Composition and Properties of Hydrogen Peroxide Decomposing Systems in Extracellular and Total Extracts from Needles of Norway Spruce (Picea abies L., Karst.)

Integrative multi-omics analyses of date palm (Phoenix dactylifera) roots and leaves reveal how the halophyte land plant copes with sea water

Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.

Blue and Red LED Lights Differently Affect Growth Responses and Biochemical Parameters in Lentil (Lens culinaris)

Light-emitting diodes are an attractive tool for improving the yield and quality of plant products. This study investigated the effect of different light intensity and spectral composition on the growth, bioactive compound content, and antioxidant metabolism of lentil (Lens culinaris Medik.) seedlings after 3 and 5 days of LED treatment. Two monochromatic light quality × three light intensity treatments were tested: red light (RL) and blue light (BL) at photosynthetic photon flux density (PPFD) of 100, 300, and 500 μmol m-2 s-1. Both light quality and intensity did not affect germination. At both harvest times, the length of seedling growth under BL appeared to decrease, while RL stimulated the growth with an average increase of 26.7% and 62% compared to BL and seedlings grown in the darkness (D). A significant blue light effect was detected on ascorbate reduced form, with an average increase of 35% and 50% compared to RL-grown plantlets in the two days of harvesting, respectively. The content of chlorophyll and carotenoids largely varied according to the wavelength and intensity applied and the age of the seedlings. Lipid peroxidation increased with increasing light intensity in both treatments, and a strong H2O2 formation occurred in BL. These results suggest that red light can promote the elongation of lentil seedlings, while blue light enhances the bioactive compounds and the antioxidant responses.

Multi-omics analysis of xylem sap uncovers dynamic modulation of poplar defenses by ammonium and nitrate

Xylem sap is the major transport route for nutrients from roots to shoots. In the present study, we investigated how variations in nitrogen (N) nutrition affected the metabolome and proteome of xylem sap and the growth of the xylem endophyte Brennaria salicis, and we also report transcriptional re-wiring of leaf defenses in poplar (Populus × canescens). We supplied poplars with high, intermediate or low concentrations of ammonium or nitrate. We identified 288 unique proteins in xylem sap. Approximately 85% of the xylem sap proteins were shared among ammonium- and nitrate-supplied plants. The number of proteins increased with increasing N supply but the major functional categories (catabolic processes, cell wall-related enzymes, defense) were unaffected. Ammonium nutrition caused higher abundances of amino acids and carbohydrates, whereas nitrate caused higher malate levels in xylem sap. Pipecolic acid and N-hydroxy-pipecolic acid increased, whereas salicylic acid and jasmonoyl-isoleucine decreased, with increasing N nutrition. Untargeted metabolome analyses revealed 2179 features in xylem sap, of which 863 were differentially affected by N treatments. We identified 124 metabolites, mainly from specialized metabolism of the groups of salicinoids, phenylpropanoids, phenolics, flavonoids, and benzoates. Their abundances increased with decreasing N, except coumarins. Brennaria salicis growth was reduced in nutrient-supplemented xylem sap of low- and high- NO₃^- -fed plants compared to that of NH₄⁺ -fed plants. The drastic changes in xylem sap composition caused massive changes in the transcriptional landscape of leaves and recruited defenses related to systemic acquired and induced systemic resistance. Our study uncovers unexpected complexity and variability of xylem composition with consequences for plant defenses.

Physiological and Biochemical Traits of Two Major Arabidopsis Accessions, Col-0 and Ws, Under Salinity

Salinity affects plant growth and development as shown with the glycophyte model plant, Arabidopsis thaliana (Arabidopsis). Two Arabidopsis accessions, Wassilewskija (Ws) and Columbia (Col-0), are widely used to generate mutants available from various Arabidopsis seed resources. However, these two ecotypes are known to be salt-sensitive with different degrees of tolerance. In our study, 3-week-old Col-0 and Ws plants were treated with and without 150 mM NaCl for 48, 72, or 96 h, and several physiological and biochemical traits were characterized on shoots to identify any specific traits in their tolerance to salinity. Before salt treatment was carried out, a different phenotype was observed between Col-0 and Ws, whose main inflorescence stem became elongated in contrast to Col-0, which only displayed rosette leaves. Our results showed that Col-0 and Ws were both affected by salt stress with limited growth associated with a reduction in nutrient uptake, a degradation of photosynthetic pigments, an increase in protein degradation, as well as showing changes in carbohydrate metabolism and cell wall composition. These traits were often more pronounced in Col-0 and occurred usually earlier than in Ws. Tandem Mass Tags quantitative proteomics data correlated well with the physiological and biochemical results. The Col-0 response to salt stress was specifically characterized by a greater accumulation of osmoprotectants such as anthocyanin, galactinol, and raffinose; a lower reactive oxygen detoxification capacity; and a transient reduction in galacturonic acid content. Pectin degradation was associated with an overaccumulation of the wall-associated kinase 1, WAK1, which plays a role in cell wall integrity (CWI) upon salt stress exposure. Under control conditions, Ws produced more antioxidant enzymes than Col-0. Fewer specific changes occurred in Ws in response to salt stress apart from a higher number of different fascilin-like arabinogalactan proteins and a greater abundance of expansin-like proteins, which could participate in CWI. Altogether, these data indicate that Col-0 and Ws trigger similar mechanisms to cope with salt stress, and specific changes are more likely related to the developmental stage than to their respective genetic background.

Foliar traits of sessile oak (Quercus petraea Liebl) seedlings are largely determined by site properties rather than seed origin

Due to climate change, sessile oak (Quercus petraea) seedlings experience an increasing risk of drought during regeneration of forest stands by management practices. The present study was aimed at elucidating the potential of sessile oak seedlings originating from sites with different aridity and nitrogen (N) supply to acclimate to contrasting water availability. For this purpose, a free-air cross-exchange experiment was conducted between a dry and a humid forest stand with high and low soil N contents, respectively, during two consecutive years differing in aridity before harvest. Almost all structural and physiological foliar traits analyzed did not differ consistently between seed origins during both years, when cultivated at the same site. As an exception, the arid provenance upregulated foliar ascorbate contents under drought, whereas the humid provenance accumulated the phenolic antioxidants vescalagin and castalagin (VC) under favorable weather conditions and consumed VC upon drought. Apparently, differences in long-term aridity at the forest sites resulted in only few genetically fixed differences in foliar traits between the provenances. However, structural and physiological traits strongly responded to soil N contents and weather conditions before harvest. Foliar N contents and their partitioning were mostly determined by the differences in soil N availability at the sites, but still were modulated by weather conditions before harvest. In the first year, differences in aridity before harvest resulted in differences between most foliar traits. In the second year, when weather conditions at both sites were considerably similar and more arid compared to the first year, differences in foliar traits were almost negligible. This pattern was observed irrespective of seed origin. These results support the view that leaves of sessile oak seedlings generally possess a high plasticity to cope with extreme differences in aridity by immediate acclimation responses that are even better developed in plants of arid origin.

