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Using dill (Anethum graveolens L.) as a model herb, we revealnovel associations between metabolite profile and sensory quality, by integrating non-target metabolomics with sensory data. Low night temperatures and exposure to UV-enriched light was used to modulate plant metabolism, thereby improving sensory quality. Plant age is a crucial factor associated with accumulation of dill ether and α-phellandrene, volatile compounds associated with dill flavour. However, sensory analysis showed that neither of these compounds has any strong association with dill taste. Rather, amino acids alanine, phenylalanine, glutamic acid, valine, and leucine increased in samples exposed to eustress and were positively associated with dill and sour taste. Increases in amino acids and organic acids changed the taste from lemon/grass to a more bitter/pungent dill-related taste. Our approach reveals a novel approach to establish links between effects of eustressors on sensory quality, and may be applicable to a broad range of crops., Funding Agencies:Faculty for Business, Science and Technology at Örebro University Örebro University Vice Chancellor's strategic research programme on 'Food and Health' Science Foundation Ireland S16/IA/4418

Ultraviolet (UV) light induces a stocky phenotype in many plant species. In this study, we investigate this effect with regard to specific UV wavebands (UV-A or UV-B) and the cause for this dwarfing. UV-A- or UV-B-enrichment of growth light both resulted in a smaller cucumber (Cucumis sativus L.) phenotype, exhibiting decreased stem and petiole lengths and leaf area (LA). Effects were larger in plants grown in UV-B- than in UV-A-enriched light. In plants grown in UV-A-enriched light, decreases in stem and petiole lengths were similar independent of tissue age. In the presence of UV-B radiation, stems and petioles were progressively shorter the younger the tissue. Also, plants grown under UV-A-enriched light significantly reallocated photosynthates from shoot to root and also had thicker leaves with decreased specific LA. Our data therefore imply different morphological plant regulatory mechanisms under UV-A and UV-B radiation. There was no evidence of stress in the UV-exposed plants, neither in photosynthetic parameters, total chlorophyll content, or in accumulation of damaged DNA (cyclobutane pyrimidine dimers). The abscisic acid content of the plants also was consistent with non-stress conditions. Parameters such as total leaf antioxidant activity, leaf adaxial epidermal flavonol content and foliar total UV-absorbing pigment levels revealed successful UV acclimation of the plants. Thus, the UV-induced dwarfing, which displayed different phenotypes depending on UV wavelengths, occurred in healthy cucumber plants, implying a regulatory adjustment as part of the UV acclimation processes involving UV-A and/or UV-B photoreceptors., Funding agencies:Science Foundation Ireland (S16/IA/4418)Flemish Science Foundation (FWO, grant G000515N)China Scholarship Council (CSC no. 201406320076)

Conspecific negative density dependence in tree species can have major consequences for structuring of communities, yet in temperate forests this phenomenon remains largely unexplored. We investigated density-dependent recruitment in the long-lived conifer yew (Taxus baccata L.), for which low levels of regeneration have been linked with reduced light availability beneath conspecific canopies and speculative autotoxic effects. We combined in situ assessment of yew regeneration in a temperate forest in southwest Ireland with ex situ pot experiments to assess whether light and/or beneath conspecific canopy conditions inhibit the germination and early growth of yew. In field experiments, recruitment was related to distance from adult conspecifics, with higher levels of regeneration found in areas not beneath yew canopies. However, reduced light availability beneath the dense yew canopy was not responsible for this pattern, with abundant seedlings found in areas of equivalent or even lower light availability. Pot experiments showed that seedling survival was highest in deep shade treatments. Experiments also demonstrated that the addition of yew needles negatively affected seedling growth, but not seed germination. Together, our results suggest that under natural forest conditions, the absence of regeneration beneath mature yew canopies, often attributed to low light availability, may at least be partly related to substances in yew canopy or leaf leachates.

UVB radiation is biologically active; in plants, it can induce a range of molecular, biochemical, morphological and developmental responses. Although much progress has been made in elucidating UVB perception and signalling pathways under controlled laboratory conditions, understanding of the adaptive, ecological role of UVB responses is still very limited. In this study, we looked at the functional role of UVR8 under outdoor light conditions, by studying growth, photosynthetic competence and accumulation of UV absorbing pigments in a mutant lacking functional UVR8 protein. It was found that the influence of UVB on morphology is restricted to summer and is independent of UVR8. In contrast, UVB had an effect on the content of UV-absorbing pigments and the maximal efficiency of photosystem II of photosynthesis in the uvr8-1 mutant throughout the year. It is concluded that the UVR8 photoreceptor plays a role throughout the year, in the temperate climate zone, even when UVB levels are relatively low.

Invasive alien plant species are usually characterized by a growth rate higher than their native competitors, and this higher rate can be achieved through the opportunistic use of plant nutrients. The growth of the invasive alien duckweed Lemna minuta and the co-generic native Lemna minor were compared under different conditions of nutrient availability. The two species were grown for one week under fully controlled conditions on medium containing increasing concentrations of NO3−-N, NH4+-N and PO43—P. The effects of different concentrations and ratios of Ca and Mg on growth were also determined. At the end of the experiment the Relative Growth Rate (RGR) of the plants was calculated on the basis of the biomass and number of fronds. The data highlighted that Lemna minuta outgrew L. minor under conditions of high phosphate supply while, when phosphate concentrations in the medium were low, it grew less than L. minor. However, L. minuta is not simply an opportunistic species as we observed relative tolerance to imbalances in Ca-Mg ratio in the growth medium. The different responses observed when the L. minor and L. minuta were grown at specific concentrations of P, Ca and Mg suggest that these elements are potential determinants of the invasibility of freshwaters and that they should be considered in future field studies.

