Moss flavonoids and their ultrastructural localization under enhanced UV-B radiation

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.

Cell wall‐bound ultraviolet‐screening compounds explain the high ultraviolet tolerance of the Antarctic moss, Ceratodon purpureus

“…The three species were shown to possess contrasting responses to enhanced UV-BR, with concentrations of methanolsoluble UV-screening compounds increasing in Vaccinium myrtillus and Vaccinium uliginosum, whereas the concentration of cell wall-bound UV-screening compounds increased in Vaccinium vitis-idaea (Semerdjieva et al, 2000). Cell wall-bound flavonoids were visualized microscopically in two moss species from central Finland, and methanol-soluble UV-screening compounds were shown to respond to seasonal changes in the radiation environment (Taipale & Huttunen, 2002). Cell wall-bound UV-screening compounds were not quantified in the latter study, but microscopic examination suggested no increase in cell wall-bound flavonoids in response to enhanced UV-BR (Taipale & Huttunen, 2002).…”

“…Cell wall‐bound flavonoids were visualized microscopically in two moss species from central Finland, and methanol‐soluble UV‐screening compounds were shown to respond to seasonal changes in the radiation environment (Taipale & Huttunen, 2002). Cell wall‐bound UV‐screening compounds were not quantified in the latter study, but microscopic examination suggested no increase in cell wall‐bound flavonoids in response to enhanced UV‐BR (Taipale & Huttunen, 2002).…”

Seasonal variations in UV‐absorbing compounds and physiological characteristics in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia over a 3‐year period

“…Seasonal variation in physiological variables associated with UV radiation exposure have been reported in bryophytes (Dunn and Robinson 2006, Huttunen et al 2005b, Lappalainen et al 2008, Newsham 2003, Newsham et al 2002, 2005, Snell et al 2007, Taipale and Huttunen 2002). Other studies have considered interannual variations (Gehrke 1998, 1999, Huttunen et al 2005b, Lappalainen et al 2008, Newsham et al 2002, Robson et al 2003, Rozema et al 2006, Searles et al 2002), sometimes with the aim of reconstructing past levels of UV (Huttunen et al 2005a).…”

Effects of enhanced UV-B radiation on hydroxycinnamic acid derivatives extracted from different cell compartments in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia

“…In this sense, liverworts, as bryophytes in general, would constitute a highly suitable model system for studying the differentiation of soluble (mainly vacuolar) and insoluble cell wall‐bound UVAC fractions. However, this issue has been little studied (Clarke and Robinson 2008, Snell et al 2009, Taipale and Huttunen 2002), in spite that it could contribute to obtain a clearer understanding of the role of the different UVAC in plants. Among the mentioned studies, Clarke and Robinson (2008) measured the bulk UV absorbance of methanolic extracts in the methanol‐soluble and alkali‐extractable cell wall‐bound fractions of three Antarctic mosses, Taipale and Huttunen (2002) assessed the location of flavonoids in two Arctic mosses, both in the cell wall and intracellularly, and Snell et al (2009) identified the anthocyanidin riccionidin A in the cell walls of the liverwort Cephaloziella varians .…”