Anthocyanic vacuolar inclusions - their nature and significance in flower colouration

The petals of a number of flowers are shown to contain similar intensely co loured intravacuolar bodies referred to herein as anthocyanic vacuolar incl usions (AVIs). The AVIs in a blue-grey carnation and in purple lisianthus h ave been studied in detail. AVIs occur predominantly in the adaxial epiderm al cells and their presence is shown to have a major influence on flower co lour by enhancing both intensity and blueness. The latter effect is especia lly dramatic in the carnation where the normally pink pelargonidin pigments produce a blue-grey colouration. In lisianthus, the presence of large AVIs produces marked colour intensification in the inner zone of the petal by c oncentrating anthocyanins above levels that would be possible in vacuolar s olution. Electron microscopy studies on lisianthus epidermal tissue failed to detect a membrane boundary in AVI bodies. AVIs isolated from lisianthus cells are shown to have a protein matrix. Bound to this matrix are four cya nidin and delphinidin acylated 3,5-diglycosides (three, new to lisianthus), which are relatively minor anthocyanins in whole petal extracts where acyl ated delphinidin triglycosides predominate. Flavonol glycosides were not bo und. A high level of anthocyanin structural specificity in this association is thus implied. The specificity and effectiveness of this anthocyanin "tr apping" is confirmed by the presence in the surrounding vacuolar solution o f only delphinidin triglycosides, accompanied by the full range of flavonol glycosides. "Trapped" anthocyanins are shown to differ from solution antho cyanins only in that they lack a terminal rhamnose on the 3-linked galactos e. The results of this study define for the first time the substantial effe ct AVIs have on flower colour, and provide insights into their nature and t heir specificity as vacuolar anthocyanin traps. (C) 2000 Elsevier Science L td. All rights reserved.