Alleviation of Adverse Effects of Copper on Allium cepa L. by Eexogenous Ascorbic Acid Application

In this study ameliorative effects of ascorbic acid (0.5 mM) on onion (Allium cepa L. cv. Red Azarshahr) under copper stress (Cu: 6.5 μM) were studied. Fresh weights of leaves and roots were reduced in seven week old plants under excess copper condition. Cu stress also reduced membrane stability index in leaves. There was a considerable increase in H2O2 content and lipid peroxidation in both roots and leaves of plants under excess Cu. Leaves anthocyanin contents, leaves and roots phenolic compounds, soluble proteins and proline contents were increased in response to Cu toxicity. The fresh weights of leaves and roots were improved during addition of ascorbic acid to root medium in stressed and non-stressed plants. Exogenous ascorbic acid significantly increased membrane stability index in Cu stressed plants. We find considerable reduction in anthocyanins, phenolic compounds and proline with ascorbic acid treatments in all plants. Ascorbic acid application also reduced H2O2 content and prevented lipid peroxidation in leaves and roots during presence or absence of excess Cu. Treatment of plants with ascorbic acid increased soluble proteins content only in non-stressed plants. The results demonstrate that root applied ascorbic acid ameliorated the copper induced oxidative adverse effects on onion growth.