Abstract
The plastocyanin (PC) gene of Arabidopsis thaliana is activated independently of light during early seedling development. In etiolated seedlings, PC mRNA levels increase transiently and a maximum dark level is reached after 2 d of growth in darkness. In etiolated transgenic seedlings carrying a chimeric PC-promoter: luciferase fusion gene, luciferase activity is similarly increased after 2 d of growth. The transient increase in PC mRNA and luciferase activity levels can be repressed by sucrose. Nonmetabolizable sugars and polyethylene glycol do not have a major effect on PC gene expression. Also, light-grown seedlings show a similar transient and sucrose-sensitive increase in PC mRNA levels and luciferase activity, as in dark-grown seedlings, but here expression levels are 15- fold higher. These findings suggest the presence of a sucrose-sensitive, developmentally controlled expression mechanism that operates independently of light.