The role of cotyledons in the establishment of Suaeda physophora seedlings

The role of cotyledons in seedling establishment of the euhalophyte Suaeda physophora under non-saline and saline conditions (addition of 1 mM or 400 mM NaCl) was investigated. Survival and fresh and dry weights were greater for seedlings grown in the light (12-h light/12-h dark) than in the dark (24-h dark). The shading of cotyledons tended to decrease shoot height, shoot organic dry weight, number of leaves, and survival of seedlings regardless of NaCl treatment, but the effect of cotyledon shading was greater with 400 mM NaCl. Concentrations of Na⁺ were higher in cotyledons than in leaves, regardless of NaCl treatment. The K⁺/Na⁺ ratio was lower in cotyledons than in leaves for seedlings treated with 1 mM NaCl but not for seedlings treated with 400 mM NaCl. Addition of 400 mM NaCl decreased oxygen production in cotyledons but especially in leaves. These results are consistent with the hypothesis that, by generating oxygen via photosynthesis and by compartmentalizing Na⁺, cotyledons are crucial for the establishment of S. physophora seedlings in saline environments.     

Effects of salinity and nitric oxide donor sodium nitroprusside (SNP) on development and salt secretion of salt glands of Limonium bicolor

NO, as a signaling molecule, is involved in abiotic stresses. Limonium bicolor seedlings were treated with 200 mM NaCl combined with 0.05 mM SNP for 20 days to study the effects of NO on development and salt-secretion rates of salt glands. It was shown that the total number of salt glands on adaxial surfaces under condition of 200 mM NaCl containing 0.05 mM SNP treatment increased significantly compared with that under 200 mM NaCl treatment. Na⁺ secretion rate per leaf under 200 mM NaCl containing 0.05 mM SNP was significantly higher than that under 200 mM NaCl without SNP. However, there was no significant difference in salt-secretion rate of individual salt glands between 200 mM NaCl containing 0.05 mM SNP treatment and 200 mM NaCl treatment. Although there was no significant difference in salt-secretion rate of individual glands, Na⁺ concentration in the leaves treated with 200 mM NaCl solution containing SNP was significantly lower than that treated with 200 mM NaCl solution. Treatment with 200 mM NaCl solution containing SNP caused a remarkable increase in Na⁺ concentration in salt glands. Obviously, the efficiency of the secretion process per gland was enhanced by adding SNP to NaCl. The results showed NO may enhance the salt secretion by inducing more dermatogen cells to develop into salt glands and by enhancing the efficiency of the secretion process per gland.     

Exogenous application of free polyamines enhance salt tolerance of pistachio (Pistacia vera L.) seedlings

The protective effects of free polyamines (PAs) against salinity stress were investigated for pistachio seedlings (Pistacia vera cv. Badami-Zarand) in a controlled greenhouse. Seedlings were treated with 25, 50, 100 and 150 mM of salts including NaCl, CaCl₂ and MgCl₂. Foliar treatments of putrescine, spermidine (Spd) and spermine (Spm) (0.1 and 1 mM) were applied during the salinity period. Results showed that growth characteristics of pistachio seedlings decreased under salinity stress and the application of PAs efficiently reduced the adverse effects of salt stress. PAs reduced the severe effects of salt stress in pistachio seedlings neither by increasing the activities of peroxidase and ascorbate peroxidase nor by increasing the proline content but by increasing the activities of superoxide dismutase and catalase and decreasing the hydrogen peroxide (H₂O₂) activity. PAs treated seedlings showed a lower Na⁺:K⁺ ratio and Cl^? in leaves suggesting the role of PAs in balancing the ion exchange and better Na⁺:K⁺ discrimination under salt stress condition. These results showed the promising potential use of PAs especially Spm and Spd for reducing the negative effects of salinity stress and improving the growth of pistachio seedlings.     

