Occurrence of interactions between individual Sr~(2+)- and Ca~(2+)-effects on maize root and shoot growth and Sr~(2+), Ca~(2+) and Mg~(2+) contents, and membrane potential: Consequences on predicting Sr~(2+)-impact

摘要

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 [0-0.01-1-10mM] 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 Mg2* 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.