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

Abstract

The presence of a phytochrome pool down-regulated by light and the occurrence of high-irradiance responses to far-red light are well documented in angiosperms but not in gymnosperms. A pool of phytochrome was identified in Pinus elliottii and Pseudotsuga menziesii seedlings grown in darkness with a monoclonal antibody developed against oat phytochrome A. This pool was barely detectable in light-grown tissues. Dark-grown conifer seedlings transferred to continuous red light showed a gradual decrease of the levels of immunodetectable phytochrome. This decrease was significantly slower in gymnosperms than in angiosperms. Dark-grown seedlings of P. elliottii and P. menziesii showed enhanced growth of the cotyledonary whorl and increased anthocyanin pigmentation of the hypocotyl, but no hypocotyl-growth inhibition in response 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.