Biopotentials along the stem of Helianthus in association with short-term translocation of 14C and chilling

Abstract

Tracer experiments using 14CO2 fed to leaves and [14C]sucrose fed directly to stems show that localized chilling of a sunflower stem temporarily stops or reduces translocation for 10–15 min. The reduction of translocation seems to extend along the entire stem above and below the chilled section. Biopotential measurements along the stem indicate a cyclic change which corresponds closely in time with the dislocation of translocation. Similar biopotential cycles occur when the top of the plant is given a 100% humidity shock. The translocation profiles obtained are bidirectional from the feeding area and bimodal. In other words, there is a massive portion moving at about 30–100 cm h−1 preceded by a faster but much smaller portion moving at speeds up to 720 cm h−1. Both portions are interspersed with peaks or pulses along them. These pulses are probably moving and, if so, are difficult to explain by a pressure-driven mass-flow mechanism alone.