Fluorescence and photochemical characterization of phytochrome in de-etiolated pea mutant lip

Abstract

The red-light-absorbing form of phytochrome, Pr, and its phototransformation into the first stable photoproduct, lumi-R, under red light ( λ r = 667 nm) and back under far-red light ( λ fr = 696 nm) at 85 K were investigated with the use of low temperature fluorescence spectroscopy in the stems and roots of lip mutant pea seedlings, which have many of the characteristics of light-grown plants even when grown in the dark (S. Frances et al., Plant Cell, 4 (1992) 1519–1530). The spectroscopic and photochemical parameters of Pr were found to be similar in wild-type and lip mutant etiolated seedlings. The two Pr forms with high and low extents of phototransformation into lumi-R, i.e. Pr′ and Pr″ respectively, detected at low temperatures (V. Sineshchekov, Photochem. Photobiol., 59 (1994) 77–86) were shown to be roughly equivalent in the wild-type and the lip mutant pea. Fluence time-response curves for the phototransformation of Pr′ into lumi-R and back in lip stems revealed three subpopulations of Pr similar to those obtained in the wild-type pea. The total phytochrome content [P tot] determined from the Pr fluorescence intensity in the stems of the mutant was approximately 30% of the wild type. However, mutant and wild-type roots contained similar amounts of Pr. Thus any contribution to the mutant phenotype made by phytochrome may be due to changes in the total concentration of phytochrome rather than variations in the relative content or modification of the various Pr species.