Characterisation of Bioactive Ingredients in Extracts of Fresh and Dried Coniferous Trees for the Development of Sustainable Packaging Materials

Background: Coniferous woods (Abies nordmanniana (Stev.) Spach, Abies procera Rehd, Picea abies (L.) H.Karst, and Picea pungens Engelm.) could contain useful secondary metabolites to produce sustainable packaging materials, e.g., by substitution of harmful petrol-based additives in plastic packaging. This study aims to characterise the antioxidant and light-absorbing properties and ingredients of different coniferous wood extracts with regard to different plant fragments and drying conditions. Furthermore, the valorisation of used Christmas trees is evaluated. Methods: Different drying and extraction techniques were applied with the extracts being characterised by determining the total phenolic content (TPC), total antioxidant capacity (TAC), and absorbance in the ultraviolet range (UV). Gas chromatography coupled with mass spectrometry (GC-MS) and an acid–butanol assay (ABA) were used to characterise the extract constituents. Results: All the extracts show a considerably high UV absorbance while interspecies differences did occur. All the fresh and some of the dried biomass extracts reached utilisable TAC and TPC values. A simplified extraction setup for industrial application is evaluated; comparable TAC results could be reached with modifications. Conclusion: Coniferous woods are a promising renewable resource for preparation of sustainable antioxidants and photostabilisers. This particularly applies to Christmas trees used for up to 12 days. After extraction, the biomass can be fully valorised by incorporation in paper packaging.

Transporters and ascorbate-glutathione metabolism for differential cadmium accumulation and tolerance in two contrasting willow genotypes

Salix matsudana Koidz is a low cadmium (Cd)-accumulating willow, whereas its cultivated variety, Salix matsudana var. matsudana f. umbraculifera Rehd., is a high Cd-accumulating and tolerant willow (HCW). The physiological and molecular mechanisms underlying differential Cd accumulation and tolerance in the two Salix species are poorly understood. Here, we confirmed that the differential Cd translocation capacity from roots to the shoots leads to the differential Cd accumulation in their aboveground parts between these two willow genotypes. Cadmium accumulation happens preferentially in the transport pathway, and Cd is mainly located in the vacuolar, cell wall and intercellular space in HCW bark by cadmium location analysis at tissue and subcellular levels. Comparative transcriptome analysis revealed that higher expressions of several metal transporter genes (ATP-binding cassette transporters, K+ transporters/channels, yellow stripe-like proteins, zinc-regulated transporter/iron-regulated transporter-like proteins, etc.) are involved in root uptake and translocation capacity in HCW; meanwhile, ascorbate-glutathione metabolic pathways play essential roles in Cd detoxification and higher tolerance of the Cd-accumulator HCW. These results lay the foundation for further understanding the molecular mechanisms of Cd accumulation in woody plants and provide new insights into molecular-assisted-screening woody plant varieties for phytoremediation.

The Apoplastic and Symplastic Antioxidant System in Onion: Response to Long-Term Salt Stress

The response of apoplastic antioxidant systems in root and leaf tissues from two onion genotypes ('Texas 502', salt-sensitive and 'Granex 429', salt-resistant) in response to salinity was studied. Electrolyte leakage data indicated the membrane integrity impairing by the effect of salts, especially in 'Texas 502'. We detected superoxide dismutase (SOD) and peroxidase (POX) activity in the root and leaf apoplastic fractions from onion plants. Salinity increased SOD activity in the root symplast of 'Texas 502' and in 'Granex 429' leaves. In contrast, salinity reduced SOD activity in the leaf and root apoplastic fractions from 'Texas 502'. In 'Granex 429', salt-stress increased leaf apoplastic POX activity and symplastic catalase (CAT) activity of both organs, but a decline in root apoplastic POX from 'Texas 502' took place. Salt-stress increased monodehydroascorbate reductase (MDHAR) in root and leaf symplast and in root glutathione reductase GR, mainly in 'Granex 429', but only in this genotype, leaf dehydroascorbate reductase (DHAR) activity increased. In contrast, a decline in leaf GR was produced only in 'Texas 502'. Salinity increased leaf ASC levels, and no accumulation of dehydroascorbate (DHA) was observed in roots in both cases. These responses increased the redox state of ascorbate, especially in roots. In contrast, salinity declined reduced glutathione (GSH), but oxidised glutathione (GSSG) was accumulated in leaves, decreasing the redox state of glutathione. Salinity slightly increased root GSH concentration in the salt-tolerant genotype and was unchanged in the salt-sensitive genotype, but no accumulation of GSSG was produced, favoring the rise and/or maintenance of the redox state of the glutathione. These results suggest that the lower sensitivity to salt in 'Granex 429' could be related to a better performance of the antioxidant machinery under salinity conditions.

Climate and development modulate the metabolome and antioxidative system of date palm leaves

Date palms are remarkably tolerant to environmental stresses, but the mechanisms involved remain poorly characterized. Leaf metabolome profiling was therefore performed on mature (ML) and young (YL) leaves of 2-year-old date palm seedlings that had been grown in climate chambers that simulate summer and winter conditions in eastern Saudi Arabia. Cultivation under high temperature (summer climate) resulted in higher YL H2O2 leaf levels despite increases in dehydroascorbate reductase (DHAR) activities. The levels of raffinose and galactinol, tricarboxylic acid cycle intermediates, and total amino acids were higher under these conditions, particularly in YL. The accumulation of unsaturated fatty acids, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid, was lower in ML. In contrast, the amounts of saturated tetradecanoic acid and heptadecanoic acid were increased in YL under summer climate conditions. The accumulation of phenolic compounds was favored under summer conditions, while flavonoids accumulated under lower temperature (winter climate) conditions. YL displayed stronger hydration, lower H2O2 levels, and more negative δ 13C values, indicating effective reactive oxygen species scavenging. These findings, which demonstrate the substantial metabolic adjustments that facilitate tolerance to the high temperatures in YL and ML, suggest that YL may be more responsive to climate change.

