In the field of chronobiology, this thing is considered a powerful entrainer.
In the field of chronobiology, this thing is considered a powerful entrainer. This thing is generated by GFP, making that protein suitable as a reporter. As proven by an experiment conducted with shoots of grass with their coleoptiles mutilated or removed, auxin was found to control the tropic ("troh-pick") response to this phenomenon. When rhodopsin interacts with this thing, rhodopsin is bleached. By disrupting melatonin secretion, it interferes with circadian rhythms. P680 and P700, in the photosystems, are designed to capture this thing. For 10 points, name this phenomenon which interacts with chlorophyll to initiate photosynthesis. 
In the field of chronobiology, this thing is considered a powerful entrainer.
light [or photons; or obvious equivalents] 