Photosynthetic capacity is related to the cellular and subcellular partitioning of Na+, K+ and Cl- in salt-affected barley and durum wheat

The capacity of plants to tolerate high levels of salinity depends on the ability to exclude salt from the shoot, or to tolerate high concentrations of salt in the leaf (tissue tolerance). It is widely held that a major component of tissue tolerance is the capacity to compartmentalize salt into safe storage places such as vacuoles. This mechanism would avoid toxic effects of salt on photosynthesis and other key metabolic processes. To test this, the relationship between photosynthetic capacity and the cellular and subcellular distribution of Na+, K+ and Cl- was studied in salt-sensitive durum wheat (cv. Wollaroi) and salt-tolerant barley (cv. Franklin) seedlings grown in a range of salinity treatments. Photosynthetic capacity parameters (Vcmax, Jmax) of salt-stressed Wollaroi decreased at a lower leaf Na+ concentration than in Franklin. Vacuolar concentrations of Na+, K+ and Cl- in mesophyll and epidermal cells were measured using cryo-scanning electron microscopy (SEM) X-ray microanalysis. In both species, the vacuolar Na+ concentration was similar in mesophyll and epidermal cells, whereas K+ was at higher concentrations in the mesophyll, and Cl- higher in the epidermis. The calculated cytoplasmic Na+ concentration increased to higher concentrations with increasing bulk leaf Na+ concentration in Wollaroi compared to Franklin. Vacuolar K+ concentration was lower in the epidermal cells of Franklin than Wollaroi, resulting in higher cytoplasmic K+ concentrations and a higher K+ : Na+ ratio. This study indicated that the maintenance of photosynthetic capacity (and the resulting greater salt tolerance) at higher leaf Na+ levels of barley compared to durum wheat was associated with the maintenance of higher K+, lower Na+ and the resulting higher K+ : Na+ in the cytoplasm of mesophyll cells of barley.     

Additive effects of Na+ and Cl- ions on barley growth under salinity stress

Soil salinity affects large areas of the world's cultivated land, causing significant reductions in crop yield. Despite the fact that most plants accumulate both sodium (Na(+)) and chloride (Cl(-)) ions in high concentrations in their shoot tissues when grown in saline soils, most research on salt tolerance in annual plants has focused on the toxic effects of Na(+) accumulation. It has previously been suggested that Cl(-) toxicity may also be an important cause of growth reduction in barley plants. Here, the extent to which specific ion toxicities of Na(+) and Cl(-) reduce the growth of barley grown in saline soils is shown under varying salinity treatments using four barley genotypes differing in their salt tolerance in solution and soil-based systems. High Na(+), Cl(-), and NaCl separately reduced the growth of barley, however, the reductions in growth and photosynthesis were greatest under NaCl stress and were mainly additive of the effects of Na(+) and Cl(-) stress. The results demonstrated that Na(+) and Cl(-) exclusion among barley genotypes are independent mechanisms and different genotypes expressed different combinations of the two mechanisms. High concentrations of Na(+) reduced K(+) and Ca(2+) uptake and reduced photosynthesis mainly by reducing stomatal conductance. By comparison, high Cl(-) concentration reduced photosynthetic capacity due to non-stomatal effects: there was chlorophyll degradation, and a reduction in the actual quantum yield of PSII electron transport which was associated with both photochemical quenching and the efficiency of excitation energy capture. The results also showed that there are fundamental differences in salinity responses between soil and solution culture, and that the importance of the different mechanisms of salt damage varies according to the system under which the plants were grown.     