Lemna minuta Kunth is an invasive, alien duckweed that is present throughout much of Europe, where it competes with native congeneric Lemna minor Linnaeus. Previously, L. minuta was found to grow faster than L. minor. The aim of this study was to determine whether the rapid growth of invasive L. minuta is based on differential light utilisation. For this purpose, the growth performance of L. minuta was compared with that of L. minor under a range of different light intensities. Both physiological and morphological parameters were determined. L. minuta showed a higher Relative Growth Rate (RGR) than L. minor when grown under medium and high intensities. Further analysis showed that, at high light intensities, L. minuta has a higher Net Assimilation Rate (NAR), and displays more photochemical quenching (qP) and a higher quantum yield (Y(II)) than L. minor. In contrast under low light intensities L. minor displayed a marginally higher RGR, due to a greater Leaf Area Ratio (LAR), and higher chlorophyll content than L. minuta. The results indicate two distinct light utilisation strategies, and reveal that the invasive species L. minuta takes more advantage from high intensity light conditions. In turn, this may influence plant distribution and, consequently, ecosystem management by relevant authorities.

A substantial number of Lemnaceae are invasive outside their natural distribution area. Lemna minuta is considered invasive in several European countries, where it can occur in the same habitat as invasive Azolla filiculoides and native Lemna minor. In this study the presence, abundance and growth rates of all three species were monitored across 24 natural ponds and in a series of mesocosms in order to explore the importance of species invasiveness and habitat invisibility. Field monitoring showed that the distribution of the three species of macrophytes is heterogeneous in space and time. However, the data show no association of nutrient or light levels with plant distribution. Indeed, using reciprocal transplanting experiments it was demonstrated that all species are able to grow in all ponds, even ponds where the species do not naturally occur. It is concluded that distribution of L. minor, L. minuta, and A. filiculoides is not limited by the prevailing physicochemical characteristics of the ponds during the summer period. Remarkably, in these experiments A. filiculoides displayed the highest RGR, and exerted a negative influence on growth rates and surface cover of L. minor and L. minuta. Despite such apparent invasiveness, A. filiculoides was relatively rare in the study area. Rather, the species most abundant was L. minor which has the lowest RGR under field conditions in summer. Therefore, this study shows that the invasiveness of the species during the summer months is not necessarily reflected in the actual distribution pattern in natural ponds. In fact, alien L. minuta and A. filiculoides are under-represented in the monitored area. It is concluded that the interaction of several factors, including growth under winter-conditions and/or dispersal after disturbances, is the major determinant of the abundance and heterogeneous distribution of L. minor, L. minuta, and A. filiculoides in the study area.

Primary producers exposed to ultraviolet (UV) radiation accumulate a range of metabolites as part of their UV-acclimation response. These metabolites play an important role in plant and algal UV protection. We investigated whether UV protection is transferred to consumers that feed on UV-acclimated algal biomass and showed that the copepod Tigriopus brevicornis (O. F. Muller, 1776) displays increased UV tolerance when fed on UV-acclimated Enteromorpha sp. (Clorophyta). We conclude that dietary transfer of metabolites produced in UV-acclimated biomass underlies the increased UV protection of the copepods. The data emphasise the complexity of the effects of UV radiation on the rock pool ecosystem.

A 2-year study explored metabolic and phenotypic plasticity of sun-acclimated Vitis vinifera cv. Pinot noir leaves collected from 12 locations across a 36.69-49.98°N latitudinal gradient. Leaf morphological and biochemical parameters were analysed in the context of meteorological parameters and the latitudinal gradient. We found that leaf fresh weight and area were negatively correlated with both global and ultraviolet (UV) radiation, cumulated global radiation being a stronger correlator. Cumulative UV radiation (sumUVR) was the strongest correlator with most leaf metabolites and pigments. Leaf UV-absorbing pigments, total antioxidant capacities, and phenolic compounds increased with increasing sumUVR, whereas total carotenoids and xanthophylls decreased. Despite of this reallocation of metabolic resources from carotenoids to phenolics, an increase in xanthophyll-cycle pigments (the sum of the amounts of three xanthophylls: violaxanthin, antheraxanthin, and zeaxanthin) with increasing sumUVR indicates active, dynamic protection for the photosynthetic apparatus. In addition, increased amounts of flavonoids (quercetin glycosides) and constitutive β-carotene and α-tocopherol pools provide antioxidant protection against reactive oxygen species. However, rather than a continuum of plant acclimation responses, principal component analysis indicates clusters of metabolic states across the explored 1,500-km-long latitudinal gradient. This study emphasizes the physiological component of plant responses to latitudinal gradients and reveals the physiological plasticity that may act to complement genetic adaptations.

Key message Photosynthetic capacity of yew needles depends primarily on light environment, with little evidence that developmental stage is a determinant photosynthetic performance. However, needle morphology is mostly determined by plant size. Abstract Populations of yew Taxus baccata are often characterized by a lack of natural regeneration and stands of this species have been afforded priority conservation status within the European Union. Light availability is known to be a key factor influencing recruitment dynamics in yew. To explore potential size-related responses to light, we investigated the distribution, photosynthetic efficiency and needle morphological traits in yew across a gradient of light availability at Atlantic oak woodland in southwest Ireland. Young plants were more common in shaded areas whereas saplings and juvenile yews were distributed in areas of higher light availability. Photosynthetic capacity of yew needles was found to depend primarily on light environment, with little evidence that the developmental stage is a determinant of photosynthetic performance. Photoinhibition was evident in needles sampled from high light environments across all demographic size classes. However, larger plants also showed particularly strong needle morphological responses (needle length, width, thickness, and specific leaf area) to light levels, which were mostly lacking in seedlings. We conclude that there is a dual control of yew light responses; the efficiency of the photosynthetic light reactions is largely linked to the light environment in which the plants grew, while needle morphology is mostly determined by the size of the plants. The findings of this study highlight the importance of considering all life-history stages and multiple traits when evaluating species response to light availability.

