Internal Gln/Glu Ratio as a Potential Regulatory Parameter for the Expression of a Cytosolic Glutamine Synthetase Gene of Radish in Cultured Cells

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The radish Gln1;1 gene encodes cytosolic glutamine synthetase, and is strongly expressed during senescence of cotyledons [Watanabe et al. (1994) Plant Mol. Biol. 26:1807]. We showed previously that nitrogenous compounds exogenously applied to the cotyledons significantly affected the transcript level of the gene during senescence, suggesting that the gene is possibly under metabolic control by cellular nitrogen status. To investigate such metabolic regulation of the gene, we tested the response of the gene to the changes in cellular nitrogen status, using radish cultured cells. Northern blotting and measurement of free amino acids in the cells showed that the radish cells accumulating glutamine at high levels exhibited contrasting low levels of Gln1;1 transcripts. Further and detailed study provided evidences suggesting that the transcript level was regulated in response to the ratio of cellular glutamine to glutamate, but not to the glutamine level alone.
日本植物生理学会の論文