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.

SummaryOne-year-old sour orange seedlings were labelled with either 14 CO2 or 14 C-sucrose, taken up by the midrib of one mature leaf. An unexpectedly high transport velocity (2,040 cm h-1) was detected during the first 60 min after labelling, followed later by a slow transport (1.17 cm h-1) which started 19 h after labelling with 14 CO2. Similar results (rapid flow of 2,400 cm h-1) were obtained when 14 C-sucrose was applied to one mature leaf of 15-day-old bean (Phaseolus vulgaris) seedlings; in this case, however, the slow movement started 3 min after application. Ringing citrus seedlings did not affect the rapid transport, but the slow phloem translocation was retarded. In both modes of translocation radioactivity was found in the wood regardless of ringing.

SummaryRinging one-year-old sour orange seedlings caused decreases in the starch level and respiration in the roots and in the level of NPK in the upper and lower parts of the plant. One month after ringing the decrease in starch level stopped and respiration rates returned to those of non-ringed seedlings. An addition of 10-4 M GA3 to the nutrient solution of non-ringed seedlings caused a rise in starch level in the main root; an addition of 10-6 or 10-5 M GA3, however, did not offset the decrease in starch level caused by ringing. Ringing did not interfere with the synthesis of starch from 14 C-sucrose added to the nutrient solution one month after ringing. Irrigation stress (and P deficiency in rough lemon seedlings) enhanced the ringing-induced decrease in starch level in the main root.

Girdling of Citrus aurantium seedlings inhibited translocation of 14C-sucrose from leaves to roots, yet starch accumulation was observed in all parts of the seedlings including roots. Results indicated that girdling triggered starch accumulation in roots independent of carbohydrate transport from the leaves. The increase in starch content of leaves was accompanied by a decrease in the specific activity of the accumulated starch. Girdling also caused an increase in fresh weight in all parts of the seedling and a decrease in percentage dry weight of rootlets.