Effects of water deficit on photosynthetic rate and osmotic adjustment in tetraploid wheats

Osmotic adjustment, accumulation of soluble saccharides, and photosynthetic gas exchange were studied in five durum wheat (Triticum turgidum L. var. durum) and one wild emmer wheat (Triticum turgidum L. var. dicoccoïdes) cultivars of contrasting drought tolerance and yield stability. Soil water contents (SWC) were 100, 31, 20, and 12 % of maximum capillary capacity. Under mild water stress (SWC 31 to 20 %), osmotic adjustment capacity and high accumulation of saccharides were found in cv. Cham1, a high yielding and drought tolerant cultivar, and in var. dicoccoïdes, while lowest values were noted in the durum wheat landraces Oued-Zenati and Jennah-Khotifa. Under more severe water stress (SWC 12 %), the cv. Cham1 maintained higher net photosynthetic rate (PN) than other genotypes. The observed changes in the ratio intercellular/ambient CO2 concentration (ci/ca) indicated that under mild and severe water stress, the decrease in PN was mainly due to stomatal and non-stomatal factors, respectively.     

Growth and some metabolic activities ofScenedesmus obliquus cultivated under different NaCl concentrations

The physiological response ofScenedesmus obliquus to salinity (NaCl concentration of 40, 80, 120, 60 and 200 mM) for 7 d (long-term experiments) or 2 h (short-term experiments) was followed. Cell number, dry matter and the content of photosynthetic pigments decreased with the rise of NaCl concentration. However, the photosynthetic O₂ evolution mostly increased with the increase of NaCl concentration up to 80 mM, and respiration (dark O₂ uptake) was markedly promoted. Photosynthesis/respiration ratio went in concomitance with the cell number, dry matter or chlorophyll content. Contents of soluble saccharides and soluble proteins increased with the rise of salinization, while the content of insoluble and total saccharides or proteins decreased. Proline content increased greatly with salinization, whereas of other free amino acids were mostly reduced, especially at higher salinities. Similarly, the lipoid contents of salinizedScenedesmus obliquus were obviously higher than those of the control cultures.     

Saccharide Content and Growth Parameters in Relation with Flooding Tolerance in Rice

Pre-submergence reserve saccharides was found adequate to substantiate the survival of tolerant cultivar under flooding. Survival percentage declined in both tolerant and susceptible cultivars with less saccharide content. However, it was more apparent in susceptible cultivar. Plant height, fresh and dry mass of shoots, leaf mass/area ratio and starch content per plant before flooding showed significant positive association with submergence tolerance. Hence, the improved seedling vigour could be used to increase submergence tolerance.     

Growth attributes,biochemical modulations,antioxidant enzymatic metabolism and yield in Brassica napus varieties for salinity tolerance

Improvement in salinity tolerance of plants is of immense significance as salt stress particularly threatens the productivity of agricultural crops. This study was designed to assess the tolerance level of six Brassica napus varieties (Super, Sandal, Faisal, CON-111, AC Excel and Punjab) under different levels of salinity (0, 50, 100, 150 & 200 mM) with three replications under CRD. Salt induced osmotic stress curtailed the plant growth attributes, photosynthetic pigments and disturbed ionic homeostasis (K⁺, Na⁺, Ca^2+, Cl^-) but least disturbance as compared to control was found in Super and Sandal cultivars. Punjab canola and AC Excel canola cultivars were least tolerant to salinity because these displayed greater decline in all growth and biochemical attributes. Plants subjected to NaCl induced stress exhibited considerable decline in all attributes under study with proline as exception. Antioxidants (CAT, SOD & POD) showed an obvious change in Canola plants under stress, but greatest decline was displayed at 200 mM NaCl level in all six cultivars. Over all these attributes presented a comparatively stable trend in super and sandal cultivars. This shows presence of physiological resilience and metabolic capacity in these two cultivars to tackle salinity. Similarly, all yield attributes displayed adverse behavior under 150 mM & 200 mM salinity stress. Our results demonstrated that Super and Sandal cultivars of Brassica napus exhibit good performance in salinity tolerance and can be good option for cultivation in salt affected areas.     

