Translocation

• Translocation - Plants transports assimilates in phloem from source to sink

  • Energy needed - Draw up substances
  • Assimilates - Products of photosynthesis
  • Sucrose - Main assimilate
• Sources

  • Green leaves and stems
  • Storage organs e.g. tubers
  • Food stores in germinating seeds
• Sinks:

  • Growing roots / Actively absorbing minerals
  • Actively dividing meristems
  • Developing seeds
• Phloem loading - the movement of sucrose from the leaves to the rest of the plant
• The apoplast route - the movement of substances through the cell wall of a plant

  Occurs in the Companion cells - Sucrose moves into cytoplasm in and active process:

  1. H+ actively pump out into surrounding tissue with ATP
  2. H+ back to companion cell down conc. gradient with a co-transport protein
  3. Increased sucrose conc. in CC

  Results in:

  1. Water moves into CC and plasmodesmata by osmosis
  2. Build up of turgor pressure - Solute accumulation in source phloem
• Phloem unloading - the movement of sucrose from the leaves to the rest of the plant

  • Unloaded when needed
  • Diffusion - Converted to another substance after to maintain conc. gradient of sucrose
  • Loss of solutes in phloem - Increased WP - Water moves out via osmosis