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
Résumé
Occurrence of functional interactions between Sr2+ and Ca2+ were investigated on maize plants grown under hydroponic conditions in presence of various mixtures of SrCl2 [0-0.01-1-10 mM] and CaCl2 [0-0.2-2-20 mM]. External [Ca2+] modulated the effect of Sr2+ on the plant dry weight, and on the Sr2+, Ca2+ and Mg2+ contents of roots and shoots. An intermediary functional step between external [Sr2+] and [Ca2+], and organ ion content, occurred at the plasma membrane of cortical root cells where Sr2+ and Ca2+ could influence ion uptake by acting on membrane potential. The decrease of the Sr2+-evoked membrane depolarization induced by Ca2+ could not solely be attributed to the Ca2+-effect on the resting membrane potential. Most of the time the individual effects of Sr2+ and Ca2+ were not additive, as these two ions clearly interacted with each other to jointly affect the plant physiology. In spite of these interactions, both [Sr2+]ext or [Sr2+]ext/[Ca2+]ext ratio values seemed to enable a correct prediction of the Sr2+-effects on the plant. However using the [Sr2+]ext/[Ca2+]ext ratio improved significantly the adequacy of prediction compared to the use of [Sr2+]ext alone, as it increased up to 25% the proportion of variability accounted for by the model.