GLUCOSE FEEDING OF INTACT WHEAT PLANTS REPRESSES THE EXPRESSION OF A NUMBER OF CALVIN CYCLE GENES

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 th e primary leaf was affected by this treatment, In glucose-fed plants a decrease in levels of mRNA encoding several Calvin cycle enzymes (fru ctose 1,6-bisphosphatase, sedoheptulose 1,7-bisphosphatase, phosphogly cerate kinase and Rubisco Small Subunit) was found to correspond to an increase in the internal levels of glucose, In control plants endogen ous 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 t ip, Conversely, Calvin cycle transcripts were seen to decrease in the oldest tip sections, In glucose-fed plants, the endogenous glucose lev els were increased throughout the leaf but Calvin cycle RNA levels wer e most markedly reduced in the mid-leaf section, These data indicate t hat the changing metabolic status of the cells from the base to the ti p of the primary wheat leaf may play a role in the regulation of Calvi n cycle gene expression during normal leaf development.