Fig. 3.

Hormonal interactions regulating plant responses to abiotic stresses and defenses against biotic agents. Arrow heads indicate a positive interaction, whereas a T end, indicates an inhibitory effect. Abscisic acid (ABA) has strong synergistic effects on JA-dependent defenses, while jasmonic acid (JA) promotes ABA-mediated stomatal closure and leaf senescence, but not primary root growth. Dashed arrows indicate the mixed effects of ethylene (ET) on JA-dependent defenses: ET induces defense responses to necrotrophic pathogens and some responses to insect herbivores but suppresses other insect induced defenses. ABA and ET strongly antagonize each other in many responses, but both induce leaf senescence. Interactions between JA and gibberellic acid (GA) or auxin (AUX) to mediate growth-defense balance are also indicated