My study is focused on green algal photobionts - lichenized algae from the genera Asterochloris and Trebouxia (the last was studied in a lesser extent). The principal objectives of the thesis can be characterized as follows: 1) to investigate the chloroplast morphology in lichenized algae Asterochloris and Trebouxia; 2) to study the photobiont diversity in lichen community growing in heavy metal polluted habitats; 3) to inventorize the photobionts in selected lichen taxa (Lepraria, Stereocaulon) in order to reveal their ecological requirements. Using confocal microscopy, significant differences in the chloroplast structure of lichenized and cultured (free-living) algae were detected. Moreover, algae exhibited gradual changes in chloroplast shape and structure during successive phases of cultivation - from the relatively simple lichenized form to the complex lobate chloroplast with several ontogenetic (morphological) stages observable in mature axenic cultures. Several Asterochloris lineages and one Trebouxia species were detected in terricolous lichen community from metal-polluted habitats using phylogenetic analysis of algal ITS sequences. All these lineages represented photobionts with broad ecological amplitude and worldwide distribution. In several taxa of pioneer lichens, low specificity as..
