Action of UV and visible radiation on chlorophyll fluorescence from dark-adapted grape leaves (Vitis vinifera L.)

Effects of UVA disappearance and presence on the acylated anthocyanins formation in grape berries

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UVA block inhibited acylated anthocyanin formation.

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UVA presence promoted acylated anthocyanin formation.

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Peonidin for acetylation and p-coumaroylation primarily respond to UVA.

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A total of 3962 DEGs and 136 DAMs were identified.

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VvMYBA1 played a key role in co-expression network.

Ultraviolet A (UVA), the major component of the UV, plays a crucial role in formatting the characteristics of color in wine grapes by influencing its anthocyanin composition and contents. Results showed that anthocyanin biosynthesis was suppressed by UVA screening and enhanced by irradiation. The acetylation and p-coumaroylation of anthocyanins were more pronounced and showed positive correlation with a* and negative correlation with L*, b*, C*, and h, thereby leading to changes in color. Weighted gene co-expression network analysis showed that two modules (red and turquoise) were significantly related to the acetylation and p-coumaroylation of peonidin. In addition, relative gene expression assays and correlation analysis also indicated that VvMYBA1 might influence anthocyanin accumulation by directly regulating VvOMT expression and increasing the flux to the vacuole through VvGST4. In conclusion, the results helped in improving our understanding of the role of UVA in skin color formation.

Metabolic programming of Rhododendron chrysanthum leaves following exposure to UVB irradiation

Excessive UVB reaching the earth is a cause for concern. To decipher the mechanism concerning UVB resistance of plants, we studied the effects of UVB radiation on photosynthesis and metabolic profiling of Rhododendron chrysanthum Pall. by applying 2.3Wm-2 of UVB radiation for 2days. Results showed that maximum quantum yield of PSII (Fv/Fm) and effective quantum yield of PSII (φPSII) decreased by 7.95% and 8.36%, respectively, following UVB exposure. Twenty five known metabolites were identified as most important by two different methods, including univariate and multivariate statistical analyses. Treatment of R. chrysanthum with UVB increased the abundance of flavonoids, organic acids, and amino acids by 62%, 22%, and 5%, respectively. UVB irradiation also induced about 1.18-fold increase in 11 top-ranked metabolites identified: five organic acids (d-2,3-dihydroxypropanoic acid, maleic acid, glyceric acid, fumaric acid and suberic acid), four amino acids (l-norleucine, 3-oxoalanine, l-serine and glycine), and two fatty acids (pelargonic acid and myristoleic acid). In addition, UVB irradiation increased the intermediate products of arginine biosynthesis and the TCA cycle. Taken together, the accumulation of flavonoids, organic acids, amino acids and fatty acids, accompanied by enhancement of TCA cycle and arginine biosynthesis, may protect R. chrysanthum plants against UVB deleterious effects.

Climate Change Enhanced Carotenoid Pro-Vitamin A Levels of Selected Plantain Cultivars

Diet diversification and the exploitation of traditional, micronutrient-rich germplasm of staple crops are generally regarded as sustainable and low-cost approaches to increase the micronutrient intake of resource-poor people. Sun's UV index was collected daily throughout the year. The study assessed the seasonality of provitamin A carotenoids in three plantain cultivars in response to climatic condition. Fruits were harvested at three maturities and freeze-dried before analysis. The results showed that there were high levels of the sun's UV-B radiations throughout the year with the highest occurring from November to May when the area experienced clear skies with minimal cloud cover. These high levels of the sun's UV-B index occurred between 9.00 h GMT and 17.00 h GMT. The study also showed that α-carotene content increased with maturity in "Apantu" during the rainy seasons ranging from 95 to 172 μg/100 g of dry pulp. Similar trends were observed during the dry season with a range of 28 to 489 μg/100 g. The α-carotene contents were very high in the periods of high sun's UV-B radiations compared to the periods of low sun's UV-B radiations. The α-carotene levels in the giant French plantains showed similar trends. Intermediate French "Oniaba" and False Horn "Apantu" plantain cultivar showed the highest content of β-carotene during the dry season. The high provitamin A carotenoid levels in the cultivars coincided with the high levels of the sun's UV index.

