Pigments and Colour Variation in Flowers of Lagerstroemia indica

Abstract

1. To understand the mechanism of flower colour variations from red to purple in crape myrtle cultivars, absorption spectra and Hunter's L, a, b values of intact petals were measured. In this study 67 cyanic plants were classified into two groups : red group, λ_max' 524544 nm; b/a, (- 0.183) (+0.165) : purple group, λ_max, 555 570 nm; b/a, (-0.785) (-0.442). Relatively strong absorption about 360 nm was recognized in purple flowers, and high negative correlation (r = -0.897^***) was obtained between b/a and E360/EVIS _max.
2. Three anthocyanins from the red and purple flowers were isolated, analysed chromatographically and spectrally, and their ratios determined.
All 67 plants contained the 3-glucosides of delphinidin, petunidin, and malvidin as the major anthocyanins. The ratios among these anthocyanins varied widely, but had no correlation to Hue values (b/a), except that in the red group there was a negative correlation between b/a and the relative malvidin 3-glucoside concentration, and a positive one between b/a and relative delphinidin 3-glucoside conc.
3. The pH values measured by tightly pressing the petals to a flat electrode varied from 4.2 to 5.1, but there was no correlation between these values and flower colour. 4. Crude aqueous extracts from the red and purple flowers were partitioned with ethyl acetate and the organic fraction was concentrated; the aqueous fraction was dissolved in a buffer solution. Visible absorption maxima shifted bathochromically when the above two fractions from red and purple flowers were combined.
5. Ellagic acid derivatives detected in the purple flowers are assumed to be the main agents for the blueing of the 'flowers in crape myrtle.