XVI International Botanical Congess

Red- and far-red light signals are perceived by the phytochromes and regulate all aspects of plant development. Higher plants possess multiple phytochromes and in Arabidopsis thaliana the phytochrome family comprises five members, the apoproteins of which are encoded by five discrete genes, PHYA-PHYE. A genetic approach is being used to elucidate the functions of members of the phytochrome family and, to date, mutants that are null for phytochromes A, B, D and E have been isolated and characterised. The functions of phyA and phyB in seed germination and seedling de-etiolation have been fairly well defined. These phytochromes, along with phyD and phyE, also play important roles in the perception of red:far-red ratio light signals and the initiation of responses that from part of the shade avoidance syndrome. These shade avoidance responses are typified by increased elongation growth and accelerated flowering. Analysis of single-, double- and triple-mutants indicates that many of the functions of phyD and phyE are largely redundant in the presence of phyB and that phyD and phyE have overlapping, but discrete functions.