The role of reactive oxygen species in hormonal responses

Enzyme regulation patterns in fungal inoculated wheat may reflect resistance and tolerance towards an insect herbivore

Seed inoculation with entomopathogenic fungi (EPF) causes plant-mediated effects against arthropod herbivores, but the responses vary among EPF isolates. We used a wheat model system with three isolates representing Beauveria bassiana and Metarhizium spp. causing either negative or positive effects against the aphid Rhopalosiphum padi. Activities of six carbohydrate enzymes increased in plants showing biomass build-up after EPF inoculations. However, only aldolase activity showed positive correlation with R. padi numbers. Plants inoculated with M. robertsii hosted fewest aphids and showed increased activity of superoxide dismutase, implying a defense strategy of resistance towards herbivores. In M. brunneum-inoculated plants, hosting most R. padi, activities of catalase and glutathione reductase were increased suggesting enhanced detoxification responses towards aphids. However, M. brunneum simultaneously increased plant growth indicating that this isolate may cause the plant to tolerate herbivory. EPF seed inoculants may therefore mediate either tolerance or resistance towards biotic stress in plants in an isolate-dependent manner.

Nano zinc oxide mediated resuscitation of aged Cajanus cajan via modulating aquaporin, cell cycle regulatory genes and hormonal responses

KEY MESSAGE

Nanoparticle pretreatment improved the health of aged Cajanus cajan seeds viz., regulation of redox status, gene expression, and restoration of hormonal homeostasis. Ageing deteriorates the quality of seeds by lowering their vigor and viability, and terminating with loss of germination. These days, nanotechnology has been seen to revolutionize the agricultural sectors, and particularly nano zinc oxide (nZnO) has gained considerable interests due to its distinctive properties. The aim of the present work was to decipher the possibilities of using nZnO to rejuvenate accelerated aged (AA) seeds of Cajanus cajan. Both chemically (CnZnO) and green (GnZnO; synthesized using Moringa oleifera) fabricated nZnOs were characterized via standard techniques to interpret their purity, size, and shape. Experimental results revealed erratic germination with a decline in viability and membrane stability as outcomes of reactive oxygen intermediate (ROI) buildup in AA seeds. Application of nZnO substantially rebated the accrual of ROI, along with enhanced production of antioxidants, α-amylase activity, total sugar, protein and DNA content. Higher level of zinc was assessed qualitatively/ histologically and quantitatively in nZnO pulsed AA seeds, supporting germination without inducing toxicity. Meantime, augmentation in the gibberellic acid with a simultaneous reduction in the abscisic acid level were noted in nZnO invigorated seeds than that determined in the AA seeds, suggesting possible involvement of ROI in hormonal signalling. Furthermore, nZnO-subjected AA seeds unveiled differential expression of aquaporins and cell cycle regulatory genes. Summarizing, among CnZnO and GnZnO, later one holds better potential for a revival of AA seeds of Cajanus cajan by providing considerable tolerance against ageing-associated deterioration via recouping the cellular redox homeostasis, hormonal signaling, and alteration in expression patterns of aquaporin and cell cycle regulatory genes.

The cold-responsive C-repeat binding factors in Betula platyphylla Suk. positively regulate cold tolerance

Cold stress is one of the most destructive abiotic stresses limiting plant growth and development. CBF (C-repeat binding factor) transcription factors and their roles in cold response have been identified in Arabidopsis as well as several other plant species. However, the biological functions and related molecular mechanisms of CBFs in birch (Betula platyphylla Suk.) remain undetermined. In this study, five cold-responsive BpCBF genes, BpCBF1, BpCBF2, BpCBF7, BpCBF10 and BpCBF12 were cloned. Via protoplast transformation, BpCBF7 was found to be localized in nucleus. The result of yeast one hybrid assay validated the binding of BpCBF7 to the CRT/DRE (C-repeat/dehydration responsive element) elements in the promoter of BpERF1.1 gene. By overexpressing and repressing BpCBFs in birch plants, it was proven that BpCBFs play positive roles in the cold tolerance. At the metabolic level, BpCBFs OE lines had lower ROS accumulation, as well as higher activities of antioxidant enzymes (SOD, POD and CAT) and higher accumulation of protective substances (soluble sugar, soluble protein and proline). Via yeast one hybrid and co-transformation of effector and reporter vectors assay, it was proven that BpCBF7 can regulate the expression of BpERF5 and BpZAT10 genes by directly binding to their promoters. An interacting protein of BpCBF7, BpWRKY17, was identified by yeast two hybrid library sequencing and the interaction was validated with in vivo methods. These results indicates that BpCBFs can increase the cold tolerance of birch plants, partly by gene regulation and protein interaction. This study provides a reference for the research on CBF transcription factors and genetic improvement of forest trees upon abiotic stresses.

Mitochondrial VOLTAGE-DEPENDENT ANION CHANNEL 3 regulates stomatal closure by abscisic acid signaling

In Arabidopsis (Arabidopsis thaliana), stomatal closure mediated by abscisic acid (ABA) is redundantly controlled by ABA receptor family proteins (PYRABACTIN RESISTANCE 1 [PYR1]/PYR1-LIKE [PYLs]) and subclass III SUCROSE NONFERMENTING 1 (SNF1)-RELATED PROTEIN KINASES 2 (SnRK2s). Among these proteins, the roles of PYR1, PYL2, and SnRK2.6 are more dominant. A recent discovery showed that ABA-induced accumulation of reactive oxygen species (ROS) in mitochondria promotes stomatal closure. By analyzing stomatal movements in an array of single and higher order mutants, we revealed that the mitochondrial protein VOLTAGE-DEPENDENT ANION CHANNEL 3 (VDAC3) jointly regulates ABA-mediated stomatal closure with a specialized set of PYLs and SnRK2s by affecting cellular and mitochondrial ROS accumulation. VDAC3 interacted with 9 PYLs and all 3 subclass III SnRK2s. Single mutation in VDAC3, PYLs (except PYR1 and PYL2), or SnRK2.2/2.3 had little effect on ABA-mediated stomatal closure. However, knocking out PYR1, PYL1/2/4/8, or SnRK2.2/2.3 in vdac3 mutants resulted in significantly delayed or attenuated ABA-mediated stomatal closure, despite the presence of other PYLs or SnRK2s conferring redundant functions. We found that cellular and mitochondrial accumulation of ROS induced by ABA was altered in vdac3pyl1 mutants. Moreover, H2O2 treatment restored ABA-induced stomatal closure in mutants with decreased stomatal sensitivity to ABA. Our work reveals that VDAC3 ensures redundant control of ABA-mediated stomatal closure by canonical ABA signaling components.

CmWRKY6-1-CmWRKY15-like transcriptional cascade negatively regulates the resistance to fusarium oxysporum infection in Chrysanthemum morifolium

Chrysanthemum Fusarium wilt is a soil-borne disease that causes serious economic losses to the chrysanthemum industry. However, the molecular mechanism underlying the response of chrysanthemum WRKY to Fusarium oxysporum infection remains largely unknown. In this study, we isolated CmWRKY6-1 from chrysanthemum 'Jinba' and identified it as a transcriptional repressor localized in the nucleus via subcellular localization and transcriptional activation assays. We found that CmWRKY6-1 negatively regulated resistance to F. oxysporum and affected reactive oxygen species (ROS) and salicylic acid (SA) pathways using transgenic experiments and transcriptomic analysis. Moreover, CmWRKY6-1 bound to the W-box element on the CmWRKY15-like promoter and inhibited its expression. Additionally, we observed that CmWRKY15-like silencing in chrysanthemum reduced its resistance to F. oxysporum via transgenic experiments. In conclusion, we revealed the mechanism underlying the CmWRKY6-1-CmWRKY15-like cascade response to F. oxysporum infection in chrysanthemum and demonstrated that CmWRKY6-1 and CmWRKY15-like regulates the immune system.

