A quick incorporation of ^<13>N into the soluble high-molecular compound in rice (Oryza sativa L.) roots by application of ^<13>N-labeled nitrate/nitrite(Plant Nutrition)

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The nitrate/nitrite response, which occurs within minutes for the gene expression of the primary nitrogen metabolism in higher-plant roots, has almost been described, but the intermediate signaling molecule that exerts in signal transduction remains to be elucidated. It is hypothesized that the constitutively present signaling molecule may bind quickly to exogenously applied nitrate/nitrite to transduce the nitrate/nitrite signal. To examine the quick binding of nitrate/nitrite to high-molecular compounds, which may include intermediate signaling molecules, in the roots of the rice plant (Oryza sativa L.), the segmented roots of rice seedlings were exposed to nitrogen-13 (^<13>N)-labeled nitrate/nitrite for either 2 or 5min at 25℃. The supernatant of the Tris-buffer root extract was separated by a desalting pre-packed column. The incorporation of ^<13>N into the high-molecular fraction was identified by ^<13>N feeding for 2min, and by ^<13>N feeding for 5min, however, the amount of ^<13>N incorporation was not increased. Although the findings are preliminary, it was clearly demonstrated that ^<13>N-labeled nitrate/nitrite was quickly incorporated into a limited amount of the soluble high-molecular compound(s). The formation of NO_x-bound proteins, which may play a role in nitrate/nitrite signal transduction, is discussed.