Floral secondary metabolites in context of biotic and abiotic stress factors

Floral displays constitute signals conveyed to potential pollinators by pigments and fragrance compounds, which are secondary metabolites biosynthesized through a limited number of major metabolic pathways. In recent years, the role of defensive secondary metabolites, targeted to tolerate/resist herbivory, pathogen-borne diseases and other kinds of stress, has become apparent in the context of floral displays. Apart from pigments and volatile compounds, these defensive compounds include alkaloids, specialized molecules such as glucosinolates (in Brassicaceae), and proanthocyanidin phenolics. All these functionally overlapping groups of metabolites vary in floral concentrations under different kinds of environmental conditions as well as due to endogenous regulatory factors, resulting in metabolic and functional synergies or trade-offs according to the physiological status of the flowers. In this review, we discuss such associations among varying secondary metabolites in flowers, and their implications in context of plant stress-response mechanisms.