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Role of Nanoparticles in Enhancing Crop Tolerance to Abiotic Stress: A Comprehensive Review

Plants are subjected to a wide range of abiotic stresses, such as heat, cold, drought, salinity, flooding, and heavy metals. Generally, abiotic stresses have adverse impacts on plant growth and development which affects agricultural productivity, causing food security problems, and resulting in economic losses. To reduce the negative effects of environmental stress on crop plants, novel technologies, such as nanotechnology, have emerged. Implementing nanotechnology in modern agriculture can also help improve the efficiency of water usage, prevent plant diseases, ensure food security, reduce environmental pollution, and enhance sustainability. In this regard, nanoparticles (NPs) can help combat nutrient deficiencies, promote stress tolerance, and improve the yield and quality of crops. This can be achieved by stimulating the activity of certain enzymes, increasing the contents (e.g., chlorophyll) and efficiency of photosynthesis, and controlling plant pathogens. The use of nanoscale agrochemicals, including nanopesticides, nanoherbicides, and nanofertilizers, has recently acquired increasing interest as potential plant-enhancing technologies. This review acknowledges the positive impacts of NPs in sustainable agriculture, and highlights their adverse effects on the environment, health, and food chain. Here, the role and scope of NPs as a practical tool to enhance yield and mitigate the detrimental effects of abiotic stresses in crops are described. The future perspective of nanoparticles in agriculture has also been discussed.

Chitosan and nematophagous fungi for sustainable management of nematode pests

Plants are exposed to large number of threats caused by herbivores and pathogens which cause important losses on crops. Plant pathogens such as nematodes can cause severe damage and losses in food security crops worldwide. Chemical pesticides were extendedly used for nematode management. However, due to their adverse effects on human health and the environment, they are now facing strong limitations by regulatory organisations such as EFSA (European Food Safety Authority). Therefore, there is an urgent need for alternative and efficient control measures, such as biological control agents or bio-based plant protection compounds. In this scenario, chitosan, a non-toxic polymer obtained from seafood waste mainly, is becoming increasingly important. Chitosan is the N-deacetylated form of chitin. Chitosan is effective in the control of plant pests and diseases. It also induces plants defence mechanisms. Chitosan is also compatible with some biocontrol microorganisms mainly entomopathogenic and nematophagous fungi. Some of them are antagonists of nematode pests of plants and animals. The nematophagous biocontrol fungus Pochonia chlamydosporia has been widely studied for sustainable management of nematodes affecting economically important crops and for its capability to grow with chitosan as only nutrient source. This fungus infects nematode eggs using hyphal tips and appressoria. Pochonia chlamydosporia also colonizes plant roots endophytically, stimulating plant defences by induction of salicylic and jasmonic acid biosynthesis and favours plant growth and development. Therefore, the combined use of chitosan and nematophagous fungi could be a novel strategy for the biological control of nematodes and other root pathogens of food security crops.

Involvement of Arabidopsis Acyl Carrier Protein 1 in PAMP-Triggered Immunity

Plant fatty acids (FAs) and lipids are essential in storing energy and act as structural components for cell membranes and signaling molecules for plant growth and stress responses. Acyl carrier proteins (ACPs) are small acidic proteins that covalently bind the fatty acyl intermediates during the elongation of FAs. The Arabidopsis thaliana ACP family has eight members. Through reverse genetic, molecular, and biochemical approaches, we have discovered that ACP1 localizes to the chloroplast and limits the magnitude of pattern-triggered immunity (PTI) against the bacterial pathogen Pseudomonas syringae pv. tomato. Mutant acp1 plants have reduced levels of linolenic acid (18:3), which is the primary precursor for biosynthesis of the phytohormone jasmonic acid (JA), and a corresponding decrease in the abundance of JA. Consistent with the known antagonistic relationship between JA and salicylic acid (SA), acp1 mutant plants also accumulate a higher level of SA and display corresponding shifts in JA- and SA-regulated transcriptional outputs. Moreover, methyl JA and linolenic acid treatments cause an apparently enhanced decrease of resistance against P. syringae pv. tomato in acp1 mutants than that in WT plants. The ability of ACP1 to prevent this hormone imbalance likely underlies its negative impact on PTI in plant defense. Thus, ACP1 links FA metabolism to stress hormone homeostasis to be negatively involved in PTI in Arabidopsis plant defense. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Species-Level Differences in Osmoprotectants and Antioxidants Contribute to Stress Tolerance of Quercus robur L., and Q. cerris L. Seedlings under Water Deficit and High Temperatures

The general aim of this work was to compare the leaf-level responses of different protective components to water deficit and high temperatures in Quercus cerris L. and Quercus robur L. Several biochemical components of the osmotic adjustment and antioxidant system were investigated together with changes in hormones. Q. cerris and Q. robur seedlings responded to water deficit and high temperatures by: (1) activating a different pattern of osmoregulation and antioxidant mechanisms depending on the species and on the nature of the stress; (2) upregulating the synthesis of a newly-explored osmoprotectant, dimethylsulphoniopropionate (DMSP); (3) trading-off between metabolites; and (4) modulating hormone levels. Under water deficit, Q. cerris had a higher antioxidant capacity compared to Q. robur, which showed a lower investment in the antioxidant system. In both species, exposure to high temperatures induced a strong osmoregulation capacity that appeared largely conferred by DMSP in Q. cerris and by glycine betaine in Q. robur. Collectively, the more stress-responsive compounds in each species were those present at a significant basal level in non-stress conditions. Our results were discussed in terms of pre-adaptation and stress-induced metabolic patterns as related to species-specific stress tolerance features.

The acceleration of yellow lupine flower abscission by jasmonates is accompanied by lipid-related events in abscission zone cells

Yellow lupine is an economically important crop. This species has been used as a great model for abscission processes for several years due to extreme flower abortion, which takes place in the abscission zone (AZ). AZ activation involves modifications of cell walls, membranes, and cellular structure. In this paper, we applied physiological, molecular, biochemical, and instrumental methods to explore lipid-associated changes and the possible involvement of lipid-derived phytohormones - jasmonates (JAs) - in flower AZ activation. Our comprehensive analyses revealed that natural abscission is accompanied by the upregulation of peroxidase, which reflects a disruption of redox balance and/or lipids peroxidation in AZ cell membranes. Redox imbalance was confirmed by appearance of malondialdehyde. Lipid-related processes involved the specific localization and increased level and activity of lipase and LOX, enzymes associated with cell membrane rupture, and JA biosynthesis. Lipid-hydrolyzing phospholipase D, implicated previously in abscission, is also found in naturally active AZs. Observed changes are accompanied by the accumulation of jasmonates, both free jasmonic acid and its methyl ester. The JA derivative exhibited higher biological activity than the nonconjugated form. Overall, our study shed new light on the lipid and phytohormonal regulation of AZ functioning supporting a role of JAs during abscission-associated events.

