Nitrogen fixation and ammonium assimilation in rice inoculated with Klebsiella oxytoca R15

Abstract

Biochemistry and physical alteration were demonstrate in Klebsiella-rice association using Klebsiella oxytoca R 15 and rice cv. RD7 as model of study. Colonization of rice roots by K. oxytoca R 15 were shown to produce root curling, branching and root hair proliferation on day 7-21 after inoculation as demonstrate by stereomicroscopic and scanning electron microscopic techniques. Nitrogen-fixing cativity of associative K. oxytoca R 15 as determined by acetylene reduction assay significantly increased on day 2-10 after inoculation, about 50 fold on day 10 wheras in associative rice plants, ammonium assimilation via root cytosolic GS remains more or less similar with or without bacterial colonization, but in the leaf, the specific activity of cytosolic GS determined by transferase activity increased about 30 % above control non-inoculated rice plant, while the root GS and total proteins of root and leaf were not affected by bacterial inoculation. The root and leaf cytosolic proteins of the subunit molecular weight 48 kDa, which cross-reacts with anti-GS of maize were demonstrated by SDS-PAGE and Westernblot analysis to be slightly increased with time after inoculation. Specific Iocalization of rice cytosolic GS by immunogold-protein A labeling technique showed the same result. This studies indicate that the fixed-nitrogen was assimilated by associative Klebsiella and most likely was transferred to the leaf in certain form of amino acids.