Methyl jasmonate stimulates the de novo biosynthesis of vitamin C in plant cell suspensions

Jasmonic Acid Seed Treatment Stimulates Insecticide Detoxification in Brassica juncea L

The present study focused on assessing the effects of jasmonic acid (JA) seed treatment on the physiology of Brassica juncea seedlings grown under imidacloprid (IMI) toxicity. It has been observed that IMI application declined the chlorophyll content and growth of seedlings. However, JA seed treatment resulted in the significant recovery of chlorophyll content and seedling growth. Contents of oxidative stress markers like superoxide anion, hydrogen peroxide, and malondialdehyde were enhanced with IMI application, but JA seed treatment significantly reduced their contents. Antioxidative defense system was activated with IMI application which was further triggered after JA seed treatment. Activities of antioxidative enzymes and contents of non-enzymatic antioxidants were enhanced with the application of IMI as well as JA seed treatment. JA seed treatment also regulated the gene expression of various enzymes under IMI stress. These enzymes included respiratory burst oxidase (RBO), Ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO), NADH-ubiquinone oxidoreductase (NADH), carboxylesterase (CXE), chlorophyllase (CHLASE), cytochrome P450 monooxygenase (P450). JA seed treatment up-regulated the expressions of RUBISCO, NADH, CXE, and P450 under IMI toxicity. However, expressions of RBO and CHLASE were down-regulated in seedlings germinated from JA seed treatment and grown in presence of IMI. Seed soaking with JA also resulted in a significant reduction of IMI residues in B. juncea seedlings. The present study concluded that seed soaking with JA could efficiently reduce the IMI toxicity by triggering the IMI detoxification system in intact plants.

Molecular cloning, in-silico characterization and functional validation of monodehydroascorbate reductase gene in Eleusine coracana

Ascorbic acid is a ubiquitous water soluble antioxidant that plays a critical role in plant growth and environmental stress tolerance. It acts as a free radical scavenger as well as a source of reducing power for several cellular processes. Because of its pivotal role in regulating plant growth under optimal as well as sub-optimal conditions, it becomes obligatory for plants to maintain a pool of reduced ascorbic acid. Several cellular processes help in maintaining the reduced ascorbic acid pool, by regulating its synthesis and regeneration processes. Current study demonstrates that monodehydroascorbate reductase is an important enzyme responsible for maintaining the reduced ascorbate pool, by optimizing the recycling of oxidized ascorbate. Cloning and functional characterization of this important stress inducible gene is of great significance for its imperative use in plant stress management. Therefore, we have cloned and functionally validated the role of monodehydroascorbate reductase gene (mdar) from a drought tolerant variety of Eleusine coracana. The cloned Ecmdar gene comprises of 1437bp CDS, encoding a 478 amino acid long polypeptide. The active site analysis showed presence of conserved Tyr₃₄₈ residue, facilitating the catalytic activity in electron transfer mechanism. qPCR expression profiling of Ecmdar under stress indicated that it is an early responsive gene. The analysis of Ecmdar overexpressing Arabidopsis transgenic lines suggests that monodehydroascorbate reductase acts as a key stress regulator by modulating the activity of antioxidant enzymes to strengthen the ROS scavenging ability and maintains ROS homeostasis. Thus, it is evident that Ecmdar is an important gene for cellular homeostasis and its over-expression could be successfully used to strengthen stress tolerance in crop plants.

Characterization of Two Arabidopsis L-Gulono-1,4-lactone Oxidases, AtGulLO3 and AtGulLO5, Involved in Ascorbate Biosynthesis

L-Ascorbic acid (AsA, vitamin C) is an essential antioxidant for plants and animals. There are four known ascorbate biosynthetic pathways in plants: the L-galactose, L-gulose, D-galacturonate, and myo-inositol routes. These pathways converge into two AsA precursors: L-galactono-1,4-lactone and L-gulono-1,4-lactone (L-GulL). This work focuses on the study of L-gulono-1,4-lactone oxidase (GulLO), the enzyme that works at the intersect of the gulose and inositol pathways. Previous studies have shown that feeding L-gulono-1,4-lactone to multiple plants leads to increased AsA. There are also reports showing GulLO activity in plants. We describe the first detailed characterization of a plant enzyme specific to oxidize L-GulL to AsA. We successfully purified a recombinant Arabidopsis GulLO enzyme (called AtGulLO5) in a transient expression system. The biochemical properties of this enzyme are similar to the ones of bacterial isozymes in terms of substrate specificity, subcellular localization, use of flavin adenine dinucleotide (FAD) as electron acceptor, and specific activity. AtGulLO5 is an exclusive dehydrogenase with an absolute specificity for L-GulL as substrate thus differing from the existing plant L-galactono-1,4-lactone dehydrogenases and mammalian GulLOs. Feeding L-GulL to N. benthamiana leaves expressing AtGulLO5 constructs led to increased foliar AsA content, but it was not different from that of controls, most likely due to the observed low catalytic efficiency of AtGulLO5. Similar results were also obtained with another member of the AtGulLO family (AtGulLO3) that appears to have a rapid protein turnover. We propose that AsA synthesis through L-GulL in plants is regulated at the post-transcriptional level by limiting GulLO enzyme availability.

Evaluation of the Nutritional Quality of Chinese Kale (Brassica alboglabra Bailey) Using UHPLC-Quadrupole-Orbitrap MS/MS-Based Metabolomics

Chinese kale (Brassica alboglabra Bailey) is a widely consumed vegetable which is rich in antioxidants and anticarcinogenic compounds. Herein, we used an untargeted ultra-high-performance liquid chromatography (UHPLC)-Quadrupole-Orbitrap MS/MS-based metabolomics strategy to study the nutrient profiles of Chinese kale. Seven Chinese kale cultivars and three different edible parts were evaluated, and amino acids, sugars, organic acids, glucosinolates and phenolic compounds were analysed simultaneously. We found that two cultivars, a purple-stem cultivar W1 and a yellow-flower cultivar Y1, had more health-promoting compounds than others. The multivariate statistical analysis results showed that gluconapin was the most important contributor for discriminating both cultivars and edible parts. The purple-stem cultivar W1 had higher levels of some phenolic acids and flavonoids than the green stem cultivars. Compared to stems and leaves, the inflorescences contained more amino acids, glucosinolates and most of the phenolic acids. Meanwhile, the stems had the least amounts of phenolic compounds among the organs tested. Metabolomics is a powerful approach for the comprehensive understanding of vegetable nutritional quality. The results provide the basis for future metabolomics-guided breeding and nutritional quality improvement.

Ascorbic Acid Alleviates Water Stress in Young Peach Trees and Improves Their Performance after Rewatering

Exogenous application of biochemicals has been found to improve water stress tolerance in herbaceous crops but there are limited studies on deciduous fruit trees. The goal of this research was to study if ascorbic acid applications could improve physiological mechanisms associated with water stress tolerance in young fruit trees. Ascorbic acid was foliarly applied at a concentration of 250 ppm to water-stressed and well-watered peach trees (control) of two cultivars ('Scarletprince' and 'CaroTiger'). Trees received either one or two applications, and 1 week after the second application all trees were rewatered to field capacity. Upon rewatering, CO₂ assimilation and stomatal conductance of water-stressed 'Scarletprince' trees sprayed with ascorbic acid (one or two applications) were similar to those of well-irrigated trees, but water-stressed trees that had not received ascorbic acid did not recover photosynthetical functions. Also, water status in sprayed water-stressed 'Scarletprince' trees was improved to values similar to control trees. On the other hand, water-stressed 'CaroTiger' trees needed two applications of ascorbic acid to reach values of CO₂ assimilation similar to control trees but these applications did not improve their water status. In general terms, different response mechanisms to cope with water stress in presence of ascorbic acid were found in each cultivar, with 'Scarletprince' trees preferentially using proline as compatible solute and 'CaroTiger' trees relying on stomatal regulation. The application of ascorbic acid reduced cell membrane damage and increased catalase activity in water-stressed trees of both cultivars. These results suggest that foliar applications of ascorbic acid could be used as a management practice for improving water stress tolerance of young trees under suboptimal water regimes.

