José Tarquinio Prisco

Solute accumulation and distribution during shoot and leaf development in two sorghum genotypes under salt stress

Abstract Seedlings of two forage sorghum genotypes (Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na+ and Cl−), organic solutes (carbohydrates, amino acids and proline), and reduction of K+ content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size. All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K+ ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance.

Effects of salt stress on plant growth, stomatal response and solute accumulation of different maize genotypes

Seeds from eight different maize genotypes (BR3123, BR5004, BR5011, BR5026, BR5033, CMS50, D766 and ICI8447) were sown in vermiculite, and after germination they were transplanted into nutrient solution or nutrient solution containing 100 mmol.L-1 of NaCl and placed in a greenhouse. During the experimental period plant growth (dry matter, shoot to root dry mass ratio, leaf area, relative growth rate, and net assimilation rate), leaf temperature, stomatal conductance, transpiration, predawn water potential, sodium, potassium, soluble amino acids and soluble carbohydrate contents were determined in both control and salt stressed plants of all genotypes studied. Salt stress reduced plant growth of all genotypes but the genotypes BR5033 and BR5011 were characterized as the most salt-tolerant and salt-sensitive, respectively. Stomatal response of the salt-tolerant genotype was not affected by salinity. Among the studied parameters, shoot to root dry mass ratio, leaf sodium content and leaf soluble organic solute content showed no relation with salt tolerance, i.e., they could not be considered as good morpho-physiological markers for maize salt tolerance. In contrast, sodium and soluble organic solutes accumulation in the roots as a result of salt stress appeared to play an important role in the acclimation to salt stress of the maize genotypes studied, suggesting that they could be used as physiological markers during the screening for salt tolerance.

Physiological responses of NaCl stressed cowpea plants grown in nutrient solution supplemented with CaCl2

Pitiuba cowpea (Vigna unguiculata (L.) Walp.) plants were grown in nutrient solution and kept in a greenhouse up to pre-flowering stage. They were subjected to four different treatments: nutrient solution; nutrient solution containing 75 mmol.L-1 NaCl; nutrient solution containing 75 mmol.L-1 NaCl and 5 mmol.L-1 CaCl2; and nutrient solution containing 75 mmol.L-1 NaCl and 10 mmol.L-1 CaCl2. Salt stress strongly inhibited plant growth, caused a disturbance in plant-water balance, and increased the total content of inorganic solutes in the different plant parts, due mainly to accumulation of Na+ and Cl-. It also increased leaf and root soluble carbohydrates, reduced soluble amino nitrogen both in root tips and in the youngest trifoliate leaves, and reduced proline levels in root tips. Although the addition of CaCl2 to the root environment of salt stressed plants caused a reduction in Na+ content, specially in roots, it did not ameliorate the salt stress effects on plant-water relations and growth. Therefore, the results obtained do not support the hypothesis that supplemental calcium would ameliorate the inhibitory effects of NaCl-stress.

Acumulação de biomassa e extração de nutrientes por plantas de feijão-de-corda irrigadas com água salina em diferentes estádios de desenvolvimento

Due to the limited availability of low salinity waters, the use of water of moderate to high salinity in agriculture is a close reality in the expansion of irrigated farms. The objective of this research was to evaluate the effect of irrigation with saline water, applied at different development stages of cowpea plants, on growth and nutrient uptake. The experiment was set up in the field during the dry season. A completely randomized block design, with five treatments and five replications was adopted. The treatments studied were: T1 - groundwater with electrical conductivity (ECw) of 0.8dS m-1 during the whole crop cycle; T2 - saline water (ECw = 5.0dS m-1) during the whole crop cycle; T3, T4 and T5 - saline water from 0 to the 22nd day after sowing (DAS), from the 23rd to the 42nd DAS and from the 43rd to 62nd DAS, respectively. The plants subjected to T3, T4 and T5 were irrigated with groundwater in the other stages of the crop cycle. At 8, 23, 43 and 63DAS plants were collected for evaluation of plant growth, Na, Cl, K, Ca, N, P, Fe, Cu, Zn and Mn contents and distribution in plant parts. The application of saline water during the whole crop cycle (T2) and during the germination and initial plant development (T3) caused, respectively, inhibition and retardation of plant growth. Cowpea plants removed the minerals in the following decreasing sequence: N > K > Cl > Ca > Na > P > Fe > Mn > Zn > Cu, but the continuous use of saline water (T2) reduced the total uptake of all nutrients, except for Na. The minerals Na, Cl, K, Ca, Fe and Mn were distributed preferentially in the vegetative parts of the plant, while most of the N and P were translocated to the pods.

