Invertase and auxin-induced elongation in internodal segments of Phaseolus vulgaris

A close positive correlation was observed between segment elongation and the specific activity of soluble acid invertase in stem segments of P. vulgaris incubated for 21 hr in the presence of IAA or of several synthetic auxins and auxin analogues. Optimum concentrations for the stimulation of growth and invertase activity were similar and varied from 10^?6 M (2,4-D) through 10^?5 M (IAA, IBA, α-NAA, β-NAA) to greater than 10^?4 (IPA, PoAA, trans-cinnamic acid). The weak activity of trans-cinnamic acid, a competitive inhibitor of auxin action, may have resulted from cis-trans isomerization during incubation. The concentration of hexose sugars in the segments fell during incubation in the presence of auxin, the greatest decline in hexose concentration occurring in the presence of compounds exhibiting the greatest stimulation of growth.