C. Inputs other than light can set the circadian clock. Microarray analysis of dirunal and circadian-regulated genes in Arabidopsis .
Cells have internal oscillators that operate independently of light stimulus.
However, the circadian clock can be reset by light. The oscillator must be trained by inputs. A complete mechanistic model for the oscillator does not yet exist, but genes encoding some of the components have been identified. Schaffer et al. 2-label gene array experiments using 11,521 Arabidopsis ESTs representing 7800 unique genes .