• Hemiptera (also known as true bugs) is an order of insects that have?highly-adapted mouthparts?for?piercing?and?sucking
• Many hemipterans (such as?aphids) use these mouthparts for?feeding on phloem sap
• This behaviour has been used by scientists to investigate?transport in the phloem?of plants to better understand, for example,?how it occurs?and the?speed?at which it occurs

Investigating phloem transport rates using aphid stylets

• Aphids penetrate the phloem using mouthparts known as?stylets?(these are a bit like microscopic pipettes)
• If the aphid is first anaesthetised, its head and body can be removed?leaving the stylet still in place
• Due to the?pressure?of phloem sap in the sieve tube, sap will?continue to flow?out of the stylet, forming a drop at the end of the severed stylet
• At this point, the?flow rate?of the phloem sap can be measured and a?sample?can be taken from it to analyse its?composition

Aphids can be used by scientists to investigate transport in the phloem of plants

NOS: Developments in scientific research follow improvements in apparatus; experimental methods for measuring phloem transport rates using aphid stylets and radioactively-labelled carbon dioxide were only possible when radioisotopes became available

• Using?radioactive isotopes?(also known as radioisotopes) in scientific research only became possible after 1945 because their use was developed for work on the atomic bomb during the Second World War
• For example,?carbon-14?(¹⁴C) is an?isotope?of carbon that is?radioactive
  • It is possible to generate?carbon dioxide that contains carbon-14; this would be written as?¹⁴CO₂
• It was discovered that if leaves were exposed to?¹⁴CO₂?whilst they were?photosynthesising?(by surrounding a leaf with a polythene bag filled with?¹⁴CO₂), the?leaves would produce?¹⁴C-labelled sugars
• Using autoradiography, these?¹⁴C-labelled sugars could then be?traced during translocation?throughout the plant?and also?detected in phloem sap flowing out?of aphid stylets
• These techniques enabled scientists to investigate the?speed of phloem transport?and how sugars are?distributed between sources and sinks?in plants

¹⁴C-labelled sugars can be traced during translocation throughout planta by detection in phloem sap flowing out of aphid stylets

• • Sugars are?produced?in sources (photosynthesising leaves) while sugars are?delivered to?sinks (roots, young shoots and developing seeds)