**4. Conclusion**

Chalcones and aurones, which provide yellow pigmentation in the flowers of several ornamental species, are relatively rare types of flavonoids [49]. The UV spectra of both compounds are characterized by an intense band I and diminished band II absorption [50]. The major absorption band in chalcones (band I) usually occurs in the range 340–390 nm. Band II is usually a minor peak in the 220–270 nm region, while the long wavelength absorption band in aurones is usually found in the 370–430 nm region. They produce the strongest yellow colors owing to their absorbance at longer wavelengths compared to the other types [50, 51]. Chalcones, flavonols, flavones or anthocyanins usually accumulate in sex organs of flowers, including the pollen. In contrast to man, some insects, especially bees, can perceive in the near ultraviolet (340–380 nm) as well as in the visible region. However, insects are possibly attracted to pollen whose color contrasts against petals due to UV reflective or absorptive

Pollination is an essential step in the reproductive process of the world's nearly 300,000 species of flowering plants because it is usually required for the production of seeds. Pollination can result from the action of abiotic forces such as wind and water, but 80% of the Angiosperms rely on animals, including bats, flies, butterflies, beetles and other insects [52]. Such diversity

The interactions between organisms are fundamental for the determination of plant abundance and distribution pattern in the community, of the productivity of several cultivated species and of the degree of interference on weeds [53]. Weeds are one of the most important factors that impose limitations on the development of agricultural activity in the world and are difficult to eradicate. The success of weeds in different cropping systems is associated, in part, with their ability to produce, store and release to the environment chemicals with

Allelopathy can be defined as a process by which compounds from the metabolism of a plant are released, preventing the germination, growth and development of other neighboring plants [55]. These compounds are involved in plant-plant interactions or allelopathy [56] and may influence, for example, in the vegetation of a local, in the succession of plants, in the germination of seeds and in the cultures productivity, among others [57]. Among the main groups of compounds with allelopathic potential are highlighted the benzoquinones, coumarins, flavonoids, terpenoids, glycosides, phenolic acids, alkaloids, rotenoids, catechins and

Although flavonoids have many roles in plants, in relation to their role in allelopathy and the inhibition of seedling root growth [56], the activity of flavonoids in plant-plant interactions can be positive or negative [60]. The negative relations are mainly based on inhibiting germi-

Some flavonoids present a level of phytotoxicity, indicating that allelopathy could be a beneficial function of the flavonoids to the producing plant [65]. Although the relative role of flavonoids in allelopathic interference has been less well-characterized than of some secondary metabolites, some examples of their involvement in autotoxicity and allelopathy are reported

nation and growth of other plants seedlings [56], as depicted in **Table 1**.

is acquired through evolutionary processes to ensure successful reproduction [44].

flavonoids [46].

10 Flavonoids - From Biosynthesis to Human Health

**3.2. Allelopathy**

tannins [58, 59].

allelopathic properties [54].

Flavonoids are found in most plant tissues, provide a range of colors that attract pollinators, and, in fruit, they probably serve to attract frugivores that assist in seed dispersal. All of these pigments also function as antioxidants and sunscreens, absorbing wavelengths of ultraviolet. Their biosynthesis appears to be ubiquitous in plants and evolved early during land plant (from primitive green algae) evolution, aiding in plant protection and signaling. The precise mechanism by which flavonoids participate in allelopathy is still unknown, but the significance of allelopathy has gained more attention in agriculture, for example. Plant-plant interactions can influence or determine diversity, productivity and reproduction of a plant community beyond reduction or inhibition of weed growth.
