Molecular Basis for Nitrogen Remobilization with Leaf Senescence

研究了在平均和低光照条件下生长的水稻叶片衰老过程中叶绿体蛋白含量的变化。两种光照下衰老叶片的Rubisco和LHCII含量存在明显差异。低照度叶片中LHC - II的降低比Rubisco的降低晚得多，而平均照度叶片中Rubisco的降低紧随其后。这些结果表明，即使在感觉叶片中，RuBP羧基化能力与光收获能力的比值也可以通过调节来适应给定的光照，并且这种适应主要是由蛋白质降解水平控制的。研究了水稻叶片中与氮代谢和再动员相关的酶如GSI、GSII、Fd-GOGAT和NADH-GOGAT水平的变化。GSII Fd-GOGAT改变协调伴随二磷酸核酮糖羧化酶的寿命 ... 更多的叶子,而水平的GSI衰老期间变化不大。NADH-GOGAT在发育叶片中的活性高于成熟叶片和衰老叶片。GSI和NADH-GOGAT在维管束组织中大量存在，表明这些酶参与了组织中氮化合物的装载和卸载。比较了水稻穗成熟过程中优势穗和劣势穗氮素、干物质、谷蛋白及其mRNA的积累量。谷蛋白及其mRNA在下层小穗中的积累比上层小穗晚得多。结果表明，低穗积累的滞后与胚乳组织发育较晚有关。用小麦叶片纯化后的叶绿体裂解物测定了对Rubisco的蛋白水解活性。活性在酸性范围内高于碱性范围。抗CBZ-Gly-Pro-Gly-Gly-Pro-Ala的总叶内肽酶活性约40%存在于叶绿体部位。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