Abstract
ABSTRACTThe effects of Ca2+ and cell turgor on Na+ influx were examined in two charophytes, lamprothamnium papulo‐SUM (salt‐tolerant) and Chara corallina (salt‐sensitive), to try to identify causes of salinity toxicity. Mortality was associated with Na+ influx, with the two species showing similar sensitivities to high Na+ influx. In Lamprothamnium, toxic influxes of Na+ occurred at much higher external Na+ concentrations than in Chara. The differences in Na+ influx at the same Na+ concentration were not due to different responses to external Ca2+. Lamprothamnium adjusts its turgor in response to increasing NaCl whereas Chara cannot. In solutions of KC1 up to at least 200 mol m‐3, however, Chara regulated turgor, and when KC1 was subsequently replaced with NaCl, Na+ influx was low and similar to that in Lamprothamnium at the same Na* concentration. Chara cells which were not turgor‐adjusted in KCI had Na+ influxes 2‐5‐fold higher than the turgid cells. Thus, it appears that turgor is a major determinant of Na+ influx, and therefore of cell survival. We found no evidence that the mechanism of Na+ influx in Chara is different from that in Lamprothamnium. Higher susceptibility of Chara to NaCl seems to result from inability to regulate turgor, in turn leading to toxic Na+ influx.
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