#pressureFlowTheory
#PressureFlowHypothesis
#PressureFlowMechanism
#PhloemTransport
#pressureflowtheory1styearbiology
#pressureflow-massflowhypothesis
#FSCbiology
#Irtisamsbiology
Sugars move (translocate) from source to sink, but how? The most commonly accepted hypothesis to explain the movement of sugars in phloem is the pressure flow model for phloem transport. This hypothesis accounts for several observations:
Phloem is under pressure
Translocation stops if the phloem tissue is killed
Translocation proceeds in both directions simultaneously (but not within the same tube)
Translocation is inhibited by compounds that stop production of ATP in the sugar source
In very general terms, the pressure flow model works like this: a high concentration of sugar at the source creates a low solute potential (Ψs), which draws water into the phloem from the adjacent xylem. This creates a high pressure potential (Ψp), or high turgor pressure, in the phloem. The high turgor pressure drives movement of phloem sap by “bulk flow” from source to sink, where the sugars are rapidly removed from the phloem at the sink. Removal of the sugar increases the Ψs, which causes water to leave the phloem and return to the xylem, decreasing Ψp.
This video provides a concise overview of sugar sources, sinks, and the pressure flow hypothesis:
Fsc Biology lectures series by irtisamsbiology chapter 14