Transport of Malic Acid in Cells of CAM Plants

Abstract

Accumulation of organic-acid anions and particularly of malate in the vacuole is involved in many functions of higher plants. Examples are: osmotic adjustments in general (Cram 1976); plant nutrition, e.g. surplus uptake of cations over anions (Torii and Laties 1966; Osmond and Laties 1969) or OH- production during reduction of inorganic anions like NO3 - and SO4 2- (Osmond 1976; Smith and Raven 1976); extension growth associated with the acid-growth mechanism (Haschke and Lüttge 1977); and shrinking and swelling of cells in turgor-dependent movements as in stomata (Raschke 1979). In all of these examples vacuolar malate accumulation is an integral part of biophysical/biochemical pH-stat mechanisms (Smith and Raven 1976).