Hydrogen gas promotes the adventitious rooting in cucumber under cadmium stress

Hydrogen gas (H2) plays an important role in plant development and stress responses. Here, cucumber (Cucumis sativus L.) explants were used to investigate the roles of H2 in adventitious root development under cadmium (Cd) stress and its physiological mechanism. The results showed that hydrogen-rich water (HRW) promoted adventitious rooting under Cd stress and 50% HRW obtained the maximal biological response. Compared with Cd treatment, HRW + Cd treatment significantly reduced the content of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide radical (O2-), thiobarbituric acid reactive substances (TBARS), ascorbic acid (AsA) and reduced glutathione (GSH), as well as relative electrical conductivity (REC), lipoxygenase (LOX) activity, AsA/docosahexaenoic acid (DHA) ratio, and GSH/oxidized glutathione (GSSG) ratio, while increasing DHA and GSSG content. HRW + Cd treatment also significantly increased in the activity and related gene expression of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). Additionally, HRW + Cd treatment increased the contents of osmotic adjustment substances, as well as the activities of peroxidase (POD) and polyphenol oxidase (PPO), while significantly decreasing indoleacetic acid oxidase (IAAO) activity. In summary, H2 could induce adventitious rooting under Cd stress by decreasing the oxidative damage, increasing osmotic adjustment substance content and regulating rooting-related enzyme activity.

The oxidation of dehydroascorbic acid and 2,3-diketogulonate by distinct reactive oxygen species

l-Ascorbate, dehydro-l-ascorbic acid (DHA), and 2,3-diketo-l-gulonate (DKG) can all quench reactive oxygen species (ROS) in plants and animals. The vitamin C oxidation products thereby formed are investigated here. DHA and DKG were incubated aerobically at pH 4.7 with peroxide (H2O2), 'superoxide' (a ∼50 : 50 mixture of [Formula: see text] and [Formula: see text]), hydroxyl radicals (•OH, formed in Fenton mixtures), and illuminated riboflavin (generating singlet oxygen, 1O2). Products were monitored electrophoretically. DHA quenched H2O2 far more effectively than superoxide, but the main products in both cases were 4-O-oxalyl-l-threonate (4-OxT) and smaller amounts of 3-OxT and OxA + threonate. H2O2, but not superoxide, also yielded cyclic-OxT. Dilute Fenton mixture almost completely oxidised a 50-fold excess of DHA, indicating that it generated oxidant(s) greatly exceeding the theoretical •OH yield; it yielded oxalate, threonate, and OxT. 1O2 had no effect on DHA. DKG was oxidatively decarboxylated by H2O2, Fenton mixture, and 1O2, forming a newly characterised product, 2-oxo-l-threo-pentonate (OTP; '2-keto-l-xylonate'). Superoxide yielded negligible OTP. Prolonged H2O2 treatment oxidatively decarboxylated OTP to threonate. Oxidation of DKG by H2O2, Fenton mixture, or 1O2 also gave traces of 4-OxT but no detectable 3-OxT or cyclic-OxT. In conclusion, DHA and DKG yield different oxidation products when attacked by different ROS. DHA is more readily oxidised by H2O2 and superoxide; DKG more readily by 1O2 The diverse products are potential signals, enabling organisms to respond appropriately to diverse stresses. Also, the reaction-product 'fingerprints' are analytically useful, indicating which ROS are acting in vivo.

Comparative proteomic analysis reveals the roots response to low root-zone temperature in Malus baccata

Soil temperature is known to affect plant growth and productivity. In this study we found that low root-zone temperature (LRT) inhibited the growth of apple (Malus baccata Borkh.) seedlings. To elucidate the molecular mechanism of LRT response, we performed comparative proteome analysis of the apple roots under LRT for 6 days. Total proteins of roots were extracted and separated by two-dimensional gel electrophoresis (2-DE) and 29 differentially accumulated proteins were successfully identified by MALDI-TOF/TOF mass spectrometry. They were involved in protein transport/processing/degradation (21%), glycometabolism (20%), response to stress (14%), oxidoreductase activity (14%), protein binding (7%), RNA metabolism (7%), amino acid biosynthesis (3%) and others (14%). The results revealed that LRT inhibited glycometabolism and RNA metabolism. The up-regulated proteins which were associated with oxidoreductase activity, protein metabolism and defense response, might be involved in protection mechanisms against LRT stress in the apple seedlings. Subsequently, 8 proteins were selected for the mRNA quantification analysis, and we found 6 of them were consistently regulated between protein and mRNA levels. In addition, the enzyme activities in ascorbate-glutathione (AsA-GSH) cycle were determined, and APX activity was increased and GR activity was decreased under LRT, in consistent with the protein levels. This study provides new insights into the molecular mechanisms of M. baccata in responding to LRT.

Mycorrhiza-Triggered Transcriptomic and Metabolomic Networks Impinge on Herbivore Fitness

Symbioses between plants and mycorrhizal fungi are ubiquitous in ecosystems and strengthen the plants' defense against aboveground herbivores. Here, we studied the underlying regulatory networks and biochemical mechanisms in leaves induced by ectomycorrhizae that modify herbivore interactions. Feeding damage and oviposition by the widespread poplar leaf beetle Chrysomela populi were reduced on the ectomycorrhizal hybrid poplar Populus × canescens Integration of transcriptomics, metabolomics, and volatile emission patterns via mass difference networks demonstrated changes in nitrogen allocation in the leaves of mycorrhizal poplars, down-regulation of phenolic pathways, and up-regulation of defensive systems, including protease inhibitors, chitinases, and aldoxime biosynthesis. Ectomycorrhizae had a systemic influence on jasmonate-related signaling transcripts. Our results suggest that ectomycorrhizae prime wounding responses and shift resources from constitutive phenol-based to specialized protective compounds. Consequently, symbiosis with ectomycorrhizal fungi enabled poplars to respond to leaf beetle feeding with a more effective arsenal of defense mechanisms compared with nonmycorrhizal poplars, thus demonstrating the importance of belowground plant-microbe associations in mitigating aboveground biotic stress.

