A light-regulated pool of phytochrome and rudimentary high-irradiance responses under far-red light in Pinus elliottii and Pseudotsuga menziesii

The presence of a phytochrome pool down-regulated by light and the occurren ce of high-irradiance responses to far-red light are well documented in ang iosperms but not in gymnosperms. A pool ct phytochrome was identified in Pi nus elliottii and Pseudotsuga menziesii seedlings grown in darkness with a monoclonal antibody developed against oat phytochrome A. This pool was bare ly detectable in light-grown tissues. Dark-grown conifer seedlings transfer red to continuous red light showed a gradual decrease of the levels of immu nodetectable phytochrome. This decrease was significantly slower in gymnosp erms than in angiosperms. Dark-grown seedlings of P. elliottii and P. menzi esii showed enhanced growth of the cotyledonary whorl and increased anthocy anin pigmentation of the hypocotyl, but no hypocotyl-growth inhibition in r esponse to continuous far-red light. Hourly pulses were significantly less effective than continuous far-red light. The response to far-red light was not observed in seedlings pretreated with red light to reduce the levels of immunodetectable phytochrome. Rudiments of phytochrome A-like function and kinetics are present in P. elliottii and P. menziesii.