Energetics of the response of maize coleoptile tissue to indoleacetic acid : Characterization by flow calorimetry as a function of time, IAA concentration, and pH.

Indole-3-acetic acid (IAA) promotes an increase in steady-state heat production by corn (Zea mays L.) coleoptile tissue; this increase is associated with an elevation in aerobic respiration rates. A detailed time dependence of the exothermic response to IAA was obtained using flow calorimetry. The latent period and magnitude of response were evaluated as a function of IAA concentration and pH. The data indicate that more than one response may occur. The optimal change in heat production was produced by an IAA concentration of 3·10(-5) M. It was initiated within 5 min after the start of the IAA treatment, and reached a magnitude in excess of 25% of the tissue's basal heat production. Concentrations of IAA greater than 1·10(-4) M resulted in diminished response(s), but the effect was strongly pH dependent. Several possibilities for the increased heat production triggered by IAA are discussed.