The basis for ABA as an important signal is that both salt stress and water deficit can induce a rapid and massive accumulation of ABA in plant tissues. This process itself is a cellular signaling cascade, in which the perception of salt- or water deficit signal or the initial triggering for ABA accumulation is the most important step.

It is well known that the second messengers and protein kinases or phosphatases are pivotal signal components mediating various responses of plants to biotic and abiotic stimuli. It was suggested that Ca2+ might also play vital roles in water or salt stress-induced

ABA accumulation. However some studies reported that ROS were involved in stress-induced ABA accumulation.