Nitrogen metabolism and remobilization during senescence
Nitrogen metabolism and remobilization during senescence
复制标题
DOI：
10.1093/jexbot/53.370.927
复制
发表时间：
2002-04-01
影响因子：
6.9
通讯作者：
Feller, U
中科院分区：
文献类型：
--
作者：
Hörtensteiner, S;Feller, U
衰老是一个高度有组织、有良好调控的过程。C3植物叶肉叶绿体中的氮素可能占细胞总氮的75%。叶绿体蛋白质的降解在衰老的早期阶段开始，释放出来的氨基酸可以输出到植物的生长部分(如成熟的果实)。Rubisco和其他基质酶可以在分离的叶绿体中降解，这意味着参与了胞质多肽水解酶的作用。是否需要ATP，以及基质蛋白是否在降解之前被修饰(例如，被活性氧修饰)，这些问题仍在争论中。一些蛋白质，特别是半胱氨酸蛋白酶，已被证明在衰老过程中特异表达。它们对叶绿体蛋白质的普遍降解的贡献尚不清楚。在完整细胞中积累的多肽片段和抑制剂的研究表明，基质蛋白可能存在多种降解途径，在特定条件下也可能涉及空泡内肽酶。与类囊体膜相关的叶绿素结合蛋白的分解还没有得到很好的研究。这些蛋白质的降解需要叶绿素的同时分解代谢。在过去的十年中，叶绿素的分解已被阐明。有趣的是，叶绿素中存在的氮并不是从衰老的叶片中输出的，而是以线性四吡咯分解代谢的形式留在细胞内，积累在液泡中。叶绿素和叶绿体蛋白的降解途径部分是相互关联的。
Senescence is a highly organized and well-regulated process. As much as 75% of total cellular nitrogen may be located in mesophyll chloroplasts of C-3-plants. Proteolysis of chloroplast proteins begins in an early phase of senescence and the liberated amino acids can be exported to growing parts of the plant (e.g. maturing fruits). Rubisco and other stromal enzymes can be degraded in isolated chloroplasts, implying the involvement of plastidial peptide hydrolases. Whether or not ATP is required and if stromal proteins are modified (e.g. by reactive oxygen species) prior to their degradation are questions still under debate. Several proteins, in particular cysteine proteases, have been demonstrated to be specifically expressed during senescence. Their contribution to the general degradation of chloroplast proteins is unclear. The accumulation in intact cells of peptide fragments and inhibitor studies suggest that multiple degradation pathways may exist for stromal proteins and that vacuolar endopeptidases might also be involved under certain conditions. The breakdown of chlorophyll-binding proteins associated with the thylakoid membrane is less well investigated. The degradation of these proteins requires the simultaneous catabolism of chlorophylls. The breakdown of chlorophylls has been elucidated during the last decade. Interestingly, nitrogen present in chlorophyll is not exported from senescencing leaves, but remains within the cells in the form of linear tetrapyrrolic catabolites that accumulate in the vacuole. The degradation pathways for chlorophylls and chloroplast proteins are partially interconnected.