New methods to isolate organic materials from silicified phytoliths reveal fragmented glycoproteins but no DNA

Phytoliths are abundant in many archaeological sites, and can provide information on past vegetation. Very few analyses of their chemical composition have been made. Our measurements of the δ¹³C composition of modern wheat phytoliths suggest the presence of relatively large amounts of sugars and/or proteins in the water-soluble fraction, and lipids in the insoluble fraction. Other experimental approaches demonstrate that modern wheat phytoliths contain large quantities of glyco-conjugated proteins in a degraded state. One open question is whether or not phytoliths contain original DNA of the mother plant. Extracting protected ancient DNA from phytoliths would open many opportunities for progress in archaeobotanical studies. In order to address this question, we developed a method to dissolve phytoliths under conditions that do not degrade naked DNA, and showed that only a minimal amount of DNA was lost during the procedure. A hypersensitive assay did not, however, detect any DNA in extracts of phytoliths from an unburned phytolith-rich layer in Iron-Age sediments from Tel Dor, Israel. Extractions from modern phytolith samples of wheat also failed to provide any indication of DNA. We conclude that DNA is absent or not routinely recoverable in a random assembly of siliceous phytoliths.