Molecular Basis for Nitrogen Remobilization with Leaf Senescence

研究了水稻叶片在平均和低光照下衰老过程中叶绿体蛋白质含量的变化。两种光照下衰老叶片的Rubisco和LHCII含量存在明显差异。低光照下叶片LHC Ⅱ的下降比Rubisco的下降晚得多，而平均光照下叶片LHC Ⅱ的下降比Rubisco的下降晚得多。这些结果表明，即使在感光叶片中，RuBP羧化能力与捕光能力的比值也可以调节，以适应给定的光照，这种适应主要受蛋白质降解水平的控制，与氮代谢和再动员有关的酶如GSI，GSII，Fd-GOGAT，和NADH-GOGAT在水稻叶片寿命期间进行了检测。GSII和Fd-GOGAT与Rubisco在整个生命周期中协调变化， 关于我们 叶片衰老过程中GSI含量变化不大。NADH-GOGAT在发育叶片中的活性相对高于成熟和衰老叶片。GSI和NADH-GOGAT在维管束组织中分布丰富，表明这两种酶参与了组织中氮素的装卸。比较了上级颖花和弱势颖花成熟过程中氮素、干物质、谷蛋白及其mRNA的积累。谷蛋白及其mRNA在下位小穗中的积累开始较上级小穗晚。用纯化的小麦叶片叶绿体裂解液测定了其对Rubisco的蛋白水解活性。在酸性pH范围内的活性高于碱性pH范围。叶片内肽酶对CBZ-Gly-Pro-Gly-Gly-Pro-Ala的活性约40%存在于叶绿体组分中。少

Changes in the amounts of chloroplast proteins were examined in the leaves of rice grown under average and low irradiances during senescence. Clear differences were observed in Rubisco and LHCII between the leaves senesced under the two irradiances. The decrease of LHC II occurred much later than that of Rubisco in the leaves with the low irradiance, while it follwed soon after the decrease of Rubisco in the leaves with the average irradiances. These results suggested that ratio of capacity of light harvesting to that of RuBP carboxylation can be regulated in the manner to adapt to a given irradiance even in the senscing leaves as in growing leaves and that the adaptation can be mainly controled by the levels of protein degradation.Changes in the levels of enzymes related to nitrogen metabolism and remobilization such as GSI,GSII,Fd-GOGAT,and NADH-GOGAT were examined during the life span of a rice leaf. GSII and Fd-GOGAT changed coordinately with Rubisco throughout the life span of the … More leaf, while the levels of GSI changed little during senescence. NADH-GOGAT was relatively more active in the developing leaves than the mature and senescing leaves. GSI and NADH-GOGAT were located abundantly in vascular-bundle tissues, suggesting that these enzymes are involved in loading and unloading of nitrogen compounds in the tissues.Accumulation of nitrogen, dry matter, glutelin and its mRNA were compared between superior spikelets and inferior spikelets during ripening of rice ear. Accumulation of glutelin and its mRNA started much later in the inferior spikelets than the superior spike lets. It was suggested that the retardation of the accumulation in the inferior spikelets was attributed to the late development of endosperm tissues.Proteolytic activity against Rubisco was assayd with the lysates of the purified chloroplasts from wheat leaves. The activity was higher in acidic pH ranges than alkaline pH ranges. About 40% of the total-leaf endopeptidase activity against CBZ-Gly-Pro-Gly-Gly-Pro-Ala was found in the chloroplast fraction. Less