| Abstract: |
Botanical remains found in archaeological contexts have often been exposed to heat before incorporation into the burial environment. Modern barley seeds heated in a regime from gentle to charring conditions were examined for the preservation of both DNA and proteins. Seeds heated up to 150 Celsius did not appear visibly charred while the degree of charring increased with both temperature and time at 200 Celsius and above. Protein preservation was assessed by amino acid analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. DNA preservation was determined by high performance liquid chromatography (HPLC) analysis of nucleic acids, gel electrophoresis, and amplification of a range of sizes of polymerase chain reaction (PCR) targets. Extended heating at 100 Celsius had little effect although higher temperatures caused the chemical modification and degradation of both protein and DNA as well as the failure of immunological detection by Western blotting and PCR. Amino acids and nucleic acids exhibited greater thermal stability than the parent biomolecules. No change in nucleic acid base composition was observed in 150 Celsius heated seeds, although partial charring (200 Celsius) resulted in the total loss of all bases. Amino acids were more stable -- the overall level present in whole seed hydrolysates of partially charred (200 Celsius) seeds differed little from an unheated sample although lysine, arginine, threonine and serine showed decreased levels. Higher temperatures resulted in the progressive loss of individual amino acids. The extensive chemical modification to both DNA and protein and the failure of Western blotting and PCR at sub-charring temperatures suggest that heated and charred seeds are poor candidates for studies using the techniques of molecular biology.
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