Reactive Oxygen Species Accumulation In Roots Research Articles

Reactive oxygen species (ROS) modulate nitrogen signaling using temporal transcriptome analysis in foxtail millet.

Reactive oxygen species (ROS) is a chemically reactive chemical substance containing oxygen and a natural by-product of normal oxygen metabolism. Excessive ROS affect the growth process of crops, which will lead to the decrease of yield. Nitrogen, as a critical nutrient element in plants and plays a vital role in plant growth and crop production. Nitrate is the primary nitrogen source available to plants in agricultural soil and various natural environments. However, the molecular mechanism of ROS-nitrate crosstalk is still unclear. In this study, we used the foxtail millet (Setaria italica L.) as the material to figure it out. Here, we show that excessive NaCl inhibits nitrate-promoted plant growth and nitrogen use efficiency (NUE). NaCl induces ROS accumulation in roots, and ROS inhibits nitrate-induced gene expression in a short time. Surprisingly, low concentration ROS slight promotes and high concentration of ROS inhibits foxtail millet growth under long-term H2O2 treatment. These results may open a new perspective for further exploration of ROS-nitrate signaling pathway in plants.

OsRR26, a type-B response regulator, modulates salinity tolerance in rice via phytohormone-mediated ROS accumulation in roots and influencing reproductive development.

OsRR26 is a cytokinin-responsive response regulator that promotes phytohormone-mediated ROS accumulation in rice roots, regulates seedling growth, spikelet fertility, awn development, represses NADPH oxidases, and negatively affects salinity tolerance. Plant two-component systems (TCS) play a pivotal role in phytohormone signaling, stress responses, and circadian rhythm. However, a significant knowledge gap exists regarding TCS in rice. In this study, we utilized a functional genomics approach to elucidate the role of OsRR26, a type-B response regulator in rice. Our results demonstrate that OsRR26 is responsive to cytokinin, ABA, and salinity stress, serving as the ortholog of Arabidopsis ARR11. OsRR26 primarily localizes to the nucleus and plays a crucial role in seedling growth, spikelet fertility, and the suppression of awn development. Exogenous application of cytokinin led to distinct patterns of reactive oxygen species (ROS) accumulation in the roots of both WT and transgenic plants (OsRR26OE and OsRR26KD), indicating the potential involvement of OsRR26 in cytokinin-mediated ROS signaling in roots. The application of exogenous ABA resulted in varied cellular compartmentalization of ROS between the WT and transgenic lines. Stress tolerance assays of these plants revealed that OsRR26 functions as a negative regulator of salinity stress tolerance across different developmental stages in rice. Physiological and biochemical analyses unveiled that the knockdown of OsRR26 enhances salinity tolerance, characterized by improved chlorophyll retention and the accumulation of soluble sugars, K+ content, and amino acids, particularly proline.

Characterization of OsPIN2 Mutants Reveal Novel Roles for Reactive Oxygen Species in Modulating Not Only Root Gravitropism but Also Hypoxia Tolerance in Rice Seedlings.

Tolerance to submergence-induced hypoxia is an important agronomic trait especially for crops in lowland and flooding-affected areas. Although rice (Oryza sativa) is considered a flood-tolerant crop, only limited cultivars display strong tolerance to prolonged submergence and/or hypoxic stress. Therefore, characterization of hypoxic resistant genes and/or germplasms have important theoretical and practical significance for rice breeding and sustained improvements. Previous investigations have demonstrated that loss-of-function of OsPIN2, a gene encoding an auxin efflux transporter, results in the loss of root gravitropism due to disrupted auxin transport in the root tip. In this study, we revealed a novel connection between OsPIN2 and reactive oxygen species (ROS) in modulating root gravitropism and hypoxia tolerance in rice. It is shown that the OsPIN2 mutant had decreased accumulation of ROS in root tip, due to the downregulation of glycolate oxidase encoding gene OsGOX6, one of the main H2O2 sources. The morphological defects of root including waved rooting and agravitropism in OsPIN2 mutant may be rescued partly by exogenous application of H2O2. The OsPIN2 mutant exhibited increased resistance to ROS toxicity in roots due to treatment with H2O2. Furthermore, it is shown that the OsPIN2 mutant had increased tolerance to hypoxic stress accompanied by lower ROS accumulation in roots, because the hypoxia stress led to over production of ROS in the roots of the wild type but not in that of OsPIN2 mutant. Accordingly, the anoxic resistance-related gene SUB1B showed differential expression in the root of the WT and OsPIN2 mutant in response to hypoxic conditions. Notably, compared with the wild type, the OsPIN2 mutant displayed a different pattern of auxin distribution in the root under hypoxia stress. It was shown that hypoxia stress caused a significant increase in auxin distribution in the root tip of the WT but not in that of the war1 mutant. In summary, these results suggested that OsPIN2 may play a role in regulating ROS accumulation probably via mediating auxin transport and distribution in the root tip, affecting root gravitropism and hypoxic tolerance in rice seedlings. These findings may contribute to the genetic improvement and identification of potential hypoxic tolerant lines in rice.

