Plant Physiology 83:878-883 (1987)
© 1987 American Society of Plant Biologists
Environmental and Stress Physiology
Protein Degradation in Lemna with Particular Reference to Ribulose Bisphosphate Carboxylase
II. The Effect of Nutrient Starvation
Ricardo B. Ferreira and
David D. Davies
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
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.
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