AGGREGATION OF HIGHER-PLANT XANTHOPHYLLS - DIFFERENCES IN ABSORPTION-SPECTRA AND IN THE DEPENDENCY ON SOLVENT POLARITY

The absorption spectra of the six major xanthophylls found in the light harvesting complexes of higher plants have been determined for monomeric and aggregated forms in ethanol and in ethanol/water mixtures respectively. The apparent polarity of each xanthophyll, determined from the ethanol/water ratio required to induce aggregation, was neoxanthin > violaxanthin = lactucaxanthin > lutein > antheraxanthin > zeaxanthin. Aggregation leads to a increase in absorbance at 380 nm and a decrease in the bands near 450 nm and 480 nm in all cases. In addition, aggregation leads to the appearance of a minor band at wavelengths greater than 500 nm. The wavelength maximum of this band was found to correlate with the apparent polarity of each xanthophyll. The possible significance of these differences in physical properties and of pigment aggregation in the physiological function of xanthophylls and the xanthophyll cycle are discussed.