[Localization of mannitol biosynthesis in the marine brown alga Fucus serratus].

Tips of fronds of Fucus serratus L. were exposed to H(14)CO3 in the light for periods of 10, 30, 60, and 180s, fixed in petrol ether at-70° C, and subsequently lyophilized. Pheoplasts (=chloroplasts) were isolated using the nonaqueous technique of Thalacker et al. (1959). After extraction and chromatography percentage (14)C activity and distribution of individual photoassimilates between pheoplasts and other compartments of assimilating cells were analyzed. Eighty percent of [(14)C]-phosphate esters were found within the pheoplasts after 10s (14)C-assimilation, whereas only 25% were found there after 30s. After 10s [(14)C] mannitol is almost totally localized within the plastids, but after 180s the major part has been localized outside the pheoplasts. On the basis of these data the pheoplasts are regarded to be the only sites of primary mannitol biosynthesis during photosynthesis in Fucus.