Rahat Nazar

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).

Phytohormones and Abiotic Stress Tolerance in Plants

Signal transduction of pytohormones under abiotic stresses.- Cross-talks on phytohormones signaling pathways under optimal and stressful conditions.- Phytohormones in salinity tolerance: ethylene and gibberellins cross talk.- Nitric oxide metabolism under environmental stress conditions.- Auxin as part of wound-healing response in plants.- Interaction between ethylene, auxin, light and microtubules during low-pH induced root hair formation in lettuce seedlings.- Cytokinin homeostasis.- Origin of brassinosteroids and their role in oxidative stress in plants.- Hormonal intermediates in the protective action of exogenous phytohormones in plants under salinity: A case study on wheat.- The role of phytohormones in the control of plant adaptation to oxygen depletion.- Stress hormones associated to sunflower germplasms with different sensitivity to drought.- An insight into the relationship between jasmonates and salicylic acid in salt tolerance.

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.

The application of ethephon (an ethylene releaser) increases growth, photosynthesis and nitrogen accumulation in mustard (Brassica juncea L.) under high nitrogen levels

Ethephon (2-chloroethyl phosphonic acid), an ethylene-releasing compound, influences growth and photosynthesis of mustard (Brassica juncea L. Czern & Coss.). We show the effect of nitrogen availability on ethylene evolution and how this affects growth, photosynthesis and nitrogen accumulation. Ethylene evolution in the control with low N (100 mg N kg(-1) soil) was two-times higher than with high N (200 mg N kg(-1) soil). The application of 100-400 microl x l(-1) ethephon post-flowering, i.e. 60 days after sowing, on plants receiving low or high N further increased ethylene evolution. Leaf area, relative growth rate (RGR), photosynthesis, leaf nitrate reductase (NR) activity and leaf N reached a maximum with application of 200 microl x l(-1) ethephon and high N. The results suggest that the application of ethephon influences growth, photosynthesis and N accumulation, depending on the amount of nitrogen in the soil.

Increased activity of ATP-sulfurylase and increased contents of cysteine and glutathione reduce high cadmium-induced oxidative stress in mustard cultivar with high photosynthetic potential.

Cadmium is known to reduce photosynthesis and overall growth of plants. Plants adopt several mechanisms of Cd detoxification, such as accumulation of sulfur-rich compounds, like glutathione (GSH) and its precursor cysteine. The accumulation of GSH is regulated by the activity of ATP-sulfurylase, a rate-limiting enzyme in sulfur assimilation. The carbon of Cys is provided through photosynthesis. Thus, a plant with the higher photosynthetic potential and ATP-sulfurylase activity may have the higher contents of Cys and GSH and therefore may provide for a greater tolerance to Cd stress. Mustard (Brassica juncea L. Czern and Coss.) cvs. Varuna (high photosynthetic potential) and RH30 (low photosynthetic potential) were subjected to 0 and 200 mg Cd/kg soil, and the activity of ATP-sulfurylase, the contents of Cys and GSH, oxidative stress, and activities of antioxidant enzymes were studied. Under 200 mg Cd/kg soil, cv. Varuna showed an increased ATP-sulfurylase activity, the higher contents of Cys and GSH, and the net photosynthetic rate than cv. RH30. In contrast, the activity of superoxide dismutase, the contents of thiobarbituric acid-reactive substances, and H2O2, and electrolyte leakage were found to be greater in cv. RH30 showing an increased oxidative stress than cv. Varuna. However, the activities of ascorbate peroxidase and glutathione reductase were greater in cv. Varuna than cv. RH30. The results show that a greater ATP-sulfurylase activity, an enhanced production of Cys and GSH, and an efficient antioxidant enzyme system in the high photosynthetic mustard cv. Varuna helped to the reduce the oxidative stress maintaing high photosynthesis.

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.

ATP-sulfurylase activity, photosynthesis, and shoot dry mass of mustard (Brassica juncea L.) cultivars differing in sulfur accumulation capacity

Sulfur (S) is an essential nutrient element required in a large quantity by mustard. S regulates photosynthesis and plant growth through improving nitrogen (N) acquisition. Mustard cultivars Alankar, Varuna, Pusa Jai Kisan, and SS2 differing in S accumulation capacity calculated as sulfate transport index (STI) were tested for ATP-sulfurylase activity, S and N accumulation, photosynthesis, and shoot dry mass (DM) at 30 and 60 d after sowing (DAS). The activity of ATP-sulfurylase, shoot N content, net photosynthetic rate (PN), leaf area, and shoot DM of the cultivars were in the order: Pusa Jai Kisan>Alankar>Varuna>SS2. ATP-sulfurylase activity was strongly and positively correlated with PN and shoot DM in all the cultivars. Hence ATP-sulfurylase activity may be used as a physiological trait for augmenting photosynthesis and shoot DM.

Cadmium effects on carbonic anhydrase, photosynthesis, dry mass and antioxidative enzymes in wheat (Triticum aestivum) under low and sufficient zinc

Abstract Leaf carbonic anhydrase (CA) activity, net photosynthetic rate (PN), stomatal conductance (gS) and plant dry mass (DM) exhibited a dose-dependent response to cadmium (Cd) in wheat (Triticum aestivum L.) grown under low and sufficient zinc (Zn) levels at 30 d after seedling emergence in sand culture. Cadmium at 10 µM concentration enhanced CA, PN and DM at low Zn level but these remain unaltered at sufficient Zn. Stomatal conductance decreased with increasing CdCl2 concentration at both the Zn levels. Cd higher than 10 µM inhibited the characteristics irrespective of Zn level. The activity of superoxide dismutase (SOD) was not saturated the with highest Cd concentration (50µM) at both the Zn levels. However, the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) increased up to 25 µM Cd and decreased at 50 µM Cd at both the Zn levels. It is suggested that CA activity was induced at low Cd (10 µM) under low Zn level increasing the photosynthesis. The synergies among the activities of antioxidative enzymes helped to maintain CA and thus photosynthesis and plant DM at low Cd concentration under low Zn level.

Osmolytes and Plants Acclimation to Changing Environment: Emerging Omics Technologies

Plants being sessile are challenged by biotic and abiotic stresses. Osmotic adjustment has been shown to be an effective component of stress tolerance, and accumulation of osmoprotectants (proline, glycine betaine, gamma-aminobutyric acid and sugars) is a common response observed in different plant systems. Information on the metabolic pathways of these compatible solutes for their regulation, enzymes involved and compartmentalisation are well characterised in most important plant species. Such information has prompted researchers to devise strategies for improvement of plant tolerance through the accumulation of osmolytes in plants by expression of core biosynthetic enzymes or their derivatives and expression of related transporters. Pathway engineering for overproduction of compatible solutes is being attempted through stress-inducible and/or tissuespecifi c regulation in order to avoid primary metabolic costs and minimise the pleiotropic effects. Understanding the mechanisms by which plants perceive environmental signals and transmit them to cellular machinery to activate adaptive responses is crucial for the development of crop improvement strategies to impart stress tolerance.