A Comparison of the Effect of Lead (Pb) on the Slow Vacuolar (SV) and Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

Little is known about the effect of lead on the activity of the vacuolar K+ channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl2) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K+, the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl2 was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K+ fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb2+ reduces the growth of plant cells.

iTRAQ-Based Proteomics Analysis of Response to Solanum tuberosum Leaves Treated with the Plant Phytotoxin Thaxtomin A

Thaxtomin A (TA) is a phytotoxin secreted by Streptomyces scabies that causes common scab in potatoes. However, the mechanism of potato proteomic changes in response to TA is barely known. In this study, the proteomic changes in potato leaves treated with TA were determined using the Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) technique. A total of 693 proteins were considered as differentially expressed proteins (DEPs) following a comparison of leaves treated with TA and sterile water (as a control). Among the identified DEPs, 460 and 233 were upregulated and downregulated, respectively. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, many DEPs were found to be involved in defense and stress responses. Most DEPs were grouped in carbohydrate metabolism, amino acid metabolism, energy metabolism, and secondary metabolism including oxidation-reduction process, response to stress, plant-pathogen interaction, and plant hormone signal transduction. In this study, we analyzed the changes in proteins to elucidate the mechanism of potato response to TA, and we provided a molecular basis to further study the interaction between plant and TA. These results also offer the option for potato breeding through analysis of the resistant common scab.

Nitric oxide-mediated alternative pathway alleviates aluminum-induced programmed cell death in soybean root tips

Alternative pathway (AP) plays essential roles in plant adaptation to environmental stress. However, the exact role of AP in response to aluminum (Al) toxicity remains elusive. We here provide solid evidences that the activated AP capacity in root tips of soybean alleviated Al toxicity. Furthermore, inhibition of AP by pharmacological or transgenic approach aggravated Al-induced programmed cell death (PCD) occurrence mediated through reactive oxygen species (ROS)-dependent mitochondrial pathway. Our results also demonstrated that nitric oxide (NO) plays a negative role in PCD occurrence caused by Al in soybean root tips. Interestingly, the alleviating effect of NO on Al-induced PCD could be blocked by AP inhibition. Further investigation showed that NO mediates the induction of AP resulting from the upregulation of AOX expression and pyruvate content in Al-treated root tips of soybean. Taken together, our results clearly suggest that AP participates in the alleviation of Al toxicity and also plays a critical role in the alleviating effect of NO on Al-induced PCD occurrence, which will open up new avenues for the improvement of plant growth in acidic soils.

Structural characterization of a polysaccharide from dry mycelium of Penicillium chrysogenum that induces resistance to Tobacco mosaic virus in tobacco plants

Polysaccharides are essential macromolecules that are present in all living organisms. They have a range of biological activities, such as antiviral, antioxidant, immunity-enhancing, and anticancer activities. In this study, a polysaccharide (PCPS) was separated and extracted from dry mycelium of Penicillium chrysogenum by a boiling water step and gel-filtration chromatography. Its structure was characterized by high performance gel-permeation chromatography, chemical derivative, and nuclear magnetic resonance analyses. The results showed that PCPS is a neutral galactomannan with an apparent molecular weight of 19.5 kDa. We evaluated the antiviral activity of PCPS. In half-leaf assays of tobacco plants, the protective effect of PCPS against Tobacco mosaic virus (TMV) was stronger than the protective effects of ningnanmycin and oligosaccharins. Electron microscopy analyses showed that PCPS can directly inactivate viral particles. The mechanism of the antiviral activity of PCPS was explored in a preliminary study. PCPS induced the production of NO and H2O2 to initiate an early defense response. Treatment with PCPS resulted in increased transcript levels of the genes PAL, 4CL, LPO, and increased activities of phenylalanine lyase and peroxidase, which improved the TMV resistance of Nicotiana glutinosa. Expression of the PR-1b gene was also activated during the defense response.

H2O2Accumulation, Host Cell Death and Differential Levels of Proteins Related to Photosynthesis, Redox Homeostasis, and Required for Viral Replication Explain the Resistance of EMS-mutagenized Cowpea to Cowpea Severe Mosaic Virus

Infection with Cowpea severe mosaic virus (CPSMV) represents one of the main limitations for cowpea (Vigna unguiculata L. Walp.) productivity due to the severity of the disease symptoms, frequency of incidence, and difficulties in dissemination control. This study aimed to identify the proteins and metabolic pathways associated with the susceptibility and resistance of cowpea plants to CPSMV. Therefore, we treated the seeds of a naturally susceptible cowpea genotype (CE-31) with the mutagenic agent ethyl methane sulfonate (EMS) and compared the secondary leaf proteomic profile of the mutagenized resistant plants inoculated with CPSMV (MCPI plant group) to those of the naturally susceptible cowpea genotype CE-31 inoculated (CPI) and noninoculated (CPU) with CPSMV. MCPI responded to CPSMV by accumulating proteins involved in the oxidative burst, increasing H₂O₂ generation, promoting leaf cell death (LCD), increasing the synthesis of defense proteins, and decreasing host factors important for the establishment of CPSMV infection. In contrast, CPI accumulated several host factors that favor CPSMV infection and did not accumulate H₂O₂ or present LCD, which allowed CPSMV replication and systemic dissemination. Based on these results, we propose that the differential abundance of defense proteins and proteins involved in the oxidative burst, LCD, and the decrease in cowpea protein factors required for CPSMV replication are associated with the resistance trait acquired by the MCPI plant group.

Comparative proteomic analysis reveals that exogenous 6-benzyladenine (6-BA) improves the defense system activity of waterlogged summer maize

BACKGROUND

Exogenous 6-benzyladenine (6-BA) could improve leaf defense system activity. In order to better understand the regulation mechanism of exogenous 6-benzyladenine (6-BA) on waterlogged summer maize, three treatments including control (CK), waterlogging at the third leaf stage for 6 days (V3-6), and application of 100 mg dm- 3 6-BA after waterlogging for 6 days (V3-6-B), were employed using summer maize hybrid DengHai 605 (DH605) as the experimental material. We used a labeling liquid chromatography-based quantitative proteomics approach with tandem mass tags to determine the changes in leaf protein abundance level at the tasseling stage.

RESULTS

Waterlogging significantly hindered plant growth and decreased the activities of SOD, POD and CAT. In addition, the activity of LOX was significantly increased after waterlogging. As a result, the content of MDA and H2O2 was significantly increased which incurred serious damages on cell membrane and cellular metabolism of summer maize. And, the leaf emergence rate, plant height and grain yield were significantly decreased by waterlogging. However, application of 6-BA effectively mitigated these adverse effects induced by waterlogging. Compared with V3-6, SOD, POD and CAT activity of V3-6-B were increased by 6.9, 12.4, and 18.5%, LOX were decreased by 13.6%. As a consequence, the contents of MDA and H2O2 in V3-6-B were decreased by 22.1 and 17.2%, respectively, compared to that of V3-6. In addition, the leaf emergence rate, plant height and grain yield were significantly increased by application of 6-BA. Based on proteomics profiling, the proteins involved in protein metabolism, ROS scavenging and fatty acid metabolism were significantly regulated by 6-BA, which suggested that application of 6-BA exaggerated the defensive response of summer maize at proteomic level.

CONCLUSIONS

These results demonstrated that 6-BA had contrastive effects on waterlogged summer maize. By regulating key proteins related to ROS scavenging and fatty acid metabolism, 6-BA effectively increased the defense system activity of waterlogged summer maize, then balanced the protein metabolism and improved the plant physiological traits and grain yield.

Genome-wide identification of small heat-shock protein (HSP20) gene family in grape and expression profile during berry development

BACKGROUND

Studies have shown that HSP20 (heat-shock protein 20) genes play important roles in regulating plant growth, development, and stress response. However, the grape HSP20 gene family has not been well studied.

RESULTS

A total of 48 VvHSP20 genes were identified from the grape genome, which were divided into 11 subfamilies (CI, CII, CIII, CV, CVI, CVII, MI, MII, ER, CP and PX/Po) based on a phylogenetic analysis and subcellular localization. Further structural analysis showed that most of the VvHSP20 genes (93.8%) had no intron or only one intron, while genes that clustered together based on a phylogenetic tree had similar motifs and evolutionarily conserved structures. The HSP20s share a conservedα-crystalline domain (ACD) and the different components of the ACD domain suggest the functional diversity of VvHSP20s. In addition, the 48 VvHSP20 genes were distributed on 12 grape chromosomes and the majority of VvHSP20 genes were located at the proximal or distal ends of chromosomes. Chromosome mapping indicated that four groups of VvHSP20 genes were identified as tandem duplication genes. Phytohormone responsive, abiotic and biotic stress-responsive, and plant development-related cis-elements were identified from the cis-regulatory elements analysis of VvHSP20s. The expression profiles of VvHSP20s genes (VvHSP20-1, 11, 14, 17, 18, 19, 20, 24, 25, 28, 31, 39, 42, and 43) were largely similar between RNA-Seq and qRT-PCR analysis after hydrogen peroxide (H₂O₂) treatment. The results showed that most VvHSP20s were down-regulated by H₂O₂ treatment during fruit development. VvHSP20s genes were indeed found to be involved in the grape berry development and differences in their transcriptional levels may be the result of functional differentiation during evolution.

