Alternative methods for sampling and preservation of photosynthetic pigments and tocopherols in plant material from remote locations

Abstract

Current methods for the study of pigments involve freezing in liquid nitrogen and storage at −80°C or lyophilization until HPLC analysis. These requirements greatly restrict ecophysiological research in remote areas where such resources are hardly available. We aimed to overcome such limitations by developing several techniques not requiring freezing or lyophilization. Two species with contrasting foliar characteristics (Olea europaea and Taraxacum officinale) were chosen. Seven preservation methods were designed, optimized and tested in a field trial. These protocols were compared with a control immediately frozen after collection. Pigments and tocopherols were analysed by HPLC. Main artefacts were chlorophyll epimerization or phaeophytinization, carotenoid isomerization, altered de-epoxidation index and tocopherol degradation. Among all methods, sample desiccation in silica gel provides robust samples (pigment composition was unaffected by storage time or temperature) and almost unaltered pigment profiles, except for a shift in epoxidation state. Although liquid nitrogen freezing and subsequent lyophilization or freezer storage were preferred, when these facilities are either not available or not suitable for long-distance transport, desiccation with silica gel, passive extraction in acetone and/or storage of fresh samples in water vapour saturated atmospheres enable a complete pigment characterization. Silica gel is advisable for long-term sample conservation.