Secondary Metabolites: Attracting Pollinators

Abstract

Flowers present visual and chemical signals that mediate the interaction between plants and pollinators, who transfer pollen between flowers of different plants while foraging for nectar and/or pollen. This process favours the sexual reproduction of plants and covers the energy requirements of floral visitors. Colour and floral scent, as well as the chemical composition of nectar and pollen that constitute floral rewards, are among the attraction attributes. The expression of these attributes is the result of the production of a set of secondary metabolites such as pigments, volatile organic compounds and chemical compounds in nectar and pollen. In addition to attracting pollinators, these metabolites can repel natural enemies of plants (florivores, nectar robbers, microorganisms) or pollinators (pathogens), potentially affecting the outcome of pollination, and eventually the production of fruits and seeds. Key Concepts Most flowering plants that depend on pollinators for reproducing sexually have developed visual (colour) and chemical (scent) floral signals, as well as floral rewards (pollen and nectar), to increase the attraction of pollinators. Secondary metabolites produced by flowering plants mediate the visual and chemical communication between plants and other organisms. While this communication is essential for pollination, it can also mediate the interaction of plants with florivores, nectar robbers, seed predators, microorganisms and pollinator pathogens that could affect pollination. Pollinators are able to perceive variation in visual and chemical attributes of plants from the same or different species, affecting visitation rates and plant fitness. Pigments are the secondary metabolites responsible for the synthesis of colour in different floral organs (petals, sepals, sexual organs) and floral rewards (pollen and nectar). Floral volatiles are organic compounds emitted by flowers that mediate chemical communication in specialist and generalist plant–pollinators interactions. Secondary metabolites in the nectar of various species include alkaloids, phenols and nonessential amino acids that can affect the preferences and foraging behaviour of pollinators, either by attracting or deterring them. The impact of secondary metabolites in attracting different pollinators can result in pre‐reproductive isolation between plants and eventually contribute to their divergence.

Towards the flower economics spectrum

“…drought reduces flower size; Galen, 1999) or by acting on floral traits that may not themselves be related directly to reproductive assurance but that may affect other floral functions (e.g. florivores may influence the expression of chemical defensive compounds in nectar, Sosenski & Parra‐Tabla, 2019; flowers may respond to nectar robbers by producing involutions that incur a higher carbon cost; Guzmán et al ., 2017). Nonpollinator agents of selection can also affect flowers indirectly, by acting on other organs that affect floral traits (e.g.…”

Biometric evaluation and nutrients of the corn, pearl millet, and sorghum crops

“…However, the NDF curves overlapped for corn and pearl millet, highlighting the lower values of fiber content in sorghum (Figure 2 D). This result could be explained by the fact that sorghum produces tannin, a secondary metabolite that protects the plant against pathogens or herbivores, by attracting pollinators or plant-plant competition agents, but also acts as a plant carbon drain during its formation (Sosenski & Parra-Tabla, 2019). In addition, the used sorghum cultivar, BRS 810, has a brown midrib (BMr) gene related to a lower lignin deposition in the cell wall according to the same authors.…”

Plant Extracts as Antimicrobial Agents in Sustainable Conservation of Erythrina caffra (Fabaceae) Historical Trees

“…A characteristic of aromatic plants is the presence of complex mixture of aliphatic, aromatic and terpene compounds, that generally have a powerful role in plant interaction and pollinator attraction [30,31]. Their extracts (EO, HAE) have aromatic components, which give distinctive flavour, odour or scent to each plant.…”