CONCLUSIONS

Our results provide valuable information on the evolutionary relationship of genes in the VvHSP20 family, which is useful for future studies on the functional characteristics of VvHSP20 genes in grape.

Intermittent lead-induced stress on antioxidant enzyme activity and subcellular distribution of Pb in Pogonatherum crinitum seedlings

Pogonatherum crinitum is a promising lead (Pb) hyperaccumulator due to its high Pb tolerance and accumulation ability. However, the mechanisms that support Pb accumulation and tolerance in P. crinitum are not yet clearly understood. An indoor hydroponic experiment was conducted by cultivating P. crinitum seedlings exposed to intermittent Pb stress for 60 days, divided into four stages (T1, T2, T3 and T4), with a 15-day duration per stage. The following concentrations of Pb were used: 0, 500, 0, 500 mg·l^-1 and 0, 1000, 0, 1000 mg·l^-1 ). Antioxidant enzyme activity, Pb concentration and subcellular distribution of Pb were measured at each of the above stages. The results showed that superoxide dismutase (SOD) activity in shoots, and SOD, peroxidase (POD) and malondialdehyde (MDA) activity in shoots and roots significantly increased from T1 (no Pb stress) to T2 (Pb stress) in both 500 mg·l^-1 and 1000 mg·l^-1 treatments; however, no significant difference was noted between stages T3 (no Pb stress) and T4 (Pb stress). There was no obvious effect of Pb stress on catalase (CAT) activity in shoots and roots among different stages. The Pb concentration in shoots was up to 5090.90 mg·kg^-1 and 7573.57 mg·kg^-1 , and the bioconcentration factor (BFC) was 10.18 and 7.57 for the 500 mg·l^-1 and 1000 mg·l^-1 treatments, respectively, which confirmed the Pb hyperaccumulator characteristics of P. crinitum. For plants under Pb stress, most of the Pb was fixed in the cell walls, with a smaller amount in leaves and root vacuoles. Both SOD and POD scavenging of reactive oxygen radicals and fixing and compartmentalisation of Pb in the cell wall might play important roles in detoxification of P. crinitum seedlings in response to Pb stress. There was no phased response of P. crinitum to intermittent Pb stress and the physiological response to Pb stress may be contiguous.

Waterlogging-induced adventitious root formation in cucumber is regulated by ethylene and auxin through reactive oxygen species signalling

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP), the auxin transport inhibitor 1-naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin-induced AR formation was inhibited by 1-MCP, although ethylene-induced AR formation was not inhibited by NPA. Both ethylene- and auxin-induced AR formation were counteracted by DPI. These results indicate that auxin-induced AR formation is dependent on ethylene, whereas ethylene-induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene- and auxin-induced AR formation in cucumber plants.

Structure and function of class III pistil-specific extensin-like protein in interspecific reproductive barriers

BACKGROUND

The transmitting tissue of the style is the pathway for pollen tube growth to the ovules and has components that function in recognizing and discriminating appropriate pollen genotypes. In Nicotiana tabacum, the class III pistil extensin-like (PELPIII) arabinogalactan protein is essential for the inhibition of N. obtusifolia pollen tube growth. The transmitting tissue-specific (TTS) arabinogalactan protein amino acid sequence and expression pattern is similar to PELPIII, but it facilitates self-pollinated N. tabacum. The TTS and PELPIII arabinogalactan protein can be divided into the less conserved N-terminal (NTD) and the more conserved C-terminal (CTD) domains. This research tested whether the NTD is the key domain in determining PELPIII function in the inhibition of interspecific pollen tube growth. Three variant PELPIII gene constructs were produced where the PELPIII NTD was exchanged with the TTS NTD and a single amino acid change (cysteine to alanine) was introduced into the PELPIII NTD. The PELPIII variants of N. tabacum were tested for activity by measuring the inhibition N. obtusifolia pollen tube growth by using them to complement a 3'UTR RNAi transgenic line with reduced PELPIII mRNA.

RESULTS

The RNAi N. tabacum line had reduced PELPIII mRNA accumulation and reduced inhibition of N. obtusifolia pollen tube growth, but had no effect on self-pollen tube growth or pollen tube growth of 12 other Nicotiana species. The NTD of PELPIII with either the PELPIII or TTS CTDs complemented the loss PELPIII activity in the RNAi transgenic line as measured by inhibition of N. obtusifolia pollen tube growth. The TTS NTD with the PELPIII CTD and a variant PELPIII with a cysteine to alanine mutation in its NTD failed to complement the loss of PELPIII activity and did not inhibit N. obtusifolia pollen tube growth.

CONCLUSION

The NTD is a key determinant in PELPIII's function in regulating interspecific pollen tube growth and is a first step toward understanding the mechanism of how PELPIII NTD regulates pollen tube growth.

The role of SIPK signaling pathway in antioxidant activity and programmed cell death of tobacco cells after exposure to cadmium

Cadmium (Cd) toxicity induces oxidative burst and leads to programmed cell death (PCD) in plant cells. The role of salicylic acid-induced protein kinase (SIPK) signaling pathway in Cd-induced oxidative stress was investigated in suspension-cultured tobacco (Nicotiana tabacum L. cv. Barley 21). The cells were pretreated with 40 μM PD98059 (inhibitor of MAPKK) and then exposed to 50 μM Cd for 24 h. The percentages of cell viability, apoptosis, necrosis, and the content of reactive oxygen species (ROS) were monitored by flow cytometry. Expression of PCD related gene (Hsr203J) and the contents of certain signaling molecules were measured as well. The results showed that Cd increased the expression of SIPK, Hsr203J, and CAT genes, the activities of catalase and caspase-3-like enzymes. Addition of PD98059 inhibitor reduced the expression of Hsr203J and CAT genes, decreased CAT activity, but increased ROS and SA contents, and caspase-3-like activity and apoptosis rate. The highest apoptosis level was accompanied by the highest level of Hsr203J gene expression. From the results it can be suggested that upon treatment of tobacco cells with Cd, internal SA content increased and induced the SIPK signaling pathway, thereby inhibited the antioxidant system and led to PCD.

G proteins sculp root architecture in response to nitrogen in rice and Arabidopsis

Nitrogen is a key nutrient for plant growth and development. Plants regulate nitrogen availability and uptake efficiency through controlling root architecture. While the heterotrimeric G protein complex is an important element to regulate root morphology, it remains unknown whether the G protein regulates the root architecture in response to nitrogen supply. We used rice and Arabidopsis G protein mutants to study the root architecture in response to different nitrogen concentrations. We found that nitrogen inhibits root horizontal projection area (network area), root perimeter, total length, but not root diameter (average root width). Nitrogen influenced bushiness and root spatial distribution by inhibiting horizontal growth and promoting vertical expansion. The dynamic changes of the rice G protein mutant DK22 at different concentrations of nitrogen from day 7 to day 9 were different from the wild type with regard to bushiness and spatial distribution. The agb1-2 mutant in Arabidopsis lacked the inhibitory effect of nitrate on root growth. The heterotrimeric G protein complex regulates the inhibitory effect on root growth caused by high nitrogen supply and root spatial distribution in response to different nitrogen concentrations.

Auxin signaling: a big question to be addressed by small molecules

Providing a mechanistic understanding of the crucial roles of the phytohormone auxin has been an important and coherent aspect of plant biology research. Since its discovery more than a century ago, prominent advances have been made in the understanding of auxin action, ranging from metabolism and transport to cellular and transcriptional responses. However, there is a long road ahead before a thorough understanding of its complex effects is achieved, because a lot of key information is still missing. The availability of an increasing number of technically advanced scientific tools has boosted the basic discoveries in auxin biology. A plethora of bioactive small molecules, consisting of the synthetic auxin-like herbicides and the more specific auxin-related compounds, developed as a result of the exploration of chemical space by chemical biology, have made the tool box for auxin research more comprehensive. This review mainly focuses on the compounds targeting the auxin co-receptor complex, demonstrates the various ways to use them, and shows clear examples of important basic knowledge obtained by their usage. Application of these precise chemical tools, together with an increasing amount of structural information for the major components in auxin action, will certainly aid in strengthening our insights into the complexity and diversity of auxin response.

