Salt sensitivity and K/Na selectivity in Setaria verticillata

We have studied the effect of salinity on the development and mineral nutrition of Setaria verticillata, a summer wild graminaceae. Measurement of biomass deposition in different organs showed that Setaria is very sensitive to salinity. Even the lowest NaCl concentration of 50 mM caused a significant reduction of dry weight production for both roots and aerial parts. At concentrations higher than 50 mM, dry matter deposition was more diminished in roots than shoot, resulting in higher shoot/root ratios. The tissues of plants grown in the presence of NaCl contained high concentrations of Na and Cl, with an excess of the former ion as compared to the latter, especially in the shoots. The aptitude of the plants for K vs. Na discrimination was estimated from the K/(K+Na) ratio in tissues. The values of this ratio were similar in roots and shoots, suggesting that the former organs controlled the K/Na selectivity of the latter. The K/(K+Na) ratio diminished as the concentration of NaCl in the medium was augmented, but it remained systematically higher than in the medium. This indicates that, even at the highest NaCl concentrations, the plants conserved a significant control on their K/Na nutrition. However, there was a striking parallelism between the inhibition of the growth and the decrease of K/(K+Na) ratio in tissues in response to increasing NaCl concentrations in the medium. We hypothesize that sensitivity of Setaria to NaCl is strongly dependent on the inhibiting effect of NaCl on K nutrition.