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Title: EFFECTS OF LOW TEMPERATURE ON THE CIRCADIAN RHYTHM IN NITRATE REDUCTASE ACTIVITY IN TOMATO

Author
item JONES, TAMARA - PLANT BIO UOFI URB IL
item Ort, Donald

Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/28/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: In chilling sensitive plant species, such as tomato, low temperature treatment delays the progress of the circadian clock for the transcription of certain genes (Marino-Catt and Ort 1992, Proc Natl Acad. Sci. USA 89:3731-3735). We have further demonstrated chill-induced delays in the carcadin rhythm in sucrose phosphate synthase (SPS) activity as a result of the disruption of the circadian control of SPS phosphorylation state. In tomato, nitrate reductase (NR) also exhibits a circadian rhythm in activity under both constant light and constant dark conditions. Inhibitor studies show that the dark-circadian in NR activity is the result of a circadian oscillation in NR protein phosphorylation state. Okadaic acid completely inhibits the dark-circadian rise in NR activity. Interestingly, the transcription inhibitor, cordycepin, and the translation inhibitor, cycloheximide, do not disrupt the circadian rise in activity, showing that changes in NR cellular protein level are not involved in this circadian pattern of activity. Notably, these results also suggest that a circadian pattern in the synthesis of NR phosphatase is not required differing from what we found for the circadian oscillation of SPS activity in tomato. An overnight chilling treatment delays the circadian rhythm in NR activity. Inhibitor studies show that the circadian rhythm in NR phosphatase activity is disrupted by low temperature, resulting in inappropriate NR activity. This work was supported in part by the USDA National Research Initiative Competitive Grants Program (grant No. 91-37100-6620).