Laura Monforte

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

We studied the diel responses of the liverwort Jungermannia exsertifolia subsp. cordifolia to radiation changes under laboratory conditions. The samples were exposed to three radiation regimes: P (only PAR), PA (PAR+UV-A), and PAB (PAR+UV-A+UV-B). The day was divided in four periods: darkness, a first low-PAR period, the high-PAR plus UV period, and a second low-PAR period. After 15 days of culture, we measured photosynthetic pigments, chlorophyll fluorescence and UV-absorbing compounds in the four periods of the day on two consecutive days. With respect to UV-absorbing compounds, we analyzed their global amount (as the bulk UV absorbance of methanolic extracts) and the concentration of seven hydroxycinnamic acid derivatives, both in the soluble (mainly vacuolar) and insoluble (cell wall-bound) fractions of the plant extracts. PAB samples increased the bulk UV absorbance of the soluble and insoluble fractions, and the concentrations of p-coumaroylmalic acid in the soluble fraction and p-coumaric acid in the cell wall. Most of these variables showed significant diel changes and responded within a few hours to radiation changes (more strongly to UV-B), increasing at the end of the period of high-PAR plus UV. F(v)/F(m), Φ(PSII), NPQ and the components of the xanthophyll cycle showed significant and quick diel changes in response to high PAR, UV-A and UV-B radiation, indicating dynamic photoinhibition and protection of PSII from excess radiation through the xanthophyll cycle. Thus, the liverwort showed a dynamic protection and acclimation capacity to the irradiance level and spectral characteristics of the radiation received.

Effects of UV exclusion on the physiology and phenolic composition of leaves and berries of Vitis vinifera cv. Graciano

BACKGROUND Ultraviolet (UV) radiation induces adaptive responses that can be used for plant production improvement. The aim of this study was to assess the effect of solar UV exclusion on the physiology and phenolic compounds of leaves and berry skins of Vitis vinifera L. cv. Graciano under field conditions. Phenolic compounds were analyzed globally and individually in both the vacuolar fraction and, for the first time in grapevine, the cell wall-bound fraction. These different locations may represent diverse modalities of phenolic response to and protection against UV. RESULTS UV exclusion led to a decrease in Fv /Fm in leaves, revealing that solar UV is needed for adequate photoprotection. Only p-caffeoyl-tartaric acid from the soluble fraction of leaves and myricetin-3-O-glucoside from the soluble fraction of berry skins were significantly higher in the presence of UV radiation, and thus they could play a role in UV protection. Other hydroxycinnamic acids, flavonols, flavanols and stilbenes did not respond to UV exclusion. CONCLUSION UV exclusion led to subtle changes in leaves and berry skins of Graciano cultivar, which would be well adapted to current UV levels. This may help support decision-making on viticultural practices modifying UV exposure of leaves and berries, which could improve grape and wine quality.

Cell compartmentation of UV-absorbing compounds in two aquatic mosses under enhanced UV-B

Abstract The effects of enhanced UV-B radiation on UV-absorbing compounds (UVAC), the maximum quantum yield of photosystem II (Fv/Fm), DNA integrity, and the sclerophylly index, were analyzed in the mosses Bryum pseudotriquetrum and Fontinalis antipyretica. The study was performed for 31 days under laboratory conditions. Enhanced UV-B increased the bulk level of the vacuolar soluble UVAC (SUVAC) in both mosses and the concentration of two different soluble kaempferols in B. pseudotriquetrum. However, enhanced UV-B had no effect on the bulk level of cell wall-bound insoluble UVAC (WUVAC) in both mosses and the concentration of insoluble p-coumaric acid in F. antipyretica. Thus, the insoluble fraction would be less UV-B-responsive than the soluble one. This probably happened because (1) the constitutively high bulk level of WUVAC (and noticeably higher than that of SUVAC) would already provide a sufficiently effective protection; and (2) WUVAC would be relatively immobilized in the cell wall, which would limit the reaction capacity of these compounds to UV-B. The protective mechanisms developed by both mosses could not totally prevent UV-B damage, which was indicated by the modest decrease of Fv/Fm and the increase in DNA damage. We discuss the ecological and phylogenetic implications of the differences in UVAC compartmentation between liverworts and mosses.