Downregulation of lncRNA PpL-T31511 and Pp-miRn182 Promotes Hydrogen Cyanamide-Induced Endodormancy Release through the PP2C-H2O2 Pathway in Pear (Pyrus pyrifolia)

Bud endodormancy is an important, complex process subject to both genetic and epigenetic control, the mechanism of which is still unclear. The endogenous hormone abscisic acid (ABA) and its signaling pathway play important roles in the endodormancy process, in which the type 2C protein phosphatases (PP2Cs) is key to the ABA signal pathway. Due to its excellent effect on endodormancy release, hydrogen cyanamide (HC) treatment is considered an effective measure to study the mechanism of endodormancy release. In this study, RNA-Seq analysis was conducted on endodormant floral buds of pear (Pyrus pyrifolia) with HC treatment, and the HC-induced PP2C gene PpPP2C1 was identified. Next, software prediction, expression tests and transient assays revealed that lncRNA PpL-T31511-derived Pp-miRn182 targets PpPP2C1. The expression analysis showed that HC treatment upregulated the expression of PpPP2C1 and downregulated the expression of PpL-T31511 and Pp-miRn182. Moreover, HC treatment inhibited the accumulation of ABA signaling pathway-related genes and hydrogen peroxide (H₂O₂). Furthermore, overexpression of Pp-miRn182 reduced the inhibitory effect of PpPP2C1 on the H₂O₂ content. In summary, our study suggests that downregulation of PpL-T31511-derived Pp-miRn182 promotes HC-induced endodormancy release in pear plants through the PP2C-H₂O₂ pathway.

Persistence of the Effects of Se-Fertilization in Olive Trees over Time, Monitored with the Cytosolic Ca2+ and with the Germination of Pollen

Selenium (Se) is an important micronutrient for living organisms, since it is involved in several physiological and metabolic processes. Biofortification with Se increases the nutritional and qualitative values of foods in Se-deficient regions and increases tolerance to oxidative stress in olive trees. Many studies have shown that Se, in addition to improving the qualitative and nutritional properties of EVO oil, also improves the plant's response to abiotic stress. This study addressed this issue by monitoring the effects of Se on cytosolic Ca²⁺ and on the germination of olive pollen grains in oxidative stress. The olive trees subjected to treatment with Na-selenate in the field produced pollen with a Se content 6-8 times higher than the controls, even after 20 months from the treatment. Moreover, part of the micronutrient was organic in selenium methionine. The higher selenium content did not produce toxic effects in the pollen, rather it antagonized the undesirable effects of oxidative stress in the parameters under study. The persistence of the beneficial effects of selenium observed over time in pollens, in addition to bringing out an undisputed adaptability of olive trees to the micronutrient, suggested the opportunity to reduce the number of treatments in the field.

Involvement of Reactive Oxygen Species in ABA-Induced Increase in Hydraulic Conductivity and Aquaporin Abundance

The role of reactive oxygen species (ROS) in ABA-induced increase in hydraulic conductivity was hypothesized to be dependent on an increase in aquaporin water channel (AQP) abundance. Single ABA application or its combination with ROS manipulators (ROS scavenger ascorbic acid and NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI)) were studied on detached roots of barley plants. We measured the osmotically driven flow rate of xylem sap and calculated root hydraulic conductivity. In parallel, immunolocalization of ABA and HvPIP2;2 AQPs was performed with corresponding specific antibodies. ABA treatment increased the flow rate of xylem, root hydraulic conductivity and immunostaining for ABA and HvPIP2;2, while the addition of antioxidants prevented the effects of this hormone. The obtained results confirmed the involvement of ROS in ABA effect on hydraulic conductivity, in particular, the importance of H₂O₂ production by ABA-treated plants for the effect of this hormone on AQP abundance.

24-epibrassinolide alleviates postharvest yellowing of broccoli via improving its antioxidant capacity

Postharvest crop yellowing is a major concern in the broccoli industry. The effect and underlying mechanisms of 24-epibrassinolide (EBR) treatment on yellowing in postharvest broccoli were investigated. Treatment with 2 µM EBR markedly inhibited the increase of the yellowing index and L* values, causing higher retention of the metric hue angle and chlorophyll content compared to the control. Treatment also alleviated oxidative damage by preventing the accumulation of malondialdehyde and superoxide anion (O₂^•-). The ascorbic acid content of broccoli reached its lowest value at the end of its shelf life, whereas that of the treated sample was obviously higher than the control. Moreover, treated broccoli exhibited higher superoxide dismutase, ascorbate peroxidase, and phenylalanine ammonia-lyase activities. Multivariate statistical analysis further demonstrated the effective enhancement of EBR treatment on antioxidant enzymes. These results indicate that exogenous application of EBR ameliorates postharvest yellowing by improving the antioxidant capacity of broccoli.

TaRac6 Is a Potential Susceptibility Factor by Regulating the ROS Burst Negatively in the Wheat-Puccinia striiformis f. sp. tritici Interaction

Rac/Rop proteins play important roles in the regulation of cell growth and plant defense responses. However, the function of Rac/Rop proteins in wheat remains largely unknown. In this study, a small G protein gene, designated as TaRac6, was characterized from wheat (Triticum aestivum) in response to Puccinia striiformis f. sp. tritici (Pst) and was found to be highly homologous to the Rac proteins identified in other plant species. Transient expression analyses of the TaRac6-GFP fusion protein in Nicotiana benthamiana leaves showed that TaRac6 was localized in the whole cell. Furthermore, transient expression of TaRac6 inhibited Bax-triggered plant cell death (PCD) in N. benthamiana. Transcript accumulation of TaRac6 was increased at 24 h post-inoculation (hpi) in the compatible interaction between wheat and Pst, while it was not induced in an incompatible interaction. More importantly, silencing of TaRac6 by virus induced gene silencing (VIGS) enhanced the resistance of wheat (Suwon 11) to Pst (CYR31) by producing fewer uredinia. Histological observations revealed that the hypha growth of Pst was markedly inhibited along with more H₂O₂ generated in the TaRac6-silenced leaves in response to Pst. Moreover, transcript levels of TaCAT were significantly down-regulated, while those of TaSOD and TaNOX were significantly up-regulated. These results suggest that TaRac6 functions as a potential susceptibility factor, which negatively regulate the reactive oxygen species (ROS) burst in the wheat-Pst interaction.

WRKY33-PIF4 loop is required for the regulation of H2O2 homeostasis

The reactive oxygen species (ROS) are continuously produced and are essential for mediating the growth and development of plants. However too much accumulation of ROS can result in the oxidative damage to cells, especially under the adverse environmental conditions. Plants have evolved sophisticated strategies to regulate the homeostasis of H₂O₂. In this study, we generated transgenic Arabidopsis plants in the Ws ecotype (Ws) background in which WRKY33 is co-suppressed (csWRKY33/Ws). Compared with Ws, csWRKY33/Ws plants accumulate more H₂O₂. RNA-seq analysis indicated that in csWRKY33/Ws plants, expression of oxidative stress related genes such as ascorbate peroxidase 2 (APX2) is affected. Over-expression of APX2 can rescue the phenotype of csWRKY33/Ws, suggesting that the changes in the growth of csWRKY33/Ws is duo to the higher accumulation of H₂O₂. Analysis of the CHIP-seq data suggested that WRKY33 can directly regulate the expression of PIF4, vice versa. qPCR analysis also confirmed that the mutual regulation between WRKY33 and PIF4. Similar to that of csWRKY33/Ws, and the accumulation of H₂O₂ in pif4 also increased. Taken together, our results reveal a WRKY33-PIF4 regulatory loop that appears to play an important role in regulating the growth and development of seedlings by mediating H₂O₂ homeostasis.