Consequences of Sphaeropsis tip blight disease for the phytohormone profile and antioxidative metabolism of its pine host

Phytopathogenic fungi infections induce plant defence responses that mediate changes in metabolic and signalling processes with severe consequences for plant growth and development. Sphaeropsis tip blight, induced by the endophytic fungus Sphaeropsis sapinea that spreads from stem tissues to the needles, is the most widespread disease of conifer forests causing dramatic economic losses. However, metabolic consequences of this disease on bark and wood tissues of its host are largely unexplored. Here, we show that diseased host pines experience tissue dehydration in both bark and wood. Increased cytokinin and declined indole-3-acetic acid levels were observed in both tissues and increased jasmonic acid and abscisic acid levels exclusively in the wood. Increased lignin contents at the expense of holo-cellulose with declined structural biomass of the wood reflect cell wall fortification by S. sapinea infection. These changes are consistent with H₂ O₂ accumulation in the wood, required for lignin polymerization. Accumulation of H₂ O₂ was associated with more oxidized redox states of glutathione and ascorbate pools. These findings indicate that S. sapinea affects both phytohormone signalling and the antioxidative defence system in stem tissues of its pine host during the infection process.

The effects of Mg enrichment of vegetable sprouts on Mg concentration, yield and ROS generation

BACKGROUND

Two-thirds of the world's population do not consume the recommended amount of Mg, hence the demand for the production of Mg-enriched plants. Sprouts represent promising targets for enrichment. This study evaluated the effects of enriching broccoli, radish, alfalfa and mung bean sprouts with Mg (50-300 mg L(-1) ) on (i) the concentration of Mg and other ions, (ii) biomass accumulation, (iii) levels of reactive oxygen species (ROS), and (iv) the activity/content of enzymatic and non-enzymatic components of antioxidative systems.

RESULTS

Enrichment of sprouts with Mg led to a significant increase in Mg concentration, especially in alfalfa (increase of 23-152 %), without depletion of other ions. A higher Mg concentration had a minor effect on biomass accumulation, but increased, often significantly, ROS generation and affected enzymatic and non-enzymatic antioxidative systems. The level of O2 (•-) increased most in broccoli, by 59-158%, while OH(•) increased most in radish, by 200-350%.

CONCLUSIONS

Enrichment of sprouts with Mg is possible, but attention must be paid to elevated ROS levels in food. Mung bean sprouts are best suited to enrichment as they make a considerable contribution to the daily supplementation of Mg, at still low levels of ROS in enriched plants. © 2015 Society of Chemical Industry.

Boron bridging of rhamnogalacturonan-II is promoted in vitro by cationic chaperones, including polyhistidine and wall glycoproteins

Dimerization of rhamnogalacturonan-II (RG-II) via boron cross-links contributes to the assembly and biophysical properties of the cell wall. Pure RG-II is efficiently dimerized by boric acid (B(OH)3 ) in vitro only if nonbiological agents for example Pb(2+) are added. By contrast, newly synthesized RG-II domains dimerize very rapidly in vivo. We investigated biological agents that might enable this. We tested for three such agents: novel enzymes, borate-transferring ligands and cationic 'chaperones' that facilitate the close approach of two polyanionic RG-II molecules. Dimerization was monitored electrophoretically. Parsley shoot cell-wall enzymes did not affect RG-II dimerization in vitro. Borate-binding ligands (apiose, dehydroascorbic acid, alditols) and small organic cations (including polyamines) also lacked consistent effects. Polylysine bound permanently to RG-II, precluding electrophoretic analysis. However, another polycation, polyhistidine, strongly promoted RG-II dimerization by B(OH)3 without irreversible polyhistidine-RG-II complexation. Likewise, partially purified spinach extensins (histidine/lysine-rich cationic glycoproteins), strongly promoted RG-II dimerization by B(OH)3 in vitro. Thus certain polycations, including polyhistidine and wall glycoproteins, can chaperone RG-II, manoeuvring this polyanionic polysaccharide domain such that boron-bridging is favoured. These chaperones dissociate from RG-II after facilitating its dimerization, indicating that they act catalytically rather than stoichiometrically. We propose a natural role for extensin-RG-II interaction in steering cell-wall assembly.

Carbon allocation from source to sink leaf tissue in relation to flavonoid biosynthesis in variegated Pelargonium zonale under UV-B radiation and high PAR intensity

We studied the specific effects of high photosynthetically active radiation (PAR, 400-700 nm) and ecologically relevant UV-B radiation (0.90 W m(-2)) on antioxidative and phenolic metabolism by exploiting the green-white leaf variegation of Pelargonium zonale plants. This is a suitable model system for examining "source-sink" interactions within the same leaf. High PAR intensity (1350 μmol m(-2) s(-1)) and UV-B radiation induced different responses in green and white leaf sectors. High PAR intensity had a greater influence on green tissue, triggering the accumulation of phenylpropanoids and flavonoids with strong antioxidative function. Induced phenolics, together with ascorbate, ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (CAT, EC 1.11.1.6) provided efficient defense against potential oxidative pressure. UV-B-induced up-regulation of non-phenolic H2O2 scavengers in green leaf sectors was greater than high PAR-induced changes, indicating a UV-B role in antioxidative defense under light excess; on the contrary, minimal effects were observed in white tissue. However, UV-B radiation had greater influence on phenolics in white leaf sections compared to green ones, inducing accumulation of phenolic glycosides whose function was UV-B screening rather than antioxidative. By stimulation of starch and sucrose breakdown and carbon allocation in the form of soluble sugars from "source" (green) tissue to "sink" (white) tissue, UV-B radiation compensated the absence of photosynthetic activity and phenylpropanoid and flavonoid biosynthesis in white sectors.

Apoplastic antioxidant enzyme responses to chronic free-air ozone exposure in two different ozone-sensitive wheat cultivars

The effects of elevated ozone concentrations [O3] on two different ozone-sensitive wheat (Triticum aestivum L.) cultivars [Yangmai16 (Y16) and Yannong19 (Y19)] were investigated to determine the different apoplastic antioxidant mechanisms under O3-FACE (free-air controlled enrichment) condition. The results indicated that elevated [O3] (1.5 × ambient [O3]) induced increases in the production of superoxide anion (O2(-)), hydroxyl radical (HO), hydrogen peroxide (H2O2) and lipid peroxidation, and these results were more pronounced in the apoplasts of Y19 than in those of Y16. Apoplastic antioxidant enzymes were developmentally regulated and the effect of elevated [O3] depended on the developmental stage of wheat for both cultivars. In cultivar Y19, continuous O3 stress induced a decrease in the activity of apoplastic superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7) and ascorbate peroxidase (APX; EC 1.11.1.11) in the later growing stages, indicating Y19 appears to be the more sensitive cultivar and is prone to oxidative stress. The strategic response of antioxidant enzymes activities by Y16 in four different plant development stages (booting, flowering, filling and ripening) resulted in O3 stress-induced antioxidant defense responses, which indicated its higher tolerance to O3 stress. The same patterns of activity of apoplastic SOD and APX isozymes were observed in both Y16 and Y19 cultivars, while POD isozymes differed by cultivar in terms of the pattern of bands. The results of the present study show that O3 tolerance can be improved by regulating apoplastic ROS metabolism through the responses of apoplastic antioxidant enzymes to O3 stress in different plant development stages.

