Reactive Oxygen Species in Plant Cell Walls

Nanobiotechnology-mediated regulation of reactive oxygen species homeostasis under heat and drought stress in plants

Global warming causes heat and drought stress in plants, which affects crop production. In addition to osmotic stress and protein inactivation, reactive oxygen species (ROS) overaccumulation under heat and drought stress is a secondary stress that further impairs plant performance. Chloroplasts, mitochondria, peroxisomes, and apoplasts are the main ROS generation sites in heat- and drought-stressed plants. In this review, we summarize ROS generation and scavenging in heat- and drought-stressed plants and highlight the potential applications of plant nanobiotechnology for enhancing plant tolerance to these stresses.

Reduction of oxidative damage in prostate tissue caused by radiation and/or chloroquine by apocynin

Prostate damage can occur in men due to age and genetic factors, especially when exposed to external factors. Radiation (RAD) is a prominent factor leading to oxidative stress and potential prostate damage. Additionally, chloroquine (CQ), used in malaria treatment, can induce oxidative stress in a dose-dependent manner. Therefore, reducing and preventing oxidative damage in prostate tissue caused by external factors is crucial. Rats used in the study were divided into seven groups, CQ, apocynin (APO), RAD, CQ + APO, CQ + RAD, APO + RAD, CQ + APO + RAD. Subsequently, in vivo biochemical parameters of prostate tissues were examined, including reduced glutathione, lipid peroxidation, superoxide dismutase, glutathione reductase, glutathione peroxidase, glutathione-S-transferase activities, and total antioxidant status, total oxidant status, reactive oxygen species, oxidative stress index, advanced oxidation protein products and histologically. The in vivo results presented in our study showed that APO reduced oxidative stress and had a protective effect on prostate tissue in the CQ, RAD, and CQ + RAD groups as a results of biochemical and histological experiments. Additionally, in silico studies revealed a higher binding affinity of diapocynin to target proteins compared to APO. As a histological results, RAD and CQ alone or in combination did not induce damage in prostate tissues, whereas mild histopathological findings such as hyperemia and haemorrhage were observed in all APO-treated groups. The results suggest that the use of APO for the treatment of oxidative damage induced by CQ and RAD in rats.

Biochemical Aspects of the Spiral Grain Formation in Scots Pine (Pinus Sylvestris L.) Wood. Some Differences and Similarities with Biochemical Indicators of Abnormal Xylogenesis in Karelian Birch (Betula Pendula Roth Var. Carelica (Mercl.) Hämet-Ahti)

BACKGROUND

AOS enzymes can be biochemical indicators of abnormal xylogenesis in Scots pine, and this mechanism has similar features with the metabolic base of abnormal xylogenesis in Karelian birch.

OBJECTIVE

AOS enzymes' activity in 150-300-year-old Pinus sylvestris L. wood with straight-- grained wood and right-twisted spiral-grained wood, expressed in varying degrees (5-20 angle), grew in three sample plots in lingonberry and blueberry pine forest stands of different ages (100-300 years) in the middle taiga subzone in the Republic of Karelia.

METHODS

Plant tissues were ground in liquid nitrogen in a uniform mass and homogenized at 4°C in the buffer containing 50 mM HEPES (pH 7.5), 1 mM EDTA, 1 mM EGTA, 3 mM DTT, 5 mM MgCl2 and 0.5 mM PMSF. After 20 min extraction, the homogenate was centrifuged at 10000 g for 20 min (MPW-351R, Poland). The sediment was washed in the buffer thrice. The pooled supernatant and sediment were dialyzed at 4°C for 18-20 h against a tenfold diluted homogenization buffer. The enzymes' activity was determined spectrophotometrically (Spectrophotometer SF-2000, OKB Spectr, Russia). Proteins in the extracts were quantified by the method of Bradford.

