|Jones, Tamara - UNIV OF ILLINOIS, URBANA|
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 cordycepin do not prevent the decline in circadian SPS activity. These observations indicate that SPS-phosphatase 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 circadian rhythm in SPS activity via effects on its phosphorylation state.