4-Deoxyaurone Formation in Bidens ferulifolia (Jacq.) DC

Abstract

The formation of 4-deoxyaurones, which serve as UV nectar guides in Bidens ferulifolia (Jacq.) DC., was established by combination of UV photography, mass spectrometry, and biochemical assays and the key step in aurone formation was studied. The yellow flowering ornamental plant accumulates deoxy type anthochlor pigments (6′-deoxychalcones and the corresponding 4-deoxyaurones) in the basal part of the flower surface whilst the apex contains only yellow carotenoids. For UV sensitive pollinating insects, this appears as a bicoloured floral pattern which can be visualized in situ by specific ammonia staining of the anthochlor pigments. The petal back side, in contrast, shows a faintly UV absorbing centre and UV absorbing rays along the otherwise UV reflecting petal apex. Matrix-free UV laser desorption/ionisation mass spectrometric imaging (LDI-MSI) indicated the presence of 9 anthochlors in the UV absorbing areas. The prevalent pigments were derivatives of okanin and maritimetin. Enzyme preparations from flowers, leaves, stems and roots of B. ferulifolia and from plants, which do not accumulate aurones e.g. Arabidopsis thaliana, were able to convert chalcones to aurones. Thus, aurone formation could be catalyzed by a widespread enzyme and seems to depend mainly on a specific biochemical background, which favours the formation of aurones at the expense of flavonoids. In contrast to 4-hydroxyaurone formation, hydroxylation and oxidative cyclization to the 4-deoxyaurones does not occur in one single step but is catalyzed by two separate enzymes, chalcone 3-hydroxylase and aurone synthase (catechol oxidase reaction). Aurone formation shows an optimum at pH 7.5 or above, which is another striking contrast to 4-hydroxyaurone formation in Antirrhinum majus L. This is the first example of a plant catechol oxidase type enzyme being involved in the flavonoid pathway and in an anabolic reaction in general.

Aurone synthase is a catechol oxidase with hydroxylase activity and provides insights into the mechanism of plant polyphenol oxidases

“…Recently, it has been reported that aurone biosynthesis in Asteraceae species (4-deoxyaurone formation) (14) differs in various aspects from the 4-hydroxyaurone biosynthesis in A. majus. A PPO homolog, termed aurone synthase (AUS1, Uniprot A0A075DN54), was assigned to be involved in 4-deoxyaurone biosynthesis in petals of Coreopsis grandiflora (tickseed, Asteraceae) (15,16).…”

Visual and odour cues: plant responses to pollination and herbivory affect the behaviour of flower visitors

“…Depending on the spatial distribution of the phenolic compounds within a flower petal (Svatos ; Miosic et al . ), changes induced by pollination may result in changes in the visual cues used by pollinators such as nectar guides or the overall flower colour. Moreover, changes in the biosynthesis of phenolic compounds may influence the biosynthesis of aromatic volatile compounds and vice versa , and therefore modify traits exploited by pollinators (Dormont et al .…”

“…When regarding the effects of pollination, B. nigra plants responded by drastically down-regulating the levels of some of the phenolic compounds, more strongly so in response to pollination than in response to herbivory. Depending on the spatial distribution of the phenolic compounds within a flower petal (Svatos 2010;Miosic et al 2013), changes induced by pollination may result in changes in the visual cues used by pollinators such as nectar guides or the overall flower colour. Moreover, changes in the biosynthesis of phenolic compounds may influence the biosynthesis of aromatic volatile compounds and vice versa, and therefore modify traits exploited by pollinators (Dormont et al 2014).…”

Flavonoids and Essential Oil of Bidens cernua of Polish Origin and in Vitro Antimicrobial Activity of the Oil

“…The presence of 7-O-glucosides of apigenin and luteolin in Bidens species such as B. tripartita or B. frondosa has been reported [11,14]. The presence of hydroxyaurones and chalcones such as maritimetin and flavanomarein in Bidens species (B. andina, B. ferulifolia) has an important meaning and has been described as main polyphenolics in the genus [15,16].…”