Abstract
Various Azotobacter cultures were isolated from the rhizosphere of maize. Ten fast growing cultures were selected (numbered as Zr, __Zig), and evaluated far their potential to produce auxins (IAA-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 Z4 was the most efficient auxin (3.1 leg IAA-equivalents ml.'') producer in the absence of L-TRP. Supplementation of the medium with L-TRP @ 10-3 and 10-4M stimulated auxin production by almost 2-fold over the unarnended control. Various environmental factors strongly affected L-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.
Muhammad Khalid, Muhammad Arshad, Azeem Khatid , Zahir Ahmad Zahir. (2001) Biosynthesis of auxins by azotobacter, The Journal Soil & Environment , Volume 20, Issue 4.
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