Fluorescence and Photochemical Investigations of Phytochrome in Higher Plants

Abstract

In higher plants, photoreceptor phytochrome (phy)—photoisomerizing biliprotein working as a light-driven molecular switch—is represented by a small family of phytochrome gene products with phyA and phyB as major species. phyA is unique among other phytochromes mediating photoresponse modes specific only for this pigment (far-red light induced) and also photoresponses characteristic of phyB and other minor phys (red light induced). In our group, in vivo fluorescence investigations of phytochrome were initiated and two native phyA pools—posttranslationally modified PHYA gene products designated phyA′ and phyA″—were detected in dicots and monocots. They differ by spectroscopic and photochemical parameters, by abundance and distribution in etiolated plant tissues, by light stability, and other phenomenological characteristics, and, most importantly, by their functional properties. This may explain, at least partially, the nature of the uniqueness of the phyA action. In this paper, the data on the phyA polymorphism are summarized with attention to the applied experimental approach.

Protein Phosphatase Activity and Acidic/Alkaline Balance as Factors Regulating the State of Phytochrome A and its Two Native Pools in the Plant Cell

“…For this, we used etiolated maize seedlings and followed variations in the spectroscopic and photochemical parameters of phyA, which depend on plant organ/tissues and on the stage of its development. In agreement with our earlier findings of the phyA heterogeneity , we can interpret them as a manifestation of the presence of the two phyA species in the cell—the longer wavelength, at low temperatures photochemically active species phyA′ and the shorter wavelength at low temperatures photochemically inactive phyA′′. Evaluations of their content in tissues (this work and ) have shown that it changes in the growing etiolated plant, even tissue specific, as observed by the phyA′/phyA′′ content in a developing maize root.…”

“…Low‐temperature emission spectra (λ ex = 633 nm, normalized at the maximum) of phytochrome A in the maize root tip (Kubanskaya var.) at the initial stage 1 of its development: emerging root ( L = 0.7 mm), root at the end of stage 1 ( L = 2 mm).…”

“…mesocotyls at their base (raw spectra) and of phytochrome in this tissue (difference spectra) (b). The spectra were taken after freezing the sample in the dark at 77 K and after its warming up at 85 K and saturating illumination with full laser light at this temperature (λ a = 632.8 nm, I = 6.5 W m − 2 , 10 min) partially transforming the initial red‐absorbing phytochrome form, Pr, into the first stable at low temperatures photoproduct, lumi‐R . Curve 3 is a fluorescence spectrum of maize tissue which contains virtually no phytochrome in its Pr form—old maize roots at their base taken after saturating red illumination ( I = 6.5 W m − 2 , 5 min) at room temperature to convert phytochrome in its Pr form into Pfr.…”

“…phyA, which is the predominant phytochrome in etiolated seedlings, whose major fraction is light labile, shows a quite different behavior: it promotes irreversible effects in the whole range of its absorption spectrum under very weak light (very low fluence responses [VLFR]) and under high fluence rates with the maximum activity in the far‐red region (high‐irradiance responses, HIR). Along with these well established properties of phyA, it may perform as well the LFR functions characteristic for phyB . In particular, active phyA is translocated to the nucleus with the help of FHY1 and FHL, possibly via their red (R)/far‐red (FR) light reversible phosphorylation .…”

“…These different functions and properties of phyA were explained by its heterogeneity (see Refs. ). With the use of low‐temperature fluorescence spectroscopy two phyA types, phyA′ and phyA′′, were detected in wild‐type mono‐ and dicotous plants and their phy mutants.…”