Occurrence of interactions between individual Sr2+- and Ca2+-effects on maize root and shoot growth and Sr2+, Ca2+ and Mg2+ contents, and membrane potential: Consequences on predicting Sr2+-impact

Abstract Occurrence of functional interactions between Sr 2+ and Ca 2+ were investigated on maize plants grown under hydroponic conditions in presence of various mixtures of SrCl 2 [0–0.01–1–10 mM] and CaCl 2 [0–0.2–2–20 mM]. External [Ca 2+ ] modulated the effect of Sr 2+ on the plant dry weight, and on the Sr 2+ , Ca 2+ and Mg 2+ contents of roots and shoots. An intermediary functional step between external [Sr 2+ ] and [Ca 2+ ], and organ ion content, occurred at the plasma membrane of cortical root cells where Sr 2+ and Ca 2+ could influence ion uptake by acting on membrane potential. The decrease of the Sr 2+ -evoked membrane depolarization induced by Ca 2+ could not solely be attributed to the Ca 2+ -effect on the resting membrane potential. Most of the time the individual effects of Sr 2+ and Ca 2+ were not additive, as these two ions clearly interacted with each other to jointly affect the plant physiology. In spite of these interactions, both [Sr 2+ ] ext or [Sr 2+ ] ext /[Ca 2+ ] ext ratio values seemed to enable a correct prediction of the Sr 2+ -effects on the plant. However using the [Sr 2+ ] ext /[Ca 2+ ] ext ratio improved significantly the adequacy of prediction compared to the use of [Sr 2+ ] ext alone, as it increased up to 25% the proportion of variability accounted for by the model.