Cannabis tyres

PlantI started my post-graduate scientific career as a plant biochemist (phytochemist to be more precise). Once talking to a geologist about how fascinating plants are, he replied, “plants just get in the way of the rocks,” and so I guess your interests very much depend on your viewpoint. I moved up the career evolutionary  tree from plants to clinical pharmacology, and clinical pharmacologists had one prospect in common with geologists, they also thought plants were boring. Clinical pharmacologists and geologists are both wrong.

The Flemish chemist and physiologist Jan Baptist van Helmont (1580-1644) showed his dedication to phytochemistry when he weighed a growing tree and the soil in its pot every day for five years. The tree gained weight, but the soil remained unchanged and so he concluded the increase in weight must have come from water perculating up through the roots. We know today Van Helmont was only half right. Imagine a lonely carbon atom in a molecule of carbon dioxide, minding its own business, just quietly causing climate change, when it wanders into a leaf. There photosynthesis, powered by the energy of sunlight, captures carbon from atmospheric carbon dioxide, splits water drawn up through the roots, and joins the molecular fragments together to make a substance called 3-phosphoglycerate. And from this molecule, it makes all the stuff of plants. This is itself amazing, because those vegetables you had with your dinner, that tea or coffee you just drank and the cotton vest you’re wearing, contains carbon that, a short time ago, was floating around in the air.

Proving my interests reflect my viewpoint, my early efforts with phytochemistry focused on substances called terpenes, and these still hold a fascination for me to this day. Carbon in terpenes, like all carbon in plants, ultimately came from carbon dioxide, but it’s their journey forward that interests me most. As its name implies, turpentine (or turps) used as a solvent and paint-thinner comes from plant terpenes, but that same phytochemical pathway branches out in many directions. From the same terpene origins, comes the fragrance of plants from lavender (linalool) to oranges and lemons (limonene) and pine disinfectant (pinene). Condense a few more terpenes together and you get plant sterols. Some margarines, for example, are rich in β-sitosterol, a plant sterol with cholesterol-lowering properties. Keep going, joining up more terpenes and you end up with rubber, which oozes out of tapped rubber trees as latex. Take a side branch of terpene phytochemistry starting with geraniol, which gives geraniums their aroma, and you finish up following a more notorious route to cannabidiol. All these substances are towns and villages along the same photochemical road, where you can stop and sample, or carry on to the next destination.

So next time you watch that TV traffic cop show, where boy racers have burned rubber and provided a positive test for cannabis, remember as they put the cuffs on the miscreants, the rubber in the tyres and the weed they smoked have an unseen phytochemical connection. Now tell me that’s boring – I dare you.

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