Photosynthesis and Biomass Improvement in Rice

在水稻红细胞启动子的调控下，通过农杆菌介导水稻红细胞正义基因或反义基因的转化，获得了具有不同量核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的转基因水稻植株。虽然Rubisco含量在某种意义上提高到野生型Rubisco的150%，但CO_2同化对细胞间CO_2分压的响应分析（A: Ci曲线）并未显示Rubisco含量的提高导致CO_2限制光合作用的增加。另外，在100 Pa CO_2条件下，一些感态转化线表现出光合作用下降的趋势。这是由体内Rubisco的部分失活引起的。在抗红细胞的植物中，研究了不同叶位Rubisco蛋白、rbcL和rbcS mRNA水平以及其他几种卡尔文循环酶活性的变化。Rubisco含量的降低总是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不同基因型间无差异，反义植物中只有低位置的Rubisco含量相对较高。由于在叶片中未检测到rbc mRNA水平，这些结果表明Rubisco降解的抑制发生在反义植物的衰老叶片中。因此，Rubisco在叶片衰老过程中可能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.