The present work investigates short root development in Pinus sylvestris and the formation of ectomycorrhiza in these roots by Suillus bovinus. At the beginning of the thesis work no information about the regulation of short root development at the molecular level was available. One aim of the present work was to identify genes and proteins that are specifically activated during short root development and to follow their expression during ectomycorrhiza formation (I, II). The second aim of the present work was to clarify the role of cytoskeletal proteins and their regulation during the establishment of P. sylvestris-S. bovinus symbiosis. Therefore, the expression pattern of tubulins (III) and actin (IV) were analysed, and the isolation and characterisation of genes for regulators of the cytoskeletal organization (Schmidt and Hall 1998) was initiated in Suillus bovinus (V).