Photosynthesis and Biomass Improvement in Rice

转基因水稻（Oryza sativa L.）通过农杆菌介导的水稻rbcS启动子控制下的水稻rbcS正义或反义基因转化获得了具有不同量的核酮糖-1，5-二磷酸羧化酶/加氧酶（Rubisco）的植株。尽管在某些意义上rbcS突变体中Rubisco含量增加到野生型Rubisco的150%，但CO_2同化对胞间CO_2分压的响应分析（A：Ci曲线）并未表明Rubisco含量的增加导致CO_2限制光合作用的增加。此外，在100 Pa CO_2下，几个有义转化体系的光合作用下降。结果表明，rbcS抗性植株的Rubisco蛋白质含量、rbcL和rbcS mRNA水平以及其他几种Calvin循环酶活性均发生了变化。Rubisco含量的降低往往导致光合作用的降低，特别是在低CO_2条件下。其他酶活性和叶绿素含量在基因型间无差异，但只有低位叶片Rubisco含量在反义植株中保持较高水平。由于在其叶片中未检测到rbcS mRNA水平，这些结果表明，在反义植物的衰老叶片中发生了Rubisco降解的抑制。因此，Rubisco在叶片衰老过程中存在一种特定的降解机制。

Transgenic rice (Oryza sativa L.) plants with different amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were obtained by the Agrobacterium-mediated transformation with the rice rbcS sense or antisense gene under the control of the rice rbcS promoter. Although Rubisco content was enhanced up to 150% wild type Rubisco in some sense-rbcS transformant, the analyses of the response of CO_2 assimilation to intercellular CO_2 partial pressure (A : Ci curve) did not show that enhancement of Rubisco content leads to an increase in CO_2-limited photosynthesis. In addition, several the sense transformant lines show decreased photosynthesis at 100 Pa CO_2. This was caused by partial deactivation of Rubisco in vivo.For the anti-rbcS plants, changes in the levels of protein and rbcL and rbcS mRNA of Rubisco and in the activities other several Calvin-cycle enzymes were examined in the leaves at different leaf positions. A decrease in Rubisco content always led to decreased photosynthesis, especially under low CO_2 conditions. Although no differences the activities of other enzymes and chlorophyll content were found between genotypes, only Rubisco content in leaves at lower positions remained relatively higher levels in antisense plants. Since rbcS mRNA levels were not detected in their leaves, these results indicate that suppression of Rubisco degradation occurred in the senescent leaves of the antisense plants. Thus, the existence of a specific degradation mechanism(s) of Rubisco during leaf senescence is suggested to be in vivo.