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Alkaloids: a Bitter Story

To plants, an important group of weapons in their battle to prevent being eaten are the chemicals known to human chemists as ‘alkaloids’. These are defined as chemicals that contain nitrogen in a ring-like structure and that have been made by some plant or another. At least five thousand different alkaloids have been described. Plants are particularly well qualified to make alkaloids because they generally have adequate access to nitrogen a little bit of investment into a small amount of alkaloid can pay off with major benefits in pest control plants are really innovative and skilful at chemical syntheses. They have had millennia in which to practise.

Alkaloids act as pesticides

Like most of the unusual chemicals found in plants, alkaloids were evolved as protectants against plant-eating pests. Humans were not in the equation. Many alkaloids have no more effect on us than a bitter taste and an upset stomach. Others are potentially lethal because they act as nerve poisons or liver toxins. More or less coincidentally, some alkaloids are potent pharmaceuticals, both beneficial and dangerous. Some examples include quinine, codeine, morphine, scopolamine, and nicotine.

Nicotine

Nicotine is probably the plant drug most widely used by humans. Nicotine is a relatively simple chemical and is made by a number of unrelated plants, but it is not a particularly successful pesticide. For instance, tobacco and petunia plants, which rely on nicotine protection, are often targeted by large numbers of pests, showing that it is relatively simple for pests to adapt to nicotine. In the days when gardeners had no better insecticide than nicotine sulphate, it was more or less a toss-up whether the aphids or the gardener would be first to succumb.

Datura (Thorn Apple)

One alkaloid-producing plant that you should know about is the thorn apple (Datura), a relative of tobacco. Toxic alkaloids like hyoscyamine and scopolamine are present, especially in the seeds, but also in the leaves. Perhaps the ready availability of Datura species, both wild and as garden plants explains why datura is such a commonly misused drug. That is really stupid because datura is more likely to cause ‘bad trips’ or death rather than any pleasurable effects.

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