**Flavonoids: Classification, Biosynthesis and Chemical Ecology**

Erica L. Santos, Beatriz Helena L.N. Sales Maia, Aurea P. Ferriani and Sirlei Dias Teixeira

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67861

#### **Abstract**

Flavonoids are natural products widely distributed in the plant kingdom and form one of the main classes of secondary metabolites. They display a large range of structures and ecological significance (e.g., such as the colored pigments in many flower petals), serve as chemotaxonomic marker compounds and have a variety of biological activities. Therefore, they have been extensively investigated but the interest in them is still increasing. The topics that will be discussed in this chapter describe the regulation of flavonoid biosynthesis, the roles of flavonoids in flowers, fruits and roots and mechanisms involved in pollination and their specific functions in the plant.

**Keywords:** flavonoids, biosynthesis, pollination, allelochemicals, chemical ecology

### **1. Introduction**

Flavonoids represent a highly diverse class of polyphenolic secondary metabolites, which are abundant in spermatophytes (seed-bearing vascular land plants: gymnosperms (cycades, conifers, ginkos and gnetophytes) and angiosperms) [1–3] but have also been reported from primitive taxa, such as bryophytes (nonvascular land plants, including liverworts, hornworts and mosses) [4, 5], pteridophytes (seedless vascular land plants, i.e., lycophytes, horsetails and all ferns) [6, 7] and algae [8, 9]. Overall, about 10,000 flavonoids have been recorded which represent the third largest group of natural products following the alkaloids (12,000) and terpenoids (30,000) [1, 10].

Flavonoids are essential constituents of the cells of all higher plants [11]. Plants have evolved to produce flavonoids to protect themselves against fungal parasites, herbivores, pathogens

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and ultraviolet (UV) radiation [10]. They resemble in their regulatory properties most of the lipid-soluble vitamins but serve, in addition, due to their color, as communicators with the environment. Flavonoids are recognized by pollinators, for example, insects, birds and animals, which contribute to the dispersion of seeds [11]. They act as symbionts, as allelochemicals, as antimicrobial and antiherbivory factors [10, 12]. Many studies have shown that flavonoids exhibit biological and pharmacological activities, including antioxidant, cytotoxic, anticancer, antiviral, antibacterial, anti-inflammatory, antiallergic, antithrombotic, cardioprotective, hepatoprotective, neuroprotective, antimalarial, antileishmanial, antitrypanosomal and antiamebial properties [13–15].

The topics that will be discussed in this chapter describe the regulation of flavonoid biosynthesis, the roles of flavonoids in flowers, fruits and roots and mechanisms involved in pollination and their specific functions in the plant.
