Experimental systems to assess the effects of reactive oxygen species in plant tissues

Influence of Abiotic and Biotic Elicitors on Organogenesis, Biomass Accumulation, and Production of Key Secondary Metabolites in Asteraceae Plants

The medicinal plants of the Asteraceae family are a valuable source of bioactive secondary metabolites, including polyphenols, phenolic acids, flavonoids, acetylenes, sesquiterpene lactones, triterpenes, etc. Under stressful conditions, the plants develop these secondary substances to carry out physiological tasks in plant cells. Secondary Asteraceae metabolites that are of the greatest interest to consumers are artemisinin (an anti-malarial drug from Artemisia annua L.-sweet wormwood), steviol glycosides (an intense sweetener from Stevia rebaudiana Bert.-stevia), caffeic acid derivatives (with a broad spectrum of biological activities synthesized from Echinacea purpurea (L.) Moench-echinacea and Cichorium intybus L.-chicory), helenalin and dihydrohelenalin (anti-inflammatory drug from Arnica montana L.-mountain arnica), parthenolide ("medieval aspirin" from Tanacetum parthenium (L.) Sch.Bip.-feverfew), and silymarin (liver-protective medicine from Silybum marianum (L.) Gaertn.-milk thistle). The necessity to enhance secondary metabolite synthesis has arisen due to the widespread use of these metabolites in numerous industrial sectors. Elicitation is an effective strategy to enhance the production of secondary metabolites in in vitro cultures. Suitable technological platforms for the production of phytochemicals are cell suspension, shoots, and hairy root cultures. Numerous reports describe an enhanced accumulation of desired metabolites after the application of various abiotic and biotic elicitors. Elicitors induce transcriptional changes in biosynthetic genes, leading to the metabolic reprogramming of secondary metabolism and clarifying the mechanism of the synthesis of bioactive compounds. This review summarizes biotechnological investigations concerning the biosynthesis of medicinally essential metabolites in plants of the Asteraceae family after various elicitor treatments.

Between eustress and distress: UVB induced changes in carotenoid accumulation in halophytic Salicornia europaea

Halophytes are potential future crops with a valuable nutritional profile. Produced in indoor farming, they are considered to contribute to sustainable and resilient food systems. Indoor farms operate using artificial light. In this context narrowband and low dose UVB radiation can be used to increase plant secondary metabolites, such as carotenoids, and provide an improved nutritional profile for a human diet. UVB radiation can cause eustress or distress in the plant depending on the lighting situation. The aim of this study was to identify the doses of UVB that lead to either eustress or distress and to analyze these responses in Salicornia europaea. Therefore, S. europaea plants were exposed to different UVB radiation levels, low, medium and high, and analyzed for reactive oxygen species (ROS), plant hormones, amino acids, and photosynthetic pigments. High UVB treatment was found to affect phenotype and growth, and the metabolite profile was affected in a UVB dose-dependent manner. Specifically, medium UVB radiation resulted in an increase in carotenoids, whereas high UVB resulted in a decrease. We also observed an altered oxidative stress status and increased SA and decreased ABA contents in response to UVB treatment. This was supported by the results of menadione treatment that induces oxidative stress in plants, which also indicated an altered oxidative stress status in combination with altered carotenoid content. Thus, we show that a moderate dose of UVB can increase the carotenoid content of S. europaea. Furthermore, the UVB stress-dependent response led to a better understanding of carotenoid accumulation upon UVB exposure, which can be used to improve lighting systems and in turn the nutritional profile of future crops in indoor farming.

