12 h). Forty-three cold-induced polymorphic fragments were randomly selected and further analyzed, and three of the cloned fragments were homologous to genes encoding alcohol dehydrogenase, UDP-glucosyltransferase and polygalacturonase-inhibiting protein. These candidate genes verified the existence of different expressive patterns between chilling and freezing. Our results showed that C. bungeana responded to cold stresses rapidly through the alterations of DNA methylation, and that chilling and freezing induced different DNA methylation changes. Therefore, we conclude that epigenetic modifications can potentially serve as a rapid and flexible mechanism for C. bungeana to adapt to the intricate cold stresses in the alpine areas.

Nitric Oxide Mediates 5-Aminolevulinic Acid-Induced Antioxidant Defense in Leaves of Elymus nutans Griseb. Exposed to Chilling Stress

Nitric oxide (NO) and 5-aminolevulinic acid (ALA) are both extremely important signalling molecules employed by plants to control many aspects of physiology. In the present study, the role of NO in ALA-induced antioxidant defense in leaves of two sources of Elymus nutans Griseb. (Damxung, DX and Zhengdao, ZD) was investigated. Chilling stress enhanced electrolyte leakage, accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide radical in two E. nutans, which were substantially alleviated by exogenous ALA and NO application. Pretreatment with NO scavenger PTIO or NOS inhibitor L-NNA alone and in combination with ALA induced enhancements in electrolyte leakage and the accumulation of MDA, H2O2 and superoxide radical in leaves of DX and ZD exposed to chilling stress, indicating that the inhibition of NO biosynthesis reduced the chilling resistance of E. nutans and the ALA-enhanced chilling resistance. Further analyses showed that ALA and NO enhanced antioxidant defense and activated plasma membrane (PM) H+-ATPase and decreased the accumulation of ROS induced by chilling stress. A pronounced increase in nitric oxide synthase (NOS) activity and NO release by exogenous ALA treatment was found in chilling-resistant DX plants exposed to chilling stress, while only a little increase was observed in chilling-sensitive ZD. Furthermore, inhibition of NO accumulation by PTIO or L-NNA blocked the protective effect of exogenous ALA, while both exogenous NO treatment and inhibition of endogenous NO accumulation did not induce ALA production. These results suggested that NO might be a downstream signal mediating ALA-induced chilling resistance in E. nutans.

Abscisic acid enhances tolerance of wheat seedlings to drought and regulates transcript levels of genes encoding ascorbate-glutathione biosynthesis

Glutathione (GSH) and ascorbate (ASA) are associated with the abscisic acid (ABA)-induced abiotic tolerance in higher plant, however, its molecular mechanism remains obscure. In this study, exogenous application (10 μM) of ABA significantly increased the tolerance of seedlings of common wheat (Triticum aestivum L.) suffering from 5 days of 15% polyethylene glycol (PEG)-stimulated drought stress, as demonstrated by increased shoot lengths and shoot and root dry weights, while showing decreased content of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Under drought stress conditions, ABA markedly increased content of GSH and ASA in both leaves and roots of ABA-treated plants. Temporal and spatial expression patterns of eight genes encoding ASA and GSH synthesis-related enzymes were measured using quantitative real-time reverse transcription polymerase chain reaction (qPCR). The results showed that ABA temporally regulated the transcript levels of genes encoding ASA-GSH cycle enzymes. Moreover, these genes exhibited differential expression patterns between the root and leaf organs of ABA-treated wheat seedlings during drought stress. These results implied that exogenous ABA increased the levels of GSH and ASA in drought-stressed wheat seedlings in time- and organ-specific manners. Moreover, the transcriptional profiles of ASA-GSH synthesis-related enzyme genes in the leaf tissue were compared between ABA- and salicylic acid (SA)-treated wheat seedlings under PEG-stimulated drought stress, suggesting that they increased the content of ASA and GSH by differentially regulating expression levels of ASA-GSH synthesis enzyme genes. Our results increase our understanding of the molecular mechanism of ABA-induced drought tolerance in higher plants.

H2O2 mediates the crosstalk of brassinosteroid and abscisic acid in tomato responses to heat and oxidative stresses

The production of H2O2 is critical for brassinosteroid (BR)- and abscisic acid (ABA)-induced stress tolerance in plants. In this study, the relationship between BR and ABA in the induction of H2O2 production and their roles in response to heat and paraquat (PQ) oxidative stresses were studied in tomato. Both BR and ABA induced increases in RBOH1 gene expression, NADPH oxidase activity, apoplastic H2O2 accumulation, and heat and PQ stress tolerance in wild-type plants. BR could only induced transient increases in these responses in the ABA biosynthetic mutant notabilis (not), whereas ABA induced strong and prolonged increases in these responses in the BR biosynthetic mutant d (^im) compared with wild-type plants. ABA levels were reduced in the BR biosynthetic mutant but could be elevated by exogenous BR. Silencing of RBOH1 compromised BR-induced apoplastic H2O2 production, ABA accumulation, and PQ stress responses; however, ABA-induced PQ stress responses were largely unchanged in the RBOH1-silenced plants. BR induces stress tolerance involving a positive feedback mechanism in which BR induces a rapid and transient H2O2 production by NADPH oxidase. The process in turn triggers increased ABA biosynthesis, leading to further increases in H2O2 production and prolonged stress tolerance. ABA induces H2O2 production in both the apoplastic and chloroplastic compartments.

