Encarnación Núñez-Olivera

Solar ultraviolet radiation is necessary to enhance grapevine fruit ripening transcriptional and phenolic responses

BackgroundUltraviolet (UV) radiation modulates secondary metabolism in the skin of Vitis vinifera L. berries, which affects the final composition of both grapes and wines. The expression of several phenylpropanoid biosynthesis-related genes is regulated by UV radiation in grape berries. However, the complete portion of transcriptome and ripening processes influenced by solar UV radiation in grapes remains unknown.ResultsWhole genome arrays were used to identify the berry skin transcriptome modulated by the UV radiation received naturally in a mid-altitude Tempranillo vineyard. UV radiation-blocking and transmitting filters were used to generate the experimental conditions. The expression of 121 genes was significantly altered by solar UV radiation. Functional enrichment analysis of altered transcripts mainly pointed out that secondary metabolism-related transcripts were induced by UV radiation including VvFLS1, VvGT5 and VvGT6 flavonol biosynthetic genes and monoterpenoid biosynthetic genes. Berry skin phenolic composition was also analysed to search for correlation with gene expression changes and UV-increased flavonols accumulation was the most evident impact. Among regulatory genes, novel UV radiation-responsive transcription factors including VvMYB24 and three bHLH, together with known grapevine UV-responsive genes such as VvMYBF1, were identified. A transcriptomic meta-analysis revealed that genes up-regulated by UV radiation in the berry skin were also enriched in homologs of Arabidopsis UVR8 UV-B photoreceptor-dependent UV-B -responsive genes. Indeed, a search of the grapevine reference genomic sequence identified UV-B signalling pathway homologs and among them, VvHY5-1, VvHY5-2 and VvRUP were up-regulated by UV radiation in the berry skin.ConclusionsResults suggest that the UV-B radiation-specific signalling pathway is activated in the skin of grapes grown at mid-altitudes. The biosynthesis and accumulation of secondary metabolites, which are appreciated in winemaking and potentially confer cross-tolerance, were almost specifically triggered. This draws attention to viticultural practices that increase solar UV radiation on vineyards as they may improve grape features.

Different physiological responses of two aquatic bryophytes to enhanced ultraviolet-B radiation

Abstract Two aquatic bryophytes, the moss Fontinalis antipyretica Hedw. and the foliose liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váña were analysed with regard to their ultraviolet-B (UV-B) tolerance. The plants were cultivated in the laboratory for 36 days under three different radiation regimes which were set up using appropriate lamps and filters: P (PAR alone, control), PA (PAR + UV-A) and PAB (PAR + UV-A + UV-B). The two bryophytes responded differently to the enhancement in UV-B radiation, while UV-A radiation had only a slight biological effect. The samples of the moss which were irradiated with UV-B showed, with respect to the control, decreases in the chlorophyll and carotenoids concentration, the chlorophyll a/b quotient, the chlorophylls/phaeopigments ratios, the net photosynthesis rates, the light saturation point, the maximum quantum yield of photosystem II (Fv/Fm) and the apparent electron transport rate (ETR). They also showed increases in the sclerophylly index and the dark respiration rates. The majority of these changes are indicative of plant stress and some of them had been found previously in bryophytes exposed to enhanced UV-B radiation. However, the UV-B-irradiated samples of the liverwort only showed a decrease in Fv/Fm, which might be the most sensitive physiological variable to UV-B, together with an increase in the concentration of UV-absorbing compounds. This defence mechanism, rarely described in bryophytes, would enable the liverwort to have a higher tolerance than the moss against UV-B radiation, at least under the specific experimental conditions used in this study. Also, the increment of UV-absorbing compounds in the liverwort, which seems to be a specific response to the enhancement in UV-B radiation, might be a useful ecophysiological tool in the bioindication of this phenomenon; long-term field research is needed to confirm this usefulness. The different UV-B tolerances of the species studied may be related, to a certain extent, with their different distribution and ecology. Given that UV-B tolerance depends on the species, bryophytes should not be grouped as a single functional type in the prediction of the consequences of a hypothetic enhancement in UV-B radiation.

Physiological changes and UV protection in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia along an altitudinal gradient of UV-B radiation