Inductive responses of some organic metabolites for osmotic homeostasis in peanut (Arachis hypogaea L.) seedlings during salt stress

The salt tolerance of peanut (Arachis hypogaea L.) seedlings was evaluated by analyzing growth, nutrient uptake, electrolyte leakage, lipid peroxidation and alterations in levels of some organic metabolites under NaCl stress. The plant height, leaf area and plant biomass decreased significantly in salt-treated seedlings as compared with control. The relative water content (RWC %) of leaf decreased by 16 % at high concentrations of NaCl. There was an increase in the lipid peroxidation level and decrease in the electrolyte leakage at high concentrations of NaCl. The total free amino acid and proline contents of leaf increased by 5.5- and 43-folds, respectively in 150 mM NaCl-treated plants as compared with control. Total sugar and starch content increased significantly at high concentrations of NaCl. Chl a, Chl b, total chlorophyll and carotenoid contents decreased significantly at high salinity. Na⁺ contents of leaf, stem and root increased in dose-dependent manner. K⁺ content remained unaffected in leaf and root and decreased in stem by salinity. The results from present study reveal that the peanut plants have an efficient adaptive mechanism to tolerate high salinity by maintaining adequate leaf water status associated with growth restriction. In order to circumvent the stress resulting from high salinity, the levels of some organic metabolites such as total free amino acids, proline, total sugars and starch were elevated. The elevated levels of the organic metabolites may possibly have some role in maintenance of osmotic homeostasis, nutrient uptake and adequate tissue water status in peanut seedlings under high-salinity conditions.     

Salt tolerance of a cash crop halophyte Suaeda fruticosa: biochemical responses to salt and exogenous chemical treatments

Suaeda fruticosa Forssk is a leaf succulent obligate halophyte that produces numerous seeds under saline conditions. Seeds are a good source of high quality edible oil and leaves are capable of removing substantial amount of salt from the saline soil besides many other economic usages. Little is known about the biochemical basis of salt tolerance in this species. We studied some biochemical responses of S. fruticosa to different exogenous treatments under non-saline (0 mM), moderate (300 mM) or high (600 mM) NaCl levels. Eight-week-old seedlings were sprayed twice a week with distilled water, hydrogen peroxide (H₂O₂, 100 μM), glycine betaine (GB, 10 mM), or ascorbic acid (AsA, 20 mM) for 30 days. At moderate (300 mM) NaCl, leaf Na⁺, Ca²⁺ and osmolality increased, along with unchanged ROS and antioxidant enzyme activities, possibly causing a better plant growth. Plants grew slowly at 600 mM NaCl to avoid leaf Na⁺ buildup relative to those at 300 mM NaCl. Exogenous application of distilled water and H₂O₂ improved ROS scavenging mechanisms, although growth was unaffected. ASA and GB alleviated salt-induced growth inhibition at 600 mM NaCl through enhancing the antioxidant defense system and osmotic and ion homeostasis, respectively.     

两种野生灌木幼苗对干旱和盐交叉胁迫的生理响应

长枝木蓼(Ateaphaxis viegata)和刺叶锦鸡儿(Caragana acanthophulla)是乌鲁木齐周边植被组成的重要种,在植被恢复中具有潜在价值。该文通过盆栽控水控盐法研究两种野生灌木幼苗在不同程度的干旱和盐交叉胁迫下的生理反应。结果表明,干旱和盐交叉胁迫下,长枝木蓼可溶性糖增幅较刺叶锦鸡儿大;轻度交叉胁迫时,两种灌木的可溶性糖含量高于仅干旱胁迫或盐胁迫下的。中度和重度交叉胁迫下,长枝木蓼叶片丙二醛含量增幅高于刺叶锦鸡儿。交叉胁迫下,两种灌木叶片叶绿素含量下降,且长枝木蓼叶片的叶绿素含量降幅大于刺叶锦鸡儿。因膜系统的过氧化作用,使MDA含量升高。轻度干旱胁迫提高了两种野生灌木对盐胁迫的耐受能力。两种灌木能很好地适应中度交叉胁迫,重度交叉胁迫对两种灌木的伤害很大,但也能生存。综合比较各参数发现,刺叶锦鸡儿更耐早,而长枝木蓼更耐盐;综合比较各生理参数发现,刺叶锦鸡儿对干旱和盐胁迫的耐受能力较长枝木蓼强。     

Ameliorating effect of triacontanol on salt stressederythrina variegata seedlings. Changes in growth,biomass, pigments and solute accumulation

Erythrina variegata Lam. seedlings were grown under low (100 mM NaCl) and high (250 mM NaCl) salinity. Seedlings exposed to high salinity for 10 d showed significant reduction in growth rate and biomass production while the root/shoot ratio increased. In contrast to pigment and protein contents, starch and saccharide contents increased in salt stressed seedlings. When the seedlings were subsequently sprayed with triacontanol (1 mg kg^-1) the salinity effect was partially ameliorated and growth, biomass, chlorophyll and carotenoid contents increased.     

