Ethene is an important plant growth substance, and plays an essential role in the triggering of ripening in many fruits. The precise nature of the ethene receptor on plant cells and the molecular basis of its action is not fully understood, but research is currently being carried out with mutants defective in this particular control system. The production of ethene occurs during a short part of the ripening process.

Presence of ethene can be detected by a relatively simple biological assay, using germinating seedlings.

The assay

This technique is based on certain responses made by young seedlings, grown in the dark, then exposed to ethene. The morphology of the seedlings treated with ethene changes noticeably, compared to controls. For example, the ethene-treated seedlings are shorter, with decreased length of hypocotyl and root are fatter, with increased girth of hypocotyl tend to respond less to gravity (diatropism) tend to have more extensive and longer root hairs The technique uses 2-day old seedlings. To detect ethene released from fruit, batches of seedlings are exposed to the fruit for one day. The morphology of exposed and control seedlings is then compared after two further days of growth.

The assay method can be used to determine the period of ethene production by ripening fruit. However, in order to study the production of ethene by some fruit on a daily basis, some forward planning is needed, because each day the fruit needs to be provided with a fresh batch of 2-day old seedlings

So, if you wish to follow the production of ethene by a ripening banana over a 5-day period, you need to sow seeds 2 days before the first seedlings were to be exposed, and then every day for the next 4 days. This will provide the supply of fresh seedlings required. The period of maximum ethene production is likely to last for less than a day.

Seeds of any reasonably robust dicotyledonous species could be used - promising results have been achieved with fenugreek seeds (Trigonella foenum-graecum). Avoid very large seeds (such as broad bean) as they simply take too long to develop sufficiently for the experiment.

• Sow the seeds (minimum of 10) on moist filter paper in shallow dishes (e.g. petri dish base). The roots and shoots should then be clearly seen, and easy to measure.
  
  
• Keep all the seeds in a light-proof cupboard - after sowing, during exposure, and during the subsequent two days of post-exposure development.
  
  
• Place the ripening fruit in a plastic box (e.g. 2 litre ice-cream box) with a dish of seedlings and seal it with a plastic lid. (The ethene gas diffuses very easily, so it is important to seal the container.) Set up a control box, containing another dish of seedlings, but no fruit. Place the sealed boxes in the same light-proof cupboard.
  
  
• After every 12 or 24 hours, remove the dishes of seedlings in both boxes and replace them with fresh ones (grown to the same age as the original ones). Allow the earlier pair of dishes to develop further for 24 hours, before making any measurements.
  
  
• Make quick records of the contents of the dishes by taking photographs, or lay the seeds on a sheet of acetate and photocopy them against a background of graph paper (to provide a scale). Photos give a useful record, but may also provide an opportunity to make measurements later, directly off the computer screen, if a digital camera is used.
  

The control measurements are important, as they provide a baseline comparison for measuring the influence of ethene on exposed seedlings. It might be useful to express the changes in the seedlings exposed to ethene, as a percentage change from the controls.

Premature senescence of cut-flowers exposed to ethene is another phenomenon that can be studied in this manner.

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