Crescimento e níveis de solutos orgânicos e inorgânicos em cultivares de Vigna unguiculata submetidos à salinidade

Os efeitos da salinidade no crescimento e nos teores de solutos orgânicos e inorgânicos foram analisados em sete cultivares de Vigna unguiculata. As plantas foram cultivadas em solucao nutritiva sem NaCl (controle) e com NaCl a 75 mM (estresse salino), em casa de vegetacao. Apos 14 dias da semeadura, adicionou-se 25 mM de sal diariamente, durante tres dias, perfazendo o total de 75 mM. A coleta foi realizada no 33o dia. A salinidade reduziu a materia seca de todos os cultivares, sendo Pitiuba e Vita 5 os menos afetados e TVU o que sofreu maior reducao. A suculencia foliar e o indice de esclerofilia foram concordantes com o grau de tolerância, aumentando significativamente, em funcao da salinidade, apenas nos cultivares com menores reducoes nas materias secas. Contrariamente, a relacao raiz/parte aerea teve maior aumento nos cultivares mais afetados. Os teores de Na+ e Cl- foliares aumentaram em resposta ao estresse salino, sendo o Na+ acumulado em niveis maiores nos cultivares mais afetados, especialmente no TVU. Os niveis de K+ foliar, que se mostraram mais elevados que os de Na+ e Cl-, foram poucos afetados pela salinidade, de modo que a relacao Na+/K+ aumentou mais nos cultivares mais afetados e, possivelmente, se constituiu num fator importante para a maior reducao em seus crescimentos. As variacoes nos teores de prolina, carboidratos soluveis e N-aminossoluveis em resposta a salinidade indicam uma falta de proporcionalidade entre seus niveis e o grau de tolerância a salinidade nos cultivares de feijao-de-corda estudados.

Catalase plays a key role in salt stress acclimation induced by hydrogen peroxide pretreatment in maize.

Pretreatment in plants is recognized as a valuable strategy to stimulate plant defenses, leading to better plant development. This study evaluated the effects of H₂O₂ leaf spraying pretreatment on plant growth and investigated the antioxidative mechanisms involved in the response of maize plants to salt stress. It was found that salinity reduced maize seedling growth when compared to control conditions, and H₂O₂ foliar spraying was effective in minimizing this effect. Analysis of the antioxidative enzymes catalase (EC 1.11.1.6), guaiacol peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.1) and superoxide dismutase (EC 1.15.1.1) revealed that H₂O₂ spraying increased antioxidant enzyme activities. Catalase (CAT) was the most responsive of these enzymes to H₂O₂, with higher activity early (48 h) in the treatment, while guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) were responsive only at later stages (240 h) of treatment. Increased CAT activity appears linked to gene expression regulation. Lower malondialdehyde levels were detected in plants with higher CAT activity, which may result from the protective function of this enzyme. Overall, we can conclude that pretreatment with H₂O₂ leaf spraying was able to reduce the deleterious effects of salinity on seedling growth and lipid peroxidation. These responses could be attributed to the ability of H₂O₂ to induce antioxidant defenses, especially CAT activity.

Antioxidant-enzymatic system of two sorghum genotypes differing in salt tolerance

Two forage sorghum genotypes were studied: CSF18 (salt-sensitive) and CSF20 (salt-tolerant). Shoot growth reduction as a result of salt stress was stronger in the salt sensitive genotype compared to the salt tolerant one. When the two genotypes were subjected to salt stress (75 mM NaCl) no significant change in lipid peroxidation was observed. However, salt stress induced increases in superoxide dismutase and catalase activities in both genotypes. These salt-induced increases were higher in the salt-tolerant genotype. Peroxidase activity was differentially affected by salt stress in the two genotypes. The activities of these peroxidases were decreased by salt stress in the salt-sensitive genotype and increased in the salt-tolerant genotype. In addition, the activity ratio between the superoxide dismutase and the H2O2-scavenging enzymes was higher in the salt-sensitive genotype. The results obtained support the hypothesis that the higher efficiency of the antioxidant-enzymatic system of the CSF20 genotype could be considered as one of the factors responsible for its tolerance to salt stress. Therefore, it is suggested that the ratio between superoxide dismutase and H2O2-scavenging enzyme activities could be used as a working hypothesis for a biochemical marker for salt tolerance in sorghum.