Physiological and proteomic analysis of salinity tolerance of the halotolerant cyanobacterium <Emphasis Type="Italic">Anabaena</Emphasis> sp

The halotolerant cyanobacterium Anabaena sp was grown under NaCl concentration of 0, 170 and 515 mM and physiological and proteomic analysis was performed. At 515 mM NaCl the cyanobacterium showed reduced photosynthetic activities and significant increase in soluble sugar content, proline and SOD activity. On the other hand Anabaena sp grown at 170 mM NaCl showed optimal growth, photosynthetic activities and comparatively low soluble sugar content, proline accumulation and SOD activity. The intracellular Na⁺ content of the cells increased both at 170 and 515 mM NaCl. In contrast, the K⁺ content of the cyanobacterium Anabaena sp remained stable in response to growth at identical concentration of NaCl. While cells grown at 170 mM NaCl showed highest intracellular K⁺/Na⁺ ratio, salinity level of 515 mM NaCl resulted in reduced ratio of K⁺/Na⁺. Proteomic analysis revealed 50 salt-responsive proteins in the cyanobacterium Anabaena sp under salt treatment compared with control. Ten protein spots were subjected to MALDI-TOF–MS/MS analysis and the identified proteins are involved in photosynthesis, protein folding, cell organization and energy metabolism. Differential expression of proteins related to photosynthesis, energy metabolism was observed in Anabaena sp grown at 170 mM NaCl. At 170 mM NaCl increased expression of photosynthesis related proteins and effective osmotic adjustment through increased antioxidant enzymes and modulation of intracellular ions contributed to better salinity tolerance and optimal growth. On the contrary, increased intracellular Na⁺ content coupled with down regulation of photosynthetic and energy related proteins resulted in reduced growth at 515 mM NaCl. Therefore reduced growth at 515 mM NaCl could be due to accumulation of Na⁺ ions and requirement to maintain higher organic osmolytes and antioxidants which is energy intensive. The results thus show that the basis of salt tolerance is different when the halotolerant cyanobacterium Anabaena sp is grown under low and high salinity levels.     

Effect of varying NaCl doses on flavonoid production in suspension cells of Ginkgo biloba: relationship to chlorophyll fluorescence,ion homeostasis,antioxidant system and ultrastructure

Ginkgo suspension cells were used to investigate the mechanism that governs the shift between primary and secondary metabolism under NaCl elicitation. The production of three flavonol glycosides, chlorophyll fluorescence, ion content, the antioxidant system, and the cellular ultrastructure in the presence of NaCl doses from 5 to 175 mM were examined. At low salt doses (5–50 mM), cell growth and flavonol glycosides accumulation were stimulated without damaging cell structure or inducing oxidative stress by maintaining high K⁺ and chlorophyll content. At moderate salt doses (75–125 mM), the cells could withstand the salt stress without an impact on survival by changing internal cellular structure, maintaining high levels of K⁺ and Ca²⁺ and increasing anti-oxidative enzyme activities rather than flavonol glycosides to counteract the inhibition of the photosystem II, the accumulation of Na⁺ and hydrogen peroxide (H₂O₂) in the cells. This allowed cells to divert their metabolism from growth to defense-related pathways and tolerate NaCl stress. At higher salinity (150–175 mM), the cellular structure was damaged, and the high Na⁺ and low K⁺ content led to osmotic stress, and therefore, the stimulation of peroxidase (POD) and catalase (CAT) was not enough to cope with high H₂O₂ accumulation. The high production of flavonol glycosides may be a response of elicitation stimulation to serious damage at 175 mM NaCl. In conclusion, the use of 175 mM NaCl may be desirable for the induction of flavonol glycoside production in Ginkgo suspension cells.     