Transcriptomic analysis of poco1, a mitochondrial pentatricopeptide repeat protein mutant in Arabidopsis thaliana

BACKGROUND

Flowering is a crucial stage during plant development. Plants may respond to unfavorable conditions by accelerating reproductive processes like flowering. In a recent study, we showed that PRECOCIOUS1 (POCO1) is a mitochondrial pentatricopeptide repeat (PPR) protein involved in flowering time and abscisic acid (ABA) signaling in Arabidopsis thaliana. Here, we use RNA-seq data to investigate global gene expression alteration in the poco1 mutant.

RESULTS

RNA-seq analysis was performed during different developmental stages for wild-type and poco1 plants. The most profound differences in gene expression were found when wild-type and poco1 plants of the same developmental stage were compared. Coverage analysis confirmed the T-DNA insertion in POCO1, which was concomitant with truncated transcripts. Many biological processes were found to be enriched. Several flowering-related genes such as FLOWERING LOCUS T (FT), which may be involved in the early-flowering phenotype of poco1, were differentially regulated. Numerous ABA-associated genes, including the core components of ABA signaling such as ABA receptors, protein phosphatases, protein kinases, and ABA-responsive element (ABRE) binding proteins (AREBs)/ABRE-binding factors (ABFs) as well as important genes for stomatal function, were mostly down-regulated in poco1. Drought and oxidative stress-related genes, including ABA-induced stress genes, were differentially regulated. RNA-seq analysis also uncovered differentially regulated genes encoding various classes of transcription factors and genes involved in cellular signaling. Furthermore, the expression of stress-associated nuclear genes encoding mitochondrial proteins (NGEMPs) was found to be altered in poco1. Redox-related genes were affected, suggesting that the redox state in poco1 might be altered.

CONCLUSION

The identification of various enriched biological processes indicates that complex regulatory mechanisms underlie poco1 development. Differentially regulated genes associated with flowering may contribute to the early-flowering phenotype of poco1. Our data suggest the involvement of POCO1 in the early ABA signaling process. The down-regulation of many ABA-related genes suggests an association of poco1 mutation with the ABA signaling deficiency. This condition further affects the expression of many stress-related, especially drought-associated genes in poco1, consistent with the drought sensitivity of poco1. poco1 mutation also affects the expression of genes associated with the cellular regulation, redox, and mitochondrial perturbation.

Maize NCP1 negatively regulates drought and ABA responses through interacting with and inhibiting the activity of transcription factor ABP9

NCP1, a NINJA family protein lacking EAR motif, acts as a negative regulator of ABA signaling by interacting with and inhibiting the activity of transcriptional activator ABP9. The phytohormone abscisic acid plays a pivotal role in regulating plant responses to a variety of abiotic stresses including drought and salinity. Maize ABP9 is an ABRE-binding bZIP transcription activator that enhances plant tolerance to multiple stresses by positively regulating ABA signaling, but the molecular mechanism by which ABP9 is regulated in mediating ABA responses remains unknown. Here, we report the identification of an ABP9-interacting protein, named ABP Nine Complex Protein 1 (NCP1) and its functional characterization. NCP1 belongs to the recently identified NINJA family proteins, but lacks the conserved EAR motif, which is a hallmark of this class of transcriptional repressors. In vitro and in vivo assays confirmed that NCP1 physically interacts with ABP9 and that they are co-localized in the nucleus. In addition, NCP1 and ABP9 are similarly induced with similar patterns by ABA treatment and osmotic stress. Interestingly, NCP1 over-expressing Arabidopsis plants exhibited a reduced sensitivity to ABA and decreased drought tolerance. Transient assay in maize protoplasts showed that NCP1 inhibits the activity of ABP9 in activating ABRE-mediated reporter gene expression, a notion further supported by genetic analysis of drought and ABA responses in the transgenic plants over-expressing both ABP9 and NCP1. These data together suggest that NCP1 is a novel negative regulator of ABA signaling via interacting with and inhibiting the activity of ABP9.

Comprehensive analysis of the Gossypium hirsutum L. respiratory burst oxidase homolog (Ghrboh) gene family

BACKGROUND

Plant NADPH oxidase (NOX), also known as respiratory burst oxidase homolog (rboh), encoded by the rboh gene, is a key enzyme in the reactive oxygen species (ROS) metabolic network. It catalyzes the formation of the superoxide anion (O2•-), a type of ROS. In recent years, various studies had shown that members of the plant rboh gene family were involved in plant growth and developmental processes as well as in biotic and abiotic stress responses, but little is known about its functional role in upland cotton.

RESULTS

In the present study, 26 putative Ghrboh genes were identified and characterized. They were phylogenetically classified into six subfamilies and distributed at different densities across 18 of the 26 chromosomes or scaffolds. Their exon-intron structures, conserved domains, synteny and collinearity, gene family evolution, regulation mediated by cis-acting elements and microRNAs (miRNAs) were predicted and analyzed. Additionally, expression profiles of Ghrboh gene family were analyzed in different tissues/organs and at different developmental stages and under different abiotic stresses, using RNA-Seq data and real-time PCR. These profiling studies indicated that the Ghrboh genes exhibited temporal and spatial specificity with respect to expression, and might play important roles in cotton development and in stress tolerance through modulating NOX-dependent ROS induction and other signaling pathways.

CONCLUSIONS

This comprehensive analysis of the characteristics of the Ghrboh gene family determined features such as sequence, synteny and collinearity, phylogenetic and evolutionary relationship, expression patterns, and cis-element- and miRNA-mediated regulation of gene expression. Our results will provide valuable information to help with further gene cloning, evolutionary analysis, and biological function analysis of cotton rbohs.

Phosphoinositide 3-Kinase Promotes Oxidative Burst, Stomatal Closure and Plant Immunity in Bacterial Invasion

Phosphoinositide 3-kinase (PI3K) plays a vital role in plant response to abiotic stress. However, the role of PI3K in plant immunity is largely unknown. This study showed that PI3K enhanced Arabidopsis resistance to Pseudomonas syringae pv tomato DC3000 (Pst DC3000) and Pst DC3000 (avrRpt2). Overexpression of AtVPS34 promoted stomatal closure while PI3K inhibitors blocked that after spray inoculation. Additionally, gene expression of AtVPS34 was increased upon infection by Pst DC3000 (avrRpt2), and SA upregulated AtVPS34 gene expression in this process. Furthermore, overexpression of AtVPS34 enhanced PR gene expression after syringe infiltration with Pst DC3000 (avrRpt2), while PI3K inhibitors inhibited that. The production of hydrogen peroxide and the expression of gene encoding antioxidant enzyme were both enhanced in AtVPS34 overexpressing lines after spray inoculation or syringe infiltration with Pst DC3000 (avrRpt2). Collectively, these results unraveled a novel and broad role of PI3K in plant immunity which promoted stomatal closure and PR gene expression possibly via regulating ROS production.

OsFPFL4 is Involved in the Root and Flower Development by Affecting Auxin Levels and ROS Accumulation in Rice (Oryza sativa)

BACKGROUND

FPF1 (flowering-promoting factor 1) is one of the important family involved in the genetic control of flowering time in plant. Until now, limited knowledge concerning FPF1 family in rice has been understood.

