Potassium is indispensable for plant growth. Recently, a role of K + channels has emerged in sensing and transducing stress and nutrient status. Tetraethylammonium (TEA +) is a specific blocker of K + transport and affects K + channel gene expression. Two barley varieties with contrasting salinity tolerance, and a chlorophyll bless mutant, were grown either in the presence of TEA + alone or combined with NaCl, at two different concentrations of external K + and Ca 2+ , and were analyzed nine days after germination. Chlorophyll a transients monitored via JIP-tests were used to evaluate the state of the photosynthetic machinery. In contrast to reported responses to K + deficiency, TEA + inhibited shoot growth while inducing root growth and increasing photosynthetic performance. Both TEA + and NaCl induced the appearance of negative K-bands in OJIP kinetics and an increase in PIABS, indicating a stimulation of photosynthesis by increased sink strength in the context of root to shoot signaling.