Shabina Syeed

Salicylic acid alleviates decreases in photosynthesis under salt stress by enhancing nitrogen and sulfur assimilation and antioxidant metabolism differentially in two mungbean cultivars.

Salicylic acid (SA) is known to affect photosynthesis under normal conditions and induces tolerance in plants to biotic and abiotic stresses through influencing physiological processes. In this study, physiological processes were compared in salt-tolerant (Pusa Vishal) and salt-sensitive (T44) cultivars of mungbean and examined how much these processes were induced by SA treatment to alleviate decrease in photosynthesis under salt stress. Cultivar T44 accumulated higher leaf Na(+) and Cl(-) content and exhibited greater oxidative stress than Pusa Vishal. Activity of antioxidant enzymes, ascorbate peroxidase (APX) and glutathione reductase (GR) was greater in Pusa Vishal than T44. Contrarily, activity of superoxide dismutase (SOD) was greater in T44. The greater accumulation of leaf nitrogen and sulfur through higher activity of their assimilating enzymes, nitrate reductase (NR) and ATP-sulfurylase (ATPS) increased reduced glutathione (GSH) content more conspicuously in Pusa Vishal than T44. Application of 0.5 mM SA increased nitrogen and sulfur assimilation, GSH content and activity of APX and GR. This resulted in the increase in photosynthesis under non-saline condition and alleviated the decrease in photosynthesis under salt stress. It also helped in restricting Na(+) and Cl(-) content in leaf, and maintaining higher efficiency of PSII, photosynthetic N-use efficiency (NUE) and water relations in Pusa Vishal. However, application of 1.0 mM SA resulted in inhibitory effects. The effect of SA was more pronounced in Pusa Vishal than T44. These results indicate that SA application alleviates the salt-induced decrease in photosynthesis mainly through inducing the activity of NR and ATPS, and increasing antioxidant metabolism to a greater extent in Pusa Vishal than T44.

Exogenously-sourced ethylene increases stomatal conductance, photosynthesis, and growth under optimal and deficient nitrogen fertilization in mustard

In order to ascertain the stomatal and photosynthetic responses of mustard to ethylene under varying N availability, photosynthetic characteristics of mustard grown with optimal (80 mg N kg−1 soil) or low (40 mg N kg−1 soil) N were studied after the application of an ethylene-releasing compound, ethephon (2-chloroethyl phosphonic acid) at 40 days after sowing (DAS). The availability of N influenced ethylene evolution and affected stomatal conductance and photosynthesis. The effect of ethylene was smaller under deficient N where plants contained higher glucose (Glc) sensitivity, despite high ethylene evolution even in the absence of ethephon, potentially because the plants were less sensitive to ethylene per se. Ethephon application at each level of N increased ethylene and decreased Glc sensitivity, which increased photosynthesis via its effect on the photosynthetic machinery and effects on stomatal conductance. Plants grown with sufficient-N and treated with 200 μl l−1 ethephon exhibited optimal ethylene, the greatest stomatal conductance and photosynthesis, and growth. These plants made maximum use of available N and exhibited the highest nitrogen-use efficiency (NUE).

Photosynthesis, Growth and Antioxidant Metabolism in Mustard (Brassica juncea L.) Cultivars Differing in Cadmium Tolerance

