Control of the Entry into S Phase by Phytochrome and Blue Light Receptor in the First Cell Cycle of Fern Spores

Abstract

Phytochrome- and a blue light receptor-dependent pathway antagonistically regulate the first mitosis in spores of the fern Adiantum capillus-veneris L. This study focused on determining which phase(s) of the cell cycle is positively regulated by phytochrome and negatively regulated by a blue light receptor in germinating spores. Incorporation of the radioactivity of 3 H-thymidine into the acid-insoluble material prepared from the spores indicated that phytochrome in the PFR form induced the entry into S phase of the first cell cycle in the spores 20-28 h after irradiation with red light. Blue light treatment before or after red light treatment totally prevented the PFR-induced DNA synthesis. Brief irradiation with red, far-red or blue light showed no effects on mitosis if the irradiation was given 28 h after the red light induction, during S and M phases. These results indicate that phytochrome and a blue light receptor regulate the entry into S phase during the first cell cycle of fern spores.