Cross-talk between reactive oxygen species and polyamines in regulation of ion transport across the plasma membrane: Implications for plant adaptive responses

Many stresses are associated with increased accumulation of reactive oxygen species (ROS) and polyamines (PAs). PAs act as ROS scavengers, but export of putrescine and/or PAs to the apoplast and their catabolization by amine oxidases gives rise to H₂O₂ and other ROS, including hydroxyl radicals (^•OH). PA catabolization-based signalling in apoplast is implemented in plant development and programmed cell death and in plant responses to a variety of biotic and abiotic stresses. Central to ROS signalling is the induction of Ca²⁺ influx across the plasma membrane. Different ion conductances may be activated, depending on ROS, plant species, and tissue. Both H₂O₂ and ^•OH can activate hyperpolarization-activated Ca²⁺-permeable channels. ^•OH is also able to activate both outward K⁺ current and weakly voltage-dependent conductance (ROSIC), with a variable cation-to-anion selectivity and sensitive to a variety of cation and anion channel blockers. Unexpectedly, PAs potentiated ^•OH-induced K⁺ efflux in vivo, as well as ROSIC in isolated protoplasts. This synergistic effect is restricted to the mature root zone and is more pronounced in salt-sensitive cultivars compared with salt-tolerant ones. ROS and PAs suppress the activity of some constitutively expressed K⁺ and non-selective cation channels. In addition, both ^•OH and PAs activate plasma membrane Ca²⁺-ATPase and affect H⁺ pumping. Overall, ^•OH and PAs may provoke a substantial remodelling of cation and anion conductance at the plasma membrane and affect Ca²⁺ signalling.