The important ecological significance of secondary metabolites are:
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They act as a defense compounds which are characterized by the irritant and toxic nature. Example in Mucona pruriens the compound 5- hydroxyl tryptamine is considered to be responsible for the irritant property which causes the red weal’s on touch.
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The plant synthesizes greater forms of secondary metabolites than the animals since the plants cannot escape from the predators by mobility so they have evolved this chemical defense mechanism to protect. Example in Mimosa pudica closes its leaves in response to the physical stimulus so as to protect from the herbivores.
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It is also involved in the plant pathogen interaction: Certain metabolites also provide protection against the pathogens and predators. The example is the resistance of the plant Phaseolus lunatus to Phytophthora phaseoli which causes the downy mildew.
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Some of the secondary metabolites are involved in the plant - plant interaction: A classical example of the plant - plant interaction is jugulone. This is a compound which is an inactive precursor which is produced by the walnut tree. The oxidized jugulone is the active form which can inhibit the growth of the herbaceous plants. It will result in the atlast the dominance of shrubs.
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It also produces the phyto alexins: The synthesis of protecting compounds the phyto alexins occurs by the stimulus such as the invasion of the fungus into the plant tissue. The phyto alexins are different for different plant species. The isoflavanoids are produced by the members of the family leguminosae whereas the phyto alexins from the Solanaceae are terpenoids. The Vicca faba has the phyto alexins which is an ester of highly unsaturated straight chain fatty acids.
