Abstract
The involvement of ethylene in reversal of salt (NaCl; 50 mM) stress on photosynthetic activity and growth by salicylic acid (SA; 0.5 mM) together with sulfur (S; 2.0 mM) was studied in mustard (Brassica juncea L. cv. Pusa Vijay). Application of SA plus SO42− improved photosynthetic activity through markedly increased S-assimilation, strengthening antioxidant defense system and limiting NaCl-accrued oxidative consequences more conspicuously than their individual effect in B. juncea under 50 mM NaCl stress. Since SA acts as an inhibitor of ethylene and S-assimilation is associated with ethylene synthesis, we tried to figure out the interaction of ethylene in SA and SO42−-mediated salt tolerance. The involvement of ethylene was studied by supplementing salt-treated plants with 200 µL L−1 ethephon (an ethylene-releasing compound) or 100 µM norbornadiene (NBD, ethylene action inhibitor) to SA and SO42− treatments. Ethephon supplemented to NaCl-treated plants showed optimal ethylene formation, increasing ethylene sensitivity to enhance photosynthesis by affecting antioxidative capacity of plants. SA plus SO42− treatment decreased stress ethylene production and optimized ethylene formation under NaCl stress that contributed in the maintenance of high photosynthetic rate, which was reversed with NBD. NaCl-treated plants receiving SA plus SO42− and supplemented with NBD showed inhibited photosynthetic characteristics and growth, with minimal S-assimilation capacity, activity of antioxidant enzymes and GSH content. This showed that the reversal of salt stress by SA plus SO42− was through ethylene involvement. Overall, ethylene intervened the effect of SA in the presence of SO42− to induce S-assimilation, upregulated the enzymatic and non-enzymatic antioxidants, and imparted NaCl tolerance in plants.
Highlights
One of the most damaging abiotic stresses has been soil salinity, which has resulted in significant losses in cultivated land area, crop yield, and quality (Yamaguchi and Blumwald 2005; Shahbaz and Ashraf 2013: Fatma et al 2021; Jahan et al 2021; Sehar et al 2021; Syeed et al 2021)
The combined supplementation of 0.5 mM salicylic acid (SA) and 2.0 mM SO42- maximally increased net photosynthesis, intercellular CO2 concentration, stomatal conductance and chlorophyll content under no stress or salt stress compared to 50 mM NaCl treatment (Table 1)
Maximum increase of 18.9 % in PSII activity was noted with combined application of 0.5 mM SA plus 2.0 mM SO42- to the salt grown plants compared with control
Summary
One of the most damaging abiotic stresses has been soil salinity, which has resulted in significant losses in cultivated land area, crop yield, and quality (Yamaguchi and Blumwald 2005; Shahbaz and Ashraf 2013: Fatma et al 2021; Jahan et al 2021; Sehar et al 2021; Syeed et al 2021). On the other, stressed plants tend to build up their antioxidant defense system to control the cellular ROS-level and minimize ROS-accrued consequences including lipid and protein oxidation. Major antioxidant enzymes (such as ascorbate peroxidase, APX; catalase, CAT) and non-enzymatic antioxidants (such as ascorbate, AsA; reduced glutathione, GSH; and α-tocopherol, flavonoids and proline), alone and/or cumulatively scavenge varied ROS (Sharma and Dietz 2009; Ashraf 2009; Mittal et al 2012). Applied S improved the photosynthetic capacity of the plants in salt stress by improving the cellular GSH level, modulating the major components of the ascorbate-glutathione (AsA-GSH) cycle, restricting ROS formation, and minimizing oxidative stress and its consequences (Fatma et al 2021)
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