Abstract:

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 on the basis of determining the diurnal changes of photosynthetic rate (Pn), Rubisco and RCA activities, and quantifying two enzyme contents in the leaf with immuno-diffusion method in order to understand why RCA activity decreased in the midday when its contents was high. The results showed that Rubisco mainly was located in chloroplast, and RCA were found both in chloroplast and mitochondria. The lowering of Rubisco in chloroplast as well as Rubisco activity at noon could be one of good reasons to explain the photosynthetic midday depression in leaf. The density of RCA in chloroplast reached the maximum at 14:00 and a valley at 11:00. The result much coincided with the activity of RCA in leaf. In mitochondria, the density of RCA changed abruptly in one day with the highest at 13:00 and it can well elucidate why the activities of Rubisco declined at noon when its amount was increasing. Therefore the cellular localization and/or distribution of Rubisco and RCA during a day is more important for Pn , Rubisco and RCA activities.

水稻Rubisco 和RCA 的日变化及其细胞定位
王妮妍  􊎠蒋德安  洪 健 􊎠张 峰  􊎠翁晓燕

（1. 浙江大学生命科学学院植物生理生化国家重点实验室, 杭州 310029；2.浙江大学生物技术研究所, 杭州 310029）
摘要： 采用免疫胶体金标记电镜技术对水稻(Oryza sativa 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。
关键词： 日变化； Rubisco；Rubisco 活化酶(RCA)；定位；叶绿体；线粒体

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