The Effect of Decreasing the External Salinity on the Primary Processes of Photosynthesis inDunaliella tertiolecta

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Abstract
The euryhaline unicellular green alga Dunaliella tertiolecta lost intracellular glycerol when subjected to a decrease in external salinity. After the salinity was decreased, photosynthesis was inhibited for at least the first 100 min, but dark oxygen uptake was transiently stimulated. The extent of the 519 nm field-indicating absorption change induced by photosystem I alone was inhibited by decreasing the salinity, but other photosynthetic parameters were largely unaffected. A comparison of these results with hypertonic stress indicated that although both stresses inhibit the overall process of photosynthesis, they do so by different mechanisms. Resuspending the algal cells in distilled water resulted in an inhibition of all the photosynthetic parameters measured.