Here we report the effects of a natural altitudinal gradient of UV-B radiation, from 1140 to 1816 m altitude, on the physiology of the aquatic liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váña collected in mountain streams. Photosynthetic pigments, net photosynthesis and dark respiration rates, chlorophyll fluorescence, protein concentration, sclerophylly, and UV-absorbing compounds [both global UV absorbance of methanol-extractable UV-absorbing compounds (MEUVAC) and concentrations of five individual compounds] were measured. Two new caffeic acid derivatives were discovered: 5″-(7″,8″-dihydroxycoumaroyl)-2-caffeoylmalic acid and 5″-(7″,8″-dihydroxy-7-O-β-glucosyl-coumaroyl)-2-caffeoylmalic acid, whereas three additional compounds were already known in other species: p-coumaroylmalic acid, phaselic acid (both compounds in their cis- and trans- forms) and feruloylmalic acid. Most physiological variables changed considerably along the altitudinal gradient, but only six showed significant linear relationships with altitude: MEUVAC levels, the concentrations of the two new secondary compounds, the maximal apparent electron transport rate through PSII (ETRmax) and the maximal non-photochemical quenching (NPQmax) increased with altitude, whereas photoinhibition percentage decreased. A principal components analysis (PCA) was conducted to rank the values of the physiological and ecological variables obtained along the altitudinal transect, showing that those variables correlated with altitude were responsible for the ordination of the sampling points. The liverwort was not adversely affected by the changing conditions along the altitudinal gradient and, in particular, by the increasing UV-B irradiance, probably because the characteristics shown by high-altitude populations may confer tolerance to high UV-B levels. The response to UV-B of the two new compounds suggests that they could be used as indicators of the spatial changes in UV-B radiation.

Influence of Temperature on the Effects of Artificially Enhanced UV-B Radiation on Aquatic Bryophytes Under Laboratory Conditions

We examined, under laboratory conditions, the influence of temperature (2 °C vs. 10 °C) on the physiological responses of two aquatic bryophytes from a mountain stream to artificially enhanced UV-B radiation for 82 d. These organisms may be exposed naturally to relatively low temperatures and high levels of UV-B radiation, and this combination is believed to increase the adverse effects of UV-B radiation. In the moss Fontinalis antipyretica, UV-B-treated samples showed severe physiological damages, including significant decreases in chlorophyll (Chl) and carotenoid (Car) contents, Chl a/b and Chl/phaeopigment ratios, Chl a fluorescence parameters Fv/Fm and ΦPS2, electron transport rate (ETRmax), and growth. In the liverwort Jungermannia cordifolia, UV-B radiation hardly caused any physiological change except for growth reduction. Thus, this liverwort seemed to be more tolerant to UV-B radiation than the moss under the specific experimental conditions used, maybe partly due to the accumulation of UV-B absorbing compounds. The influence of temperature on the effects of UV-B radiation depended on the species: the higher the UV-B tolerance, the lower the influence of temperature. Also, different physiological variables showed varied responses to this influence. Particularly, the lower temperature used in our study enhanced the adverse effects of UV-B radiation on important physiological variables such as Fv/Fm, growth, and Chl/phaeopigment ratios in the UV-B-sensitive F. antipyretica, but not in the more UV-B-tolerant J. cordifolia. Thus, the adverse effects of cold and UV-B radiation were apparently additive in the moss, but this additiveness was lacking in the liverwort. The Principal Components Analyses (PCA) conducted for both species with the physiological data obtained after 36 and 82 d of culture confirmed the above results. Under natural conditions, the relatively high water temperatures in summer might facilitate the acclimation of aquatic bryophytes from mountain streams to high levels of UV-B radiation. This may be relevant to predict the consequences of concomitant global warming and increasing UV-B radiation.

Effects of cadmium and enhanced UV radiation on the physiology and the concentration of UV-absorbing compounds of the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia

The aquatic liverwort Jungermannia exsertifolia subsp. cordifolia was cultivated for 15 d under controlled conditions to study the single and combined effects of cadmium and enhanced ultraviolet (UV) radiation. Both cadmium and UV radiation caused chlorophyll degradation and a decrease in the maximum quantum yield of photosystem II (PSII), together with an increase in the mechanisms of non-photochemical dissipation of energy (increase in the xanthophyll index). Cadmium was more stressing than UV radiation, since the metal also influenced photosynthesis globally and caused a decrease in net photosynthetic rates, in the effective quantum yield of photosynthetic energy conversion of PSII, and in the maximal apparent electron transport rate through PSII. Ultraviolet radiation increased the level of trans-p-coumaroylmalic acid and cadmium increased trans-phaselic and feruloylmalic acids. The increase in these compounds was probably related to both a more efficient absorption of harmful UV radiation and an enhanced protection against oxidative stress. DNA damage was specifically caused by UV-B radiation, but was intensified under the presence of cadmium, probably because the metal impairs the DNA enzymatic repair mechanisms. Ultraviolet radiation and cadmium seemed to operate additively on some physiological processes, while other responses were probably due to either factor alone.

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

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.

A Survey of the Distribution of UV-Absorbing Compounds in Aquatic Bryophytes from a Mountain Stream

Abstract Bryophytes are important primary producers in mountain streams and they should be protected against the adverse effects of the high levels of UV-B radiation typical of these environments. The accumulation of UV-absorbing compounds could be one of the mechanisms of protection. A survey of methanol-extractable UV-absorbing compounds (MEUVAC) was conducted for 14 aquatic bryophytes, 10 mosses, and four liverworts, from a mountain stream located at 2,000 m elevation. For four species, several populations were investigated. Absorbance spectra between 250 and 400 nm were obtained and the amount of MEUVAC was calculated per unit of both dry mass (DM) and surface area. Levels of MEUVAC and the absorbance spectra of UV radiation were significantly affected by species. The high levels of MEUVAC and the clearly hump-shaped spectra in the UV-B and UV-A wavelengths (280–400 nm) that were found in the liverworts contrasted with the low levels and non hump-shaped spectra generally found in the mosses (except for Polytrichum commune). Sclerophylly and intraspecific variability only had a modest influence on the results. It may be concluded that the accumulation of MEUVAC might represent a protecting mechanism against UV-B radiation in the four liverworts studied, but rarely in the mosses of this stream.

