Molecular and physiological basis of Rubisco turnover and its relation to nitrogen nutrition

氮素营养对水稻叶片出苗至衰老过程中rbc和rbcL mrna水平与Rubisco合成量关系的影响在整个实验过程中，4mm处理的红细胞和rbcL mrna水平、Rubisco合成量和N内流均大于1mm处理。两种氮素处理下，Rubisco的合成量与叶片膨大过程中两种mrna的表达量均呈良好的相关性，而与叶片膨大完成后的mrna表达量无关。Rubisco合成量与两种mrna水平的比值在完全扩增后急剧下降。另一方面，两种氮素处理下Rubisco的合成量与N的内流密切相关。这些结果表明，在水稻叶片的整个生命周期中，与叶片中Rubisco合成量更密切相关的是N流入，即N有效性，而不是红细胞和rbcL mrna的水平。免疫细胞化学电镜观察表明，在小麦自然衰老叶片中，Rubisco及其降解产物主要分布在直径为0.4 ~ 1.2 μm的球状小体中。这些含Rubisco小体（RCBS）存在于细胞质和液泡中。RCBs含有另一种基质蛋白，叶绿体谷氨酰胺合成酶，但不含类囊体蛋白。超微结构分析表明，RCBs具有双膜结构，可能来源于叶绿体包膜，并进一步被细胞质中的其他膜结构所包围。在叶片衰老早期Rubisco含量开始下降时，rcb的出现最为显著。这些结果表明RCBS可能参与了叶片衰老过程中叶绿体外Rubisco的降解过程。低温条件下完整黄瓜叶片中Rubisco大亚基在活性氧作用下的体内断裂。低温敏感黄瓜叶片在4℃光照下，观察到LSU的5个主要片段。这种分裂被活性氧清除剂完全抑制，铁刺激了这种分裂，而铁特异性螯合剂去福尔胺则抑制了这种分裂。此外，在体外二维PAGE上，这些片段与纯化的Rubisco通过oh生成系统产生的片段相同。这些结果表明，在完整的叶片中，Rubisco也会被活性氧直接裂解。少

Effects of nitrogen nutrition on the relationships between the levels of rbcS and rbcL mRNAs and the amount of Rubisco synthesized in rice leaves from emergence through senescence.The levels of rbcS and rbcL mRNAs, the amount of Rubisco synthesized, and the N influx greater for the 4 mM treatment than for the 1 mM treatment throughout the experiment. The mount of Rubisco synthesized was well correlated with the levels of both mRNAs during leaf expansion, but not after the completion of leaf expansion in both N treatments. The ratio of the amount of Rubisco synthesized to the levels of both mRNAs dramatically declined after full expansion. On the other hand, the amount of Rubisco synthesized was well correlated with the N influx in both N treatments. These results indicate that the N influx, namely, N availability, rather than the levels of rbcS and rbcL mRNAs, is more closely related to the amount of Rubisco synthesized in the leaf blade of rice throughout the life span of a leaf.Exclu … More sion of Rubisco from chloroplasts by specific bodies in naturally senescing leaves of wheatImmunocytochemical electron-microscopic observation indicated that Rubisco and/or its degradation products are localized in small spherical bodies having a diameter of 0.4-1.2 μm in naturally senescing leaves of wheat. These Rubisco containing bodies (RCBS) were found in the cytoplasm and in the vacuoles,. RCBs contained another stromal protein, chloroplastic glutamine synthetase, but not thylaloid proteins. Ultrastructural analysis suggested that RCBs had double membranes, which seemed to be derived from the chloroplast envelop, and that RCBS were further surrounded by the other membrane structures in the cytoplasm. The appearance of RCBs was the most remarkable when the amount of Rubisco started to decrease at the early phase of leaf senescence. These results suggest that RCBS might be involved in the degradation process of Rubisco out side of chloroplasts during leaf senescence.In vivo frgmentation of the large subunit of Rubisco by reactive oxygen species in an intact leaf of Cucumber under chilling conditions.When lea discs of chilling-sensitive cucumber were illuminated at 4-℃, five major fragments of the LSU were observed. This fragmentation was completely inhibited by ROS scavengers and Tiron stimulated this fragmentation, whereas an iron-specific chelator, deforoxamine, suppressed it. Further, such fragments were identical to those generated from the purified Rubisco by an-OH-generating system in vitro on two-dimensional PAGE. These results indicate that the direct fragmentation of Rubisco by reactive oxygen species also occurs in an intact leaf. Less