Floral anthocyanins in wild taxa of Petunia (Solanaceae)

The flowers of 20 native taxa of Petunia (Solanaceae) were investigated by HPLC for the occurrence of anthocyanins. The investigation revealed the presence of at least 24 anthocyanins in their flowers, of which 18 known anthocyanins isolated from the flowers of P. exserta, P. guarapuavensis, P. integrifolia, P. occidentalis, and P. reitzii were fully identified by chemical and spectral methods to be 3-glucoside of delphinidin; 3-rutinosides of cyanidin, delphinidin, and petunidin; 3-rutinoside-5-glucosides, 3-trans and -cis-p-coumaroylrutinoside-5-glucosides, and 3-trans-caffeoylrutinoside- 5-glucosides of delphinidin, petunidin; and malvidin; and 3- transcaffeoylglucosyl-trans-(caffeoyl or p-coumaroyl) rutinoside-5-glucosides of malvidin. Six novel anthocyanins were isolated from the flowers of P. occidentalis, and their structures were identified to be 3-glucosyl p- coumaroylrutinoside-5-glucosides and 3-glucosylcaffeoylrutinosides of petunidin and malvidin, and also 3-caffeoylglucosylcaffeoylrutinoside-5- glucoside and 3-caffeoylglucosyl p-coumaroylrutinoside-5-glucoside of petunidin. Out of the six pigments, petunidin 3-glucosyl p- coumaroylrutinoside-5-glucoside was unambiguously determined by spectral methods to be petunidin 3-O-[6-O-(4-O-(4-O-(β-D-glucopyranosyl)-trans-p- coumaroyl)-α-L-rhamnopyranosyl)-β-D-glucopyranoside]- 5-0 -[β-D- glucopyranoside]. The 20 native taxa of Petunia could be placed into four groups (A, B, C, and D) with one further into five subgroups (D1-D5) regarding their constituents and contents of major anthocyanins and also their pigment biosynthesis with respect to the blocks or inhibitors of the hydroxylation, glucosylation, and acylation reactions in them. The use of anthocyanins as taxonomic markers in the genus Petunia is discussed in relation to the flower colour and possible pollination vectors.