BIOSYNTHESIS OF AUXINS BY AZOTOBACTER

Abstract

Various Azotobacter cultures were isolated from the rhizosphere of maize. Ten fast growing cultures were selected (numbered as Zi, Zi, Zie), and evaluated for their potential to produce auxins (lAA-equivalents) in vitro both in the absence and presence of auxin precursor, L-tryptophan (L-TRP). Azotobacter cultures varied in their auxin producing ability and Z' was the most efficient auxin (3.1 fig lAA-equivalents mL') producer in the absence of L-TRP. Supplementation of the medium with L-TRP @ Iff1 and lfr'M stimulated auxin production by almost 2-fold over the unamended control. Various environmental factors strongly affected I.-TRP-dependent auxin biosynthesis in soil, and optimal productions were found at 6.0 mg L-TRP g'' soil, 6.0 mg glucose g~' soil, pH7.0, 40 °C temperature, shaking @ of 150 rpm, no nitrogen and 48 hours of incubation. Application of antibiotics (streptomycin or erythromycin) had inhibitory effects on auxin biosynthesis in soil.