Chromatin Remodeling Complex SWR1 Regulates Root Development by Affecting the Accumulation of Reactive Oxygen Species (ROS)

Reactive oxygen species (ROS), a type of oxygen monoelectronic reduction product, play integral roles in root growth and development. The epigenetic mechanism plays a critical role in gene transcription and expression; however, its regulation of ROS metabolism in root development is still limited. We found that the chromatin remodeling complex SWR1 regulates root length and lateral root formation in Arabidopsis. Our transcriptome results and gene ontology (GO) enrichment analysis showed that the oxidoreductase activity-related genes significantly changed in mutants for the Arabidopsis SWR1 complex components, such as arp6 and pie1, and histone variant H2A.Z triple mutant hta8 hta9 hta11. The three encoding genes in Arabidopsis are the three H2A.Z variants hta8, hta9, and hta11. Histochemical assays revealed that the SWR1 complex affects ROS accumulation in roots. Furthermore, chromatin immunoprecipitation quantitative real-time PCR (ChIP-qPCR) analysis showed that the reduced H2A.Z deposition in oxidoreductase activity-related genes caused ROS to accumulate in arp6, pie1, and hta8 hta9 hta11. H2A.Z deposition-deficient mutants decreased after the trimethylation of lysine 4 on histone H3 (H3K4me3) modifications and RNA polymerase II (Pol II) enrichment, and increased after the trimethylation of lysine 27 on histone H3 (H3K27me3) modifications, which may account for the expression change in oxidoreductase activity-related genes. In summary, our results revealed that the chromatin complex SWR1 regulates ROS accumulation in root development, highlighting the critical role of epigenetic mechanisms.

Annexin 1 Is a Component of eATP-Induced Cytosolic Calcium Elevation in Arabidopsis thaliana Roots.

Extracellular ATP (eATP) has long been established in animals as an important signalling molecule but this is less understood in plants. The identification of Arabidopsis thaliana DORN1 (Does Not Respond to Nucleotides) as the first plant eATP receptor has shown that it is fundamental to the elevation of cytosolic free Ca2+ ([Ca2+]cyt) as a possible second messenger. eATP causes other downstream responses such as increase in reactive oxygen species (ROS) and nitric oxide, plus changes in gene expression. The plasma membrane Ca2+ influx channels involved in eATP-induced [Ca2+]cyt increase remain unknown at the genetic level. Arabidopsis thaliana Annexin 1 has been found to mediate ROS-activated Ca2+ influx in root epidermis, consistent with its operating as a transport pathway. In this study, the loss of function Annexin 1 mutant was found to have impaired [Ca2+]cyt elevation in roots in response to eATP or eADP. Additionally, this annexin was implicated in modulating eATP-induced intracellular ROS accumulation in roots as well as expression of eATP-responsive genes.

Hydrogen Sulfide Alleviates Waterlogging-Induced Damage in Peach Seedlings via Enhancing Antioxidative System and Inhibiting Ethylene Synthesis.

