Phytochrome intermediates in freeze-dried tissue

Abstract

PHYTOCHROME is a plant photomorphogenetic pigment existing in two forms, Pr and Pfr, interconvertible by light, which have absorption peaks in the red and far-red regions of the spectrum respectively^1,2. Intermediates between Pr and Pfr have been studied by several techniques in vivo and in vitro including flash photolysis^3,4, low temperature spectroscopy^5–7 and measurement of the dark (d) reactions of intermediates that accumulate in conditions of pigment cycling^8–10. The pathways Pr→Pfr and Pfr→Pr have been shown to be different, but, both pathways involve an initial photoreaction of the chromophore, followed by a series of dark reactions^10,11: P698, P710, P650, P690 are intermediates having peak absorbance at 698, 710, 650 and 690 nm respectively; Pb1 and Px are intermediates having relatively weak absorption bands. I now report a technique enabling phytochrome intermediates to be studied in vivo at 0° C using a dual wavelength spectrophotometer.