The chemical form and content of available nitrogen (N) in salt marsh substrates varies considerably. On the western coast of Ireland, habitats designated as Ombrogenic Atlantic salt marshes were formed on ombrogenic peat substrate. The peat substrate in these systems has three times more ammonium than substrate from adjacent salt marsh habitats on sand and mud substrate. This study examined the extent to which the high concentration of ammonium in peat salt marsh substrate influences the N- assimilating enzyme activity of halophytes and the extent to which N metabolism differs between species. Specifically, this work investigated whether plants from peat salt marshes are more likely to assimilate ammonium than plants from non-peat substrates. Four halophyte plant species—Armeria maritima, Aster tripolium, Plantago maritime, and Triglochin maritime—were sampled from various saltmarsh habitats including three sites on peat substrate and three on non-peat substrate, comprising sand, mud and sand/mud. The activities of N-metabolising enzymes—glutamine synthetase (GS), glutamate synthase, glutamate dehydrogenase (GDH), and nitrate reductase (NR)—were quantified in shoot and root parts. Root GS activity in Armeria maritima and shoot GS activity in Triglochin maritima were positively correlated with increasing soil ammonium levels. Root NR activity in Aster tripolium and shoot NR activity in Plantago maritima were significantly higher in plants grown on non-peat substrates than peat substrates. The shoot : root GS activity ratio in Triglochin maritima on peat substrate was more than double the ratio on non-peat substrates. It is concluded that all species tested displayed differences in N-metabolising activities depending on the chemical form and/or concentration of N in the substrate, while three out of the four species were capable of taking advantage of the high levels of ammonium in peat substrates.

There is a need to reappraise the effects of UV-B radiation on plant morphology in light of improved mechanistic understanding of UV-B effects, particularly elucidation of the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor. We review responses at cell and organismal levels, and explore their underlying regulatory mechanisms, function in UV protection and consequences for plant fitness. UV-induced morphological changes include thicker leaves, shorter petioles, shorter stems, increased axillary branching and altered root:shoot ratios. At the cellular level, UV-B morphogenesis comprises changes in cell division, elongation and/or differentiation. However, notwithstanding substantial new knowledge of molecular, cellular and organismal UV-B responses, there remains a clear gap in our understanding of the interactions between these organizational levels, and how they control plant architecture. Furthermore, despite a broad consensus that UV-B induces relatively compact architecture, we note substantial diversity in reported phenotypes. This may relate to UV-induced morphological changes being underpinned by different mechanisms at high and low UV-B doses. It remains unproven whether UV-induced morphological changes have a protective function involving shading and decreased leaf penetration of UV-B, counterbalancing trade-offs such as decreased photosynthetic light capture and plant-competitive abilities. Future research will need to disentangle seemingly contradictory interactions occurring at the threshold UV dose where regulation and stress-induced morphogenesis overlap.

Macrophytes contribute significantly to the cycling of metals in aquatic systems, through accumulation during growth and release during herbivory or decomposition. Accumulation of high levels of metals has been extensively documented in Lemnaceae (duckweeds). However, the degree of trophic transfer of metals from Lemnaceae to secondary consumers remains poorly understood. This study demonstrates that zinc accumulated in Lemna minor is bioavailable to the herbivore consumer Gammarus pulex. Overall, the higher the zinc content of L. minor, the more zinc accumulated in G. pulex. Accumulation in G. pulex was such that mortality occurred when they were fed high zinc-containing L. minor. Yet, the percentage of consumed zinc retained by G. pulex actually decreased with higher zinc concentrations in L. minor. We hypothesise that this decrease reflects internal zinc metabolism, including a shift from soluble to covalently bound zinc in high zinc-containing L. minor. Consistently, relatively more zinc is lost through depuration when G. pulex is fed L. minor with high zinc content. The developed Lemna-Gammarus system is simple, easily manipulated, and sensitive enough for changes in plant zinc metabolism to be reflected in metal accumulation by the herbivore, and therefore suitable to study ecologically relevant metal cycling in aquatic ecosystems.

Ultraviolet-A radiation (UV-A: 315–400 nm) 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.

Ombrogenic Atlantic salt marshes are defined as areas of halophytic, terrestrial vegetation which are periodically flooded by the tide and have a predominant underlying organic substrate comprising of wood and/or Sphagnum peat that formed under freshwater conditions. The objective of this study was to determine to what extent salt marsh plant ecology and, specifically, vegetation composition and zonation relate to this underlying substrate of organic matter (peat). A vegetation survey was carried out on nine salt marshes, three on peat substrate and two on sand, mud and sand/mud, respectively. In parallel, key edaphic variables were measured including pH, conductivity, organic content, moisture content and nutrients: ammonium, nitrate and phosphorus. Salt marshes on peat substrate are distinct. Ammonium content was twice the maximum reported in other salt marsh studies, while the vegetation composition of salt marshes on peat substrate was significantly different from that of other salt marshes. Salt marshes on peat substrate were found to be higher in species diversity and richness and characterised by a predominantly forb and rush community. However, some common salt marsh species, such as Atriplex portulacoides and Spartina anglica were absent from salt marshes on peat. Ordination analysis revealed that zonation was primarily associated with conductivity on peat substrates. In contrast, moisture plays a greater role in zonation within non-peat salt marshes. The findings confirm that the high organic matter content of ombrogenic Atlantic salt marshes is associated with distinct vegetation composition.

