Accumulation Of Osmoprotectants Research Articles

A Putative Common Bean Chalcone O-Methyltransferase Improves Salt Tolerance in Transgenic Arabidopsis thaliana

Resolving the mechanism of salt stress tolerance in plants becomes a necessity to eventually develop salt-tolerant varieties by determining the key players in tolerance mechanism. Our previous results on transcriptome analysis of common bean under salt stress have revealed an upregulation in a putative chalconeO-methyltransferase (pvChOMT) transcript. In the present study, overexpression of pvChOMT gene in Arabidopsis transgenic lines enhanced salt tolerance. In turn, transgenic plants presented enhanced root growth, better water content, better mass preservation with osmoprotectant accumulation, and higher germination rates in saline conditions. Alignment analysis and predicted structure of pvChOMT have implicated it as the homologue of Medicago sativa chalcone O-methyltransferase (1FP1) with same substrate specificity. Promotor analysis of pvChOMT has shown a TATA box at − 145 position putative cis-acting elements within 1.5-kb upstream of the gene known to be activated through ABA-dependent and ABA-independent manner. Our results suggest that pvChOMT can be a good candidate gene to improve crops for salt stress tolerance.

Silicon Alleviates Nickel-Induced Oxidative Stress by Regulating Antioxidant Defense and Glyoxalase Systems in Mustard Plants

Soil polluted with heavy metals is a continuous threat to global crop production. The present study deals with growth, biochemical attributes, photosynthetic pigments, antioxidant responses and gyloxalase systems of mustard plants under varying concentrations of nickel (Ni) stress. Ni stress (150 µM) reduced growth (shoot length by 34.46% and root length by 52.49%), chlorophyll (57.63%), gas exchange parameters (PN by 36.84%, A by 55.61%), leaf relative water content (LRWC by 24.34%), and enhanced hydrogen peroxide (H2O2 by3.23 fold) malondialdehyde (MDA by 2.07 fold), and methylglyoxal (MG by 3.32 fold) content. Si (10− 5 M) application ameliorated the negative effects of Ni on growth, chlorophyll content, photosynthetic traits and also elevated the activities of antioxidant enzymes and enzymes associated with the ascorbate glutathione (AsA-GSH) cycle and glyoxylase systems. Nevertheless, Si application to Ni-stressed plants had an additive effect on the enzyme activities of antioxidants and enzymes of AsA-GSH cycle. Exogenous Si supplementation elevated endogenous Si content which decreased root to shoot Ni translocation and maintained optimum osmolyte and secondary metabolite accumulation. We conclude that Si-induced Ni stress tolerance in mustard plants could be correlated with the upregulation of enzymes associated with antioxidant defence, glyoxalase detoxification systems and sufficient primary and secondary osmoprotectant accumulation.

Polyamines protect mung bean [Vigna radiata (L.) Wilczek] plants against drought stress

Drought is a major environmental factor that limits crops productivity. To cope with the adverse effects of drought, plants have evolved various adaptive mechanisms, such as accumulation of osmolytes. Polyamines (PAs) play an important role in the plant growth and development and response to abiotic stresses. This experiment was conducted to investigate the role of exogenous PAs on drought tolerance of mung bean. Mung bean seeds were soaked in 0 or 100 uM putrescine (Put), spermidine (Spd), spermine (Spm), or their mixture for 10 hr. Then, treated seeds were sown in the field and were exposed to drought stress condition. The growth attributes including shoot length, biomass, leaf area index (LAI), and grain yield markedly reduced due to drought stress. Drought stress also decreased soluble protein content, relative water content (RWC), chlorophyll value, stomatal conductance (gs), and net photosynthetic rate (PN) but increased malondialdehyde (MDA), total soluble sugars (TSS), and proline contents. Nonetheless, seed priming with the mixture of PAs alleviated adverse effects of drought stress and improved all growth attributes. Exogenous application of PAs also increased soluble protein content, RWC, chlorophyll value, PN, and more increased TSS and proline contents but decreased gs and MDA level. These results indicated that seed treatment with PAs especially combined treatment of Put + Spd + Spm could enhance drought tolerance of mung bean plants through the accumulation of osmoprotectants, improving water status, chlorophyll value, and PN as well as reduction of oxidative damage.

