Physiological aspects of the production and conversion of DMSP in marine algae and higher plants

Dimethylsulphoniopropionate (DMSP) is a compound produced in several classe s of algae and higher plants that live in the marine environment. Consideri ng its generally high intracellular concentrations, DMSP has a function in the osmotic protection of algal cells. Due to the relatively slow adaptatio n of its intracellular concentrations upon salinity shifts, DMSP should, ho wever, not be considered as an osmoticum in the strict sense of being respo nsible for osmotic balance, but rather as a constitutive compatible solute. Besides salinity, other factors also appear to affect cellular DMSP quotas , but the exact regulatory mechanisms are still unclear. In this review, a brief discussion is given of the three pathways of DMSP biosynthesis that a re currently distinguished. This is followed by an overview of the factors that affect DMSP biosynthesis (light, salinity, temperature and nitrogen li mitation) in relation to its physiological functions. A new hypothesis is p resented in which DMSP production is described as an overflow mechanism for excess reduced compounds and for energy excess. Finally, the possible func tionality of the enzymatic cleavage of DMSP is discussed in the context of an overflow mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.