Glucose-6-phosphate dehydrogenase acts as a regulator of cell redox balance in rice suspension cells under salt stress

The reduced coenzyme nicotinamide-adenine dinucleotide phosphate (NADPH) is an important molecule in cellular redox balance. Glucose-6-phosphate dehydrogenase (G6PDH) is a key enzyme in the pentose phosphate pathway, the most important NADPH-generating pathway. In this study, roles of G6PDH in maintaining cell redox balance in rice suspension cells under salt stress were investigated. Results showed that the G6PDH activity decreased in the presence of 80 mM NaCl on day 2. Application of exogenous glucose stimulated the activity of G6PDH and NADPH oxidase under salt stress. Exogenous glucose also increased the ion leakage, thiobarbituric acid reactive substances and hydrogen peroxide (H₂O₂) contents in the presence of 80 mM NaCl on day 2, implying that the reduction of the G6PDH activity was necessary to avoid serious damage caused by salt stress. The NAPDH/NADP⁺ ratio increased on day 2 but decreased on day 4 under 80 mM NaCl plus glucose treatment. Diphenyleneiodonium, an NADPH oxidase inhibitor, decreased the H₂O₂ content under 80 mM NaCl treatment on day 2. These results imply that the H₂O₂ accumulation induced by glucose treatment under salt stress on day 2 was related to the NADPH oxidase. Western-blot analysis showed that the G6PDH expression was slightly induced by glucose and was obviously blocked by DPI on day 2 under salt stress. In conclusion, G6PDH plays a key role in maintaining the cell redox balance in rice suspension cells under salt stress. The coordination of G6PDH and NADPH oxidase is required in maintaining cell redox balance in salt tolerance.     

Assessment of salt tolerance of Nasturtium officinale R. Br. using physiological and biochemical parameters

Nasturtium officinale R. Br. seedlings were treated with a range of NaCl concentrations (0, 50, 100 and 150 mM) for 21 days after seedling emergence. Physiological analysis based on growth and mineral nutrition, showed a substantial decrease in leaf dry matter with 150 mM NaCl treatment. The growth decrease was correlated with nutritional imbalance and a reduction in potassium accumulation and transport to the leaves. At the same time, we noted an increase in leaf sodium and chloride accumulation and transport. Salt tolerance of N. officinale under 100 mM NaCl was associated with osmotic adjustment via Na⁺ and Cl^? and the maintenance of high K⁺/Na⁺ selectivity. Salt decreased carotenoid content more than chlorophylls and also disturbed membrane integrity by increasing malondialdehyde content and electrolyte leakage. At 150 mM NaCl, an increase in antioxidant enzyme-specific activities for superoxide dismutase, catalase and guaiacol peroxidase occurred in concert with a decrease in ascorbic acid, polyphenol, tannin and flavonoid content. These results indicate that N. officinale can maintain growth and natural antioxidant defense compounds such as, vitamin C, carotenoids, and polyphenols, when cultivated in 100 mM NaCl, but not at higher salt levels.     

Chronic mild salinity affects source leaves physiology and productivity parameters of rice plants (Oryza sativa L., cv. Taipei 309)

Aim

In rice, the top two leaves are the major carbohydrate source during grain filling. Physiological performance of these leaves under salinity may allow estimate stress-induced yield loss.

Methods

Greenhouse grown rice plants (cv. Taipei 309) were subjected to 10 and 20 mM NaCl stress levels from germination till maturity. Plant development was measured at the flowering stage and yield parameters were quantified after complete ripening of panicles.

Results

Gas exchange in the main source leaves were not significantly affected by any of the stress levels. However, growth parameters as well as total metabolizable carbohydrates content, chlorophyll content (CCI), maximal efficiency of PSII photochemistry in dark-adapted state (F _v/F _m) and lipid peroxidation were significantly affected. Rice yield, measured as total panicle production, declined to 78 and 21 % of controls in 10 and 20 mM NaCl stress, respectively. Stress-induced yield loss was positively related with the decline in CCI, F _v/F _m and K⁺/Na⁺ ratio as well as with the increase in lipid peroxidation and total soluble carbohydrate contents.

Conclusions

Though the stress levels used in this work are below what is considered the minimal critical threshold of toxicity for rice, they induce significant negative effects on plant development and yield, when present along the whole plant life cycle.     

Salt and genotype impact on antioxidative enzymes and lipid peroxidation in two rice cultivars during de-etiolation

Crop yield is severely affected by soil salinity, as salt levels that are harmful to plant growth occur in large terrestrial areas of the world. The present investigation describes the studies of enzymatic activities, in-gel assays, gene expression of some of the major antioxidative enzymes, tocopherol accumulation, lipid peroxidation, ascorbate and dehydroascorbate contents in a salt-sensitive rice genotype PB1, and a relatively salt-tolerant cultivar CSR10 in response to 200 mM NaCl. Salt solution was added to the roots of hydroponically grown 5-day-old etiolated rice seedlings, 12 h prior to transfer to cool white fluorescent?+?incandescent light (100 μmol photons m^?2 s^?1). Total tocopherol and ascorbate contents declined in salt-stressed rice seedlings. Among antioxidative enzymes, an increase in the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11), glutathione reductase (EC 1.6.4.2), and their gene expression was observed in both cultivars in response to salt stress. The salt-tolerant cultivar CSR10 resisted stress due to its early preparedness to combat oxidative stress via upregulation of gene expression and enzymatic activities of antioxidative enzymes and a higher redox status of the antioxidant ascorbate even in a non-stressed environment.     

