The rate of response of excised stem segments to auxins

Abstract

A chamber and segment holder was made in order to take measurements every minute of the elongation race of stem segments. The results show that there is a lag period before auxin induced elongation occurs. The lag phase of pea stem segments in phosphate buffer is about 12 minutes; of lupin hypocotyl segments in the same buffer is about 14 minutes but about 18 minutes in tris-maleate buffer. The response is the same whether the auxin is IAA or 2,4-D. To date similar kinetics of the stimulation of growth rate by auxins have been shown with coleoptiles, stems, and hypocotyls; in monocotyledons and dicotyledons; and with light grown and dark grown tissues. It is therefore probable that the lag period occurs generally in response to auxin. Short-term treatments with IAA indicate that cell elongation is not the primary action of auxin. Experiments with additional light indicate that there may be at least two factors contributing to the growth curve.