Influence of sulfate supply on selenium uptake dynamics and expression of sulfate/selenate transporters in selenium hyperaccumulator and nonhyperaccumulator Brassicaceae

Stanleya pinnata not only hyperaccumulates selenium (Se) to 0.5% of its dry weight, but also exhibits higher tissue Se-to-sulfur (S) ratios than other species and its surroundings. To investigate the mechanisms underlying this Se enrichment, we compared S. pinnata with the nonhyperaccumulators S. elata and Brassica juncea for selenate uptake in long- (9 d) and short-term (1 h) assays, using different concentrations of selenate and competitor sulfate. Different sulfate pre-treatments (0, 0.5, 5 mM, 3 d) were also tested for effects on selenate uptake and sulfate transporters' expression. Relative to nonhyperaccumulators, S. pinnata showed higher rates of root and shoot Se accumulation and less competitive inhibition by sulfate or by high-S pretreatment. The selenate uptake rate for S. pinnata (1 h) was three- to four-fold higher than for nonhyperaccumulators, and not significantly affected by 100-fold excess sulfate, which reduced selenate uptake by 100% in S. elata and 40% in B. juncea. Real-time reverse transcription PCR indicated constitutive upregulation in S. pinnata of sulfate transporters SULTR1;2 (root influx) and SULTR2;1 (translocation), but reduced SULTR1;1 expression (root influx). In S. pinnata, selenate uptake and translocation rates are constitutively elevated and relatively sulfate-independent. Underlying mechanisms likely include overexpression of SULTR1;2 and SULTR2;1, which may additionally have evolved enhanced specificity for selenate over sulfate.

Target proteins reprogrammed by As and As + Si treatments in Solanum lycopersicum L. fruit

BACKGROUND

Arsenic is an important contaminant of many arable soils worldwide, while silicon, one of the most abundant elements in the earth's crust, interacts with As in the context of plant metabolism. As toxicity results largely from its stimulation of reactive oxygen species, and it is believed that Si can mitigate this process through reduction of the level of oxidative stress. Experiments targeting the proteomic impact of exposure to As and Si have to date largely focused on analyses of root, shoot and seed of a range of mainly non-solanaceous species, thus it remains unclear whether oxidative stress is the most important manifestation of As toxicity in Solanum lycopersicum fruit which during ripening go through drastic physiological and molecular readjustments. The role of Si also needs to be re-evaluated.

RESULTS

A comparison was drawn between the proteomic responses to As and As + Si treatments of the fruit of two tomato cultivars (cvs. Aragon and Gladis) known to contrast for their ability to take up these elements and to translocate them into fruits. Treatments were applied at the beginning of the red ripening stage, and the fruit proteomes were captured after a 14 day period of exposure. For each cultivar, a set of differentially abundant fruit proteins (from non-treated and treated plants) were isolated by 2DGE and identified using mass spectrometry. In the fruit of cv. Aragon, the As treatment reprogrammed proteins largely involved in transcription regulation (growth- regulating factor 9-like), and cell structure (actin-51), while in the cv. Gladis, the majority of differentially expressed proteins were associated with protein ubiquitination and proteolysis (E3 ubiquitin protein, and hormones (1-aminocyclopropane 1-carboxylase).

CONCLUSIONS

The present experiments were intended to establish whether Si supplementation can be used to reverse the proteomic disturbance induced by the As treatment; this reprogram was only partial and more effective in the fruit of cv. Gladis than in that of cv. Aragon. Proteins responsible for the protection of the fruits' quality in the face of As-induced stress were identified. Moreover, supplementation with Si seemed to limit to a degree the accumulation of As in the tomato fruit of cv. Aragon.

Hydrogen peroxide produced by NADPH oxidase: a novel downstream signaling pathway in melatonin-induced stress tolerance in Solanum lycopersicum

The beneficial effects of melatonin on abiotic stress have been demonstrated in several plants. However, little is known about the signal transduction pathway of melatonin involved in the plant stress response. Here, we manipulated the melatonin levels in tomato plants through a chemical approach. The roles of melatonin in stress tolerance were studied by assessing the symptoms, chlorophyll fluorescence and stress-responsive gene expression. Moreover, both chemical and genetic approaches were used to study the roles of hydrogen peroxide (H₂ O₂ ) in melatonin-induced signal transduction in tomato plants. We found that melatonin activates NADPH oxidase (RBOH) to enhance H₂ O₂ levels by reducing its S-nitrosylation activity. Furthermore, melatonin-induced H₂ O₂ accumulation was accompanied by obtainable stress tolerance. Inhibition of RBOH or chemical scavenging of H₂ O₂ significantly reduced the melatonin-induced defense response, including reduced expression of several stress-related genes (CDPK1, MAPK1, TSPMS, ERF4, HSP80 and ERD15) and reduced antioxidative enzyme activity (SOD, CAT and APX), which were responsible for the stress tolerance. Collectively, these results revealed a novel mechanism in which RBOH activity and H₂ O₂ signaling are important components of the melatonin-induced stress tolerance in tomato plants.

Hydrogen peroxide produced by NADPH oxidase: a novel downstream signaling pathway in melatonin-induced stress tolerance in Solanum lycopersicum

The beneficial effects of melatonin on abiotic stress have been demonstrated in several plants. However, little is known about the signal transduction pathway of melatonin involved in the plant stress response. Here, we manipulated the melatonin levels in tomato plants through a chemical approach. The roles of melatonin in stress tolerance were studied by assessing the symptoms, chlorophyll fluorescence and stress-responsive gene expression. Moreover, both chemical and genetic approaches were used to study the roles of hydrogen peroxide (H₂ O₂ ) in melatonin-induced signal transduction in tomato plants. We found that melatonin activates NADPH oxidase (RBOH) to enhance H₂ O₂ levels by reducing its S-nitrosylation activity. Furthermore, melatonin-induced H₂ O₂ accumulation was accompanied by obtainable stress tolerance. Inhibition of RBOH or chemical scavenging of H₂ O₂ significantly reduced the melatonin-induced defense response, including reduced expression of several stress-related genes (CDPK1, MAPK1, TSPMS, ERF4, HSP80 and ERD15) and reduced antioxidative enzyme activity (SOD, CAT and APX), which were responsible for the stress tolerance. Collectively, these results revealed a novel mechanism in which RBOH activity and H₂ O₂ signaling are important components of the melatonin-induced stress tolerance in tomato plants.

Exogenous nitric oxide improves salt tolerance during establishment of Jatropha curcas seedlings by ameliorating oxidative damage and toxic ion accumulation

Jatropha curcas is an oilseed species that is considered an excellent alternative energy source for fossil-based fuels for growing in arid and semiarid regions, where salinity is becoming a stringent problem to crop production. Our working hypothesis was that nitric oxide (NO) priming enhances salt tolerance of J. curcas during early seedling development. Under NaCl stress, seedlings arising from NO-treated seeds showed lower accumulation of Na⁺ and Cl^- than those salinized seedlings only, which was consistent with a better growth for all analyzed time points. Also, although salinity promoted a significant increase in hydrogen peroxide (H₂O₂) content and membrane damage, the harmful effects were less aggressive in NO-primed seedlings. The lower oxidative damage in NO-primed stressed seedlings was attributed to operation of a powerful antioxidant system, including greater glutathione (GSH) and ascorbate (AsA) contents as well as catalase (CAT) and glutathione reductase (GR) enzyme activities in both endosperm and embryo axis. Priming with NO also was found to rapidly up-regulate the JcCAT1, JcCAT2, JcGR1 and JcGR2 gene expression in embryo axis, suggesting that NO-induced salt responses include functional and transcriptional regulations. Thus, NO almost completely abolished the deleterious salinity effects on reserve mobilization and seedling growth. In conclusion, NO priming improves salt tolerance of J. curcas during seedling establishment by inducing an effective antioxidant system and limiting toxic ion and reactive oxygen species (ROS) accumulation.

Protection of sunflower seed and sunflower meal protein with malic acid and heat: effects on in vitro ruminal fermentation and methane production

BACKGROUND

Combined malic acid-heat treatments of protein supplements have been shown to reduce ruminal protein degradation, but there is no information on their possible influence on ruminal fermentation and methane emissions. This study aimed to investigate the effects of the treatment of sunflower meal (SM) and sunflower seed (SS) with malic acid and subsequent drying at 150°C for 1 (MAL1) or 3 h (MAL3) on in vitro rumen fermentation and methane emission using ruminal fluid from sheep as inoculum.

