Question

Briefly describe the Munch pressure flow hypothesis. How does polymer trapping fit into this scenario?

Answer 1

The theory behind the Mass flow hypothesis which is also called a pressure-flow hypothesis describes the movement of sap via the phloem, proposed by the German physiologist Ernst Munch in 1930. A highly concentrated organic sugar especially sugar in the cells of phloem from a source like a leaf forms a diffusion gradient that draws water in the cells from adjacent xylem. This develops turgor pressure in the phloem which is also called hydrostatic pressure. When the movement of minerals and water via xylem is driven mostly by negative pressure and movement via phloem is driven by hydrostatic pressure.
Passive phloem loading transports solutes freely through plasmodesma in the symplast of the minor veins of leaves. This process is referred to as polymer-trapping, in which simple solutes such as sucrose are synthesized into larger molecules such as stachyose or raffinose in intermediary cells.