Effect of Osmotic Stress with PEG6000 on Osmotic Adjustment Solute in Seedling Leaves of Chenopodium album L.

[ Objective] The purpose was to discuss drought resistance mechanism of Chenopodium album L. and supply theoretical basis and practical guidance for artificial cultivation and popularization of C. album. [ Method] C. album seedlings grown to 6th leaf stage were conducted osmotic stress treatment with PEG6000 osmotic whose concentration was set up as 0, 5%, 10% and 20% and the various physiological indices of the 3rd -5th function leaves in upper plant were determined after being treated for 0, 1,3, 5, 7 and 9 d. [ Result] Under osmotic stress with 5% PGE, the relative water content （RWC） of C. album reduced less. Under osmotic stress with 10%, the RWC in seedling leaves of C. album decreased to 62% on the fifth day and the leaves began to wither. Under osmotic stress with 20%, the RWC in seedling leaves of C. album decreased to 61.9% on the third day and the leaves appeared withering, and the RWC decreased to 48.6% on the 7th day and the leaves were dry and yellow. Proline contents in seedling leaves of C. album under osmotic stress with 5%, 10% and 20% PEG were 7.64, 10.9 and 29.4 times of CK on the 7th day. [ Conclusion] C. album hed some adaptability to moderate osmotic stress, but the PEG osmotic stress with high concentration and long time might lead to severe damage on C. album.

Effects of Nitrogen Application on Osmotic Adjustmentof Ramie (Boehmeria nivea L.) with Different NitrogenEfficiency

Ramie (Boehmeria nivea L.) is one of the most important fiber crops and biomass materials. However, previous studies showed that ramie presented a very low nitrogen agronomy efficiency (NAE, 23.2%~27.8%) in traditional farming, and the nitrogen fertilizer was applied excessively in ramie field. Plant osmotic adjustment (OA) responses to environmental stresses positively and exhibits improvements in plant tolerance. Whereas results varied due to the complexity of plant-environment interactions and lack of insights of specific species. In order to improve ramie production through osmoregulation, our current study investigated the role of nitrogen application and osmotic adjustment in improving the growth and yield in two varieties of ramie (H2000-03 and Ceheng Jiama) with contrasting nitrogen use efficiency (NUE) grown at 5 different N rates including N0, N6, N9, N12 and N15;0, 6, 9, 12 and 15 mmol/L N, respectively. The results showed that ramie adapted to different nitrogen rates through OA and significant differences of osmolyte content between varieties only presented at the particular growth stage. Obvious inflexion of yield, osmolyte content involving proline, soluble protein (SP), soluble sugar (SS) and malonaldehyde (MDA);nitrogen sensitive index (NSI) and comprehensive evaluation (D) in both varieties were observed. Our results recommended that the overall lifting of OA at a lower N level and at the proper growth stage would be a reasonable approach for improving ramie NUE.

Exogenous Glycine Betaine Reduces Drought Damage by Mediating Osmotic Adjustment and Enhancing Antioxidant Defense in Phoebe hunanensis

Drought stress negatively impacts growth and physiological processes in plants.The foliar application of glycine betaine(GB)is an effective and low-cost approach to improve the drought tolerance of trees.This study examined the effect of exogenously applied GB on the cell membrane permeability,osmotic adjustment,and antioxidant enzyme activities of Phoebe hunanensis Hand.-Mazz under drought stress.Two levels(0 and 800 mL)of water irrigation were tested under different applied GB concentrations(0,50,100,and 200 mM).Drought stress decreased the relative water content by 58.5%while increased the electric conductivity,malondialdehyde,proline,soluble proteins,soluble sugars,and antioxidant enzyme activities(superoxide dismutase,catalase,peroxidase)by up to 62.9%,42.4%,87.0%,19.1%,60.5%,68.3%,71.7%,and 83.8%,respectively,on the 25^(th) day.The foliar application of GB,especially at 100 mM,increased the relative water content of P.hunanensis leaves under drought stress.The concentration of GB from 50 to 100 mM effectively alleviated the improvement of cell membrane permeability and inhibited the accumulation of membrane lipid peroxidation products.Under drought stress,the concentrations of proline,soluble proteins,and soluble sugars in the leaves of P.hunanensis increased as the applied GB concentration was increased and the water stress time was prolonged.Exogenously applied GB decreased oxidative stress and improved antioxidant enzyme activities as compared with treatments without GB application.Furthermore,the physiological and biochemical indexes of P.hunanensis showed a certain dose effect on exogenous GB concentration.These results suggest that GB helps maintain the drought tolerance of P.hunanensis.

