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-veneris during both the haploid gametophyte and diploid sporophyte phases. In this study, we have investigated the role of the photoreceptor phytochrome in haploid spore germination and regulation of expression of mRNA encoding the major light-harvesting polypeptides of photosystem II (Lhcb mRNAs). Both of these responses appear to be induced by phytochrome and inhibited by blue light, acting through separate photoreceptor(s). Characteristics of phytochrome action were similar for both responses, showing no induction in the very low fluence range and an "escape" from far-red reversal for 50% of the response by 6 h. Overall, these results show that phytochrome regulates both a morphological and a molecular process in haploid fern spores, and that these processes may share a common signal transduction pathway