Higher plants appear to have some signalling molecules that are similar to those in animals. Early events in the response of plant cell to many physiological stimuli share common features, such as membrane depolarization and elevation in cytosolic free calcium level. Ca2+ has a vital role in mediating plant responses to external stimuli of both abiotic origin (e.g. light, cold, heat, movement, hypoxia and drought) and biotic origin (e.g. phytohormones, pathogens, interaction with symbionts). Recently, tremendous progress has been made in understanding the role of Ca2+ as a second messenger in plants. It has been shown that plasma membrane Ca2+ channels and vacuolar Ca2+ release channels may participate in multiple signalling pathways in higher plants. Ca(2+)-dependent modulation of cellular processes occurs via intracellular calcium-binding proteins, of which calmodulin is one of the best characterized. It is well documented that calcium is involved in light-induced, phytochrome-controlled signal transduction pathways in higher plants.