Effects of 1-butyl-3-methylimidazolium chloride on the photosynthetic system and metabolism of maize (Zea mays L.) seedlings

Ionic liquids (ILs) are widely used in various chemical processes. However, a growing number of studies have found that ILs are potentially toxic to different types of living organisms, including crops. The present study analysed the effects of 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) on the photosynthetic system and metabolism of maize seedlings. Results showed that [C₄mim]Cl could significantly reduce maize leaf chlorophyll level and cause extensive leaf bleaching. The activity of photosystem II (PSII) was significantly inhibited when seedlings exposed to higher concentration of [C₄mim]Cl. The maximum quantum yield of PSII and the potential efficiency of PSII were reduced by 63% and 88% under 800 mg/L [C₄mim]Cl treatment in comparison with the control treatment. The RNA sequencing analysis performed to examine gene expression profiles of maize leaves under [C₄mim]Cl treatment revealed 639 differentially expressed genes (DEGs), 115 of which were categorized into different metabolic pathways. Among these DEGs, the seven genes involved in the photosynthetic Calvin cycle were down-regulated by [C₄mim]Cl exposure. For carbohydrates and amino acids metabolism, the genes for starch synthesis were down-regulated, while the genes for amino acids and protein degradation were up-regulated. The changes observed in these major metabolic pathways might be an important reason for [C₄mim]Cl toxicity.

Linking chloroplast relocation to different responses of photosynthesis to blue and red radiation in low and high light-acclimated leaves of Arabidopsis thaliana (L.)

Low light (LL) and high light (HL)-acclimated plants of A. thaliana were exposed to blue (BB) or red (RR) light or to a mixture of blue and red light (BR) of incrementally increasing intensities. The light response of photosystem II was measured by pulse amplitude-modulated chlorophyll fluorescence and that of photosystem I by near infrared difference spectroscopy. The LL but not HL leaves exhibited blue light-specific responses which were assigned to relocation of chloroplasts from the dark to the light-avoidance arrangement. Blue light (BB and BR) decreased the minimum fluorescence ([Formula: see text]) more than RR light. This extra reduction of the [Formula: see text] was stronger than theoretically predicted for [Formula: see text] quenching by energy dissipation but actual measurement and theory agreed in RR treatments. The extra [Formula: see text] reduction was assigned to decreased light absorption of chloroplasts in the avoidance position. A maximum reduction of 30% was calculated. Increasing intensities of blue light affected the fluorescence parameters NPQ and q_P to a lesser degree than red light. After correcting for the optical effects of chloroplast relocation, the NPQ responded similarly to blue and red light. The same correction method diminished the color-specific variations in q_P but did not abolish it; thus strongly indicating the presence of another blue light effect which also moderates excitation pressure in PSII but cannot be ascribed to absorption variations. Only after RR exposure, a post-illumination overshoot of [Formula: see text] and fast oxidation of PSI electron acceptors occurred, thus, suggesting an electron flow from stromal reductants to the plastoquinone pool.

Distinct physiological and metabolic reprogramming by highbush blueberry (Vaccinium corymbosum) cultivars revealed during long-term UV-B radiation

Despite the Montreal protocol and the eventual recovery of the ozone layer over Antarctica, there are still concerns about increased levels of ultraviolet-B (UV-B) radiation in the Southern Hemisphere. UV-B induces physiological, biochemical and morphological stress responses in plants, which are species-specific and different even for closely related cultivars. In woody plant species, understanding of long-term mechanisms to cope with UV-B-induced stress is limited. Therefore, a greenhouse UV-B daily course simulation was performed for 21 days with two blueberry cultivars (Legacy and Bluegold) under UV-B_BE irradiance doses of 0, 0.07 and 0.19 W m^-2 . Morphological changes, photosynthetic performance, antioxidants, lipid peroxidation and metabolic features were evaluated. We found that both cultivars behaved differently under UV-B exposure, with Legacy being a UV-B-resistant cultivar. Interestingly, Legacy used a combined strategy: initially, in the first week of exposure its photoprotective compounds increased, coping with the intake of UV-B radiation (avoidance strategy), and then, increasing its antioxidant capacity. These strategies proved to be UV-B radiation dose dependent. The avoidance strategy is triggered early under high UV-B radiation in Legacy. Moreover, the rapid metabolic reprogramming capacity of this cultivar, in contrast to Bluegold, seems to be the most relevant contribution to its UV-B stress-coping strategy.

