Effect of Indoleacetic Acid on Growth and Antioxidant Properties in Glycine Max Seedlings Exposed to Aluminium Toxicity

Two-week-old soybean (Glycine max) plants were subjected to factorial combination of five levels of aluminum chloride (0, 50, 100, 200 and 300 μM) and three levels of indoleacetic acid (IAA) (0, 50 and 100 μM). In the absence of IAA, treatment with increasing levels of Al progressively decreased net assimilation rate (NAR) and leaf water content per unit area (LWCA), but it increased the antioxidant enzyme activities, phenolic compounds and anthocyanin content. Aluminum concentration was increased in leaves and roots. Aluminum stress showed a substantial subtractive (p≤0.05) effect on plant growth. Exogenous IAA raised (p≤0.05) the activity of antioxidant enzymes and changed the content of anthocyanin and Al accumulation in roots and leaves depending on its concentration. Having been combined together, IAA and Al had additive effects on antioxidant enzyme activities, but their effects on NAR, LWCA, phenolic compounds, anthocyanin content and Al accumulation were moderate. Exogenous IAA counteracted the deleterious effects of Al stress and helped plants to grow successfully under these adverse conditions.