Abstract
Polyamines (PAs) regulate growth and stress responses in plants. Among the vitally important roles of PAs is a modulation of ion transport across vacuolar and plasma membranes. PAs at micromolar concentrations block two major vacuolar cation channels, namely, the slow (SV = TPC1, tandem-pore calcium channel) and the fast (FV) activating ones. These effects are direct and fully reversible, with a potency descending in a sequence Spm > Spd > Put. However, effects of polyamines on the plasma membrane cation and K+-selective channels are hardly dependent on the PA species, display a relatively low affinity, and are indirect. Plants widely implement a mechanism, including the PAs export to the apoplast and catabolization therein, resulting in a generation of reactive oxygen species (ROS). ROS in turn activate a variety of ion conductances, underlying Ca2+ influx and/or K+ efflux across the plasma membrane. PAs assist hydroxyl radicals (·OH) in the activation of nonselective conductance, permeable for cations and small anions (ROSIC), and both ROS and PAs activate the Ca2+- and alter the H+-pumping across the plasma membrane. Possible implications for the stress tolerance of ion transport modulation by polyamines and their catabolites are discussed.
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