XVI International Botanical Congess

The complex differentiative processes in lichens are partly regulated by phytohormones, among them ethylene. The effect of ethylene could be observed in lichen cultures. Several morphogenetic aspects and the balance between the bionts are influenced and controlled by ethylene. Both bionts may be responsible for ethylene production as green algae, cyanobacteria and ascomycetes are all able to synthesize the phytohormone. Experiments on the biosynthetic pathway and on the amount of ethylene produced under certain conditions have shown that significant differences exist between the three groups of bionts and between isolated bionts and the intact lichen as well. Obviously, special aspects of ethylene synthesis in lichens evolved during the long co-evolution of the bionts. These observations may help with the understanding of lichen evolution and of different taxa of lichens.