Ultraviolet-absorbing compounds from the cell walls of an aquatic liverwort are more efficiently extracted by alkaline than by enzymatic digestion

Abstract

The accumulation of ultraviolet-absorbing compounds (UVACs) within the cell walls of bryophytes provides a spatially uniform filter of ultraviolet-B (UV-B) radiation, and thus represents an important protective mechanism against its adverse effects. Here, the abilities of several cell-wall-degrading enzymes and of alkali (NaOH) in extracting cell-wall-bound UVACs from the aquatic liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váňa were compared, in order to select the most appropriate extraction method and to achieve the most reliable assessment of the degree of protection afforded by UVACs against UV-B. We analysed both the overall level of UVACs and the concentrations of two hydroxycinnamic acids (p-coumaric acid and ferulic acid). The most effective extraction (statistically significant) of cell-wall-bound UVACs, in terms both of their overall levels and of the concentrations of individual compounds, was achieved using alkaline digestion, which was more efficient than any of the enzymatic digestions trialled. This may be attributable to the ability of the alkali to break simultaneously both hydrogen bonds and covalent bonds within the cell wall, including ester linkages between phenolics and carbohydrates. In addition, alkaline digestion was more rapid than enzymatic digestions, and was not excessively aggressive, because the molecular integrity of the individual compounds analysed was preserved. Thus, alkaline digestion can be recommended for the extraction of cell-wall-bound UVACs in J. exsertifolia subsp. cordifolia, whether these compounds are to be evaluated overall or individually.

Keywords:

• Bryophytes
• p-Coumaric acid
• Ferulic acid
• Hydroxycinnamic acids
• Jungermannia exsertifolia subsp. cordifolia

Acknowledgements

We are grateful to the Ministerio de Ciencia e Innovación of Spain and FEDER funds (Project CGL2011-26977) for financial support. Laura Monforte benefited from a grant of the Gobierno de La Rioja (PRED2010/16). Gabriel Fabón benefited from the Projects Colabora 2008/04 and 2009/07 (Gobierno de La Rioja, Spain). The Dirección General de Medio Natural (Gobierno de La Rioja) kindly authorised our sample collection in the protected Natural Park of Sierra Cebollera. This work is integrated into the COST (European Cooperation in Science and Technology) Action FA0906 of the European Union ‘UV-B radiation: a specific regulator of plant growth and food quality in a changing climate’.

Taxonomic Additions and Changes: Nil.