Using a portable hydrogen cyanide gas meter to uncover a dynamic phytochemical landscape

Over 3000 species of plants and animals release toxic hydrogen cyanide (HCN) gas when their tissues are crushed. To investigate the role of cyanogenesis in Passiflora-herbivore interactions, we developed an inexpensive, rapid, sensitive method for measuring HCN emissions from crushed tissues.

The method includes crushed tissue confinement in a closed chamber, where cyanogenesis reactions occur, followed by evacuation of gas to a portable HCN meter. Parts per million readings are repeated at 5-min intervals until HCN is depleted. Three versions of the closed reaction chamber apparatus were tested: plastic cup, airtight combination mortar-pestle, and glass desiccator jar.

We calibrated the method by comparing with a closed chamber measurement apparatus. The procedure's repeatability was demonstrated with a standard curve using known quantities of cyanogenic glycoside standard. Data collected with this method were also compared with the conventional colorimetric procedure. We processed over 2000 samples using this technique, revealing diverse elements of cyanogenic variation.

These methods produced well-defined data with minimal error. Results illustrated a one to four order-of-magnitude variation at organizational levels ranging from individual leaves to the entire Passiflora community. We now have a promising tool for uncovering the HCN phytochemical landscape in unprecedented detail.