ROLE OF BICARBONATE CHLORIDE EXCHANGE IN REGULATION OF CYTOSOLIC PH

We investigated the role of bicarbonate in processes of pH(c) regulati on in protoplasts isolated from sugar beet root cell suspension cultur e (Beta vulgaris L.). On ''disconnection'' of plasmalemma H+-ATPase-th e main component of the biophysical pH-stat of the plant cell-in the p resence of DES or EDAPC, introduction of bicarbonate stimulates relaxa tion of pH(c) following artificial acidosis induced by isobutyrate-BTP . Such preservation of pH(c) relaxation when bicarbonate was present i n the medium did not depend on activity of H+-ATPase, was suppressed i n the presence of anion transport inhibitors (DIDS, furosemide, ethacr ynic acid), and was sensitive to a transmembrane gradient of chloride ions. The obtained data enable us to hypothesize that the plasmalemma houses a bicarbonate/chloride exchange mechanism that is one more comp onent of the biophysical pH-stat of isolated protoplasts.