translocation

translocation

movement of assimilates through the phloem from the source to the sink

flow

multidirectional requiring ATP

companion cell

provides ATP to fuel active transport

sucrose concentration

high in companion cell so sucrose moves to phloem sieve tube element by diffusion

water potential gradient

moves from surroundings into the phloem sieve tube element and companion cell

sink

sucrose and water diffuse out the sieve tube element

mass flow

water potential gradient creates high hydrostatic pressure so sucrose moves

source

sugars are loaded actively into sieve tube creating water potential gradient so water moves from xylem into phloem sap

hydrostatic pressure

causes mass flow so sap moves through phloem

sink processes

sucrose actively transported out of phloem creating high water potential…water moves out the phloem to the xylem

co-transport

sucrose and hydrogen ions

H+ and sucrose co-transporter

a protein for translocation