DROUGHT-INDUCED UNKNOWN PROTEIN 1 positively modulates drought tolerance in cultivated alfalfa(Medicago sativa L.)

Alfalfa is the most widely cultivated perennial legume forage crop worldwide.Drought is one of the major environmental factors influencing alfalfa productivity.However,the molecular mechanisms underlying alfalfa responses to drought stress are still largely unknown.This study identified a drought-inducible gene of unknown function,designated as Medicago sativa DROUGHT-INDUCED UNKNOWN PROTEIN 1(MsDIUP1).MsDIUP1 was localized to the nucleus,chloroplast,and plasma membranes.Overexpression of MsDIUP1 in Arabidopsis resulted in increased tolerance to drought,with higher seed germination,root length,fresh weight,and survival rate than in wild-type(WT)plants.Consistently,analysis of MsDIUP1 over-expression(OE)alfalfa plants revealed that MsDIUP1 also increased tolerance to drought stress,accompanied by physiological changes including reduced malondialdehyde(MDA)content and increased osmoprotectants accumulation(free proline and soluble sugar),relative to the WT.In contrast,disruption of MsDIUP1 expression by RNA interference(RNAi)in alfalfa resulted in a droughthypersensitive phenotype,with a lower chlorophyll content,higher MDA content,and less osmoprotectants accumulation than that of the WT.Transcript profiling of alfalfa WT,OE,and RNAi plants during drought stress showed differential responses for genes involved in stress signaling,antioxidant defense,and osmotic adjustment.Taken together,these results reveal a positive role for MsDIUP1 in regulating drought tolerance.

Physiological Changes in Leaves of Medicago falcata Under Low-Temperature Stress

Low temperature significantly restricts crop yield and quality.Medicago falcata(M.falcata)is a typical legume species that exhibits great capacity of tolerance to low temperature.To understand the low-temperature responses in M.falcata,the electrolyte leakage and lipid peroxidation level,and activities of superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD),and contents of reduced glutathione(GSH),soluble protein,soluble sugar and proline were investigated in low-temperature-stressed M.falcata leaves.The electrolyte leakage and malondialdehyde(MDA)content increased,and could be used to quantify low-temperature damage at cellular level.And then,the significant change of SOD,POD and CAT activities,and GSH content reflected the higher reactive oxygen species(ROS)scavenging capacity in M.falcata.In addition,the significant change of soluble protein,soluble sugar and proline contents helped to maintain osmotic equilibrium,energy supply and protein functions.These nine physiological traits were analyzed by gray relational grade analysis and ranked from the highest to the lowest as follows:electrolyte leakage,GSH,proline,soluble protein,MDA,soluble sugar,SOD,CAT and POD,and illustrated that the electrolyte leakage level,GSH and proline contents should be selected and measured priority in M.falcata low-temperature tolerance to improve measurement efficiency.

Response Mechanism of Plants to Drought Stress

Drought stress is an important factor affecting plant growth and development.It will provide a theoretical basis for cultivating new stress-resistant varieties and improving water utilization rate of plants by studying the regulation mechanism of osmotic adjustment and water transportation under drought stress,and understanding the physiological and biochemical characteristics and stress resistance mechanism.

