Microfibril angle in wood of Scots pine trees (Pinus sylvestris) after irradiation from the Chernobyl nuclear reactor accident Mirela Tulik a, * , Aleksandra Rusin b a Department of Forest Botany, Warsaw Agricultural University, 159 Nowairsynowska str., PL-02-776 Warsaw, Poland b Botanical Garden – Centre for Biological Diversity Conservation of the Polish Academy of Sciences, 2 Prawdziwka str., PL-02-973 Warsaw, Poland Received 26 May 2003; accepted 6 August 2004 The angle of microfibrils in the S 2 layer in wood deposited after the Chernobyl incident was changed. Abstract The secondary cell wall structure of tracheids of Scots pine (Pinus sylvestris L.), especially the angle of microfibrils in the S 2 layer, was examined in wood deposited prior to and after the Chernobyl accident in 1986. Microscopic analysis was carried out on wood samples collected in October 1997 from breast height of three pine trees 16, 30 and 42 years old. The polluted site was located in a distance of 5 km south from the Chernobyl nuclear power plant where radioactive contamination in 1997 was 3.7 ! 10 5 kBq m ÿ2 . Anatomical analysis showed that the structure of the secondary cell wall in tracheids formed after the Chernobyl accident was changed. Changes occurred both in S 2 and S 3 layers. The angle of microfibrils in S 2 layer in wood deposited after the Chernobyl accident was different in comparison to this measured in wood formed prior to the disaster. The intensity of the changes, i.e. alteration of the microfibrils angle in S 2 layer and unusual pattern of the S 3 layer, depended on the age of the tree and was most intensive in a young tree. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Chernobyl accident; Microfibril angle; Pinus sylvestris; Secondary cell wall; Tracheids; Wood 1. Introduction The secondary cell wall of tracheids is made up of multiple layers, formed at different periods during cell differentiation. There are primary layer P, and three secondary layers, S 1 ,S 2 and S 3 (Timell, 1986). Each layer is composed of cellulose crystalline fibrils as a framework, oriented at a different angle with reference to the cell’s long axis, and embedded in isotropic hemicellulose–lignin skeleton as a matrix. The S 1 layer is the thinnest of all S layers and it is hardly detectable under light microscope. The S 1 layer is only 0.1–0.35 mm thick and the cellulose microfibrils are oriented at a large angle toward the long axis of the tracheids, typically 60  –80  (Barnett et al., 1997; Plomion et al., 2001). The thickest layer of the secondary cell wall that plays an important role with regard to mechanical support is S 2 layer (Megraw, 1986; Cave and Walker, 1994; Kretsch- mann et al., 1997; Yamamoto and Kojima, 1999). It represents 75–85% of the total thickness of the tracheids cell wall. The microfibril angle (MFA) in this layer is small, 5  –30  to the cell long axis and the thickness fluctuates between 1 and 10 mm. MFA varies with cambial age, growth rate, and height within the stem of a conifer tree and is under genetic control (Donaldson, 1992; Cave and Walker, 1994). The S 3 layer is relatively * Corresponding author. Tel.: C48 22 5938032; fax: C48 22 5938022. E-mail address: tulik@wl.sggw.waw.pl (M. Tulik). 0269-7491/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.08.009 Environmental Pollution 134 (2005) 195–199 www.elsevier.com/locate/envpol