The Contribution of Organic Solutes to Osmotic Balance in Some Green Algae
Sorbitol and proline accumulate to osmotically significant concentrations in two Stichococcus species and Klebsormidium marinum. The extent of osmotic balance by these and other organic solutes depends on the isolate within this group of predominantly non- vacuolate algae. Sucrose, proline and sorbitol accumulate in the lichen alga Hyalococcus dermatocarponis, but concentrations on an osmotic basis are low. Sucrose and glutamic acid are significant solutes in the likely non-vacuolate Klebsormidium flaccidum and Klebsormidium sterile. A similar set of solutes accumulates in Ulothrix fimbriata, a freshwater algae that is highly vacuolate and less euryhaline. Two small eustigmatophycean algae and one small chlorophyte accumulate organic solutes to a moderate degree during salinity stress; mannitol and proline in the marine eustigmatophyte and proline in the marine chlorophyte. Enteromorpha intestinalis, a seaweed, accumulates sucrose, but at low levels. Osmotic balance in these algae may also include other solutes, compartmentation, or other factors. The role of organic solutes in osmotic balance is variable, and depends on details of physiology and ultrastructure.