UV-A radiation effects on higher plants: Exploring the known unknown

Ultraviolet-A radiation (UV-A: 315-400nm) is a component of solar radiation that exerts a wide range of physiological responses in plants. Currently, field attenuation experiments are the most reliable source of information on the effects of UV-A. Common plant responses to UV-A include both inhibitory and stimulatory effects on biomass accumulation and morphology. UV-A effects on biomass accumulation can differ from those on root: shoot ratio, and distinct responses are described for different leaf tissues. Inhibitory and enhancing effects of UV-A on photosynthesis are also analysed, as well as activation of photoprotective responses, including UV-absorbing pigments. UV-A-induced leaf flavonoids are highly compound-specific and species-dependent. Many of the effects on growth and development exerted by UV-A are distinct to those triggered by UV-B and vary considerably in terms of the direction the response takes. Such differences may reflect diverse UV-perception mechanisms with multiple photoreceptors operating in the UV-A range and/or variations in the experimental approaches used. This review highlights a role that various photoreceptors (UVR8, phototropins, phytochromes and cryptochromes) may play in plant responses to UV-A when dose, wavelength and other conditions are taken into account.

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 F_v/F_m 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 (UV_BE) was correlated with the leaf and berry skin contents of quercetins and kaempferols; relationships were linear except for the exponential relationship between UV_BE dose and berry skin kaempferols. This opens management possibilities to modify kaempferol and quercetin contents in grapevine through UV manipulation.

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.

Simple rain-shelter cultivation prolongs accumulation period of anthocyanins in wine grape berries

Simple rain-shelter cultivation is normally applied during the grape growth season in continental monsoon climates aiming to reduce the occurrence of diseases caused by excessive rainfall. However, whether or not this cultivation practice affects the composition and concentration of phenolic compounds in wine grapes remains unclear. The objective of this study was to investigate the effect of rain-shelter cultivation on the accumulation of anthocyanins in wine grapes (Vitis vinifera L. Cabernet Sauvignon) grown in eastern China. The results showed that rain-shelter cultivation, compared with the open-field, extended the period of rapid accumulation of sugar, increased the soluble solid content in the grape berries, and delayed the senescence of the green leaves at harvest. The concentrations of most anthocyanins were significantly enhanced in the rain-shelter cultivated grapes, and their content increases were closely correlated with the accumulation of sugar. However, the compositions of anthocyanins in the berries were not altered. Correspondingly, the expressions of VvF3'H, VvF3'5'H, and VvUFGT were greatly up-regulated and this rising trend appeared to continue until berry maturation. These results suggested that rain-shelter cultivation might help to improve the quality of wine grape berries by prolonging the life of functional leaves and hence increasing the assimilation products.

Excess Ca(2+) does not alleviate but increases the toxicity of Hg(2+) to photosystem II in Synechocystis sp. (Cyanophyta)

This study demonstrated that excess Ca(2+) increased the toxicity of Hg(2+) to PSII of cyanobacterium Synechocystis sp. using fast rise chlorophyll fluorescence test. Excess Ca(2+) increased the inhibitory effect of Hg(2+) on O2 evolution. Exposure to Hg(2+) caused increase in functional antenna size (ABS/RC), trapping rate of reaction center (TR0/RC), dissipated energy flux per reaction center (DI0/RC) and maximum quantum yield of non-photochemical deexcitation ( [Formula: see text] ), indicating that some reaction centers were transformed to dissipation sinks under Hg(2+) stress. Hg(2+) stress slowed down electron transport on both donor side and acceptor side and caused accumulation of P680(+). Excess Ca(2+) intensified all the Hg(2+) toxic effects on PSII function and led to dysfunction of PSII. The number of reaction centers that were transformed into dissipation sinks increased with increasing Ca(2+) concentration.

Deriving fluorometer-specific values of relative PSI fluorescence intensity from quenching of F(0) fluorescence in leaves of Arabidopsis thaliana and Zea mays

The effect of stepwise increments of red light intensities on pulse-amplitude modulated (PAM) chlorophyll (Chl) fluorescence from leaves of A. thaliana and Z. mays was investigated. Minimum and maximum fluorescence were measured before illumination (F(0) and F(M), respectively) and at the end of each light step (F'(0) and F'(M), respectively). Calculated F'(0) values derived from F(0), F(M) and F'(M) fluorescence according to Oxborough and Baker (1997) were lower than the corresponding measured F'(0) values. Based on the concept that calculated F'(0) values are under-estimated because the underlying theory ignores PSI fluorescence, a method was devised to gain relative PSI fluorescence intensities from differences between calculated and measured F'(0). This method yields fluorometer-specific PSI data as its input data (F(0), F(M), F'(0) and F'(M)) depend solely on the spectral properties of the fluorometer used. Under the present conditions, the PSI contribution to F (0) fluorescence was 0.24 in A. thaliana and it was independent on the light acclimation status; the corresponding value was 0.50 in Z. mays. Correction for PSI fluorescence affected Z. mays most: the linear relationship between PSI and PSII photochemical yields was clearly shifted toward the one-to-one proportionality line and maximum electron transport was increased by 50 %. Further, correction for PSI fluorescence increased the PSII reaction center-specific parameter, 1/F(0) - 1/F(M), up to 50 % in A. thaliana and up to 400 % in Z. mays.

