Calmodulin and calmodulin‐mediated processes in plants

The Ca2+ ‐binding protein calmodulin is found in all plants investigated so far. The comparison of the biochemical and functional properties reveals that it is structurally conserved and functionally preserved throughout the plant and animal kingdom. Among the plant enzymes so far known to be dependent on the Ca2+ ‐calmodulin complex are NAD kinase(s), Ca2+ ‐transport ATPase, quinate: NAD+ oxidoreductase, soluble and membrane bound protein kinases, and H+ ‐transport ATPase. Calmodulin may play also an important role in the regulation of other cellular reactions, such as hormone‐mediated processes, secretion of enzymes, and contractile mechanisms. On the basis of the NAD kinase and its regulation by light and Ca2+ ‐calmodulin, it is suggested that changes in the cellular, free Ca2+ concentration following stimulation may alter the metabolism of a plant cell. According to this suggestion free Ca2+ may act as a second messenger in plants much as it does in animal cells.