Phytochrome Regulation of Expression of mRNA Encoding the Major Light-Harvesting Chlorophyll a/b-Binding Proteins of Photosystem II in the Haploid Phase of Adiantum capillus-veneris

Light regulates development in the fern Adiantum capillus-venerisduring both the haploid gametophyte and diploid sporophyte phases.In this study, we have investigated the role of the photoreceptorphytochrome in haploid spore germination and regulation of expressionof mRNA encoding the major light-harvesting polypeptides ofphotosystem II {Lhcb mRNAs). Both of these responses appearto be induced by phytochrome and inhibited by blue light, acting.throughseparate photoreceptor(s). Characteristics of phytochrome actionwere similar for both responses, showing no induction in thevery low fluence range and an ‘escape’ from far-redreversal for 50% of the response by 6 h. Overall, these resultsshow that phytochrome regulates both a morphological and a molecularprocess in haploid fern spores, and that these processes mayshare a common signal transduction pathway. (Received February 4, 1998; Accepted April 8, 1998)