A critical comparison of two high-throughput ascorbate analyses methods for plant samples

Ascorbate (AsA) is an important metabolite involved in stress response and development of plants. Therefore it is necessary to quantify the AsA content in many fields of plant science, including high throughput and critical applications. In this study we compared two different microplate-based AsA assays, which are suitable for high throughput applications: an ascorbate oxidase (AO)-based assay and a dipyridyl (DPD)-based assay. These methods were compared in critical applications, i.e. (i) when AsA concentrations were very low such as in apoplastic extracts, (ii) when plants contained pigments interfering with the spectrometric measurements, and (iii) when plants contained high iron concentration interfering with the color reactions. The precision of measurements was higher with the DPD method, as illustrated by higher recovery rates of internal AsA standards. On the other hand, the AO method was more sensitive to low levels of AsA. This was an advantage in determining apoplastic AsA concentration in rice, which was substantially lower than that of whole tissues. The AO method also had the advantage that plant pigments and high iron concentrations in plants tissues did not interfere with the analysis, as opposed to the DPD assay. In conclusion, both assays had advantages and the choice of a suitable method depends on the specific application.

Physiological and biochemical responses of Quercus pubescens to air warming and drought on acidic and calcareous soils

The drought- and thermo-tolerant Quercus pubescens, a tree species growing on both acidic and calcareous soils in the sub-Mediterranean region, was exposed to soil drought (-60% to -80% soil water content) and air warming (+1.2 °C daytime temperature), singly and in combination. The experiment was conducted on two natural forest soils with similar texture but different pH (acidic and calcareous soils). The physiological (photosynthesis) and biochemical (antioxidant system) responses of Q. pubescens were investigated. On acidic soil, Q. pubescens had a higher reactive oxygen species (ROS) content than on calcareous soil, confirming that this species is better adapted to the latter soil type. A down-regulation of ascorbate-glutathione cycle enzymes suggests that ROS were used as signalling molecules. Air warming stimulated stomatal opening, while soil drought induced stomatal closure in the late afternoon and reduced Rubisco carboxylation efficiency. Photosynthetic performance in the combined treatment was higher than under single drought stress and similar to control and air warming. Q. pubescens biochemical responses depended on soil pH. On acidic soil, Q. pubescens trees exposed to air warming used ROS as signalling molecules. On calcareous soil, these trees were able to balance both soil drought and air warming stress, avoiding ROS toxic effects by increasing antioxidant enzyme activitiy and maintaining a high enzymatic antioxidant defence. When combined, drought and air warming induced either more severe (higher oxidative pressure and impairment of the light-harvesting complex) or different responses (decline of the thermal energy dissipation capacity) relative to the single stressors. Overall, however, Q. pubescens preserved the functionality of the photosynthetic apparatus and controlled the antioxidant system response, thus confirming its drought and thermo-tolerance and therefore its potential to adapt to the ongoing climate change.

Cadmium tolerance in six poplar species

Selection of poplar species with greater Cd tolerance and exploiting the physiological mechanisms involved in Cd tolerance are crucial for application of these species to phyto-remediation. The aim of this study is to investigate variation in Cd tolerance among the six poplar species and its underlying physiological mechanisms. Cuttings of six Populus species were cultivated for 10 weeks before exposure to either 0 or 200 μM CdSO(4) for 20 days. Gas exchange in mature leaves was determined by a portable photosynthesis system. Cd concentrations in tissues were analyzed by a flame atomic absorbance spectrometry. Subsequently, Cd amount per plant, bio-concentration factor (BCF) and translocation factor (T (f)) were calculated. Nonenzymatic compounds and activities of antioxidative enzymes in tissues were analyzed spectrophotometrically. Cd exposure caused decline in photosynthesis in four poplar species including Populus cathayana (zhonghua 1). Among the six species, P. cathayana (zhonghua 1) displayed the highest Cd concentrations in tissues, the largest Cd amount in aerial parts, the highest BCF in aerial parts and T (f) under Cd exposure. Under Cd stress, increases in total soluble sugars in roots but decreases in starch in roots, wood, and leaves of P. cathayana (zhonghua 1) were found. Induced O (2) (•-) and H(2)O(2) production in roots and leaves, and increases in free proline, soluble phenolics, and activities of antioxidative enzymes were observed in P. cathayana (zhonghua 1). Based on results of this pot experiment, it is concluded that P. cathayana (zhonghua 1) is superior to other five species for Cd phyto-remediation, and its well-coordinated physiological changes under Cd exposure confer the great Cd tolerance of this species.

Verticillium longisporum infection affects the leaf apoplastic proteome, metabolome, and cell wall properties in Arabidopsis thaliana

Verticillium longisporum (VL) is one of the most devastating diseases in important oil crops from the family of Brassicaceae. The fungus resides for much time of its life cycle in the extracellular fluid of the vascular system, where it cannot be controlled by conventional fungicides. To obtain insights into the biology of VL-plant interaction in the apoplast, the secretome consisting of the extracellular proteome and metabolome as well as cell wall properties were studied in the model Brassicaceae, Arabidopsis thaliana. VL infection resulted in increased production of cell wall material with an altered composition of carbohydrate polymers and increased lignification. The abundance of several hundred soluble metabolites changed in the apoplast of VL-infected plants including signalling and defence compounds such as glycosides of salicylic acid, lignans and dihydroxybenzoic acid as well as oxylipins. The extracellular proteome of healthy leaves was enriched in antifungal proteins. VL caused specific increases in six apoplast proteins (three peroxidases PRX52, PRX34, P37, serine carboxypeptidase SCPL20, α-galactosidase AGAL2 and a germin-like protein GLP3), which have functions in defence and cell wall modification. The abundance of a lectin-like, chitin-inducible protein (CILLP) was reduced. Since the transcript levels of most of the induced proteins were not elevated until late infection time points (>20 dpi), whereas those of CILLP and GLP3 were reduced at earlier time points, our results may suggest that VL enhances its virulence by rapid down-regulation and delay of induction of plant defence genes.

