CHARACTERISTICS OF PHOTOSYNTHETIC APPARATUS OF AQUATIC FERN SALVINIA NATANS FLOATING AND SUBMERGED FRONDS.

We analyzed chloroplast ultrastructure, microstructure of fronds surfaces, pigment's content and efficient use of light by photosynthetic apparatus in floating and submerged fronds of water fern Salvinia natans at different stages of development. In parenchymal cells of floating fronds average chloroplast cross-section area at intensive growth stage (June) was 5.56 gm2. Well-developed system of thylakoid membranes formed numerous gram. Up to four starch grains occurred. In submerged fronds chloroplasts cross-section area was 2.16 gm2. Degradation of grana thylakoid membrane and disruption of intergranal connections were revealed in fronds in stage of sporocarp formation (September). Rows of plastoglobules were found in chloroplasts of floating frond. Starch grains were almost entirely absent in stroma. Adaxial surface of floating fronds had simple structure stomata. The abaxial surface had no stomata and the cuticle was not developed. Pigment's content in floating fronds was twice higher than that of submerged ones. During development of fern a content of pigments raised up in the floating leaves. At stage of sporocarps formation the chlorophyll and carotenoid content reduced. Floating fronds showed an effective operation of chloroplast photosynthetic electron-transport chain. Submerged fronds exposed to intensive light were characterized by decrease of efficiency of PSII and increase of nonphotochemical quenching of chlorophyll fluorescence. [ABSTRACT FROM AUTHOR]