Effect of Auxins (2,4-Dichlorophenoxyacetic acid, Indole-3-Acetic Acid and Naphthaleneacetic Acid) on the Accumulation of γ-Aminobutyric Acid in Excised Rice Root Tips

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γ-Aminobutyric acid (GABA) accumulation occurs in cultured rice cells when ammonium is added to the medium [Kishinami and Ojima (1980) Plant Cell Physiol. 21: 581-589]. Whether this phenomenon occurs in rice plant tissues was examined with respect to exogenously supplied auxins: 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-acetic acid (IAA) and naphthaleneacetic acid (NAA). In intact rice plants grown in medium containing ammonium without auxin, glutamine first increased, then asparagine gradually increased. In both shoots and roots, the asparagine content became the highest among four amino acids after 4 days of culture period. GABA did not increase at all, its level remaining low in both shoots and roots throughout the culture period. GABA accumulation was observed in excised rice root tips when they were incubated in the medium containing ammonium in the presence of 2,4-D, IAA or NAA. In the absence of auxin, however, excised rice root tips accumulated asparagine and glutamine, but not GABA. Rice root segments obtained from a region in which root cells had already developed to maturity did not accumulate GABA but asparagine and glutamine in the presence of both ammonium and 2,4-D. These results suggest that GABA accumulation occurs in rapidly growing and dividing tissue, such as the apical meristem of rice root in the presence of auxin during ammonium assimilation.
日本植物生理学会の論文