RESULTS

As a homologue of AtFPF1, FPF1-like protein 4 of rice (OsFPFL4) is expressed in various tissues of plants. The functions of OsFPFL4 in rice were investigated by the reverse genetics approaches. Plants overexpressing OsFPFL4 have shorter primary root, more lateral roots and adventitious roots than wild type; however, RNA interference (RNAi) of OsFPFL4 significantly inhibits the growth of root system, and also delays the flowering time in rice. Interestingly, increased or repressed expression of OsFPFL4 leads to shrunken anthers and abnormal pollen grains. It is well recognized that auxin plays important roles in plant root and flower development, and the root elongation is also regulated by reactive oxygen species (ROS) homeostasis. Here, our results show that rice plants overexpressing OsFPFL4 accumulate more auxin in the shoot and root, whereas RNAi lines have less auxin than wild type. As expected, the transcript levels of genes responsible for auxin biosynthesis and polar transport are altered in these OsFPFL4 transgenic plants. As to ROS, slightly higher ROS levels were detected in overexpression root and inflorescence than the counterparts of wild type; however, the ROS levels were significantly increased in the RNAi lines, due to increased expression of ROS-producers and reduced expression of ROS-scavengers.

CONCLUSION

Our results reveal that OsFPFL4 is involved in modulating the root and flower development by affecting auxin and ROS homeostasis in rice plants. OsFPFL4 controls auxin accumulation via affecting auxin biosynthesis and transport, and also modulates ROS homeostasis by balancing ROS producing and scavenging. Thus, auxin-mediated ROS production might play a role in regulating redox status, which controls plant root and flower development.

Ascorbic Acid Priming Enhances Seed Germination and Seedling Growth of Winter Wheat under Low Temperature Due to Late Sowing in Pakistan

Poor seed germination is a crucial yield-limiting factor when winter wheat is sown under low temperature. The objective of this study was to evaluate the role of ascorbic acid (AsA) in the extenuation of the harmful effects of low temperature at early and reproductive stages of wheat during 2016–2017 (15 November to 15 December). A two-year experiment was conducted using a randomized complete block design with split plot arrangement and with three replicates. Sowing dates (15 November and 15 December) were allotted to the main plot while seed priming (control, hydro-priming, and AsA priming) were allotted to the sub-plot. Results demonstrated that AsA priming significantly boosted different yield characteristics including chlorophyll content, tillers per unit area, number of grains per spike, and 1000-grain weight, contributing higher productivity and biomass during 2016–2017. The results further revealed that AsA could induce the up-regulation of diverse antioxidants (super oxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), thus offsetting the adverse effects of sub-supra optimum temperatures of late sowing wheat. It is therefore concluded in this work that AsA priming enhances stand establishment, yield and yield-related traits, antioxidant enzyme activities, and chlorophyll contents when wheat is sown under low temperature.

Selenium maintains cytosolic Ca2+ homeostasis and preserves germination rates of maize pollen under H2O2-induced oxidative stress

Selenium (Se) displays antioxidant properties that can be exploited, in plants, to counteract abiotic stresses caused by overly-produced reactive oxygen species (ROS). Here, we show that fertigation of maize crops with sodium selenate effectively protects pollen against oxidative stress. Pollen isolated from Se-treated plants (Se1) and untreated controls (Se0) was incubated in vitro with H₂O₂ to produce oxidative challenge. Given the impact of ROS on Ca²⁺ homeostasis and Ca²⁺-dependent signaling, cytosolic Ca²⁺ was measured to monitor cellular perturbations. We found that H₂O₂ disrupted Ca²⁺ homeostasis in Se0 pollen only, while Se1 samples were preserved. The same trend was observed when Se0 samples were treated with sodium selenate or Se-methionine, which recapitulated in vitro the protective capacity of Se-fertigation. Furthermore, we found that germination rates were much better retained in Se1 as compared to Se0 (46% vs 8%, respectively) after exposure to 20 mM H₂O₂. The same was observed with Se0 pollen treated with Se-methionine, which is the organic form of Se into which most fertigated sodium selenate converts in the plant. These results, together, show a close correlation between ROS, Ca²⁺ homeostasis and pollen fertility, and provide strong evidence that Se-fertigation is an excellent approach to preserve or enhance agricultural productivity.

Overexpression of a CPYC-Type Glutaredoxin, OsGrxC2.2, Causes Abnormal Embryos and an Increased Grain Weight in Rice

Glutaredoxins (Grxs) are a ubiquitous group of oxidoreductase enzymes that are important in plant growth and development; however, the functions of rice Grxs have not been fully elucidated. In this paper, we showed that one of the Grxs, encoded by OsGrxC2.2, exhibited Grx activity. Furthermore, we demonstrated that OsGrxC2.2 was able to regulate embryo development during embryogenesis. Transgenic rice lines overexpressing OsGrxC2.2 unexpectedly exhibited degenerate embryos as well as embryoless seeds. Our data indicated that the embryonic abnormalities occurred at an early stage during embryogenesis. We found that the expression of several endodermal layer marker genes for embryo development, such as OSH1 (apical region marker), OsSCR (L2 ground tissue marker), and OsPNH1 (L3 vascular tissue marker), were significantly decreased in the OsGrxC2.2-overexpressed transgenic rice lines. In contrast, the transcript levels of the majority of protodermal layer markers, including HAZ1, ROC2, ROC3, and RAmy1A, and the shoot apical meristem marker HB, showed little change between the wild-type (WT) and OsGrxC2.2-overexpressing embryos. Surprisingly, the seed weight of the overexpressed transgenic rice was remarkably increased in comparison to that of the WT. These results indicate that the overexpression of OsGrxC2.2 interferes with the normal embryogenesis of rice embryos and leads to increased grain weight. To the best of our knowledge, this is the first report that OsGrxC2.2 is a rice embryo development-associated gene.

Differential Function of Endogenous and Exogenous Abscisic Acid during Bacterial Pattern-Induced Production of Reactive Oxygen Species in Arabidopsis

Abscisic acid (ABA) plays important roles in positively or negatively regulating plant disease resistance to pathogens. Here, we reassess the role of endogenous and exogenous ABA by using: 35S::ABA2, a previously reported transgenic Arabidopsis line with increased endogenous ABA levels; aba2-1, a previously reported ABA2 mutant with reduced endogenous ABA levels; and exogenous application of ABA. We found that bacterial susceptibility promoted by exogenous ABA was suppressed in 35S::ABA2 plants. The 35S::ABA2 and aba2-1 plants displayed elevated and reduced levels, respectively, of bacterial flagellin peptide (flg22)-induced H₂O₂. Surprisingly, ABA pre-treatment reduced flg22-induced H₂O₂ generation. Exogenous, but not endogenous ABA, increased catalase activity. Loss of nicotinamide adenine dinucleotide phosphate oxidase genes, RBOHD and RBOHF, restored exogenous ABA-promoted bacterial susceptibility of 35S::ABA2 transgenic plants. In addition, endogenous and exogenous ABA had similar effects on callose deposition and salicylic acid (SA) signaling. These results reveal an underlying difference between endogenous and exogenous ABA in regulating plant defense responses. Given that some plant pathogens are able to synthesize ABA and affect endogenous ABA levels in plants, our results highlight the importance of reactive oxygen species in the dual function of ABA during plant-pathogen interactions.

