Release of reactive oxygen intermediates (superoxide radicals, hydrogen peroxide, and hydroxyl radicals) and peroxidase in germinating radish seeds controlled by light, gibberellin, and abscisic acid

The interaction between miR165/166 and miR160 regulates Arabidopsis thaliana seed size, weight, and number in a ROS-dependent manner

MAIN CONCLUSION

Our data link the miR165/166- and miR160-mediated regulatory modules to ROS and seed formation. Trade-offs of seed size, weight, and number probably require control of the expression of miR165/166 by miR160, modulation of ROS metabolism by miR165/166, and miR160 abundance by ROS-induced oxidative modifications The cycle of plant life and its yield productivity depends fundamentally on the establishment of the trade-offs of seed size, weight, and number. For annual plants, seed number should simply be a positive function of vegetative biomass and a negative function of seed size and/or weight. However, extensive natural variation within species is observed for these traits, for which an optimal solution is environmentally dependent. Understanding the miRNA-mediated post-transcriptional regulation of gene expression determining seed phenotype and number is crucial from both an evolutionary and applied perspective. Although extensive research has concentrated on the individual roles of miRNAs in plant life, fewer studies have centred on their functional interactions, hence this study aimed to examine whether the module of miR165/miR166 and/or miR160 interactions is involved in forming Arabidopsis thaliana seeds, and/or has an impact on their features. Considering that reactive oxygen species (ROS) are among key players in seed-related processes, it was also intriguing to verify if the mechanism of action of these miRNAs is associated with the ROS pathway. The plant material used in this study consisted of flower buds, green siliques, and freshly harvested seeds, of wild type (WT), and STTM165/166 and STTM160 × 165/166 mutants of A. thaliana plants which are powerful tools for functional analysis of miRNAs in plants. The novel results obtained during physiological phenotyping together with two-tailed qRT-PCR analysis of mature miR165, miR166, miR160, and spectrofluorimetric measurement of apoplastic hydrogen peroxide (H2O2) for the first time revealed that interaction between miR165/miR166 and miR160 may regulate seed size, weight and number in ROS-dependent manner.

Synergistic effects of silicon and goethite co-application in alleviating cadmium stress in rice (Oryza sativa L.): Insights into plant growth and iron plaque formation mechanisms

Rice is one of the most important staple food crops; however, it is prone to cadmium (Cd) accumulation, which has negative health effects. Therefore, methods to reduce Cd uptake by rice are necessary. At present, there is limited research on the effects of co-application of silicon (Si) and goethite in mitigating Cd stress in rice. Furthermore, the specific mechanisms underlying the effects of their combined application on iron plaque formation in rice roots remain unclear. Therefore, this study analyzed the effects of the combined application of Si and goethite on the biomass, physiological stress indicators, Cd concentration, and iron plaques of rice using hydroponic experiments. The results revealed that co-treatment with both Si and goethite increased the plant height and dry weight, superoxide dismutase and catalase activities, photosynthetic pigment concentration, and root activity. Moreover, this treatment decreased the malondialdehyde concentration, repaired epidermal cells, reduced the Cd concentration in the roots by 57.2 %, and increased the number of iron plaques and Cd concentration by 150.9 % and 266.2 % in the amorphous and crystalline fractions, respectively. The Cd/Fe ratio in amorphous iron plaques also increased. Our findings suggest that goethite serves as a raw material for iron plaque formation, while Si enhances the oxidation capacity of rice roots. The application of a combination of Si and goethite increases the quantity and quality of iron plaques, enhancing its Cd fixation capacity. This study provides theoretical evidence for the effective inhibition of Cd uptake by iron plaques in rice, providing insights into methods for the remediation of Cd contamination.

Regulation of seed germination: ROS, epigenetic, and hormonal aspects

BACKGROUND

The whole life of a plant is regulated by complex environmental or hormonal signaling networks that control genomic stability, environmental signal transduction, and gene expression affecting plant development and viability. Seed germination, responsible for the transformation from seed to seedling, is a key initiation step in plant growth and is controlled by unique physiological and biochemical processes. It is continuously modulated by various factors including epigenetic modifications, hormone transport, ROS signaling, and interaction among them. ROS showed versatile crucial functions in seed germination including various physiological oxidations to nucleic acid, protein, lipid, or chromatin in the cytoplasm, cell wall, and nucleus.

AIM

of review: This review intends to provide novel insights into underlying mechanisms of seed germination especially associated with the ROS, and considers how these versatile regulatory mechanisms can be developed as useful tools for crop improvement.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We have summarized the generation and elimination of ROS during seed germination, with a specific focus on uncovering and understanding the mechanisms of seed germination at the level of phytohormones, ROS, and epigenetic switches, as well as the close connections between them. The findings exhibit that ROS plays multiple roles in regulating the ethylene, ABA, and GA homeostasis as well as the Ca2+ signaling, NO signaling, and MAPK cascade in seed germination via either the signal trigger or the oxidative modifier agent. Further, ROS shows the potential in the nuclear genome remodeling and some epigenetic modifiers function, although the detailed mechanisms are unclear in seed germination. We propose that ROS functions as a hub in the complex network regulating seed germination.

The association of protein-bound methionine sulfoxide with proteomic basis for aging in beech seeds

BACKGROUND

European beech (Fagus sylvatica L.) trees produce seeds irregularly; therefore, it is necessary to store beech seeds for forestation. Despite the acquisition of desiccation tolerance during development, beech seeds are classified as intermediate because they lose viability during long-term storage faster than typical orthodox seeds. In this study, beech seeds stored for short (3 years) or long (20 years) periods under optimal conditions and displaying 92 and 30% germination capacity, respectively, were compared.

