A further analysis of reciprocating flow in phloem tubes
A more stringent mathematical treatment of reciprocating flow in phloem tubes has shown that the original model (Miller 1973) would be too inefficient to provide a quantitative explanation for the rate of solute dispersion within the tube. A modification is suggested in which the mobile phase consists of the sieve tube sap, and the companion cells constitute the static phase. Lateral diffusion of the solute between these two phases could occur through the cell wall barrier separating them via plasmodesmata and would follow first-order kinetics. It is shown that for optimum dispersion in such a model, the period of oscillation should be about 3.6 times the half life of the lateral diffusion process. Estimates of the various parameters involved indicate that such a mechanism, if driven by protoplasmic streaming, predicts a dispersion coefficient of the same order as those found experimentally.