Exogenous application of indole acetic acid (IAA) and giberrelic acid (GA3) induces changes in carbon and nitrogen metabolisms that affect tobacco (Nicotiana tabacum L.) production

Experiments, both pot and field trial, were conducted to examine the effects of exogenously applied IAA and GA(3) (at 0, 10, 20 and 30 days after topping) individually or in combination, on growth and C and N metabolisms of tobacco (Nicotiana tabacum L.). Application of IAA or GA(3), at low concentrations had a promising effect in terms of promoting the yield and quality of tobacco. The key enzymes' activities were also enhanced by low PGRs concentrations, which is known to be involved in the C and N metabolisms. The combined treatment of the two PGRs was more effective than the PGRs applied individually in improving the activities of nitrate reductase (NR), invertase (INV) and amylase (AMY) finally resulting in improved soluble sugars, reducing sugars, starch, total C and N, soluble proteins and nicotine content. The optimum levels for improvement of C and N metabolites were found to be GA(3) at 50 mg/L and IAA at 30 mg/L.