Effects of drought stress and plant cultivar type on demographic characteristics of the rose-grain aphid, Metopolophium dirhodum (Hemiptera: Aphididae)

Drought is a substantial threat to cereal production under global climatic change scenarios, albeit its aftermath on arthropod pests is yet contentious. To address this issue, demographic characteristics of Metopolophium dirhodum (Walker, 1849) (Hemiptera: Aphididae) were studied on one drought-susceptible wheat cultivar and one drought-tolerant wheat cultivar under different water treatments. Some physiological and biochemical features of wheat cultivars including leaf soluble sugar and proline contents and antioxidant enzymes activities were also investigated. Significant differences occurred in the developmental period, survival, and fecundity of M. dirhodum between wheat cultivars under various water treatments. The impact of intermediate and severe water stress on M. dirhodum was neutral and negative for the tolerant cultivar and negative for the water-susceptible cultivar, respectively. Under severe water stress, on both wheat cultivars, the aphids had low net reproductive rates and finite and intrinsic rates of increase in comparison with those reared on unstressed plants. In total, drought resulted in lower growth of population and reduced survival of aphids. Hence, in the context of projected climatic changes, acute water deficiency could probably result in reducing the abundance and menace of outburst of M. dirhodum. However, it should be noted that the potential likelihood of M. dirhodum eruptions can be drastically affected by the degree of drought intensity and host plant cultivar.

Evaluating the Role of Exogenously Applied Ascorbic Acid in Rescuing Soybean Plant Health in The Presence of Pathogen-Induced Oxidative Stress

Charcoal rot, caused by the soilborne hemibiotrophic fungus Macrophomina phaseolina, is a prevalent and economically significant plant disease. It is hypothesized that M. phaseolina induces oxidative stress-mediated senescence in plants. Infection by M. phaseolina results in the host’s accumulation of reactive oxygen species (ROS) that contribute toward basal defense. However, the production of ROS could also lead to cellular damage and senescence in host tissue. This study aimed to determine if ascorbic acid, a ROS scavenging molecule, could quench M. phaseolina-induced hydrogen peroxide (H₂O₂) generation in a soybean-M. phaseolina pathosystem. In vitro sensitivity tests showed that M. phaseolina isolates were sensitive to L-ascorbic acid (LAA) at concentrations of 10.5 to 14.3 mM based on IC₅₀ (half-maximal inhibitory concentration) data. In planta cut-stem assays demonstrated that pre-treatment with 10 mM of either LAA (reduced form) or DHAA (dehydroascorbic acid; oxidized form) significantly decreased lesion length compared to the non-pretreated control and post-treatments with both ascorbic acid forms after M. phaseolina inoculation. Further, H₂O₂ quantification from ascorbic acid-pretreated tissue followed by M. phaseolina inoculation showed significantly less accumulation of H₂O₂ than the inoculated control or the mock-inoculated control. This result demonstrated that M. phaseolina not only induced H₂O₂ after host infection but also increased ROS-mediated senescence. This study shows the potential of ascorbic acid, an effective ROS scavenger, to limit ROS-mediated senescence associated with M. phaseolina infection.

Computational Analysis of Alternative Photosynthetic Electron Flows Linked With Oxidative Stress

During photosynthesis, organisms respond to their energy demand and ensure the supply of energy and redox equivalents that sustain metabolism. Hence, the photosynthetic apparatus can, and in fact should, be treated as an integrated supply-demand system. Any imbalance in the energy produced and consumed can lead to adverse reactions, such as the production of reactive oxygen species (ROS). Reaction centres of both photosystems are known sites of ROS production. Here, we investigate in particular the central role of Photosystem I (PSI) in this tightly regulated system. Using a computational approach we have expanded a previously published mechanistic model of C3 photosynthesis by including ROS producing and scavenging reactions around PSI. These include two water to water reactions mediated by Plastid terminal oxidase (PTOX) and Mehler and the ascorbate-glutathione (ASC-GSH) cycle, as a main non-enzymatic antioxidant. We have used this model to predict flux distributions through alternative electron pathways under various environmental stress conditions by systematically varying light intensity and enzymatic activity of key reactions. In particular, we studied the link between ROS formation and activation of pathways around PSI as potential scavenging mechanisms. This work shines light on the role of alternative electron pathways in photosynthetic acclimation and investigates the effect of environmental perturbations on PSI activity in the context of metabolic productivity.

