Glucose feeding of intact wheat plants represses the expression of a number of Calvin cycle genes

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Abstract
The photosynthetic capacity and Rubisco levels of primary wheat leaves were reduced significantly in plants grown on media supplemented with 1 % glucose. Neither the chlorophyll content nor the growth rate of the primary leaf was affected by this treatment. In glucose‐fed plants a decrease in levels of mRNA encoding several Calvin cycle enzymes (fructose 1,6‐bisphosphatase, sedoheptulose 1,7‐bisphosphatase, phosphoglycerate kinase and Rubisco Small Subunit) was found to correspond to an increase in the internal levels of glucose. In control plants endogenous levels of glucose and sucrose were measured in leaf sections from the base to the tip of the primary leaf, which revealed a gradient of each of these sugars within the leaf, with the highest levels at the tip. Conversely, Calvin cycle transcripts were seen to decrease in the oldest tip sections. In glucose‐fed plants, the endogenous glucose levels were increased throughout the leaf but Calvin cycle RNA levels were most markedly reduced in the mid‐leaf section. These data indicate that the changing metabolic status of the cells from the base to the tip of the primary wheat leaf may play a role in the regulation of Calvin cycle gene expression during normal leaf development.