Effects of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria on growth and reactive oxygen metabolism of tomato fruits under low saline conditions

Land salinization is a major form of land degradation,which is not conducive to the growth and quality of fruits and vegetables.Plant salt tolerance can be enhanced by arbuscular mycorrhizal fungi(AMF)or plant growth-promoting rhizobacteria(PGPR).This study examined the effects of inoculation with PGPR singly or in combination with AMF,on the growth and quality of tomato fruits under low saline conditions.Tomatoes were cultivated in a greenhouse with sterilized soil,inoculated with PGPR,AMF,or co-inoculated with PGPR and AMF,and NaCl solution(1%)was added to the soil.The results indicated that AMF+PGPR decreased the roots and shoot biomass accumulation,and increased the number and fresh biomass in tomato fruits to a certain extent compared with non-inoculated plants.PGPR and AMF mediated the level of reactive oxygen and lipid peroxidation,the accumulation of antioxidants,and the activity of antioxidant enzymes,including proanthocyanidins,flavonoids,ascorbic acid,superoxide dismutase,peroxidase,and total antioxidant capacity.Furthermore,PGPR,AMF,and PGPR+AMF improved the overall osmotic adjustments and accumulation of soluble sugars and soluble proteins.Therefore,the AMF-Funneliformis mosseae and PGPR-Bacillus subtilis can potentially alleviate the adverse effects of salt stress and be applied as a biofertilizer in agricultural practice.

Physiology of Cold Resistance of Amorpha fruticosa L. cv. Jinye

With two-year-old Amorpha fruticosa L. cv. Jinye and A. fruticosa as the research objects, the relative conductivity, MDA content, soluble sugar content, solu- ble protein content and proline content in leaf were determined during natural drop in temperature, and the SOD, POD and COD activity in leaf were determined under artificial low temperature to explore the adaptability of A. fruticosa L. cv. Jinye to low temperature. The results showed that with the decrease in natural temperature, the content of MDA in A. fruticosa L. cv. Jinye was lower than that in the control, and the contents of osmotic adjustment substances （soluble sugar, soluble protein and proline） increased, indicating that A. fruticosa L. cv. Jinye had a stronger toler- ance to low temperature compared with A. fruticosa. The activity of SOD, POD and CAT in A. fruticosa L. cv. Jinye increased continuously, higher than that in the con- trol, indicating that the resisting ability of A. fruticosa L. cv. Jinye against low tem- perature was superior to that of the control. There was no significant difference in relative conductivity between A. fruticosa L. cv. Jinye and A. fruticosa.

Molecular mechanisms of salinity tolerance in rice

Salinity is one of the major abiotic stresses which impose constraints to plant growth and production.Rice(Oryza sativa L.)is one of the most important staple food crops and a model monocot plant.Its production is expanding into regions that are affected by soil salinity,requiring cultivars more tolerant to saline conditions.Understanding the molecular mechanisms of such tolerance could lay a foundation for varietal improvement of salt tolerance in rice.In spite of extensive studies exploring the mechanism of salt tolerance,there has been limited progress in breeding for increased salinity tolerance.In this review,we summarize the information about the major molecular mechanisms underlying salinity tolerance in rice and further discuss the limitations in breeding for salinity tolerance.We show that numerous gene families and interaction networks are involved in the regulation of rice responses to salinity,prompting a need for a comprehensive functional analysis.We also show that most studies are based on whole-plant level analyses with only a few reports focused on tissue-and/or cell-specific gene expression.More details of salt-responsive channel and transporter activities at tissue-and cell-specific level still need to be documented before these traits can be incorporated into elite rice germplasm.Thus,future studies should focus on diversity of available genetic resources and,particular,wild rice relatives,to reincorporate salinity tolerance traits lost during domestication.

Physiological response of four wolfberry (Lycium Linn.) species under drought stress

We studied gas-exchange, chlorophyll pigments, lipid peroxidation, antioxidant enzymes, and biomass partitioning responses in seedlings of four wolfberry species （Lycium chinense Mill. var. potaninii （Pojark.） A. M. Lu, Lycium chinense Mill., Lycium barbarum L., and Lycium yunnanense Kuang ＆ A. M. Lu） under four water supply regimes. In all four species, drought affected seedlings in terms of chlorophyll content, net photosynthesis rate （Pn）＇ transpiration rate （E）, and lipid peroxidation. Drought also increased some antioxidant enzyme activities, such as peroxidase （POD）, catalase （CAT）, superoxide dismutase （SOD）, and ascorbate peroxidase （APX）. Significant changes in dry biomass partitioning also occurred in response to water stress. In particular, dry biomass of leaves and fruits decreased significantly. L. chinense Mill. and L. barbarum L. possessed greater drought tolerance and exhibited superior antioxidant processing ability and other related physiological traits compared to the other two species. L. chinense Mill. was the most tolerant to all levels of drought. In contrast,L, yunnanense Kuang ＆ A. M. Lu was more affected by water supply and had the lowest resistance to drought stress. These findings would provide some important information regarding genetic resources for future forest tree improvement in relation to drought tolerance.

