Plant microsomes contain a protein clearly related to a calcium-binding protein, calsequestrin, originally found in the sarcoplasmic reticulum of muscle cells, responsible for the rapid release and uptake of Ca(2+) within the cells. The location and role of calsequestrin in plant cells is unknown.
Calsequestrin is a high capacity low affinity Ca2+-binding protein thought to be essential for the function of the intracellular rapid releasable Ca2+ pool of a variety of animal cells. Here we show that two types of plant tissues, cultured Streptanthus tortuosus cells and spinach leaves, contain a