Single Amino Acid Exchange in ACTIN2 Confers Increased Tolerance to Oxidative Stress in Arabidopsis der1-3 Mutant

Single-point mutation in the ACTIN2 gene of the der1-3 mutant revealed that ACTIN2 is an essential actin isovariant required for root hair tip growth, and leads to shorter, thinner and more randomly oriented actin filaments in comparison to the wild-type C24 genotype. The actin cytoskeleton has been linked to plant defense against oxidative stress, but it is not clear how altered structural organization and dynamics of actin filaments may help plants to cope with oxidative stress. In this study, we characterized root growth, plant biomass, actin organization and antioxidant activity of the der1-3 mutant under oxidative stress induced by paraquat and H₂O₂. Under these conditions, plant growth was better in the der1-3 mutant, while the actin cytoskeleton in the der1-3 carrying pro35S::GFP:FABD2 construct showed a lower bundling rate and higher dynamicity. Biochemical analyses documented a lower degree of lipid peroxidation, and an elevated capacity to decompose superoxide and hydrogen peroxide. These results support the view that the der1-3 mutant is more resistant to oxidative stress. We propose that alterations in the actin cytoskeleton, increased sensitivity of ACTIN to reducing agent dithiothreitol (DTT), along with the increased capacity to decompose reactive oxygen species encourage the enhanced tolerance of this mutant against oxidative stress.

The Effect of Methylmercury Exposure on Astrocyte of Cerebellar Cortex of White Rats (Rattus novergicus)

The aim of this research was to investigate the effect of different dose methylmercury (II) chloride on astrocyte in cerebellar cortex of white rat (Rattus norvegicus) exposed. This study used randomized control design using 15 adult female Wistar rats weight 180-200 g of body weight. Before treatment the white rats was adapted in a week, then randomly divided into 3 groups each consist of 5 rats. P0 as control were given 0.5 ml aquades, P1 and P2 were given 0.1 and 0.2 mg/kg/day respectively. All groups were given treatment per oral in 30 days with sonde. The data was analyzed by ANOVA, Duncan's multiple range (Duncan's Multiple Range Test). White rats exposed by methylmercury (II) chloride, had a significant differences in the percentage of necrotic astrocyte (p<0.05). Methylmercury chloride exposure increases the number of necrotic astrocytes on white rat.

An Ascophyllum nodosum-Derived Biostimulant Protects Model and Crop Plants from Oxidative Stress

Abiotic stresses, which at the molecular level leads to oxidative damage, are major determinants of crop yield loss worldwide. Therefore, considerable efforts are directed towards developing strategies for their limitation and mitigation. Here the superoxide-inducing agent paraquat (PQ) was used to generate oxidative stress in the model species Arabidopsis thaliana and the crops tomato and pepper. Pre-treatment with the biostimulant SuperFifty (SF) effectively and universally suppressed PQ-induced leaf lesions, H₂O₂ build up, cell destruction and photosynthesis inhibition. To further investigate the stress responses and SF-induced protection at the molecular level, we investigated the metabolites by GC-MS metabolomics. PQ induced specific metabolic changes such as accumulation of free amino acids (AA) and stress metabolites. These changes were fully prevented by the SF pre-treatment. Moreover, the metabolic changes of the specific groups were tightly correlating with their phenotypic characteristics. Overall, this study presents physiological and metabolomics data which shows that SF protects against oxidative stress in all three plant species.

Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress

Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N-acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5-hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.

The Impact of Drought Stress on Antioxidant Responses and Accumulation of Flavonolignans in Milk Thistle (Silybum marianum (L.) Gaertn)

Biosynthesis and accumulation of flavonolignans in plants are influenced by different environmental conditions. Biosynthesis and accumulation of silymarin in milk thistle (Silybum marianum L.) were studied under drought stress with respect to the antioxidant defense system at the physiological and gene expression level. The results revealed a reduction in leaf chlorophyll, ascorbic acid, and glutathione contents. In contrast, H2O2, proline, and antioxidative enzyme activities, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), were increased. These results confirmed that milk thistle undergoes oxidative stress under drought stress. Furthermore, transcription levels of APX, SOD, CAT, 1-Cys-Prx, and PrxQ were significantly increased in milk thistle under drought stress. Overall this suggests that protection against reactive oxygen species and peroxidation reactions in milk thistle are provided by enzymatic and non-enzymatic antioxidants. Flavonolignans from milk thistle seeds after different drought treatments were quantified by high-performance liquid chromatography (HPLC) and showed that severe drought stress enhanced the accumulation of silymarin and its components compared with seeds from the control (100% water capacity). Silybin is the major silymarin component and the most bioactive ingredient of the milk thistle extract. Silybin accumulation was the highest among all silymarin components in seeds obtained from drought-stressed plants. The expression of the chalcone synthase (CHS) genes (CHS1, CHS2, and CHS3), which are associated with the silybin biosynthetic pathway, was also increased during drought stress. These results indicated that milk thistle exhibits tolerance to drought stress and that seed derived from severe drought-stressed plants had higher levels of silymarin.

