While yeasts have only a single CaM gene, plants and vertebrates contain an evolutionarily conserved form of CaM genes. The difference between plants and animals in Ca signaling is that the plants contain an extended family of the CaM in addition to the evolutionarily conserved form. Calmodulins play an essential role in plant development and adaptation to environmental stimuli.
Calcium plays a key role in the structural integrity of the cell wall and the membrane system of the cell. However, high calcium levels can be toxic to a plant's cellular energy metabolism and, hence, the Ca concentration in the cytosol is maintained at a submicromolar level by removing the cytosolic Ca to either the apoplast or the lumen of the intracellular organelles. Ca pulses created due to increased influx and efflux act as cellular signals in response to external stimuli such as hormones, light, gravity, abiotic stress factors and also interactions with pathogens.