Analysis on the network of nitrogen partitioning and nitrogen metabolism affecting to the photosynthetic activities of leaves in crop plants

为阐明光合活性维持的生理机制，本文对光合活性相关的氮代谢网络进行了研究，重点研究了氮的吸收、同化和分配。大豆品种开花后叶片衰老速度较慢，在整个成熟期保持较高的光合速率。相较于Enrei， Tachinagaha保持了更高的rubisco和氮含量。叶片含氮量低的主要原因是植株氮素积累较少，同时氮素向豆荚的分配较多。Enrei叶片中脱落酸的含量在成熟后期迅速增加。另一方面，在成熟过程中，脱落酸的含量是稳定的。脱落酸的增加与rubisco的减少呈负相关。一种高产水稻品种akenhoshi的叶片在整个成熟阶段比Nipponbare的叶片保持更高的光合作用速率。光合活性与叶片rubisco和氮含量密切相关。叶片含氮量高的原因是植物体内氮的积累较多，此外，氮在叶片中的分配也较多。Rubisco含量与rbcL和rbcS mrna水平密切相关。rubisco的高水平维持是由于氮分配到叶片的增加，而不是由于细胞分裂素处理的植物氮吸收的增加。水分胁迫导致水稻叶片中Rubisco和氮素的降低与根系分泌物中细胞分裂素水平的降低密切相关。水分胁迫加速了rubisco在叶片中的降解。

To clarify the physiological mechanisms of the maintenance of photosynthetic activity, the network of nitrogen metabolism associated with the photosynthetic activity was investigated, focusing on the nitrogen absorption, assimilation and partitioning.1. The leaves of the soybean cultivar Tachinagaha senesce more slowly after flowering and maintain a higher rate of photosynthesis throughout the ripening period than the leaves of the Enrei cultivar. Tachinagaha maintained higher levels of rubisco and nitrogen of leaves than those of Enrei. The low leaf nitrogen content was caused by the smaller accumulation of nitrogen in plants, and in addition, by the greater partitioning of nitrogen to pods.2. The levels of abscisic acid in Enrei leaves were increased rapidly at the late stage of ripening. In other hand, the levels of abscisic acid in Tachinagaha leaves were stable during ripening. There was a negative correlation with the increase of abscisic acid and the decrease of rubisco.3. The leaves of a high yielding rice cultivar, Akenohoshi maintain a higher rate of photosynthesis throughout the ripening stage than the leaves of Nipponbare. The photosynthetic activity was closely correlated with leaf levels of rubisco and nitrogen. The high leaf nitrogen content was achieved by the greater accumulation of nitrogen in plants, and in addition, by the greater partitioning of nitrogen to leaves.4. There was a close correlation between the Rubisco content and the levels of rbcL and rbcS mRNAs. The maintenance of high levels of rubisco was caused by an increase in nitrogen partitioning to leaves and not by an increase in nitrogen absorption by plants treated with cytokinin.5. The depression of the Rubisco and nitrogen in rice leaves caused by water stress was closely correlated with the decrease of the level of cytokinin in root exudate. The rubisco degradation in leaves was accelerated by water stress.