The Combined Influence of Zinc and Epibrassinolide Increase Tolerance to Salt Stress in Brassica napus L.

The separate foliar application of zinc (Zn) and epibrassinolide (EBL) have widely proved tolerance to several abiotic stresses, but their combined effect exposed to oxidative stress is an untouched area of investigation. In order to evaluate the physiological mechanism of salt stress tolerance, a pot experiment was conducted. The results revealed that chlorophyll content, efficiency of photosystem ΙΙ, total leaf area, total biomass, membrane stability index and relative water content decreased under 100 mM NaCl concentration whereas, the foliar application of Zn and EBL alone and in combination increased these parameters. In addition, an increase in accumulation of osmoprotectants and antioxidant enzymes activity was noted under stressed conditions, which was more pronounced in rapeseed plants (Brassica napus L.) treated with combined application of Zn and EBL. Salt stress increased H₂O₂ and MDA content, while the exogenous application of Zn and EBL decreased these oxidative stress markers. It is concluded that Zinc and EBL reduced toxic effect of salinity, while its combined application showed an additive effect and significantly enhanced salt tolerance.

Heterologous expression of the AtDREB1A gene in tomato confers tolerance to chilling stress

Tomato is highly sensitive to chilling stress (0 - 12 °C) which severely affects plant growth and development. Transgenic tomato plants expressing the AtDREB1A gene under the control of the rd29A promoter were evaluated for its tolerance to chilling stress by exposing them to 4 °C for 5 d. The cold stress caused an increase in production of reactive oxygen species, however, transgenic plants had an effective antioxidant system due to an enhanced synthesis of catalase (CAT), superoxide dismutase (SOD), and ascorbate and so the reduced content of hydrogen peroxide and superoxide anions. Transgenic plants showed a slightly less reduction of chlorophyll and carotenoid content compared to wild-type plants. Similarly, a higher relative water content and a less electrolyte leakage were observed in transgenic plants. Accumulation of osmoprotectants, like proline and soluble sugars, helped transgenic plants to maintain a proper osmotic balance under the cold stress. Stress-responsive genes pyrroline-5-carboxylate synthase, CAT, SOD, and lipid peroxidase showed enhanced expressions under the cold stress in transgenic plants compared to wild-type plants. A recurrent exposure to the cold stress at the reproductive stage showed even higher expressions of these genes as compared to plants exposed to the cold stress for the first time. Thus, transgenic plants showed a better adaptation to the cold stress than non-transgenic plants by acquiring the stress memory of the stress experienced at the seedling stage.

Salt stress induces changes in genetic composition, proline content and subcellular organization in potato (Solanum tuberosum L.)

Several abiotic stresses including salinity impact plant growth and reduce the productivity of many plants and field crops. Plantlets produced in vitro by tissue culture technique offer a direct and fast approach to investigate the mechanism of stress adaptation. The present study estimated the survival percentage of two potato (Solanum tuberosum L.) cultivars (Spunta and Valor) under salt stress as abiotic stresses. Some biochemical alterations and ultrastructural responses of plantlets were examined. Moreover, genetic diversity was also studied using RAPD technique. The results showed that, with the increase of external stress there was a significant decrease in the survival percentage, significant accumulation of osmoprotectants (proline) and induction of DNA damages. Furthermore, there were closing of stomatal apertures, changesin chloroplast ultrastructure and cell intercellular spaces markedly decreased. Additionally,high salt stress (150 and 200mM NaCl) caused complete inhibition of plantlet growth. Thepresent work provides insight view for the adaptation of potato plantlets to salt stress throughaccumulating of osmoprotectants and change in molecular and ultrastructure traits.