The role of cotyledon metabolism in the establishment of quinoa (Chenopodium quinoa) seedlings growing under salinity

A growth chamber experiment was conducted to assess the effect of salinity on emergence, growth, water status, photosynthetic pigments, osmolyte accumulation, and ionic content of quinoa seedlings (Chenopodium quinoa). The aim was to test the hypothesis that quinoa seedlings are well adapted to grow under salinity due to their ability to adjust the metabolic functionality of their cotyledons. Seedlings were grown for 21 days at 250 mM NaCl from the start of the germination. Germination percentage and cotyledon area were not affected by salt whereas seedling height decreased 15%. FW increased in both control and salt-treated cotyledons, but the increase was higher under salinity. DW only increased in salt-treated cotyledons. The DW/FW ratio did not show significant differences between treatments. Relative water content, chlorophyll, carotenoids, lipids, and proteins were significantly lower under salinity. Total soluble sugars, sucrose and glucose concentrations were higher in salt-treated than in control cotyledons. Ion concentration showed a different distribution pattern. Na⁺ and Cl^? concentrations were higher under salinity, while an inverse result was observed for K⁺ concentration. Proline and glycinebetaine concentrations increased under salinity, but the increase was higher in the former than the latter. The osmoprotective role of proline, glycinebetaine, and soluble sugars is discussed.     

In vitro evaluation of phenolic and osmolite compounds,ionic content,and antioxidant activity in safflower (<Emphasis Type="Italic">Carthamus tinctorius</Emphasis> L.) under salinity stress

Carthamus tinctorius L., rich in antioxidant compounds, is a herbal medicine. Biochemical mechanisms of adaptation to salinity stress in safflower are still poorly understood at the cellular level. For this purpose, callus cultures of four different genotypes of safflower were used in this study to evaluate changes in their biochemical (ionic content, proline, and glycine betaine), total phenolics content (TPC), total flavonoids content (TFD), antioxidant responses (2,2-diphenyl-1-picrylhydrazyl: DPPH assay and carotenoid content), and lipid peroxidation (malon dialdehyde content: MDA) under salinity stress. The calluses derived from hypocotyls were exposed to in vitro salt stress at different concentrations of sodium chloride (0, 100, 200, and 300 mM). A reducing trend was observed in K⁺ and carotenoid reserves of the calluses with increasing NaCl concentration while an increasing trend was observed in Na⁺ content, proline, MDA, TPC, TFD, and DPPH activity under the same conditions. Callus glycine betaine content was found to decrease in the medium containing 100 mM NaCl but increased beyond this concentration up to 300 mM NaCl. Positive and significant correlations were recognized between DPPH and total phenolics as well as DPPH and total flavonoid contents, demonstrating that phenolics are the main contributors to the potential antioxidant activity of safflower at the cellular level. Overall, the salt-tolerant genotypes of Mex.2-137 and Mex.2-138 were found capable of being processed for the production of secondary metabolites via NaCl elicitation.     

Effects of foliar applications of nitric oxide and salicylic acid on salt-induced changes in photosynthesis and antioxidative metabolism of cotton seedlings