Physiology of cashew plants grown under adverse conditions

The cashew (Anacardium occidentale L.) is an important crop for semi-arid agriculture and contributes to the social and economical development of several world regions, including the northeast of Brazil. In spite of its importance, very few studies aim to understand the effects of abiotic stresses on the development and yield of the cashew. This review covers the research on cashew ecophysiology, with emphasis on the effects of water and salt stress on its development, mineral nutrition and gas exchange processes. The results presented here were obtained at different plant growth stages and under different environmental conditions of soil and climate. The ecophysiological significance of this information is also discussed.

Morpho-physiological responses of cowpea leaves to salt stress

The effect of salt stress of known intensity and duration on morpho-physiological changes in leaves of different ages from cowpea [Vigna unguiculata (L.) Walp.] plants was studied, aiming for a better understanding of the acclimation process of the whole-plant. Seeds were sown in vermiculite and seedlings were transferred to plastic trays containing aerated nutrient solution, and kept in a greenhouse. When the first trifoliate leaf emerged the seedlings were transplanted into 3 L plastic pots containing aerated nutrient solution. Salt additions started 5 d later, and the salt-treated plants received 25 mmol L-1 per day until reaching a final concentration of 75 mmol L-1. During the experimental period primary leaves and the 1st, 2nd, and 3rd trifoliate leaves were used for measurements of net photosynthesis, leaf area, leaf succulence, specific leaf mass, ions and chlorophyll concentrations. Growth analysis of the whole-plant was performed at the end of the experimental period. Salinity did not affect net photosynthesis, but reduced dry mass production and the number of lateral branches. Leaf concentrations of Na+, Cl-, K+ and P increased in salt-stressed plants, but these responses were dependent upon stress duration and leaf age. The higher concentration of potentially toxic ions (Na+ and Cl-) in older leaves could contribute to the reduced ion accumulation in growing tissues, but the tendency of K and P accumulation in leaves appeared to be the result of reduced re-translocation, i.e., not related to plant acclimation. Salinity also increased the source/sink ratio, leaf succulence, specific leaf mass, and chlorophyll accumulation per unit of leaf area, suggesting that the observed changes could be part of an integrated mechanism of whole-plant acclimation to salt stress.

Physiological and biochemical changes occurring in dwarf-cashew seedlings subjected to salt stress

The effects of salt stress on some physiological and biochemical traits were evaluated in dwarf-cashew seedlings at the same developmental stage. Seeds were sown in trays containing vermiculite moistened with distilled water or with NaCl solutions having different electrical conductivities: 0.7, 1.8, 6.0, 9.8, 13.4, 17.4 and 20.6 dS m-1. Salinity delayed and inhibited seedling growth and development, particularly in the shoot. Concentrations of Na+ and Cl-, but not of K+, increased with increasing stress severity. With the exception of proline, concentration of organic solutes was only marginally affected by salt stress. Catalase activity in leaves increased slightly as a result of salt stress, whereas guaiacol peroxidase activity was induced only under low levels of salt. In contrast, activities of guaiacol peroxidase and ascorbate peroxidase increased dramatically in roots. Apparently, roots were better protected against oxidative damage than shoots, as judged from the decrease in lipid peroxidation in root tissues. In leaves, expression of 75 proteins, evaluated by 2D electrophoresis, was altered by salt stress: 35 of them increased their expression and three were apparently de novo synthesized. In roots, 69 proteins were modified by salt stress: 34 proteins increased their expression and two proteins appeared only in stressed seedlings. The changes in protein patterns were caused by the imposed salt stress rather than by a response to the developmental stage. Overall, these responses could play an important role in salt stress acclimation of cashew seedlings.