Nutrient uptake and management under saline conditions in the xerohalophyte: Tecticornia indica (Willd.) subsp. indica

In the present investigation, we studied uptake and management of the major cations in the xerohalophyte, Tecticornia indica (Willd.) subsp. indica as subjected to salinity. Plants were grown under greenhouse conditions at various salinity levels (0, 100, 200 and 400 mM NaCl) over 110 days. At harvest, they were separated into shoots and roots then analyzed for water contents, dry weights (DW), and Na+, K+, Ca2+, and Mg2+ contents. Plants showed a growth optimum at 200 mM NaCl and much better tissue hydration under saline than non-saline conditions. At this salt concentration (200 mM NaCl), shoot Na+ content reached its highest value (7.9 mmol · g-?1 DW). In spite of such stressful conditions, salt-treated plants maintained adequate K+, Ca2+, and Mg2+ status even under severe saline conditions. This was mainly due to their aptitude to selectively acquire these essential cations and efficiently use them for biomass production.     

Modification of the response of saline stressed tomato plants by the correction of cation disorders

The interactions between NaCl and other major nutrients have been generally observed in plants. Decreases of nutrient uptake under saline conditions normally appear in tomato plants grown under saline conditions. In this work, the effect of increased external Ca, K and Mg concentrations under saline conditions has been investigated. Tomato plants (Lycopersicon esculentum, Mill) were grown in a greenhouse, in 120 L capacity containers, filled with continuously aerated Hoagland nutrient solution. Treatments were added to observe the combined effect of two NaCl levels (30 and 60 mM) and three levels of Ca, K and Mg (in mM ratios of 4:6:1, 7:9:2 and 10:12:3; treatments C₁, C₂ and C₃ respectively) on growth, fruit yield and water relations. Saline treatments decreased the growth, which was partly restored with the C₂ treatment and totally with the C₃ treatment. A good association was observed between the electric conductivity of the medium and the water or osmotic potential of the leaves, independent of the type of treatment (salinity or cation ratio). Salinity at 30 and 60 mM NaCl reduced the fruit yield compared with that obtained at 0 mM NaCl. However, there was an increase, as a consequence of the application of treatments C₂ and C₃, in each saline treatment. At a high salinity level (60 mM), the ratios Na/K, Na/Ca and Na/Mg in young leaves decreased as a consequence of cation treatments. Higher concentrations of sugars in leaves and fruits were obtained after increasing the salinity and cation concentrations. Also, sucrose phosphate synthase activity in leaves and fruits was increased after the treatments, but there was no measurable invertase activity in fruits. Therefore, the concentrations of Ca, K and Mg in the nutrient solution could be important factors in the hydroponic culture of tomato grown under saline conditions.     

Effects of Salinity on the Extensibility and Ca Availability in the Expanding Region of Growing Barley Leaves

The growth of barley (Hordeum vulgare L.) leaves is reduced by salinity. We used the Instron extensometric technique to measure the reversible and irreversible compliance of the expanding regions of growing barley leaves from plants exposed to 1, 40, 80 and 120 mM NaCl in nutrient solution. Two barley cultivars differing in salinity resistance (cv ‘Arivat’ and cv ‘Briggs’) were compared over 5d of leaf growth. During the period of most active leaf expansion, salinity reduced reversible compliance and increased compliance in the leaf segments, although responses to salinity were complex and changed over the course of leaf expansion. Salinity increased irreversible compliance more in the salt-sensitive cultivar Arivat than in the more salt-tolerant cultivar Briggs. Elemental analysis of the basal leaf segments used for extensometry revealed an accumulation of Na and a depletion of Ca in segments from salinized plants, resulting in very high Na: Ca ratios in salinized expanding tissue. The concentrations of K and Mg in basal leaf tissue were elevated by salinity. Our data do support the hypothesis that the inhibition of leaf expansion by salinity stress is mediated by a decline in irreversible extensibility. We suggest that reduced Ca availability in expanding leaf tissue may contribute to growth reduction in salt-stressed barley seedlings.     