Overexpression of SlOFP20 in Tomato Affects Plant Growth, Chlorophyll Accumulation, and Leaf Senescence

Previous studies have shown that OVATE family proteins (OFPs) participate in various aspects of plant growth and development. How OFPs affect leaf chlorophyll accumulation and leaf senescence has not been reported yet. Here, we found that overexpression of SlOFP20 in tomato not only impacted plant architecture but also enhanced the leaf chlorophyll accumulation and retarded leaf senescence. Gene expression analysis of SlGLK1, SlGLK2, and HY5, encoding transcription factors that are putatively involved in chloroplast development and chlorophyll levels, were significantly up-regulated in SlOFP20-OE lines. Both chlorophyll biosynthesis and degradation genes were distinctly regulated in transgenic plants. Moreover, SlOFP20-OE plants accumulated more starch and soluble sugar than wild-type plants, indicating that an increased chlorophyll content conferred some higher photosynthetic performance in SlOFP20-OE plants. Furthermore, The levels of leaf senescence-related indexes, such as hydrogen peroxide, malondialdehyde, and antioxidant enzymes activities, were differently altered, too. SlOFP20 overexpression repressed the expression of senescence-related genes, SAG12, RAV1, and WRKY53. Moreover, abscisic acid and ethylene synthesis genes were down-regulated in transgenic lines. These results provide new insights into how SlOFP20 regulates chlorophyll accumulation and leaf senescence.

MADS-Box Genes Are Key Components of Genetic Regulatory Networks Involved in Abiotic Stress and Plastic Developmental Responses in Plants

Plants, as sessile organisms, adapt to different stressful conditions, such as drought, salinity, extreme temperatures, and nutrient deficiency, via plastic developmental and growth responses. Depending on the intensity and the developmental phase in which it is imposed, a stress condition may lead to a broad range of responses at the morphological, physiological, biochemical, and molecular levels. Transcription factors are key components of regulatory networks that integrate environmental cues and concert responses at the cellular level, including those that imply a stressful condition. Despite the fact that several studies have started to identify various members of the MADS-box gene family as important molecular components involved in different types of stress responses, we still lack an integrated view of their role in these processes. In this review, we analyze the function and regulation of MADS-box gene family members in response to drought, salt, cold, heat, and oxidative stress conditions in different developmental processes of several plants. In addition, we suggest that MADS-box genes are key components of gene regulatory networks involved in plant responses to stress and plant developmental plasticity in response to seasonal changes in environmental conditions.

S-metolachlor promotes oxidative stress in green microalga Parachlorella kessleri - A potential environmental and health risk for higher organisms

The estimation of the toxic influences of herbicide products on non-target aquatic organisms is essential for evaluation of environmental contamination. We assessed the effects of the herbicide S-metolachlor (S-MET) on unicellular green microalga Parachlorella kessleri during 4-72 in vitro exposure to concentrations in the range 2-200μg/L. The results have shown that S-MET had a significant effect on algae, even in doses 10 and 20 times lower than the EC50 values obtained for P. kessleri (EC50-72h=1090μg/L). It generates reactive oxygen species in algae, decreases their growth and photosynthetic pigment concentration, changes their ultrastructure and alters the cellular antioxidant defence capacities. The levels of protein adducts with the reactive aldehyde 4-hydroxy-2-nonenal (HNE), the end-product of lipid peroxidation, were significantly elevated in S-MET treated cells revealing the insufficient effectiveness of P. kessleri antioxidant mechanisms and persistent lipid peroxidation. Since algae are fundamental aquatic food component, the damaged algal cells, still capable of dividing while having persistently increased content of HNE upon S-MET contamination could represent an important environmental toxic factor that might further affect higher organisms in the food chain.

