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

Abstract

We examined the responses of ultraviolet-absorbing compounds (UVAC) to enhanced UV-B radiation in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia for 31 days under laboratory conditions. Samples were exposed to three radiation regimes: P (only photosynthetic radiation), PA (photosynthetic + UV-A radiation) and PAB (photosynthetic + UV-A + UV-B radiation). We measured both the bulk UV absorbance of the methanolic extracts and the levels of individual UVAC. In both cases, the methanol-soluble and the methanol-insoluble, alkali-extractable cell wall-bound fractions were analyzed. The bulk UV absorbance of the soluble fraction was higher than that of the cell wall-bound fraction. The bulk UV absorbances of both fractions increased under enhanced UV-B (PAB regime). Five different hydroxycinnamic acid (HCA) derivatives were found in the soluble fraction and two additional ones in the cell wall-bound fraction, among which only p-coumaroylmalic acid in the soluble fraction and p-coumaric acid in the cell wall-bound fraction increased under enhanced UV-B. The maximum quantum yield of PSII (F(v) /F(m)) decreased and DNA damage (amount of thymine dimers) strongly increased under enhanced UV-B, showing UV-B-induced damage. We conclude that methanol-soluble and cell wall-bound fractions of the liverwort studied have different UVAC, and each individual compound may respond in a different way to UV-B radiation. Thus, the analysis of individual UVAC in both the methanol-soluble and cell wall-bound fractions is advisable to better evaluate the protection mechanisms of liverworts against UV-B radiation. In particular, p-coumaric acid and p-coumaroylmalic acid seem to be especially UV-B responsive and merit further investigation.

Dynamic response of UV-absorbing compounds, quantum yield and the xanthophyll cycle to diel changes in UV-B and photosynthetic radiations in an aquatic liverwort

“…The clear increase in the bulk UV absorbance of both soluble and insoluble fractions that took place in the PAB samples, together with the increase in the concentrations of C1 and C6, corroborates the fidelity of these variables in the response of J. cordifolia to enhanced UV-B under laboratory conditions (Fabón et al, 2010). C1 and/or C6 have also been used in the reconstruction of past UV-B (Blokker et al, 2006;Lomax et al, 2008;Otero et al, 2009) and as field biomarkers of present UV-B (Ruhland et al, 2005;Núñez-Olivera et al, 2009) in different plant species including J. cordifolia.…”

“…After this last period, the fluorescent tubes were switched off and the darkness period started again. Other culture conditions were similar to those applied in the pre-culture, and were described in detail by Fabón et al (2010). Covering the tubes with specific UV cut-off filters, three radiation regimes were established (in five replicates for each regime):…”

“…UV-absorbing compounds were analyzed following Fabón et al (2010). In brief, fresh shoot apices were frozen in liquid N 2 and ground in a TissueLyser (Qiagen, Hilden, Germany), and then 5 ml of methanol:water:7 M HCl (70:29:1, v/v/v) was added for extraction (24 h at 4 • C in the dark).…”

“…The maximum quantum yield of PSII, F v /F m (after dark adaptation), the effective quantum yield of PSII (˚P SII : (F m − F t )/F m ), and the non-photochemical quenching (NPQ: (F m − F m )/F m ), were measured with a portable pulse amplitude modulation fluorometer (MINI-PAM, Walz, Effeltrich, Germany), following Fabón et al (2010).…”

“…The differentiation between the soluble (mainly vacuolar) and the insoluble (cell wall-bound) fractions may be important because the cell wall-bound compounds would provide a more spatially uniform UV screen than the intracellular compounds (Clarke and Robinson, 2008). In addition, the analysis of individual UV-absorbing compounds represents a useful complement to the global estimation of UV protection provided by the bulk UV absorbance, since each compound may respond to UV in a different manner (Fabón et al, 2010;Morales et al, 2010). It is also remarkable that there is only one study on the diel changes in the responses to UV radiation in liverworts (Conde-Álvarez et al, 2002).…”