Cold hardiness estimation of Pinus densiflora var. zhangwuensis based on changes in ionic leakage, chlorophyll fluorescence and other physiological activities under cold stress

Pinus densiflora var. zhangwuensis grows fast, and its drought and salinity resistance are better than Pinus sylvestris var. mongolica. We compared cold hardiness and mechanisms of cold hardiness between the two species, to provide a theoretical basis for promoting and applying P. densiflora var. zhangwuensis in cold regions. A cold stress experiment was carried out on 3-year-old plantlets of P. densiflora var. zhangwuensis and P. sylvestris var. mon- golica after hardening at five temperature regimes, 5, -10, -20, -40, and -60 ℃, respectively. Some indices of needle samples for both species were measured, such as relative conductivity （REL）, maximum photochemical efficiency （Fv/Fm）, malondialdehyde （MDA）, catalase （CAT）, proline （Pro）, soluble sugar （SS）, and stomata density. REL and MDA values of both species after hard- ening had the same trend of increasing, but the trend was opposite in Fv/Fm value with increasing cold stress. Com- pared with P. sylvestris var. mongolica, the P. densiflora var. zhangwuensis had smaller increases in REL and MDA, and a smaller decline in Fv/Fm during cold stress. Com- pared to the control, REL growth of P. densiflora var. zhangwuensis and P. sylvestris var. mongolica at -60 ℃were 0.41 and 0.60, and MDA growth was 29.94 mol g-1 FW and 47.80 mol g-1 FW, and Fv/Fm declines were 0.08 and 0.27. Half-lethal temperatures （LT50） calculated by logistic equation for P. densiflora var. zhangwuensis and P. sylvestris var. mongolica were -58.23 and -50.34 ℃, respectively. These data suggest that cold resistance of P. densiflora var. zhangwuensis is stronger than that of P. sylvestris var. mongolica. Cold-resistance mechanisms of the two species differed. In response to cold stress, P. sylvestris var. mongolica had strong osmotic adjustment ability because of higher Pro and SS content, while P. densiflora var. zhangwuensis had strong antioxidant ability due to stronger CAT activity. Stomata density and diameter of P. densiflora var. zhangwuensis were smaller, as were single leaf area and number of leaves per plant, both characteristics promoting survival in a cold environment. Greater shoot height and total biomass of seedlings of P. densiflora var. zhangwuensis might be another reason for its stronger cold tolerance.

Some Physiological Responses of Chinese Iris to Salt Stress

Chinese iris （Iris lactea Pall. var. chinensis （Fisch） Koidz.）, a robust iridaceous plant, is widespread in arid and semiarid regions with high salinity. However, the mechanism of its salt tolerance is not well understood. In this study, plant growth, water status, content and distribution of inorganic ions, cell membrane permeability, and proline content of I. laetea under salt stress were investigated using nutrient solutions with six NaCl concentrations ranging from 0 to 350 mmol L^-1. The results indicated that the biomass, height, fresh weight, K^＋ content, and K^＋/Na^＋ and Ca^2＋/Na^＋ ratios decreased with increasing NaCl stress, whereas plant water deficit and contents of Na^＋ and Cl- increased with increasing NaCl stress. In all salt treatments, water deficit of shoots was found to be higher than that of roots and had a positive correlation with salt concentration. When the NaCl concentration was less than 280 mmol L^-1, the ion absorption selectivity ratio and the transportation selectivity ratio sharply increased with increasing NaCl stress. Under medium salt stress, I. lactea exhibited a strong K^＋ selective absorption and the transportation of K^＋ from roots to shoots increased, whereas Na^＋ was not transported and was mostly retained in roots. The plants were able to maintain osmotic adjustment through the accumulation of Na^＋, Cl-, and proline. On the basis of its biomass production under salt stress, I. lactea could be considered as a facultative halophyte.

