Phytotoxin

Phytotoxin is an umbrella term that refers to substances (known as phytotoxic substances) that are inhibitory to the growth of or poisonous to plants. Phytotoxic substances may result from human activity, as with herbicides, or they may be produced by plants, by microorganisms, or by naturally occurring chemical reactions. A good soil will protect plants from toxic concentrations of such substances by ventilating gases, decomposing or adsorbing organic toxins, or suppressing toxin-producing organisms.

The term is also sometimes used, on the contrary, to describe toxic chemicals produced by plants themselves, which function as defensive agents against their predators. Most examples pertaining to this definition of phytotoxin are members of various classes of secondary metabolites, including alkaloids, terpenes, and especially phenolics, though not all such compounds are toxic or serve defensive purposes. Phytotoxins may also be toxic to humans.

Alkaloids are derived from amino acids, and contain nitrogen. They are medically important by interfering with components of the nervous system affecting membrane transport, protein synthesis, and enzyme activities. They generally have a bitter taste. Alkaloids usually end in -ine (caffeine, nicotine, cocaine, morphine, ephedrine).

Terpenes are made of water-insoluble lipids, and synthesized from acetyl-CoA or basic intermediates of glycolysis They often end in -ol (menthol) and comprise the majority of plant essential oils.

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