Peach (Prunus persica L. Batsch) is a shallow root fruit tree with poor waterlogging tolerance. Hydrogen sulfide (H2S) is a signal molecule which regulates the adaptation of plants to adverse environments. Nevertheless, the effects of exogenous applications of H2S in fruit tree species especially in peach trees under waterlogging stress have been scarcely researched. Thus, the goal of this research was to investigate the alleviating effect of exogenous H2S on peach seedlings under waterlogging stress. In the present study, we found that the effect of exogenous H2S depended on the concentration and 0.2 mM sodium hydrosulfide (NaHS) showed the best remission effect on peach seedlings under waterlogging stress. Waterlogging significantly reduced the stomatal opening, net photosynthetic rate, and Fv/Fm of peach seedlings. The results of histochemical staining and physiological and biochemical tests showed that waterlogging stress increased the number of cell deaths and amounts of reactive oxygen species (ROS) accumulated in leaves, increased the number of root cell deaths, significantly increased the electrolyte permeability, O2.– production rate, H2O2 content and ethylene synthesis rate of roots, and significantly reduced root activity. With prolonged stress, antioxidative enzyme activity increased initially and then decreased. Under waterlogging stress, application of 0.2 mM NaHS increased the number of stomatal openings, improved the chlorophyll content, and photosynthetic capacity of peach seedlings. Exogenous H2S enhanced antioxidative system and significantly alleviate cell death of roots and leaves of peach seedlings caused by waterlogging stress through reducing ROS accumulation in roots and leaves. H2S can improve the activity and proline content of roots, reduce oxidative damage, alleviated lipid peroxidation, and inhibit ethylene synthesis. The H2S scavenger hypotaurine partially eliminated the effect of exogenous H2S on alleviating waterlogging stress of peach seedlings. Collectively, our results provide an insight into the protective role of H2S in waterlogging-stressed peach seedlings and suggest H2S as a potential candidate in reducing waterlogging-induced damage in peach seedlings.

Plant elicitor peptides promote plant defences against nematodes in soybean.

Plant elicitor peptides (Peps) are widely distributed among angiosperms, and have been shown to amplify immune responses in multiple plant families. Here, we characterize three Peps from soybean (Glycine max) and describe their effects on plant defences against two damaging agricultural pests, the root-knot nematode (Meloidogyne incognita) and the soybean cyst nematode (Heterodera glycines). Seed treatments with exogenous GmPep1, GmPep2 or GmPep3 significantly reduced the reproduction of both nematodes. Pep treatment also protected plants from the inhibitory effects of root-knot nematodes on above-ground growth, and up-regulated basal expression levels of nematode-responsive defence genes. GmPep1 induced the expression of its propeptide precursor (GmPROPEP1), a nucleotide-binding site leucine-rich repeat protein (NBS-LRR), a pectin methylesterase inhibitor (PMEI), Respiratory Burst Oxidase Protein D (RBOHD) and the accumulation of reactive oxygen species (ROS) in leaves. In addition, GmPep2 and GmPep3 seed treatments up-regulated RBOHD expression and ROS accumulation in roots and leaves. These results suggest that GmPeps activate plant defences through systemic transcriptional reprogramming and ROS signalling, and that Pep seed treatments represent a potential strategy for nematode management.

Vermicompost humic acids modulate the accumulation and metabolism of ROS in rice plants

This work aims to determine the reactive oxygen species (ROS) accumulation, gene expression, anti-oxidant enzyme activity, and derived effects on membrane lipid peroxidation and certain stress markers (proline and malondialdehyde-MDA) in the roots of unstressed and PEG-stressed rice plants associated with vermicompost humic acid (VCHA) application. The results show that the application of VCHA to the roots of unstressed rice plants caused a slight but significant increase in root ROS accumulation and the gene expression and activity of the major anti-oxidant enzymes (superoxide dismutase and peroxidase). This action did not have negative effects on root development, and an increase in both root growth and root proliferation occurred. However, the root proline and MDA concentrations and the root permeability results indicate the development of a type of mild stress associated with VCHA application. When VCHA was applied to PEG-stressed plants, a clear alleviation of the inhibition in root development linked to PEG-mediated osmotic stress was observed. This was associated with a reduction in root ROS production and anti-oxidant enzymatic activity caused by osmotic stress. This alleviation of stress caused by VCHA was also reflected as a reduction in the PEG-mediated concentration of MDA in the root as well as root permeability. In summary, the beneficial action of VCHA on the root development of unstressed or PEG-stressed rice plants clearly involves the modulation of ROS accumulation in roots.

