Change in intracellular Ca levels is used as a signature for diverse responses towards mechanical stimuli, osmotic and salt treatments, and cold and heat shocks. Different root cell types show a different Ca response to osmotic and salt stresses and this implies the cellular specificities of Ca patterns. In response to external stress CaM activates glutamate decarboxylase (GAD) that catalyzes the conversion of -glutamate to GABA. A tight control on the GABA synthesis is important for plant development and, hence, increased GABA levels can essentially affect plant development. Therefore, external stress can affect plant growth and development and CaM are involved in that pathway controlling this effect.