Allelopathic effects of lichen secondary metabolites and their naturally occurring mixtures on cultures of aposymbiotically grown lichen photobiont Trebouxia erici (Chlorophyta)

In the present work, the phytotoxic effects of secondary metabolites extracted from five lichen species (Cladonia arbuscula var. mitis, Cladonia furcata, Hypogymnia physodes, Evernia prunastri and Ramalina farinacea) on cultures of the aposymbiotically grown lichen photobiont Trebouxia erici were evaluated. Toxicity of single secondary metabolites, as well as their naturally occurred mixtures in the lichens was tested at the two selected doses, 0.1 mg/disk and 0.01 mg/disk. Application of all tested metabolites decreased the growth of photobiont cells in a dose dependent manner. However, based on selected physiological parameters, e.g. composition of assimilation pigments, fluorescence of chlorophyll a, content of soluble proteins, production of TBARS and ROS, differential phytotoxicity of tested compounds and their mixtures was confirmed. It appears that most of the secondary metabolites tested in the present study may be functioning as allelochemicals which are controlling the cell division of the algal partner inside the thallus. The allelochemicals may play a key role in maintaining the balance between the symbionts forming the lichen thallus.