Phytopigment and DNA determinations in long-time formalin-preserved trap samples

This study was specifically designed for sediment trap researchers and ocea nographers working with organic material which is fixed in situ with formal in and analysed several months after collection. The effects of long-term f ormalin storage on phytopigment and DNA determinations were tested on seawa ter, algal cultures and trap material. DNA determinations in formalin-prese rved samples were hampered by the use of specific flurochromes (i.e. Thiazo le Orange and Hoechst). In contrast, the use of DABA (diaminobenzoic acid) reagent allowed these problems to be overcome, making DNA determination fea sible in formalin-preserved samples without any interference. DNA concentra tions measured in all samples did not change significantly with long-time f ormalin storage (up to 9 mo), indicating that, independently from the quant ity and the source of genetic material, non significant DNA losses occurred . In contrast, chloropigment concentrations in formalin-preserved samples s ignificantly decreased. The decreasing temporal pattern of chlorophyll a (c hl a) concentrations in formalin-preserved algal culture and seawater sampl es was similar, suggesting that chi a degradation is independent from the i nitial pigment concentration. A possible explanation for the strong decreas e in chi a concentrations is changes in its molecular structure. The recove ry of total chloroplastic pigments in trap samples was higher than the reco very of chi a observed in algal cultures and seawater samples. Such discrep ancy appears to be due to the different degradation rates of the phaeopigme nts after their fixation in the sediment traps.