Overexpression of StGA2ox1 Gene Increases the Tolerance to Abiotic Stress in Transgenic Potato (Solanum tuberosum L.) Plants.

It has been known that GA2ox is one kind of key enzyme gene in the gibberellin synthesis pathway, which plays important regulatory roles throughout plant whole growth and development. In this article, one of the GA2ox family genes, designated StGA2ox1, was isolated from potato (Solanum tuberosum L.). The full length of cDNA is 1005bp, and the cDNA corresponds to a protein of 334 amino acids; this protein was classified in a group with NtGA2ox3 based on multiple sequence alignments and phylogenetic characterization. A plant expression vector pCAEZ1383-StGA2ox1 was established. qRT-PCR showed that the expression of RD28, DREB1, WRKY1, and SnRK2 genes in StGA2ox1 transgenic plant is higher than that in non-transformed control under dehydration, low temperature conditions, and abscisic acid treatments. Overexpression of StGA2ox1 cDNA in transgenic potato plants exhibited an improved salt, drought, exogenous hormone, and low temperature stress tolerance in comparison to the non-transformed plant. The enhanced stress tolerance may be associated with the subsequent accumulation of proline osmoprotectant in addition to a better control of chlorophyll, carotenoids, and water loss. These data suggest that the StGA2ox1 is involved in the regulation of plant growth and tolerance in potato by regulating the synthesis of gibberellin.

A CIPK protein kinase targets sucrose transporter MdSUT2.2 at Ser254 for phosphorylation to enhance salt tolerance.

Soil salinity is one of the major abiotic stressors that negatively affect crop growth and yield. Salt stress can regulate antioxidants and the accumulation of osmoprotectants. In the study, a sucrose transporter MdSUT2.2 was identified in apple. Overexpression of MdSUT2.2 gene increased salt tolerance in the transgenic apple, compared with the WT control "Gala." In addition, it was found that protein MdSUT2.2 was phosphorylated at Ser254 site in response to salt. A DUAL membrane yeast hybridization system through an apple cDNA library demonstrated that a protein kinase MdCIPK13 interacted with MdSUT2.2. A series of transgenic analysis in apple calli showed that MdCIPK13 was required for the salt-induced phosphorylation of MdSUT2.2 protein and enhanced its stability and transport activity. Finally, it was found that MdCIPK13 improved salt resistance in an MdSUT2.2-dependent manner. These findings had enriched our understanding of the molecular mechanisms underlying abiotic stress.

Cold stress modulates osmolytes and antioxidant system in Calendula officinalis

Understanding the mechanism of adaptation to low-temperature stress is very crucial for developing cold-tolerant crop plants. The present study was used to investigate the response of Calendula officinalis (C. officinalis) to cold stress (CS). Seeds of C. officinalis were grown at normal temperature of 25 °C for 14 days and then shifted to a growth chamber set at 4 °C. The response of C. officinalis seedlings to cold stress was evaluated by estimating the relative growth changes, chlorophyll, electrolyte leakage (EL) and the content of malondialdehyde (MDA), proline, glycine betaine (GB), total soluble sugars, trehalose, total protein content and fatty acid profile. Enzymatic activity of antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) was also assessed. Moreover, transcript expression of cold-responsive genes [APX, CAT, dehydration-responsive element-binding protein (DREB1), GR and SOD] was also evaluated on homology basis. We measured and compared these indices of seedlings leaves under low temperature (4 °C) and normal temperature (25 °C) and observed that on exposure to CS, C. officinalis shows higher accumulation of osmoprotectants (proline, soluble sugars, glycine betaine and trehalose), phenolics and proteins, and increased antioxidant enzyme activity (APX, GR and SOD) except CAT activity, which declined in cold-stressed plants. Transcript expression of cold-responsive genes (SOD, CAT, APX, GR and DREB1) was found to be upregulated under cold stress. Overall, our study suggests that cold exposure/CS, besides eliciting various biochemical/physiological responses, triggers various pathways causing differential gene expression, consequently leading to differential protein expression. Further, this is the first report of C. officinalis under cold stress that may help us in exploring the mechanism of cold tolerance in future.

