| Abstract: | Laboratory studies have indicated that Na+, K+ (together with Cl? the presumed counter-ion to these cations), NO3? and mannitol represent the major cellular osmotica in Laminaria digitata (Huds.) Lamour. The cellular content of NO3? (together with a fraction of the K+ pool which acts as the counter-ion to NO3?) was found to be inversely proportional to that of mannitol, suggesting that L. digitata maintains a constant turgor by means of an isotonic substitution between these compounds. An analysis of the seasonal changes in solute content in an Arbroath (Scotland) population of L. digitata confirmed this hypothesis and indicated that the total pool of stored photosynthate was partitioned between the interconvertible carbohydrates mannitol and laminaran (which has a much lower osmotic potential than mannitol) depending on the size of the cellular pool of NO3?. |
