Protein phosphatase activity and acidic/alkaline balance as factors regulating the state of phytochrome A and its two native pools in the plant cell

摘要

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′′. Phytochrome A (phyA) exists in two forms, phyA′ and phyA′′, what may explain the diverse modes of its action. With the use of phyA fluorescence and photochemistry, it was shown that [phyA′]/[phyA′′] in etiolated maize tissues correlated with their pH. Inhibition of the PP1 and PP2A phosphatases with okadaic and cantharidic acids brought about phyA′ decline and/or concomitant increase of phyA′′ in coleoptiles and mesocotyls (see Figure), but had no effect in roots. Thus, pH and phosphorylation status may regulate [phyA′]/[phyA″] via alteration of the processes of phyA′ destruction and/or its transformation into the more stable phyA″.