Some Properties of Sucrose Translocation in Bean (Phaseolus vulgaris L.)

Abstract

Summary A rapid translocation of radioactivity was observed in bean after feeding labelled sucrose to the mid-vein of primary leaves. The measured speed (1000–2000 m/hr, or two orders of magnitude greater than previously found: 20–50 m/hr) appears to remain a function of incubation time in experiments suggesting velocities greater than those actually found. The rapid translocation was not affected either by the label used (3H- or 14C-label-led sucrose) or by pretreating the cut mid-vein with sucrose. Rhythmic changes in the levels of radioactivity were observed in roots as well as in other plant organs, and those measured along the stem showed characteristic peaks of zonal accumulation. Rhythmicity was also observed while comparing the 3H- and 14C-labelled sucrose introduced at constant intervals into the same mid-vein. Although these results confirm that the translocation of externally supplied radioactive markers may have some rhythmic quality, its meaning remains uncertain. The possibility that rhythmic changes in the levels of radioactivity may indicate the existence of a «pulse-like» or «wave-like» property of translocation in plant is discussed in the light of various hypotheses.