CONTROL OF SODIUM INFLUX BY CALCIUM AND TURGOR IN 2 CHAROPHYTES DIFFERING IN SALINITY TOLERANCE

The effects of Ca2+ and cell turgor on Na+ influx were examined in two charophytes, Lamprothamnium papulosum (salt-tolerant) and Chara coral lina (salt-sensitive), to try to identify causes of salinity toxicity, Mortality was associated with Na+ influx, with the two species showin g similar sensitivities to high Na+ influx, In Lamprothamnium, toxic i nfluxes of Na+ occurred at much higher external Na+ concentrations tha n in Chara, The differences in Na+ influx at the same Na+ concentratio n were not due to different responses to external Ca2+, Lamprothamnium adjusts its turgor in response to increasing NaCl whereas Chara canno t, In solutions of KCI up to at least 200 mol m(-3), however, Chara re gulated turgor, and when KCl was subsequently replaced with NaCl, Nainflux was low and similar to that in Lamprothamnium at the same Na+ c oncentration. Chara cells which were not turgor-adjusted in KCl had Na + influxes 2-5-fold higher than the turgid cells, Thus, it appears tha t turgor is a major determinant of Na+ influx, and therefore of cell s urvival, We found no evidence that the mechanism of Na+ influx in Char a is different from that in Lamprothamnium, Higher susceptibility of C hara to NaCl seems to result from inability to regulate turgor, in tur n leading to toxic Na+ influx.