Transcriptional profiling of genes involved in ascorbic acid biosynthesis, recycling, and degradation during three leaf developmental stages in celery

Ascorbic acid (AsA) is an important nutrient in the human body and performs various healthy functions. With considerable medicinal properties, celery (Apium graveolens L.) could be a good source of AsA for human health. However, the biosynthetic, recycling, and degradation pathways of AsA in celery have yet to be characterized. To study the metabolic pathways involved in AsA, the genes involved in AsA biosynthesis, recycling, and degradation were isolated from celery, and their expression profiles and AsA levels were analyzed in the leaf blades and petioles of two celery varieties at three different growth stages. AsA levels were higher in 'Ventura' compared with 'Liuhehuangxinqin' in both tissues possibly because of different transcription levels of genes, such as L-galactose dehydrogenase (GalDH), L-galactono-1,4-lactone dehydrogenase (GalLDH), and glutathione reductase (GR). Results revealed that the D-mannose/L-galactose pathway may be the predominant pathway in celery, and the D-galacturonic acid pathway appeared to contribute largely to AsA accumulation in petioles than in leaf blades in 'Liuhehuangxinqin.' AsA contents are regulated by complex regulatory mechanisms and vary at different growth stages, tissues, and varieties in celery. The results provide novel insights into AsA metabolic pathways in leaf during celery growth and development.

Vitamins for enhancing plant resistance

This paper provides an overview on vitamins with inducing activities in plants, the molecular and cellular mechanisms implicated, and the hormonal signalling-network regulating this process. Moreover, it reports how vitamins might be part of the molecular events linked to induced resistance by the conventional elicitors. Induced resistance (IR), exploiting the plant innate-defense system is a sustainable strategy for plant disease control. In the last decade, vitamins have been proven to act as inducers of disease resistance, and these findings have received an important attention owing to their safety and cost effectiveness. Vitamins, including thiamine (TH, vitamin B1), riboflavin (RF, vitamin B2), menadione sodium bisulfite (MSB, vitamin K3), Para-aminobenzoic acid (PABA, vitamin Bx), and folic acid (FA, vitamin B9) provided an efficient protection against a wide range of pathogens through the modulation of specific host-defense facets. However, other vitamins, such as ascorbic acid (AA, vitamin C) and tocopherols (vitamin E), have been shown to be a part of the molecular mechanisms associated to IR. The present review is the first to summarize what vitamins are acting as inducers of disease resistance in plants and how could they be modulated by the conventional elicitors. Thus, this report provides an overview on the protective abilities of vitamins and the molecular and cellular mechanisms underlying their activities. Moreover, it describes the hormonal-signalling network regulating vitamin-signal transduction during IR. Finally, a biochemical model describing how vitamins are involved in the establishment of IR process is discussed.

Accumulation of anthocyanins and flavonols in black currants (Ribes nigrum L.) by pre-harvest methyl jasmonate treatments

BACKGROUND

Chemical elicitation is one of the most effective methods currently used to enrich plant foods in bioactive compounds. Methyl jasmonate (MJ) has been described as a very useful elicitor of some plant compounds, polyphenols among them. The objective of this study was to determine the effects of pre-harvest MJ application on the increase in the main flavonoids and the antioxidant properties of black currant (Ribes nigrum) cultivars.

RESULTS

Significant enhancement of individual and total anthocyanins was measured after elicitation with MJ, particularly when a concentration of 0.2 mmol L(-1) was used. Total anthocyanins increased from 28288.74 ± 253.65 to 43561.08 ± 145.87 mg kg(-1) in Ben Hope black currants after elicitation with 0.2 mmol L(-1) MJ. Similarly, an increase from 35986.04 ± 287.98 to 41320.22 ± 109.38 mg kg(-1) was estimated in Ben Alder cultivar. Black currant flavonols were not individually affected by the treatment; however, total flavonols increased from 3115.21 ± 12.11 to 3268.41 ± 8.91 mg kg(-1) in Ben Hope and from 3016.38 ± 10.07 to 3110.95 ± 8.57 mg kg(-1) in Ben Alder. Antioxidant properties of black currants as measured by DPPH and ABTS assays improved proportionally to the increase in flavonoid content after MJ elicitation.

CONCLUSION

Pre-harvest elicitation with MJ is proposed as a useful tool to enhance contents of anthocyanins and flavonols as well as free radical-scavenging activity of black currants. The functional black currants obtained here can be interesting for industry, for consumption as fresh fruits and for production of juice and jam. © 2015 Society of Chemical Industry.

Ascorbic acid accumulates as a defense response to Turnip mosaic virus in resistant Brassica rapa cultivars

We initially observed that Brassica rapa cultivars containing the Turnip mosaic virus (TuMV) resistance gene, Rnt1-1, accumulated a high level of endogenous ascorbic acid (AS) and dehydroascobic acid (DHA) when infected with TuMV. We here hypothesized a possible contribution of an elevated level of AS+DHA (TAA) to the Rnt1-1-mediated resistance, and conducted a series of experiments using B. rapa and Arabidopsis plants. The application of l-galactose (the key substrate in AS synthesis) to a susceptible cultivar could increase the TAA level ~2-fold, and simultaneously lead to some degree of enhanced viral resistance. To confirm some positive correlation between TAA levels and viral resistance, we analyzed two Arabidopsis knockout mutants (ao and vtc1) in the AS pathways; the TAA levels were significantly increased and decreased in ao and vtc1 plants, respectively. While the ao plants showed enhanced resistance to TuMV, vtc1 plants were more susceptible than the control, supporting our hypothesis. When we analyzed the expression profiles of the genes involved in the AS pathways upon TuMV infection, we found that the observed TAA increase was mainly brought about by the reduction of AS oxidation and activation of AS recycling. We then investigated the secondary signals that regulate endogenous TAA levels in response to viral infection, and found that jasmonic acid (JA) might play an important role in TAA accumulation. In conclusion, we reason that the elevated TAA accumulation in B. rapa plants would be at least partly mediated by the JA-dependent signaling pathway and may significantly contribute to viral resistance.

