Source—sink characteristics of carbon transport in Chara hispida
Abstract Rates of uptake of 14C-labelled inorganic carbon were measured for whole Chara hispida plants, detached parts of the shoot and isolated (split-chamber technique) apices, lateral branchlets and rhizoid—node complexes. 
 
The rates of inorganic carbon uptake by the rhizoid—node complex expressed per gram fresh weight whole plant were three to four orders of magnitude less than the uptake for the whole plant. Up to 70% of the carbon taken up by the rhizoid—node complex was translocated to the shoot. After 12 h exposure to 14C-labelled inorganic carbon the concentration of 14C was greater in apices than in uppermost or central internodal cells and in all lateral branchlets, regardless of whether label was supplied to the whole plant or isolated rhizoid—node complexes. Measurement of inorganic carbon uptake by detached internodal cells and detached and isolated apices and lateral branchlets showed that lateral branchlets had the greatest rates of inorganic carbon uptake. During 12 h exposure to 14C, isolated lateral branchlets translocated to the attached shoot 55% of the labelled carbon taken up; for isolated apices this value was only 13%. 
 
It is concluded that it is highly unlikely that the rhizoid of Chara hispida could acquire a significant fraction of the whole plant requirement for inorganic carbon and that apices are sink regions for photosynthate while lateral branchlets are source regions.