Pronounced altitudinal and latitudinal UV-B gradients exist across the earth. Therefore, we hypothesised thatplants from different geographic origins differ in the regulation and/or magnitude of UV-protection. EightArabidopsis accessions with different geographic origins (altitude between 32 and 3016 m) were raised underPhotosynthetic Active Radiation (PAR), PAR + UV-A or PAR + UV-A + UV-B radiation for 10 days, afterwhich UV-B protection of photosynthesis was assessed by measuring the consequences of exposure to a pulseof acute UV-B. We found significant variation in UV-B protection among accessions exposed to PAR or PAR +UV-A. Yet, all accessions raised under PAR + UV-A + UV-B were well protected. Thus, differences betweenaccessions are not about UV-B protection per se, but rather about regulation of UV-B protection which variesfrom constitutive to inducible by UV-A and/or UV-B. Particularly striking are differential UV-A responses,whereby some high altitude accessions lack UV-A regulated accumulation of UV-absorbing pigments, but showa strong UV-A induced m

Chlorophyll-a fluorescence is an effective tool for measuring photosynthesis. Photosynthesis is particularly sensitive to the presence of zinc or other metals. Plant age and developmental stage strongly influence the effects of metals on the photosynthetic apparatus. However, there is little information on how this may affect toxicological assessment in plants. In this study, three Lemnaceae species were exposed to a range of zinc concentration in static, batch exposures for seven days, as detailed for Lemnaceae toxicity testing in OECD guidelines. Effects of zinc on photosynthetic performance in the three species were measured over the seven days. The maximum quantum efficiency of photosystem II, Fv/Fm, the effective quantum efficiency, Y(II), and photochemical quenching, qP, were measured in mature and young fronds, as well as along a developmental gradient within fronds. Fv/Fm and Y(II) in young, emerging Landoltia punctata fronds were more severely impacted by zinc than in developed, mature fronds. Furthermore, younger proximal sections of L. punctata fronds were more impacted than older distal frond sections. Overall, Fv/Fm and Y(II) also tended to be more affected by zinc in young, compared to mature, Lemna gibba and Lemna minor fronds. Single colony, time-point or leaf-zone analyses may not, therefore, show the full biological picture of the impact of a toxicant, while species-specific differences need also to be considered. Therefore, selection of Lemnaceae species and developmental stages of fronds should be given careful consideration when using chlorophyll-a fluorometry for assessing chemical toxicity in Lemnaceae.

Epidemiological studies have revealed an inverse association between the consumption of fruit, vegetables, and herbs and the risk of both cancer and cardiovascular disease. This protective effect is mostly due to secondary metabolites present in plant tissues. During the last decade, it has become increasingly clear that UV-B radiation is an important regulator of plant secondary metabolism. Low, ecologically-relevant UV-B levels trigger distinct changes in the accumulation of, among others, phenolic compounds, carotenoids and glucosinolates. Fundamental understanding of plant UV-B perception and responses opens up new opportunities for crop manipulation. Thus, targeted low dosage UV-B radiation treatments as emerging technology may be used to generate fruit, vegetables, and herbs enriched with secondary plant metabolites for either fresh consumption or as a source for functional foods and nutraceuticals, resulting in increased ingestion of these health-promoting substances. The UV-B induced accumulation of secondary plant metabolites is likely to have evolved as a plant defense response against harmful UV-B radiation. However, UV-B induced secondary metabolites also alter other trophic interactions, for example by altering plant herbivore resistance. Thus, UV-B driven metabolic changes in the plant's secondary metabolism have benefits for both ends of the bio-based food chain, i.e., for plants themselves as well as for humans.

Lemnaceae are currently the only freshwater plants required for regulatory toxicity testing of pesticides and other chemicals. Toxicological protocols allow for the use of different Lemnaceae species in tests. However, few studies have compared the relative sensitivity of individual duckweed species. Zinc is an essential plant nutrient but is also a common pollutant in aquatic environments and elevated levels are phytotoxic. This study shows that four species of Lemnaceae differ in their relative sensitivities to zinc sulphate, a commonly used reference chemical. Comparative zinc sensitivity, in order, from most tolerant to most sensitive was: Landoltia punctata > Lemna minor > Wolffia brasiliensis > Lemna gibba. Zinc sensitivity was also endpoint dependant. EC50 values typically increased in order of: specific biomass growth rate

The rise in ultraviolet-B (UV-B) (280-315 nm) radiation levels, that is a consequence of stratospheric ozone layer depletion, has triggered extensive research on the effects of UV-B on plants. Plants raised under natural sunlight conditions are generally well protected from the potentially harmful effects of UV-B radiation. However, it is mostly unknown to which extent UV protection is constitutive and/or induced. In this study, we have analysed the role of constitutive and inducible protection responses in avoiding UV-B damage to photosystem II of photosynthesis. We have assayed the UV susceptibility of photosystem II in 224 Arabidopsis thaliana accessions from across the Northern hemisphere, and found a continuum of constitutive UV-protection levels, with some accessions being UV sensitive and others UV tolerant. Statistical analysis showed only very weak associations between constitutive UV tolerance and the geographic origin of accessions. Instead, most of the variance in constitutive UV-B protection of photosynthesis is present at the level of local Arabidopsis populations originating in the same geographic and climatic area. The variance in constitutive UV protection is, however, small compared to the amplitude of environmentally induced changes in UV protection. Thus, our data emphasise the importance of inducible responses for the protection of photosystem II against UV-B. Remarkably, the conditions that induce UV-protective responses vary; accessions from lower latitudes were found to switch-on UV defences more readily than those of higher latitudes. Such altered regulation of induction may comprise a suitable adaptation response when levels of a stressor are fluctuating in the short term, but predictable over longer periods.

Plants are sessile organisms, and consequently cannot avoid exposure to stressful environmental conditions. Exposure to mild stress conditions can induce active acclimation responses, while more severe conditions cause metabolic disruptions. A common plant acclimation response to a variety of environmental stressors is the accumulation of antioxidants and secondary metabolites. For example, ultraviolet-B (UV-B) radiation impacts on the levels of a broad range of metabolites, including phenolic, terpenoid and alkaloid compounds. Our survey of the literature reveals that the levels of some of these metabolites increase following UV-B exposure, while those of others decrease, change transiently or are differently affected by low and high UV-doses. This includes several compounds that are pharmacologically active and/or nutritionally important. We conclude that the complex patterns of stress-induced changes in plant metabolites need to be studied in more detail to determine impacts on the nutritional and pharmacological characteristics of food products. Claims that UV-B acclimated plants have nutritional benefits are currently unproven.