Ion allocation in two different salt-tolerant Mediterranean Medicago species

The relationship between Na+, major cation concentrations and salt tolerance under long-term saline conditions of Medicago arborea and Medicago citrina was studied. Plants were grown in solution culture in 1, 50, 100, or 200 mmol/L NaCl for 30 days in a climate-controlled greenhouse. Stem and petiole growth was the most affected by salt in both species. Leaf growth was inhibited in M. arborea, with increased salt, while only the 200 mmol/L NaCl-treated M. citrina plants were significantly affected. Both species had the highest Na+ concentrations in the shoots, however, the allocation pattern was different; M. arborea showed the highest concentrations in the leaf blades, whereas M. citrina distributed the salt into the petioles. K+/Na+ ratio decreased with salt in both species; however, leaf K+ use efficiency (g leaf DW mg-1 leaf K+) was higher in M. citrina. The difference in Na+ allocation and cation concentrations found in these medic species and their importance is discussed in relation to their response to NaCl salinity.     

Effects of sodium chloride stress and calcium supply on growth, potassium uptake, and internal chloride and sodium levels of winter wheat seedlings

The effects of saline conditions on the K+ (86Rb), Na+ and Cl- uptake and growth of 6-day-old wheat (Triticum aestivum L. cv. GK Szeged) seedlings were studied in the absence and presence of Ca2+. It was found that on direct NaCl treatment the K+ uptake of the roots in the absence of Ca2+ declined significantly with increasing salinity. The reverse was true, however, in the case of NaCl pretreatment: seedlings grown under highly saline conditions (50 mM NaCl) absorbed more K+ than those pretreated with low levels of NaCl (1 or 10 mM NaCl). The data indicate a definite Na(+)-induced K+ uptake inhibition and/or feed-back regulation in the K+ uptake of roots under the above-mentioned growth conditions. As regards the Ca2+ effect, it was established that supplemental Ca2+ counteracts the unfavourable effect of saline conditions as concerns both the K+ uptake of the roots and the dry matter yield of the seedlings. The internal concentrations of Na+ and Cl- in the seedlings increased in proportion to increasing salinity. Marked differences were experienced, however, in the internal concentrations of Na+ and Cl- in the roots and shoots, respectively. It was concluded that under these experimental conditions the salt tolerance of wheat could be related to its capability of restricting the transport of Na+ at low and moderate levels to the shoots, where it is highly toxic.     

Enhancement of nitrate uptake and growth of barley seedlings by calcium under saline conditions

The effect of Ca2+ on NO3- assimilation in young barley (Hordeum vulgare L. var CM 72) seedlings in the presence and absence of NaCl was studied. Calcium increased the activity of the NO3- transporter under saline conditions, but had little effect under nonsaline conditions. Calcium decreased the induction period for the NO3- transporter under both saline and nonsaline conditions but had little effect on its apparent Km for NO3- both in the presence and absence of NaCl. The enhancement of NO3- transport by Ca2+ under saline conditions was dependent on the presence of Ca2+ in the uptake solution along with the salt, since Ca2+ had no effect when supplied before or after salinity stress. Although Mn2+ and Mg2+ enhanced NO3- uptake under saline conditions, neither was as effective as Ca2+. In longer studies, increasing the Ca2+ concentration in saline nutrient solutions resulted in increases in NO3- assimilation and seedling growth.     

CHARACTERISTICS OF SALTS SECRETED BY TAMARIX APHYLLA

The composition and concentration of salts secreted by the salt glands of Tamarix aphylla L. grown under controlled nutrient conditions were determined. Eight ions, Na, K, Mg, Ca, Cl, NO₃, HCO₃, and SO₄, constituted 99 % + of the dry weight of salts secreted by plants grown on half-strength Hoagland's solution. The divalent cations Mg and Ca accounted for most of the cations; HCO₃ comprised about 60 % of the anions. The micronutrients B, Mn, Cu, Zn, and Mo were present in enriched concentrations in the secretion. The composition of the secretions was highly dependent on the composition of the root environment. The predominating cation in the saline culture solutions was also the predominant cation secreted. The accompanying anion in the culture solution influences the cation composition of the secreted salt. The concentration of the salt gland secretion averaged 0.5n , a 50-fold increase in concentration over the nutrient solution in which the plants were grown.     