The endogenous nitric oxide mediates selenium-induced phytotoxicity by promoting ROS generation in Brassica rapa.

Selenium (Se) is suggested as an emerging pollutant in agricultural environment because of the increasing anthropogenic release of Se, which in turn results in phytotoxicity. The most common consequence of Se-induced toxicity in plants is oxidative injury, but how Se induces reactive oxygen species (ROS) burst remains unclear. In this work, histofluorescent staining was applied to monitor the dynamics of ROS and nitric oxide (NO) in the root of Brassica rapa under Se(IV) stress. Se(IV)-induced faster accumulation of NO than ROS. Both NO and ROS accumulation were positively correlated with Se(IV)-induced inhibition of root growth. The NO accumulation was nitrate reductase (NR)- and nitric oxide synthase (NOS)-dependent while ROS accumulation was NADPH oxidase-dependent. The removal of NO by NR inhibitor, NOS inhibitor, and NO scavenger could alleviate Se(IV)-induced expression of Br_Rbohs coding for NADPH oxidase and the following ROS accumulation in roots, which further resulted in the amelioration of Se(IV)-induced oxidative injury and growth inhibition. Thus, we proposed that the endogenous NO played a toxic role in B. rapa under Se(IV) stress by triggering ROS burst. Such findings can be used to evaluate the toxic effects of Se contamination on crop plants.

Metabolism of Reactive Oxygen Species Involved in Increasing Root Vigour of Cotton Seedlings by Soaking Seeds with Mepiquat Chloride

The plant growth regulator, mepiquat chloride(1,1-dimethylpiperidinium chloride, DPC) has been used worldwide to suppress excessive growth in cotton plants. It also increases the root vigour of cotton plants. To reveal the possible role of reactive oxygen species(ROS) involved, we conducted a experiment to investigate the effect of soaking seed with 200 mg L–1 mepiquat chloride(DPC) on root vigour of cotton(Gossypium hirsutum L.) seedlings by using a cotton cv. Guoxin 3. The results showed that soaking seed with DPC could significantly increase the root vigour of cotton seedlings with two expanded cotyledons. Root viability estimated by 2,3,5-triphenyl tetrazolium chloride(TTC) reduction and root respiratory rate were increased by 167% and 90% in DPC treatment. The average OD of in situ TTC staining in DPC treated root tips was 0.3-fold higher than that of control. At 300 μm from the root apex away, DPC treatment resulted in a 36% increase of net K+ influx. The result of acridine orange staining suggested that seedlings treated with DPC had less apoptotic cells in root elongation zone compared with control. In addition, DPC treatment significantly altered the activities of antioxidant enzyme and ROS accumulation in roots of cotton seedlings. Catalase(CAT), ascorbate peroxidase(APX) and glutathione reductase(GR) were enhanced, but superoxide dismutase(SOD) was reduced, which therefore resulted in 56% less H2O2 accumulation and lighter diaminobenzidine staining(H2O2 histochemical detection in situ) in roots compared with control. Another type of ROS, O2-, its production rate also decreased by 65% in roots treated with DPC. Taken together, we speculated that the increased root vigour of cotton seedlings by soaking seed with DPC may be partially explained by improvement of ROS metabolism.