Nitric oxide (NO) is a plant signaling compound known to mitigate key physiological processes and salicylic acid (SA) is considered to be a signaling molecule that plays a key role in growth, development, and defense responses in plants under stress conditions. This work investigated the effects of sodium nitroprusside (SNP, a donor of NO) and SA on salt-tolerance of cotton (Gossypium hirsutum L.) seedlings by examining growth, photosynthetic performance, total osmoregulation substance content, antioxidative enzymes and H⁺-ATPase enzyme subjected to 100 mM NaCl. Addition of 100 mM NaCl inhibited the growth and photosynthetic parameters of cotton seedlings, and dramatically increased the electrolyte leakage, the plant contents of proline, lipid peroxidation (malondialdehyde), hydrogen peroxide (H₂O₂) and Na. Furthermore, antioxidant enzyme activities were restrained. Foliar applications of 0.1 mM SNP or/and 0.1 mM SA led to increase in the growth rate and photosynthesis, including photosystem II, net photosynthetic rate and transpiration rate, improvement of reactive oxygen species-scavenging enzymes activities and reduction of H₂O₂ accumulation in cotton seedlings induced by NaCl. In addition, membrane transport and function were facilitated by decreasing leaf electrolyte leakage, improving ion absorption and activating the osmotic-regulated substances metabolic. Further investigation also showed that SNP and SA alleviated the inhibition of H⁺-ATPase in plasma membrane induced by NaCl. The present study showed that foliar application of SNP and SA alone mitigated the adverse effect of salinity, while the combined application proved to be even more effective in alleviating the adverse effects of NaCl stress.     

Improving NaCl resistance of red-osier dogwood: role of CaCl2 and CaSO4

The influence of Ca²⁺ salts on the resistance of red-osier dogwood (Cornus sericea) seedlings to salinity was investigated. Red-osier dogwood seedlings were exposed to 5 and 10 mM of CaCl₂ or CaSO₄ in the presence or absence of 50 mM NaCl for 40 days in a controlled environment. Seedlings exposed to CaCl₂ and CaSO₄ recovered from NaCl-induced transpiration reduction after 20 days at a concentration of 10 mM and after 30 days at a concentration of 5 mM; while in absence of additional Ca²⁺, the seedlings recovered only after 40 days. Addition of 10 mM Ca²⁺ to NaCl treatment also limited the accumulation of proline in leaf tissues and caused an increase in leaf and lateral shoot K⁺ content. These results suggest that 10 mM Ca²⁺ could alleviate, at least in part, the osmotic effect of NaCl on red-osier dogwood via control of stomatal closure. On the other hand, ion analysis showed that Ca²⁺ addition was able to reduce the NaCl-induced Na⁺ concentration only in stem tissues suggesting that Ca²⁺ had only a limited effect on the ionic stress. The present study also showed an unexpected NaCl-induced increase in Ca²⁺ content of leaves, lateral shoots and stems that was not observed in our previous hydroponics experiments and seems to be more characteristic of plants growing on sandy soils.     

Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.     

Salt and osmotic stress tolerances of the C<Subscript>3</Subscript>–C<Subscript>4</Subscript> xero-halophyte <Emphasis Type="Italic">Bassia sedoides</Emphasis> from two populations differ in productivity and genetic polymorphism

The morphological, biochemical and genetic characteristics of two Bassia sedoides (Chenopodiaceae) populations in the Southern Urals were studied. The plants of the Makan and Podolsk populations differ in growth (approximately 10-fold), in water and potassium contents and Na⁺/K⁺ ratio. On the basis of the genetic assay (by isozymes, RAPD and ISSR markers) of B. sedoides from the Makan and Podolsk populations, the intraspecific differences have been identified. The more productive Makan population showed greater genetic polymorphism, whereas the less productive Podolsk population showed less genetic polymorphism. The seedlings of B. sedoides from the Makan and Podolsk populations were cultivated under low and moderate salinity (100 and 200 mM NaCl, respectively) and equivalent osmoticity generated by the two PEG concentrations. Both populations were sensitive to dehydration initiated by PEG. Podolsk seedlings were more sensitive to osmotic stress and were characterised by an increase in proline content. Low salinity (100 mM NaCl) was necessary for optimal growth of seedlings from the Makan population. They showed significantly increased fresh biomass and number of lateral shoots. The maximal growth of seedlings from Podolsk was under 0–100 mM NaCl, and their biomass was approximately 1.4-fold lower than that of the Makan seedlings. Under moderate salinity (200 mM NaCl), the Makan seedlings were more salt tolerant than the Podolsk seedlings because of maintaining a low Na⁺/K⁺ ratio. Under natural conditions, the excess of Na⁺/K⁺ ratio compared with values for optimal growth under laboratory conditions was approximately threefold for the Makan plants and approximately fivefold for the Podolsk plants. High values of the Na⁺/K⁺ ratio under natural conditions indicate a deficit of potassium in the soil. Perhaps, the degree of potassium deficiency is one of the factors influencing the differences in productivity and the level of genetic variation of B. sedoides under natural conditions.     

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.