Effect of salinity on growth, ion content, and cell wall chemistry in Atriplex prostrata (Chenopodiaceae)

Atriplex prostrata Boucher, a facultative halophyte, exhibits significant reduction in height and biomass and in the width of the cortex and vascular tissue under saline conditions. Therefore, the goal of this investigation was to determine the effect of salinity on plant growth as well as on the patterns of lignification, peroxidase activity, and extensin deposition. Biomass, leaf area, internode length, water potential, photosynthesis, transpiration, and ion content were measured. In addition, lignin, peroxidase, and extensin were, respectively, examined via phloroglucinol staining, peroxidase staining, and immunostaining with extensin antibody on tissue prints of free-hand stem sections. Length of internodes and leaf area significantly decreased with increased salinity, and net photosynthesis declined dramatically as well. There was a significant accumulation of Na+ in organs when plants were grown in saline solutions, while the concentration of K+, Ca2+, and Mg2+ decreased. The signals in tissue prints showed that soluble peroxidase and extensin accumulated in the first three internodes of A. prostrata grown under saline conditions. In contrast, lignification was reduced under saline growth conditions in the third and fourth internodes. These results indicate that extensin may replace lignin in providing mechanical support for cells, while stems remain in a juvenile stage because of growth retardation caused by salinity.     

Separating multiple, short-term, deleterious effects of saline solutions on the growth of cowpea seedlings

? Reductions in plant growth as a result of salinity are of global importance in natural and agricultural landscapes. ? Short-term (48-h) solution culture experiments studied 404 treatments with seedlings of cowpea (Vigna unguiculata cv Caloona) to examine the multiple deleterious effects of calcium (Ca), magnesium (Mg), sodium (Na) or potassium (K). ? Growth was poorly related to the ion activities in the bulk solution, but was closely related to the calculated activities at the outer surface of the plasma membrane, {I(z)}?°. The addition of Mg, Na or K may induce Ca deficiency in roots by driving {Ca2+}?° to < 1.6 mM. Shoots were more sensitive than roots to osmolarity. Specific ion toxicities reduced root elongation in the order Ca2+ > Mg2+ > Na+ > K+. The addition of K and, to a lesser extent, Ca alleviated the toxic effects of Na. Thus, Ca is essential but may also be intoxicating or ameliorative. ? The data demonstrate that the short-term growth of cowpea seedlings in saline solutions may be limited by Ca deficiency, osmotic effects and specific ion toxicities, and K and Ca alleviate Na toxicity. A multiple regression model related root growth to osmolarity and {I(z)}?° (R2=0.924), allowing the quantification of their effects.     

盐胁迫下柚和橘幼苗体内矿质元素变化的比较研究

采用沙培法,对盐胁迫下坪山柚和福橘幼苗体内矿质元素的变化进行了研究。结果表明,随着NaCl浓度的增加,坪山柚和福橘幼苗根部及地上部Na^＋、Cl-含量增加,且相同浓度下,福橘比坪山柚高。40mmol／L NaCI胁迫下,坪山柚和福橘幼苗地上部的K^＋、Fe含量,根部的Ca^2＋、Mg^2＋、Zn含量显著下降,而根部Fe含量及地上部Zn含量显著增加。随NaCl浓度增大,坪山柚根部K^＋含量,地上部Ca^2＋、Mg^2＋含量变化不明显,而福橘根部、地上部上述离子含量在NaCl浓度≥160mmol／L时均显著下降。因此,根部K^＋含量,地上部Ca^2＋、Mg^2＋含量存在品种问差异,或许可作为耐盐性鉴定指标。NaCl胁迫降低坪山柚和福橘幼苗根部及地上部P、Mn含量,而Cu含量在较高浓度NaCl胁迫下显著增加。NaCl胁迫明显降低坪山柚和福橘幼苗地上部K^＋／Na^＋、Ca^2＋／Na^＋和Mg^2＋／Na^＋值,其中K^＋／Na^＋值的变化可考虑作为柑橘耐盐性鉴定的指标。     

