70 Naturwissenschaften 87, 70–75 (2000) Q Springer-Verlag 2000 DNA Changes in Tissues Entrapped in Plant Resins (the Precursors of Amber) S.O. Rogers (Y) College of Environmental Science and Forestry, State University of New York, 1 Forestry Drive, Syracuse, NY 13210, USA e-mail: sorogers6mailbox.syr.edu K. Langenegger, O. Holdenrieder Section of Forest Pathology and Dendrology, Department of Forest and Wood Sciences, Swiss Federal Institute of Technology, ETH-Zentrurn, CH-8092 Zürich, Switzerland Received: 23 March 1999 / Accepted in revised form: 16 September 1999 Abstract There have been many reports character- izing DNA from amber, which is a fossil version of plant resin. Here we report an investigation of the effects of plant resin (from Pseudotsuga menziesii) and drying conditions on the preservation of DNA in biological tissues. We examined the degree of de- gradation of the DNA by agarose gel electrophore- sis of extracted DNA, by polymerase chain reaction, and by DNA sequencing. The plant resin alone ap- peared to cause little or no damage to DNA. Tissue immersed in plant resin that dried rapidly (exposed to sunlight) contained DNA with little apparent damage. Tissue immersed in the resin that was dried slowly (in shade without sunlight) contained DNA with some degradation (3.5% nucleotide changes). The tissue that was immersed in the resin that was constantly hydrated (by immersion in water) yielded DNA that was severely damaged (50–62% nucleo- tide changes). Transversions outnumbered transi- tions in these samples by a ratio of 1.4 : 1. A piece of Baltic amber immersed in water for 5 days appeared to be impervious to the water. Thus amber inclu- sions that initially dried rapidly have the potential to yield undamaged DNA. Those that dried slowly may contain damaged DNA and may be unsuitable for phylogenetic and other studies. Introduction Amber is a fossil version of plant resin (Anderson and Crelling 1995). While called a fossil, in reality it undergoes a process that differs from fossilization, mainly that of drying and hardening. These resins are a defense of the plant that are capable of entrap- ping and preserving the physical structure of micro- organisms, insects, plants, and other organisms (Poi- nar 1992; Poinar and Poinar 1994). They generally contain a high proportion of volatile terpenes that evaporate during hardening (Anderson and Crelling 1995). The drying process also desiccates the entrap- ped tissues and organisms, which is thought to be the primary mode of biological preservation in am- ber. Over the past decade several reports have been published on DNA sequences from amber inclu- sions and fossils up to 140 million years old (Bé- ruad-Colomb et al. 1995; Cano et al. 1992a,b, 1993, 1994; Golenberg 1994; Handt et al. 1994; DeSalle et al. 1992, 1993; Poinar et al. 1994; Richards et al. 1995; Rogers 1994; Taylor 1996). However, on the- oretical grounds this is hundreds to thousands of times greater than the calculations on DNA longevi- ty indicate (Austin et al. 1997a,b; Lindahl 1993). Tests on the authenticity of ancient DNA samples have been proposed and/or performed (e.g., Austin et al. 1997a,b; Poinar et al. 1996; Walden and Ro- bertson 1997; Wang et al. 1997), with the authentici- ty of some specimens being questioned. While much has been written about the authenticity of DNA se- quences from amber inclusions and other fossil spec- imens, we found no studies of the potential damag- ing effects of plant resins or the processes involved in preserving DNA in amber. We report here an in- itial study on the effects of plant resins and drying conditions on DNA in biological specimens. Materials and Methods Resin was collected in a sterile 5-ml syringe from the resin blisters on the bark of several Douglas fir (Pseudotsuga menziesii) trees on Uetliberg, near