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) affects development, photosynthesis, and hormonal homeostasis in hybrid aspen (Populus tremula L. × P. tremuloides)

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) was first described as a protein involved in salicylic acid (SA)-, ethylene-, and reactive oxygen species (ROS)-dependent defense and acclimation responses. It is a molecular regulator of biotic and abiotic stress-induced programmed cell death. Its role is relatively well known in annual plants, such as Arabidopsis thaliana or Nicotiana benthamiana. However, little is known about its functions in woody plants. Therefore, in this study, we aimed to characterize the function of EDS1 in the Populus tremula L. × P. tremuloides hybrid grown for several seasons in the natural environment. We used two transgenic lines, eds1-7 and eds1-12, with decreased EDS1 expression levels in this study. The observed changes in physiological and biochemical parameters corresponded with the EDS1 silencing level. Both transgenic lines produced more lateral shoots in comparison to the wild-type (WT) plants, which resulted in the modification of tree morphology. Photosynthetic parameters, such as quantum yield of photosystem II (ϕPSII), photochemical and non-photochemical quenching (qP and NPQ, respectively), as well as chlorophyll content were found to be increased in both transgenic lines, which resulted in changes in photosynthetic efficiency. Our data also revealed lower foliar concentrations of SA and ROS, the latter resulting most probably from more efficient antioxidant system in both transgenic lines. In addition, our data indicated significantly decreased rate of leaf senescence during several autumn seasons. Transcriptomic analysis revealed deregulation of 2215 and 376 genes in eds1-12 and eds1-7, respectively, and also revealed 207 genes that were commonly deregulated in both transgenic lines. The deregulation was primarily observed in the genes involved in photosynthesis, signaling, hormonal metabolism, and development, which was found to agree with the results of biochemical and physiological tests. In general, our data proved that poplar EDS1 affects tree morphology, photosynthetic efficiency, ROS and SA metabolism, as well as leaf senescence.

Rice Premature Leaf Senescence 2, Encoding a Glycosyltransferase (GT), Is Involved in Leaf Senescence

Premature leaf senescence (PLS), which has a significant impact on yield, is caused by various underlying mechanisms. Glycosyltransferases, which function in glycosyl transfer from activated nucleotides to aglycones, are involved in diverse biological processes, but their roles in rice leaf senescence remain elusive. Here, we isolated and characterized a leaf senescence-related gene from the Premature Leaf Senescent mutant (pls2). The mutant phenotype began with leaf yellowing at tillering and resulted in PLS during the reproductive stage. Leaf senescence was associated with an increase in hydrogen peroxide (H₂O₂) content accompanied with pronounced decreases in net photosynthetic rate, stomatal conductance, and transpiration rate. Map-based cloning revealed that a mutation in LOC_Os03g15840 (PLS2), a putative glycosyltransferase- encoding gene, was responsible for the defective phenotype. PLS2 expression was detected in all tissues surveyed, but predominantly in leaf mesophyll cells. Subcellular localization of the PLS2 was in the endoplasmic reticulum. The pls2 mutant accumulated higher levels of sucrose together with decreased expression of sucrose metabolizing genes compared with wild type. These data suggested that the PLS2 allele is essential for normal leaf senescence and its mutation resulted in PLS.

