Studies on seasonal variation of plant hormones,nitrogen flixation and indole acetic acid metabolism in root nodulus ofButea monosperma (Lam.) Taub.

Summary Mature nodules ofButea monosperma (Lam.) Taub. (B. monosperma) contained higher amounts of indole acetic acid-like (IAA), cytokinin-like (CK), gibberellic acid-like (GA) and abscisic acid-like (ABA) substances, and were more active in IAA metabolism and nitrogen fixation. Roots contained lower amount of all the hormones. The higher level of IAA in the nodules than the roots was due to more synthesis from tryptophan and simultaneously less destruction by IAA oxidase. IAA oxidase, in turn, was regulated by phenols.Regardless of the hormone levels, the nodules of a particular age attained a fixed size indicating that regulation of formation and growth of the nodules are not the sole function of the nodular hormones. Seasonal studies on the mature nodules showed positive relation of nitrogenase (N₂ase) with IAA and CK, and negative relation with GA and ABA.