Cadmium interferes with auxin physiology and lignification in poplar

Cadmium (Cd) is a phytotoxic heavy metal that causes rapid growth reduction. To investigate if Cd interferes with the metabolism of auxin, a major growth hormone in plants, poplars (Populus × canescens) expressing a heterologous GH3::GUS reporter gene were exposed to 50 μM Cd in hydroponic solutions. Growth, photosynthetic performance, lignification, peroxidase activity, auxin concentration, and GUS staining were determined in order to record the activities of GH3 enzymes in the stem apex, the elongation zone, wood in the zone of radial growth, and in roots. Cd-induced growth reductions were tissue-specific decreasing in the order: roots>wood>shoot elongation and leaf initiation, whereas Cd concentrations increased in the order: leaves Collapse

Key Words

• auxin
• cadmium
• growth
• heavy metal
• lignification
• populus×canescens

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MESH Headings

• Cadmium/toxicity
• Indoleacetic Acids/metabolism
• Lignin/metabolism
• Oxidative Stress/drug effects
• Plant Leaves/drug effects
• Plant Leaves/metabolism
• Plant Roots/drug effects
• Plant Roots/metabolism
• Plant Stems/drug effects
• Plant Stems/metabolism
• Populus/drug effects
• Populus/metabolism

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Affiliation(s)

Mudawi Elobeid Abteilung Forstbotanik und Baumphysiologie, Büsgen-Institut, Georg-August Universität, Büsgenweg 2, 37077 Göttingen, Germany
Cornelia Göbel Abteilung Biochemie, Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Justus-von-Liebig-Weg 11, Georg-August-Universität, 37077 Göttingen, Germany
Ivo Feussner Abteilung Biochemie, Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Justus-von-Liebig-Weg 11, Georg-August-Universität, 37077 Göttingen, Germany
Andrea Polle Abteilung Forstbotanik und Baumphysiologie, Büsgen-Institut, Georg-August Universität, Büsgenweg 2, 37077 Göttingen, Germany

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Net cadmium flux and accumulation reveal tissue-specific oxidative stress and detoxification in Populus × canescens

To characterize the dynamics of Cd²⁺ flux in the rhizosphere and to study cadmium (Cd) plant-internal partitioning in roots, wood, bark and leaves in relation to energy metabolism, reactive oxygen species (ROS) formation and antioxidants, Populus × canescens plantlets were exposed to either 0 or 50 µM CdSO₄ for up to 20 days in the nutrient solution. A strong net Cd²⁺ influx in root apex was observed after Cd exposure for 24 h, even if net Cd²⁺ influx decreased gradually in roots. A large amount of Cd was accumulated in roots. Cd ions were uploaded via the xylem to leaves and further transported to the phloem where significant accumulation was detected. Cd accumulation led to decreased photosynthetic carbon assimilation but not to the depletion in soluble carbohydrates. Increased levels of ROS were present in all tissues, except the bark of Cd-exposed poplars. To combat Cd-induced superoxide and hydrogen peroxide, P. × canescens appeared to rely mainly on the formation of soluble phenolics as these compounds showed the highest accumulation in the bark and the lowest in wood. Other potential radical scavengers such as proline, sugar alcohols and antioxidant enzymes showed tissue- and exposure time-specific responses to Cd. These results indicate a complex pattern of internal Cd allocation in P. × canescens resulting in higher ROS stress in wood than in bark and intermediate responses in roots and leaves, probably because of differential capacities of these tissues for the production of protective phenolic compounds.

Growth at elevated ozone or elevated carbon dioxide concentration alters antioxidant capacity and response to acute oxidative stress in soybean (Glycine max)

Soybeans (Glycine max Merr.) were grown at elevated carbon dioxide concentration ([CO(2)]) or chronic elevated ozone concentration ([O(3)]; 90 ppb), and then exposed to an acute O(3) stress (200 ppb for 4 h) in order to test the hypothesis that the atmospheric environment alters the total antioxidant capacity of plants, and their capacity to respond to an acute oxidative stress. Total antioxidant metabolism, antioxidant enzyme activity, and antioxidant transcript abundance were characterized before, immediately after, and during recovery from the acute O(3) treatment. Growth at chronic elevated [O(3)] increased the total antioxidant capacity of plants, while growth at elevated [CO(2)] decreased the total antioxidant capacity. Changes in total antioxidant capacity were matched by changes in ascorbate content, but not phenolic content. The growth environment significantly altered the pattern of antioxidant transcript and enzyme response to the acute O(3) stress. Following the acute oxidative stress, there was an immediate transcriptional reprogramming that allowed for maintained or increased antioxidant enzyme activities in plants grown at elevated [O(3)]. Growth at elevated [CO(2)] appeared to increase the response of antioxidant enzymes to acute oxidative stress, but dampened and delayed the transcriptional response. These results provide evidence that the growth environment alters the antioxidant system, the immediate response to an acute oxidative stress, and the timing over which plants return to initial antioxidant levels. The results also indicate that future elevated [CO(2)] and [O(3)] will differentially affect the antioxidant system.

Apoplastic ascorbate contributes to the differential ozone sensitivity in two varieties of winter wheat under fully open-air field conditions

We studied leaf apoplastic ascorbates in relation to ozone (O(3)) sensitivity in two winter wheat (Triticum aestivum L.) varieties: Yangfumai 2 (Y2) and Yangmai 16 (Y16). The plants were exposed to elevated O(3) concentration 27% higher than the ambient O(3) concentration in a fully open-air field from tillering stage until final maturity. The less sensitive variety Y16 had higher concentration of reduced ascorbate in the apoplast and leaf tissue by 33.5% and 12.0%, respectively, than those in the more sensitive variety Y2, whereas no varietal difference was detected in the decline of reduced ascorbate concentration in response to elevated O(3). No effects of O(3) or variety were detected in either oxidized ascorbate or the redox state of ascorbate in the apoplast and leaf tissue. The lower ascorbate concentrations in both apoplast and leaf tissue should have contributed to the higher O(3) sensitivity in variety Y2.

Contrasting ozone sensitivity in related evergreen and deciduous shrubs

Plant responses to enhanced ozone levels have been studied in two pairs of evergreen-deciduous species (Pistacia terebinthus vs. P. lentiscus; Viburnum lantana vs. V. tinus) in Open Top Chambers. Ozone induced widespread visible injury, significantly reduced CO(2) assimilation and stomatal conductance (g(s)), impaired Rubisco efficiency and regeneration capacity (V(c,max,)J(max)) and altered fluorescence parameters only in the deciduous species. Differences in stomatal conductance could not explain the observed differences in sensitivity. In control plants, deciduous species showed higher superoxide dismutase (SOD) activity than their evergreen counterparts, suggesting metabolic differences that could make them more prone to redox imbalances. Ozone induced increases in SOD and/or peroxidase activities in all the species, but only evergreens were able to cope with the oxidative stress. The relevancy of these results for the effective ozone flux approach and for the current ozone Critical Levels is also discussed.

