Interactive effects of copper and ascorbic acid on some physiological characters in Allium cepa L.

Ascorbic acid as a water soluble antioxidant molecule، participates in many physiological processes such as resistance to environmental stresses. To evaluate the effects of copper stress (6. 5 μM) and application of ascorbic acid through rooting medium (0. 5 mM) on some physiological characters of onion plants (Allium cepa L. cv. Red Azarshahr)، a completely randomized design with four replications was conducted. Results showed that excess Cu reduced the dry weight of roots and leaves، as well as content of photosynthetic pigments and K+ of seven-week-old plants. Exogenous ascorbic acid significantly improved dry weight of roots and leaves with increasing content of K+ and photosynthetic pigments in both the non-stressed and Cu-stressed plants. Cu stress led to accumulation of free amino acids and soluble sugars in roots and leaves. Treatment with exogenous ascorbic acid considerably reduced the contents of these compounds in both non-stressed and Cu-stressed plants. There was considerable reduction in osmotic potential at full turgor and significant increase in osmotic adjustment in leaves of Cu-stressed plants. Application of exogenous ascorbic acid had no effect on osmotic potential at full turgor، but significantly increased osmotic adjustment. In leaves of Cu-stressed plants K+ was the minor contributor to osmotic potential at full turgor. Also، by adding ascorbic acid، K+ contribution was increased in leaves of non-stressed and Cu-stressed plants. Results of the present study indicated that usage of exogenous ascorbic acid reduced harmful effects of copper stress and increased resistance to copper stress in onion plants.