Cytosolic Glucose-6-Phosphate Dehydrogenase Is Involved in Seed Germination and Root Growth Under Salinity in Arabidopsis

Glucose-6-phosphate dehydrogenase (G6PDH or G6PD) is the key regulatory enzyme in the oxidative pentose phosphate pathway (OPPP). The cytosolic isoforms including G6PD5 and G6PD6 account for the major part of the G6PD total activity in plant cells. Here, we characterized the Arabidopsis single null mutant g6pd5 and g6pd6 and double mutant g6pd5/6. Compared to wild type, the mutant seeds showed a reduced germination rate and root elongation under salt stress. The seeds and seedlings lacking G6PD5 and G6PD6 accumulate more reactive oxygen species (ROS) than the wild type under salt stress. Cytosolic G6PD (cy-G6PD) affected the expression of NADPH oxidases and the G6PD enzymatic activities in the mutant atrbohD/F, in which the NADPH oxidases genes are disrupted by T-DNA insertion and generation of ROS is inhibited, were lower than that in the wild type. The NADPH level in mutants was decreased under salt stress. In addition, we found that G6PD5 and G6PD6 affected the activities and transcript levels of various antioxidant enzymes in response to salt stress, especially the ascorbate peroxidase and glutathione reductase. Exogenous application of ascorbate acid and glutathione rescued the seed and root phenotype of g6pd5/6 under salt stress. Interestingly, the cytosolic G6PD negatively modulated the NaCl-blocked primary root growth under salt stress in the root meristem and elongation zone.

Involvement of G6PD5 in ABA response during seed germination and root growth in Arabidopsis

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PDH or G6PD) functions in supply of NADPH, which is required for plant defense responses to stresses. However, whether G6PD functions in the abscisic acid (ABA) signaling pathway remains to be elucidated. In this study, we investigated the involvement of the cytosolic G6PD5 in the ABA signaling pathway in Arabidopsis.

RESULTS

We characterized the Arabidopsis single null mutant g6pd5. Phenotypic analysis showed that the mutant is more sensitive to ABA during seed germination and root growth, whereas G6PD5-overexpressing plants are less sensitive to ABA compared to wild type (WT). Furthermore, ABA induces excessive accumulation of reactive oxygen species (ROS) in mutant seeds and seedlings. G6PD5 participates in the reduction of H₂O₂ to H₂O in the ascorbate-glutathione cycle. In addition, we found that G6PD5 suppressed the expression of Abscisic Acid Insensitive 5 (ABI5), the major ABA signaling component in dormancy control. When G6PD5 was overexpressed, the ABA signaling pathway was inactivated. Consistently, G6PD5 negatively modulates ABA-blocked primary root growth in the meristem and elongation zones. Of note, the suppression of root elongation by ABA is triggered by the cell cycle B-type cyclin CYCB1.

CONCLUSIONS

This study showed that G6PD5 is involved in the ABA-mediated seed germination and root growth by suppressing ABI5.

Selenium-Enriched Pollen Grains of Olea europaea L.: Ca2+ Signaling and Germination Under Oxidative Stress

Selenium (Se) shows antioxidant properties that can be exploited in plants to combat abiotic stresses caused by reactive oxygen species produced in excess (ROS). Here, we show that the Se-fertilization of olive trees with sodium selenate effectively protects the pollen from oxidative stress. Pollen isolated from plants treated with Se or from untreated controls was incubated in vitro with H₂O₂ to produce an oxidative challenge. Given the impact of ROS on Ca²⁺ homeostasis and Ca²⁺-dependent signaling, cytosolic Ca²⁺ was measured to monitor cellular perturbations. We found that H₂O₂ interrupted Ca²⁺ homeostasis only in untreated pollen, while in samples treated in vitro with sodium selenate or selenium methionine, Ca²⁺ homeostasis was preserved. Furthermore, germination rates were considerably better maintained in Se-fertilized pollen compared to non-fertilized pollen (30% vs. 15%, respectively) after exposure to 1 mM H₂O₂. The same was observed with pollen treated in vitro with Se-methionine, which is the organic form of Se, in which part of the fertigated sodium selenate is converted in the plant. Combined, our results show a close correlation between ROS, Ca²⁺ homeostasis, and pollen fertility and provide clear evidence that Se-fertilization is a potential approach to preserve or improve agricultural productivity.

Interplay between the unfolded protein response and reactive oxygen species: a dynamic duo

Secretory proteins undergo modifications such as glycosylation and disulphide bond formation before proper folding, and move to their final destination via the endomembrane system. Accumulation of unfolded proteins in the endoplasmic reticulum (ER) due to suboptimal environmental conditions triggers a response called the unfolded protein response (UPR), which induces a set of genes that elevate protein folding capacity in the ER. This review aims to establish a connection among ER stress, UPR, and reactive oxygen species (ROS), which remains an unexplored topic in plants. For this, we focused on mechanisms of ROS production originating from ER stress, the interaction between ER stress and overall ROS signalling process in the cell, and the interaction of ER stress with other organellar ROS signalling pathways such as of the mitochondria and chloroplasts. The roles of the UPR during plant hormone signalling and abiotic and biotic stress responses are also discussed in connection with redox and ROS signalling.

A preliminary analysis of the effects of bisphenol A on the plant root growth via changes in endogenous plant hormones

Bisphenol A (BPA) is ubiquitous in the environment worldwide, affecting plant growth and development. Endogenous plant hormones serve as switches that regulate plant growth and development. However, plants have different physiological requirements and environmental adaptive capacities during the different growth stages. Here, we investigated the effects of BPA on soybean (Glycine max L.) root growth at the three growth stages and analyzed the mechanisms underlying the effects of BPA on the root growth by assessing changes in endogenous hormone. The results showed that low concentration of BPA (1.5mgL-1) improved root growth (except at the seed-filling stage), increased indole-3-acetic acid (IAA) content at the first two growth stages, and increased zeatin (ZT) content and decreased gibberellic acid (GA3) content at the seedling stage. But low concentration of BPA caused decreased ethylene (ETH) contents and constant abscisic acid (ABA) content at all three stages. However, BPA at moderate and high concentrations (6.0 and 12.0mgL-1) inhibited root growth, causing the decreased IAA, GA3 and ETH contents and increased ABA content at all three growth stages. The change degrees of above indices were weakened with prolonging the growth stages. After BPA withdrawal, both the root growth and the hormone contents recovered (with the exception of ZT and ETH), and the recovery degrees had negative correlation with the BPA exposure concentration and had positive correlation with the growth stage. Changes in residual BPA content in the roots were also observed at different BPA concentrations and different growth stages. Our results demonstrated the effects of BPA on root growth were related to BPA-induced changes in hormone, which performed differently at various growth stages.

