Abstract
Both laboratory- and field-grown Mesembryanthemum crystallinum plants exhibited large scale diurnal ion fluctuations. In mesophyll tissue, potassium and sodium levels varied in conjunction with acid levels while chloride levels varied in opposition. Thus, dark CO(2) fixation in this Crassulacean acid metabolism species seems analogous to the common plant process of malate synthesis to balance cation surplus. Sodium levels in the epidermis appeared to fluctuate in opposition to those in the mesophyll. It is proposed that inorganic cations cycle between mesophyll and epidermal tissue to balance malate accumulation and to produce stomatal opening in the dark.