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 theoccurrence of high-irradiance responses to far-red light are welldocumented in angiosperms but not in gymnosperms. A pool of phytochrome wasidentified in Pinus elliottii andPseudotsuga menziesii seedlings grown in darkness witha monoclonal antibody developed against oat phytochrome A. This pool wasbarely detectable in light-grown tissues. Dark-grown conifer seedlingstransferred to continuous red light showed a gradual decrease of the levelsof immunodetectable phytochrome. This decrease was significantly slower ingymnosperms than in angiosperms. Dark-grown seedlings of P.elliottii and P. menziesii showed enhancedgrowth of the cotyledonary whorl and increased anthocyanin pigmentation ofthe hypocotyl, but no hypocotyl-growth inhibition in response to continuousfar-red light. Hourly pulses were significantly less effective thancontinuos far-red light. The response to far-red light was not observed inseedlings pretreated with red light to reduce the levels ofimmunodetectable phytochrome. Rudiments of phytochrome A-like function andkinetics are present in P. elliottii and P.menziesii.