Endogenous growth inhibitors, nodulation and nitrogen fixation in soybean under drought and treated with gibberellic acid and abscisic acid
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Abstract
Soybean plants (Glycine max L. Merrill) that had reached full nodulation were submitted to physiological water stress by using polyethylene glycol (PEG 6000). Gibberellin A and/or abscisic acid were sprayed in an attempt to alleviate or mimic the stress. After rewatering the plants, endogenous growth inhibitors in the root system, nitrogenase activity (as per root or nodule basis), number of nodules per plant, and the fresh and dry weight of nodules and roots per plant and per treatment were investigated. Drought depressed both nodulation and nitrogenase activity and increased the levels of growth inhibitors in roots. However, ABA increased symbiotic N2 fixation activity in control plants growing in field capacity and also partially reversed the deleterious effects of drought. Gibberellin A had no action on control plants but annulled the effects of ABA. There was no correlation between the levels of growth inhibitors promoted by exogenous application of growth regulators and the nitrogenase activity and weight of nodules. Thus, the diminution in nodulation and the reductive capacity of the system is not due to inhibitors accumulated in roots by the effect of drought.
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