EFFECT OF SOIL MICROORGANISMS ON THE GROWTH OF ROOTS IN RICE SEEDLINGS : II. Nitrite Formation by Rhizoplane Microorganisms and the Effect of Nitrite on the Root Development under Aseptic Condition

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Nitrite formation by rhizoplane microorganisms of rice seedlings was examined in comparison with that by nonrhizosphere paddy soil microorganisms. Effect of nitrite on root growth of rice seedlings was also investigated under aseptic water culture condition. Rhizoplane microorganisms accumulated much nitrite than the other microorganisms in a root extract medium. The accumulated nitrite maintained a stationary level for more than 2 days. In glucose enriched media, both group of microorganisms accumulated nitrite only temporarily. Formation of lateral roots and root hairs was stimulated in the solution containing 1.12-11.2 ppm NO_2^--N but elongation of primary roots was depressed under 5.6-11.2ppm NO_2^--N concentrations. Growth of rice seedlings was inhibited at concentrations higher than 5.6 ppm. Comparative studies indicated that effect of soil microorganisms on root morphology would have been caused by nitrite produced by rhizoplane microorganisms. Additional Index Words : nitrite formation, rhizoplane microorganisms, rice root, aseptic culture.
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