Contenido de osmoprotectores, ácido ascórbico y ascorbato peroxidasa en hojas de frijol sometidas a estrés por sequía


 
 
 La acumulación de osmoprotectores en plantas que se encuentran en condiciones de estrés por sequía, le permiten contrarrestar el efecto negativo que le provoca dichas condición ambiental. En el presente trabajo se estudió la respuesta bioquímica de plantas de frijol con base en la acumulación de carbohidratos solubles, almidón, ácido ascórbico, así como la actividad de la enzima ascorbato peroxidasa, en las hojas simples y en las dos primeras hojas trifolioladas de la variedad resistente, Pinto Villa, y la susceptible a sequía Bayo Madero, ambas de raza Durango. Las plantas de ambas variedades se sometieron a tres tratamientos de humedad, riego, sequía y riego de recuperación. Con respecto a Bayo Madero, Pinto Villa mostró una mayor respuesta de tolerancia al estrés de humedad relacionada con: altas concentraciones de prolina, de ácido ascórbico y mayor actividad de la enzima ascorbato peroxidasa, ésta última en el tratamiento de sequía. En relación a la cantidad de carbohidratos solubles, Bayo Madero fue estadísticamente superior (p< 0.05) a Pinto Villa, lo cual puede indicar que estos compuestos están siendo utilizados por la planta para sintetizar otros compuestos osmoprotectores como la prolina y que pueden considerarse como indicadores importantes para clasificar especies vegetales que sobrevivan y cumplan su ciclo biológico bajo condiciones de estrés de humedad.
 
 

The GARP/MYB-related grape transcription factor AQUILO improves cold tolerance and promotes the accumulation of raffinose family oligosaccharides

Grapevine (Vitis vinifera L.) is a widely cultivated fruit crop whose growth and productivity are greatly affected by low temperatures. On the other hand, wild Vitis species represent valuable genetic resources of natural stress tolerance. We have isolated and characterized a MYB-like gene encoding a putative GARP-type transcription factor from Amur grape (V. amurensis) designated as VaAQUILO. AQUILO (AQ) is induced by cold in both V. amurensis and V. vinifera, and its overexpression results in significantly improved tolerance to cold both in transgenic Arabidopsis and in Amur grape calli. In Arabidopsis, the ectopic expression of VaAQ increased antioxidant enzyme activities and up-regulated reactive oxygen species- (ROS) scavenging-related genes. Comparative mRNA sequencing profiling of 35S:VaAQ Arabidopsis plants suggests that this transcription factor is related to phosphate homeostasis like their Arabidopsis closest homologues: AtHRS1 and AtHHO2. However, when a cold stress is imposed, AQ is tightly associated with the cold-responsive pathway and with the raffinose family oligosaccharides (RFOs), as observed by the up-regulation of galactinol synthase (GoLS) and raffinose synthase genes. Gene co-expression network (GCN) and cis-regulatory element (CRE) analyses in grapevine indicated AQ as potentially regulating VvGoLS genes. Increased RFO content was confirmed in both transgenic Arabidopsis and Amur grape calli overexpressing VaAQ. Taken together, our results imply that AQ improves cold tolerance through promoting the accumulation of osmoprotectants.

Regulatory Gene Networks in Drought Stress Responses and Resistance in Plants.

Plant responses to drought stress have been analyzed extensively to reveal complex regulatory gene networks, including the detection of water deficit signals, as well as the physiological, cellular, and molecular responses. Plants recognize water deficit conditions at their roots and transmit this signal to their shoots to synthesize abscisic acid (ABA) in their leaves. ABA is a key phytohormone that regulates physiological and molecular responses to drought stress, such as stomatal closure, gene expression, and the accumulation of osmoprotectants and stress proteins. ABA transporters function as the first step for propagating synthesized ABA. To prevent water loss, ABA influx in guard cells is detected by several protein kinases, such as SnRK2s and MAPKs that regulate stomatal closure. ABA mediates a wide variety of gene expression machineries with stress-responsive transcription factors, including DREBs and AREBs, to acquire drought stress resistance in whole tissues. In this chapter, we summarize recent advances in drought stress signaling, focusing on gene networks in cellular and intercellular stress responses and drought resistance.

