A reassessment of the influence of NAA on aerenchyma formation in maize roots

summary The effect of 1‐naphthylacetic acid (NAA: 10 −9 to 10 −5 M) on extension growth and aerenchyma formation in second‐whorl adventitious roots of Zea mays L. (cv. LG11) was examined. Treatments were applied continuously for 12, 8 or 3 d following initial periods in NAA‐free solution. NAA at 10 −9 M stimulated root elongation, but with increasing concentrations there was a progressive inhibition of growth. Gas space was increased by low levels of NAA and appeared to be reduced by the higher levels. When root length was taken into consideration, however, no NAA treatment produced less aerenchyma than would be expected from control roots of similar length in stagnant NAA‐free media, and there was some evidence that the NAA had promoted aerenchyma formation. Since NAA promotes ethene formation in roots the results would accord with an NAA induced ethene effect.