Sulfur Deprivation Results in Oxidative Perturbation in Chlorella sorokiniana (211/8k)

Sulfur deficiency in plant cells has not been considered as a potential abiotic factor that can induce oxidative stress. We studied the antioxidant defense system of Chlorella sorokiniana cultured under sulfur (S) deficiency, imposed for a maximum period of 24 h, to evaluate the effect of an S shortage on oxidative stress. S deprivation induced an immediate (30 min) but transient increase in the intracellular H2O2 content, which suggests that S limitation can lead to a temporary redox disturbance. After 24 h, S deficiency in Chlorella cells decreased the glutathione content to <10% of the value measured in cells that were not subjected to S deprivation. Consequently, we assumed that the cellular antioxidative mechanisms could be altered by a decrease in the total glutathione content. The total ascorbate pool increased within 2 h after the initiation of S depletion, and remained high until 6 h; however, ascorbate regeneration was inhibited under limited S conditions, indicated by a significant decrease in the ascorbate/dehydroascorbate (AsA/DHA) ratios. Furthermore, ascorbate peroxidase (APX) and superoxide dismutase (SOD) were activated under S deficiency, but we assumed that these enzymes were involved in maintaining the cellular H2O2 balance for at least 4 h after the initiation of S starvation. We concluded that S deprivation triggers redox changes and induces antioxidant enzyme activities in Chlorella cells. The accumulation of total ascorbate, changes in the reduced glutathione/oxidized glutathione (GSH/GSSG) ratios and an increase in the activity of SOD and APX enzymes indicate that oxidative perturbation occurs during S deprivation.

Phyto-Extraction of Nickel by Linum usitatissimum in Association with Glomus intraradices

Plants show enhanced phytoremediation of heavy metal contaminated soils particularly in response to fungal inoculation. Present study was conducted to find out the influence of Nickel (Ni) toxicity on plant biomass, growth, chlorophyll content, proline production and metal accumulation by L. usitatissimum (flax) in the presence of Glomus intraradices. Flax seedlings of both inoculated with G. intraradices and non-inoculated were exposed to different concentrations i.e., 250, 350 and 500 ppm of Ni at different time intervals. Analysis of physiological parameters revealed that Ni depressed the growth and photosynthetic activity of plants. However, the inoculation of plants with arbuscular mycorrhizae (G. intraradices) partially helped in the alleviation of Ni toxicity as indicated by improved plant growth under Ni stress. Ni uptake of non- mycorrhizal flax plants was increased by 98% as compared to control conditions whereas inoculated plants showed 19% more uptake when compared with the non-inoculated plants. Mycorrhizal plants exhibited increasing capacity to remediate contaminated soils along with improved growth. Thus, AM assisted phytoremediation helps in the accumulation of Ni in plants to reclaim Ni toxic soils. Based on our findings, it can be concluded that the role of flax plants and mycorrhizal fungi is extremely important in phytoremediation.

Synergistic effects of drought stress and photoperiods on phenology and secondary metabolism of Silybum marianum

Silybum marianum is an important medicinal plant of the family Asteraceae, well known for its set of bioactive isomeric mixture of secondary metabolites "silymarin", primarily acting as a hepato-protective agent. Abiotic stress augments plant secondary metabolism in different plant tissues to withstand harsh environmental fluctuations. In the current study, our aim was to induce drought stress in vitro on S. marianum under the influence of different photoperiod treatments to study the effects, with respect to variations in secondary metabolic profile and plant growth and development. S. marianum was extremely vulnerable to different levels of mannitol-induced drought stress. Water deficiency inhibited root induction completely and retarded plant growth was observed; however, phytochemical analysis revealed enhanced accumulation of total phenolic content (TPC), total flavonoid content (TFC), and total protein content along with several antioxidative enzymes. Secondary metabolic content was positively regulated with increasing degree of drought stress. A dependent correlation of seed germination frequency at mild drought stress and antioxidative activities was established with 2 weeks dark + 2 weeks 16/8 h photoperiod treatment, respectively, whereas a positive correlation existed for TPC and TFC when 4 weeks 16/8 h photoperiod treatment was applied. The effects of drought stress are discussed in relation to phenology, seed germination frequency, biomass build up, antioxidative potential, and secondary metabolites accumulation.