RESULTS

The study showed that the activity of SS, ApInv, CAT, POD and PPO in xylem and PPO in phloem were biochemical indicators for abnormal wood of P. sylvestris. We noticed an increase in sucrose metabolism in the apoplast and the activity of POD and PPO under spiral-grain wood formation like under figured wood formation earlier. We assume that the alternative pathway of sucrose metabolism (an indicator of abnormal xylogenesis in B. pendula var. carelica plants) that lead to restructuring of AOS enzymes have the same biochemical regularities in the spiral-grain wood formation in P. sylvestris.

CONCLUSION

The study showed that the differences in the AOS enzyme's activity in P. sylvestris during the formation of straight-grained and spiral-grained wood were revealed for the first time. The increased CAT, POD and PPO activities in xylem with a decrease in SS and an increase in Ap- Inv during spiral-grained wood formation can be biochemical markers of these structural anomalies. Metabolic regularities found in the AOS enzyme complex during spiral-grained wood formation do not contradict those found earlier during figured wood formation in B. pendula var. carelica. The identified patterns can form the base for diagnostics of P. sylvestris wood quality in forest seed plantations and in their natural growth, which is necessary both for fundamental science and in various industry areas while high-quality material harvesting.

Abscisic acid-induced cytoplasmic translocation of constitutive photomorphogenic 1 enhances reactive oxygen species accumulation through the HY5-ABI5 pathway to modulate seed germination

Seed germination is a physiological process regulated by multiple factors. Abscisic acid (ABA) can inhibit seed germination to improve seedling survival under conditions of abiotic stress, and this process is often regulated by light signals. Constitutive photomorphogenic 1 (COP1) is an upstream core repressor of light signals and is involved in several ABA responses. Here, we demonstrate that COP1 is a negative regulator of the ABA-mediated inhibition of seed germination. Disruption of COP1 enhanced Arabidopsis seed sensitivity to ABA and increased reactive oxygen species (ROS) levels. In seeds, ABA induced the translocation of COP1 to the cytoplasm, resulting in enhanced ABA-induced ROS levels. Genetic evidence indicated that HY5 and ABI5 act downstream of COP1 in the ABA-mediated inhibition of seed germination. ABA-induced COP1 cytoplasmic localization increased HY5 and ABI5 protein levels in the nucleus, leading to increased expression of ABI5 target genes and ROS levels in seeds. Together, our results reveal that ABA-induced cytoplasmic translocation of COP1 activates the HY5-ABI5 pathway to promote the expression of ABA-responsive genes and the accumulation of ROS during ABA-mediated inhibition of seed germination. These findings enhance the role of COP1 in the ABA signal transduction pathway.

Non-esterified Fatty Acid Induce Dairy Cow Hepatocytes Apoptosis via the Mitochondria-Mediated ROS-JNK/ERK Signaling Pathway

Elevated plasma non-esterified fatty acid (NEFA) levels and hepatocytes damage are characteristics of ketosis in dairy cows. Oxidative stress is associated with the pathogenesis of NEFA-induced liver damage. However, the exact mechanism by which oxidative stress mediates NEFA-induced hepatocytes apoptosis and liver injury remains poorly understood. The results of the present study demonstrated that NEFA contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c (cyt c) into the cytosol, leading to hepatocytes apoptosis. Besides, NEFA triggered apoptosis in dairy cow hepatocytes via the regulation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), caspase 9 and poly (ADP-ribose) polymerase (PARP). Pretreatment with the inhibitor SP600125 or PD98059 or the antioxidant N-acetylcysteine (NAC) revealed that NEFA-ROS-JNK/ERK-mediated mitochondrial signaling pathway plays a crucial role in NEFA-induced hepatocytes apoptosis. Moreover, the results suggested that the transcription factors p53 and Nrf2 function downstream of this NEFA-ROS-JNK/ERK pathway and are involved in NEFA-induced hepatocytes apoptosis. In conclusion, these findings indicate that the NEFA-ROS-JNK/ERK-mediated mitochondrial pathway plays an important role in NEFA-induced dairy cow hepatocytes apoptosis and strongly suggests that the inhibitors SP600125 and PD98059 and the antioxidant NAC may be developed as therapeutics to prevent hyperlipidemia-induced apoptotic damage in ketotic dairy cows.

