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

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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