Responses of Pisum sativum L. to Exogenous Indole Acetic Acid Application Under Manganese Toxicity

Responses of pea (Pisum sativum L.) seedlings to manganese (50, 100 and 250 mu M) and indole acetic acid (10 and 100 mu M) treatments were investigated. Single and combined exposure of pea to manganese and 100 mu M indole acetic acid decreased root and shoot fresh mass, chlorophyll, carotenoids, protein and nitrogen while ammonium content increased compared to the control. Combined treatment of pea with 250 mu M manganese and 100 mu M indole acetic acid decreased root and shoot fresh mass by 54% and 51%, chlorophyll and carotenoids by 31% and 26%, root and shoot protein by 47% and 44%, and root and shoot nitrogen by 44% and 40%, respectively. Activities of glutamine synthetase and glutamate synthase were decreased by the exposure of manganese and 100 mu M indole acetic acid while glutamate dehydrogenase activity increased. Combined application of 250 mu M manganese and 100 mu M indole acetic acid decreased root and shoot glutamine synthetase activity by 44% and 39%, and glutamate synthase activity by 39% and 37% while root and shoot glutamate dehydrogenase activity increased by 47% and 42%, respectively compared to the control. In contrast, application of 10 mu M indole acetic acid together with manganese decreased the negative impacts of manganese, and promoted seedling growth compared to the manganese treatments alone. This study has shown that 10 mu M indole acetic acid protected pea seedlings appreciably from manganese toxicity by regulating ammonium content and the activities of enzymes of ammonium assimilation, while 100 mu M of indole acetic acid exhibited opposite response under manganese toxicity.