No abstract

A study was made of methanol-extractable UV-B-absorbing pigments under enhanced UV-B treatment. UV-B-absorbing pigments in two common ectohydric mosses showed seasonal variation during the summer months. Pigment contents were highest in June, decreased in July, and thereafter remained unchanged until September. In Hylocomium splendens, a significant increase of pigments was observed at the end of the experiment. The intracellular localization of caffeine-stabilized flavonoids was manifested as dark electron-dense deposits in the cell walls and intracellular dark deposits in the cell plasma. The dark deposits in the cell walls of Pleurozium schreberi were located either in the outer part of the cell wall or in the middle lamellae of the wall structures. Hylocomium splendens had a stratified cell-wall structure, in which three dark electron-dense cell layers could be identified. Intracellular deposits were located in different parts of the cell, but electron-dense deposits were observed at the cell margins and in the proximity of the nucleus. Although certain cell ultrastructural disturbances (for example, lipid accumulation, chloroplast disintegration) in moss leaf cells were observed, the short-term UV-B treatment did not increase the intensity of the dark deposits.