Effects of ambient solar UV radiation on grapevine leaf physiology and berry phenolic composition along one entire season under Mediterranean field conditions

In the present study we assessed the effects of ambient solar UV exclusion on leaf physiology, and leaf and berry skin phenolic composition, of a major grapevine cultivar (Tempranillo) grown under typically Mediterranean field conditions over an entire season. In general, the effects of time were stronger than those of UV radiation. Ambient UV caused a little stressing effect (eustress) on leaf physiology, with decreasing net photosynthesis rates and stomatal conductances. However, it was not accompanied by alterations in Fv/Fm or photosynthetic pigments, and was partially counterbalanced by the UV-induced accumulation of protective flavonols. Consequently, Tempranillo leaves are notably adapted to current UV levels. The responses of berry skin phenolic compounds were diverse, moderate, and mostly transitory. At harvest, the clearest response in UV-exposed berries was again flavonol accumulation, together with a decrease in the flavonol hydroxylation level. Contrarily, responses of anthocyanins, flavanols, stilbenes and hydroxycinnamic derivatives were much more subtle or nonexistent. Kaempferols were the only compounds whose leaf and berry skin contents were correlated, which suggests a mostly different regulation of phenolic metabolism for each organ. Interestingly, the dose of biologically effective UV radiation (UVBE) was correlated with the leaf and berry skin contents of quercetins and kaempferols; relationships were linear except for the exponential relationship between UVBE dose and berry skin kaempferols. This opens management possibilities to modify kaempferol and quercetin contents in grapevine through UV manipulation.

Among- and within-genus variability of the UV-absorption capacity in saxicolous mosses

Abstract We studied the among- and within-genus variability of UV protection in 23 mosses belonging to the genera Andreaea, Grimmia and Racomitrium, which were collected from sun-exposed rocks in northern and central Portugal mountains. We explored the influence of genus, species and environmental factors on their UV-absorption capacity, differentiating the soluble UV-absorbing compounds (SUVAC, mainly located in the vacuoles) and the insoluble ones (WUVAC, bound to the cell wall). All the physiological variables were significantly affected by both the genus and the species, which clearly reflects the influence of genetics on the levels and compartmentation of UV-absorbing compounds (UVAC). The physiological variables analyzed were also significantly influenced by both micro- (for example, substrate and orientation) and macro-scale (chain of mountains) variables. In addition, this study showed the interaction between genetics and the environmental factors known to enhance UV exposure (for example, higher altitudes and lower latitudes and slopes) on the level and compartmentation of UV-absorbing compounds.

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.

Phenolic compounds from different bryophyte species and cell compartments respond specifically to ultraviolet radiation, but not particularly quickly

To study the potential quick responses to ultraviolet (UV) radiation of bryophyte phenolic compounds, we cultivated two thalloid liverworts, two leafy liverworts, and two mosses under three moderate realistic UV levels in the laboratory for 22 days. At the end of the daylight period on the first and last culture days, we measured the bulk levels and individual contents of phenolic UV-absorbing compounds (UVACs) of each species, differentiating in both cases the UVACs located in the methanol-soluble (mainly vacuolar) and -insoluble (cell wall-bound) fractions (SUVACs and IUVACs, respectively). The bulk levels of SUVACs and IUVACs mostly showed linear or hyperbolic relationships with the UV dose applied. Thirteen flavones (apigenin and luteolin derivatives) and two hydroxycinnamic acids (p-coumaric and ferulic acids) were identified in the soluble and insoluble fractions, respectively. Only two compounds (p-coumaric and ferulic acids) from the insoluble fraction of the leafy liverwort Plagiochila asplenioides showed a significant quick accumulation in response to UV radiation in the first day of culture, whereas six UVACs (mainly soluble apigenin and luteolin derivatives) from different species (mainly liverworts) were significantly accumulated at the end of the culture. In conclusion, the responses of bryophyte UVACs to UV radiation were influenced by the specific compound considered, the fraction in which each UVAC was located, the global or individual way of UVACs quantification, the bryophyte species and evolutionary lineage, and the experimental conditions used. Particularly, SUVACs were more UV-responsive than IUVACs and liverworts than mosses, and responses were not especially quick.

First Data on the Effects of Ultraviolet Radiation on Phenolic Compounds in the Model Hornwort Anthoceros agrestis

