Kinetic experiments on the nature of the growth mechanism in oat coleoptile cells

Abstract

A method was devised for following the growth rate of oat coleoptile cylinders with sufficient precision to measure the growth that occurred in 1 minute; the solution treating the section could be completely replaced with a different solution within 15 seconds. It was found that response of the elongation rate to changes in temperature was complete within 20 seconds, with a Q10 of about 3.5 in the temperature range 2-23[deg]C, and that response to treatment with cyanide, or to treatment with oxygen when the tissue had been deprived of it, was completed in a few minutes. The results are interpreted as indicating that the rate of elongation is controlled directly by the rate of a metabolic reaction or reactions rather than by a physical property like steady-flow viscosity, and hence that the growth mechanism has the character of a chemorheological process as opposed to a plastic flow.The growth rate of oat coleoptile cylinders becomes promoted, after auxin is added, only after a lag of about 10-15 minutes at 23[deg]C. This lag is not determined primarily by the rate of penetration of auxin into the tissue; it is approximately twice as long at 13[deg]C. This is considered to indicate that the action of auxin is not directly upon the growth-controlling reaction, but affects the latter indirectly via temperature-sensitive metabolic pathways.