IBDP Biology- Translocation

In this IBDP Biology blog post, we will look into the process of translocation and how thephloem aids this particular process.

Translocation

Translocation: Transport of organic compounds (sugars and amino acids) made during photosynthesis in the phloem sieve tubes

Plants do not transport Glucose it must be converted into Sucrose

Translocation of sap can occur in any direction always moving from a source to a sink

Sap: Mixture of water, carbohydrates, minerals, amino acids and plant hormones

Source: Photosynthesizing tissues and other plant organs that can export sugars to other parts of the plant

Sink: Plant organs that cannot produce sugars but need it for respiration or storage 

Translocation Steps 

• Sugars produced by photosynthesizing tissues or other sources are actively loaded using ATP into the sieve tubes by companion cells. This causes solute concentration to build up in the sieve tubes
• High concentration of solutes in sieve tubes at the source leads to water entering sieve tubes by osmosis from neighbouring xylem vessels this creates high hydrostatic pressure
• Hydrostatic pressure gradients is present between the sap at the source and the sink
• High hydrostatic pressure causes movement of water and carbohydrates through the pores of sieve plates down the tube towards the sink
• At the sink companion cells actively unload the sieve tube, some carbs converted starch or stored while some are used for respiration
• Concentration of solute decreases in phloem sieve tubes at the sink, water then exists sieve tubes by osmosis creating low hydrostatic pressure
• As sap goes from source to sink transported from area of high hydrostatic pressure to an area of low hydrostatic pressure

Translocation Rate using Radioactive Isotopes 

Radioactive isotopes can track sucrose movement during translocation. The radioactivity can be used to traced using photographic film

Plant is grown in lab

• One leaf is exposed to carbon dioxide containing a radioactive isotope C14 for short period
• What happens to 14CO2 within the leaf before any translocation occurs?

14CO2 taken up by photosynthesis and 14C incorporated into glucose and then sucrose

After 6 hours plants frozen in liquid nitrogen. Suggest why plant must be frozen quickly.

Freezing plants will prevent any further translocation of sucrose. Kills phloem cells  

That is all!

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References:

• https://www.google.com/url?sa=i&url=https%3A%2F%2Fnobowa.com%2Fplants-use-water%2F&psig=AOvVaw1WfdBt1s24LaLVtzP3SUfs&ust=1626978389139000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCOie_fnk9PECFQAAAAAdAAAAABAV
• https://www.google.com/url?sa=i&url=https%3A%2F%2Forganismalbio.biosci.gatech.edu%2Fnutrition-transport-and-homeostasis%2Fplant-transport-processes-ii%2F&psig=AOvVaw1WfdBt1s24LaLVtzP3SUfs&ust=1626978389139000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCOie_fnk9PECFQAAAAAdAAAAABAm

Drafted by Venetia (Biology)