XCT Inhibits Red Light Input to the Clock.
(A) and (B) Period length of CCR2pro:LUC expression in xct mutants assayed in constant red (A) and constant blue (B) light of various fluence rates (n = 5 to 12). Mutants are more responsive than Col to increased fluence rates of red light (A) (P < 0.01 by analysis of variance [ANOVA]) but not blue light (B) (P > 0.1 by ANOVA).
(C) Period fluence rate response curve for toc1 mutants in constant red light (n = 12). The pace of the clock in toc1-1 responds to red light at the same rate as Col (P > 0.1 by ANOVA), whereas toc1-2 demonstrates an increased rate of period change from Col with increasing red light (P < 0.01 by ANOVA).
(D) Phase response curve of CCR2pro:LUC expression. Red light pulses were given at the indicated circadian time, and the magnitude of the resulting circadian phase shift in the peak of CCR2pro:LUC expression is shown on the y axis. Error bars represent the se of response. Shaded and filled bars represent subjective day and night, respectively.