Calcium‐salinity interactions affect ion transport in Chara corallina

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Abstract
Detached internodes of Chara corallina survived in solutions containing 100 mol m−3 NaCl when the external concentration of Ca2+ was greater than 1 mol m−3. Na+ influx was roughly proportional to external Na+ up to 100 mol m−3 NaCl. Na+ influx involved two components: a Ca2+‐insensitive influx which allowed the passage of Na+ independently of external Ca2+; and a Ca2+‐inhibitable mechanism where Na+ influx was inversely proportional to external Ca2+. The Ca2+‐inhibitable Na+ influx was similar to the Ca2+‐inhibitable K+ influx. Mg2+ and Ba2+ were able to substitute for Ca2+ in partially inhibiting Na+ influx in the absence of external Ca2+. The effect of Ca2+ appears specific to Na+ and K+ influx since the effects of a Ca2+‐free solution on the influx of some other cations, anions and neutral compounds is small. It is suggested that Na+ influx via the Ca2+‐inhibitable mechanism represents Na+ leakage through K+ channels and that cell death at high salinity occurs due to a cytotoxic Na+ influx via this mechanism.