Photosynthetic pigments and ultrastructure of chloroplasts of the fern Dryopteris filix-mas (L.) Schott in various phenological phases of development

A comparative analysis of the photosynthetic pigments content, frond anatomic structure and chloroplast ultrastructure in the various developmental phases of the sporophyte of the leptosporangial fern Dryopteris filix-mas (L.) Schott that belongs to the lower layer plants and grows in shade was carried out. Observations were conducted in the phase of an intensive growth (April), sori ripening (May), spores dissemination (June), summer vegetation (July) as well as vegetation completion and aboveground part die-off (October). The chlorophyll a and b content in fronds was found to increase during the first three phenological phases and reached its maximum in the phase of spores dissemination. A specific feature turned out to be a relatively high content of carotenoids in the first four phases of development. In the phase of vegetation completion and aboveground part die-off the pigments content in frond tissues significantly decreased. The pigments content in fronds of summer green fern D. filix-mas was lower than that of winter green fern Polystichum aculeatum (L.) Roth. The frond anatomic structure was studied by means of the scanning electron microscope using freeze-dried cross-sections. The frond parenchyma was found to be divided into palisade and spongy tissues. The chloroplast ultrastructure was studied using the transmission electron microscope. It was revealed that in the phase of sori ripening the frond mesophyll cells contained elongated lens-like chloroplasts with an electron-dense stroma, which had big starch grains and sometimes plastoglobules. In the parenchyma cells, chloroplasts are in close proximity to the plasmalemma. In the phase of vegetation completion and aboveground part die-off, chloroplasts in cells of the assimilating parenchyma showed a partial deformation in the stroma lamellae and emergence of numerous plastoglobules. The number of starch grains in plastids significantly reduced. The comparison analysis of the photosynthetic pigments composition and content and chloroplast ultrastructure in the various developmental phases of the sporophyte of the Dryopteris filix-mas indicated that the successful existence in shade conditions and changes in the temperature regime along with other features provide a specific structural-functional organization of the photosynthetic apparatus.