The Effects of Salinity upon Ion Content and Ion Transport of the Marine RedAlga Porphyra purpurea(Roth) C.Ag.

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Abstract
Ion contents and concentrations (K+, Na+, Cl−, Ca2+, Mg2+, SO2−4, NO−3, HPOJ2−4, amino and organic acids) of P. purpurea have been studied in relation to salinity variation. Cells were shown to accumulate large amounts of K+ and Cl− against their respective gradients of electrochemical potential in all dilute and concentrated seawater media. Active influx of SOJ2−4, NO−3, and HPOJ2−4 is also suggested, while Na+ is actively excluded from cells under hyposaline and hypersaline conditions. The relative proportions of individual components of the internal osmotic potential were found to change according to the external salt concentration. KCL forms the major fraction of ∑πj} in concentrated seawater media while K+-amino acids form the major fraction in dilute seawaters. Other intracellular solutes comprise less than 15% oft∑πj, in all media. Unidirectional fluxes of K+ and Cl− were studied by radioisotopic means. Fluxes of K+ and Cl− are reduced in hyposaline media, as is absolute KCL content per cell. Intracelhilar KCL content was also found to be markedly dependent upon external K+ concentration, rather than water potential. Changes in KC1 levels induced by salinity variation occur over a 6 h period.