Endocellular distribution of calcium and Ca‐ATPases in horse‐bean roots: Possible relation to the ecological status of the plant

Abstract

The endocellular distribution of calcium has been determined and Ca‐ATPase activity measured in subcellular fractions of various species: horse‐bean ( Vicia faba L., var. minor), barley ( Hordeum vulgare L., var. Astrix), wheat ( Triticum vulgare L., var. Hardy), lupine ( Lupinus luteus L., var. Weiko III), oat ( Avena sativa L. var. Zelma) which grow differently on calcareous media. The vacuolar calcium concentrations are below thermodynamic equilibrium with the medium for all plants. The deficit in vacuolar calcium is accentuated in plants which prefer calcareous soils. Membranes of such plants show weak affinity for calcium and also considerable Ca‐ATPase activity. It is suggested that low vacuolar concentration is a consequence of low cytoplasmic concentration. The role of Ca‐ATPases and the physicochemical properties of membranes in counteracting high external calcium is discussed.