Photocontrol of the Germination of Onoclea Spores

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Abstract
The physiological nature of photoinduced germination of O. sensibilis L. spores was investigated by temporarily administering a range of temperatures, particularly 40.degree. C, before and after short light treatment. Controls were germinated at 25.degree. C. The preinduction phase, during which photosensitivity is maximally developed in the dark, is sensitive to temperature. Treatment at 40.degree. C for 8 or more h reduces the developed photosensitivity to a minimal level, but the inhibition by 40.degree. C treatment is reversed slowly after subsequent incubation at 25.degree. C in the dark. The postinduction phase, in which dark processes lead to stain uptake and eventually to visible protrusion, is also sensitive to temperature. Inhibition by 40.degree. C occurs shortly after photoinduction, but disappears 6 or more h after irradiation. Postinduction spores whose germination is inhibited by 40.degree. C treatment recover the ability to germinate after subsequent incubation at 25.degree. C, plus a 2nd light treatment. The inhibition and recovery take place faster in postinduction spores than in preinduction spores. In addition, escape from 40.degree. C inhibition is found in the postinduction phase but not in the preinduction phase. Temperatures lower than 25.degree. C exert slow inhibition of both pre- and postinduction processes and 30-35.degree. C act to stimulate germination. In comparison with earlier work with anaerobiosis and cycloheximide, the postinduction step inhibited by 40.degree. C can be located shortly after the step inhibited by anaerobiosis but before the cycloheximide-sensitive step.