The Translocation of Sugar in Sieve Tubes

Abstract

A theory is put forward to account for the translocation of sugars in terms of electrokinetic forces developed in the cytoplasm of the sieve plates. A major role is suggested for potassium as responsible both for the movement of solution and for maintaining the necessary potentials across the sieve plates. The mechanism for the latter invokes the active uptake of potassium (or some other ion) by the companion cells. It is suggested that in the overall process of conduction there are features which can be described as involving the elements of inertia and positive energy feedback, and that a possible result of these would be longitudinal oscillations in the phloem columns which might assume importance as the seat of rhythms and as a background for photoperiodic effects, and which might be adjusted to an imposed period by callose constrictions. The mechanism put for ward would seem to be physically adequate even for very lengthy phloem columns, and it would seem possible for it to accommodate most, if not all, of the major experimental facts. It implies the active transport of water, as well as of sugars and other chemical species.