As pointed out previously (Patten and Glick, 2002), plant growth is promoted directly by both IAA and ACC deaminase. Notwithstanding minor changes in IAA synthesis (a 7.5e17.5% decrease or a 3.1% increase) in the mutants, we believe that the decrease in plant growth promotion that is observed under stressful conditions comes primarily from the absence of ACC deaminase in the mutant strains.
Based on unpublished observations in our laboratory, changes in the bacterial IAA concentration of this magnitude are unlikely to have any significant effect on plant growth promotion.