Movement of Substances in Plants

• Path of water through plants

  • methylene blue shows where water has travelled as it stains xylem blue

  
• Path of food substances through plants- The “Ringing” Experiment

  • the ring of the bark with the phloem is removed from the stem of a woody plant
  • after some time, the stem above the cut region swells up
  • with the phloem removed, food substances from the leaves cannot reach the stem below the cut region and accumulate above the cut region

  
• Using Aphids in Translocation Studies

  • Insects such as aphids feed on plant juices
  • the stylet of each aphid penetrates the leaf or stem
  • the aphid can be anaesthetised with carbon dioxide while it is feeding, the body of the aphid is cut off, leaving only the stylet in the plant tissue
  • a liquid which contains sucrose and amino acids will exude from the cut end of the stylet
  • the stylet shows the translocation of sugars and amino acids occur in the phloem
• isotopes in translocation studies

  • carbon-14 is a radioactive carbon isotope that can be detected by an x ray photographic film
  • a leaf is provided with carbon dioxide containing radioactive carbon
  • when photosynthesis takes place, the sugars formed will contain radioactive carbon
  • the stem is cut and a section of it is exposed onto an x ray photographic film, radioactive substances are present in the phloem

  
• Translocation


  • translocation is the transport of manufactured food substances, such as sugars and amino acids, in plants