David Cooper, Facebook asked:
Do plants that undergo stress produce protective substances that are beneficial to a human diet?
John - Well, it’s a little bit difficult to answer that question directly, but certainly, methyl salicylate, which is the chemical in the oil of wintergreen and which was of course related to the chemistry from which we got aspirin – an extremely useful chemical for most of us when we have a headache and so on – actually is produced under stress. So the plants are indeed producing something that is nominally useful to us, but don't forget that this is being done in an evolutionary context. If the plant, when it’s attacked by us, with our hoe or with our scythe or with our herbicide, could do something to stop us actually making this deployment then of course, it would be doing very, very well. And in fact, plants will be seen by so-called perhaps epigenetic effects to avoid the blades of our lawnmower.