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K⁺ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na⁺ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na⁺ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na⁺ in the shoot. Increased leaf sap K⁺, controlled Na⁺ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.     

Response of tomato cultivars to salinity

The responses of five tomato cultivars (L. esculentum Mill) of different degrees of salt tolerance were examined over a range of 0 to 140 mM NaCl applied for 3 and 10 weeks. Judged by both Na and Cl accumulations and maintenance of K, Ca and Mg contents with increasing salinity, the most tolerant cultivars (Pera and GC-72) showed different responses. The greater salt tolerance of cv Pera was associated with a higher Cl and Na accumulation and a lower K content in the shoot than those found in the other cultivars, typical of a halophytic response to salinity. However, the greater salt tolerance of cv GC-72 was associated with a retention of Na and Cl in the root, restriction of their translocation to the shoot and maintenance of potassium selectivity under saline conditions. The salt tolerance mechanisms that operated in the remaining cultivars were similar to that of cv GC-72, as at first they excluded Na and Cl from the shoots, accumulating them in the roots; with longer treatment, the ability to regulate Na and Cl concentrations in the plant was lost only in the most salt sensitive cultivar (Volgogradskij), resulting in a massive influx of both ions into the shoot.The salt sensitivity of some tomato cultivars to salinity could be due to both the toxic effect of Na and Cl ions and nutritional imbalance induced by salinity, as plant growth was inversely correlated with Na and Cl contents and directly correlated with K and Ca contents. This study displays that there is not a single salt tolerance mechanism, since different physiological responses among tomato cultivars have been found.     

Effects of salinity and heat-shock on wheat seedling growth and content of carbohydrates,proteins and amino acids

The effects of salinity (0, 50, 100, 150, and 200 mM NaCl) and heat-shock (42°C) and their interactions on germination, seedling growth, and some relevant metabolic changes of two cultivars (cv. Giza 155 and cv. Stork) of wheat (Triticum vulgaris L.) were studied. Germination studies indicate that plants tolerated salinity up to 100 mM NaCl. The lengths of roots and shoots and their water content, as well as fresh and dry matter yield of cv. Giza 155 seedlings remained more or less unchanged up to 100 mM NaCl and of cv. Stork up to 50 mM NaCl. Salinity induced progressive increase in soluble carbohydrates, soluble proteins and proline in cv. Giza 155 and in soluble proteins, proline and other free amino acids in cv. Stork. However, under the higher salinity levels, in cv. Giza 155 increase in soluble carbohydrates was accompanied by lose in other free amino acids, whereas in cv. Stork an opposite effect was obtained. Heat-shock treatment (42°C for 24 h) induced a significant decrease in the final germination percentage, the shoot and root lengths, fresh matter yield and the water content. The dry matter yield of the two cultivars was considerably increased as compared with the corresponding treatments with NaCl only. Heat-shock treatment resulted in a significant increase, in the amount of soluble carbohydrates and proline in salt treated seedlings of both cultivars. The pattern of changes in amino acids was opposite to that of soluble proteins, indicating that the increase in soluble proteins was at the expense of other amino acids in cv. Giza 155 andvice versa in cv. Stork.     

