Primary Alcohols, Substrates for Phospholipase D-Catalyzed Transphosphatidylation, Suppress the Cytokinin Action

Abstract

Cytokinins have been recognised as potent plant growth regulators since 1955 (Skoog, 1994). However, it is only recently that elucidation of the molecular mechanism of their perception and signal transduction has come about (Schmülling, 2001; Hutchinson and Kieber, 2002; Romanov, 2002). Cytokinin receptors discovered so far are integral transmembrane proteins belonging to the family of receptor histidine kinases. The downstream signaling obviously occurs via the phosphorelay pathway including phosphotransmitters (HP) and response regulator (RR) proteins (Schmülling, 2001; Hutchinson and Kieber, 2002; Romanov, 2002). A parallel set of data obtained by means of pharmacological analysis indicated the possible involvement of other signaling components, in particular phospholipase D (PLD), in the early events triggered by cytokinins (Romanov et al., 2000; Romanov et al., 2002). Taking into account that the transduction of a defined signal inside the cell is a complex process usually comprising crosstalk among different signaling elements, both these sets of data are not necessarily contradictory. For example, subtly tuned hormone signaling pathways comprising Ca²⁺, PLD, cyclic GMP, protein kinase(s), protein phosphatase(s), calmodulin, and G-proteins constitute an integrated network in the aleurone and stomatal guard cells (Ritchie et al., 2002).