How can the secondary metabolites help the plant that produce them ?

Plants face huge daily risks to their existence. These range from large animals and herbivorous insects to fungi and microbes; and abiotically can be debated with drought and excess solar radiation for example.

The secondary metabolites may exert several roles in the host plant, the defense metabolism being unquestionable. The defense metabolites may be stored in the plant in their inactive form (phytoerycipins) or, they are only produced when the plant is attacked (phytoalexins).

Among the 3 main categories of secondary metabolites are highlighted some compounds and their function. From the Terpenos family, Monoterpenoids and Sesquiterpenoids are the main constituents of essential oils that can be toxic to insects and also serve as protection against fungal and bacterial attacks. For example, pine trees have alpha and beta pinellas that function as insect repellents; also Chrysanthemum Pyrethrins work with insect neurotoxins. Tannins and Anthocyanins are examples of Phenolic Compounds, which function as inhibitors of salivary proteins and digestive enzymes, and as protection against harmful effects caused by ultraviolet radiation, respectively. In the case of Alkaloids, the Caffeine that is toxic to insects and fungi is highlighted; and cyanogenic glycosides, which can be converted into hydrogen cyanide by enzymes also produced by the plant. These enzymes and the cyanogenic glycosides are in different compartments and when there is attack by a herbivore they join and form hydrogen cyanide that affects the cellular respiration in aerobic organisms, thus poisoning herbivores consuming it.