Ultraviolet B (UV-B) acclimation comprises complex and poorly understood changes in plant metabolism. The effects of chronic and ecologically relevant UV-B dose rates on Arabidopsis thaliana were determined. The UV-B acclimation process was studied by measuring radiation effects on morphology, physiology, biochemistry and gene expression. Chronic UV-B radiation did not affect photosynthesis or the expression of stress responsive genes, which indicated that the UV-acclimated plants were not stressed. UV-induced morphological changes in acclimated plants included decreased rosette diameter, decreased inflorescence height and increased numbers of flowering stems, indicating that chronic UV-B treatment caused a redistribution rather than a cessation of growth. Gene expression profiling indicated that UV-induced morphogenesis was associated with subtle changes in phytohormone (auxins, brassinosteroids and gibberellins) homeostasis and the cell wall. Based on the comparison of gene expression profiles, it is concluded that acclimation to low, chronic dose rates of UV-B is distinct from that to acute, stress-inducing UV-B dose rates. Hence, UV-B-induced morphogenesis is functionally uncoupled from stress responses.

Plants exposed to sub-lethal abiotic stress conditions exhibit a broad range of morphogenic responses. Despite the diversity of phenotypes, a generic 'stress-induced morphogenic response' can be recognized that appears to be carefully orchestrated and comprises three components: (a) inhibition of cell elongation, (b) localized stimulation of cell division and (c) alterations in cell differentiation status. It is hypothesized that the similarities in the morphogenic responses induced by distinct stresses, reflect common molecular processes such as increased ROS-production and altered phytohormone transport and/or metabolism. The stress-induced morphogenic response (SIMR) is postulated to be part of a general acclimation strategy, whereby plant growth is redirected to diminish stress exposure.

Exposure to ultraviolet-B radiation (UVB) radiation affects plants in multiple ways, including effects on the photosynthetic apparatus. The carbon dioxide reduction reactions are affected as well as the light reactions, especially those of photosystem II. In the literature several UVB chromophores are suggested, including redox-active tyrosines, plastosemiquinones, and the manganese cluster of the water-splitting complex. We measured the damage by UVB radiation given together with a small component of photosynthetically active radiation (PAR) in a triazine-resistant biotype and a wild-type of Chenopodium album. The damage was estimated by chlorophyll fluorescence measurements and was larger in the resistant plants. We were able to show that the concentration of the semireduced primary quinone electron acceptor of photosystem II is higher in the resistant plants, under all radiation conditions tested. This finding and additional results support the hypothesis that plastosemiquinones are photosensitizers for UVB radiation; absorption of UVB light by these quinones initiates reactions leading to damage to photosystem II.

The physiological role of class III peroxidases (EC 1.11.1.7) in controlling plant growth and development has been investigated by over-expression of both native and heterologous peroxidases. However, it has remained an enigma as to why the phenotypes of different peroxidase over-expressing transgenics vary. In order to resolve the conflicting information about the consequences of peroxidase over-expression, we have explored the role of the subcellular targeting of HRP-C in controlling stem growth, root development, axillary branching and abiotic stress tolerance in tobacco (Nicotiana tabacum L.). Altering the sub-cellular targeting of vacuolar HRP-C, such that over-expressed peroxidase accumulates in the cytoplasm and cell wall, induced phenotypic changes that are typically associated with altered auxin homeostasis, and over-expression of cell wall located peroxidases. We conclude that sub-cellular targeting is a determinant of the phenotype of peroxidase over-expressing plants.

Natural variation for photosynthetic traits was studied by determining chlorophyll fluorescence parameters in a collection of Arabidopsis accessions. This screen revealed only one single accession (Ely), exhibiting photosynthetic characteristics markedly different from all others, while a few lines showed small but significant variation. Detailed genetic and physiological analyses showed reduced fitness for Ely compared with the standard laboratory strain Ler for various growth parameters. At low temperature (15 degrees C), Ely had a higher electron transport rate than Ler, indicating increased photosystem II efficiency under this condition, while at high temperature (30 degrees C) the opposite was observed. Ely had a high sensitivity to UV-B radiation compared with Ler and was atrazine resistant. This atrazine-resistance and related chlorophyll fluorescence traits were maternally inherited, pointing towards chloroplast-located gene(s). Definite proof that Ely is atrazine-resistant was obtained by sequencing the psbA gene, encoding the D1 protein of photosystem II, revealing a point mutation causing the same amino acid change as found in other atrazine-resistant species. Additional nuclear encoded genetic variation was also present, as was concluded from the small but significant differences in phenotype between Ely and its reciprocal crosses with Ler. It was concluded that the photosynthetic yield is highly conserved and that only severe selection pressure results in marked variations in photosynthetic performance.

Plants raised under field conditions are acclimated to ambient levels of solar UV-B radiation. Morphogenic responses are part of the UV-B acclimation process and have been hypothesized to contribute to UV avoidance. UV-B induced morphogenic responses include inhibition of hypocotyl and stem elongation, leaf curling, leaf thickening and increased axillary branching. So far, neither the photosensory nor the signal transduction mechanism involved in UV-B mediated morphogenesis has been identified. The combination of classical photobiological techniques and Arabidopsis genetic resources comprises a powerful tool for the analysis of morphogenic responses. However, no morphogenic mutants, specifically altered in their response to UV-B, have yet been identified. In this paper we discuss the possibility that some UV-B driven morphogenic responses do not involve a dedicated photosensory system, but rather are a consequence of UV-B induced changes in secondary metabolism. UV-B induced flavonoid aglycones and phenol-oxidizing peroxidases can affect, respectively, polar auxin transport and auxin catabolism, and hence plant architecture. Integration of genetic, photobiological, biochemical and physiological approaches is necessary to fully appraise the ecophysiological role of UV-B radiation in controlling plant architecture.

