Potassium fluxes and reactive oxygen species production as potential indicators of salt tolerance in Cucumis sativus

Salt stress, among other abiotic stresses, has a high impact on crop yield. Salt tolerance is a multifactorial trait that involves the ability of cells to retain K ions, regulate reactive O species (ROS) production, and synthesise new molecules to cope with osmotic stress. In the present work, two different cultivars of Cucumis sativus L. (cv. Parys, sensitive; cv. Polan, tolerant) were selected based on their germination capabilities under 100mM NaCl. The capacity of these two cultivars to tolerate salt stress was analysed using several different physiological and genetic approaches. K+ fluxes from roots, as an immediate response to salinity, showed the higher ability of cv. Polan to maintain K+ compared with cv. Parys, according to the expression level of inward rectifying potassium channel 1 (AKT1). ROS production was also investigated in both cultivars and a higher basal ROS level was observed in cv. Polan than in cv. Parys. Concurrently, an increased basal level of respiratory burst oxidase homologue F (RBOHF) gene was also found, as well as a strong induction of the ethylene responsive factor 109 (ERF109) transcription factor after salt treatment in cv. Polan. Our data suggest that roots' ability to retain K+, a higher level of RBOHF and a strong induction of ERF109 should all be considered important components for salt tolerance in C. sativus.