Altered Cell Wall Plasticity Can Restrict Plant Growth under Ammonium Nutrition

Plants mainly utilize inorganic forms of nitrogen (N), such as nitrate (NO3-) and ammonium (NH4+). However, the composition of the N source is important, because excess of NH4+ promotes morphological disorders. Plants cultured on NH4+ as the sole N source exhibit serious growth inhibition, commonly referred to as "ammonium toxicity syndrome." NH4+-mediated suppression of growth may be attributable to both repression of cell elongation and reduction of cell division. The precondition for cell enlargement is the expansion of the cell wall, which requires the loosening of the cell wall polymers. Therefore, to understand how NH4+ nutrition may trigger growth retardation in plants, properties of their cell walls were analyzed. We found that Arabidopsis thaliana using NH4+ as the sole N source has smaller cells with relatively thicker cell walls. Moreover, cellulose, which is the main load-bearing polysaccharide revealed a denser assembly of microfibrils. Consequently, the leaf blade tissue showed elevated tensile strength and indicated higher cell wall stiffness. These changes might be related to changes in polysaccharide and ion content of cell walls. Further, NH4+ toxicity was associated with altered activities of cell wall modifying proteins. The lower activity and/or expression of pectin hydrolyzing enzymes and expansins might limit cell wall expansion. Additionally, the higher activity of cell wall peroxidases can lead to higher cross-linking of cell wall polymers. Overall, the NH4+-mediated inhibition of growth is related to a more rigid cell wall structure, which limits expansion of cells. The changes in cell wall composition were also indicated by decreased expression of Feronia, a receptor-like kinase involved in the control of cell wall extension.

Transcriptomic Profiling Reveals Differentially Expressed Genes Associated with Pine Wood Nematode Resistance in Masson Pine (Pinus massoniana Lamb.)

Pine wilt disease caused by pine wood nematode (Bursaphelenchus xylophilus, PWN) is a severe forest disease of the genus Pinus. Masson pine as an important timber and oleoresin resource in South China, is the major species infected by pine wilt disease. However, the underlying mechanism of pine resistance is still unclear. Here, we performed a transcriptomics analysis to identify differentially expressed genes associated with resistance to PWN infection. By comparing the expression profiles of resistant and susceptible trees inoculated with PWN at 1, 15, or 30 days post-inoculation (dpi), 260, 371 and 152 differentially expressed genes (DEGs) in resistant trees and 756, 2179 and 398 DEGs in susceptible trees were obtained. Gene Ontology enrichment analysis of DEGs revealed that the most significant biological processes were "syncytium formation" in the resistant phenotype and "response to stress" and "terpenoid biosynthesis" in the susceptible phenotype at 1 and 15 dpi, respectively. Furthermore, some key DEGs with potential regulatory roles to PWN infection, including expansins, pinene synthases and reactive oxidation species (ROS)-related genes were evaluated in detail. Finally, we propose that the biosynthesis of oleoresin and capability of ROS scavenging are pivotal to the high resistance of PWN.

Gene Mining for Proline Based Signaling Proteins in Cell Wall of Arabidopsis thaliana

The cell wall (CW) as a first line of defense against biotic and abiotic stresses is of primary importance in plant biology. The proteins associated with cell walls play a significant role in determining a plant's sustainability to adverse environmental conditions. In this work, the genes encoding cell wall proteins (CWPs) in Arabidopsis were identified and functionally classified using geneMANIA and GENEVESTIGATOR with published microarrays data. This yielded 1605 genes, out of which 58 genes encoded proline-rich proteins (PRPs) and glycine-rich proteins (GRPs). Here, we have focused on the cellular compartmentalization, biological processes, and molecular functioning of proline-rich CWPs along with their expression at different plant developmental stages. The mined genes were categorized into five classes on the basis of the type of PRPs encoded in the cell wall of Arabidopsis thaliana. We review the domain structure and function of each class of protein, many with respect to the developmental stages of the plant. We have then used networks, hierarchical clustering and correlations to analyze co-expression, co-localization, genetic, and physical interactions and shared protein domains of these PRPs. This has given us further insight into these functionally important CWPs and identified a number of potentially new cell-wall related proteins in A. thaliana.