Silicon improves salinity tolerance in wheat plants

Durum wheat (Triticum durum cv. Gediz-75) and bread wheat (Triticum aestivum cv. Izmir-85) were grown in a complete nutrient solution in a growth room to investigate effect of silicone supplied to the nutrient solution on plants grown at salt stress. The experiment was a 2 × 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicone (Si) in nutrient solution, 0.25 and 0.50 mM, as Na₂SiO₃. The plants grown at 100 mM NaCl produced less dry matter and chlorophyll content than those without NaCl. Supplementary Si at both 0.25 and 0.5 mM ameliorated the negative effects of salinity on plant dry matter and chlorophyll content. Membrane permeability and proline content in leaves increased with addition of 100 mM NaCl and these increases were decreased with Si treatments. Sodium (Na) concentration in plant tissues increased in both leaves and roots of plants in the high NaCl treatment and Si treatments lowered significantly the concentrations of Na in both leaves and roots. Bread wheat was more tolerant to salinity than durum wheat. The accumulation of Na in roots indicates a possible mechanism whereby bread wheat copes with salinity in the rooting medium and/or may indicate the existence of an inhibition mechanism of Na transport to leaves. Concentrations of both Ca and K were lower in the plants grown at high NaCl than in those in the control treatment and these two element concentrations were increased by Si treatments in both shoots and roots but remained lower than control values in most cases.     

Macro nutrient cation uptake by plants

Summary In pot experiments with barley, mustard, leek, lettuce and spinach, and in a field experiment with 30 cultivars of barley uptakes of K, Mg, Ca, Na and N were studied at varying concentrations and activities of these cations in the soil solution.The sum of macro cations (K, Mg, Ca, Na) in meq per 100 g aerial plant parts were independent of the chemical composition of the soil solution, but dependent on plant species and on the N concentration in the plant.The ratios of mean net inflows of Mg, Ca and K into plants and corresponding cation activity ratios (a_Mg/a_Ca and ) in the soil solution were linearly related and highly correlated under conditions in which growth rate and/or rate of incorporation into new tissues constituted the rate determining step of cation uptake. Consequently, mean net inflows of K, Mg and Ca were independent of ion concentration and ion activity of K, Mg or Ca in the soil solution under the conditions of constant activity ratio.The results agree with the concept that plants have a finite cation uptake capacity, and that plants are in a equilibrium-like state with the activities of K, Mg, and Ca ions in the soil solution. The results indicate that both ratios and content of exchangeable cations should be considered in our evaluation of soil test data.     

盐胁迫对弗吉尼亚栎生长及矿质离子吸收、运输和分配的影响

以低浓度(50 mmol.L-1)和高浓度(150 mmol.L-1)NaC l处理弗吉尼亚栎(Quercus virginiana)2年生扦插苗,研究了弗吉尼亚栎生长和根系形态学参数变化以及Na+、K+、Ca2+、Mg2+、NO3-等矿质离子在不同器官的吸收、运输和分配。结果表明,盐胁迫不同程度促进了地上部和根系生长,地上部和根系干重、根长、表面积和体积在低浓度盐胁迫下明显增加(P0.05),而在高浓度盐胁迫下变化不大。随着根系对Na+和C l-吸收的增加,K+、Ca2+、Mg2+在根部和茎部的积累明显降低,矿质离子由根部向茎部运输的能力在低浓度盐胁迫增加而高浓度下受到抑制。叶片在低浓度和高浓度盐胁迫下对K+、NO3-具有很强的选择吸收能力,这对于维持叶片离子平衡和正常的光合作用及代谢过程具有重要意义。Na+和C l-在根部的浓度远远大于地上部,说明弗吉尼亚栎根系对盐离子具有较高的耐受性,而减少盐离子在地上部的积累,对于维持地上部的正常生长具有重要意义,这也是弗吉尼亚栎对盐胁迫的适应机制之一。     