Hydrogen sulfide: a new endogenous player in an old mechanism of plant tolerance to high salinity

ABSTRACT High salinity affects plants due to stimulation of osmotic stress. Cell signaling triggered by nitric oxide (NO) and hydrogen sulfide (H2S) activates a cascade of biochemical events that culminate in plant tolerance to abiotic and biotic stresses. For instance, the NO/H2S-stimulated biochemical events that occur in plants during response to high salinity include the control of reactive oxygen species, activation of antioxidant system, accumulation of osmoprotectants in cytosol, induction of K+ uptake and Na+ cell extrusion or its vacuolar compartmentation among others. This review is a compilation of what we have learned in the last 10 years about NO participation during cell signaling in response to high salinity as well as the role of H2S, a new player in the mechanism of plant tolerance to salt stress. The main sources of NO and H2S in plant cells is also discussed together with the evidence of interplay between both signaling molecules during response to stress.

Plant growth-promoting endophyte Piriformospora indica alleviates salinity stress in Medicago truncatula

Piriformospora indica, a cultivable root endophytic fungus, induces growth promotion as well as biotic stress resistance and tolerance to abiotic stress in a broad range of host plants. In this study, the potential protection for M Medicago truncatula plants from salinity stress by P. indica was explored. The improved plant growth under severe saline condition was exhibited in P. indica-colonized lines. Moreover, the antioxidant enzymes activities and hyphae density in roots were increased by the endophyte under high salt concentration. Conversely, reduced malondialdehyde (MDA) activity, Na+ content and relative electrolyte conductivity (REC) were observed in P. indica colonized plants. Especially, osmoprotectant proline accumulated and the expression of Delta 1-Pyrroline-5-carboxylate synthetase gene (P5CS2) was induced. The defense related genes PR1 and PR10 and the transcription factors MtAlfin1-like and C2H2-type zinc finger protein MtZfp-c2h2 were induced by P. indica colonization as well. Further work indicated that salinity resistance was increased in overexpressing P5CS2, MtAlfin1-like and MtZfp-c2h2 transgenic M. truncatula plants. Interestingly, our data showed that the transcription factors MtAlfin1-like and MtZfp-c2h2 were positively contributed to P. indica colonization. These results demonstrate that tolerance to salinity stress was conferred by P. indica in M. truncatula via accumulation of osmoprotectant, stimulating antioxidant enzymes and the expression of defense-related genes. This work revealed the potential application of P. indica's as a plant growth-promoting fungus for the target improvement either in crop protection or in the salinized soil improvement indirectly.

Transcriptomic, biochemical and physio-anatomical investigations shed more light on responses to drought stress in two contrasting sesame genotypes

Sesame is an important oilseed crop with a high oil quality. It is prone to drought stress in the arid and semi-arid areas where it is widely grown. This study aims to decipher the response of tolerant (DT) and sensitive (DS) genotypes to progressive drought based on transcriptome, biochemical and physio-anatomical characterizations. Results indicated that under severe stress, DT relied on a well-functioning taproot while DS displayed a disintegrated root due to collapsed cortical cells. This was attributed to a higher accumulation of osmoprotectants and strong activity of antioxidant enzymes especially peroxidases in DT. From roots, DT could supply water to the aboveground tissues to ensure photosynthetic activities and improve endurance under stress. Temporal transcriptome sequencing under drought further confirmed that DT strongly activated genes related to antioxidant activity, osmoprotection and hormonal signaling pathways including abscisic acid and Ethylene. Furthermore, DT displayed unique differentially expressed genes in root functioning as peroxidases, interleukin receptor-associated kinase, heat shock proteins, APETALA2/ethylene-responsive element-binding protein and mitogen activated protein kinase, to effectively scavenge reactive oxygen species and preserve root cell integrity. Finally, 61 candidate genes conferring higher drought tolerance in DT were discovered and may constitute useful resources for drought tolerance improvement in sesame.

