Chen M H, Liu L F, Chen Y R, Wu H K, Yu S M
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, ROC.
Plant J. 1994 Nov;6(5):625-36. doi: 10.1046/j.1365-313x.1994.6050625.x.
A rice suspension cell culture system has been established to study how sugar depletion regulates alpha-amylase expression, carbohydrate metabolism, and other physiological and cellular changes. It is shown here that a group of 44 kDa alpha-amylases are constitutively expressed whether or not the cells are starved of sucrose. However, expression of a new group of alpha-amylases of 46 kDa is dramatically induced when cells are starved of sucrose. Cellular sugar and starch were rapidly consumed and metabolic activity was decreased in the starved cells. Extensive autophagy also occurred in the starved cells, which caused an increase in vacuolar volume and degradation of cytoplasmic constituents including amyloplasts. Immunocytochemical studies revealed that alpha-amylases are localized in starch granules within amyloplasts, in cell walls, and in some of the vacuoles. The presence of putative signal sequences in the N-termini of nine rice alpha-amylases suggests hitherto unidentified pathways for import of alpha-amylases into amyloplasts. The studies show that differential alpha-amylase expression, carbohydrate metabolism, metabolic activity, and vacuolar autophagy are coordinately regulated by the sugar level in the medium. As the starved suspension cells exhibit some sugar-regulated characteristics of alpha-amylase expression in germinating rice embryos as well as physiological changes similar to those in senescing cells, this system represents an ideal tool for studying cellular, biochemical, and molecular biological aspects of alpha-amylase gene regulation, carbohydrate metabolism, senescence, and protein targeting in plants.
已建立水稻悬浮细胞培养系统，以研究糖耗尽如何调节α-淀粉酶表达、碳水化合物代谢及其他生理和细胞变化。本文表明，无论细胞是否缺乏蔗糖，一组44 kDa的α-淀粉酶都会组成性表达。然而，当细胞缺乏蔗糖时，一组新的46 kDa的α-淀粉酶的表达会显著诱导。饥饿细胞中细胞糖和淀粉迅速消耗，代谢活性降低。饥饿细胞中也发生了广泛的自噬，这导致液泡体积增加和包括造粉体在内的细胞质成分降解。免疫细胞化学研究表明，α-淀粉酶定位于造粉体内的淀粉颗粒、细胞壁和一些液泡中。9种水稻α-淀粉酶N端存在推定信号序列，提示α-淀粉酶导入造粉体存在迄今未明确的途径。研究表明，α-淀粉酶的差异表达、碳水化合物代谢、代谢活性和液泡自噬受培养基中糖水平的协同调节。由于饥饿的悬浮细胞表现出萌发水稻胚中α-淀粉酶表达的一些糖调节特征以及与衰老细胞相似的生理变化，该系统是研究植物中α-淀粉酶基因调控、碳水化合物代谢、衰老和蛋白质靶向的细胞、生化和分子生物学方面的理想工具。
