Analysis of Flowering Induced by L-Pipecolic Acid in Lemna

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Previosly L-Pipecolic acid was isolated as a flower-inducing substance from Lemna extracts. A subsequent study demonstrated that L-pipecolic acid is effective in inducing flowering of many strains of Lemna. The mechanism by which L-pipecolic acid induces flowering in Lemna remains, however, to be determined. In order to clarify the flowering mechanism induced by L-pipecolic acid in Lemna, biosynthesis and metabolism of L-pipecolic acid was investigated in relation to flowering. In addition, analysis of gene and protein specifically induced by L-pipecolic acid was carried out.Lysine was found to have flower-inducing activity in Lemna, and the effect of lysine on flowering was found to be enhanced in the presence of lysine catabolite, alpha-aminoadipic acid. These results suggested that the flowering of Lemna might be induced by L-pipecolic acid, derived from exogenously applied lysine. Amino-acid analysis indicated that the level of L-pipecolic acid increased several fold by exogenous application of lysine to the medium. In addition, the conversion of lysine to L-pipecolic acid was demonstrated definitively by metabolic study using deuterium labeled lysine. Thus, the present study indicates that conversion of lysine to L-pipecolic acid induces flowering of Lemna. L-Pipecolic acid can induce flowering of Lemna by the addition of this compound to the medium. Using this system, gene and protein induced by L-pipecolic acid were examined. Treatment of L-pipecolic acid tended to increase total RNA,however, no significant change of gene expression was found. Furthermore, no specific protein induced by L-pipecolic acid was found.