Jasmonates: Multifunctional Roles in Stress Tolerance

Jasmonates (JAs) [Jasmonic acid (JA) and methyl jasmonates (MeJAs)] are known to take part in various physiological processes. Exogenous application of JAs so far tested on different plants under abiotic stresses particularly salinity, drought, and temperature (low/high) conditions have proved effective in improving plant stress tolerance. However, its extent of effectiveness entirely depends on the type of plant species tested or its concentration. The effects of introgression or silencing of different JA- and Me-JA-related genes have been summarized in this review, which have shown a substantial role in improving crop yield and quality in different plants under stress or non-stress conditions. Regulation of JAs synthesis is impaired in stressed as well as unstressed plant cells/tissues, which is believed to be associated with a variety of metabolic events including signal transduction. Although, mitogen activated protein kinases (MAPKs) are important components of JA signaling and biosynthesis pathways, nitric oxide, ROS, calcium, ABA, ethylene, and salicylic acid are also important mediators of plant growth and development during JA signal transduction and synthesis. The exploration of other signaling molecules can be beneficial to examine the details of underlying molecular mechanisms of JA signal transduction. Much work is to be done in near future to find the proper answers of the questions like action of JA related metabolites, and identification of universal JA receptors etc. Complete signaling pathways involving MAPKs, CDPK, TGA, SIPK, WIPK, and WRKY transcription factors are yet to be investigated to understand the complete mechanism of action of JAs.

Molecular Farming in Artemisia annua, a Promising Approach to Improve Anti-malarial Drug Production

Malaria is a parasite infection affecting millions of people worldwide. Even though progress has been made in prevention and treatment of the disease; an estimated 214 million cases of malaria occurred in 2015, resulting in 438,000 estimated deaths; most of them occurring in Africa among children under the age of five. This article aims to review the epidemiology, future risk factors and current treatments of malaria, with particular focus on the promising potential of molecular farming that uses metabolic engineering in plants as an effective anti-malarial solution. Malaria represents an example of how a health problem may, on one hand, influence the proper development of a country, due to its burden of the disease. On the other hand, it constitutes an opportunity for lucrative business of diverse stakeholders. In contrast, plant biofarming is proposed here as a sustainable, promising, alternative for the production, not only of natural herbal repellents for malaria prevention but also for the production of sustainable anti-malarial drugs, like artemisinin (AN), used for primary parasite infection treatments. AN, a sesquiterpene lactone, is a natural anti-malarial compound that can be found in Artemisia annua. However, the low concentration of AN in the plant makes this molecule relatively expensive and difficult to produce in order to meet the current worldwide demand of Artemisinin Combination Therapies (ACTs), especially for economically disadvantaged people in developing countries. The biosynthetic pathway of AN, a process that takes place only in glandular secretory trichomes of A. annua, is relatively well elucidated. Significant efforts have been made using plant genetic engineering to increase production of this compound. These include diverse genetic manipulation approaches, such as studies on diverse transcription factors which have been shown to regulate the AN genetic pathway and other biological processes. Results look promising; however, further efforts should be addressed toward optimization of the most cost-effective biofarming approaches for synthesis and production of medicines against the malaria parasite.

Methyl Jasmonate Regulates Antioxidant Defense and Suppresses Arsenic Uptake in Brassica napus L

Methyl jasmonate (MJ) is an important plant growth regulator, involved in plant defense against abiotic stresses, however, its possible function in response to metal stress is poorly understood. In the present study, the effect of MJ on physiological and biochemical changes of the plants exposed to arsenic (As) stress were investigated in two Brassica napus L. cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type). The As treatment at 200 μM was more phytotoxic, however, its combined application with MJ resulted in significant increase in leaf chlorophyll fluorescence, biomass production and reduced malondialdehyde content compared with As stressed plants. The application of MJ minimized the oxidative stress, as revealed via a lower level of reactive oxygen species (ROS) synthesis (H2O2 and OH(-)) in leaves and the maintenance of high redox states of glutathione and ascorbate. Enhanced enzymatic activities and gene expression of important antioxidants (SOD, APX, CAT, POD), secondary metabolites (PAL, PPO, CAD) and induction of lypoxygenase gene suggest that MJ plays an effective role in the regulation of multiple transcriptional pathways which were involved in oxidative stress responses. The content of As was higher in yellow seeded plants (cv. Zheda 622) as compared to black seeded plants (ZS 758). The application of MJ significantly reduced the As content in leaves and roots of both cultivars. Findings of the present study reveal that MJ improves ROS scavenging through enhanced antioxidant defense system, secondary metabolite and reduced As contents in both the cultivars.

Jasmonic Acid Modulates the Physio-Biochemical Attributes, Antioxidant Enzyme Activity, and Gene Expression in Glycine max under Nickel Toxicity

In present study, we evaluated the effects of Jasmonic acid (JA) on physio-biochemical attributes, antioxidant enzyme activity, and gene expression in soybean (Glycine max L.) plants subjected to nickel (Ni) stress. Ni stress decreases the shoot and root length and chlorophyll content by 37.23, 38.31, and 39.21%, respectively, over the control. However, application of JA was found to improve the chlorophyll content and length of shoot and root of Ni-fed seedlings. Plants supplemented with JA restores the chlorophyll fluorescence, which was disturbed by Ni stress. The present study demonstrated increase in proline, glycinebetaine, total protein, and total soluble sugar (TSS) by 33.09, 51.26, 22.58, and 49.15%, respectively, under Ni toxicity over the control. Addition of JA to Ni stressed plants further enhanced the above parameters. Ni stress increases hydrogen peroxide (H2O2) by 68.49%, lipid peroxidation (MDA) by 50.57% and NADPH oxidase by 50.92% over the control. Supplementation of JA minimizes the accumulation of H2O2, MDA, and NADPH oxidase, which helps in stabilization of biomolecules. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) increases by 40.04, 28.22, 48.53, and 56.79%, respectively, over the control in Ni treated seedlings and further enhancement in the antioxidant activity was observed by the application of JA. Ni treated soybean seedlings showed increase in expression of Fe-SOD by 77.62, CAT by 15.25, POD by 58.33, and APX by 80.58% over the control. Nevertheless, application of JA further enhanced the expression of the above genes in the present study. Our results signified that Ni stress caused negative impacts on soybean seedlings, but, co-application of JA facilitate the seedlings to combat the detrimental effects of Ni through enhanced osmolytes, activity of antioxidant enzymes and gene expression.

Ascorbic acid mitigation of water stress-inhibition of root growth in association with oxidative defense in tall fescue (Festuca arundinacea Schreb.)

Root growth inhibition by water stress may be related to oxidative damages. The objectives of this study were to determine whether exogenous application of ascorbic acid (ASA) could mitigate root growth decline due to water stress and whether ASA effects on root growth could be regulated through activating non-enzymatic or enzymatic antioxidant systems in perennial grass species. Tall fescue (Festuca arundinacea Schreb. cv. "K-31") plants were grown in nutrient solution, and polyethylene glycol (PEG)-8000 was added into the solution to induce water stress. For exogenous ASA treatment, ASA (5 mM) was added into the solution with or without PEG-8000. Plants treated with ASA under water stress showed significantly increased root growth rate, and those roots had significantly lower content of reactive oxygen species (ROS) (H2O2 and O[Formula: see text] content) than those without ASA treatment. Malondialdehyde content in root tips treated with ASA under water stress was also significantly reduced compared with those under water stress alone. In addition, free ascorbate and total ascorbate content were significantly higher in roots treated with ASA under water stress than those without ASA treatment. The enzymatic activities for ROS scavenging-related genes were not significantly altered by ASA treatment under water stress, while transcript abundances of genes encoding superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monohydroascorbate reductase showed significant decreases in the root elongation zone and significant increases in the root maturation zone treated with ASA under water stress. Transcripts of genes for expansins and xyloglucan endotransglycosylases showed increased abundances in ASA-treated root maturation zone under water stress, indicating that ASA could accelerated cell wall loosening and cell expansion. The results suggested that exogenous treatment of roots with ASA enhanced root elongation under water stress, which could be attributed by increasing non-enzymatic antioxidant production, suppressing ROS toxicity and up-regulating gene expression of cell-wall loosening proteins controlling cell expansion.

