A reappraisal of the use of DMSO for the extraction and determination of chlorophylls a and b in lichens and higher plants

The use of DMSO for the extraction and determination of chlorophylls a and b in lichens and higher plants was reevaluated. Because of differences between the absorption spectra of pure chlorophylls a and b in DMSO and 80% acetone, formulae to calculate the individual concentrations of chlorophyll a, chlorophyll b and total (a + b) chlorophyll in pigment extracts were redetermined for specific use with DMSO. In lichens, the problem of chlorophyll degradation resulting from the presence of acidic lichen substances was specifically addressed. Repeated washing of thalli with carbonate-saturated 100% acetone followed by extraction in DMSO containing PVPi minimized the conversion of chlorophylls to phaeophytin during extraction of chlorophylls from lichens for which the content of lichen substances was characterized. In lichens containing significant quantities of acidic compounds, the modified DMSO assay proved superior to 80% acetone for the extraction and determination of chlorophyll a and b concentrations. In a range of higher plants, determinations of chlorophyll a and b concentrations were virtually identical when the modified DMSO assay was compared with the traditional method of chlorophyll extraction using 80% acetone. Moreover, DMSO extracts could be cold-stored for up to 7 days with no significant loss of chlorophylls a or b, or changes in the a/b ratio. Potential eco-physiological applications of the modified DMSO assay, which eliminates the necessity for grinding plant material and centrifuging plant extracts, are discussed.