RESULTS

Compared with untreated samples, the MAL3 treatment reduced (P < 0.05) the dry matter effective degradability (DMED) by 78% and 46% for SS and SM, respectively, indicating heat damage. The MAL1 treatment reduced the DMED of SS by 22%, but did not affect (P > 0.05) total volatile fatty acid production for any feed. This treatment also increased (P < 0.05) the propionate proportion (by 17.7% and 15.6% for SS and SM, respectively) and decreased (P < 0.05) methane production (by 15.5% and 11.3%, respectively) and ammonia-N concentrations (by 26.5% and 14.5%, respectively).

CONCLUSION

The MAL1 treatment was effective in reducing both ammonia-N concentrations and methane emissions without depressing SS and SM fermentation, but more research is needed to formulate environmentally cleaner diets for ruminants. © 2016 Society of Chemical Industry.

The germin-like protein OsGLP2-1 enhances resistance to fungal blast and bacterial blight in rice

This is the first report that GLP gene (OsGLP2-1) is involved in panicle blast and bacterial blight resistance in rice. In addition to its resistance to blast and bacterial blight, OsGLP2-1 has also been reported to co-localize with a QTLs for sheath blight resistance in rice. These suggest that the disease resistance provided by OsGLP2-1 is quantitative and broad spectrum. Its good resistance to these major diseases in rice makes it to be a promising target in rice breeding. Rice (Oryza sativa) blast caused by Magnaporthe oryzae and bacterial blight caused by Xanthomonas oryzae pv. oryzae are the two most destructive rice diseases worldwide. Germin-like protein (GLP) gene family is one of the important defense gene families which have been reported to be involved in disease resistance in plants. Although GLP proteins have been demonstrated to positively regulate leaf blast resistance in rice, their involvement in resistance to panicle blast and bacterial blight, has not been reported. In this study, we reported that one of the rice GLP genes, OsGLP2-1, was significantly induced by blast fungus. Overexpression of OsGLP2-1 quantitatively enhanced resistance to leaf blast, panicle blast and bacterial blight. The temporal and spatial expression analysis revealed that OsGLP2-1is highly expressed in leaves and panicles and sub-localized in the cell wall. Compared with empty vector transformed (control) plants, the OsGLP2-1 overexpressing plants exhibited higher levels of H₂O₂ both before and after pathogen inoculation. Moreover, OsGLP2-1 was significantly induced by jasmonic acid (JA). Overexpression of OsGLP2-1 induced three well-characterized defense-related genes which are associated in JA-dependent pathway after pathogen infection. Higher endogenous level of JA was also identified in OsGLP2-1 overexpressing plants than in control plants both before and after pathogen inoculation. Together, these results suggest that OsGLP2-1 functions as a positive regulator to modulate disease resistance. Its good quantitative resistance to the two major diseases in rice makes it to be a promising target in rice breeding.

The germin-like protein OsGLP2-1 enhances resistance to fungal blast and bacterial blight in rice

This is the first report that GLP gene (OsGLP2-1) is involved in panicle blast and bacterial blight resistance in rice. In addition to its resistance to blast and bacterial blight, OsGLP2-1 has also been reported to co-localize with a QTLs for sheath blight resistance in rice. These suggest that the disease resistance provided by OsGLP2-1 is quantitative and broad spectrum. Its good resistance to these major diseases in rice makes it to be a promising target in rice breeding. Rice (Oryza sativa) blast caused by Magnaporthe oryzae and bacterial blight caused by Xanthomonas oryzae pv. oryzae are the two most destructive rice diseases worldwide. Germin-like protein (GLP) gene family is one of the important defense gene families which have been reported to be involved in disease resistance in plants. Although GLP proteins have been demonstrated to positively regulate leaf blast resistance in rice, their involvement in resistance to panicle blast and bacterial blight, has not been reported. In this study, we reported that one of the rice GLP genes, OsGLP2-1, was significantly induced by blast fungus. Overexpression of OsGLP2-1 quantitatively enhanced resistance to leaf blast, panicle blast and bacterial blight. The temporal and spatial expression analysis revealed that OsGLP2-1is highly expressed in leaves and panicles and sub-localized in the cell wall. Compared with empty vector transformed (control) plants, the OsGLP2-1 overexpressing plants exhibited higher levels of H₂O₂ both before and after pathogen inoculation. Moreover, OsGLP2-1 was significantly induced by jasmonic acid (JA). Overexpression of OsGLP2-1 induced three well-characterized defense-related genes which are associated in JA-dependent pathway after pathogen infection. Higher endogenous level of JA was also identified in OsGLP2-1 overexpressing plants than in control plants both before and after pathogen inoculation. Together, these results suggest that OsGLP2-1 functions as a positive regulator to modulate disease resistance. Its good quantitative resistance to the two major diseases in rice makes it to be a promising target in rice breeding.

Early habituation of maize (Zea mays) suspension-cultured cells to 2,6-dichlorobenzonitrile is associated with the enhancement of antioxidant status

The cellulose biosynthesis inhibitor 2,6-dichlorobenzonitrile (DCB) has been widely used to gain insights into cell wall composition and architecture. Studies of changes during early habituation to DCB can provide information on mechanisms that allow tolerance/habituation to DCB. In this context, maize-cultured cells with a reduced amount of cellulose (∼20%) were obtained by stepwise habituation to low DCB concentrations. The results reported here attempt to elucidate the putative role of an antioxidant strategy during incipient habituation. The short-term exposure to DCB of non-habituated maize-cultured cells induced a substantial increase in oxidative damage. Concomitantly, short-term treated cells presented an increase in class III peroxidase and glutathione S-transferase activities and total glutathione content. Maize cells habituated to 0.3-1 µM DCB (incipient habituation) were characterized by a reduction in the relative cell growth rate, an enhancement of ascorbate peroxidase and class III peroxidase activities, and a net increment in total glutathione content. Moreover, these cell lines showed increased levels of glutathione S-transferase activity. Changes in antioxidant/conjugation status enabled 0.3 and 0.5 µM DCB-habituated cells to control lipid peroxidation levels, but this was not the case of maize cells habituated to 1 μM DCB, which despite showing an increased antioxidant capacity were not capable of reducing the oxidative damage to control levels. The results reported here confirm that exposure and incipient habituation of maize cells to DCB are associated with an enhancement in antioxidant/conjugation activities which could play a role in incipient DCB habituation of maize-cultured cells.

Nitric oxide is required for hydrogen gas-induced adventitious root formation in cucumber

Hydrogen gas (H2) is involved in plant development and stress responses. Cucumber explants were used to study whether nitric oxide (NO) is involved in H2-induced adventitious root development. The results revealed that 50% and 100% hydrogen-rich water (HRW) apparently promoted the development of adventitious root in cucumber. While, the responses of HRW-induced adventitious rooting were blocked by a specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), NO synthase (NOS) enzyme inhibitor N(G)-nitro-l-arginine methylester hydrochloride (l-NAME) and nitrate reductase (NR) inhibitor NaN3. HRW also increased NO content and NOS and NR activity both in a dose- and time-dependent fashion. Moreover, molecular evidence showed that HRW up-regulated NR genes expression in explants. The results indicate the importance of NOS and NR enzymes, which might be responsible for NO production in explants during H2-induced root organogenesis. Additionally, peroxidase (POD) and indoleacetic acid oxidase (IAAO) activity was significantly decreased in the explants treated with HRW, while HRW treatment significantly increased polyphenol oxidase (PPO) activity. In addition, cPTIO, l-NAME and NaN3 inhibited the actions of HRW on the activity of these enzymes. Together, NO may be involved in H2-induced adventitious rooting, and NO may be acting downstream in plant H2 signaling cascade.