Transcriptome analysis of Porphyridium purpureum under salinities of 0 and 68

The most prominent biological characteristic of Porphyridium purpureum is their unique extracellular sulfated polysaccharides that plays an important protective role against salt stress.Adaptation to stress is associated with metabolic adjustments.However,the molecular mechanisms underlying such metabolic changes remain elusive.This study presents the fi rst transcriptome profi ling of P.purpureum.A total of 8019 assembled transcripts were identifi ed,annotated,and classifi ed into diff erent biological categories and pathways based on a BLAST analysis against various databases.The in-depth analysis revealed that many of the diff erentially expressed genes in P.purpureum under salinities of 68 and 0 involved polysaccharide metabolism.A comparison of the gene expression levels under diff erent salinities revealed that the polysaccharide synthetic pathway was signifi cantly upregulated under the 68 salinity condition.The increased expression of the FBP,pfkA,CS,pgm,USP,UGP2,galE,and MPI transcripts in the polysaccharide synthetic pathway and the increase in ATP2 and ATP6 transcripts in the energy metabolic pathway revealed the molecular mechanism of high-salt adaptation.This sequencing dataset and analysis could serve as a valuable resource to study the mechanisms involved in abiotic stress tolerance in Rhodophyta.

Molecular Mechanism of Rice in Response to Salt Stress

Rice is moderately sensitive to salinity,and the response to salt stress is a complex process,including the perception and transduction of salt stress signal,the activation of specific transcriptional factors and the expression of downstream stress-responsive genes.The functions of Na+ transporters which are involved in the maintenance and reconstruction of the ion homeostasis,transcriptional regulators and osmotic regulation genes were reviewed.Salt tolerance of plants are enhanced by Na+ vacuolar compartmentation or efflux or high levels of osmoprotectants accumulation in cytoplasm.

Osmoregulators in Hymenaea courbaril and Hymenaea stigonocarpa under water stress and rehydration

The objective of this work was to evaluate the effect of different water deficiency and rehydration levels on the concentrations of osmoregulators in two plant species（Hymenaea courbaril and H. Stigonocarpa） in the Amazon. We adopted a 2×5×5 factorial system,referring to 2 species（H. courbaril and H. stigonocarpa）and 5 stages of hydration and rehydration. The five hydration and rehydration stages were established in:（1）Control treatment E0;（2） Plants with 13 days of stress after incubation—E13;（3） Plants with 26 days of stress E26;（4）The plants that were established after 26 days after incubation and rehydrated for two days（RD2）;（5） rehydrated for two days（RD4）. The plants that were established after 26 days after incubation and rehydrated for four days. The experiment totaled fifty young plants with five replicates.Biochemical measurements were performed at the beginning of the experiment（E0） at 13（E13） and 26（E26） days after the water stress, in which the plants were rehydrated,repeating the analyses after two（RD2） and four（RD4）days. Both species increased the sucrose concentration by18%, with a decrease of 52% in starch content. The RD4 time presented the highest mean starch concentration(0.19 mmol g-1 of the residue for H. courbaril and0.27 mmol g;of residue for H. stigonocarpa). Increased proline concentrations were recorded for controls until RD2 for both species. For glycine betaine, the highest increases in treatments E26 and RD2 were observed for the H. courbaril species. Our rehydration period was not sufficient for total recovery of pre-stress concentrations of all studied solutes.

