Secondary metabolites are useful to plants in many respects. They may discourage browsers, parasites and insects (since they may be toxic to these species), they may protect the plant against climatic extremes (extreme cold, heat or moisture), they may also perform a signalling function (i.e. some form of communication).

One of the major function is "Plant Protection"

I agree with David Walwyn . In addition, some secondary metabolites attract pollinators and help in seed dispersal. They also assist in competition among plants.

Plants produce many organic compounds : primary and secondary metabolites. Primary metabolites (proteins, sugars, lipids) are essential for plants, for growth and development, while secondary metabolites (alkaloids, phenolics, terpenoids, ..) are used especially for protection and contact in their environment.

Secondary metabolites are part of biology and physiology of the plant, they served many physiological functions, in addition to their roles in defensive ability of the plant against fungi, bacteria, viruses and parasites.

The importance of secondary metabolites for plant

1-Secondary metabolites with no apparent roles in growth and developments of plant but they play roles to protect plants from predators and pathogens (toxicity and repellency to herbivores and microbes).

2-They are pollinator attractants like volatile and coloring matter in roses.

3-They are represent chemical adaptation to environmental stress conditions (biotic and abiotic stresses). @