Leaf aquaporin transcript abundance in peanut genotypes diverging in expression of the limited-transpiration trait when subjected to differing vapor pressure deficits and aquaporin inhibitors

A plant trait currently being exploited to decrease crop yield loss under water-deficit conditions is limited-transpiration rate (TRlim ) under high atmospheric vapor pressure deficit (VPD) conditions. Although limited genotype comparisons for the TRlim trait have been performed in peanut (Arachis hypogaea), no detailed study to describe the basis for this trait in peanut has been reported. Since it has been hypothesized that the TRlim trait may be a result of low leaf hydraulic conductance associated with aquaporins (AQPs), the first objective of this study was to examine a possible correlation of TRlim to leaf AQP transcriptional profiles in six peanut cultivars. Five of the studied cultivars were selected because they expressed TRlim while the cultivar York did not. Transcripts of six AQPs were measured. Under exposure to high vapor pressure deficit, cultivar C 76-16 had decreased AQP transcript abundance for four of the six AQPs but in York only one AQP had decreased abundance. The second objective was to explore the influence of AQP inhibitors mercury and silver on expression of TRlim and AQP transcription profiles. Quantitative RT-PCR data were compared in cultivars York and C 76-16, which had the extreme response in TR to VPD. Inhibitor treatment resulted in increased abundance of AQP transcripts in both. The results of these experiments indicate that AQP transcript abundance itself may not be useful in identifying genotypes expressing the TRlim trait under high VPD conditions.

Common ragweed (Ambrosia artemisiifolia L.): allergenicity and molecular characterization of pollen after plant exposure to elevated NO2

Ragweed pollen is the main cause of allergenic diseases in Northern America, and the weed has become a spreading neophyte in Europe. Climate change and air pollution are speculated to affect the allergenic potential of pollen. The objective of this study was to investigate the effects of NO2 , a major air pollutant, under controlled conditions, on the allergenicity of ragweed pollen. Ragweed was exposed to different levels of NO2 throughout the entire growing season, and its pollen further analysed. Spectroscopic analysis showed increased outer cell wall polymers and decreased amounts of pectin. Proteome studies using two-dimensional difference gel electrophoresis and liquid chromatography-tandem mass spectrometry indicated increased amounts of several Amb a 1 isoforms and of another allergen with great homology to enolase Hev b 9 from rubber tree. Analysis of protein S-nitrosylation identified nitrosylated proteins in pollen from both conditions, including Amb a 1 isoforms. However, elevated NO2 significantly enhanced the overall nitrosylation. Finally, we demonstrated increased overall pollen allergenicity by immunoblotting using ragweed antisera, showing a significantly higher allergenicity for Amb a 1. The data highlight a direct influence of elevated NO2 on the increased allergenicity of ragweed pollen and a direct correlation with an increased risk for human health.

Evaluation of several flocculants for flocculating microalgae

Flocculation of microalgae with chitosan, polyacrylamide, Al2(SO4)3, NaOH and HNO3 was evaluated. Their flocculation efficiencies and optimal dosages were discussed. The effects of the flocculants on cells viability were also investigated and the cells were found to be intact during the flocculation process. Moreover, the effects of flocculants on the extractions were evaluated. Lipid content after flocculants treatments showed no significant differences. Carbohydrate content was lower but protein content was higher after NaOH treatment than those after other treatments. Furthermore, the five flocculated media maintained approximate growth yields to that of the fresh medium in microalgal cultivation, indicating the five flocculated media could be recycled, thereby reducing the cost of biodiesel production from microalgae. Finally, economic comparison of the flocculants was made and the cost of using HNO3, including flocculating cells and recycling medium, was found to be the lowest.

Evaluation of proteome alterations induced by cadmium stress in sunflower (Helianthus annuus L.) cultures

The present study evaluates, at a proteomic level, changes in protein abundance in sunflower leaves in the absence or presence (at 50 or 700mg) of cadmium (as CdCl2). At the end of the cultivation period (45 days), proteins are extracted from leaves with phenol, separated by two-dimensional difference gel electrophoresis (2-D DIGE), and excised from the gels. The differential protein abundances (for proteins differing by more than 1.8 fold, which corresponds to 90% variation) are characterized using nESI-LC-MS/MS. The protein content decreases by approximately 41% in plants treated with 700mg Cd compared with control plants. By comparing all groups of plants evaluated in this study (Control vs. Cd-lower, Control vs. Cd-higher and Cd-lower vs. Cd-higher), 39 proteins are found differential and 18 accurately identified; the control vs. Cd-higher treatment is that presenting the most differential proteins. From identified proteins, those involved in energy and disease/defense (including stress), are the ribulose bisphosphate carboxylase large chain, transketolase, and heat shock proteins are the most differential abundant proteins. Thus, at the present study, photosynthesis is the main process affected by Cd in sunflowers, although these plants are highly tolerant to Cd.

Evaluation of proteome alterations induced by cadmium stress in sunflower (Helianthus annuus L.) cultures

The present study evaluates, at a proteomic level, changes in protein abundance in sunflower leaves in the absence or presence (at 50 or 700mg) of cadmium (as CdCl2). At the end of the cultivation period (45 days), proteins are extracted from leaves with phenol, separated by two-dimensional difference gel electrophoresis (2-D DIGE), and excised from the gels. The differential protein abundances (for proteins differing by more than 1.8 fold, which corresponds to 90% variation) are characterized using nESI-LC-MS/MS. The protein content decreases by approximately 41% in plants treated with 700mg Cd compared with control plants. By comparing all groups of plants evaluated in this study (Control vs. Cd-lower, Control vs. Cd-higher and Cd-lower vs. Cd-higher), 39 proteins are found differential and 18 accurately identified; the control vs. Cd-higher treatment is that presenting the most differential proteins. From identified proteins, those involved in energy and disease/defense (including stress), are the ribulose bisphosphate carboxylase large chain, transketolase, and heat shock proteins are the most differential abundant proteins. Thus, at the present study, photosynthesis is the main process affected by Cd in sunflowers, although these plants are highly tolerant to Cd.

Brassica napus responses to short-term excessive copper treatment with decrease of photosynthetic pigments, differential expression of heavy metal homeostasis genes including activation of gene NRAMP4 involved in photosystem II stabilization

In the present study, the influence of 50 and 100 µM CuSO4 was investigated starting from 3 h till 72 h treatment of 4-weeks Brassica napus plants. High CuSO4 concentrations in nutrient medium resulted in the rapid copper accumulation in plants, especially in roots, much slower and to lower degree in leaves. Copper excess induced early decrease in the leaf water content and temporary leaf wilting. The decrease in content of photosynthetic pigments became significant to 24 h of excessive copper treatments and reached 35 % decrease to 72 h, but there were no significant changes in maximum quantum efficiency of photosystem II photochemistry. The copper excess affected the expression of ten genes involved in heavy metal homeostasis and copper detoxification. The results showed the differential and organ-specific expression of most genes. The potential roles of copper-activated genes encoding heavy metal transporters (ZIP5, NRAMP4, YSL2, and MRP1), metallothioneins (MT1a and MT2b), low-molecular chelator synthesis enzymes (PCS1 and NAS2), and metallochaperones (CCS and HIPP06) in heavy metal homeostasis and copper ion detoxification were discussed. The highest increase in gene expression was shown for NRAMP4 in leaves in spite of relatively moderate Cu accumulation there. The opinion was advanced that the NRAMP4 activation can be considered among the early reactions in the defense of the photosystem II against copper excess.

Proteomic analysis of changes in the Kandelia candel chloroplast proteins reveals pathways associated with salt tolerance

The plant chloroplast is one of the most sensitive organelles in response to salt stress. Chloroplast proteins extracted from seedling leaves were separated by two-dimensional gel electrophoresis (2-DE). More than 600 protein spots could be distinguished on each gel. Fifty-eight differentially expressed protein spots were detected, of which 46 could be identified through matrix-assisted laser desorption ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). These proteins were found to be involved in multiple aspects of chloroplast metabolism pathways such as photosynthesis, ATP synthesis, detoxification and antioxidation processes, nitrogen assimilation and fixation, protein metabolism, and tetrapyrrole biosynthesis. The results indicated that K. candel could withstand up to 500 mM NaCl stress for a measured period of 3 days, by maintaining normal or high photosynthetic electron transfer efficiency and an only slightly stimulated Calvin cycle. Meanwhile, we found that ROS scavenging, nitrogen assimilation, protein degradation and chaperone function in chloroplasts were also of importance for salt tolerance of K. candel. The ultrastructural and physiological data agree with chloroplast proteome results. These findings allow further exploration of our knowledge on salt adaptation in woody halophytes and may contribute to the development of more salt-tolerant plants in the future.

