Abstract
We isolated an Arabidopsis mutant (sicy-192) whose cotyledon greening was inhibited by treatments with sugars, such as sucrose and glucose. In the mutant, the gene encoding plastidic alkaline/neutral invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys. The greening of cotyledons in the knockout-INV-E lines was not inhibited by treatment with the sugars. In addition, the knockout-INV-E lines expressing an INV-E:C294Y gene had the same phenotype as sicy-192. On treatment with sucrose, the expression of photosynthesis-related genes was weaker in seedlings of mutant plants than wild-type seedlings, while the activity of nitrate reductase was stronger in the mutant plants than wild-type plants. These findings suggest that INV-E is regulated for maintenance of the level of sucrose or its metabolites in plastids, preventing an imbalance between the supply of nitrogen to cells via nitrate assimilation and the demand for nitrogen for development of the photosynthetic apparatus.
