Mineral Nutrition: Divalent Cations, Transport and Compartmentation

“Heavy metals” and “trace elements” were last reviewed in this series by Lonera-gan (1982) and Fe was also covered in Luttge and Clarkson (1985). The physiology and ecophysiology of “heavy metal plants” is discussed by Ernst (1982). In this review we will discuss the membrane transport and internal compartmentation of divalent cations in the light of what has been discovered about calcium. We do this without exhaustive reference to the frequently reviewed calcium literature (Evans 1988). The divalent cations encountered by plants make up a diverse group of elements some of which have major nutrient functions, others have well-recognized roles as trace elements, others such as nickel and cobalt are suspected trace elements while others, frequently concentrated by the activities of man, are highly toxic to most plants. To introduce some cohesion into the review, we have concentrated on possible ways in which their activities in the cytoplasm might be controlled. We have excluded Fe2+ from this review because of the specialized nature of its absorption by roots.