Ferreira R B, Davies D D
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
Plant Physiol. 1987 Apr;83(4):878-83. doi: 10.1104/pp.83.4.878.
The concept of ribulose bisphosphate carboxylase as a storage protein is not supported in the case of Lemna minor, where the enzyme appears to be particularly stable under conditions of nitrogen starvation. Total nutrient starvation in light and in the dark induced the degradation of this enzyme, but not at an enhanced rate compared with other leaf proteins and, surprisingly, darkness inhibited the degradation of chlorophyll which occurs with total nutrient starvation in the light. The data suggest that Lemna is not programmed to senesce in response to nutrient starvation. Differences in the pattern of protein degradation, which occurred under the stress conditions employed, are not consistent with a simple model of protein degradation in which the degradative system is assumed to be located in the vacuole. The data is best explained by a dual system in which cytosolic proteins are degraded by a vacuolar/lysosomal system and chloroplast proteins are degraded within the chloroplast. Whatever the system of degradation, our data do not support the proposed correlation between the rate of protein degradation and either protein charge or size.
在浮萍（Lemna minor）中，核酮糖二磷酸羧化酶作为一种储存蛋白的概念并不成立，在这种植物中，该酶在氮饥饿条件下似乎特别稳定。光照和黑暗条件下的完全营养饥饿都会诱导这种酶的降解，但与其他叶片蛋白相比，其降解速率并未加快，而且令人惊讶的是，黑暗抑制了在光照条件下完全营养饥饿时发生的叶绿素降解。数据表明，浮萍并没有因营养饥饿而衰老的程序。在所采用的胁迫条件下发生的蛋白质降解模式差异，与蛋白质降解的简单模型不一致，在该模型中，降解系统被认为位于液泡中。数据最好用双重系统来解释，即胞质蛋白由液泡/溶酶体系统降解，叶绿体蛋白在叶绿体内降解。无论降解系统如何，我们的数据都不支持蛋白质降解速率与蛋白质电荷或大小之间的拟相关关系。
