Circadian regulation of sucrose phosphate synthase activity in tomato by protein phosphatase activity

Tamara L. Jones, Donald R. Ort

Research output: Contribution to journalArticlepeer-review


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 protein 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, an inhibitor of transcript synthesis and processing, has the same effect. Both of these inhibitors also prevent the activation phase of the circadian rhythm in SPS activity. Conversely, cycloheximide and cordycepin do not prevent the decline in circadian SPS activity that normally occurs at night. These observations indicate that SPS phosphatase activity but not SPS kinase activity is controlled, directly or indirectly, at the level of gene expression. Taken together, these data imply that there is a circadian rhythm controlling the transcription of a protein phosphatase that subsequently dictates the circadian rhythm in SPS activity via effects on this enzyme's phosphorylation state.

Original languageEnglish (US)
Pages (from-to)1167-1175
Number of pages9
JournalPlant physiology
Issue number4
StatePublished - Apr 1997

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science


Dive into the research topics of 'Circadian regulation of sucrose phosphate synthase activity in tomato by protein phosphatase activity'. Together they form a unique fingerprint.

Cite this