Two mustard (Brassica juncea L. Czern and Coss.) cultivars, Pusa Jai Kisan and SS2 differing in cadmium (Cd) tolerance were treated with 0, 25 and 50 μmol L^(-1) Cd to study the physiological basis of difference in Cd tolerance. Cultivar SS2 (Cd sensitive) accumulated greater Cd in leaves than Pusa Jai Kisan (Cd tolerant). Further, SS2 also exhibited higher contents of thiobarbituric acid reactive substances (TBARS) and H2O2 and electrolyte leakage. However, the activities of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were higher in Pusa Jai Kisan than those in SS2. Contrarily, the activity of superoxide dismutase (SOD) was higher in SS2 than that in Pusa Jai Kisan and was the greatest at 25 μmol L^(-1) Cd. Treatment of 25 μmol L^(-1) Cd induced the maximum activity of enzymes. However, the activity of GR increased up to 50 μmol L^(-1) Cd in both the cultivars. The non-enzymatic antioxidants ascorbate (AsA) and glutathione (GSH) were higher in Pusa Jai Kisan than that in SS2, whereas dehydroascorbate (DHA) and oxidized glutathione (GSSG) were higher in SS2. Photosynthesis and growth were adversely and maximally decreased by 50 μmol L^(-1) Cd treatment in both the cultivars, but SS2 exhibited greater reductions. The protection of photosynthesis and growth and lesser reduction in Pusa Jai Kisan were associated with its capacity to restrict accumulation of Cd in leaves resulting in lower level of TBARS and H2O2 and electrolyte leakage. Moreover, Pusa Jai Kisan exhibited efficient antioxidant metabolism for removal of Cd-induced reactive oxygen species.

Salinity Tolerance in Plants: Revisiting the Role of Sulfur Metabolites

Salinity is becoming a major threat to plant productivity loss in agricultural system. Plants respond to saline environment by modulating the inherent mechanisms to adjust to the changing environment. The understanding of the mechanisms that plants operate under saline environment is essential beginning in efforts to reduce the adverse effects of salinity stress. The agricultural system is tightly linked with the fertilizer input and thus the judicious application of fertilizers is expected to lead positive effects in reversing the salinity effects. Sulfur is a macronutrient with essential roles in plant development under optimal and stressful environment. Several compounds are synthesized from sulfur metabolism useful in reversing the adverse effects of abiotic stress because of their free radicals scavenging property. Sulfur-containing metabolites, amino acids (cysteine and methionine), vitamins (biotin and thiamine), thioredoxin system, glutathione lipoic acid and glucosinolats have potential to promote or modify physiological and molecular processes under salinity stress in plants. Thus, modulation of sulfur metabolites production could alter physiological and molecular mechanisms to provide tolerance against salinity. The present review discusses the role of sulfur-containing compounds in modifying various physiological and molecular processes in plants to confer salinity tolerance in plants.

An Insight into the Role of Salicylic Acid and Jasmonic Acid in Salt Stress Tolerance

Phytohormones are organic compounds that in small amount promote, inhibit, or modify physiological processes in plants. Researchers have recognized salicylic acid (SA) and jasmonic acid (JA) as a potential hormone. Application of SA and JA could provide tolerance against biotic and abiotic stresses such as salinity, temperature stress, heavy metal stress, etc. The role of SA and JA in the protection against abiotic stress is played by its ability to induce expression of genes coding proteins. A low concentration of SA and JA appears to be effective in tolerance to stress by enhancing physiological processes and improving salt tolerance by its effect on biochemical and molecular mechanisms. The present review gives an insight into the role of SA and JA in inducing various physiological responses in plants under salinity stress, and an interaction between these two phytohormones is also discussed.

Sulfur in the Alleviation of Cadmium-Induced Oxidative Stress in Plants

The toxicity of cadmium (Cd) is an emerging environmental problem that has attracted the attention of plant scientists all over the world. It deteriorates soil, plant and human health. Researchers have focused their attention in evolving strategies to reduce its toxicity at cellular, molecular and/or whole plant level. Sulfur is an important plant nutrient that takes part in plant metabolism and provides vigor to plants under stressful environments. This nutrient element could be used in agricultural system for reducing Cd toxicity and increasing sustainability. Sulfur uptake results in the formation of the first stable product cysteine through a cascade of enzymatic reactions. The formation of cysteine leads to the synthesis of glutathione, a nonenzymatic antioxidant known to be involved in Cd detoxification either through quenching reactive oxygen species or formation of phytochelatin that binds Cd and sequester it into vacuole. Manipulation of sulfur-assimilating enzymes, cysteine, glutathione and/or phytochelatin content could possibly lead to Cd detoxification. The present work gives insight into the role of sulfur in the alleviation of Cd stress.