マメ科植物における水およびリン利用効率の遺伝的改良

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We have studied mechanisms of N_2 fixation with the aim to enhance legume crop productivity under phosphonls (P) deficiency. Our findings are as follows :1. N_2 fixation in Medicago truncatula is mediated through an N-feedback mechanism that is closely related to nodule carbon metabolism under P stress. The critical role of asparagine in the down-regulation of N_2 fixation was revealed.2. M. truncatula had a higher symbiotic N_2 fixation than M. sativa under P deprivation conditions, which was related to the ability to increase the organic acid concentration in nodules, namely malate.3. The improved efficiency in chickpea symbiois was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes related to the nodule carbon and nitrogen metabolisms.