Redox proteomics and physiological responses in Cistus albidus shrubs subjected to long-term summer drought followed by recovery

The interaction between enzymatic and non-enzymatic antioxidants, endogenous levels of ABA and ABA-GE, the rapid recuperation of photosynthetic proteins under re-watering as well the high level of antioxidant proteins in previously drought-stressed plants under re-watering conditions, will contribute to drought resistance in plants subjected to a long-term drought stress under Mediterranean field conditions. This work provides an overview of the mechanisms of Cistus albidus acclimation to long-term summer drought followed by re-watering in Mediterranean field conditions. To better understand the molecular mechanisms of drought resistance in these plants, a proteomic study using 2-DE and MALDI-TOF/TOF MS/MS was performed on leaves from these shrubs. The analysis identified 57 differentially expressed proteins in water-stressed plants when contrasted to well watered. Water-stressed plants showed an increase, both qualitatively and quantitatively, in HSPs, and downregulation of photosynthesis and carbon metabolism enzymes. Under drought conditions, there was considerable upregulation of enzymes related to redox homeostasis, DHA reductase, Glyoxalase, SOD and isoflavone reductase. However, upregulation of catalase was not observed until after re-watering was carried out. Drought treatment caused an enhancement in antioxidant defense responses that can be modulated by ABA, and its catabolites, ABA-GE, as well as JA. Furthermore, quantification of protein carbonylation was shown to be a useful marker of the relationship between water and oxidative stress, and showed that there was only moderate oxidative stress in C. albidus plants subjected to water stress. After re-watering plants recovered although the levels of ABA-GE and antioxidant enzymes still remain higher than in well-watered plants. We expect that our results will provide new data on summer acclimation to drought stress in Mediterranean shrubs.

Influence of modified atmosphere packaging on 'Star Ruby' grapefruit phytochemicals

Modified atmosphere packaging (MAP) can extend the shelf life of salads, vegetables, and fruits by generating a storage environment with low O2, high CO2, and high humidity. The current study investigates the effect of modified atmosphere and humidity generated by two plastic films, microperforated bags (MIPBs) and macroperforated bags (MAPBs), on the levels of phytochemicals present in 'Star Ruby' grapefruits (Citrus paradisi, Macf.) stored for 16 weeks at 10 °C. Control fruits were stored without any packaging film. Juice samples were analyzed every 4 weeks for ascorbic acid, carotenoids, limonoids, flavonoids, and furocoumarins and assessed for quality parameters. MAP significantly reduced weight loss compared to control grapefruits. Control fruits had more β-carotene, lycopene, and furocoumarin compared with the fruits in MAP. Flavonoid content was highest in fruits stored in MAPB (P < 0.05), while fruits stored in MIPB showed no significant difference in flavonoid content compared to control (P > 0.05). The MAP treatments did not significantly affect ascorbic acid, limonoids, or fruit quality parameters, including total soluble solids, acidity, ripening ratio, decay and disorders, fruit taste, and off-flavors after 16 weeks of storage. These results suggest that MAP can be used to maintain the quality of 'Star Ruby' grapefruit with no detrimental effect on health-promoting phytochemicals.

A generic approach for "shotgun" analysis of the soluble proteome of plant cell suspension cultures

Cell suspension cultures from different plant species act as important model systems for studying cellular processes in plant biology and are often used as "green factories" for the production of valuable secondary metabolites and recombinant proteins. While mass spectrometry based proteome analysis techniques are ideally suited to study plant cell metabolism and other fundamental cellular processes from a birds eye perspective, they remain underused in plant studies. We describe a comprehensive sample preparation and multidimensional 'shotgun' proteomics strategy that can be generically applied to plant cell suspension cultures. This strategy was optimized and tested on an Arabidopsis thaliana ecotype Landsberg erecta culture. Furthermore, the implementation of strong cation exchange chromatography as a peptide fractionation step is elaborately tested. Its utility in mass spectrometry based proteome analysis is discussed. Using the presented analytical platform, over 13,000 unique peptides and 2640 proteins could be identified from a single plant cell suspension sample. Finally, the experimental setup is validated using Nicotiana tabacum cv. "Bright Yellow-2" (BY-2) plant cell suspension cultures, thereby demonstrating that the presented analytical platform can also be valuable tool in proteome analysis of non-genomic model systems.

Transcriptional and post-transcriptional regulation of the jasmonate signalling pathway in response to abiotic and harvesting stress in Hevea brasiliensis

BACKGROUND

Latex harvesting in Hevea brasiliensis amounts to strong abiotic stress that can cause a halt in production in the most susceptible clones. Although the role of jasmonic acid has been suggested in laticifer differentiation, its role in latex production and in the response to harvesting stress has received very little attention. Only a few key genes acting in the COI-JAZ-MYC module have been isolated and studied at transcriptional level.

RESULTS

Use of a reference transcriptome obtained on rubber clone PB 260 covering a large number of tissues under different environmental conditions enabled us to identify 24 contigs implicated in the jasmonate signalling pathway in the rubber tree. An analysis of their expression profile by qPCR, combined with hierarchical clustering, suggested that the jasmonate signalling pathway is highly activated in laticifer cells and, more particularly, in the response to harvesting stress. By comparison with their genomic sequences, the existence of regulation by alternative splicing was discovered for JAZ transcripts in response to harvesting stress. Lastly, positive transcriptional regulation of the HbJAZ_1405 gene by MYC was demonstrated.

CONCLUSION

This study led to the identification of all actors of jasmonate signalling pathway and revealed a specific gene expression pattern in latex cells. In-depth analysis of this regulation showed alternative splicing that has been previously shown in Arabidopsis. Interestingly, genotypic variation was observed in Hevea clones with contrasting latex metabolism. This result suggests an involvement of jasmonate signalling pathway in latex production. The data suggest that specific variability of the JA pathway may have some major consequences for resistance to stress. The data support the hypothesis that a better understanding of transcriptional regulations of jasmonate pathway during harvesting stress, along with the use of genotypic diversity in response to such stress, can be used to improve resistance to stress and rubber production in Hevea.

Role of L-ascorbate in alleviating abiotic stresses in crop plants

L-ascorbic acid (vitamin C) is a major antioxidant in plants and plays a significant role in mitigation of excessive cellular reactive oxygen species activities caused by number of abiotic stresses. Plant ascorbate levels change differentially in response to varying environmental stress conditions, depending on the degree of stress and species sensitivity. Successful modulation of ascorbate biosynthesis through genetic manipulation of genes involved in biosynthesis, catabolism and recycling of ascorbate has been achieved. Recently, role of ascorbate in alleviating number of abiotic stresses has been highlighted in crop plants. In this article, we discuss the current understanding of ascorbate biosynthesis and its antioxidant role in order to increase our comprehension of how ascorbate helps plants to counteract or cope with various abiotic stresses.