Impact of UV-B irradiation on photosynthetic performance and chloroplast membrane components in Oryza sativa L

The impact of UV-B radiation on photosynthetic related parameters was studied in Oryza sativa L. cv. Safari plants, after an UV-B irradiation performed 1h per day for 7days (between 8 and 14days after germination) with a ten narrow-band (λ 311nm) that resulted in a total biological effective UV-B (UVB(BE)) of 2.975kJm(-2)day(-1) and a total of 20.825kJm(-2). Gas exchange measurements were severely affected, showing reductions higher than 80% in net photosynthesis (P(n)), stomatal conductance and photosynthetic capacity (A(max)), 1day after the end of the 7-days UV-B treatment. Similarly, several fluorescence parameters (F(o), F(v)/F(m), Fv'/Fm', ϕ(e), q(P) and q(E)) and thylakoid electron transport (involving both photosystems) were also severely reduced. Concomitantly, a decline of xanthophylls, carotenes, Chl a, Chl (a+b) and Chl (a/b) values was accompanied by the increase of the lipoperoxidation level in chloroplast membranes, altogether reflecting a loss of protection against oxidative stress. Seven days after of the end of UV-B treatment, most fluorescence parameters recovered, but in P(n), A(max), thylakoid electron transport rates, Chl a and lipid classes, as well as the level of lipoperoxidation, the impacts were even stronger than immediately after the end of stress, denoting a clear loss of performance of photosynthetic structures. However, only a moderate impact on total lipids was observed, accompanied by some changes in the relative weight of the major chloroplast membrane lipid classes, with emphasis on the decrease of MGDG and the increase of phospholipids. That suggested an ability to de novo lipid synthesis allowing qualitative changes in the lipid matrix. Notably, the leaves developed after the end of UV-B irradiation showed a much lower impact, with significantly decreased values only in P(n) and g(s), rises in several fluorescence parameters, thylakoid electron transport, photosynthetic pigments (xanthophylls and chls) and DEPS, while lipid classes presented values close to control. The results showed a global impact of UV-B in the photosynthetic structures and performance in irradiated leaves, but revealed also a low impairment extent in the leaves entirely developed after the end of the irradiation, reflecting a remarkable recovery of the plant after the end of stress, what could constitute an advantage under occasional UV-B exposure events in this vital worldwide staple food crop.

Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterols

We investigated the interactions of abscisic acid (ABA) in the responses of grape leaf tissues to contrasting ultraviolet (UV)-B treatments. One-year-old field-grown plants of Vitis vinifera L. were exposed to photosynthetically active radiation (PAR) where solar UV-B was eliminated by using polyester filters, or where PAR was supplemented with UV-B irradiation. Treatments combinations included weekly foliar sprays of ABA or a water control. The levels of UV-B absorbing flavonols, quercetin and kaempferol were significantly decreased by filtering out UV-B, while applied ABA increased their content. Concentration of two hydroxycinnamic acids, caffeic and ferulic acids, were also increased by ABA, but not affected by plus UV-B (+UV-B) treatments. Levels of carotenoids and activities of the antioxidant enzymes, catalase, ascorbate peroxidase and peroxidase were elevated by +ABA treatments, but only if +UV-B was given. Cell membrane beta-sitosterol was enhanced by ABA independently of +UV-B. Changes in photoprotective compounds, antioxidant enzymatic activities and sterols were correlated with lessened membrane harm by UV-B, as assessed by ion leakage. Oxidative damage expressed as malondialdehyde content was increased under +UV-B treatments. Our results suggest that the defence system of grape leaf tissues against UV-B is activated by UV-B irradiation with ABA acting downstream in the signalling pathway.

Intra- and interspecific differences of 10 barley and 10 tomato cultivars in response to short-time UV-B radiation: a study analysing thermoluminescence, fluorescence, gas-exchange and biochemical parameters

The impact of UV-B radiation on 10 genotypically different barley and tomato cultivars was tested in a predictive study to screen for potentially UV-tolerant accessions and to analyze underlying mechanisms for UV-B sensitivity. Plant response was analyzed by measuring thermoluminescence, fluorescence, gas exchange and antioxidant status. Generally, barley cultivars proved to be much more sensitive against UV-B radiation than tomato cultivars. Statistical cluster analysis could resolve two barley groups with distinct differences in reaction patterns. The UV-B sensitive group showed a stronger loss in PSII photochemistry and a lower gas-exchange performance and regulation after UV-B radiation compared to the more tolerant group. The results indicate that photosynthetic light and dark reactions have to play optimally in concert to render plants more tolerant against UV-B radiation. Hence, measuring thermoluminescence/fluorescence and gas exchange in parallel will have much higher potential in identifying tolerant cultivars and will help to understand the underlying mechanisms.