Nonredundant functions of Arabidopsis LecRK-V.2 and LecRK-VII.1 in controlling stomatal immunity and jasmonate-mediated stomatal closure

Stomatal immunity restricts bacterial entry to leaves through the recognition of microbe-associated molecular patterns (MAMPs) by pattern-recognition receptors (PRRs) and downstream abscisic acid and salicylic acid signaling. Through a reverse genetics approach, we characterized the function of the L-type lectin receptor kinase-V.2 (LecRK-V.2) and -VII.1 (LecRK-VII.1). Analyses of interactions with the PRR FLAGELLIN SENSING2 (FLS2) were performed by co-immunoprecipitation and bimolecular fluorescence complementation and whole-cell patch-clamp analyses were used to evaluate guard cell Ca²⁺ -permeable cation channels. The Arabidopsis thaliana LecRK-V.2 and LecRK-VII.1 and notably their kinase activities were required for full activation of stomatal immunity. Knockout lecrk-V.2 and lecrk-VII.1 mutants were hyper-susceptible to Pseudomonas syringae infection and showed defective stomatal closure in response to bacteria or to the MAMPs flagellin and EF-Tu. By contrast, Arabidopsis over-expressing LecRK-V.2 or LecRK-VII.1 demonstrated a potentiated stomatal immunity. LecRK-V.2 and LecRK-VII.1 are shown to be part of the FLS2 PRR complex. In addition, LecRK-V.2 and LecRK-VII.1 were critical for methyl jasmonate (MeJA)-mediated stomatal closure, notably for MeJA-induced activation of guard cell Ca²⁺ -permeable cation channels. This study highlights the role of LecRK-V.2 and LecRK-VII.1 in stomatal immunity at the FLS2 PRR complex and in MeJA-mediated stomatal closure.

Transcriptome profiling provides insights into dormancy release during cold storage of Lilium pumilum

Background

Bulbs of the ornamental flower Lilium pumilum enter a period of dormancy after flowering in spring, and require exposure to cold for a period of time in order to release dormancy. Previous studies focused mainly on anatomical, physiological and biochemical changes during dormancy release. There are no dormancy studies of the northern cold-hardy wild species of Lilium at the molecular level. This study observed bulb cell and starch granule ultrastructures during cold storage; and analysed the transcriptome using sequencing. The combination of morphological and transcriptomic methods provides valuable insights into dormancy release during cold storage of Lilium pumilum.

Results

Ultrastructural changes reflected dormancy release during cold storage of the bulbs. We compared gene expression levels among samples at 0 (S1 stage), 30 (S2 stage), 60 (S3 stage) and 90 (S4 stage) d of cold storage, with 0 d as the control. The data showed that some regulatory pathways such as carbohydrate metabolism and plant hormone signal transduction were activated to break dormancy. Some differentially expressed genes (DEGs) related to antioxidant activity, epigenetic modification and transcription factors were induced to respond to low temperature conditions. These genes constituted a complex regulatory mechanism of dormancy release.

Conclusions

Cytological data related to dormancy regulation was obtained through histomorphological observation; transcriptome sequencing provided comprehensive sequences and digital gene expression tag profiling (DGE) data, and bulb cell ultrastructural changes were closely related to DEGs. The novel Lilium pumilum genetic information from this study provides a reference for the regulation of dormancy by genetic engineering using molecular biology tools.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4536-x) contains supplementary material, which is available to authorized users.

Glucohexaose-induced protein phosphatase 2C regulates cell redox status of cucumber seedling

Protein Phosphatase 2C (PP2C) is an important phosphatase-like protein in eukaryotic organisms that can negatively regulate protein kinase cascade abscisic acid (ABA) signal system through phosphorylation and carry out vital roles in various cell processes. The previous study indicated that the accumulation of reactive oxygen species (ROS) is a part of mechanism of glucohexaose-induced resistance in cucumber cotyledons, and CsPP2C80s might play a crucial role in processes related to ROS produce and signal transduction. To identify the mechanism of CsPP2C80s involved in glucohexaose and ABA signaling regulating cell redox status, the effects of glucohexaose and ROS inhibitor pretreatment on endogenous ABA content and ABA signaling genes expression levels of cucumber seedlings were analysed. These results suggest that cucumber CsPP2C80s are involved in ROS accumulation and ABA signal transduction pathway induced by glucohexaose, CsPP2C80s play a positive regulatory role in process of ABA combined with ABA receptors (PYLs) to activate SNF1-related protein kinases 2 (SnRK2s) and regulate NADPH oxidase to produce extracellular hydrogen peroxide (H2O2), providing unequivocal molecular evidence of PP2C-mediated ABA response mechanisms functioning in cell redox status induced by glucohexaose.

Abscisic acid mediated differential growth responses of root and shoot of Vigna radiata (L.) Wilczek seedlings under water stress

Water stress is a common problem in Indian agriculture and recent global climate change has aggravated this problem further. Plants have an adaptive response to water scarcity as reflected in differential root and shoot growth. In case of Vigna radiata seedlings we have observed earlier promotion of root growth while inhibition of shoot (hypocotyl) growth under mild water stress, which is probably mediated by ABA. However, the exact mechanism of ABA action is far from clear. The present study attempts to elucidate the action of ABA through apoplastic reactive oxygen species (ROS) and its impact upon antioxidant defence system during the growth of root and shoot under water stress. Thus promotion of root growth by application of exogenous ABA (10 μM) and mild water stress (ψ -0.5 MPa) may be correlated with enhanced apoplastic ROS production possibly by activating plasma membrane located NADPH oxidase (NOX) enzyme. On the contrary, in hypocotyls where growth was rather inhibited by application of water stress or ABA, neither NOX activity nor ROS accumulation was significantly detected upon these treatments. Overall activity of antioxidant enzymes [superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.1) and catalase (CAT, EC 1.11.1.6)] was high and somewhat promoted by ABA and water stress treatment in roots compared to hypocotyls. A possible ROS-mediated role of ABA in promoting growth and antioxidant activity in roots under water stress has been proposed.

Tracing the role of plant proteins in the response to metal toxicity: a comprehensive review

Plants are sessile in nature, but are capable to evade from high level concentration of heavy metals like Cd, Hg, Cu, through various metabolic pathways. Some of the pathways regulate normal metabolism in plants, whereas others are required for for their survival under metal toxicity. Different plant proteins act as transporters to transfer metal from one organelle to the other and further eliminate it out from the plants. Initially, exposure of heavy metals/metalloids to plants lead to over expression of proteins which in turn stimulate other stress-related genes. Further, they activate signalling mechanism like MAPK cascade, Cd-Calmodulin signalling pathway, and oxidation signalling pathway that lead to generation of ROS (reactive oxygen species). Once these ROS (highly unstable) are formed, they generate free radicals which react with macromolecules like proteins and DNA. This has negative impact on plant growth and leads to ageing and, eventually, cell death. The uncontrolled, destructive processes damage plants physiologically and ultimately lead to oxidative stress. Activation of antioxidant enzymes like SOD (superoxide dismutase) and CAT (catalase) allows plants to cope under oxidative stress conditions. Among plant proteins, some of the antioxidant enzymes like glutathione, and APX (ascorbate peroxidase) play defensive roles against abiotic stress in plants. Chaperones help in protein folding to maintain protein stability under stress conditions. With this background, the present review gives a brief account of the functions, localization and expression pattern of plant proteins against metal/metalloid toxicity. Moreover, the aim of this review is also to summarize the cutting edge research of plant protein and metal interfaces and their future prospects.

Induction of auxin biosynthesis and WOX5 repression mediate changes in root development in Arabidopsis exposed to chitosan

Chitosan is a natural polymer with applications in agriculture, which causes plasma membrane permeabilisation and induction of intracellular reactive oxygen species (ROS) in plants. Chitosan has been mostly applied in the phylloplane to control plant diseases and to enhance plant defences, but has also been considered for controlling root pests. However, the effect of chitosan on roots is virtually unknown. In this work, we show that chitosan interfered with auxin homeostasis in Arabidopsis roots, promoting a 2-3 fold accumulation of indole acetic acid (IAA). We observed chitosan dose-dependent alterations of auxin synthesis, transport and signalling in Arabidopsis roots. As a consequence, high doses of chitosan reduce WOX5 expression in the root apical meristem and arrest root growth. Chitosan also propitiates accumulation of salicylic (SA) and jasmonic (JA) acids in Arabidopsis roots by induction of genes involved in their biosynthesis and signalling. In addition, high-dose chitosan irrigation of tomato and barley plants also arrests root development. Tomato root apices treated with chitosan showed isodiametric cells respect to rectangular cells in the controls. We found that chitosan causes strong alterations in root cell morphology. Our results highlight the importance of considering chitosan dose during agronomical applications to the rhizosphere.

