Translocation Rate

• Aphids


  A group of insects, belonging to the order Hemiptera, which feed primarily on sap extracted from phloem
• Measuring phloem transport using aphids

  1. Grow plant in lab with leaves sealed in CO2 chamber

  2. Leaves convert CO2 to radioactively-labelled sugars via photosynthesis

  3. Aphids positioned along plant and encouraged to feed on phloem sap

  4. Aphid stylet severed and sap collected at different positions

  5. Sap analysed for presence of radioactively-labelled sugars

  6. Translocation rate calculated based on time taken for radioisotope to be detected at different positions
• Factors affecting translocation rate

  • Concentration of dissolved sugars in phloem sap
  • Rate of photosynthesis (affected by light, CO2, temperature)
  • Rate of cellular respiration (affected by plant stress)
  • Rate of transpiration
  • Diameter of sieve tubes (varies between plant species)
• What do aphids use to pierce a plant's sieve tube?

  Stylets
• If the stylet is severed, sap will continue to flow from the plant due to the hydrostatic pressure within the sieve tube