Extra-Cellular But Extra-Ordinarily Important for Cells: Apoplastic Reactive Oxygen Species Metabolism

Reactive oxygen species (ROS), by their very nature, are highly reactive, and it is no surprise that they can cause damage to organic molecules. In cells, ROS are produced as byproducts of many metabolic reactions, but plants are prepared for this ROS output. Even though extracellular ROS generation constitutes only a minor part of a cell's total ROS level, this fraction is of extraordinary importance. In an active apoplastic ROS burst, it is mainly the respiratory burst oxidases and peroxidases that are engaged, and defects of these enzymes can affect plant development and stress responses. It must be highlighted that there are also other less well-known enzymatic or non-enzymatic ROS sources. There is a need for ROS detoxification in the apoplast, and almost all cellular antioxidants are present in this space, but the activity of antioxidant enzymes and the concentration of low-mass antioxidants is very low. The low antioxidant efficiency in the apoplast allows ROS to accumulate easily, which is a condition for ROS signaling. Therefore, the apoplastic ROS/antioxidant homeostasis is actively engaged in the reception and reaction to many biotic and abiotic stresses.

[From the conception of «oxidizing stress» to the conception of «cell signaling modulation»]

We discuss the current conception of "oxidizing stress" which covers a wide group of various interrelated phenomena including higher production of reactive oxygen species (ROS) and oxidative damage of cellular molecular components. Currently the term of oxidizing stress is used for the description of pro-oxidant and antioxidant imbalance, with the prevalence of the former, that results in the damage of biological molecules and cellular structures. However ROS do not play a single role in oxidative metabolism. There are also active nitrogen forms, reactive forms of carbon, chlorine and sulphur. These highly reactive molecules are involved in many reactions and play a great role in the regulation of different metabolic processes in the body. These reactions underlie such pathological processes as heart ischemia, atherosclerosis, cerebral ischemia and different types of inflammation. An effect of highly reactive molecules on the destruction of biologically important molecular in different stressful conditions is determined by the reactions they are involved in. But the balance of oxidizers and antioxidants should not be considered as a unified system because main cellular redox systems are not in the redox equilibrium. In this view, a search for an optimal oxidizer that impacts on the modulation of cellular signal pathways related with ROS development is the most effective way in the development of antioxidant therapy.

In comparison with nitrate nutrition, ammonium nutrition increases growth of the frostbite1 Arabidopsis mutant

Ammonium nutrition inhibits the growth of many plant species, including Arabidopsis thaliana. The toxicity of ammonium is associated with changes in the cellular redox state. The cellular oxidant/antioxidant balance is controlled by mitochondrial electron transport chain. In this study, we analysed the redox metabolism of frostbite1 (fro1) plants, which lack mitochondrial respiratory chain complex I. Surprisingly, the growth of fro1 plants increased under ammonium nutrition. Ammonium nutrition increased the reduction level of pyridine nucleotides in the leaves of wild-type plants, but not in the leaves of fro1 mutant plants. The observed higher activities of type II NADH dehydrogenases and cytochrome c oxidase in the mitochondrial electron transport chain may improve the energy metabolism of fro1 plants grown on ammonium. Additionally, the observed changes in reactive oxygen species (ROS) metabolism in the apoplast may be important for determining the growth of fro1 under ammonium nutrition. Moreover, bioinformatic analyses showed that the gene expression changes in fro1 plants significantly overlap with the changes previously observed in plants with a modified apoplastic pH. Overall, the results suggest a pronounced connection between the mitochondrial redox system and the apoplastic pH and ROS levels, which may modify cell wall plasticity and influence growth.

