Acropetal effects of IAA upon the wave-like pattern in the basipetal efflux of natural growth substances of Fraxinus excelsior L.

Abstract

Basipetal efflux of natural growth substances from the cambial region of a successive series of short sections of the stem of Fraxinus excelsior L. was measured by Went's oat coleoptile curvature bioassay. A wave-like pattern of stimulation by natural growth substances collected after efflux of only 10 min in agar containing 0.56 µM synthetic IAA was observed, confirming to earlier findings in other species. Both inhibitory and stimulatory effects were recorded, however, the oscillations were manifested in stimulation, which is probably due to natural auxin. IAA applied for 1 h directly to the cut surface of the lateral branch, distal to the stem segment used for the measurements of natural auxin efflux, caused acropetal modulations of the wave-like pattern. The results seem to indicate that the auxin-wave system analogous to that already described for other trees operates also in the cambial region of the Fraxinus excelsior L. stem. Modulations of such waves caused by IAA (seen as phase shift) can be propagated acropetally at a rate excluding direct action of molecules of auxin at the site of measurement.