Study of Water Relations and Solutes Accumulation in Two Rice Genotypes under NaCI Stress during Seedling Stage

In order to study osmotic adjustment and accumulation of anions and cations in rice （Oryza sativa L.） seedlings under NaCl stress, a greenhouse experiment was conducted using two rice cultivars including IR651 （tolerant） and IR29 （sensitive）. Seedlings were grown in Youshida nutrient solution. Salinity treatments were imposed 21 days after sowing with 0 and 100 mM NaCI and seedlings were harvested 0, 72, 120 and 240 hour after salinization. Water （ψw） and osmotic （ψs） potentials, total soluble sugars and inorganic ions （Na＋. K＋, Cl-, Ca2＋ and Mg2＋） concentrations and osmotic adjustment were determined in sixth （youngest） leaf. Salinity caused a substantial biomass reduction in rice seedlings, ψs reduction in IR29 was occurred more than IR651. Water potential decreased in both the cultivars under stress conditions, but IR651 was able to maintain higher ψw and kept better growth till the end of the experiment. Osmotic adjustment was observed in IR651 was about 10 times more than in IR29. K＋ accumulation decreased in both cultivars under stress condition while Na＋ accumulation increased in both the cultivars with higher increase in IR29 seedlings. CI concentration increased in youngest leaf of both IR29 and IR651. Our results showed that tolerant cultivar was able to make osmotic adjustment faster than the sensitive cultivar using high accumulation of solutes especially total soluble sugars.

Effects of excessive nitrogen fertilizer and soil moisture deficiency on antioxidant enzyme system and osmotic adjustment in tomato seedlings

Long-term excessive application of nitrogen fertilizer induces secondary salinization of soil,which results in inhibiting plant growth.In addition,soil moisture deficiency also affects plant growth.To investigate the effects of excessive nitrogen fertilizer and soil moisture deficiency on the antioxidant enzyme system,plant water relations analyzed through pressure-volume(P-V)curve,and photosynthetic light response parameters in tomato(Solanum lycopersicum L.Myoko)seedlings,an indoor experiment of about 50 d was conducted using two irrigation water amounts based on field capacity(soil moisture deficiency:50%-80%;adequate water:70%-80%),two nitrogen fertilizer rates(moderate nitrogen;excessive nitrogen fertilizer:0.585 g/pot)and two types of irrigation water(tap water and microbial diluent).The results showed that excessive nitrogen fertilizer(N)and soil moisture deficiency(W)reduced the biomass of tomato seedlings.In comparison to CK(combination of adequate water and tap water quality),microbial dilution(EM)increased plant biomass by 5.2%.Also,the nitrogen application increased chlorophyll relative contents(SPAD).The maximum net photosynthetic rate(Pc)decreased with nitrogen application and increased with EM application and irrigation amount.Excessive nitrogen application increased the plant nitrate reductase activity(NR).The plant NR in the N treatment showed a 13.0%increase compared to CK,and the plant NR in the treatment of nitrogen application with water deficiency(WN)increased 34.0%compared to water deficiency(W).After applying excessive nitrogen,N,EM-N,WN,EM-WN respectively increased the plant nitrate reductase activity by 13.0%,22.9%,34.0%,and 28.6%,compared with the corresponding treatment with moderate nitrogen(i.e.,CK,EM,W and EM-W).In addition,the activities of antioxidant enzymes[superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)]in four treatments of nitrogen application(N,EM-N,WN,EM-WN)also increased significantly.Both soil moisture and nitrogen fertilizer significantly affect the parameters of osmotic adjustment,which is manifested in the reduction of osmotic potential(π_(FT)),and the increase in the osmotic concentration(C_(osm))and concentration difference(ΔC_(osm)).But the decrease in the relative water content of apoplast(ζ_(ap))indicated that water deficiency and excessive nitrogen reduced the water absorption and water retention capacity of tomatoes to a certain extent.In conclusion,excessive nitrogen application and soil moisture deficiency inhibit plant growth significantly in this experiment.Meanwhile,microbial dilution can alleviate excessive nitrogen fertilizer and water stress to some extent,but the effect was not significant.

