Salinity Affects Intracellular Calcium in Corn Root Protoplasts

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Abstract
Previous work with the fluorescent Ca probe chlorotetracycline (CTC) showed that salinity displaces Ca from membranes of root cells. Using a variety of indirect approaches, we studied whether salinity displaces Ca from the cell surface or from internal membranes of corn (Zea mays L. cv Pioneer 3377) root protoplasts. Preloading the cells with supplemental Ca counteracted subsequent NaCl effects on CTC fluorescence. CTC quenching by exogenous EGTA was not competitive with CTC quenching by NaCl. The Ca channel reagent (+)-202-791 had significant interactions with the effect of NaCl on CTC fluorescence. The effect of NaCl on CTC fluorescence was attenuated by pretreatment with Li, but was restored by inositol. Salinity increased Na influx, decreased Ca influx, and increased Ca efflux from the cells. Fluorescence anisotropy indicated that NaCl decreased the fluidity of the external face of the plasmalemma but increased the fluidity of cell membranes in general. Our results suggest that salinity displaces Ca associated with intracellular membranes through activation of the phosphoinositide system and depletion of intracellular Ca pools.