Abstract: The time course of elongation and oxygen consumption of wheat coleoptile segments in 38μM ABA solution and 5 × 10-5 M 2,4-DNP solution were investigated. At the same time, effects of exogenous ATP (1 mM) on elongation and ABA response in wheat coleoptile segments were observed. Within the first hour of treatment, ABA and 2,4-DNP rapidly inhibited elongation in the coleoptile segments. Exogenous ATP stimulates elongation in coleoptile segments. When segments pretreated with ATP and then transfered into ABA solution, elongation in coleopfile segments were not inhibited. On the basis of the similarities of action pattern of ABA and 2,4-DNP and marked decrease of ABA inhibiting effect in presence of exogenous ATP, it is testified that uncoupling of respiration and oxidative phosphorylation is one of ABA important effects, so it is suggested that ABA inhibiting elongation of wheat coleoptile segments by decreasing tissue energy (ATP) levels necessary for synthetic reactions, including nucleic acid and protein, and associated with elongation.