Spatial H2O2 signaling specificity: H2O2 from chloroplasts and peroxisomes modulates the plant transcriptome differentially

Hydrogen peroxide (H2O2) operates as a signaling molecule in eukaryotes, but the specificity of its signaling capacities remains largely unrevealed. Here, we analyzed whether a moderate production of H2O2 from two different plant cellular compartments has divergent effects on the plant transcriptome. Arabidopsis thaliana overexpressing glycolate oxidase in the chloroplast (Fahnenstich et al., 2008; Balazadeh et al., 2012) and plants deficient in peroxisomal catalase (Queval et al., 2007; Inzé et al., 2012) were grown under non-photorespiratory conditions and then transferred to photorespiratory conditions to foster the production of H2O2 in both organelles. We show that H2O2 originating in a specific organelle induces two types of responses: one that integrates signals independently from the subcellular site of H2O2 production and another that is dependent on the H2O2 production site. H2O2 produced in peroxisomes induces transcripts involved in protein repair responses, while H2O2 produced in chloroplasts induces early signaling responses, including transcription factors and biosynthetic genes involved in production of secondary signaling messengers. There is a significant bias towards the induction of genes involved in responses to wounding and pathogen attack by chloroplastic-produced H2O2, including indolic glucosinolates-, camalexin-, and stigmasterol-biosynthetic genes. These transcriptional responses were accompanied by the accumulation of 4-methoxy-indol-3-ylmethyl glucosinolate and stigmasterol.

Sulfur dioxide induced programmed cell death in Vicia guard cells

Sulfur dioxide (SO(2)) induced nuclear condensation and nuclear fragmentation and rapid loss of guard cell viability in detached epidermis of Vicia leaves at concentrations of 1 mM and higher (3 h exposure). Caspase inhibitors Z-Asp-CH(2)-DCB (0.1 mM) and TLCK (0.1 mM) markedly suppressed SO(2)-induced cell death. The typical nuclear morphological changes and the inhibition effects of caspase inhibitors suggest the activation of a programmed cell death (PCD) pathway. SO(2)-induced cell death can be blocked by either antioxidants (0.1 mM AsA or 200 U/mL CAT) or Ca(2+) antagonists (0.1mM EGTA or LaCl(3)). AsA and CAT also blocked SO(2)-induced ROS production and [Ca(2+)](cyt) increase. However, EGTA and LaCl(3) can inhibit SO(2)-induced [Ca(2+)](cyt) increase, but cannot suppress SO(2)-induced ROS production. Our results indicate that high concentrations of SO(2) induce guard cell death via a PCD pathway through ROS mediating [Ca(2+)](cyt) elevation, which causes harmful effects to plants.

Bioaccumulation and catabolism of prometryne in green algae

Investigation on organic xenobiotics bioaccumulation/biodegradation in green algae is of great importance from environmental point of view because widespread distribution of these compounds in agricultural areas has become one of the major problems in aquatic ecosystem. Also, new technology needs to be developed for environmental detection and re-usage of the compounds as bioresources. Prometryne as a herbicide is widely used for killing annual grasses in China and other developing countries. However, overuse of the pesticide results in high risks to contamination to aquatic environments. In this study, we focused on analysis of bioaccumulation and degradation of prometryne in Chlamydomonas reinhardtii, a green alga, along with its adaptive response to prometryne toxicity. C. reinhardtii treated with prometryne at 2.5-12.5 μg L(-1) for 4 d or 7.5 μg L(-1) for 1-6 d accumulated a large quantity of prometryne, with more than 2 mg kg(-1) fresh weight in cells exposed to 10 μg L(-1) prometryne. Moreover, it showed a great ability to degrade simultaneously the cell-accumulated prometryne. Such uptake and catabolism of prometryne led to the rapid removal of prometryne from media. Physiological and molecular analysis revealed that toxicology was associated with accumulation of prometryne in the cells. The biological processes of degradation can be interpreted as an internal tolerance mechanism. These results suggest that the green alga is useful in bioremediation of prometryne-contaminated aquatic ecosystems.

