Translocation Flashcards
what does translocation mean
Movement of assimilates throughout a plant, from the source to the sink whilst using ATP.
Where does translocation occur
Phloem
what is a source
part of a plant which loads materials into the transport system
what is a sink
part of a plant which removes/ requires the materials
Give an example of a source
-Leaves; photosynthesise and sugars made are moved around plant
Why is sucrose used for transportation over glucose
Allows for more efficient energy transfer due to sucrose being a disaccharide
More stable of a molecule than glucose, less likely to react during transportation
How can the roots be a sink and a source
Sink- Receive their sugars and store as a starch
Source-starch converted to sugar and transported to growing part of plant
Give an example of a sink
-roots- receive sugar and store as starch
Why is it important that companion cells are live cells, during phloem loading
it generates the ATP for the sucrose loading
what is the first step of translocation
Hydrogen ions are pumped out of the proton pump on the companion cell using ATP.
After the proton pump, pumps out the hydrogen ions. what is the next step
Due to the proton conc. grad. Naturally the hydrogen ions will want to move back into the companion cell’s cytoplasm
They move through a cotransporter protein intrinsic to the cell wall of the CC.
Cotransport will only work if H+ if accomodated with sucrose.
They then both move into the companion cell
What happens to sucrose after it has been cotransported into the companion cell
There will be a higher sucrose concentration in cc than sieve tube.
Naturally sucrose will diffuse through plasmodesmata into the sieve tube elements.
Decreasing water potential inside sieve tube
After sucrose is in the sieve tubes via diffusion through plasmodesmata, water potential is lower in the sieve tube than the companion cell
How does this impact the behaviour of the water in the companion cell
Water will want to travel down the WP gradient. From high (cc) to low (STE).
Generates Turgor pressure in the sieve tube element.
How does turgor pressure help in transport of assimilates in the sieve tube
enables Mass flow of assimilates to different places of phloem