High Salt Tolerance of a Bradyrhizobium Strain and Its Promotion of the Growth of Stylosanthes guianensis.

Salinity is a serious limiting factor for the growth of rhizobia. Some rhizobia are tolerant to salt stress and promote plant growth, but the mechanisms underlying these effects are poorly characterized. The growth responses and osmoprotectants in four Bradyrhizobium strains were examined under salt stress in this study. Two-dimensional electrophoresis (2-DE) and mass spectrometry were conducted to investigate protein profiles in rhizobia exposed to salt stress. Subsequently, salt tolerance in stylo (Stylosanthes guianensis) inoculated with rhizobia was further detected in hydroponics. Results showed that the Bradyrhizobium strain RJS9-2 exhibited higher salt tolerance than the other three Bradyrhizobium strains. RJS9-2 was able to grow at 0.35 M NaCl treatment, while the other three Bradyrhizobium strains did not grow at 0.1 M NaCl treatment. Salt stress induced IAA production, and accumulation of proline, betaine, ectoine, and trehalose was observed in RJS9-2 but not in PN13-1. Proteomics analysis identified 14 proteins regulated by salt stress in RJS9-2 that were mainly related to the ABC transporter, stress response, and protein metabolism. Furthermore, under saline conditions, the nodule number, plant dry weight, and N concentration in stylo plants inoculated with RJS9-2 were higher than those in plants inoculated with PN13-1. These results suggest that the tolerance of RJS9-2 to salt stress may be achieved by the coordination of indole-3-acetic acid (IAA) production, osmoprotectant accumulation, and protein expression, thus promoting stylo growth.

Heat responsive proteome changes reveal molecular mechanisms underlying heat tolerance in chickpea

Understanding the molecular differences in plant genotypes contrasting for heat sensitivity can provide useful insights into the mechanisms that confer heat tolerance in plants. This study focuses on comparative physiological and proteomic analyses of heat-sensitive (ICC16374) and heat-tolerant (JG14) genotypes of chickpea (Cicer arietinum L.) under heat stress impositions at anthesis. Heat stress reduced leaf water content, chlorophyll content and membrane integrity with a greater impact on the sensitive genotype compared to the tolerant one that had higher total antioxidant capacity and osmolyte accumulation, and consequently less oxidative damage. This study identified a set of 482 heat-responsive proteins in the tolerant genotype using comparative gel-free proteomics. Besides heat shock proteins, proteins such as acetyl-CoA carboxylase, pyrroline-5-carboxylate synthase (P5CS), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), phenylalanine ammonia-lyase (PAL) 2, ATP synthase, glycosyltransferase, sucrose synthase and late embryogenesis abundant (LEA) proteins were strongly associated with heat tolerance in chickpea. Several crucial proteins were induced by heat exclusively in the heat-tolerant genotype. Comparative proteome profiling and pathway analysis revealed mitigating strategies including, accumulation of osmoprotectants, protected membrane transport, ribosome and secondary metabolite synthesis, activation of antioxidant and defense compounds, amino acid biosynthesis, and hormonal modulation that might play key roles in chickpea heat tolerance. This study potentially contributes to improved stress resilience by advancing our understanding on the mechanisms of heat tolerance in chickpea.

Aminolevulinic acid and nitric oxide regulate oxidative defense and secondary metabolisms in canola (Brassica napus L.) under drought stress.

