A Flavin Mononucleotide-Binding Aquaporin in the Plant Plasma Membrane: A Candidate for Photoreceptor?

Abstract

In plants and fungi some of the blue light photoreceptors must reside in or at the plasma membrane, and most, if not all, should work with “bound” flavins. A riboflavin binding protein was characterized, initially as sites of reversible association in membrane material from several higher plants ([Hertel et al 1980]) and from the lower fungus Phycomyces ([Dohrmann 1983], [Flores et al 1999]). We showed that it was a PIP1-type aquaporin in a higher plant ([Lorenz et al 2003]). The sheer amount of this binding protein is impressive: it constitutes more than 1% of the total plasma membrane. Comparing flavoproteins, e.g., of Phycomyces, in the non-mitochondrial membranes, about five times more of our protein was present than the sum of all other flavoproteins.A similar predominance is seen in plasma membranes of higher plants. (Whether the flavin binding proteins, described by [Dederichs et al 1999] and by [Neumann and Hertel 1994] in flagellar preparations of Chlamydomonas and Euglena, respectively, are homologous, remains to be investigated.)