Synergistic action of indole acetic acid with homobrassinolide in easing the NaCl-induced toxicity in Solanum melongena L. seedlings

In the current work, the influence of indole-3-acetic acid (IAA; 10(-5) M) and 28-homobrassinolide (HBL; 10(-8) M) alone or in combination was explored in Solanum melongena L. seedlings treated with sodium chloride (NaCl). The NaCl at different concentrations (5 mM and 15 mM) reduced growth attributes, photosynthetic pigments as well as photosynthesis, and enhanced the dark respiratory rate, and these effects were accompanied with Na+ and reactive oxygen species (ROS) accumulation in leaf tissues. Moreover, NaCl reduced the proficiency of PS II with the increasing doses of selected stress which is apparent from the declined values of F-v/F-m (Phi_P-0), & x470;(0) (Psi_0), phi(E0) (Phi_E0) and PIABS, and augmented values of energy fluxes: ABS/RC, ET0/RC, TR0/RC and DI0/RC. The NaCl treatment caused substantial reduction in nitrate and nitrite contents, activities of nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase, and increased ammonium content and glutamate dehydrogenase activity. Enhanced level of ROS, i.e. superoxide radical (O-2(center dot-)) and hydrogen peroxide (H2O2) under NaCl stress amplified the lipid peroxidation product malondialdehyde (MDA), in spite of considerable upsurge in performance of superoxide dismutase, peroxidase, catalase, glutathione-S-transferase enzymes and amount of non-protein thiol, cysteine and proline. Exogenous supplementation of IAA and HBL considerably assuaged the NaCl-induced collapse in growth attributes by manipulating the structural and functional features of photosynthetic apparatus. The ameliorating effect of IAA and HBL, in combination, was due to (1) substantial decrease in Na+ accumulation, (2) improvement in PS II efficiency and nitrogen metabolism and (3) reduced oxidative damage in S. melongena L. due to stimulatory response of antioxidants that keeps the level of oxidants under limit in the seedlings. Thus, the overall results campaigned that IAA and HBL act synergistically to overcome the toxic effects that NaCl had on S. melongena L. seedlings.