Mechanical wounds usually break the protective layers of an organism. As a consequence, pathogens can easily infect. Wounded cells that were torn die due to necrotic reactions. Other nearby cells respond to the injury by changing their internal cell functions; biochemical shunts start. Chemical and physical boundaries that may resist spread of the microorganisms within the tree begin to form. The pathogen interacts with the tree. If the tree responses are stronger than those of the pathogen, the spread of the pathogen is restricted. A crucial role plays the availability of carbon, a source of building blocks and energy for both the tree and the pathogen. After infection of sound black locust trunks with wood destroying fungi (Phellinus robiniae, Laetiporus sulphureus), starch and sucrose degradation was accelerated. Moreover, defence reactions of wood, lead to the induction of acid invertases not present in the sound tissue. Aim of our work is to characterize the spatial and temporal distribution of these plant derived acid invertases by biochemical, immunological and molecular (RT-PCR) approaches