Overexpression of tomato GDP-L-galactose phosphorylase gene in tobacco improves tolerance to chilling stress

KEY MESSAGE

The overexpression of tomato GDP- l -galactose phosphorylase gene enhanced tolerance to chilling stress and reduced photoinhibition of photosystems I and II in transgenic tobacco. Chilling stress is a crucial factor that limits the geographical distribution and yield of chilling-sensitive plants. Ascorbate (AsA) protects plants by scavenging reactive oxygen species and reduces photoinhibition by promoting the conversion of violaxanthin to zeaxanthin in the xanthophyll cycle to dissipate excess excitation energy. Possible mechanisms of AsA for plant photoprotection under chilling stress were investigated by isolating the tomato GDP-L-galactose phosphorylase gene (SlGGP) and producing transgenic tobacco plants with overexpression of SlGGP. The transgenic plants subjected to chilling stress accumulated less H(2)O(2), demonstrated lower levels of ion leakage and malondialdehyde, and acquired higher net photosynthetic rate, higher maximum photochemical efficiency of PSII, and higher D1 protein content compared with the wild-type (WT) plants. The transgenic plants subjected to chilling stress also showed higher GDP-L-galactose phosphorylase activity, increased AsA content as well as ascorbate peroxidase and oxidizable P700 activities than WT plants. Thus, SlGGP overexpression is crucial in promoting AsA synthesis and alleviating photoinhibition of two photosystems.

Effect of methyl jasmonate on cadmium uptake and antioxidative capacity in Kandelia obovata seedlings under cadmium stress

This study investigated the effects of methyl jasmonate (MeJA) on chlorophyll concentration, lipid peroxidation, Cd uptake, antioxidative capacity, and type-2 metallothionein gene (KoMT2) expression in the leaves of Kandelia obovata seedlings exposed to Cd stress. Deleterious effects, including decreased chlorophyll content and increased malondialdehyde concentration, were observed in leaves of K. obovata after 9d of 200μmol L(-1) Cd treatment. Application of MeJA (0.1 to 1μmol L(-1)) increased the concentration of ascorbic acid and the activities of catalase and ascorbate peroxidase in the leaves of K. obovata, which helped alleviate the oxidative damage induced by Cd stress. The concentration of endogenous jasmonic acid in the leaves of K. obovata was decreased by Cd but was positively stimulated by exogenous MeJA. The expression of KoMT2 in the leaves was enhanced after 9d of 200μmol L(-1) Cd treatment, while the exogenous application of MeJA significantly restored the expression of KoMT2. Exogenous MeJA also inhibited the uptake of Cd to the aboveground part (leaves) of the seedlings, which helped reduce direct damages of Cd to the photosynthetic organ of the plant. The reduced uptake of Cd might be a result of stomatal closure and decreased transpiration by exogenous MeJA.

Multiple feedbacks between chloroplast and whole plant in the context of plant adaptation and acclimation to the environment

This review focuses on feedback pathways that serve to match plant energy acquisition with plant energy utilization, and thereby aid in the optimization of chloroplast and whole-plant function in a given environment. First, the role of source-sink signalling in adjusting photosynthetic capacity (light harvesting, photochemistry and carbon fixation) to meet whole-plant carbohydrate demand is briefly reviewed. Contrasting overall outcomes, i.e. increased plant growth versus plant growth arrest, are described and related to respective contrasting environments that either do or do not present opportunities for plant growth. Next, new insights into chloroplast-generated oxidative signals, and their modulation by specific components of the chloroplast's photoprotective network, are reviewed with respect to their ability to block foliar phloem-loading complexes, and, thereby, affect both plant growth and plant biotic defences. Lastly, carbon export capacity is described as a newly identified tuning point that has been subjected to the evolution of differential responses in plant varieties (ecotypes) and species from different geographical origins with contrasting environmental challenges.

A review (research and patents) on jasmonic acid and its derivatives

In medicinal chemistry there is a growing interest in using small molecules, including plant stress hormones. Jasmonic acid (JA) and its volatile methyl ester (MJ), collectively termed jasmonates, are lipid-derived cyclopentanone compounds that occur ubiquitously and exclusively in the plant kingdom. This review covers the synthesis, usage, and biological activities of JA and its derivatives. A brief overview of the available information on JA and its features is given, followed by a detailed review of JA and its derivatives as drugs and prodrugs; the properties in plants and the synthesis in recent patents are described. This review shows the direction of long-term drug/nutraceutical safety trials and provides insights for future research in this area. Research on JA continues to be of major interest. Recent innovations offer hope for the development of new therapeutics in related fields. It is anticipated that several analogs can be advanced to preclinical and clinical studies.

Proteome reference maps of the Lotus japonicus nodule and root

Legume symbiosis with rhizobia results in the formation of a specialized organ, the root nodule, where atmospheric dinitrogen is reduced to ammonia. In Lotus japonicus (Lotus), several genes involved in nodule development or nodule function have been defined using biochemistry, genetic approaches, and high-throughput transcriptomics. We have employed proteomics to further understand nodule development. Two developmental stages representing nodules prior to nitrogen fixation (white) and mature nitrogen fixing nodules (red) were compared with roots. In addition, the proteome of a spontaneous nodule formation mutant (snf1) was determined. From nodules and roots, 780 and 790 protein spots from 2D gels were identified and approximately 45% of the corresponding unique gene accessions were common. Including a previous proteomics set from Lotus pod and seed, the common gene accessions were decreased to 7%. Interestingly, an indication of more pronounced PTMs in nodules than in roots was determined. Between the two nodule developmental stages, higher levels of pathogen-related 10 proteins, HSPs, and proteins involved in redox processes were found in white nodules, suggesting a higher stress level at this developmental stage. In contrast, protein spots corresponding to nodulins such as leghemoglobin, asparagine synthetase, sucrose synthase, and glutamine synthetase were prevalent in red nodules. The distinct biochemical state of nodules was further highlighted by the conspicuous presence of several nitrilases, ascorbate metabolic enzymes, and putative rhizobial effectors.

Physicochemical and thermodynamic characterization of the encapsulation of methyl jasmonate by natural and modified cyclodextrins using reversed-phase high-pressure liquid chromatography

Although the combinations of methyl jasmonate (MeJA) and cyclodextrins (CDs) have been used by different authors to stimulate the production of several metabolites, no study has been published about the possible formation of MeJA-CD complexes when these two molecules are added together to the reaction medium as elicitors. For this reason and because knowledge of the possible complexation process of MeJA with CD under different physicochemical conditions is essential if these two molecules are to be used in cell cultures, this paper looks at the complexation of MeJA with natural and modified CDs using a reversed-phase high-pressure liquid chromatography (RP-HPLC) system. The interaction of MeJA with β-CD was more efficient than with α- and γ-CDs. However, a modified CD, HP-β-CD, was the most effective of all of the CDs tested. Moreover, MeJA formed complexes with CD with a 1:1 stoichiometry, and the formation constants of these complexes were strongly dependent upon the temperature of the mobile phase used but not the pH. To obtain information about the mechanism of the affinity of MeJA for CD, the thermodynamic parameters ΔG°, ΔH°, and ΔS° were calculated. Finally, molecular modeling studies were carried out to propose which molecular interactions are established in the complexation process.

