Studies on the action of abscisic acid on IAA-induced rapid growth of Avena coleoptile segments.

A linear displacement transducer has been used to monitor the growth of a column of Avena coleoptile segments in flowing solution. IAA at 10(-5)M in phosphate buffer of pH7 promotes growth after a latent period of 10.9 min, the initial maximum growth rate occurring after 25 min. Simultaneous treatment with 10(-5) M ABA does not affect either the latent period or the initial maximum growth rate in response to the IAA treatment, but subsequently gives rise to an inhibition of growth detectable after 30 min. In contrast, pretreatment with ABA for 100 min increases the duration of the latent period and reduces the initial maximum growth rate. Removal of the ABA rapidly relieves the inhibition of IAA-induced growth but a growth rate comparable to that of material treated only with IAA is never attained. Studies using 2-[(14)C]ABA and 1-[(14)C]IAA suggest that the latent period before ABA inhibition of growth is detectable is not due to a lag in ABA uptake, and that ABA is not acting by reducing IAA uptake.