Salt-sensitive and salt-tolerant barley varieties differ in the extent of potentiation of the ROS-induced K+ efflux by polyamines

Generation of high levels of polyamines and reactive oxygen species (ROS) is common under stress conditions. Our recent study on a salt-sensitive pea species revealed an interaction between natural polyamines and hydroxyl radicals in inducing non-selective conductance and stimulating Ca²⁺-ATPase pumps at the root plasma membrane (I. Zepeda-Jazo, A.M. Velarde-Buendía, R. Enríquez-Figueroa, B. Jayakumar, S. Shabala, J. Muñiz, I. Pottosin, Polyamines interact with hydroxyl radicals in activating Ca²⁺ and K²⁺ transport across the root epidermal plasma membranes, Plant Phys. 157 (2011) 1-14). In this work, we extended that study to see if interaction between polyamines and ROS may determine the extent of genotypic variation in salinity tolerance. This work was conducted using barley genotypes contrasting in salinity tolerance. Similar to our findings in pea, application of hydroxyl radicalsgenerating Cu²⁺/ascorbate mixture induced transient Ca²⁺ and K⁺ fluxes in barley roots. Putrescine and spermine alone induced only transient Ca²⁺ efflux and negligible K⁺ flux. However, both putrescine and spermine strongly potentiated hydroxyl radicals-induced K⁺ efflux and respective non-selective current. This synergistic effect was much more pronounced in a salt-sensitive cultivar Franklin as compared to a salt-tolerant TX9425. As retention of K⁺ under salt stress is a key determinant of salinity tolerance in barley, we suggest that the alteration of cytosolic K⁺ homeostasis, caused by interaction between polyamines and ROS, may have a substantial contribution to genetic variability in salt sensitivity in this species.