REGULATION OF NaCl IN JAUMEA CARNOSA (ASTERACEAE), A SALT MARSH SPECIES,AND ITS EFFECT ON LEAF SUCCULENCE

A salt marsh species, Jaumea carnosa, was used in hydroponic experiments to test the effects of increasing NaCl concentrations on leaf succulence and plant accumulations of K, Ca, Mg, Na and Cl. A nested experimental design was used with four salinity levels. Plants were grown in full Hoagland's solution plus different amounts of NaCl (0.0–1.2 osmoles). Leaf succulence was measured as percent water content as well as vertical elongation of mesophyll cells. There were no corresponding increases in leaf succulence with increasing concentrations of NaCl in the root zone. Plants receiving aerosol spray (40 mg/dm²/day) did not show significant increases in leaf succulence. Leaf succulence was significantly increased when the plants were removed from the NaCl solutions and placed in non-salinized Hoagland's solution. Osmotic concentrations of cell sap in leaf tissues showed significant increases as NaCl concentrations increased in the root zone. The concentrations of K, Ca and Mg were higher in plants grown without NaCl than in those grown with NaCl. The accumulations of K in the root tissues were always higher than those of the shoot tissues. Although there was a two-fold difference in NaCl concentrations at the highest levels, the concentrations of Na in the shoot tissues were relatively similar. The results of the Cl analyses of shoot tissues showed a similar pattern of regulation of uptake. This regulation of salt uptake may be important in preventing injury by limiting accumulations of salt in plant tissues when growing in soils of high osmotic potentials.     

土壤盐度对加拿利海枣幼苗生长与生理指标的影响

将加拿利海枣(Phoenix canariensis Hort. ex Chab.)幼苗培养在不同盐度(1.2~14.5)的土壤中,探讨土壤含盐量对其生长及生理指标的影响。结果表明:随基质盐度的提高,幼苗新生叶片数降低且叶片死亡数增加。随基质盐度的提高,叶绿素含量增加,叶绿素a/b在低盐度时增加而当盐度超过5.1时下降。土壤盐度在1.2~5.1时,MDA含量约为4.30 μmol g^-1,以后随土壤盐度的升高而升高。SOD活性在低盐时升高,土壤盐度超过10.8时,SOD活性迅速下降。盐胁迫下叶片Na⁺和Cl^-含量升高,K⁺、Ca²⁺、Mg²⁺含量及K⁺/Na⁺下降。盐胁迫导致加拿利海枣生长下降的主要原因是叶片有效光合面积减少,离子平衡破坏。这些表明加拿利海枣具有很高的耐盐能力,其幼苗在土壤盐度5.1时生长正常,当土壤盐度为10.8时才开始出现受害症状,适宜在滨海地区推广应用。     

Growth and ionic relations of six triticale cultivars as affected by salinity

Growth and ionic relations were studied in six triticale cultivars of different geographical origins grown in a greenhouse in nutrient solution with or without the addition of 100 mM NaCl. In 21 d old plants of all the six cultivars growth was little affected in the salt treatment, whereas in the subsequent three harvests during vegetative phase (after 31, 38 and 45 d), growth reduction effects of salinity were progressively pronounced. Generally, shoots of all the six cultivars accumulated relatively more K+ as compared to Na+ or Cl-. Differential accumulation of K+, Na+ and Cl- by various cultivars was coupled with variable rates of Na+ and Cl- transport from root to shoot which were — to some extent- related to cultivar differences in growth in saline root media. Chloride content of shoots of the six cultivars was negatively correlated with the relative growth reduction due to salinity at the four harvests.