Abstract Hornworts are the least species-rich bryophyte lineage, but represent a key group to understand the evolution of plants because, together with the remaining bryophyte lineages (mosses and liverworts), they constitute the earliest diverging land plants. The responses of hornworts to ultraviolet (UV) radiation are unknown, but they may be important to infer how primitive hornworts (and bryophytes in general) coped with UV upon land colonization. In this context, our aim was to show the first data on the effects of UV radiation on the accumulation patterns of phenolic UV-absorbing compounds (UVACs) in the emerging model hornwort Anthoceros agrestis. Thalli of 52 days age were exposed to photosynthetically active radiation (PAR) alone (P regime) and to a combination of PAR + UV-A + UV-B radiation (PAB regime) for 21 days, using realistic UV doses (equivalent to the natural ambient doses received in summer at mid-latitudes). At the end of the culture period, we measured the bulk levels and individual contents of phenolic UV-absorbing compounds (UVACs), differentiating in both cases the UVACs located in the methanol-soluble (mainly vacuolar) and -insoluble (cell wall-bound) fractions (SUVACs and IUVACs, respectively). Three soluble and one insoluble compounds were identified, among which the soluble rosmarinic and anthocerotonic acids are not present in any other bryophyte lineage. The bulk levels of SUVACs were higher than those of IUVACs, a physiological trait more typical of liverworts than of mosses. None of the variables measured responded significantly to UV exposure, but all of them showed an increasing trend under the PAB regime. Given that UV responsiveness of phenolic compounds depends on the UV levels used and the thallus age (with decreasing responsiveness as age increases), further research using higher UV levels and younger thalli should be conducted to more reliably establish the UV reactiveness of Anthoceros agrestis.

Spores potentially dispersed to longer distances are more tolerant to ultraviolet radiation: A case study in the moss genus Orthotrichum

PREMISE OF THE STUDY Ultraviolet (UV) radiation influences the viability of algal spores and seed-plant pollen depending on the species, the dose, and the wavelength. In bryophytes, one of the dominant groups of plants in many habitats, UV radiation could determine their spore dispersal strategy, and such data are critical for reconstructing the ancestral state in plants and for determining the distribution range and persistence of bryophyte species. METHODS Spores of four bryophyte species of the moss genus Orthotrichum that were either hygrochastic or xerochastic (spores dispersed under wet or dry conditions, respectively) were exposed to realistic doses of UV radiation under laboratory conditions. Spore viability was evaluated through germination experiments and, for the first time in bryophytes, ultrastructural observations. Given that the UV-B doses used were relatively higher than the UV-A doses, the UV effect was probably due more to UV-B than UV-A wavelengths. KEY RESULTS All four species reduced their spore germination capacity in a UV dose-dependent manner, concomitantly increasing spore ultrastructural damage (cytoplasmic and plastid alterations). Most spores eventually died when exposed to the highest UV dose. Interestingly, spores of hygrochastic species were much more UV-sensitive than those of xerochastic species. CONCLUSIONS UV tolerance determines moss spore viability, as indicated by germination capacity and ultrastructural damage, and differs between spores of species with different dispersal strategies. Specifically, the higher UV tolerance of xerochastic spores may enable them to be dispersed to longer distances than hygrochastic spores, thus extending more efficiently the distribution range of the corresponding species.

Spatial variability of ultraviolet-absorbing compounds in an aquatic liverwort and their usefulness as biomarkers of current and past UV radiation: A case study in the Atlantic–Mediterranean transition

The spatial variability of ultraviolet-absorbing compounds (UVACs) in the freshwater liverwort Jungermannia exsertifolia subsp. cordifolia was studied in mid-latitudes (the Atlantic-Mediterranean transition) across a wide lati-altitudinal gradient, with the aim of testing the usefulness of UVACs as biomarkers of current ambient levels of UV radiation. We analysed 17 samples from streams located in the main mountain ranges of the Iberian Peninsula, differentiating methanol-soluble (SUVACs, mainly located in the vacuoles) and methanol-insoluble (IUVACs, bound to cell walls) compounds, since they represent different manners to cope with UV radiation. In both fractions, the bulk level of UVACs and the concentrations of several individual compounds were measured. In addition, we measured Fv/Fm, DNA damage and sclerophylly index (SI) as possible additional UV biomarkers. UVACs showed a high variability, probably due not only to the gradients of macroenvironmental factors (UV radiation, PAR, and water temperature), but also to microenvironmental factors inherent to the dynamic nature of mountain streams. Two soluble coumarins were positively correlated with UV levels and could be used for ambient UV biomonitoring in the spatial scale. In contrast to the variability in UVACs, the relatively homogeneous values of Fv/Fm and the lack of any DNA damage made these variables useless for ambient UV biomonitoring, but suggested a strong acclimation capacity of this liverwort to changing environmental conditions (in particular, to UV levels). Finally, UVACs of fresh samples of the liverwort were compared to those of herbarium samples collected in the same lati-altitudinal gradient. SUVACs were significantly higher in fresh samples, whereas IUVACs generally showed the contrary. Thus, IUVACs were more stable than SUVACs and hence more adequate for retrospective UV biomonitoring. In conclusion, UVAC compartmentation should be taken into account for bryophyte-based UV biomonitoring in future studies.