Effects of exogenous 24-epibrassinolide on the photosynthetic membranes under non-stress conditions

In the present work the effects of exogenous 24-epibrassinolide (EBR) on functional and structural characteristics of the thylakoid membranes under non-stress conditions were evaluated 48 h after spraying of pea plants with different concentrations of EBR (0.01, 0.1 and 1.0 mg.L(-1)). The results show that the application of 0.1 mg.L(-1) EBR has the most pronounced effect on the studied characteristics of the photosynthetic membranes. The observed changes in 540 nm light scattering and in the calorimetric transitions suggest alterations in the structural organization of the thylakoid membranes after EBR treatment, which in turn influence the kinetics of oxygen evolution, accelerate the electron transport rate, increase the effective quantum yield of photosystem II and the photochemical quenching. The EBR-induced changes in the photosynthetic membranes are most probably involved in the stress tolerance of plants.

Suppression Subtractive Hybridization Analysis of Genes Regulated by Application of Exogenous Abscisic Acid in Pepper Plant (Capsicum annuum L.) Leaves under Chilling Stress

Low temperature is one of the major factors limiting pepper (Capsicum annuum L.) production during winter and early spring in non-tropical regions. Application of exogenous abscisic acid (ABA) effectively alleviates the symptoms of chilling injury, such as wilting and formation of necrotic lesions on pepper leaves; however, the underlying molecular mechanism is not understood. The aim of this study was to identify genes that are differentially up- or downregulated in ABA-pretreated hot pepper seedlings incubated at 6°C for 48 h, using a suppression subtractive hybridization (SSH) method. A total of 235 high-quality ESTs were isolated, clustered and assembled into a collection of 73 unigenes including 18 contigs and 55 singletons. A total of 37 unigenes (50.68%) showed similarities to genes with known functions in the non-redundant database; the other 36 unigenes (49.32%) showed low similarities or unknown functions. Gene ontology analysis revealed that the 37 unigenes could be classified into nine functional categories. The expression profiles of 18 selected genes were analyzed using quantitative RT-PCR; the expression levels of 10 of these genes were at least two-fold higher in the ABA-pretreated seedlings under chilling stress than water-pretreated (control) plants under chilling stress. In contrast, the other eight genes were downregulated in ABA-pretreated seedlings under chilling stress, with expression levels that were one-third or less of the levels observed in control seedlings under chilling stress. These results suggest that ABA can positively and negatively regulate genes in pepper plants under chilling stress.

Physiological and molecular changes in plants grown at low temperatures

Apart from water availability, low temperature is the most important environmental factor limiting the productivity and geographical distribution of plants across the world. To cope with cold stress, plant species have evolved several physiological and molecular adaptations to maximize cold tolerance by adjusting their metabolism. The regulation of some gene products represents an additional mechanism of cold tolerance. A consequence of these mechanisms is that plants are able to survive exposure to low temperature via a process known as cold acclimation. In this review, we briefly summarize recent progress in research and hypotheses on how sensitive plants perceive cold. We also explore how this perception is translated into changes within plants following exposure to low temperatures. Particular emphasis is placed on physiological parameters as well as transcriptional, post-transcriptional and post-translational regulation of cold-induced gene products that occur after exposure to low temperatures, leading to cold acclimation.

Hydrogen sulfide donor sodium hydrosulfide-induced heat tolerance in tobacco (Nicotiana tabacum L) suspension cultured cells and involvement of Ca(2+) and calmodulin

Hydrogen sulfide (H(2)S) is considered as a new emerging cell signal in higher plants. Hydrogen sulfide donor, sodium hydrosulfide, pretreatment significantly increased survival percentage of tobacco suspension cultured cells under heat stress and regrowth ability after heat stress, and alleviated decrease in vitality of cells, increase in electrolyte leakage and accumulation of malondialdehyde (MDA). In addition, sodium hydrosulfide-induced heat tolerance was markedly strengthened by application of exogenous Ca(2+) and its ionophore A23187, respectively, while this heat tolerance was weakened by addition of Ca(2+) chelator ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA), plasma membrane channel blocker La(3+), as well as calmodulin (CaM) antagonists chlorpromazine (CPZ) and trifluoperazine (TFP), respectively, but intracellular channel blocker ruthenium red (RR) did not. These results suggested that sodium hydrosulfide pretreatment could improve heat tolerance in tobacco suspension cultured cells and the acquisition of this heat tolerance requires the entry of extracellular Ca(2+) into cells across the plasma membrane and the mediation of intracellular CaM.