Differential responses of pea seedlings to indole acetic acid under manganese toxicity

Present study showed the responses of pea seedlings to exogenous indole acetic acid (IAA; 10 and 100 mu M) application under manganese (Mn; 50, 100 and 250 mu M) toxicity. Manganese and 100 mu M IAA alone as well as in combination decreased growth of pea seedlings compared to control. Moreover, some parameters of oxidative stress-hydrogen peroxide (H2O2) and malondialdehyde (MDA) were also increased by single and combined treatments of Mn and 100 mu M IAA compared to control. In contrast, addition of 10 mu M IAA together with Mn, alleviated Mn toxicity symptoms and promoted growth led to the decrease in H2O2 and MDA levels compared to Mn treatments alone. Under single and combined treatments of Mn and 100 mu M IAA, catalase activity decreased while superoxide dismutase and ascorbate peroxidase activities increased and glutathione reductase and dehydroascorbate reductase exhibited differential responses. However, addition of 10 mu M IAA together with Mn, increased activities of studied enzymatic antioxidants. Root and shoot reduced ascorbate (AA) and reduced glutathione (GSH) and, their reduced/oxidized ratios decreased while dehydroascorbate (DHA) and oxidized glutathione (GSSG) contents increased compared to control following single and combined treatments of Mn and 100 mu M IAA. However, supply of 10 mu M IAA together with Mn, increased AA and GSH, and their reduced/oxidized ratios in root and shoot compared to Mn treatments alone. This study thus suggests that 10 mu M of IAA was able to increase Mn tolerance in pea seedlings under Mn toxicity while opposite was noticed for 100 mu M IAA.