Phenolic composition in grape (Vitis vinifera L. cv. Malbec) ripened with different solar UV-B radiation levels by capillary zone electrophoresis

The responses of Vitis vinifera L. cv. Malbec to different solar ultraviolet-B radiation (UV-B) levels were assessed in two contrasting situations, under sunlight with full UV-B (+UV-B) and filtered UV-B (-UV-B), in three different locations at 500, 1000, and 1500 m above sea level (asl). To evaluate the effects of radiation, a simple, accurate, and rapid method for the separation and simultaneous determination of representative phenolic compounds in grape berry skins by capillary zone electrophoresis was developed. Separation was carried out in less than 20 min with 20 mM sodium tetraborate buffer containing 30% methanol, pH 9.00. The procedure is fast and reliable, and extracted grape berry skins can be directly analyzed without prior sample cleanup procedure. Berry skins from the +UV-B treatment at 1500 m asl showed the highest levels of total polyphenols anthocyanins, and resveratrol, compared with the -UV-B treatment at this altitude.

Time sequence of the damage to the acceptor and donor sides of photosystem II by UV-B radiation as evaluated by chlorophyll a fluorescence

The effects of ultraviolet-B (UV-B) radiation on photosystem II (PS II) were studied in leaves of Chenopodium album. After the treatment with UV-B the damage was estimated using chlorophyll a fluorescence techniques. Measurements of modulated fluorescence using a pulse amplitude modulated fluorometer revealed that the efficiency of photosystem II decreased both with increasing time of UV-B radiation and with increasing intensity of the UV-B. Fluorescence induction rise curves were analyzed using a mechanistic model of energy trapping. It appears that the damage by UV-B radiation occurs first at the acceptor side of photosystem II, and only later at the donor side.

Solar ultraviolet-B radiation increases phenolic content and ferric reducing antioxidant power in Avena sativa

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-320 nm) on the maximum photochemical efficiency of photosystem II (F(v)/F(m)), bulk-soluble phenolic concentrations, ferric-reducing antioxidant power (FRAP) and growth of Avena sativa. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B by either 71% (reduced UV-B) or by 19% (near-ambient UV-B) over the 52 day experiment (04 July-25 August 2002). Plants growing under near-ambient UV-B had 38% less total biomass than those under reduced UV-B. The reduction in biomass was mainly the result of a 24% lower leaf elongation rate, resulting in shorter leaves and less total leaf area than plants under reduced UV-B. In addition, plants growing under near-ambient UV-B had up to 17% lower F(v)/F(m) values early in the experiment, and this effect declined with plant age. Concentrations of bulk-soluble phenolics and FRAP values were 17 and 24% higher under near-ambient UV-B than under reduced UV-B, respectively. There was a positive relationship between bulk-soluble phenolic concentrations and FRAP values. There were no UV-B effects on concentrations of carotenoids (carotenes + xanthophylls).

Effects of UV irradiation on barley and tomato leaves: thermoluminescence as a method to screen the impact of UV radiation on crop plants

The effect of different UV intensities and irradiation times on barley and tomato leaves was investigated by analysis of thermoluminescence (TL) and chlorophyll (chl) fluorescence measurements. Epifluorescence microscopy was used to estimate the epidermal UV transmittance of leaves. In barley a strong supression of TL emission from the S₂Q_B^- (B-band) and the S₂Q_A^- (Q-band) charge recombination was observed increasing with prolonged UV exposure. Primary barley leaves were more sensitive to UV than secondary leaves. In tomato plants a decrease in the B-band only takes place at very high UV intensities and after prolonged exposure times (4 h). The impact of UV in cotyledons was more pronounced than in pinnate leaves of tomato plants. The strong differences in sensitivity to UV in the investigated barley and tomato variety may be due to different concentrations of UV screening pigments in the epidermal layer as demonstrated by epifluorescence measurements. The results show that TL has the same potential to analyse the sensitivity or tolerance of crop plants to UV irradiation as routine fluorescence techniques. Furthermore, TL is directly monitoring the radical pair states of PSII and can distinguish between UV-induced donor and acceptor site-related damage.