The effects of osmotic stress on intracellular hexitols in the marine brown alga Himanthalia elongata (L.) S.F. Gray

Changes in the intracellular concentration of the hexitols mannitol and altritol have been monitored in plants of Himanthalia elongata (L.) S.F. Gray maintained in a range of hyposaline and hypersaline media for up to 3 days. Altritol forms the major component of the low-molecular-weight organic solute fraction in H. elongata , decreasing in hyposaline media and increasing under hypersaline conditions. This is the first direct evidence that altritol may be involved in osmotic adjustment in H. elongata . Intracellular mannitol levels also varied as a direct function of the external salinity, showing a greater proportional change than altritol. Changes in intracellular hexitol concentration were shown to be independent of the rate of net photosynthesis, indicating osmotic, rather than respiratory, control of internal mannitol and altritol levels.