Osmotic adjustment and up-regulation expression of stress-responsive genes in tomato induced by soil salinity resulted from nitrate fertilization

Concerns about the soil salinity caused by excessive fertilization have prompted scientists to clarify the detailed mechanisms and find techniques to alleviate the damage caused by this kind of soil salinity.Aims of this study were to elucidate the effect of soil salinity caused by nitrate fertilization and the differences in salinity effect between nitrate salts and NaCl salt with analyses at various levels of crop physiology and molecular biology.A microbial inoculation was also tried to verify whether it could alleviate the salinity-induced loss and damages.In three experiments(Exp I,II and III),nitrate salts(NS)of Ca(NO_(3))_(2) and KNO_(3) were applied to potted tomato plants to simulate the soil salinity caused by fertilization and a microbial inoculant(MI)was applied.Photosynthesis was measured using Li-6400.Osmotic adjustment was analyzed using the mathematically modeled pressure-volume curve;O_(2)-concentration and activity of SOD and nitrate reductase were measured.Expression of nitrate reductase gene and the stress-responsive gene DREB2 was analyzed using the real-time PCR method.In Exp I and II,where the applied NS amount was moderate,NS application at low concentration induced increases in O_(2)-and MDA concentrations and plants acclimated to the soil salinity as the treatment prolonged for weeks.The acclimation was contributed by osmotic adjustment,activation of SOD and re-compartmentation of cell water between symplasm and apoplasm.These adjustments might be ultimately attributed to up-regulation of stress-responsive genes such as DREB2 as well as the nitrate reductase(NR)gene.However,in Exp III,applications of NaCl and NS at high concentration could not show positive effects as NS did.Application of MI synergistically increased the xerophytophysiological regulation caused by NS and alleviated the salinity damage in addition to its own positive effects on the tomato plants.Different from NaCl,nitrate salts at low application rate increased the total biomass and fruit yield of tomato and induced up-regulation expression of stress-responsive genes and the consequent active osmotic adjustment.However,nitrate application at high level negatively affected tomato plants irrespective of the gene up-regulations.Application of MI alleviated the salinity damage and synergistically increased the xerophytophysiological regulation caused by the soil salinity in addition to its positive effects on the tomato crop but the detailed mechanisms needed to be clarified in future further studies.

Salt Tolerance in Soybean

Soybean is an important cash crop and its productivity is significantly hampered by salt stress. High salt imposes negative impacts on growth, nodulation, agronomy traits, seed quality and quantity, and thus reduces the yield of soybean. To cope with salt stress, soybean has developed several tolerance mechanisms, including： （i） maintenance of ion homeostasis; （ii） adjustment in response to osmotic stress; （iii） restoration of osmotic balance; and （iv） other metabolic and structural adaptations. The regulatory network for abiotic stress responses in higher plants has been studied extensively in model plants such as Arabidopsis thaliana. Some homologous components involved in salt stress responses have been identified in soybean. In this review, we tried to integrate the relevant works on soybean and proposes a working model to describe its salt stress responses at the molecular level.

Photosynthetic, Physiological and Biochemical Responses of Tomato Plants to Polyethylene Glycol-Induced Water Deficit

Polyethylene glycol （PEG 6000）-induced water deficit causes physiological as well as biochemical changes in plants. The present study reports on the results of such changes in hydroponically grown tomato plants （Lycopersicon esculentum Mill. cv. Nikita）. Plants were subjected to moderate and severe levels of water stress （i.e. water potentials in the nutrient solution of- 0.51 and -1.22 MPa, respectively）. Water stress markedly affected the parameters of gas exchange. Net photosynthetic rate （Pn） decreased with the induction of water stress. Accordingly, a decrease in the transpiration rate （E） was observed. The ratio of both （Pn/E） resulted in a decrease in water use efficiency. One of the possible reasons for the reduction in Pn is structural damage to the thylakoids, which affects the photosynthetic transport of electrons. This was indicated by an increase in non-photochemical quenching and a reduction in the quantum yield of photosystem Ⅱ. Furthermore, a decrease in both leaf water potential and leaf osmotic potential was observed, which resulted in a significant osmotic adjustment during stress conditions. Analysis of the physiological responses was complemented with a study on changes in proline content. In stressed plants, a 10-fold increase in proline content was detected compared with control plants. It is clear that water stress tolerance is the result of a cumulative action of various physiological and biochemical processes, all of which were affected by PEG 6000-induced water stress.