Translocation in Polytrichum commune (Bryophyta). III. Loading of sugars in source leaves

Polytrichum commune, the common hair-cap moss, possesses a system of long-distance food-conducting cells that can be traced from leaves into stems and down through underground rhizomes. Cytochemical analysis indicates that high adenosine triphosphatase activity is associated with the membranes of sugar-conducting deuter cells in Polytrichum leaves. Incipient plasmolysis determinations reveal high solute concentrations of leaf deuters. These two lines of evidence suggest that long-distance transport of photosynthate is initiated in this species by a process analogous to phloem loading of minor veins in leaves of flowering plants. Two sets of experimental observations suggest that sugar loading in Polytrichum is coupled with the transport of protons: the moderating effects of N-ethylmaleimide, p-chloromercuribenzenesulfonic acid, sodium orthovanadate, and fusicoccin on labeled sucrose uptake (as determined by liquid scintillation techniques), and correlated effects on acid flux from isolated leaves (as determined by computer-aided titrimetry).