Carbohydrate and Proline Contents in Leaves, Roots, and Apices of Salt-Tolerant and Salt-Sensitive Wheat Cultivars1

Intra-specific variations in nonstructural carbohydrates and free proline were determined in leaves, apices, roots, and maturing seeds of two salt-tolerant cultivars (CR and Kharchia-65) and one salt-sensitive cv. Ghods of spring wheat (Triticum aestivum L.) grown in sand culture at various levels of salinity (0, 100, 200, and 300 mM NaCl and CaCl₂ at 5 : 1 molar ratio) under controlled environmental conditions. The levels of leaf, apex, and root ethanol-soluble carbohydrates, fructans, starch, and proline increased in line with elevating level of salinity in all three cultivars under investigation. The contents of proline, soluble and insoluble carbohydrates in the apex increased to levels exceeding those in the leaves and roots. Soluble carbohydrate content of salt-sensitive cv. Ghods was higher in the leaves, apices, and roots and lower in the maturing seeds than in the other cultivars at all levels of salinity except at 300 mM. The results show considerable variation in the amount of soluble, insoluble sugars, and proline among plant tissues and wheat genotypes in response to salinity. Higher soluble carbohydrates and fructan in leaves, roots and maturing seeds of stressed plants indicate that their accumulation may help plant to tolerate salinity. Salt-sensitive cv. Ghods accumulated less soluble sugars in the maturing seeds and higher soluble sugars in the apices, which might be used as an indicator in screening wheat genotypes for salinity tolerance.     

Effect of water and salt stresses on growth, chlorophyll, mineral ions and organic solutes contents, and enzymes activity in mung bean seedlings

The experiment was made by using different concentrations of polyethylene glycol (PEG) or salt solutions to decrease the osmotic potential of the growth medium to reveal the response of mung bean (Vigna radiata) to water and salt stresses. No germination (emergence of the seedling) occurred at medium osmotic potential lower than -1.0 MPa in all treatments. It was found that the activity of α-amylase and protease, and contents of proline, saccharides and the soluble proteins decreased in the germinating seeds during 3-d stress. However, after 10-d stress, the contents of organic solutes and the activity of the hydrolytic enzymes increased. Growth, chlorophyll content and mineral uptake were also significantly reduced under stress. The seedlings under water stress induced by PEG were affected much more than under salinity. This may be due to the maintenance of a higher succulence under salt stress than under PEG-induced water stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanisms of salt tolerance and interactive effects of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> inoculation on maize cultivars grown under salt stress conditions

The present work has been performed to study the growth and metabolic activities of two maize cultivars (cv. 323 and cv. 324) which are shown to have different tolerances to salt stress and to determine the effects of inoculation with Azospirillum spp. Along with identifying the mechanisms of maize salt tolerance and the role of Azospirillum (growth promoting rhizobacteria) in elevating salinity stress conditions is examined Maize cv. 323 was the most sensitive to salinity, while cultivar 324 was the most resistant of the 12 maize cultivars tested. Cultivars differences were apparent with certain growth criteria as well as related metabolic activities. The lack of a negative response to increasing NaCl concentration for water content, dry matter yield and leaf area of cv. 324 up to a concentration of – 0.6 MPa indicated salt tolerance. While for cv. 323 there was a marked inhibitory effect of salinity on growth. In the tolerant cv. 324, soluble and total saccharides, soluble protein in shoots and total protein in roots increased with salinity stress. The sensitivity of cv. 323 however was associated with depletion in saccharides and proteins. Proline accumulation was higher and detected earlier at a lower salinity concentration in the salt sensitive cv. 323 comapred to the salt tolerant cv. 324. When salt stressed maize was inoculated with Azospirillum, proline concentration declined significantly. The present study showed, in general, that the concentration of most amino acid increased on exposure to NaCl as well as when inoculated with Azospirillum. The relatively high salt tolerance of cv. 324, compared with cv. 323 was associated with a significantly high K⁺/Na⁺ ratio. Azospirillum inoculation markedly altered the selectivity of Na⁺, K⁺ and Ca⁺⁺ especially in the salt sensitive cultivar cv. 323. Azospirillum restricted Na⁺ uptake and enhanced the uptake of K⁺ and Ca⁺⁺ in cv. 323. A sharp reduction in the activity of nitrate reductase and nitrogenase in shoots and roots of both cultivars was induced by salinity stress. This reduction in NR and NA activity was highly significant at all salinity concentrations. Azospirillum inoculation stimulated NR and nitrogenase activity in both shoots and roots of both cultivars. The differential effect of Azospirillum inoculation on maize cv. 323 and cv. 324 illustrates the different sensitivity of these two cultivars to stress, but still does not provide any clues as to the key events leading to this difference.     

