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Biosynthesis of Cytokinins in Soil

Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521

* Corresponding author.

ABSTRACT

Cytokinin biosynthesis in soil by rhizosphere microorganisms may increase upon the addition of physiological precursors and affect plant growth. This study was conducted to establish the effects of the purine, adenine (ADE), the isoprenoid, isopentyl alcohol (IA), and a cytokinin-producing bacterium, on cytokinin biosynthesis in an Arlington soil (coarse-loamy, mixed thermic Haplic Durixeralf). Various concentrations of ADE were applied, separately and in combination with 8.81 x 10^–2 g IA kg^–1 soil, and an inoculum of Azotobacter chroococcum (ATCC 9043), as soil treatments. Cytokinin bioactivity, isolation, and quantification of soil extracts were monitored over a period of 7 d using the radish cotyledon bioassay and HPLC-UV spectrometry. Cytokinin production was evident as early as 2 d and reached a maximum at 5 d post-treatment. An application of 1.35 x 10^–4 g ADE kg^–1 soil, 8.81 x 10^–2 g IA kg^–1 soil, and A. chroococcum enhanced cytokinin production of zeatin riboside and t-zeatin in this soil up to 1.50- and 1.39-fold, respectively, in comparison to controls containing no precursors. The production of zeatin riboside (78.0 µg kg^–1) and t-zeatin (22.1 µg kg^–1) in the presence of ADE and IA was 1.35- and 2.44-fold greater with the inoculation of A. chroococcum, when compared to the indigenous microflora alone. This study provides information on extraction and analytical detection of cytokinins in soil and reveals that microbial biosynthesis of cytokinins can be enhanced by applying physiological precursors to soil.

Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside.

Received for publication August 10, 1988.