Ion transport in broad bean leaf mesophyll under saline conditions

Salt stress reduces the ability of mesophyll tissue to respond to light. Potassium outward rectifying channels are responsible for 84 % of Na (+) induced potassium efflux from mesophyll cells. Modulation in ion transport of broad bean (Vicia faba L.) mesophyll to light under increased apoplastic salinity stress was investigated using vibrating ion-selective microelectrodes (the MIFE technique). Increased apoplastic Na(+) significantly affected mesophyll cells ability to respond to light by modulating ion transport across their membranes. Elevated apoplastic Na(+) also induced a significant K(+) efflux from mesophyll tissue. This efflux was mediated predominately by potassium outward rectifying channels (84 %) and the remainder of the efflux was through non-selective cation channels. NaCl treatment resulted in a reduction in photosystem II efficiency in a dose- and time-dependent manner. In particular, reductions in Fv'/Fm' were linked to K(+) homeostasis in the mesophyll tissue. Increased apoplastic Na(+) concentrations induced vanadate-sensitive net H(+) efflux, presumably mediated by the plasma membrane H(+)-ATPase. It is concluded that the observed pump's activation is essential for the maintenance of membrane potential and ion homeostasis in the cytoplasm of mesophyll under salt stress.

Benzothiadiazole effect in the compatible tomato-Meloidogyne incognita interaction: changes in giant cell development and priming of two root anionic peroxidases

BTH application is effective in root-knot nematode-tomato interaction in a way that involves a delay in the formation of nematode feeding site and triggers molecular responses at several levels. The compatible interaction between root-knot nematodes and their hosts requires the nematode to overcome plant defense systems so that a sophisticated permanent feeding site (giant cells) can be produced within the host roots. It has been suggested that activators of plant defenses may provide a novel management strategy for controlling root-knot nematodes but little is known about the molecular basis by which these elicitors operate. The role of pre-treatment with Benzothiadiazole (BTH), a salicylic acid analog, in inducing resistance against Meloidogyne incognita infection was investigated in tomato roots. A decrease in galling in roots and feeding site numbers was observed following BTH treatment. Histological investigations showed a delay in formation of feeding sites in treated plants. BTH-treated galls had higher H2O2 production, lignin accumulation, and increased peroxidase activity than untreated galls. The expression of two tomato genes, Tap1 and Tap2, coding for anionic peroxidases, was examined by qRT-PCR and in situ hybridization in response to BTH. Tap1 was induced at all infection points, reaching the highest level at 15 dpi. Tap2 expression, although slightly delayed in untreated galls, increased during infection in both treated and untreated galls. The expression of Tap1 and Tap2 was observed in giant cells of untreated roots, whereas the transcripts were localized in both giant cells and in parenchyma cells surrounding the developing feeding sites in treated plants. These results show that BTH applied to tomato plants makes them more resistant to infection by nematodes, which become less effective in overcoming root defense pathway.

Ion transport in broad bean leaf mesophyll under saline conditions

Salt stress reduces the ability of mesophyll tissue to respond to light. Potassium outward rectifying channels are responsible for 84 % of Na (+) induced potassium efflux from mesophyll cells. Modulation in ion transport of broad bean (Vicia faba L.) mesophyll to light under increased apoplastic salinity stress was investigated using vibrating ion-selective microelectrodes (the MIFE technique). Increased apoplastic Na(+) significantly affected mesophyll cells ability to respond to light by modulating ion transport across their membranes. Elevated apoplastic Na(+) also induced a significant K(+) efflux from mesophyll tissue. This efflux was mediated predominately by potassium outward rectifying channels (84 %) and the remainder of the efflux was through non-selective cation channels. NaCl treatment resulted in a reduction in photosystem II efficiency in a dose- and time-dependent manner. In particular, reductions in Fv'/Fm' were linked to K(+) homeostasis in the mesophyll tissue. Increased apoplastic Na(+) concentrations induced vanadate-sensitive net H(+) efflux, presumably mediated by the plasma membrane H(+)-ATPase. It is concluded that the observed pump's activation is essential for the maintenance of membrane potential and ion homeostasis in the cytoplasm of mesophyll under salt stress.

Analysis of Clonostachys rosea-induced resistance to tomato gray mold disease in tomato leaves

Tomato gray mold disease, caused by Botrytis cinerea, is a serious disease in tomato. Clonostachys rosea is an antagonistic microorganism to B. cinerea. To investigate the induced resistance mechanism of C. rosea, we examined the effects of these microorganisms on tomato leaves, along with changes in the activities of three defense enzymes (PAL, PPO, GST), second messengers (NO, H2O2, O2(-)) and phytohormones (IAA, ABA, GA3, ZT, MeJA, SA and C2H4). Compared to the control, all treatments induced higher levels of PAL, PPO and GST activity in tomato leaves and increased NO, SA and GA3 levels. The expression of WRKY and MAPK, two important transcription factors in plant disease resistance, was upregulated in C. rosea- and C. rosea plus B. cinerea-treated samples. Two-dimensional gel electrophoresis analysis showed that two abundant proteins were present in the C. rosea plus B. cinerea-treated samples but not in the other samples. These proteins were determined (by mass spectrum analysis) to be LEXYL2 (β-xylosidase) and ATP synthase CF1 alpha subunit. Therefore, C. rosea plus B. cinerea treatment induces gray mold resistance in tomato. This study provides a basis for elucidating the mechanism of C. rosea as a biocontrol agent.

Decreased immunoglobulin E (IgE) binding to cashew allergens following sodium sulfite treatment and heating

Cashew nut and other nut allergies can result in serious and sometimes life-threatening reactions. Linear and conformational epitopes within food allergens are important for immunoglobulin E (IgE) binding. Methods that disrupt allergen structure can lower IgE binding and lessen the likelihood of food allergy reactions. Previous structural and biochemical data have indicated that 2S albumins from tree nuts and peanuts are potent allergens, and that their structures are sensitive to strong reducing agents such as dithiothreitol. This study demonstrates that the generally regarded as safe (GRAS) compound sodium sulfite effectively disrupted the structure of the cashew 2S albumin, Ana o 3, in a temperature-dependent manner. This study also showed that sulfite is effective at disrupting the disulfide bond within the cashew legumin, Ana o 2. Immunoblotting and ELISA demonstrated that the binding of cashew proteins by rabbit IgG or IgE from cashew-allergic patients was markedly lowered following treatment with sodium sulfite and heating. The results indicate that incorporation of sodium sulfite, or other food grade reagents with similar redox potential, may be useful processing methods to lower or eliminate IgE binding to food allergens.

Reduction of Antigenicity of Cry j I, Major Allergen of Japanese Cedar Pollen, by the Attachment of Polysaccharides

An attempt was made to mask the allergenic structure of a major allergen protein, Cry j I (CJI), in Japanese cedar pollen using the Maillard-type polysaccharide conjugation. The SDS-PAGE pattern of the CJI-galactomannan conjugate prepared by the Maillard reaction showed broad bands widely distributed from 50 kDa to more than 100 kDa, suggesting the attachment of galactomannan. The competitive enzyme-linked immunosorbent assay showed that the IgE antibody in the sera of cedar pollen-sensitive patients reacted strongly with CJI, while it did not react with the CJI-galactomannan conjugate. This result suggests that the antigenicity of CJI is greatly reduced by the conjugation with galactomannan.

Hitching a ride on vesicles: cauliflower mosaic virus movement protein trafficking in the endomembrane system

The transport of a viral genome from cell to cell is enabled by movement proteins (MPs) targeting the cell periphery to mediate the gating of plasmodesmata. Given their essential role in the development of viral infection, understanding the regulation of MPs is of great importance. Here, we show that cauliflower mosaic virus (CaMV) MP contains three tyrosine-based sorting signals that interact with an Arabidopsis (Arabidopsis thaliana) μA-adaptin subunit. Fluorophore-tagged MP is incorporated into vesicles labeled with the endocytic tracer N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide. The presence of at least one of the three endocytosis motifs is essential for internalization of the protein from the plasma membrane to early endosomes, for tubule formation, and for CaMV infection. In addition, we show that MP colocalizes in vesicles with the Rab GTPase AtRAB-F2b, which is resident in prevacuolar late endosomal compartments that deliver proteins to the vacuole for degradation. Altogether, these results demonstrate that CaMV MP traffics in the endocytic pathway and that virus viability depends on functional host endomembranes.

Identification and characterization of a novel chloroplast/mitochondria co-localized glutathione reductase 3 involved in salt stress response in rice

Glutathione reductases (GRs) are important components of the antioxidant machinery that plants use to respond against abiotic stresses. In rice, one cytosolic and two chloroplastic GR isoforms have been identified. In this work, we describe the cloning and characterization of the full-length cDNA encoding OsGR3, a chloroplast-localized GR that up to now was considered as a non-functional enzyme because of assumed lack of N-terminal conserved domains. The expression of OsGR3 in E. coli validated that it can be translated as a protein with GR activity. OsGR3 shows 76 and 53 % identity with OsGR1 (chloroplastic) and OsGR2 (cytosolic), respectively. Phylogenetic analysis revealed 2 chloroplastic GRs in Poaceae species, including rice, sorghum and brachypodium, but only one chloroplastic GR in dicots. A plastid transit peptide is located at the N terminus of OsGR3, and genetic transformation of rice with a GR3-GFP fusion construct further confirmed its localization in chloroplasts. Furthermore, OsGR1 and OsGR3 are also targeted to mitochondria, which suggest a combined antioxidant mechanism in both chloroplasts and mitochondria. However, both isoforms showed a distinct response to salinity: the expression of OsGR3 but not OsGR1 was induced by salt stress. In addition, the transcript level of OsGR3 was greatly increased with salicylic acid treatment but was not significantly affected by methyl jasmonate, dehydration or heat shock stress. Our results provide new clues about the possible roles of functional OsGR3 in salt stress and biotic stress tolerance.

