Role of IAA metabolizing enzymes on production of IAA in root, nodule of Cajanus cajan and its PGP Rhizobium sp

Abstract

Abstract Indole acetic acid (IAA) is a phytohormone which plays a central role in plant growth and development as a regulator of numerous biological processes. The metabolism of IAA in nodules and its symbiont is not fully elucidated. The present work was undertaken to shed some light on IAA metabolism in Cajanus cajan roots, nodules, the Rhizobium symbiont and its possible role in Rhizobia–Legume interaction. The mature root nodules of C. cajan (L) were found to contain more IAA than non nodulated root. A tryptophan pull was present in the mature nodules and young roots might have served as a precursor for IAA production. The levels of tryptophan content were also higher in nodule than root. Comparative study of IAA metabolizing enzymes, such as IAA oxidase IAA peroxidase (EC 1.11.1.7) and polyphenol oxidase (E.C. 1.14.18.1) indicated that they might have some significant role in metabolism of IAA in roots and nodules. A symbiont designated as P2 was isolated from fresh nodules of C. cajan (L) and was identified as Rhizobium sp. by phenotypic and 16S rDNA sequence analysis. The strain produced significant amount of IAA (142.5 µg/ml) under in vitro condition when l -tryptophan (0.2%) was added to the medium as precursor and also possess ACC deaminase (E.C. 4.1.99.4) activity that might be helpful for successful entry of infection thread. The presence of significant amount of IAA catabolising enzyme in nodule, root and ACC deaminase activity of its symbiont might have physiological importance in plant-microbes interaction of symbiotic phenomenon and plant growth promotion.