Polymorphism of Phytochrome A and Its Functional Implications

Photochem & Photobiology

Koppel

Shor

et al. 2012

Phytochrome A (phyA), the most versatile plant phytochrome, exists in the two isoforms, phyA' and phyA'', differing by the character of its posttranslational modification, possibly, by phosphorylation at the N-terminal extension [Sineshchekov, V. (2010) J. Botany 2010, Article ID 358372]. This heterogeneity may explain the diverse modes of phyA action. We investigated possible roles of protein phosphatases activity and pH in regulation of the phyA pools' content in etiolated seedlings of maize and their extracts using fluorescence spectroscopy and photochemistry of the pigment. The phyA'/phyA'' ratio varied depending on the state of development of seedlings and the plant tissue/organ used. This ratio qualitatively correlated with the pH in maize root tips. In extracts, it reached a maximum at pH ≈ 7.5 characteristic for the cell cytoplasm. Inhibition of phosphatases of the PP1 and PP2A types with okadaic and cantharidic acids brought about phyA' decline and/or concomitant increase of phyA'' in coleoptiles and mesocotyls, but had no effect in roots, revealing a tissue/organ specificity. Thus, pH and phosphorylation status regulate the phyA'/phyA'' equilibrium and content in the etiolated (maize) cells and this regulation is connected with alteration of the processes of phyA' destruction and/or its transformation into the more stable phyA''.

Section: Discussionsupporting

confidence: 92%

“…The experimental approach was essentially the same as that employed earlier in our research . Briefly, we used low‐temperature (77–85 K) fluorescence of phy for its in situ assay.…”

Section: Methodsmentioning

confidence: 99%

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

Photochem & Photobiology

Koppel

Shor

et al. 2012

“…The complexity of the phyA‐mediated photoresponses suggests in turn that this may be also connected with the polymorphism of this pigment. With the use of fluorescence spectroscopy and photochemistry of phy in phy mutants and transgenic plants it was found that there are two phyA populations, phyA′ and phyA″ (13–15). The most pronounced phenomenological distinction between phyA′ and phyA″ was their different photochemical activity at cryogenic temperatures ( i.e.…”

Section: Introductionmentioning

confidence: 99%

“…Experiments on phy mutants and transgenic plants with altered phyA′/phyA″ content and modified photoresponses revealed that the two phyA species have different functions (14,15). As judged by the regulation of active and inactive protochlorophyllide accumulation, growth responses and autoregulation of phyA synthesis, the light‐labile phyA′ is responsible for de‐etiolation via the HIR mode.…”

Section: Introductionmentioning

confidence: 99%

Two Native Pools of Phytochrome A in Monocots: Evidence from Fluorescence Investigations of Phytochrome Mutants of Rice

Photochem & Photobiology

Loskovich

Inagaki

et al. 2006

Fluorescence investigations of phytochrome (phy) in rice (Oryza sativa L. cv. Nipponbare) mutants deficient in phyA, phyB and phyA plus phyB were performed. Total content of the pigment (P(tot)) and its spectroscopic and photochemical characteristics were determined in different parts of the dark-grown and far-red light (FR)-grown coleoptiles. Spectroscopically, phyA in the phyB mutant was identical to phyA in the wild-type (WT) and the extent of the conversion from Pr to lumi-R at 85 K was the same for phyA in both lines and varied similarly, depending on the part of the coleoptile used. The latter finding proved that phyA in rice is heterogeneous and comprises two phyA populations, phyA' and phyA". Functional properties of phyA were also determined. In the dark the phyB mutant had a higher content of phyA, inactive protochlorophyllide (Pchlide633) and active protochlorophyllide (Pchlide655) than WT and its coleoptile was longer, indicating that phyB may affect the development of WT seedlings in the dark. Constant FR drastically reduced the content of phyA, Pchlide633 and Pchlide655 and brought about coleoptile shortening and appearance of the first leaf, whereas pulsed FR of equal fluence was less effective. This suggested that the reactions were primarily of the high irradiance responses type, which are likely to be mediated by phyA'. The effects on protochlorophyllide biosynthesis and growth responses type were more pronounced in the phyB mutant than in the WT seedlings, which can be connected with the higher phyA' content in the phyB mutant and/or phyB interference with its action in WT seedlings. In the phyA mutant induction of Pchlide633 and Pchlide655 biosynthesis was observed under constant FR, indicating that phyC may be responsible for this effect.

Two Distinct Molecular Types of Phytochrome A in Plants: Evidence of Existence and Implications for Functioning

2023

IJMS

Phytochrome (phy) system in plants comprising a small number of phytochromes with phyA and phyB as major ones is responsible for acquiring light information in the red—far-red region of the solar spectrum. It provides optimal strategy of plant development under changing light conditions throughout all its life cycle beginning from seed germination and seedling establishment to fruiting and plant senescence. phyA was shown to participate in the regulation of all this cycle what is especially evident at its early stages. It mediates three modes of reactions—the very low and low fluence responses (VLFR and LFR) and the high irradiance responses (HIR). phyA is a sole light receptor in the far-red spectral region responsible for plant’s survival under dense plant canopy where light is enriched with the far-red component. Its appearance is believed to be one of the main factors of plants’ successful evolution. So far, it is widely accepted that one molecular phyA species is responsible for its complex functional manifestations. In this review, the evidence of the existence of two distinct phyA types—major, light-labile and soluble phyA′ and minor, relatively light-stable and amphiphilic phyA″—is presented what may account for the diverse modes of phyA action.