Blue-light-absorbing photoreceptors in plants

Abstract

Evidence is presented that more than one blue-light photoreceptor plays a role in morphogenesis, and that there are at least three, distinguishable on the basis both of action spectra and other criteria, which may be found both in green plants and fungi. One of these has been tentatively identified as a flavoprotein-cytochrome complex, most probably located in the plasma membrane. Studies with oat seedlings suggest that it may be involved in photoreception for phototropism, at least for the first positive curvature response. Both photoreduction of the cytochrome, via excitation of the flavin, and phototropic sensitivity in the first positive curvature range are similarly affected by diphenylether herbicides. The second class of photoreceptors can be distinguished from the first in Neurospora by both genetic and physiological evidence, as well as by the action spectrum. It could be either flavin or carotenoid, although a different moiety is not excluded. The third class, distinguished only by action spectroscopy, shows a single sharp action peak near 475 mm, and seems unlikely to be either a flavin or a carotenoid, though they are not rigorously excluded. The first positive phototropic curvature response in maize shows a redistribution of growth consonant with the Cholodny-Went hypothesis for tropic responses, with an increase in the growth rate of the shaded side over dark controls, a concomitant decrease on the illuminated side, and no net change in overall growth rate.