IAA alleviates Cd toxicity on growth, photosynthesis and oxidative damages in eggplant seedlings

Plant growth regulator IAA (indole-3-acetic acid), besides its role in growth and development, is gaining increased attention because of its involvement in regulation of abiotic stresses. To ascertain this hypothesis, sand culture experiments were conducted to investigate the implication of IAA in regulation of Cd (cadmium) toxicity in eggplant (Solanum melongena L.) seedlings. Cd at tested doses (Cd1: 3 mg Cd kg−1 sand and Cd2: 9 mg Cd kg−1 sand) declined growth, pigment contents and photosynthesis, and increased the rate of dark respiratory oxygen uptake, and these effects were accompanied with Cd accumulation in tissues. Photochemistry of photosystem II (PS II) was analyzed by measuring chlorophyll a fluorescence kinetics-JIP test. Cd declined the efficiency of PS II in its concentration dependent manner which is evident from the decreased values of Fv/F0, Fv/Fm (ϕP0), Ψ0, ϕE0 and PIABS and increased values of F0/Fv and energy fluxes per reaction centre: ABS/RC, ET0/RC, TR0/RC and DI0/RC. Enhanced level of oxidants: superoxide radical and hydrogen peroxide under Cd stress stimulated the rate of lipid peroxidation and electrolyte leakage, despite of appreciable rise in activity of superoxide dismutase, peroxidase, catalase, glutathione-s-transferase and contents of non protein thiol and proline. Exogenous IAA application alleviated Cd induced toxicity on growth performance by improving the structural and functional attributes of photosynthetic apparatus i.e. pigment contents and photosynthetic activity. The ameliorating effect of exogenous IAA was due to (1) significant reduction in Cd uptake in roots and its translocation to leaves and (2) further rise in level/activity of antioxidants which brought the level of oxidants under control hence, minimized the oxidative damage in eggplant seedlings.