|Jones, Tamara - UNIV OF ILLINOIS, URB|
Submitted to: Photosynthesis International Congress Symposium Proceedings and Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 28, 1995
Publication Date: N/A
Technical Abstract: Sucrose phosphate synthase (SPS), a key enzyme in sucrose biosynthesis, is regulated by protein phosphorylation and shows a circadian pattern of activity in tomato. SPS is most active in its dephosphorylated state which normally coincides with daytime. Applying okadaic acid, a potent phosphatase inhibitor, prevents SPS activation. More interesting is that a brief treatment with cycloheximide, a cytoplasmic translation inhibitor, also prevents the light activation of SPS, without any effect on the amount of SPS protein. Cordycepin, a transcription inhibitor, has the same effect. Both of these inhibitors also inhibit the activation phase of the circadian rhythm in SPS activity. Conversely, cycloheximide and cordycepin do not prevent the decline in circadian SPS activity, but not SPS-kinase activity, is controlled at the level of gene expression. Taken together, it seems clear that there is a circadian rhythm controlling the transcription of SPS-phosphatase which subsequently dictates the cricadian rhythm in SPS activity via effects on its phosphorylation state.