水稻Rubisco和RCA的日变化及其细胞定位

采用免疫胶体金标记电镜技术对水稻(Oryza satova subsp.indica cv.浙农952)叶片中的Rubisco及其活化酶(RCA)进行细胞器定位和定量，同时用免疫扩散法进行叶片含量分析，研究了这两种酶含量及活力的日变化。结果表明Rubisco主要分布于叶绿体，RCA分布于叶绿体和线粒体中；光合速率(Pn)、Rubisco初始活力和RCA活力与光合日变化密切相关；在光照最强的13时，出现光合“午休”，叶绿体中Rubisco的密度有一定程度降低，而全叶的总Rubisco保持稳定，Rubisco初始活力也有明显的“午休”，这意味着体内Rubisco的活力除受RCA调节外，可能还与叶绿体中Rubisco的分布有关。RCA活力变化与叶绿体中RCA含量变化较为一致，表明RCA在叶绿体中的分布对调节其本身活力和Rubisco活性有重要作用。

Diurnal Changes of Rubisco and RCA Activities and Their Cellular Localization in Rice

The cellular localization of Rubisco and Rubisco activase (RCA) in rice (Oryza sativa subsp.indica cv. Zhenong 952) leaf was investigated with immunogold-labeled electron microscope techniques onthe basis of determining the diurnal changes of photosynthetic rate (Pn), Rubisco and RCA activities, andquantifying two enzyme contents in the leaf with immuno-diffusion method in order to understand whyRCA activity decreased in the midday when its contents was high. The results showed that Rubisco mainlywas located in chloroplast, and RCA were found both in chloroplast and mitochondria. The lowering ofRubisco in chloroplast as well as Rubisco activity at noon could be one of good reasons to explain thephotosynthetic midday depression in leaf. The density of RCA in chloroplast reached the maximum at14:00 and a valley at 11:00. The result much coincided with the activity of RCA in leaf. In mitochondria, thedensity of RCA changed abruptly in one day with the highest at 13:00 and it can well elucidate why theactivities of Rubisco declined at noon when its amount was increasing. Therefore the cellular localizationand/or distribution of Rubisco and RCA during a day is more important for Pn , Rubisco and RCA activities.