Indole acetic acid differently changes growth and nitrogen metabolism in Pisum sativum L. seedlings under chromium (VI) phytotoxicity: Implication of oxidative stress

The present study investigated impact of exogenous application of indole acetic acid (IAA; 10 and 100 μM) in pea seedlings under hexavalent chromium (Cr VI; 50, 100 and 250 μM). Cr and 100 μM IAA alone as well as in combination decreased seed germination rate compared to control. However, under Cr phytotoxicity, addition of 10 μM IAA recovered seed germination rate to the level of control. Exposure of pea seedlings to Cr and 100 μM IAA during their early stage caused decrease in fresh mass, length, protein and nitrogen contents of roots and shoots compared to control. Treatment of pea seedlings with Cr resulted in a rapid accumulation of this metal in roots and shoots. Moreover, addition of 100 μM IAA together with Cr, further increased accumulation of this metal in roots and shoots compared to Cr treatments alone. Treatment of pea seedlings with Cr and 100 μM IAA, resulted in a marked decrease in nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase (GOGAT) activities (except 50 μM Cr alone for GOGAT), and an increase in ammonium content and glutamate dehydrogenase activity. Parameters related with oxidative stress, i.e. superoxide radicals and reactive carbonyl groups (protein oxidation) were increased by Cr and 100 μM IAA compared to control. By contrast, addition of 10 μM IAA together with Cr, alleviated negative effect of Cr on growth, protein, nitrogen and nitrogen metabolism, and led to decrease in oxidative injuries caused by Cr. The data indicate that 10 μM IAA protects pea seedlings during the early growth period against Cr phytotoxicity by regulating Cr accumulation and oxidative damage. However, addition of 100 μM IAA together with Cr showed opposite responses.