The main objective of this study was to determine the effects of acclimation to ultraviolet (UV) and photosynthetically active radiation (PAR) on photoprotective mechanisms in barley leaves. Barley plants were acclimated for 7 days under three combinations of high or low UV and PAR treatments ([UV-PAR-], [UV-PAR+], [UV+PAR+]). Subsequently, plants were exposed to short-term high radiation ;stress (HRS; defined by high intensities of PAR - 1000 mu mol m(-2) s(-1), UV-A - 10 W m(-2) and UV-B 2 W m(-2) for 4 h), to test their photoprotective capacity. The barley variety sensitive to photooxidative stress (Barke) had low constitutive flavonoid content compared to the resistant variety (Bonus) under low UV and PAR intensities. The accumulation of lutonarin and 3-feruloylquinic acid, but not of saponarin, was greatly enhanced by high PAR and further increased by UV exposure. Acclimation of plants to both high UV and PAR intensities also increased the total pool of xanthophyll-cycle pigments (VAZ). Subsequent exposure to HRS revealed that prior acclimation to UV and PAR was able to ameliorate the negative consequences of HRS on photosynthesis. Both total contents of epidermal flavonols and the total pool of VAZ were closely correlated with small reductions in light-saturated CO2 assimilation rate and maximum quantum yield of photosystem II photochemistry caused by HRS. Based on these results, we conclude that growth under high PAR can substantially increase the photoprotective capacity of barley plants compared with plants grown under low PAR. However, additional UV radiation is necessary to fully induce photoprotective mechanisms in the variety Barke. This study demonstrates that UV-exposure can lead to enhanced photoprotective capacity and can contribute to the induction of tolerance to high radiation stress in barley. (C) 2015 Elsevier Masson SAS. All rights reserved.

Ultraviolet-B (UV-B) radiation has long been perceived as a stressor. However, a conceptual U-turn has taken place, and UV-B damage is now considered rare. We question whether UV-stress and UV-B-induced reactive oxygen species (ROS) are still relevant concepts, and if ROS-mediated signaling contributes to UV-B acclimation. Measurements of antioxidants and of antioxidant genes show that both low and high UV-B doses alter ROS metabolism. Yet, there is no evidence that ROS control gene expression under low UV-B. Instead, expression of antioxidant genes is linked to the UV RESISTANCE LOCUS 8 pathway. We hypothesize that low UVB doses cause ‘eustress’ (good stress) and that stimulispecific signaling pathways pre-dispose plants to a state of low alert that includes activation of antioxidant defenses., Funding agencies:COST Action FA0906UV4Growth Faculty of Business, Science, and Technology at Örebro University Science Foundation Ireland (SFI) 11/RFP.1/EOB/3303 Hungarian Scientific Research Fund OTKA NN-85349, UV-B-fotobiologi: mekanismer för perception och cellulära responser

Ultraviolet-B (UV-B) tolerance in plants has mostly been correlated with the presence of screening pigments (e.g. flavonoids) or other reductions in leaf transmittance. We have exploited the rapid turnover of the Photosystem II reaction center protein D1 as a sensitive in vivo probe for UV-B damage. We found that the aquatic monocot, Spirodela oligorrhiza, protects itself from UV-B irradiance using at least three different mechanisms. In one case, protection is correlated to the presence of UV-B screening pigments; in the second, an elevated oxygen-radical detoxifying system parallels UV-B tolerance; while in a third, UV-B tolerance is related to a mechanism involving neither screening pigments nor increased radical scavenging capacity. This demonstrates that, in vivo, a plant can complement its UV-screening and attenuation strategies by other tactics as well.

Low levels of ultraviolet (UV)-radiation alter the morphology of plants. UV-B exposure can lead to shorter petioles and shorter, narrower and/or thicker leaf blades. The resulting decrease in leaf area has been associated with inhibitory UV-B effects on biomass accumulation. In Arabidopsis, UV-B effects on leaf area have variously been attributed to altered cell division, cell expansion or combinations of these two processes. A dedicated UV-B sensory system, crosstalk between flavonoids and auxins, endoreduplication and generic Stress Induced Morphogenic Responses (SIMR) have all been proposed to contribute to the UV-B phenotype. Here, we propose that UV-mediated morphogenesis, rather than being controlled by a single regulatory pathway, is controlled by a regulatory blur involving multiple compensatory molecular and physiological feedback interactions.

Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europe (37–68◦N) to study the impact of ultraviolet radiation (UV) and climate on aboveground growth and foliar UV-B absorbing compounds. At each location, plants were grown outdoors for 5 weeks in a replicated UV-B filtration experiment consisting of open, UV-B transparent (cellulose diacetate) and UV-B opaque (polyester) environments. Fourier transform-infrared spectroscopy was used to compare plantmetabolite profiles in relation to treatment and location. UV radiation and climatic parameters were determined for each location from online sources and the data were assessed using a combination of ANOVA and multiple regression analyses. Most of the variation in growth between the locations was attributable to the combination of climatic parameters, with minimum temperature identified as an important growth constraint. However, no single environmental parameter could consistently account for the variability in plant growth. Concentrations of foliar UV-B absorbing compounds showed a positive trend with solar UV across the latitudinal gradient; however, this relationship was not consistent in all treatments. The most striking experimental outcome from this study was the effect of presence or absence of filtration frames onUV-absorbing compounds. Overall, the study demonstrates the value of an European approach in studying the impacts of natural UV across a large latitudinal gradient. We have shown the feasibility of coordinated UV filtration at multiple sites but have also highlighted the need for open controls and careful interpretation of plant responses., UV-B responses and signal transductory events in plants

