Attractive and defensive functions of the ultraviolet pigments of a flower ( Hypericum calycinum )

Abstract

The flower of Hypericum calycinum, which appears uniformly yellow to humans, bears a UV pattern, presumably visible to insects. Two categories of pigments, flavonoids and dearomatized isoprenylated phloroglucinols (DIPs), are responsible for the UV demarcations of this flower. Flavonoids had been shown previously to function as floral UV pigments, but DIPs had not been demonstrated to serve in that capacity. We found the DIPs to be present in high concentration in the anthers and ovarian wall of the flower, suggesting that the compounds also serve in defense. Indeed, feeding tests done with one of the DIPs (hypercalin A) showed the compound to be deterrent and toxic to a caterpillar (Utetheisa ornatrix). The possibility that floral UV pigments fulfill both a visual and a defensive function had not previously been contemplated. DIPs may also serve for protection of female reproductive structures in other plants, for example in hops (Humulus lupulus). The DIPs of hops are put to human use as bitter flavoring agents and preservatives in beer.nectar guides ͉ pollination ͉ plant defense ͉ dearomatized phloroglucinols ͉ flavonoids

How plant?animal interactions signal new insights in communication

“…Such syndromes might not be targeted solely at mutualists (as traditionally assumed), but might also be aimed at avoiding antagonists [23]. The most obvious example are UV-reflecting floral pigments (de-aromatized isoprenylated phloroglucinols), which are used to attract mutualists, but which also function simultaneously as chemical defence against herbivores (Figure 1d,e) [33]. Given that some of these pigments are also found in the leaves of these species, the signal function of attracting mutualists might be a pleiotropic effect of defence against herbivores [34].…”

Interaction of pollinators and herbivores on plant fitness suggests a pathway for correlated evolution of mutualism- and antagonism-related traits

“…In tropical vines of the genus Dalechampia, anthocyanins and resins involved in chemical defense against herbivores have secondarily assumed a role in pollinator attraction and reward, respectively (22)(23)(24). Hypericum dual-role, floral UV pigments mentioned earlier also may have been secondarily derived from foliar defensive compounds (21). Correlated evolution of defensive foliar anthocyanins and anthocyanin-based floral pigmentation has been documented in trees of the genus Acer (24).…”

“…In Hypericum flowers, the same UV pigments play a defensive role in the stamens and ovaries and an attractive role in the petals (21). In tropical vines of the genus Dalechampia, anthocyanins and resins involved in chemical defense against herbivores have secondarily assumed a role in pollinator attraction and reward, respectively (22)(23)(24).…”

Flavonoid Glycosides from the Flowers ofPulsatilla koreanaNakai

“…Many flowers have UV-visible patterns that specifically visible to insects, with the UV absorbing pigments concentrated in the center of the flower acting to increase attractiveness of a flower. 10 Thus, another goal of this study was to identify pharmacologically active constituents from the flowers of P. koreana. To that end, we describe our isolation procedures including solvent extraction, systematic solvent fractionation, and repeated open column chromatography using silica gel (SiO 2 ) and octadecyl silica gel (ODS) as resins, as well as structure determination based on spectroscopic analyses such as nuclear magnetic resonance (NMR), EI-MS, polarimetry, and IR.…”