Normoergic NO-dependent changes, triggered by a SAR inducer in potato, create more potent defense responses to Phytophthora infestans

In our experimental approach we examined how potato leaves exposed to a chemical agent might induce nitric oxide (NO) dependent biochemical modifications for future mobilization of an effective resistance to Phytophthora infestans. After potato leaf treatment with one of the following SAR inducers, i.e. β-aminobutyric acid (BABA), 2,6-dichloroisonicotinic acid (INA) or Laminarin, we observed enhanced NO generation concomitant with biochemical changes related to a slight superoxide anion (O2(-)) and hydrogen peroxide (H2O2) accumulation dependent on minimal NADPH oxidase and peroxidase activities, respectively. These rather normoergic changes, linked to the NO message, were mediated by the temporary down-regulation of S-nitrosoglutathione reductase (GSNOR). In turn, after challenge inoculation signal amplification promoted potato resistance manifested in the up-regulation of GSNOR activity tuned with the depletion of the SNO pool, which was observed by our team earlier (Floryszak-Wieczorek et al., 2012). Moreover, hyperergic defense responses related to an early and rapid O2(-)and H2O2 overproduction together with a temporary increase in NADPH oxidase and peroxidase activities were noted. BABA treatment was the most effective against P. infestans resulting in the enhanced activity of β-1,3-glucanase and callose deposition. Our results indicate that NO-mediated biochemical modifications might play an important role in creating more potent defense responses of potato to a subsequent P. infestans attack.

Enhanced lipoxygenase activity is involved in the stress response but not in the harmful lipid peroxidation and cell death of short-term cadmium-treated barley root tip

Root growth inhibition and radial root swelling were the characteristic symptoms of barley root tips after the short-term exposure of roots to 15 and 30μM Cd. Higher Cd concentrations caused extensive cell death and root growth arrest. Enhanced lipid peroxidation was observed as early as 1h after the short-term treatment in a Cd concentration-dependent manner. In contrast to lipid peroxidation, the induction of lipoxygenase activity was detected only 3h after the exposure of roots to 15 or 30μM Cd. In addition, it was not observed in 60μM Cd-treated root tips. The highest lipoxygenase activity was detected 6h after 15μM Cd treatment in the meristematic and elongation zone of root tip and was probably associated with the radial expansion of cells. Our results indicate that the upregulation of lipoxygenase is an important component of stress response in barley roots to toxic Cd. It is probably involved in the morphological stress response of root tips or/and in the alleviation of Cd-induced toxic alterations in plant cell membranes, but it is not responsible for the Cd-induced harmful lipid peroxidation and cell death.

Unravelling mitochondrial retrograde regulation in the abiotic stress induction of rice ALTERNATIVE OXIDASE 1 genes

Mitochondrial retrograde regulation (MRR) is the transduction of mitochondrial signals to mediate nuclear gene expression. It is not clear whether MRR is a common regulation mechanism in plant abiotic stress response. In this study, we analysed the early abiotic stress response of the rice OsAOX1 genes, and the induction of OsAOX1a and OsAOX1b (OsAOX1a/b) was selected as a working model for the stress-induced MRR studies. We found that the induction mediated by the superoxide ion (O2·(-) )-generating chemical methyl viologen was stronger than that of hydrogen peroxide (H2 O2 ). The addition of reactive oxygen species (ROS) scavengers demonstrated that the stress induction was reduced by eliminating O2·(-) . Furthermore, the stress induction did not rely on chloroplast- or cytosol-derived O2·(-) . Next, we generated transgenic plants overexpressing the superoxide dismutase (SOD) gene at different subcellular locations. The results suggest that only the mitochondrial SOD, OsMSD, attenuated the stress induction of OsAOX1a/b specifically. Therefore, our findings demonstrate that abiotic stress initiates the MRR on OsAOX1a/b and that mitochondrial O2·(-) is involved in the process.

Effect of soil salinity on physiological characteristics of functional leaves of cotton plants

This study analyzes the effects of soil salinity on fatty acid composition, antioxidative enzyme activity, lipid peroxidation, and photosynthesis in functional leaves during the flowering and boll-forming stages of two cotton cultivars, namely, CCRI-44 (salt-tolerant) and Sumian 12 (salt-sensitive), grown under different soil salinity conditions. Saturated (C16:0 and C18:0) and unsaturated fatty acid (FA) contents (C18:1), as well as superoxide dismutase activity increased, whereas high-unsaturated FA (C18:2 and C18:3) decreased, with the increase in soil salinity. The production of malondialdehyde increased with increasing lipoxygenase (LOX) activity, indicating that LOX catalyzed FA peroxidation under salt stress. Soil salinity had no significant effect on catalase (CAT) and peroxidases (POD) activity in the salt-sensitive cultivar Sumian 12, but significantly increased CAT and POD activities in the salt-tolerant cultivar CCRI-44. Net photosynthesis and stomatal conductance of the cotton cultivars decreased in response to salt stress; however, CCRI-44 showed a smaller reduction in photosynthesis than Sumian 12. The results indicated that stomatal apparatus limited leaf photosynthetic capacity in the salinity-treated plants of both cultivars. The net photosynthetic rate, maximum photochemical efficiency, and photochemical quantum yield of the cotton functional leaves showed positive correlation with double-bond index (DBI). These results suggested that salt stress caused DBI reduction and decreased the photochemical conversion efficiency of solar radiation and, thereby resulting in lower net photosynthetic rates.

Purification of protein AP-toxin from Arthrinium phaeospermum causing blight in Bambusa pervariabilis × Dendrocalamopisis grandis and its metabolic effects on four bamboo varieties

Bambusa pervariabilis × Dendrocalamopisis grandis blight is caused by a toxin produced by the fungus Arthrinium phaeospermum. In this study, a toxin fraction (P1-2-2) with an estimated molecular mass of 31 kDa was purified from a culture filtrate of this fungus by ammonium sulfate precipitation, Sephadex G-50 gel chromatography, Q Sepharose Fast Flow anion exchange resin, and Sephadex G-75 chromatography. The N-terminal amino acid sequence (i.e., H(2)N-Gln-Val-Arg-Asp-Arg-Leu-Glu-Ser-Thr) determined by Edman degradation showed homology to known serine alkaline proteases. The purified protein was named AP-toxin. Effects of the purified protein toxin on total phenol, flavonoid, total nucleic acid, DNA, RNA, soluble protein, and soluble sugar content, as well as DNase and RNase activities and disease index, were analyzed in different bamboo varieties by the impregnation method. The toxin had a significant effect on each parameter tested. In addition, a significant correlation was observed among the metabolic index, treatment time, bamboo resistance, and disease index. These data suggest that AP-toxin plays an important role in mediating the phytotoxic activities of A. phaeospermum. This study also indicates that metabolic indices could reflect the resistance indices of hybrid bamboo to blight.

Alternative oxidase 1 (Aox1) gene expression in roots of Medicago truncatula is a genotype-specific component of salt stress tolerance

Alternative oxidase (AOX) is the central component of the non-phosphorylating alternative respiratory pathway in plants and may be important for mitochondrial function during environmental stresses. Recently it has been proposed that Aox can be used as a functional marker for breeding stress tolerant plant varieties. This requires characterization of Aox alleles in plants with different degree of tolerance in a certain stress, affecting plant phenotype in a recognizable way. In this study we examined Aox1 gene expression levels in Medicago truncatula genotypes differing in salt stress tolerance, in order to uncover any correlation between Aox expression and tolerance to salt stress. Results demonstrated a specific induction of Aox1 gene expression in roots of the tolerant genotype that presented the lowest modulation in phenotypic and biochemical stress indices such as morphologic changes, protein level, lipid peroxidation and ROS generation. Similarly, in a previous study we reported that induction of antioxidant gene expression in the tolerant genotype contributed to the support of the antioxidant cellular machinery and stress tolerance. Correlation between expression patterns of the two groups of genes was revealed mainly in 48 h treated roots. Taken together, results from both experiments suggest that M. truncatula tolerance to salt stress may in part due to an efficient control of oxidative balance thanks to (i) induction of antioxidant systems and (ii) involvement of the AOX pathway. This reinforces the conclusion that differences in antioxidant mechanisms can be essential for salt stress tolerance in M. truncatula and possibly the corresponding genes, especially Aox, could be utilized as functional marker.