SNF1-Related Protein Kinases Type 2 Are Involved in Plant Responses to Cadmium Stress

Cadmium ions are notorious environmental pollutants. To adapt to cadmium-induced deleterious effects plants have developed sophisticated defense mechanisms. However, the signaling pathways underlying the plant response to cadmium are still elusive. Our data demonstrate that SnRK2s (for SNF1-related protein kinase2) are transiently activated during cadmium exposure and are involved in the regulation of plant response to this stress. Analysis of tobacco (Nicotiana tabacum) Osmotic Stress-Activated Protein Kinase activity in tobacco Bright Yellow 2 cells indicates that reactive oxygen species (ROS) and nitric oxide, produced mainly via an l-arginine-dependent process, contribute to the kinase activation in response to cadmium. SnRK2.4 is the closest homolog of tobacco Osmotic Stress-Activated Protein Kinase in Arabidopsis (Arabidopsis thaliana). Comparative analysis of seedling growth of snrk2.4 knockout mutants versus wild-type Arabidopsis suggests that SnRK2.4 is involved in the inhibition of root growth triggered by cadmium; the mutants were more tolerant to the stress. Measurements of the level of three major species of phytochelatins (PCs) in roots of plants exposed to Cd(2+) showed a similar (PC2, PC4) or lower (PC3) concentration in snrk2.4 mutants in comparison to wild-type plants. These results indicate that the enhanced tolerance of the mutants does not result from a difference in the PCs level. Additionally, we have analyzed ROS accumulation in roots subjected to Cd(2+) treatment. Our data show significantly lower Cd(2+)-induced ROS accumulation in the mutants' roots. Concluding, the obtained results indicate that SnRK2s play a role in the regulation of plant tolerance to cadmium, most probably by controlling ROS accumulation triggered by cadmium ions.

FERONIA receptor-like kinase regulates RHO GTPase signaling of root hair development

Plant RHO GTPases (RAC/ROPs) mediate multiple extracellular signals ranging from hormone to stress and regulate diverse cellular processes important for polarized cell growth, differentiation, development, reproduction, and responses to the environment. They shuttle between the GDP-bound inactive state and the GTP-bound activated state and their activation is predominantly mediated by a family of guanine nucleotide exchange factors (GEFs) referred to as ROPGEFs. Using the Arabidopsis ROPGEF1 as bait, we identified members of a receptor-like kinase (RLK) family as potential upstream regulators for RAC/ROP signaling. NADPH oxidase-derived reactive oxygen species (ROS) are emerging as important regulators for growth and development and play a crucial role in mediating RAC/ROP-regulated root hair development, a polarized cell growth process. We therefore screened T-DNA insertion mutants in these RLKs for root hair defects and found that mutations in one of them, At3g51550 encoding the FERONIA (FER) receptor-like kinase, induced severe root hair defects. We show that the fer phenotypes correlated with reduced levels of active RAC/ROPs and NADPH oxidase-dependent, auxin-regulated ROS accumulation in roots and root hairs and that up-regulating RAC/ROP signaling in fer countered the mutant phenotypes. Taken together, these observations strongly support FER as an upstream regulator for the RAC/ROP-signaled pathway that controls ROS-mediated root hair development. Moreover, FER was pulled down by ROP2 GTPase in a guanine nucleotide-regulated manner implying a dynamic signaling complex involving FER, a ROPGEF, and a RAC/ROP.

Exogenous nitric oxide improves antioxidative capacity and reduces auxin degradation in roots of Medicago truncatula seedlings under cadmium stress

The effects of nitric oxide (NO) on cadmium toxicity in Medicago truncatula seedlings were studied by investigating root growth and uptake of antioxidants, IAA and ions. Exposure to cadmium reduced root growth and NO accumulation, and increased the production of reactive oxygen species (ROS) in roots. Supplementation with NO improved root growth and reduced ROS accumulation in roots. The NO-scavenger cPTIO, the nitrate reductase (NR) inhibitor tungstate, and the NO synthase (NOS) inhibitor L-NAME all inhibited the accumulation of NO in roots and reversed the effects of NO in promoting the root growth and accumulation of proline and glutathione. Application of NO reduced auxin degradation by inhibiting the activity of IAA oxidase. Exogenous NO also enhanced the uptake of K+ and Ca2+. These results suggest that NO improves cadmium tolerance in plants by reducing oxidative damage, maintaining the auxin equilibrium and enhancing ion absorption.