ABSTRACT Photosynthetic activity is expected to be maintained during leaf senescence if the amount of Rubisco is maintained. As the mRNA level of the Rubisco gene decreases rapidly just before the stage of full expansion, its overexpression after full expansion would be effective. We previously found that the mRNA level of the Rubisco activase gene (RCA) is maintained during leaf senescence. In the present study, the Rubisco small subunit gene (RBCS) was overexpressed under the control of the promoter of RCA in rice. Although Rubisco content increased in the uppermost, fully expanded leaves of transgenic plants in comparison with that in wild-type plants, in the penultimate leaves it decreased to a level similar to that of the wild-type plants. In expanding leaves in transgenic plants, the mRNA levels of the transgene RBCS increased further, leading to increases in the mRNA levels of total RBCS and the Rubisco large subunit gene (RBCL). In the uppermost, fully expanded leaves and the penultimate fully expanded leaves, however, the mRNA levels of RBCS2 and total RBCS decreased drastically, and those of RBCL were similar to the wild-type levels. These results indicate that Rubisco content was not maintained during leaf senescence in the transgenic plants. One reason for this is that the expression of RBCS by the RCA promoter was weak in leaves at low positions. We discuss the possible reasons for this unexpected phenomenon.

中文翻译：

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Rubisco激活酶启动子调控下Rubisco小亚基基因过表达对水稻叶片不同位置Rubisco含量的影响

摘要 如果Rubisco 的量保持不变，光合活性有望在叶片衰老过程中得以保持。由于 Rubisco 基因的 mRNA 水平在完全扩增阶段之前迅速下降，因此其在完全扩增后的过度表达将是有效的。我们以前发现 Rubisco 激活酶基因 (RCA) 的 mRNA 水平在叶片衰老过程中保持不变。在本研究中，Rubisco 小亚基基因 (RBCS) 在水稻中在 RCA 启动子的控制下过表达。尽管与野生型植物相比，转基因植物最上面、完全展开的叶子中 Rubisco 含量增加，但在倒数第二个叶子中，它下降到与野生型植物相似的水平。在转基因植物中扩大叶片时，转基因 RBCS 的 mRNA 水平进一步增加，导致总 RBCS 和 Rubisco 大亚基基因 (RBCL) 的 mRNA 水平增加。然而，在最上面的完全展开的叶子和倒数第二个完全展开的叶子中，RBCS2 和总 RBCS 的 mRNA 水平急剧下降，而 RBCL 的水平与野生型相似。这些结果表明，在转基因植物的叶片衰老过程中，Rubisco 含量没有得到维持。原因之一是 RCA 启动子对 RBCS 的表达在低位叶中较弱。我们讨论了这种意外现象的可能原因。RBCL 与野生型水平相似。这些结果表明，在转基因植物的叶片衰老过程中，Rubisco 含量没有得到维持。其原因之一是 RCA 启动子对 RBCS 的表达在低位叶中较弱。我们讨论了这种意外现象的可能原因。RBCL 与野生型水平相似。这些结果表明，在转基因植物的叶片衰老过程中，Rubisco 含量没有得到维持。原因之一是 RCA 启动子对 RBCS 的表达在低位叶中较弱。我们讨论了这种意外现象的可能原因。