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

氮素营养对水稻出苗至衰老叶片中rbcs和rbcL mRNAs水平与Rubisco合成量之间关系的影响：在整个试验过程中，4 mM处理的rbcs和rbcL mRNAs水平、rbcL mRNAs的合成量以及氮素内流大于1 mM处理。在叶片展开过程中，Rubisco合成量与两种mRNAs的水平有很好的相关性，但在叶片展开完成后，两个N处理的Rubisco合成量与两个mRNAs的水平不相关。在完全扩张后，Rubisco合成量与这两个mRNAs水平的比率显著下降。另一方面，在两个氮素处理中，Rubisco的合成量与氮素内流都有很好的相关性。这些结果表明，在水稻叶片的整个生命周期中，N的内流，即N的有效性，而不是RBC和RbcL mRNAs的水平，与叶片中合成的Rubisco的数量更密切地相关。不包括…小麦自然衰老叶片叶绿体特异体多表达Rubisco免疫细胞化学电子显微镜观察表明，小麦自然衰老叶片中Rubisco和/或其降解产物定位于直径为0.4~1.2μm的小球体中。这些含Rubisco小体(RCB)存在于细胞质和液泡中。RCBs含有另一种基质蛋白--氯化谷氨酰胺合成酶，但不含海鞘蛋白。超微结构分析表明，RCBs具有双层膜，似来源于叶绿体被膜，并进一步被细胞质中的其他膜结构所包围。在叶片衰老初期，Rubisco的含量开始下降时，RCBs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侧Rubisco的降解过程。在低温条件下，黄瓜完整叶片中的Rabisco大亚基被活性氧降解。在4-℃光照下，冷敏感黄瓜的LeA圆片上观察到了5个主要的LSU片段。这种碎裂被ROS清除剂完全抑制，而TIron刺激这种碎裂，而铁特异的螯合剂deforoxamine则抑制这种碎裂。此外，这些片段与体外用-OH-生成系统从纯化的Rubisco中产生的片段在二维PAGE上是相同的。这些结果表明，在完整的叶片中也发生了由活性氧直接引起的Rubisco的碎裂。较少

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