L-Met Activates Arabidopsis GLR Ca2+ Channels Upstream of ROS Production and Regulates Stomatal Movement

Plant glutamate receptor homologs (GLRs) have long been proposed to function as ligand-gated Ca²⁺ channels, but no in planta evidence has been provided. Here, we present genetic evidence that Arabidopsis GLR3.1 and GLR3.5 form Ca²⁺ channels activated by L-methionine (L-Met) at physiological concentrations and regulate stomatal apertures and plant growth. The glr3.1/3.5 mutations resulted in a lower cytosolic Ca²⁺ level, defective Ca²⁺-induced stomatal closure, and Ca²⁺-deficient growth disorder, all of which involved L-Met. Patch-clamp analyses of guard cells showed that GLR3.1/3.5 Ca²⁺ channels are activated specifically by L-Met, with the activation abolished in glr3.1/3.5. Moreover, GLR3.1/3.5 Ca²⁺ channels are distinct from previously characterized ROS-activated Ca²⁺ channels and act upstream of ROS, providing Ca²⁺ transients necessary for the activation of NADPH oxidases. Our data indicate that GLR3.1/3.5 constitute L-Met-activated Ca²⁺ channels responsible for maintaining basal [Ca²⁺]_cyt, play a pivotal role in plant growth, and act upstream of ROS, thereby regulating stomatal aperture.

Impact of Metal and Metal Oxide Nanoparticles on Plant: A Critical Review

An increasing need of nanotechnology in various industries may cause a huge environment dispersion of nanoparticles in coming years. A concern about nanoparticles interaction with flora and fauna is raised due to a growing load of it in the environment. In recent years, several investigators have shown impact of nanoparticles on plant growth and their accumulation in food source. This review examines the research performed in the last decade to show how metal and metal oxide nanoparticles are influencing the plant metabolism. We addressed here, the impact of nanoparticle on plant in relation to its size, concentration, and exposure methodology. Based on the available reports, we proposed oxidative burst as a general mechanism through which the toxic effects of nanoparticles are spread in plants. This review summarizes the current understanding and the future possibilities of plant-nanoparticle research.

Enantioselective oxidative stress caused by chiral ionic liquids forms of 1-alkyl-3-methyl imidazolium tartrate on Scenedesmus obliquus

Ionic liquids (ILs) are widely used, but their potential threat to the environment has recently gained more attention. The enantioselective oxidative stress caused by chiral ionic liquids (CILs), such as 1-alkyl-3-methyl imidazolium tartrate (RMIM T), on Scenedesmus obliquus was demonstrated in this study. Stronger green fluorescence was observed in response to l-(+)-RMIM T treatment than to d-(+)-RMIM T treatment, which suggested that more reactive oxygen species (ROS) were stimulated by l-(+)-RMIM T. Significantly higher ROS levels were recorded during the RMIM T treatments than in the control. There were 1.13-, 1.25-, 1.43-, 1.68-, and 1.96-fold increases over levels in the control in the 3, 5, 10, 15, and 25mg/L d-(-)-HMIM T treatments, respectively, and 1.26-, 1.37-, 1.58-, 1.86- and 2.08-fold increases over levels in the control in the 3, 5, 10, 15, and 25mg/L l-(+)-HMIM T treatments, respectively. The total soluble protein content decreased as the RMIM T concentration increased. The SOD and CAT activities were stimulated at lower concentrations, but were inhibited at higher concentrations. Regression analysis implied that ROS is the major factor responsible for the oxidative damage caused by RMIM T. The ultrastructural morphology analysis showed that plasmolysis and damage to the chloroplasts, starch granule decreases, and lipid granule increased, and pyrenoid and nucleoid damage had occurred. These results showed that enantioselective oxidative stress and oxidative damage were caused by d-(+)-RMIM T and l-(+)-RMIM T, and that l-(+)-RMIM T caused more damage than d-(+)-RMIM T.

Cell physiology of mortality and immortality in a Nicotiana interspecific F1 hybrid complies with the quantitative balance between reactive oxygen and nitric oxide

The cultured cell line, GTH4, of an interspecific F1 hybrid between Nicotiana gossei Domin and N. tabacum L. died after a shift in temperature from 37°C to 26°C. Fluctuations in the cellular amounts of reactive oxygen species (ROS) and nitric oxide (NO) were detected in GTH4 after the temperature shift, but not in the mutant, GTH4S, which did not die at 26°C presumably due to the lack of genetic factors involved in cell death. The removal of ROS or NO suppressed cell death in GTH4, suggesting that ROS and NO both acted as mediators of cell death. However, excess amounts of the superoxide anion (O2-) or NO alleviated cell death. A series of experiments using generators and scavengers of ROS and NO showed that O2- affected the cellular levels of NO, and vice versa, indicating that a quantitative balance between O2- and NO was important for hybrid cell death. The combination of NO and hydrogen peroxide (H2O2) was necessary and sufficient to initiate cell death in GTH4 and GTH4S. Hypoxia, which suppressed cell death in GTH4 at 26°C, reduced the generation of H2O2 and NO, but allowed for the production of O2-, which acted as a suppressor and/or modulator of cell death. The activation of MAPK was involved in the generation of H2O2 in GTG4 cells under normoxic conditions, but promoted O2- generation under hypoxic conditions. More protective cellular conditions against ROS, as estimated by the expression levels of genes for ROS-scavenging enzymes, may be involved in the mechanisms responsible for the low cell death rate of GTH4 under hypoxic conditions.

The role of mitochondria in plant development and stress tolerance

Eukaryotic cells require orchestrated communication between nuclear and organellar genomes, perturbations in which are linked to stress response and disease in both animals and plants. In addition to mitochondria, which are found across eukaryotes, plant cells contain a second organelle, the plastid. Signaling both among the organelles (cytoplasmic) and between the cytoplasm and the nucleus (i.e. nuclear-cytoplasmic interactions (NCI)) is essential for proper cellular function. A deeper understanding of NCI and its impact on development, stress response, and long-term health is needed in both animal and plant systems. Here we focus on the role of plant mitochondria in development and stress response. We compare and contrast features of plant and animal mitochondrial genomes (mtDNA), particularly highlighting the large and highly dynamic nature of plant mtDNA. Plant-based tools are powerful, yet underutilized, resources for enhancing our fundamental understanding of NCI. These tools also have great potential for improving crop production. Across taxa, mitochondria are most abundant in cells that have high energy or nutrient demands as well as at key developmental time points. Although plant mitochondria act as integrators of signals involved in both development and stress response pathways, little is known about plant mtDNA diversity and its impact on these processes. In humans, there are strong correlations between particular mitotypes (and mtDNA mutations) and developmental differences (or disease). We propose that future work in plants should focus on defining mitotypes more carefully and investigating their functional implications as well as improving techniques to facilitate this research.