Energetics of the response of maize coleoptile tissue to indoleacetic acid

Abstract

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.

Promotion of respiration by auxin in the induction of cell division in suspension culture

“…The extent of the stimulation and its time course were very similar to those observed in the action of auxin on cell elongation (Bonner and Bandurski 1952, Audus 1960, Anderson et al 1981. These data indicate that the promotion of respiration appears to be a common event for the action of auxin on cell extension and cell division.…”

“…Under prolonged incubation the stimulation increased and reached a maximum in 60 min. A similar time course of the auxin effect on respiration of maize coleoptile sections (registered by the method of microcalorimetry) was observed by Anderson et al (1981). Our experiments on auxin uptake by cultured cells revealed that maximum content of auxins (IAA, 2,4-D) was registered in 40-60 min after auxin administration to suspension Gamburg 1981, 1982).…”

“…The auxin is believed to promote the respiration indirectly by increasing ATP consumption in enhanced cell growth, thus providing more intensive supply of ADP for mitochondria (Audus 1960, Anderson et al 1981. In this case the activity of mitochondria isolated from auxin-treated and untreated cells should not differ.…”