Influence of seasonal variation and methyl jasmonate mediated induction of glucosinolate biosynthesis on quinone reductase activity in broccoli florets

Methyl jasmonate spray treatments (250 μM) were utilized to alter glucosinolate composition in the florets of the commercial broccoli F1 hybrids 'Pirate', 'Expo', 'Green Magic', 'Imperial', and 'Gypsy' grown in replicated field plantings in 2009 and 2010. MeJA treatment significantly increased glucoraphanin (11%), gluconasturtiin (59%), and neoglucobrassicin (248%) concentrations and their hydrolysis products including sulforaphane (152%), phenethyl isothiocyanate (318%), N-methoxyindole-3-carbinol (313%), and neoascorbigen (232%) extracted from florets of these genotypes over two seasons. Increased quinone reductase (QR) activity was significantly correlated with increased levels of sulforaphane, N-methoxyindole-3-carbinol, and neoascorbigen. Partitioning experiment-wide trait variances indicated that the variability in concentrations of sulforaphane (29%), neoascorbigen (48%), and QR activity (72%) was influenced by year-associated weather variables, whereas variation in neoglucobrassicin (63%) and N-methoxyindole-3-carbinol (46%) concentrations was primarily attributed to methyl jasmonate treatment. These results suggest that methyl jasmonate treatment can enhance QR inducing activity by increased hydrolysis of glucoraphanin into sulforaphane and the hydrolysis products of neoglucobrassicin.

A DESD-box helicase functions in salinity stress tolerance by improving photosynthesis and antioxidant machinery in rice (Oryza sativa L. cv. PB1)

The exact mechanism of helicase-mediated salinity tolerance is not yet understood. We have isolated a DESD-box containing cDNA from Pisum sativum (Pea) and named it as PDH45. It is a unique member of DEAD-box helicase family; containing DESD instead of DEAD/H. PDH45 overexpression driven by constitutive cauliflower mosaic virus-35S promoter in rice transgenic [Oryza sativa L. cv. Pusa Basmati 1 (PB1)] plants confers salinity tolerance by improving the photosynthesis and antioxidant machinery. The Na(+) ion concentration and oxidative stress parameters in leaves of the NaCl (0, 100 or 200 mM) treated PDH45 overexpressing T1 transgenic lines were lower as compared to wild type (WT) rice plants under similar conditions. The 200 mM NaCl significantly reduced the leaf area, plant dry mass, net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 (Ci), chlorophyll (Chl) content in WT plants as compared to the transgenics. The T1 transgenics exhibited higher glutathione (GSH) and ascorbate (AsA) contents under salinity stress. The activities of antioxidant enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) were significantly higher in transgenics; suggesting the existence of an efficient antioxidant defence system to cope with salinity induced-oxidative damage. Yeast two-hybrid assay indicated that the PDH45 protein interacts with Cu/Zn SOD, adenosine-5'-phosphosulfate-kinase, cysteine proteinase and eIF(4G), thus confirming the involvement of ROS scavenging machinery in the transgenic plants to provide salt tolerance. Furthermore, the T2 transgenics were also able to grow, flower, and set viable seeds under continuous salinity stress of 200 mM NaCl. This study provides insights into the mechanism of PDH45 mediated salinity stress tolerance by controlling the generation of stress induced reactive oxygen species (ROS) and also by protecting the photosynthetic machinery through a strengthened antioxidant system.

Tiller number is altered in the ascorbic acid-deficient rice suppressed for L-galactono-1,4-lactone dehydrogenase

The tiller of rice (Oryza sativa L.), which determines the panicle number per plant, is an important agronomic trait for grain production. Ascorbic acid (Asc) is a major plant antioxidant that serves many functions in plants. L-Galactono-1,4-lactone dehydrogenase (GLDH, EC 1.3.2.3) is an enzyme that catalyzes the last step of Asc biosynthesis in plants. Here we show that the GLDH-suppressed transgenic rices, GI-1 and GI-2, which have constitutively low (between 30% and 50%) leaf Asc content compared with the wild-type plants, exhibit a significantly reduced tiller number. Moreover, lower growth rate and plant height were observed in the Asc-deficient plants relative to the trait values of the wild-type plants at different tillering stages. Further examination showed that the deficiency of Asc resulted in a higher lipid peroxidation, a loss of chlorophyll, a loss of carotenoids, and a lower rate of CO(2) assimilation. In addition, the level of abscisic acid was higher in GI-1 plants, while the level of jasmonic acid was higher in GI-1 and GI-2 plants at different tillering stages. The results we presented here indicated that Asc deficiency was likely responsible for the promotion of premature senescence, which was accompanied by a marked decrease in photosynthesis. These observations support the conclusion that the deficiency of Asc alters the tiller number in the GLDH-suppressed transgenics through promoting premature senescence and changing phytohormones related to senescence.

Antisense-mediated depletion of tomato GDP-L-galactose phosphorylase increases susceptibility to chilling stress

The GDP-L-galactose phosphorylase (GGP), which converts GDP-l-galactose to l-Gal-1-phosphate, is generally considered to be a key enzyme of the major ascorbate biosynthesis pathways in higher plants, but experimental evidence for its role in tomato is lacking. In the present study, the GGP gene was isolated from tomato (Solanum lycopersicum) and transient expression of SlGGP-GFP (green fluorescent protein) fusion protein in onion cells revealed the cytoplasmic and nucleus localization of the protein. Antisense transgenic tomato lines with only 50-75% ascorbate level of the wild type (WT) were obtained. Chilling treatment induced lower increase in AsA levels and redox ratio of ascorbate in antisense transgenic plants compared with WT plants. Under chilling stress, transgenic plants accumulated more malendialdehyde (MDA) and more O(2)(·-), leaked more electrolytes and showed lower maximal photochemical efficiency of PSII (Fv/Fm), net photosynthetic rate (Pn), and oxidizable P700 compared with WT plants. Furthermore, the antisense transgenic plants exhibited significantly higher H(2)O(2) level and lower ascorbate peroxidase (APX) activity. Our results suggested that GGP plays an important role in protecting plants against chilling stress by maintaining ascorbate pool and ascorbate redox state.

Emerging trade-offs - impact of photoprotectants (PsbS, xanthophylls, and vitamin E) on oxylipins as regulators of development and defense

This review summarizes evidence for a mechanistic link between plant photoprotection and the synthesis of oxylipin hormones as regulators of development and defense. Knockout mutants of Arabidopsis, deficient in various key components of the chloroplast photoprotection system, consistently produced greater concentrations of the hormone jasmonic acid or its precursor 12- oxo-phytodienoic acid (OPDA), both members of the oxylipin messenger family. Characterized plants include several mutants deficient in PsbS (an intrinsic chlorophyll-binding protein of photosystem II) or pigments (zeaxanthin and/or lutein) required for photoprotective thermal dissipation of excess excitation energy in the chloroplast and a mutant deficient in reactive oxygen detoxification via the antioxidant vitamin E (tocopherol). Evidence is also presented that certain plant defenses against herbivores or pathogens are elevated for these mutants. This evidence furthermore indicates that wild-type Arabidopsis plants possess less than maximal defenses against herbivores or pathogens, and suggest that plant lines with superior defenses against abiotic stress may have lower biotic defenses. The implications of this apparent trade-off between abiotic and biotic plant defenses for plant ecology as well as for plant breeding/engineering are explored, and the need for research further addressing this important issue is highlighted.

Ascorbate as seen through plant evolution: the rise of a successful molecule?