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.

Interactions between parasitic fungi and mosses: pegged and swollen-tipped rhizoids in Funaria and Bryum

Abstract Two kinds of parasitic fungal infections are described in the rhizoidal systems of both wild and cultured materials of Funaria hygrometrica, Bryum capillare and B. pseudotriquetrum. Protonemal and rhizoidal cells of Funaria produce pegs of host wall materialaroundsites of hyphal penetration. Similar structures appear to be much more widespread in hepatics and in Monoclea have been misinterpreted as rudimentary pegs, the characteristic feature ofpeggedrhizoids. Swollen side branch initials and the tip cells of major rhizoidal axescontaina single rozellopsidalean (Oomycota formerly Chytridiomycota) zoosporangium in Bryum pseudotriquetrum and up to three similar structures in B. capillare. Each zoosporangium produces a single exit tube. Whereas the infected cells die the subapical cells remain alive and,afterzoospore discharge, produce side branches whose tip cells also become infected. Restriction of the parasites to sidebranchinitials and rhizoid tip cells is perhaps because these are the only cells that the zoospores are able to penetrate. Nutrients translocated along rhizoids to sustaintipgrowth are diverted to nurture the fungi in infected plants. Differences between the number of zoosporangia per host cell and the number of exit tubes between different mosses suggest that more than one species of rozellopsidalean fungus may form rhizoid galls in mosses and not just Pleotracheluswildemanidescribedpreviously.Rhizoid galls appear to be genuinely uncommon in mosses but, following clarification of the differences between these and rhizoidal tubers, further discoveries may be anticipated.

Impacts of long-term enhanced UV-B radiation on bryophytes in two sub-Arctic heathland sites of contrasting water availability

BACKGROUND AND AIMS Anthropogenic depletion of stratospheric ozone in Arctic latitudes has resulted in an increase of ultraviolet-B radiation (UV-B) reaching the biosphere. UV-B exposure is known to reduce above-ground biomass and plant height, to increase DNA damage and cause accumulation of UV-absorbing compounds in polar plants. However, many studies on Arctic mosses tended to be inconclusive. The importance of different water availability in influencing UV-B impacts on lower plants in the Arctic has been poorly explored and might partially explain the observed wide variation of responses, given the importance of water in controlling bryophyte physiology. This study aimed to assess the long-term responses of three common sub-Arctic bryophytes to enhanced UV-B radiation (+UV-B) and to elucidate the influence of water supply on those responses. METHODS Responses of three sub-Arctic bryophytes (the mosses Hylocomium splendens and Polytrichum commune and the liverwort Barbilophozia lycopodioides) to +UV-B for 15 and 13 years were studied in two field experiments using lamps for UV-B enhancement with identical design and located in neighbouring areas with contrasting water availability (naturally mesic and drier sites). Responses evaluated included bryophyte abundance, growth, sporophyte production and sclerophylly; cellular protection by accumulation of UV-absorbing compounds, β-carotene, xanthophylls and development of non-photochemical quenching (NPQ); and impacts on photosynthesis performance by maximum quantum yield (F(v) /F(m)) and electron transport rate (ETR) through photosystem II (PSII) and chlorophyll concentrations. RESULTS Responses were species specific: H. splendens responded most to +UV-B, with reduction in both annual growth (-22 %) and sporophyte production (-44 %), together with increased β-carotene, violaxanthin, total chlorophyll and NPQ, and decreased zeaxanthin and de-epoxidation of the xanthophyll cycle pool (DES). Barbilophozia lycopodioides responded less to +UV-B, showing increased β-carotene and sclerophylly and decreased UV-absorbing compounds. Polytrichum commune only showed small morphogenetic changes. No effect of UV-B on bryophyte cover was observed. Water availability had profound effects on bryophyte ecophysiology, and plants showed, in general, lower growth and ETR, together with a higher photoprotection in the drier site. Water availability also influenced bryophyte responses to +UV-B and, in particular, responses were less detectable in the drier site. CONCLUSIONS Impacts of UV-B exposure on Arctic bryophytes were significant, in contrast to modest or absent UV-B effects measured in previous studies. The impacts were more easily detectable in species with high plasticity such as H. splendens and less obvious, or more subtle, under drier conditions. Species biology and water supply greatly influences the impact of UV-B on at least some Arctic bryophytes and could contribute to the wide variation of responses observed previously.