Fig. 7

Potential Trebouxia-species candidates and their developmental cycles according to own observations after Friedl [44]. Top left shows the grit crust stones with the exact origin (encircled) of each isolate with the number of the isolate in the right corner as well as the Trebouxia cluster in the colored circle. Mid row shows microscopic images of each isolate. Right row shows 4 k microscopic images of the cultures grown on agar. Bottom: Broken lines: reproduction of Trebouxia within lichen thalli as interpreted from developmental stages seen in squashed preparations of algal layers of lichens. Cell cycle A: (1) zoospore; (2) juvenile vegetative cell (autospore); (3) adult vegetative cell; (4) protoplast division, chloroplast already divided during autosporangium (type 4) formation; (5) autosporangium (type 4) containing few autospores compressed within the sporangial wall; (6) autosporangium with autospores that begin to dissociate and where new protoplast divisions occur while the autospores that begin to dissociate and where new protoplast divisions occur while the autospores still adhere within the sporangial wall; (7) some autospores of stage 6 are developed into sporangia with numerous daughter cells which either escape as nonmotile autospores (a, autosporangium) or as free-swimming zoospores (z, zoosporangium) while other autospores are developed into an autosporangia (a) with few cells where new protoplast divisions occur; (8) autosporangium of 6 dissociates into single cells. Cell cycle B: (1) zoospore; (2) juvenile vegetative cell; (3) adult vegetative cell; (4) protoplast division, chloroplast already divided into four during autosporangium (type 4.1) formation; (5) cell containing numerous protoplasts (type 5.1 autosporangium); (6) development from stage 5.1 either into a sporangium with numerous nonmotile autospores (a) or into a zoosporangium (z). Microscopic images show all cell types / developmental stages