Antioxidant enzymes regulate reactive oxygen species during pod elongation in Pisum sativum and Brassica chinensis

Previous research has focused on the involvement of reactive oxygen species (ROS) in cell wall loosening and cell extension in plant vegetative growth, but few studies have investigated ROS functions specifically in plant reproductive organs. In this study, ROS levels and antioxidant enzyme activities were assessed in Pisum sativum and Brassica chinensis pods at five developmental stages. In juvenile pods, the high levels of O2.- and .OH indicates that they had functions in cell wall loosening and cell elongation. In later developmental stages, high levels of .OH were also related to increases in cell wall thickness in lignified tissues. Throughout pod development, most of the O2.- was detected on plasma membranes of parenchyma cells and outer epidermis cells of the mesocarp, while most of the H2O2 was detected on plasma membranes of most cells throughout the mesocarp. This suggests that these sites are presumably the locations of ROS generation. The antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) apparently contributed to ROS accumulation in pod wall tissues. Furthermore, specifically SOD and POD were found to be associated with pod growth through the regulation of ROS generation and transformation. Throughout pod development, O2.- decreases were associated with increased SOD activity, while changes in H2O2 accumulation were associated with changes in CAT and POD activities. Additionally, high POD activity may contribute to the generation of(.)OH in the early development of pods. It is concluded that the ROS are produced in different sites of plasma membranes with the regulation of antioxidant enzymes, and that substantial ROS generation and accumulation are evident in cell elongation and cell wall loosening in pod wall cells.

Reactive oxygen species are involved in regulation of pollen wall cytomechanics

Production and scavenging of reactive oxygen species (ROS) in somatic plant cells is developmentally regulated and plays an important role in the modification of cell wall mechanical properties. Here we show that H2O2 and the hydroxyl radical ((•)OH) can regulate germination of tobacco pollen by modifying the mechanical properties of the pollen intine (inner layer of the pollen wall). Pollen germination was affected by addition of exogenous H2O2, (•)OH, and by antioxidants scavenging endogenous ROS: superoxide dismutase, superoxide dismutase/catalase mimic Mn-5,10,15,20-tetrakis(1-methyl-4-pyridyl)21H, 23H-porphin, or a spin-trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone, which eliminates (•)OH. The inhibiting concentrations of exogenous H2O2 and (•)OH did not decrease pollen viability, but influenced the mechanical properties of the wall. The latter were estimated by studying the resistance of pollen to hypo-osmotic shock. (•)OH caused excess loosening of the intine all over the surface of the pollen grain, disrupting polar growth induction. In contrast, H2O2, as well as partial removal of endogenous (•)OH, over-tightened the wall, impeding pollen tube emergence. Feruloyl esterase (FAE) was used as a tool to examine whether H2O2-inducible inter-polymer cross-linking is involved in the intine tightening. FAE treatment caused loosening of the intine and stimulated pollen germination and pollen tube growth, revealing ferulate cross-links in the intine. Taken together, the data suggest that pollen intine properties can be regulated differentially by ROS. (•)OH is involved in local loosening of the intine in the germination pore region, while H2O2 is necessary for intine strengthening in the rest of the wall through oxidative coupling of feruloyl polysaccharides.

Characterization of resistance to pine wood nematode infection in Pinus thunbergii using suppression subtractive hybridization

BACKGROUND

Pine wilt disease is caused by the pine wood nematode, Bursaphelenchus xylophilus, which threatens pine forests and forest ecosystems worldwide and causes serious economic losses. In the 40 years since the pathogen was identified, the physiological changes occurring as the disease progresses have been characterized using anatomical and biochemical methods, and resistant trees have been selected via breeding programs. However, no studies have assessed the molecular genetics, e.g. transcriptional changes, associated with infection-induced physiological changes in resistant or susceptible trees.

