Intracellular Solutes, Photosynthesis and Respiration of the Green Alga Blidingia minima in Response to Salinity Stress

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Abstract
The effects of different salinities ranging from 7–68‰ on the internal inorganic and organic solute concentrations, and on the photosynthesis and respiration have been investigated in the green alga Bladingia minima (Näg. ex Kütz.) Kylin. The levels of the main osmotic solutes K+, sucrose and proline increased with increasing salinities and vice versa, while Na+, Mg2+, Cl− and PO3–4 played a minor role in the osmotic acclimation. In contrast to related Enteromorpha species, B. minima exhibited high NO−3 concentrations, which decreased under hypo‐ and hypersaline conditions. B. minima differs also from Enteromorpha by accumulating the tertiary sulphonium compound DMSP in osmotically significant amounts under gentle hypersaline conditions.B. minima revealed typical characteristics of a “sun‐plant” having a high light compensation point together with a saturation of photosynthesis at high photon flux densities. The alga showed a broad photosynthetic stability under osmotic stress; only with extreme hypersaline conditions was photosynthesis partly inhibited. The rate of respiration remained constant in hypersaline media, and was stimulated under hyposaline conditions.