Effect of kinetin on water relations,photosynthesis, respiration and chlorophyll and nucleic acid contents of wheat (Triticum aestivum L.) grown under salinity

The effect of kinetin (10 g m^-3) presowing seed soaking treatment on water relations, chlorophyll (Chl) and nucleic acid contents, and photosynthetic and respiration rates in wheat (Triticum aestivum L.) grown in a greenhouse under three salinity levels (i.e. 0,6 and 9 dS m^-1 ECe) was studied. Relative water content and osmotic potential showed a progressive decline with increase in the salinity but there was an increase in chlorophyll (a+b) content in the leaves. Salinity decreased RNA content and net photosynthetic and respiration rates. Seed soaking either in water or kinetin enhanced the relative water content of leaves but reduced osmotic potential under both saline and non-saline conditions.     

Investigation of the salt tolerance of new Polish bread and durum wheat cultivars

In some regions of the world, low annual precipitation necessitates irrigation of crop plants which usually leads to soil salinity. Due to climatic changes this effect is also expected in the countries of Central Europe, and so in Poland. The aim of the study was (1) to compare tolerance to salt stress of Polish Triticum aestivum cvs. ‘Bogatka’ and ‘Banderola’ with T. durum cv. ‘Komnata’ and breeding line 121, and (2) to indicate the physiological parameter/parameters most suitable for such comparison. The investigation was performed in two experiments. In the first one, the germination ability of caryopses and coleoptiles’ growth were estimated at 0–250 mM of NaCl. The second experiment was conducted on plants grown in a glasshouse in saline soil at 0–150 mM of NaCl for 6 weeks. Salt tolerance was evaluated on the basis of following parameters: chlorophyll fluorescence, net photosynthesis rate (P _N), transpiration rate (E), stomatal conductance (g _s), cell membrane permeability (EL), proline content, fresh weight (FW), dry weight (DW), and relative water content (RWC). Highest germination of caryopses of durum cultivars was recorded at all the salinity levels; however, their coleoptiles were shorter than coleoptiles of bread wheat cultivars. Analysis of chlorophyll fluorescence showed that applied salt doses did not disturb the light phase of photosynthesis in all cultivars under study. Plants of durum wheat showed the higher dissipation of energy excess at the level of the antenna chlorophyll (DIo/CSm) under salinity as compared to plants of bread wheat. Both ‘Komnata’ and line 121 showed stronger P _N reduction as an effect of salinity. A decline of P _N was closely connected with a decrease in g _s. The P _N correlated with a decrease in DW in all studied cultivars except ‘Bogatka’. Control plants of ‘Komnata’ and line 121 were characterized by higher EL and proline level than bread wheat cultivars. An increasing cell membrane permeability correlated with a decrease of RWC in ‘Banderola’ and ‘Komnata’. The content of proline under the increasing salinity correlated with changes of RWC in ‘Banderola’, ‘Komnata’ and line 121, which indicate protectoral role of proline against dehydration of tissue. Dry weight and RWC seem to be the parameters most useful in the salt-tolerance estimation of wheat plants. Taking into account the studied parameters ‘Banderola’ could be recognized as more salt tolerant, the degree of salinity tolerance of ‘Bogatka’ is the same as line 121, while ‘Komnata’ seems to be the most salt sensitive. The salt tolerance of T. aestivum and T. durum depends on the cultivar rather than the wheat species.     

