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Volatile Organic Compounds (VOCs) are released by flowers and perceived by humans as ‘scent‘. These VOCs play a strong role in attracting pollinators to visit flowers and vary markedly between species; pollinators respond to different VOCs. There is emerging evidence that VOCs also vary within species i.e. between varieties and this can have an impact on how likely a particular variety is to attract pollinators. VOCs can be sampled using the ‘headspace sampling’ or the ‘air entrainment’ method. The air entrainment method can be used to capture the volatile compounds produced by flowers. This is also known as headspace sampling. A Barry Pye type apparatus was constructed (Figure 1), based on that used at Harper Adams University (Tom Pope and Joe Roberts, personal communication). The system uses 12V battery power (outside) or a mains adapter (indoors) to power air pumps (Neuberger NMP KNDC B). Air is first drawn through an activated carbon filter (100 cm3) to remove contaminants. All piping is 3 mm o.d. nylon (supplied by Megaflex Ltd), joined using brass or stainless steel unions (supplied by Swagelok Ltd). Separate adjustable air regulators (glass tubes with brass fittings supplied by Cole Parmer) are used to control the flow of air into (150 cm3/min) and out of (100 cm3/min) the sample bags (25 cm by 28 cm roasting bags supplied by Sainsbury’s Supermarkets Ltd)). The volatiles are collected on Tennax TA ‘Biomonitoring’ inert coated stainless steel tubes (supplied by Markes International Ltd). After sampling, these are securely capped and stored at room temperature until analysis. Entrainments can made both from isolated flowers (15 flowers per bag) in the laboratory or in the field from flowers on individual intact plants. In the latter case, leaves should also be sampled so that any data from foliage can be identified and removed from analysis. The sampling period is eight hours. The advantage of sampling flowers in situ is that the process of removing flowers potentially triggers the release of compunds associated with plant damage. Therefore the optimum method is to sample flowers on undamaged plants. After sampling the Tenax tubes are then thermally desorbed and the volatiles released are analysed using a GC-MS (Gas Chromatographic Mass-Spectrometer). The compounds can be identified using existing libraries. |