Efficient acclimation of the chloroplast antioxidant defence of Arabidopsis thaliana leaves in response to a 10- or 100-fold light increment and the possible involvement of retrograde signals

Chloroplasts are equipped with a nuclear-encoded antioxidant defence system the components of which are usually expressed at high transcript and activity levels. To significantly challenge the chloroplast antioxidant system, Arabidopsis thaliana plants, acclimated to extremely low light slightly above the light compensation point or to normal growth chamber light, were moved to high light corresponding to a 100- and 10-fold light jump, for 6 h and 24 h in order to observe the responses of the water-water cycle at the transcript, protein, enzyme activity, and metabolite levels. The plants coped efficiently with the high light regime and the photoinhibition was fully reversible. Reactive oxygen species (ROS), glutathione and ascorbate levels as well as redox states, respectively, revealed no particular oxidative stress in low-light-acclimated plants transferred to 100-fold excess light. Strong regulation of the water-water cycle enzymes at the transcript level was only partly reflected at the protein and activity levels. In general, low light plants had higher stromal (sAPX) and thylakoid ascorbate peroxidase (tAPX), dehydroascorbate reductase (DHAR), and CuZn superoxide dismutase (CuZnSOD) protein contents than normal light-grown plants. Mutants defective in components relevant for retrograde signalling, namely stn7, ex1, tpt1, and a mutant expressing E .coli catalase in the chloroplast showed unaltered transcriptional responses of water-water cycle enzymes. These findings, together with the response of marker transcripts, indicate that abscisic acid is not involved and that the plastoquinone redox state and reactive oxygen species do not play a major role in regulating the transcriptional response at t=6 h, while other marker transcripts suggest a major role for reductive power, metabolites, and lipids as signals for the response of the water-water cycle.

Expression of ROS-responsive genes and transcription factors after metabolic formation of H(2)O(2) in chloroplasts

Glycolate oxidase (GO) catalyses the oxidation of glycolate to glyoxylate, thereby consuming O(2) and producing H(2)O(2). In this work, Arabidopsis thaliana plants expressing GO in the chloroplasts (GO plants) were used to assess the expressional behavior of reactive oxygen species (ROS)-responsive genes and transcription factors (TFs) after metabolic induction of H(2)O(2) formation in chloroplasts. In this organelle, GO uses the glycolate derived from the oxygenase activity of RubisCO. Here, to identify genes responding to an abrupt production of H(2)O(2) in chloroplasts we used quantitative real-time PCR (qRT-PCR) to test the expression of 187 ROS-responsive genes and 1880 TFs after transferring GO and wild-type (WT) plants grown at high CO(2) levels to ambient CO(2) concentration. Our data revealed coordinated expression changes of genes of specific functional networks 0.5 h after metabolic induction of H(2)O(2) production in GO plants, including the induction of indole glucosinolate and camalexin biosynthesis genes. Comparative analysis using available microarray data suggests that signals for the induction of these genes through H(2)O(2) may originate in the chloroplast. The TF profiling indicated an up-regulation in GO plants of a group of genes involved in the regulation of proanthocyanidin and anthocyanin biosynthesis. Moreover, the upregulation of expression of TF and TF-interacting proteins affecting development (e.g., cell division, stem branching, flowering time, flower development) would impact growth and reproductive capacity, resulting in altered development under conditions that promote the formation of H(2)O(2).

Fluroxypyr triggers oxidative damage by producing superoxide and hydrogen peroxide in rice (Oryza sativa)

The present study has evaluated effect of fluroxypyr concentrations 0-0.8 mg l(-1) (a widely-used herbicide for controlling annual or perennial weeds growth) on selected metabolic and stress-related parameters in Oryza sativa plants after 6 days of exposure. Increasing concentrations decreased shoot growth and accumulation of chlorophylls but had no effect on root biomass. Increasing doses led also to increase in superoxide radical, hydrogen peroxide and proline accumulation, while malondialdehyde, an indicator of lipid peroxidation, was constitutively elevated. Histochemical staining with nitroblue tetrazolium and 3, 3-diaminobenzidine were positively correlated with the generation of superoxide radical and H(2)O(2). The fluroxypyr-induced oxidative stress triggered significant changes in activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase (POD). Activities of the antioxidant enzymes show a general increase at low fluroxypyr concentrations and a decrease at high fluroxypyr levels (except for POD). Analysis of naturing polyacrylamide gel electrophoresis confirmed these results. These data support the observation that fluroxypyr-triggered oxidative stress was responsible for the disturbance of the growth in the rice plants.