Involvement of Ethylene in Reversal of Salt Stress by Salicylic Acid in the Presence of Sulfur in Mustard (Brassica juncea L.)

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 mu L L-1 ethephon (an ethylene-releasing compound) or 100 mu M 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.