Physiological aspects of phytohormone production by Azospirillum brasilense Sp 7

Abstract

The culture fluid of A. brasilense Sp 7 was found to contain 15 mg/L of indole-3-acetic acid and 267 μg/L of abscisic acid. In the course of 10 days of growth of A. brasilense Sp 7 on root exudate medium one can trace well-defined dynamics of cytokinin activity within a period of 4 to 6 days of culture growth. It was shown that zeatin and zeatin-riboside were absent in the culture fluid of A. brasilense Sp 7. Azospirillum brasilense strains isolated from cereals from the Saratov Region, when grown in a tryptophan-supplemented medium for 3 days, produced indole-3-acetic acid in amounts of 72.6 to 108.9 μg/mg dry matter of intact cells. No close correlation was shown between the biosynthetic activity of indole-3-acetic acid and N2-fixation activity in 14 Azospirillum strains studied. A mathematical model was developed for indole-3-acetic acid synthesis by A. brasilense Sp 7 in relation to pH values, tryptophan concentration and temperature.