[CO2-Fixation and translocation in benthic marine algae : V. A Histoautoradiographic study of the pathway of (14)C-labelled assimilates in Laminaria hyperborea].

After local assimilation of NaH(14)CO3 by an old frond of Laminaria hyperborea, radioactive photosynthate is translocated to the growing region of the thallus. The pathway of this long-distance transport was studied by histoautoradiography. Cellular localization of the conducting channels was accomplished by new autoradiographic methods including freeze-substitution and 1 μm-cuttings of epoxy resin embedded tissue. In the autoradiographs, patches of silver grains overlying single trumpet-filaments (=Trompetenzellen) indicated that downward translocation occurs in these cells only. It could be shown that predominantly young trumpetfilaments contain the bulk of labeling. It is concluded that the young filaments rather than the older ones are particularly active in translocation. A lateral movement of labelled material was not observed except in the growing region.