A PUTATIVE ROLE OF THE XANTHOPHYLL, ZEAXANTHIN, IN BLUE-LIGHT PHOTORECEPTION OF CORN COLEOPTILES

Both flavins and carotenoids have some of the attributes expected for a photoreceptor mediating blue light-induced phototropism in plants. Besides the classical photoreceptor candidate, beta-carotene, coleoptiles contain many other carotenoids, including the main components of the xanthophyll cycle, violaxanthin and zeaxanthin. Here, dark-grown coleoptiles accumulated violaxanthin, but lacked zeaxanthin. Coleoptiles devoid of zeaxanthin did not bend in response to a blue light pulse. Coleoptile tips converted violaxanthin into zeaxanthin in the light. Manipulation of coleoptile zeaxanthin content by red light, red light plus darkness, or incubation with the inhibitor of zeaxanthin formation, dithiothreitol, resulted in a blue light-induced bending that was proportional to zeaxanthin content. These data indicate that zeaxanthin may be a blue light photoreceptor in corn coleoptiles.