Redox states of glutathione and ascorbate in root tips of poplar (Populus tremula X P. alba) depend on phloem transport from the shoot to the roots

Glutathione (GSH) and ascorbate (ASC) are important antioxidants that are involved in stress defence and cell proliferation of meristematic root cells. In principle, synthesis of ASC and GSH in the roots as well as ASC and GSH transport from the shoot to the roots by phloem mass flow is possible. However, it is not yet known whether the ASC and/or the GSH level in roots depends on the supply from the shoot. This was analysed by feeding mature leaves with [(14)C]ASC or [(35)S]GSH and subsequent detection of the radiolabel in different root fractions. Quantitative dependency of root ASC and GSH on shoot-derived ASC and GSH was investigated with poplar (Populus tremula X P. alba) trees interrupted in phloem transport. [(35)S]GSH is transported from mature leaves to the root tips, but is withdrawn from the phloem along the entire transport path. When phloem transport was interrupted, the GSH content in root tips halved within 3 d. [(14)C]ASC is also transported from mature leaves to the root tips but, in contrast to GSH, ASC is not removed from the phloem along the transport path. Accordingly, ASC accumulates in root tips. Interruption of phloem transport disturbed the level and the ASC redox state within the entire root system. Diminished total ASC levels were attributed mainly to a decline of dehydroascorbate (DHA). As the redox state of ASC is of particular significance for root growth and development, it is concluded that phloem transport of ASC may constitute a shoot to root signal to coordinate growth and development at the whole plant level.

Metabolic-dependent changes in plant cell redox power after ozone exposure

The tropospheric level of the phytotoxic air pollutant ozone has increased considerably during the last century, and is expected to continue to rise. Long-term exposure of higher plants to low ozone concentrations affects biochemical processes prior to any visible symptoms of injury. The current critical level of ozone used to determine the threshold for damaging plants (biomass loss) is still based on the seasonal sum of the external concentration above 40 nl.l(-1) (AOT40). Taking into account stomatal conductance and the internal capacity of leaf defences, a more relevant concept should be based upon the 'effective ozone flux', the balance between the stomatal flux and the intensity of cellular detoxification. The large decrease in the Rubisco/PEPc ratio reflects photosynthetic damage from ozone, and a large increase in activity of cytosolic PEPc, which allows increased malate production. Although the direct detoxification of ozone (and ROS produced from its decomposition) is carried out primarily by cell wall ascorbate, the existing level of this antioxidant is not sufficient to indicate the degree of cell sensitivity. In order to regenerate ascorbate, NAD(P)H is needed as the primary supplier of reducing power. It is hypothesised that increased activity of the catabolic pathways and associated shunts (glucose-6-phosphate dehydrogenase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, isocitrate dehydrogenase and malic enzyme) can provide sufficient NAD(P)H to maintain intracellular detoxification. Thus, measurement of the level of redox power would contribute to determination of the 'effective ozone dose', serving ultimately to improve the ozone risk index for higher plants.

On the mechanism of apoplastic H2O2 production during lignin formation and elicitation in cultured spruce cells--peroxidases after elicitation

A cell culture of Picea abies (L.) Karst. was used for studies of H(2)O(2) generation during constitutive extracellular lignin formation and after elicitation by cell wall fragments of a pathogenic fungus, Heterobasidium parviporum. Stable, micromolar levels of H(2)O(2) were present in the culture medium during lignin formation. Elicitation induced a burst of H(2)O(2), peaking at ca. 90 min after elicitation. Of exogenous reducing substrates that may be responsible for the synthesis of H(2)O(2) from O(2), NADH stimulated H(2)O(2) production irrespective of elicitation. Cysteine (Cys) and glutathione (GSH) partially scavenged the constitutive H(2)O(2), but usually increased or prolonged elicitor-induced H(2)O(2) formation. Culture medium peroxidases were not able to generate H(2)O(2) in vitro with Cys or GSH as reductants. These thiols, however, generated H(2)O(2) non-enzymically at pH 4.5. [(35)S]Sulphate feeding to spruce cells showed that endogenous sulphur-containing compounds (including GSH, GSSG and cysteic acid) existed in the culture medium. The apoplastic levels of these were, however, undetectable by the monobromobimane method suggesting that their contribution to apoplastic H(2)O(2) formation is probably minor. Azide, an inhibitor of haem-containing enzymes, slightly inhibited constitutive H(2)O(2) generation but strongly delayed the elicitor-induced H(2)O(2) accumulation. Diphenylene iodonium, an inhibitor of flavin-containing enzymes, efficiently inhibited H(2)O(2) production irrespective of elicitation. Elicitation led to downregulation of the expression of several peroxidase genes, and peroxidase activity in the culture medium was slightly reduced. Expression of three other peroxidase genes and a respiratory burst oxidase homologue (rboh) gene were upregulated. These data suggest that both peroxidases and rboh may contribute to H(2)O(2) generation.

Arsenic accumulation and speciation in maize as affected by inoculation with arbuscular mycorrhizal fungus Glomus mosseae

Effects of inoculation with arbuscular mycorrhizal (AM) fungus (Glomus mosseae) on arsenic (As) accumulation and speciation in maize were investigated by using As spiked soil at the application levels of 0, 25, 50, and 100 mg kg(-1). Inorganic As was the major species in plants, and mycorrhizal inoculation generally decreased concentrations of arsenite [As(III)] in maize roots and concentrations of As(III) and arsenate [As(V)] in the shoots. Dimethylarsenic acid (DMA) concentrations (detected in every plant sample) were higher in maize shoots for mycorrhizal than for nonmycorrhizal treatment, but no significant differences were observed for roots. Monomethylarsenic acid (MMA) was only detected in roots with mycorrhizal colonization. The uptake of As(V) was much lower by excised mycorrhizal than nonmycorrhizal roots, and the differences for the uptake of As(III) were negligible. Arsenate reductase (AR) activity was detected in maize roots, and it was reduced with mycorrhizal inoculation. Activities of peroxidase (POD) and superoxide dismutase (SOD) were detected in both maize shoots and roots, and they were suppressed by mycorrhizal inoculation. AM inoculation inhibited the uptake of As(V) and its reduction to As(III), reducing oxidation stress and thereby alleviating As toxicity to the host plant.

