Long-distance transport of 14C-Iabelled assimilates in the Fucales: nature of translocated substances in Fucus serratus

Long-distance transport of 14C-labelled (photo)assimilates was studied in Fucus serratus. Movement of label followed the source-sink relationship: the growing apical regions of this alga acted as a strong sink. The distribution of the 14C translocate, as determined from the low molecular weight fraction of the midrib, was nearly identical with that of the fed region and the sink. From these data it appears that the main translocated substance in the thallus of Fucus serratus is mannitol (80 to 87% radioactivity of the low molecular weight fractions) but translocation of amino acids and organic acids of low molecular weight occurs; it seems that there is little if any selectivity in the loading and translocating of assimilates. An analysis of the label in the pathway (midrib) and in the growing apex indicates that synthesis of polymeric compounds occurs from the transported mannitol and amino acids. These results are discussed with respect to long-distance transport in the Laminariales.