Unloading of assimilates (eg. sucrose
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The unloading of the assimilates (eg. sucrose) occurs at the
sinks
Scientists believe that the unloading of sucrose is similar to the loading of sucrose, with the sucrose being
actively transported out of the companion cells and then moving out of the phloem tissue via apoplastic or symplastic pathways
To maintain a concentration gradient in the sink tissue,
sucrose is converted into other storage molecules such as starch. This is a metabolic reaction so requires enzymes (eg. invertase which hydrolyses sucrose into glucose and fructose)
The intracellular space and walls of the sieve cells are adapted for the mass transport of sugars how
There are very few organelles, a small volume of cytoplasm and a large vacuole present in the intercellular space The phloem sap can flow easily by moving through the open corridor that has low resistance Sieve cells have thick cell walls These walls help them to withstand the pressure exerted by the mass flow of sugars
Remember that the loading of sucrose requires two protein pumps (,,,,,,,,,,,]) which are located in the companion cell surface membrane.
proton and co-transporter