Macrophytes provide food and shelter for aquatic invertebrates and fish, while also acting as reservoirs for nutrients and trace elements. Zinc accumulation has been reported for various Lemnaceae species. However, comparative accumulation across species and the link between zinc accumulation and toxicity are poorly understood. Morphological distribution and cellular storage, in either bound or soluble form, are important for zinc tolerance. This study shows differences in the uptake and accumulation of zinc by three duckweed species. Landoltia punctata and Lemna minor generally accumulated more zinc than Lemna gibba. L. minor, but not L. gibba or L. punctata, accumulated greater concentrations of zinc in roots compared to fronds when exposed to high levels of zinc. The proportion of zinc stored in the bound form relative to the soluble-form was higher in L. minor. L. punctata accumulated greater concentrations of zinc in fronds compared to roots and increased the proportion of zinc it stored in the soluble form, when exposed to high zinc levels. L. gibba is the only species that significantly accumulated zinc at low concentrations, and was zinc-sensitive. Overall, internal zinc concentrations showed no consistent correlation with toxic effect. We conclude that relationships between zinc toxicity and uptake and accumulation are species specific reflecting, among others, zinc distribution and storage. Differences in zinc distribution and storage are also likely to have implications for zinc bioavailability and trophic mobility.

The industrial use of nanoparticles is rapidly increasing, and this has given rise to concerns about potential biological impacts of engineered particles released into the environment. So far, relatively little is known about uptake, accumulation and responses to engineered nanoparticles by plants. In this study, the effects of alumina nanoparticles on growth, morphology and photosynthesis of Lemna minor were quantified. It was found that alumina nanoparticles substantially increase biomass accumulation of L. minor. Such a stimulatory effect of alumina nanoparticles on growth has not been reported previously. Enhanced biomass accumulation was paralleled by morphological adjustments such as increased root length and number of fronds per colony, and by increased photosynthetic efficiency. Metal nanoparticles have previously been shown to enhance the energy transfer efficiency of isolated reaction centres; therefore it is proposed that the mechanism underlying the alumina mediated enhancement of biomass accumulation in L. minor is associated with increased efficiencies in the light reactions of photosynthesis.

Inhibitors of photosystem II function have been shown to block electron flow in vitro by competitively displacing plastoquinone from the Q B niche on the D1 protein. Few studies have tested this well-accepted concept in vivo and none in higher plants. The D1 protein degradation assay was used to directly demonstrate, in vivo , the displacement of diuron by bromonitrothymol (BNT) at the level of the Q B niche. We show that diuron blocks D1 degradation less effectively in the presence of BNT, and that this effect of BNT can be nullified by increasing the diuron concentration. These data directly demonstrate binding-site competition at the level of the Q B niche, under the complex physiological conditions of the intact higher plant.

Plants have evolved a broad spectrum of mechanisms to ensure survival under changing and suboptimal environmental conditions. Alterations of plant architecture are commonly observed following exposure to abiotic stressors. The mechanisms behind these environmentally controlled morphogenic traits are, however, poorly understood. In this report, the effects of a low dose of chronic ultraviolet (UV) radiation on leaf development are detailed. Arabidopsis rosette leaves exposed for 7, 12, or 19 d to supplemental UV radiation expanded less compared with non-UV controls. The UV-mediated decrease in leaf expansion is associated with a decrease in adaxial pavement cell expansion. Elevated UV does not affect the number and shape of adaxial pavement cells, nor the stomatal index. Cell expansion in young Arabidopsis leaves is asynchronous along a top-to-base gradient whereas, later in development, cells localized at both the proximal and distal half expand synchronously. The prominent, UV-mediated inhibition of cell expansion in young leaves comprises effects on the early asynchronous growing stage. Subsequent cell expansion during the synchronous phase cannot nullify the UV impact established during the asynchronous phase. The developmental stage of the leaf at the onset of UV treatment determines whether UV alters cell expansion during the synchronous and/or asynchronous stage. The effect of UV radiation on adaxial epidermal cell size appears permanent, whereas leaf shape is transiently altered with a reduced length/width ratio in young leaves. The data show that UV-altered morphogenesis is a temporal- and spatial-dependent process, implying that common single time point or single leaf zone analyses are inadequate.

Chlorinated phenols, or chlorophenols, are persistent priority pollutants that are widespread in the environment. Class III peroxidases are well-characterised plant enzymes that can catalyse the oxidative dechlorination of chlorophenols. Expression of these enzymes by plants is commonly associated with plant stress, therefore limiting scope for phytoremediation. In this study, we have quantitatively compared peroxidase activity and phytotoxicity as a function of 2,4,6-trichlorophenol (TCP) concentration in three species of Lemnaceae; Lemna minor, Lemna gibba and Landoltia punctata. Effects of TCP on the growth rates of the three species differed considerably with L. punctata being the most tolerant species. TCP also affected photosynthetic parameters, causing a decrease in open photosystem II reaction centres (qP) and, in L. punctata only, a decrease in non-photochemical quenching (qN). In parallel, TCP exposure resulted in increased peroxidase activity in all three species. Peroxidase activity in L. minor and L. gibba displayed an inverse relationship with biomass accumulation, i.e. the more growth reduction the more peroxidase activity. In contrast, induction of peroxidase activity in L. punctata was bi-phasic, with a TCP-induced activity peak at concentrations that had no major effect on growth, and further induction under phytotoxic concentrations. The mechanism by which L. punctata recognises and responds to low concentrations of an anthropogenic compound, in the absence of wide-ranging stress, remains enigmatic. However, we conclude that this "window" of peroxidase production in the absence of major growth inhibition offers potential for the development of sustainable, peroxidise-mediated phytoremediation systems.