To minimize the damaging effects of stresses, plant growth regulators (PGRs) are widely used to sustain the plant life under stress-prone environments. So, a study was carried out to evaluate the response of two canola (Brassica napus L.) cultivars, Dunkeld and Cyclone, to foliar-applied two potential PGRs, nitric oxide (NO) and 5-aminolevulinic acid, under water deficit conditions. In this study, the levels of NO and ALA used were 0.02 and 0.895mM, respectively. Plants of both canola cultivars were subjected to control (100% field capacity) and water deficit (60% field capacity). Drought stress significantly decreased growth, chlorophyll pigments, relative water contents (RWC), and soluble proteins, while it increased relative membrane permeability (RMP), proline, glycinebetaine (GB), malondialdehyde (MDA), total phenolics, and activities of catalase (CAT) and peroxidase (POD) enzymes in both cultivars. Foliar application of PGRs improved growth, chlorophyll a, GB, total phenolics, CAT activity, and total soluble proteins, while it decreased RMP, MDA, and POD activity in both canola cultivars. Other physio-biochemical attributes such as chlorophyll b, RWC, hydrogen peroxide (H2O2) and proline contents as well as superoxide dismutase (SOD) activity remained unaffected due to application of PGRs. So, the results of the present study suggest that exogenous application of NO and ALA could be useful to enhance the drought tolerance of canola plants by up-regulating the oxidative defense system, osmoprotectant accumulation, and minimizing the lipid peroxidation.

Hydrogen-rich water pretreatment alters photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant activities in heat-stressed cucumber leaves

Hydrogen gas (H2) has recently been recognized as an important plant bio-regulator, inducing tolerance to several abiotic stresses. However, any role for H2 in amelioration of high-temperature-induced stress remains largely unknown. We investigated the mechanism of hydrogen-rich water (HRW)-mediated enhancement of heat-tolerance in cucumber seedlings exposed to high-temperature stress. The 3 weeks seedlings were pretreated with 50 or 100% HRW for 7 days, the effects on photosynthesis, chlorophyll content, chlorophyll fluorescence parameters, electrolyte leakage, lipid peroxidation, and antioxidant activity were examined when cucumber seedlings subjected for 3 days to heat stress treatment. With respect to samples treat with high temperature stress alone, HRW pretreatment remarkably alleviated stress-induced effects on the above parameters. Furthermore, after 3 days of treatment, HRW pretreatment also significantly increased the activities of antioxidative enzymes, promoted high-level accumulation of osmoprotectants, and upregulated HSP70 expression in cucumber leaves. All of these data suggest that pretreatment with exogenous HRW partially alleviated the detrimental effects of high-temperature stress on the growth of cucumber seedlings by improving the photosynthetic capacity, increasing the antioxidant response, and promoting the accumulation of HSP70 and osmolytes. Therefore, HRW pretreatment may improve cucumber seedlings heat-tolerance.

Phytochromes are key regulators of abiotic stress responses in tomato

Phytochromes are the best characterized and most frequently studied plant photoreceptors. A plethora of studies have revealed important roles for phytochromes in plant development, and more recently, evidence indicates that these photoreceptors also modulate responses to a multitude of abiotic and biotic stresses. Thus, the present work aimed to investigate whether tomato phytochromes phyA, phyB1 and phyB2 are involved with responses to low water potential (polyethylene glycol 6000 at Ψw of −0.3MPa), high salinity (100mM NaCl), cadmium contamination (65mM CdCl2), high temperature (42°C for six hours during three days) and ultraviolet B radiation (UV-B − 280–320nm for eight hours during three days) stresses. For this purpose, seedlings of tomato mutants impacted by phytochrome A (fri), phytochrome B1 (tri) and phytochrome B2 (phyB2) were subjected to abiotic stresses and evaluated for their growth, pigment and osmoprotectant accumulation and lipid peroxidation. Under the conditions of this study, the results did not shown large variations of phyA mutant when compared to the wild genotype. However, the tomato phytochromes B1 and B2 mainly act as negative regulators of growth, pigment maintenance and osmoprotectant accumulation during responses to the different abiotic stresses.