Effects of Salinity on Chlorophyll Fluorescence and Photosynthesis of Barley (Hordeum Vulgare L.) Grown Under a Triple-Line-Source Sprinkler System in the Field

In flag leaves of four cultivars of barley (Hordeum vulgare L.) grown in the field under a triple-line-source sprinkler system, that produces a linear soil salinity gradient, a decrease in net carbon dioxide assimilation rate (P_N) and stomatal conductance for water vapour (gs) was found. These changes were related to salinity tolerance at moderate salinity. With increasing salinity, P_N was saturated at low irradiances and stomatal frequencies increased. A decrease in photosystem 2 (PS2) efficiency was not found in the field after dark adaptation even at high salinity. Salinity induced only small decreases in the actual PS2 efficiency at midday steady-state photosynthesis, indicating that the photosynthetic electron transport was little affected by salinity. Therefore, using PS2 efficiency estimates in attached leaves is probably not a useful tool to screen barley genotypes grown under saline conditions in the field for salinity tolerance. In contrast, excised flag leaves from high salinity plots, once in the laboratory, exhibited a decrease in the variable to maximum chlorophyll fluorescence ratio as compared to excised leaves from control plants. On the other hand, the PN rate might allow for a good discrimination between tolerant and non-tolerant cultivars. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth and proline accumulation in mungbean seedlings as affected by sodium chloride

Mungbean (Vigna radiata L. Wilczek cv. Sujata and cv. K851) seedlings were grown in paper towelins in dark under 0, 0.5, 1, 2 and 3 % (m/v) NaCl salinity. Germination percentage, shoot and root length, fresh mass of both cultivars decreased with salinity. Total soluble saccharides and proline accumulated in the root and shoot of salt stressed seedlings. The proline accumulation in the root was four to five times higher than that of the shoot of NaCl treated etiolated mungbean seedlings.     

Relative salinity tolerance of rice cultivars native to North East India: a physiological,biochemical and molecular perspective

Salinity is the second most prevalent abiotic stress faced by plants, and rice is not an exception. Through this study, it has been tried upon, to study the relative salinity tolerance of eight local varieties of North East India. Preliminary screening was based on their dose- and time-dependent physiological responses to salinity stress. Among the cultivars, Tampha was found to be relatively more tolerant, whereas MSE9 the most sensitive. To further ascertain their tolerance capacity, MDA and H₂O₂ content was determined, which also confirmed the tolerance level of the two cultivars. Histochemical assays for root plasma membrane integrity and leaf and root H₂O₂ and O₂ ^? content also showed more damage in Tampha in comparison to MSE9. Finally, gene expression analysis for Na⁺/K⁺ co-transporters, OsHKT2;1, OsHKT2;3 and OsHKT2;4, was performed to observe how the expression level of these transporters varies with the tolerance capacity of these two cultivars in leaves and roots under different time frames. The study reveals Tampha to be the most tolerant and MSE9 the most sensitive when compared to the other six screened cultivars for salinity stress.     

Growth,ionic response,and gene expression of shoots and roots of perennial ryegrass under salinity stress

Growth, ionic responses, and expression of candidate genes to salinity stress were examined in two perennial ryegrass accessions differing in salinity tolerance. The salinity tolerant (PI265349) and sensitive accessions (PI231595) were subjected to 75-mM NaCl for 14 days in a growth chamber. Across two accessions, salinity stress increased shoot dry weight and concentrations of malondialdehyde (MDA) and Na⁺ in the shoots and roots, but decreased shoot Ca²⁺ and root K⁺ concentrations. Salinity stress also increased root expressions of SOS1, PIP1, and TIP1. Plant height and chlorophyll content were unaffected by salinity stress in the tolerant accession but significantly decreased in the sensitive accession. Shoot MDA content did not change in the tolerant accession but increased in the sensitive accession. A more dramatic increase in Na⁺ was found in the roots of the sensitive accession. Relative to the control, salinity stress reduced expression of SOS1, NHX1, PIP1, and TIP1 in the shoots but increased expression of these genes in the roots of the tolerant accession. Expression levels of SOS1 increased in the roots and expression of NHX1 increased in the shoots but decreased in the roots of the sensitive accession under salinity stress. A decline in PIP1 expression in the shoots and dramatic increases in TIP expression in both shoots and roots were found in the sensitive accession under salinity stress. The results suggested maintenance of plant growth and leaf chlorophyll content, lesser Na⁺ accumulation in the roots, and lower lipid peroxidation in the shoots which could be associated with salinity tolerance. The decreased expressions of SOS1, NHX1, and TIP1 in the shoots, and increased expressions of NHX1 and PIP1 in the roots might also be related to salinity tolerance in perennial ryegrass.     

