Figure 1.
(a) Schematic of a plant in which sugar and signalling molecules travel from sources, e.g. leaves, to places of storage and growth, e.g. fruits or roots. In our model, the plant is divided into three zones, a source/loading zone of length l1 (the leaf; 0 < x < x1), a translocation zone of length l2 (the stem; x1 < x < x2) and a sink/unloading zone of length l3 (the root; x2 < x < x3). (b) Diagram of how the Münch flow mechanism is thought to drive sugar translocation in plants. The surfaces of the cylindrical phloem cells of radius r are covered by a semi-permeable membrane. Sugar loaded actively into the cells at the sugar source draws water by osmosis from the surrounding tissue, thereby generating flow as the sugar solution is displaced downstream. (Online version in colour.)