Intercellular Transport and Photosynthetic Differentiation in Chara corallina

Intercellular transport of ¹⁴C-labelled photoassimilates, bothin isolated upper shoots and in isolated internode-branchletcomplexes of Chara corallina, was measured. The isolated uppershoots were composed of a primary apex, two mature internodes,and three branchlet whorls. A 10 min loading of the isolatedupper shoot with H¹⁴CO₃^– resulted in a greater accumulationof ¹⁴C in the apical complex and branchlets than in the internodes,while a subsequent 50 min chase with unlabelled solution inthe light resulted in a greater accumulation of ¹⁴C in internodesthan in other parts of the shoot. In the isolated internode-branchlet complex, when the apex wasnot detached, the amount of ¹⁴C transported from branchletsto internodes was about fives times that transported from internodesto branchlets. Removal of the apex resulted in a decrease intransport from branchlets to internodes and an increase in transportin the opposite direction. In an attempt to explain the mechanism of the polar transportof photosynthetically fixed carbon between branchlets and internodes,photosynthetic activities of both types of cells were investigated.Detached branchlets have higher photosynthetic ¹⁴C-fixationactivities than those of internodes. Chlorophyll contents, measuredin terms of surface area, in internodes and branchlets werealmost identical. The ribulose-l,5-bisphosphate carboxylase(RuBPCase) activity of branchlets was 1.6 times that of internodes,and the rate of ferricyanide-dependent evolution of oxygen inbranchlets was 1.4 times that in internodes. Key words: Chara, internode, branchlet, polar transport, photosynthesis