The decay of chlorophyll variable fluorescence after a “single turnover” flash is generally assumed to represent the reoxidation of the reduced quinone Qa. We have observed that the kinetics of this decay are very similar in a wide variety of species. Comparing 28 different species, we found an average half decay time of 314 ± 46 μsec. No systematic correlations were found between the decay rate and biochemical or physiological specializations such as C2, C4 or CAM. This indicates that structural as well as functional factors controlling photosystem II electron transfer between Qa and Qb are highly conserved. Apparently, the freedom for natural structural variations in this region is very limited. Triazine resistant plants, characterized by an altered amino acid sequence of the D1 protein, have clearly decreased rates of Qa/Qb electron transfer. We found an average half decay time of 946 ± 100 (isec (5 species). However, this three-fold decrease is much less than previously reported. Therefore, if alterations of photosystem II electron transfer efficiency contributes to an often reported reduction of “ecological fitness”, this contribution is smaller than was hitherto assumed.

A few species have evolved resistance to paraquat after repeated selection. As paraquat still inhibited NADP reduction, we hypothesized that resistance might be due to (a) detoxification of the paraquat-generated active oxygen species and (b) that resistant plants would have some cross resistance to other xenobiotic oxidants as well as to photoinhibition, which we subsequently demonstrated. The levels of plastid isozymes of the oxygen detoxification pathway: (CuZn) superoxide dismutase, ascorbate peroxidase and glutathione reductase were genetically higher in the resistant than in the sensitive biotype of Conyza bonariensis through the F2 generation. Resistance was suppressed by chelators of copper and/or zinc. Intact chloroplasts from resistant plants had less membrane damage with and without paraquat, than those from sensitive plants. Resistant Conyza plants recover from paraquat inhibition of photosynthesis in 3-4 h in high light, whereas sensitive plants died. Both resistant and sensitive plants recovered from paraquat in 3-4 h in low light intensities. Paraquat-resistant Conyza plants were cross-tolerant to SO2, atrazine, acifluorfen and to photoinhibition. Drought-tolerant maize inbreds were cross-tolerant to paraquat, SO2 and acifluorfen (compared to sensitive lines) and they also possessed higher levels of (Cu/Zn) superoxide dismutase and glutathione reductase. The tolerance to oxidant stresses in Conyza and maize increases with plant age, suggesting that the shift to resistance is a constitutive, earlier expression of the genes normally expressed later in development.

Tocopherols and tocotrienols are present in mature seeds. Yet, little is known about the physiological role and the metabolism of these compounds during seed development. Here we present data on tocopherol and tocotrienol accumulation during seed development in Vitis vinifera L. cv. Albert Lavallee (Royal). This species was chosen for its ability to synthesize both tocopherols and tocotrienols. It is shown here for the first time that during seed development there are significant differences in localization and accumulation kinetics of tocopherols and tocotrienols. Tocopherols are found homogeneously dispersed throughout all tissues of the seed, in concentrations ranging from 20 to 100 microg tocopherol per g dry weight. Tocopherol levels decrease gradually during seed development. In contrast, tocotrienols are only found in the endosperm of the seeds, accumulating in a sigmoid fashion during the maturation period of seed development. Tocotrienol levels were found to be (54+/-7.4) microg/g dry seed in 90-day-old seeds of V. vinifera L. Furthermore, tocotrienol biosynthesis is demonstrated in these seeds during tocotrienol accumulation and in an endosperm fraction isolated at 75 days after flowering.

We have studied the mechanism of UV protection in two duckweed species (Lemnaceae) by exploiting the UV sensitivity of photosystem II as an in situ sensor for radiation stress. A UV-tolerantSpirodela punctata G.F.W. Meyer ecotype had significantly higher indole-3-acetic acid (IAA) levels than a UV-sensitive ecotype. Parallel work on Lemna gibbamutants suggested that UV tolerance is linked to IAA degradation rather than to levels of free or conjugated IAA. This linkage is consistent with a role for class III phenolic peroxidases, which have been implicated both in the degradation of IAA and the cross-linking of various UV-absorbing phenolics. Biochemical analysis revealed increased activity of a specific peroxidase isozyme in both UV-tolerant duckweed lines. The hypothesis that peroxidases play a role in UV protection was tested in a direct manner using genetically modified tobacco (Nicotiana sylvestris). It was found that increased activity of the anionic peroxidase correlated with increased tolerance to UV radiation as well as decreased levels of free auxin. We conclude that phenol-oxidizing peroxidases concurrently contribute to UV protection as well as the control of leaf and plant architecture.

Both visible and UV wavelengths play an important role in controlling stomatal aperture. We have analysed effects of UV-B radiation on stomatal aperture in Vicia faba, and found them to be complex. Depending on the metabolic state of the guard cell, high fluences of UV-B either stimulate stomatal opening or stomatal closing. Neither of these responses is readily reversed, i.e. once stomata have been exposed to UV-B, they are unable to re-adjust their aperture in response to environmental stimuli like changes in light, humidity or ABA, This lack of responsiveness is unlikely to be due to widespread cellular damage, as UV-induced stomatal closure is largely reverted in response to the H + -ATPase activator fusicoccin. It is speculated that UV-B impacts upstream from the plasmalemma based enzyme complexes which facilitate the solute fluxes leading to stomatal opening. Our data may help accommodate seemingly contradictory reports on the effects of UV-B on stomatal aperture and/or conductance.

Ultraviolet-B (UV-B) radiation negatively impacts on plant growth and development. Not all plants are UV sensitive: strong tolerance to UV-B radiation is particularly found among plants that naturally occur in areas of high UV-B radiation. There is limited knowledge about the mechanisms underlying such enhanced natural tolerance. In this study, we demonstrate strong differences in UV-B tolerance among Spirodela punctata ecotypes. Tolerance is visualized as sustained photosystem II (PSII) activity and biomass accumulation in fronds exposed to UV-B radiation. We find that the enhanced tolerance is constitutive and specific for UV-radiation stress, but it does not correlate with well-characterized UV-adaptation responses like the accumulation of bulk UV-screening pigments in the epidermis, or increased oxygen radical scavenging activity.