The phosphatase/kinase balance affects phytochrome A and its native pools, phyA' and phyA″, in etiolated maize roots: evidence from the induction of phyA' destruction by a protein phosphatase inhibitor sodium fluoride.

Phytochrome A (phyA) comprises two native types, phyA' and phyA″, with distinct spectroscopic, photochemical, and functional properties, differing at the N-terminal extension, probably, by the state of phosphorylation. To find out if and how protein phosphatases (PP) affect the state of the phyA species in planta, we studied the effect of the non-specific phosphatase inhibitor NaF on etiolated maize seedlings with the use of low-temperature fluorescence spectroscopy and photochemistry. In roots, phosphatase inhibition facilitated photoreceptor destruction in its labile phyA' form and shifted the phyA'/phyA″ ratio towards the more stable phyA″. The effect of NaF was not observed in stems. It was similar, though less pronounced, in comparison to the effects of the serine/threonine PP inhibitors, okadaic and cantharidic acids (OA and CA), which likewise facilitate the destruction of phyA' in etiolated maize stems, not, however, in roots (Sineshchekov et al., Photochem. Photobiol 89:83-96, 2013). The phyA'/phyA″ balance thus depends on the kinase/phosphatase equilibrium in the root cells. The relatively low effect of NaF on phyA in roots, together with the lack of the effect of OA and CA in them, may imply that the mechanism controlling the phyA'/phyA″ balance in roots can be different from that in shoots.