Contractile roots are the most sensitive organ in <Emphasis Type="Italic">Crocus sativus</Emphasis> to salt stress

Crocus sativus corms were grown in Perlite and watered by half-strength modified Hoagland nutrient solution containing 0, 50, 100, 150, 200 mM NaCl. Growth parameters and contents of proteins, proline, polyphenols, minerals and saccharides were studied in fibrous roots, contractile roots, corms and leaves. All plants remained alive and did not display any sign of foliar damage even at 200 mM NaCl. However, the salinity decreased growth, relative water content and increased contents of proline and Na⁺ in all organs. Total protein content was increased in corms and contractile roots but decreased in fibrous roots. Changes in protein pattern were also observed. Polyphenol content was increased by salinity in all organs except the leaves. As salinity increased, content of soluble saccharides decreased except in the contractile roots.     

Effects of salinity stress on some growth,physiological, biochemical parameters and nutrients in two pistachio (Pistacia vera L.) rootstocks

In the present study, effects of salinity stress were evaluated in the leaves and roots of two pistachio cultivars (Badami-Rize-Zarand (BZ) and Badami-e-Sefid (BS)). In overall, salinity negatively affects growth of both cultivars with more pronounced effects on BS. The physiological reason of the reduction could be attributed to some extent to more depletion of photosynthetic pigment in BS. In both cultivars, salinity increased proline content. Moderate and high salinities increased the soluble sugar contents in BZ. In both cultivars, Na⁺ content increased in plant organs with increasing Na⁺ in the media. Salinity treatment decreased the Fe and Pi contents in BS cultivar, while they remained unchanged in BZ. These results show that BZ cultivar exhibits more tolerance to salinity stress than BS cultivar possibly by better growth performance, accumulating more osmolytes, lesser accumulation of toxic sodium ion and lower Na⁺/K⁺ in the shoots as well as maintaining nutrient contents.     

Effects of cytokinin on photosynthetic gas exchange, chlorophyll fluorescence parameters, antioxidative system and carbohydrate accumulation in cucumber (Cucumis sativus L.) under low light

The effects of 6-benzylaminopurine (6-BA) on plant growth, net photosynthetic rate, relative chlorophyll content, soluble protein, carbohydrates contents and antioxidant systems of cucumber (Cucumis sativus L.) under low-light environment were investigated using two different cucumber cultivars. The results showed that the weak light resulted in the remarkable decrease in plant net photosynthetic rate, relative chlorophyll content, soluble protein and carbohydrates contents, but promoted the superoxide dismutase and guaiacol peroxidase activities. However, application of 6-BA alleviated the reduction of the correlative parameters and mediated the changes of antioxidant systems. The potential mechanisms may involve the following aspects: 6-BA clearly enhanced the plants’ tolerance to low light by increasing chlorophyll content, reducing the production of superoxide radical (O ₂ ^·? ), and enhancing the quenching of hydrogen peroxide (H₂O₂), consequently alleviating the injury of photosynthetic system, and further increasing the efficiency of CO₂ assimilation, producing more carbohydrates which can meet the growth need of cucumber. Meanwhile, the present study indicated that cucumber of Europe mini type (Chunqiuwang) was more tolerant to low light than HuaNan type (Huza No.3).