PHOTOBIOLOGICAL CHARACTERIZATION OF A SPORE GERMINATION MUTANT DKG1 WITH REVERSED PHOTOREGULATION IN THE FERN CERATOPTERIS-RICHARDII

This paper describes the mutant dkg1 in the fern Ceratopteris richardi i, which shows rapid germination in darkness but is markedly inhibited by white light. Action spectra plotted at 10 nm intervals from 400 to 800 nm are presented for germination responses of wild-type and mutan t spores to photon flux densities of 0.004, 0.04 and 0.4 mumol/m2/s. T he action spectra for wild-type spores exhibit a sharp phytochrome-med iated peak at 660 nm, a broad peak from 670 to 740 nm resulting from a n apparent high irradiance response and no germination below 560 nm. I n the corresponding action spectra for mutant spores, the blue region displays rather complex fine structure with prominent minima at 450 an d 470 nm, which suggests that cryptochrome is unaltered in these spore s. The region from 550 to 640 nm shows the greatest inhibition of spor e germination, but this region exhibits no obvious fine structure, whi ch argues rather strongly against the possibility of a unique photorec eptor being active in mutant spores. The mutant spectra resemble the w ild-type spectra in the region from 650 to 800 nm, and thus phytochrom e seems normal in the mutant spores. The dkg1 mutation appears to act late in the phytochrome transduction pathway where a hypothetical coup ling protein may regulate the light-sensitive step in spore germinatio n.