When plants are attacked by herbivores or pathogens, they must respond rapidly while also preparing for potential future attacks. Calcium, a cellular second messenger, and the plant hormone jasmonic acid play important roles in this response. Within seconds of an injury, the plant generates calcium waves that relay information about the attack. At the same time, the synthesis of jasmonic acid is initiated in the chloroplast, triggering, through several intermediate steps, the expression of defense genes in the cell nucleus. ...read more read less