Ascorbate is a widespread and efficient antioxidant that has multiple functions in plants, traditionally associated with the reactions of photosynthesis. This review aims to look at ascorbate from an evolutionary perspective. Cyanobacteria, algae, and bryophytes contain lower concentrations of ascorbate than higher plants, where the molecule accumulates in high concentrations in both photosynthetic and non-photosynthetic organs and tissues. This increase in ascorbate concentration is paralleled by an increase in the number of isoforms of ascorbate peroxidase and the ascorbate regenerating enzymes mono- and dehydroascorbate reductase. One way of understanding the rise in ascorbate concentrations is to consider ascorbate as a molecule among others that has been subject to selection pressures during evolution, due to its cost or benefit for the cell and the organism. Ascorbate has a low cost in terms of synthesis and toxicity, and its benefits include protection of the glutathione pool and proper functioning of a range of enzymes. The hypothesis presented here is that these features would have favoured increasing roles for the molecule in the development and growth of multicellular organisms. This review then focuses on this diversity of roles for ascorbate in both photosynthetic and non-photosynthetic tissues of higher plants, including fruits and seeds, as well as further functions the molecule may possess by looking at other species. The review also highlights one of the trade-offs of domestication, which has often reduced or diluted ascorbate content in the quest for increased fruit growth and yield, with unknown consequences for the corresponding functional diversity, particularly in terms of stress resistance and adaptive responses to the environment.

Proteomic identification of MYC2-dependent jasmonate-regulated proteins in Arabidopsis thaliana

BACKGROUND

MYC2, a basic helix-loop-helix (bHLH) domain-containing transcription factor, participates in the jasmonate (JA) signaling pathway and is involved in the modulation of diverse JA functions. However, a comprehensive list of MYC2-dependent JA-responsive proteins has yet to be defined.

RESULTS

In this paper, we report the comparative proteomics of wild-type (WT) plants and jin1-9, a MYC2 mutant plant, in response to methyl jasmonate (MeJA) treatment. Proteins from mock/MeJA-treated jin1-9 and WT samples were extracted and separated by two-dimensional gel electrophoresis. Twenty-seven JA-mediated proteins demonstrated differential expression modulated by MYC2. We observed that MYC2 negatively regulates the accumulation of JA-dependent indolic glucosinolate-related proteins and exhibits opposite effects on the biosynthetic enzymes involved aliphatic glucosinolate pathways. In addition, proteins involved in the tricarboxylic acid cycle and a majority of the MeJA-inducible proteins that are involved in multiple protective systems against oxidative stress were reduced in jin1-9/myc2 sample compared to the WT sample. These results support a positive role for MYC2 in regulating JA-mediated carbohydrate metabolism and oxidative stress tolerance.

CONCLUSIONS

We have identified MYC2-dependent jasmonate-regulated proteins in Arabidopsis thaliana by performing two-dimensional gel electrophoresis and MALDI-TOF/TOF MS analysis. The observed pattern of protein expression suggests that MYC2 has opposite effects on the biosynthetic enzymes of indolic and aliphatic glucosinolate pathways and positively regulates JA-mediated carbohydrate metabolism and oxidative stress tolerance-related proteins. Furthermore, it is very interesting to note that MYC2 plays opposite roles in the modulation of a subset of JA-regulated photosynthetic proteins during short-term and long-term JA signaling. This study will enhance our understanding of the function of MYC2 in JA signaling in Arabidopsis thaliana.

Genetic and genome-wide transcriptomic analyses identify co-regulation of oxidative response and hormone transcript abundance with vitamin C content in tomato fruit

Background

L-ascorbic acid (AsA; vitamin C) is essential for all living plants where it functions as the main hydrosoluble antioxidant. It has diverse roles in the regulation of plant cell growth and expansion, photosynthesis, and hormone-regulated processes. AsA is also an essential component of the human diet, being tomato fruit one of the main sources of this vitamin. To identify genes responsible for AsA content in tomato fruit, transcriptomic studies followed by clustering analysis were applied to two groups of fruits with contrasting AsA content. These fruits were identified after AsA profiling of an F8 Recombinant Inbred Line (RIL) population generated from a cross between the domesticated species Solanum lycopersicum and the wild relative Solanum pimpinellifollium.

Results

We found large variability in AsA content within the RIL population with individual RILs with up to 4-fold difference in AsA content. Transcriptomic analysis identified genes whose expression correlated either positively (PVC genes) or negatively (NVC genes) with the AsA content of the fruits. Cluster analysis using SOTA allowed the identification of subsets of co-regulated genes mainly involved in hormones signaling, such as ethylene, ABA, gibberellin and auxin, rather than any of the known AsA biosynthetic genes. Data mining of the corresponding PVC and NVC orthologs in Arabidopis databases identified flagellin and other ROS-producing processes as cues resulting in differential regulation of a high percentage of the genes from both groups of co-regulated genes; more specifically, 26.6% of the orthologous PVC genes, and 15.5% of the orthologous NVC genes were induced and repressed, respectively, under flagellin22 treatment in Arabidopsis thaliana.

Conclusion

Results here reported indicate that the content of AsA in red tomato fruit from our selected RILs are not correlated with the expression of genes involved in its biosynthesis. On the contrary, the data presented here supports that AsA content in tomato fruit co-regulates with genes involved in hormone signaling and they are dependent on the oxidative status of the fruit.

The jasmonate-responsive AP2/ERF transcription factors AaERF1 and AaERF2 positively regulate artemisinin biosynthesis in Artemisia annua L

Plants of Artemisia annua produce artemisinin, a sesquiterpene lactone widely used in malaria treatment. Amorpha-4,11-diene synthase (ADS), a sesquiterpene synthase, and CYP71AV1, a P450 monooxygenase, are two key enzymes of the artemisinin biosynthesis pathway. Accumulation of artemisinin can be induced by the phytohormone jasmonate (JA). Here, we report the characterization of two JA-responsive AP2 family transcription factors--AaERF1 and AaERF2--from A. annua L. Both genes were highly expressed in inflorescences and strongly induced by JA. Yeast one-hybrid and electrophoretic mobility shift assay (EMSA) showed that they were able to bind to the CRTDREHVCBF2 (CBF2) and RAV1AAT (RAA) motifs present in both ADS and CYP71AV1 promoters. Transient expression of either AaERF1 or AaERF2 in tobacco induced the promoter activities of ADS or CYP71AV1, and the transgenic A. annua plants overexpressing either transcription factor showed elevated transcript levels of both ADS and CYP71AV1, resulting in increased accumulation of artemisinin and artemisinic acid. By contrast, the contents of these two metabolites were reduced in the RNAi transgenic lines in which expression of AaERF1 or AaERF2 was suppressed. These results demonstrate that AaERF1 and AaERF2 are two positive regulators of artemisinin biosynthesis and are of great value in genetic engineering of artemisinin production.

Neutral invertase, hexokinase and mitochondrial ROS homeostasis: emerging links between sugar metabolism, sugar signaling and ascorbate synthesis

Alkaline/neutral invertases (A/N-Invs) are unique to plants and photosynthetic bacteria. Although considerable advances have been made in our understanding of sucrose metabolic enzymes in plants, the function of A/N-Invs remained puzzling. In a recent study, we have analyzed the subcellullar localization of a cytosolic (At-A/N-InvG, At1g35580) and a mitochondrial (At-A/N-InvA, At1g56560) Arabidopsis A/N-Inv. Unexpectedly, At-A/N-InvA knockout plants showed a more severe growth defect than At-A/N-InvG knockout plants and a link between the two A/N-Invs and oxidative stress defence was found. Overexpression of At-A/N-InvA and At-A/N-InvG in leaf mesophyll protoplasts reduced the activity of the ascorbate peroxidase 2 (APX2) promoter, that was stimulated by hydrogen peroxide and abscisic acid. It is discussed here how sugars and ascorbate might contribute to mitochondrial reactive oxygen species homeostasis. We hypothesize that both mitochondrial and cytosolic A/N-Invs and mitochondria-associated hexokinases are key mediators, integrating metabolic and sugar signalling processes. 

