Chen C.; Hu X.; Gao Y.; Liang J. and Sun L. 2023. International Journal of Molecular Sciences 24(18).

Although estuarine diatoms have a wide range of salt tolerance, they are often severely stressed by elevated salt concentrations. It remains poorly understood how estuarine diatoms maintain ionic homeostasis under high-salinity conditions. Using a scanning ion-selective electrode technique, this study determined the fluxes of H⁺, Na⁺, and K⁺ involved in the acclimatization of the estuarine diatom Coscinodiscus centralis Ehrenberg after an elevation in salinity from 15 psu to 35 psu. The C. centralis cells exhibited marked H⁺ effluxes after a transient treatment (TT, 30 min) and short-term treatment (ST, 24 h). However, a drastic shift of H⁺ efflux toward an influx was induced in the long-term treatment (LT, 10 days). The Na⁺ flux under TT, ST, and LT salinity conditions was found to accelerate the Na⁺ efflux. More pronounced effects were observed under the ST and LT salinity conditions compared to the TT salinity condition. The K⁺ influx showed a significant increase under the LT salinity condition. However, the salinity-induced Na⁺/H⁺ exchange in the estuarine diatom was inhibited by amiloride and sodium orthovanadate. These results indicate that the Na⁺ extrusion in salt-stressed cells is mainly the result of an active Na⁺/H⁺ antiport across the plasma membrane. The pattern of ion fluxes under the TT and ST salinity conditions were different from those under the LT salinity conditions, suggesting an incomplete regulation of the acclimation process in the estuarine diatom under short-term salinity stress.

Net fluxes of Na⁺ from control (A), TT-stressed, (B) ST-stressed, (C) and LT-stressed (D) cells of the estuarine diatom Coscinodiscus centralis. A continuous flux recording of 7 to 8 min was conducted for each cell. Each point represents the mean of four to five individual diatoms, and bars represent the standard error of the mean. The mean fluxes of Na⁺ within the measuring periods are shown (E). Columns labeled with different letters (a and b) are significantly different at p < 0.05.