The relationship of the charasome to chloride uptake in Chara corallina: physiological and histochemical investigations

Abstract

A possible role of the charasome in terms of chloride transport into Chara corallina Klein ex. Willd., em. R.D.W. is examined. The branches of Chara contain the most charasome material and are shown to be very effective in acquiring Cl^- to support continued shoot growth. The early maturation of the branches, the rather large Cl^- fluxes into these cells, and their ability of translocate Cl^- to growing cells of the shoot indicate a special role of these branches in Cl^- accumulation. The structure of the charasome, with its extensive periplasmic space, appears especially suited as a site for H⁺−Cl^- cotransport (influx). We show, by histochemical assay, that the charasomes of mature cells contain ATPase activity; such activity is absent in growing charasomes of very young cells. ATPase activity is also associated with the plasmodesmata of C. corallina. Charasome ATPase activity and Cl^- uptake are both inhibited by p-chloromercuribenzenesulfonic acid (1 mM) or diethylstibestrol (40 μM; 45 min). The anion transport inhibitor, 4,4-diisothiocyano-2,2-disulfonic acid stilbene (1 mM) had no effect on Cl^- transport and inhibited ATPase activity only when applied after chemical fixation of the cells. Results of an attempt to demonstrate the presence of Cl^- within the cytoplasmic tubules of the charasome, using a silver precipitation technique, proved difficult to interpret because of a reaction between the silver and a cellular substance produced in the light.