McClung 9316662 Rhythmic biological phenomena which recur at approximately 24 hour intervals in the absence of environmental time cues are termed circadian rhythms, and their timing is regulated by an endogenous biological clock. The molecular basis of circadian rhythmicity is not understood in any biological system. Our study of such rhythms in Arabidopsis thalania will be continued by, 1) Investigating the ontogeny of the circadian clock and of the role of light in the induction and phasing of circadian rhythmicity in seedlings. 2) Identification and analysis of mutants with altered clock properties (specifically, altered period length) using a screen based on the circadian resistance to sulfur dioxide exposure conferred by the circadian rhythm in stomatal aperture and 3) The analysis of the circadian regulation of RCA transcription, a gene involved in carbon assimilation. %%% The experiments to be done are designed to elucidate the molecular basis by which time information is generated by the biological clock and used to regulate plant gene expression. The circadian clock regulates the expression of a number of Arabidopsis genes, including genes involved in light harvesting, in carbon assimilation, in photorespiration and in nitrogen assimilation. The interaction between the circadian clock and light indicate that any complete understanding of plant response to environmental stimuli, such as light level and light-dark regimen, must include an understanding for the endogenous capacity of plants to measure time. ***
