Under stressful conditions plant hormones, cytokinin (generally in root meristems) auxin (generally in shoot meristems), and gibberellins (generally in differentiating tissues) play a role in plant response by controlling meristem activity (Amzallag, 1999; Dodd, 2005). For example when P is deficient, auxin, ethylene and cytokinin induce morphological changes (i.e., increasing root surface, by producing more dense root hairs and cluster roots) in the plant to cope with the stress. In addition auxin is also able to influence the direct and indirect mobilization of soil P through increasing root exudates (Wittenmayer and Merbach, 2005). It has also been stated that AM alter the rate of plant hormones under stressful conditions (Suresh and Bagyaraj, 2002). It seems that the balance between the plant hormone alteration by the plant and AM
may determine the final amount and role of plant hormones on
regulating plant growth under stressful conditions