The transcription factor ABI4 Is required for the ascorbic acid-dependent regulation of growth and regulation of jasmonate-dependent defense signaling pathways in Arabidopsis

Cellular redox homeostasis is a hub for signal integration. Interactions between redox metabolism and the ABSCISIC ACID-INSENSITIVE-4 (ABI4) transcription factor were characterized in the Arabidopsis thaliana vitamin c defective1 (vtc1) and vtc2 mutants, which are defective in ascorbic acid synthesis and show a slow growth phenotype together with enhanced abscisic acid (ABA) levels relative to the wild type (Columbia-0). The 75% decrease in the leaf ascorbate pool in the vtc2 mutants was not sufficient to adversely affect GA metabolism. The transcriptome signatures of the abi4, vtc1, and vtc2 mutants showed significant overlap, with a large number of transcription factors or signaling components similarly repressed or induced. Moreover, lincomycin-dependent changes in LIGHT HARVESTING CHLOROPHYLL A/B BINDING PROTEIN 1.1 expression were comparable in these mutants, suggesting overlapping participation in chloroplast to nucleus signaling. The slow growth phenotype of vtc2 was absent in the abi4 vtc2 double mutant, as was the sugar-insensitive phenotype of the abi4 mutant. Octadecanoid derivative-responsive AP2/ERF-domain transcription factor 47 (ORA47) and AP3 (an ABI5 binding factor) transcripts were enhanced in vtc2 but repressed in abi4 vtc2, suggesting that ABI4 and ascorbate modulate growth and defense gene expression through jasmonate signaling. We conclude that low ascorbate triggers ABA- and jasmonate-dependent signaling pathways that together regulate growth through ABI4. Moreover, cellular redox homeostasis exerts a strong influence on sugar-dependent growth regulation.

Methyl jasmonate counteracts boron toxicity by preventing oxidative stress and regulating antioxidant enzyme activities and artemisinin biosynthesis in Artemisia annua L

Boron is an essential plant micronutrient, but it is phytotoxic if present in excessive amounts in soil for certain plants such as Artemisia annua L. that contains artemisinin (an important antimalarial drug) in its areal parts. Artemisinin is a sesquiterpene lactone with an endoperoxide bridge. It is quite expensive compound because the only commercial source available is A. annua and the compound present in the plant is in very low concentration. Since A. annua is a major source of the antimalarial drug and B stress is a deadly threat to its cultivation, the present research was conducted to determine whether the exogenous application of methyl jasmonate (MeJA) could combat the ill effects of excessive B present in the soil. According to the results obtained, the B toxicity induced oxidative stress and reduced the stem height as well as fresh and dry masses of the plant remarkably. The excessive amounts of soil B also lowered the net photosynthetic rate, stomatal conductance, internal CO(2) concentration and total chlorophyll content in the leaves. In contrast, the foliar application of MeJA enhanced the growth and photosynthetic efficiency both in the stressed and non-stressed plants. The excessive B levels also increased the activities of antioxidant enzymes, such as catalase, peroxidase and superoxide dismutase. Endogenous H(2)O(2) and O(2)(-) levels were also high in the stressed plants. However, the MeJA application to the stressed plants reduced the amount of lipid peroxidation and stimulated the synthesis of antioxidant enzymes, enhancing the content and yield of artemisinin as well. Thus, it was concluded that MeJA might be utilized in mitigating the B toxicity and improving the content and yield of artemisinin in A. annua plant.

A review of ascorbic acid potentialities against oxidative stress induced in plants

Ascorbic acid (AA) currently holds a significant position in plant physiology, mainly due to its possession of antioxidant and cellular reductant etc.properties and its diverse roles in plant growth and development and the regulation of a broad spectrum of plant cellular mechanisms against environmental stresses. Some researchers suggest that endogenous AA has been implicated in the promotion of plant growth and development by involvement in a complex and enigmatic array of phytohormone-regulated signalling networks that ties together different environmental stresses. As it is evident from the present review, recent progress on AA potentiality in the tolerance of plants to environmental stresses has been impressive. Indeed, AA plays an important role in resistance to oxidative stresses such as heavy metal, saline, ultra-violet etc. Rapidly increasing evidence indicates that AA is centrally involved in several physiological processes but there has been much disagreement regarding the mechanism(s) by which AA reduces the damaging effects of such stresses in plants. Perhaps the role of AA in mediating tolerance to abiotic stress (e.g. UV, salinity and temperature, etc.) will lead to a greater research focus in the near future. In addition, AA might provide a suitably attractive target for the enhancement of crop production.

Exogenous methyl jasmonate diminishes the formation of lipid-derived compounds in boiled potato (Solanum tuberosum L.)

BACKGROUND

During potato storage the tubers tend to develop off-flavours, mainly due to lipid-derived aldehydes, whose formation is increased after boiling or processing. This may become a problem when boiled or precooked potatoes are used. Methyl jasmonate (MJ) is a phytohormone capable of modifying plant and food composition. The aim of this work was to control the formation of off-flavours in different cultivars of raw potato during storage by MJ treatment.

RESULTS

The use of Carbowax 20M as support in MJ emulsion resulted in significantly (P < 0.05) lower levels of lipid-derived compounds than the use of lanolin. Levels of the lipid-derived aldehydes propanal, hep-2-enal, nonanal, oct-2-enal and hexanal, although dependent on variety, generally decreased significantly (P < 0.05) after treatment with MJ/Carbowax 20M emulsion. Sugar-derived compounds such as pyridine and furfural, however, were not affected by this treatment.

CONCLUSION

Treatment with MJ/Carbowax 20M can be used to diminish the formation of off-flavours in boiled potato. However, this treatment is not useful to avoid the sweetening caused by sugar-derived products. Additional advantages of exogenous MJ are a delay in the appearance of sprouting and aging and hence prolongation of the storage life of potato tubers.

Vitamins in plants: occurrence, biosynthesis and antioxidant function

Plant-derived vitamins are of great interest because of their impact on human health. They are essential for metabolism because of their redox chemistry and role as enzymatic cofactors, not only in animals but also in plants. Several vitamins have strong antioxidant potential, including both water-soluble (vitamins B and C) and lipid-soluble (vitamins A, E and K) compounds. Here, we review recent advances in the understanding of antioxidant roles of vitamins and present an overview of their occurrence within the plant kingdom, different organs and subcellular location; their major biosynthetic pathways, including common precursors and competitive pathways; and their antioxidant function. In particular, we discuss novel evidence for, as well as evidence against, a role of B vitamins as important antioxidants.

Antioxidants and redox regulation: changing notions in a changing world

The concepts of antioxidants and redox regulation are reconsidered in the light of recent findings, and some new future challenges for redox biology are outlined. It is suggested that antioxidants, thioredoxin-mediated redox regulation, and signal transduction mediated by reactive oxygen and nitrogen species, are all part of the same broad mechanism. The integration of different redox inputs, by affecting reversible thiol-disulfide dynamics in a set of target proteins, could result in the regulation of key processes such as proteolysis, gene expression and the functioning of selected metabolic pathways. Most interestingly, redox regulation is not just based on a binary "yes or no" response, and is therefore a convenient way to achieve graded control over the continuum of environmental variables.