Defence reactions in the apoplastic proteome of oilseed rape (Brassica napus var. napus) attenuate Verticillium longisporum growth but not disease symptoms

BACKGROUND

Verticillium longisporum is one of the most important pathogens of Brassicaceae that remains strictly in the xylem during most stages of its development. It has been suggested that disease symptoms are associated with clogging of xylem vessels. The aim of our study was to investigate extracellular defence reactions induced by V. longisporum in the xylem sap and leaf apoplast of Brassica napus var. napus in relation to the development of disease symptoms, photosynthesis and nutrient status.

RESULTS

V. longisporum (strain VL43) did not overcome the hypocotyl barrier until 3 weeks after infection although the plants showed massive stunting of the stem and mild leaf chlorosis. During this initial infection phase photosynthetic carbon assimilation, transpiration rate and nutrient elements in leaves were not affected in VL43-infected compared to non-infected plants. Proteome analysis of the leaf apoplast revealed 170 spots after 2-D-protein separation, of which 12 were significantly enhanced in response to VL43-infection. LS-MS/MS analysis and data base searches revealed matches of VL43-responsive proteins to an endochitinase, a peroxidase, a PR-4 protein and a beta-1,3-glucanase. In xylem sap three up-regulated proteins were found of which two were identified as PR-4 and beta-1,3-glucanase. Xylem sap of infected plants inhibited the growth of V. longisporum.

CONCLUSION

V. longisporum infection did not result in drought stress or nutrient limitations. Stunting and mild chlorosis were, therefore, not consequences of insufficient water and nutrient supply due to VL43-caused xylem obstruction. A distinct array of extracellular PR-proteins was activated that might have limited Verticillium spreading above the hypocotyl. In silico analysis suggested that ethylene was involved in up-regulating VL43-responsive proteins.

Pre-exposure of calli to ozone promotes tolerance of regenerated Lycopersicon esculentum cv. PKM1 plantlets against acute ozone stress

Studies were performed to evaluate the effects of pre-exposure of calli to ozone in promoting tolerance of the regenerated Lycopersicon esculentum cv. PKM1 (tomato) plantlets against acute ozone stress (AOS). Calli induced from tomato leaf explants were subjected to pre-treatment with ozone: T(1)=100 ppb, T(2)=200 ppb and T(3)=300 ppb. For the control (C) calli, charcoal-filtered air was supplied to test differential sensitivity of regenerated plantlets to acute ozone stress. All treated calli were subsequently transferred to shooting, rooting medium and acclimatized. The plantlets regenerated from the respective ozone (T(1), T(2), T(3))-treated calli are referred to here as T(1), T(2), T(3) plantlets and the plantlets regenerated from control calli are referred to as control plantlets. The frequencies of regeneration of tomato plantlets from the calli were T(1)=86%, T(2)=82% and T(3)=67%, and 92% regeneration was obtained from control calli. In order to evaluate the ozone tolerance, all the regenerated plantlets were exposed to the acute ozone exposure (AOE). After AOE, the T(2) plantlets endured remarkably well by experiencing reduced ozone stress, which was evident from the lower level of hydrogen peroxide and oxidative stress-related enzymes such as ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) activities relative to T(3), T(1) and C plantlets. All T(2) plantlets showed enhanced tolerance against AOE by upholding enhanced soluble phenol content, a higher level of foliar and apoplastic ascorbic acid, elevated dehydroascorbate reductase (EC 1.8.5.1) and glutathione content. The present study reveals that the calli pre-exposed to T(2) ozone treatment resulted in an increase in the level of antioxidants and provided the plants greater protection against acute ozone stress.

Seasonal differences and within-canopy variations of antioxidants in mature spruce (Picea abies) trees under elevated ozone in a free-air exposure system

The effect of free-air ozone fumigation and crown position on antioxidants were determined in old-growth spruce (Picea abies) trees in the seasonal course of two consecutive years (2003 and 2004). Levels of total ascorbate and its redox state in the apoplastic washing fluid (AWF) were increased under double ambient ozone concentrations (2xO3), whilst ascorbate concentrations in needle extracts were unchanged. Concentrations of apoplastic and symplastic ascorbate were significantly higher in 2003 compared to 2004 indicating a combined effect of the drought conditions in 2003 with enhanced ozone exposure. Elevated ozone had only weak effects on total glutathione levels in needle extracts, phloem exudates and xylem saps. Total and oxidised glutathione concentrations were higher in 2004 compared to 2003 and seemed to be more affected by enhanced ozone influx in the more humid year 2004 compared to the combined effect of elevated ozone and drought in 2003 as observed for ascorbate.

Hydrogen peroxide in plants: a versatile molecule of the reactive oxygen species network

Plants often face the challenge of severe environmental conditions, which include various biotic and abiotic stresses that exert adverse effects on plant growth and development. During evolution, plants have evolved complex regulatory mechanisms to adapt to various environmental stressors. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species (ROS), which are subsequently converted to hydrogen peroxide (H(2)O(2)). Even under normal conditions, higher plants produce ROS during metabolic processes. Excess concentrations of ROS result in oxidative damage to or the apoptotic death of cells. Development of an antioxidant defense system in plants protects them against oxidative stress damage. These ROS and, more particularly, H(2)O(2,) play versatile roles in normal plant physiological processes and in resistance to stresses. Recently, H(2)O(2) has been regarded as a signaling molecule and regulator of the expression of some genes in cells. This review describes various aspects of H(2)O(2) function, generation and scavenging, gene regulation and cross-links with other physiological molecules during plant growth, development and resistance responses.

Leaf extracellular ascorbate in relation to O(3) tolerance of two soybean cultivars

Soybean [Glycine max (L.) Merr.] cultivars Essex and Forrest that exhibit differences in ozone (O(3)) sensitivity were used in greenhouse experiments to investigate the role of leaf extracellular antioxidants in O(3) injury responses. Charcoal-filtered air and elevated O(3) conditions were used to assess genetic, leaf age, and O(3) effects. In both cultivars, the extracellular ascorbate pool consisted of 80-98% dehydroascorbic acid, the oxidized form of ascorbic acid (AA) that is not an antioxidant. For all combinations of genotype and O(3) treatments, extracellular AA levels were low (1-30nmolg(-1) FW) and represented 3-30% of the total antioxidant capacity. Total extracellular antioxidant capacity was twofold greater in Essex compared with Forrest, consistent with greater O(3) tolerance of Essex. The results suggest that extracellular antioxidant metabolites in addition to ascorbate contribute to detoxification of O(3) in soybean leaves and possibly affect plant sensitivity to O(3) injury.