RESULTS

We constructed seven subtractive suppression hybridization (SSH) cDNA libraries using time-course sampling of trees inoculated with pine wood nematode at 1, 3, or 7 days post-inoculation (dpi) in susceptible trees and at 1, 3, 7, or 14 dpi in resistant trees. A total of 3,299 sequences was obtained from these cDNA libraries, including from 138 to 315 non-redundant sequences in susceptible SSH libraries and from 351 to 435 in resistant SSH libraries. Using Gene Ontology hierarchy, those non-redundant sequences were classified into 15 subcategories of the biological process Gene Ontology category and 17 subcategories of the molecular function category. The transcriptional components revealed by the Gene Ontology classification clearly differed between resistant and susceptible libraries. Some transcripts were discriminative: expression of antimicrobial peptide and putative pathogenesis-related genes (e.g., PR-1b, 2, 3, 4, 5, 6) was much higher in susceptible trees than in resistant trees at every time point, whereas expression of PR-9, PR-10, and cell wall-related genes (e.g., for hydroxyproline-rich glycoprotein precursor and extensin) was higher in resistant trees than in susceptible trees at 7 and 14 dpi.

CONCLUSIONS

Following inoculation with pine wood nematode, there were marked differences between resistant and susceptible trees in transcript diversity and the timing and level of transcripts expressed in common; in particular, expression of stress response and defense genes differed. This study provided new insight into the differences in the physiological changes between resistant and susceptible trees that have been observed in anatomical and biochemical studies.

Analysis of the expression of BohLOL1, which encodes an LSD1-like zinc finger protein in Bambusa oldhamii

A cDNA, BohLOL1, encoding a protein containing three zf-LSD1 (zinc finger-Lesions Simulating Disease resistance 1) domains was cloned from growing bamboo (Bambusa oldhamii) shoots. A phylogenetic analysis revealed that BohLOL1 is a homolog of Arabidopsis LSD1 and LOL1 (LSD-one-like 1), which have been reported to act antagonistically in controlling cell death via the maintenance of reactive oxygen species homeostasis. The BohLOL1 gene was differentially expressed in various bamboo shoot tissues and was upregulated in shoots with higher rates of culm elongation. The expression level of this gene in multiple shoots of bamboo, which were cultured in vitro, was also upregulated by auxins, cytokinins, pathogen infection, 2,6-dichloroisonicotinic acid (a functional analog of salicylic acid), and hydrogen peroxide. The results suggest that BohLOL1 participates in bamboo growth and in the response to biotic stress. The DNA-binding assays and subcellular localization studies demonstrated that BohLOL1 is a nuclear DNA-binding protein. BohLOL1 might function through protein-DNA interactions and thus affect the expression of its target genes. The results of this study extend the role of plant LSD1 and LOL1 proteins from the regulation of cell death to cell growth. The growth-dependent up-regulation of BohLOL1 expression, which uniquely occurs in growing bamboo, might be one of the critical factors that contribute to the rapid growth of this remarkable plant.

Differential response of young and adult leaves to herbicide 2,4-dichlorophenoxyacetic acid in pea plants: role of reactive oxygen species

In this work the differential response of adult and young leaves from pea (Pisum sativum L.) plants to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) (23 mm) applied by foliar spraying was investigated. The concentration of 2,4-D (23 mm) and the time of treatment (72 h) were previously optimized in order to visualize its toxic effects on pea plants. Under these conditions, the herbicide induced severe disturbances in mesophyll cells structure and proliferation of vascular tissue in young leaves and increased acyl-CoA oxidase (ACX), xanthine oxidase (XOD) and lipoxygenase (LOX) activities in young leaves, and only ACX and LOX in adult leaves. This situation produced reactive oxygen species (ROS) over-accumulation favoured by the absence of significant changes in the enzymatic antioxidants, giving rise to oxidative damages to proteins and membrane lipids. An increase of ethylene took place in both young and adult leaves and the induction of genes encoding the stress proteins, PRP4A and HSP 71,2, was observed mainly in young leaves. These results suggest that ROS overproduction is a key factor in the effect of high concentrations of 2,4-D, and ROS can trigger a differential response in young and adult leaves, either epinasty development in young leaves or senescence processes in adult tissues.