Effects of exogenous application IAA on alleviating aluminum toxicity of alfalfa seedlings

Effects of different concentrations of plant growth regulator (indole-3-acetic acid, IAA) on seedling growth and physiological response under aluminum (Al) stressed alfalfa (Medicago sativa) were studied. The results showed that Al-stress significantly inhibited the alfalfa growth which indicated by the root elongation, lateral root number, under-ground biomass and above-ground biomass reduction. IAA concentrations in root tip and apical tip significantly decreased (P0.05) under Al stress. The inhibition of alfalfa growth under Al stress was alleviated by exogenous spraying IAA which indicated by the root elongation, lateral root number, under-ground biomass and above-ground biomass increase. Exogenous application of IAA also significantly decreased (P0.05) Al content, malondialdehyde (MDA) content and electrolyte leakage in the roots of Al-stressed alfalfa, as well as significantly increased (P0.05) the chlorophyll content. The optimum concentration of IAA was 6 mg·L-1 whose parameters had significant difference with that of Al-treatment along (P0.05).