Effect of peeling on IAA-induced growth in Avena coleoptiles

The act of peeling removes the epidermis exclusively from Avena coleoptiles. Peeling inhibits IAA-induced growth, by inhibiting the growth of segments incubated in the presence of IAA, and promoting that of those incubated in water. The magnitude of the inhibition of IAA-induced growth is proportional to the amount of epidermis removed. It is shown that neither lateral swelling, wounding, anaerobiosis, nor exposure to supraoptimal concentrations of IAA cause the inhibition. It is concluded that in Avena coleoptiles the epidermis regulates the rate of expansion of the underlying parenchyma cells and is the principal target of IAA-action.