Reversible Absorbance Changes and Modulation of Biological Activities by Blue Light

Abstract

For nearly half a century, carotene (carotenoproteins) and flavin (flavoproteins) have been discussed as prime candidates for photoreceptors of blue light-regulated biological processes (Bünning, 1937; Galston and Baker, 1949; Galston, 1977). With time carotenoids have lost their predominant candidacy — so far, in fact, that recently an advocatus diaboli had to step up to defend its case (Shropshire, 1980). This fate is unjust, however, since the evidence for a photoreceptor role of flavins in many blue light reactions doesn’t necessarily eliminate possible carotenid photoreceptors in others. We might have to give up the concept of one common blue light photoreceptor or even of one single compound in the class of carotenoids or flavins. For the time being we should confine ourselves to individual photoreceptors for individual blue light reactions. It is true that flavins/ flavoproteins have gained attention as photoreceptors for a wide variety of blue light responses in slime molds, fungi, algae, higher plants and even insects (Fig. 1, Ninnemann, 1980). I am inclined to add the action spectrum for induction of carotenoid biosynthesis in Neurospora by deFabo(1976) to this series (Fig. 2) which because of its small action maximum in the near uv resembles a flavin more than a carotenoid though it was not interpreted this way originally. Since Ed deFabo is present in this auditorium, I suppose we will have a second advocatus diaboli in a moment.