Phosphorus improves arsenic phytoremediation by Anadenanthera peregrina by alleviating induced oxidative stress

Due to similarities in their chemical behaviors, studies examining interactions between arsenic (As)--in special arsenate--and phosphorus (P) are important for better understanding arsenate uptake, toxicity, and accumulation in plants. We evaluated the effects of phosphate addition on plant biomass and on arsenate and phosphate uptake by Anadenanthera peregrina, an important Brazilian savanna legume. Plants were grown for 35 days in substrates that received combinations of 0, 10, 50, and 100 mg kg(-1) arsenate and 0, 200, and 400 mg kg(-1) phosphate. The addition of P increased the arsenic-phytoremediation capacity of A. peregrina by increasing As accumulation, while also alleviating As-induced oxidative stress. Arsenate phytotoxicity in A. peregrina is due to lipid peroxidation, but not hydrogen peroxide accumulation. Added P also increased the activity of important reactive oxygen species-scavenging enzymes (catalase and ascorbate peroxidase) that help prevent lipid peroxidation in leaves. Our findings suggest that applying P represents a feasible strategy for more efficient As phytoremediation using A. peregrina.

Functional analysis of a WRKY transcription factor involved in transcriptional activation of the DBAT gene in Taxus chinensis

Although the regulation of taxol biosynthesis at the transcriptional level remains unclear, 10-deacetylbaccatin III-10 β-O-acetyl transferase (DBAT) is a critical enzyme in the biosynthesis of taxol. The 1740 bp fragment 5'-flanking sequence of the dbat gene was cloned from Taxus chinensis cells. Important regulatory elements needed for activity of the dbat promoter were located by deletion analyses in T. chinensis cells. A novel WRKY transcription factor, TcWRKY1, was isolated with the yeast one-hybrid system from a T. chinensis cell cDNA library using the important regulatory elements as bait. The gene expression of TcWRKY1 in T. chinensis suspension cells was specifically induced by methyl jasmonate (MeJA). Biochemical analysis indicated that TcWRKY1 protein specifically interacts with the two W-box (TGAC) cis-elements among the important regulatory elements. Overexpression of TcWRKY1 enhanced dbat expression in T. chinensis suspension cells, and RNA interference (RNAi) reduced the level of transcripts of dbat. These results suggest that TcWRKY1 participates in regulation of taxol biosynthesis in T. chinensis cells, and that dbat is a target gene of this transcription factor. This research also provides a potential candidate gene for engineering increased taxol accumulation in Taxus cell cultures.

Potential of the aquatic fern Azolla filiculoides in biodegradation of an azo dye: modeling of experimental results by artificial neural networks

The potential of an aquatic fern, Azolla filiculoides, in phytoremediation of a mono azo dye solution, C.I. Acid Blue 92 (AB92), was studied. The effects of operational parameters such as reaction time, initial dye concentration, fern fresh weight, pH, temperature and reusability of the fern on biodegradation efficiency were investigated. The intermediate compounds produced by biodegradation process were analyzed using GC-MS analysis. An artificial neural network (ANN) model was developed to predict the biodegradation efficiency. The findings indicated that ANN provides reasonable predictive performance (R2 = 0.961). The effects of AB92 solutions (10 and 20 mg L(-1)) on growth, chlorophylls and carotenoids content, activity of antioxidant enzymes such as superoxide dismutase, peroxidase and catalase and formation of malondialdehyde were analyzed. AB92 generally showed inhibitory effects on the growth. Moreover, photosynthetic pigments in the fronds significantly decreased in the treatments. An increase was detected for lipid peroxidation and antioxidant enzymes activity, suggesting that AB92 caused reactive oxygen species production in Azolla fronds, which were scavenged by induced activities of antioxidant enzymes.

Cadmium induced physio-biochemical and molecular response in Brassica juncea

Cadmium is a hazardous heavy metal; its presence in the agricultural soil constrains the crop productivity and restricts crop plants from reaching their full genetic potential. In the present study, two Brassica juncea cultivars (Pusa Bold and Pusa Jaikisan), were exposed to different concentrations of cadmium (Cd) as cadmium chloride (CdCl2) (50 microM, 100 microM, 150 microM, and 200 microM). The effect of cadmium on seed germination ratio, changes in the root and shoot length, plant dry weight, moisture content, metal tolerance index, antioxidant enzyme activity and lipid peroxidation were studied. The consequence of cadmium stress at the molecular level was studied using a key gene Phytochelatin Synthase (PCS). The results of our study suggested that, exposure of cadmium affected the seed germination, growth rate, biomass content and antioxidant enzyme activities in the root, shoot and leaves of both the cultivars. Transcript expression of PCS was increased with increasing CdCl2 concentration in both the cultivars. Based on the results, it was concluded that, Brassica juncea Cv Pusa Jaikisan is more tolerant to cadmium toxicity than the Pusa Bold. These findings could be used to develop heavy metal stress tolerant plants and more importantly, detoxification of heavy metals in the soil.

Influence of sodium chloride on the regulation of Krebs cycle intermediates and enzymes of respiratory chain in mungbean (Vigna radiata L. Wilczek) seedlings

The effect of common salt (NaCl) on ion contents, Krebs cycle intermediates and its regulatory enzymes was investigated in growing mungbean (Vigna radiata L. Wilczek, B 105) seedlings. Sodium and chloride ion contents increased in both root and shoot whereas potassium ion content decreased in shoot of test seedlings with increasing concentrations of NaCl. Organic acids like pyruvate and citrate levels increased whereas malate level decreased under stress in both roots and shoots. Salt stress also variedly affected the activities of different enzymes of respiratory chain. The activity of pyruvate dehydrogenase (E.C. 1.2.4.1) decreased in 50 mM NaCl but increased in 100 mM and 150 mM concentrations, in both root and shoot samples. Succinate dehydrogenase (E.C. 1.3.5.1) activity was reduced in root whereas stimulated in shoot under increasing concentrations of salt. The activity of isocitrate dehydrogenase (E.C. 1.1.1.41) and malate dehydrogenase (E.C. 1.1.1.37) decreased in both root and shoot samples under salt stress. On the contrary, pretreatment of mungbean seeds with sublethal dose of NaCl was able to overcome the adverse effects of stress imposed by NaCl to variable extents with significant alterations of all the tested parameters, resulting in better growth and efficient respiration in mungbean seedlings. Thus, plants can acclimate to lethal level of salinity by pretreatment of seeds with sublethal level of NaCl, which serves to improve their health and production under saline condition, but the sublethal concentration of NaCl should be carefully chosen.

Nitric oxide inhibits the ATPase activity of the chaperone-like AAA+ ATPase CDC48, a target for S-nitrosylation in cryptogein signalling in tobacco cells

NO has important physiological functions in plants, including the adaptative response to pathogen attack. We previously demonstrated that cryptogein, an elicitor of defence reaction produced by the oomycete Phytophthora cryptogea, triggers NO synthesis in tobacco. To decipher the role of NO in tobacco cells elicited by cryptogein, in the present study we performed a proteomic approach in order to identify proteins undergoing S-nitrosylation. We provided evidence that cryptogein induced the S-nitrosylation of several proteins and identified 11 candidates, including CDC48 (cell division cycle 48), a member of the AAA+ ATPase (ATPase associated with various cellular activities) family. In vitro, NtCDC48 (Nicotiana tabacum CDC48) was shown to be poly-S-nitrosylated by NO donors and we could identify Cys(110), Cys(526) and Cys(664) as a targets for S-nitrosylation. Cys(526) is located in the Walker A motif of the D2 domain, that is involved in ATP binding and was previously reported to be regulated by oxidative modification in Drosophila. We investigated the consequence of NtCDC48 S-nitrosylation and found that NO abolished NtCDC48 ATPase activity and induced slight conformation changes in the vicinity of Cys(526). Similarly, substitution of Cys(526) by an alanine residue had an impact on NtCDC48 activity. More generally, the present study identified CDC48 as a new candidate for S-nitrosylation in plants facing biotic stress and further supports the importance of Cys(526) in the regulation of CDC48 by oxidative/nitrosative agents.