RESULTS

Aged seeds displayed increased membrane damage, manifested as electrolyte leakage and lipid peroxidation levels. Analyses have been based on embryonic axes, which contained higher levels of reactive oxygen species (ROS) and higher levels of protein-bound methionine sulfoxide (MetO) in aged seeds. Using label-free quantitative proteomics, 3,949 proteins were identified, of which 2,442 were reliably quantified pointing to 24 more abundant proteins and 35 less abundant proteins in beech seeds under long-term storage conditions. Functional analyses based on gene ontology annotations revealed that nucleic acid binding activity (molecular function), ribosome organization or biogenesis and transmembrane transport (cellular processes), translational proteins (protein class) and membranous anatomical entities (cellular compartment) were affected in aged seeds. To verify whether MetO, the oxidative posttranslational modification of proteins that can be reversed via the action of methionine sulfoxide reductase (Msr) enzymes, is involved in the aging of beech seeds, we identified and quantified 226 MetO-containing proteins, among which 9 and 19 exhibited significantly up- and downregulated MetO levels, respectively, in beech seeds under long-term storage conditions. Several Msr isoforms were identified and recognized as MsrA1-like, MsrA4, MsrB5 and MsrB5-like in beech seeds. Only MsrA1-like displayed decreased abundance in aged seeds.

CONCLUSIONS

We demonstrated that the loss of membrane integrity reflected in the elevated abundance of membrane proteins had a higher impact on seed aging progress than the MetO/Msr system. Proteome analyses enabled us to propose protein Sec61 and glyceraldehyde-3-phosphate dehydrogenase as potential longevity modulators in beech seeds.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

Smartphone and paper-based device for glucose monitoring using acetylene black-hemin nanozyme as catalyst

Glucose management is an important part of disease control for diabetes patients, thus the development of a rapid and real-time point of care testing (POCT) device for monitoring blood glucose is of great significance. In this work, a paper-based analytical device (PAD) is constructed by combining acetylene black (AB)-hemin complex modified filter paper as sensing platform with a smartphone as signal detector. Large specific surface area of AB decreases the self-associate and aggregate of hemin in aqueous solution, resulting in improved peroxidase-like activity of hemin. Compared with graphene oxide supported hemin, AB-hemin exhibits superior signal response on paper. Glucose oxidase (GOx) catalyzes the conversion of blood glucose to hydrogen peroxide, and then AB-hemin complex catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxidized products (TMB⁺) in the presence of hydrogen peroxide, thus achieving the visual detection of blood glucose. In optimal conditions, PAD provides an applicable linear range from 0.2 mM to 30 mM and a low limit of detection (LOD) (0.06 mM). Notably, the detection accuracy of the developed paper-based sensor is in good agreement with that of the commercially available blood glucose meter (p > 0.05). Moreover, the proposed PAD presents high recoveries from 95.4% to 112% (RSD ≤ 3.2%), and therefore holds great potential for glucose monitoring and diabetes diagnosis.

Noninvasive Methods to Detect Reactive Oxygen Species as a Proxy of Seed Quality

ROS homeostasis is crucial to maintain radical levels in a dynamic equilibrium within physiological ranges. Therefore, ROS quantification in seeds with different germination performance may represent a useful tool to predict the efficiency of common methods to enhance seed vigor, such as priming treatments, which are still largely empirical. In the present study, ROS levels were investigated in an experimental system composed of hydroprimed and heat-shocked seeds, thus comparing materials with improved or damaged germination potential. A preliminary phenotypic analysis of germination parameters and seedling growth allowed the selection of the best-per-forming priming protocols for species like soybean, tomato, and wheat, having relevant agroeconomic value. ROS levels were quantified by using two noninvasive assays, namely dichloro-dihydro-fluorescein diacetate (DCFH-DA) and ferrous oxidation-xylenol orange (FOX-1). qRT-PCR was used to assess the expression of genes encoding enzymes involved in ROS production (respiratory burst oxidase homolog family, RBOH) and scavenging (catalase, superoxide dismutase, and peroxidases). The correlation analyses between ROS levels and gene expression data suggest a possible use of these indicators as noninvasive approaches to evaluate seed quality. These findings are relevant given the centrality of seed quality for crop production and the potential of seed priming in sustainable agricultural practices.

Selenium treatment promotes anthocyanin accumulation in radish sprouts (Raphanus sativus L.) by its regulation of photosynthesis and sucrose transport

Red radish sprout become a popular dietary vegetable because of its unique flavor, abundant nutrients and short production cycle. As a cruciferous plant, it has strong ability to absorb and assimilate Se which can promote the content of anthocyanin in plants. However, the mechanisms of Se on anthocyanin accumulation are still unclear. In this study, we explored that appropriate Se promoted growth, antioxidant system and nutrients in radish sprouts. The enhancement of photosynthesis by Se treatment resulted in more sucrose synthesis in radish sprouts. And the transport of sucrose from cotyledon to hypocotyl promoted by Se through up-regulating the gene expression of sucrose transporters, and more sucrose increased the expression of anthocyanin biosynthesis genes to promote anthocyanin accumulation in hypocotyl. These results reveal the beneficial effect of Se on radish sprouts quality, and provide a new insight into the function of Se on sucrose-induced anthocyanin accumulation in radish sprouts.

Magnetically Separable Photoactive Nanofiber Membranes for Photocatalytic and Antibacterial Applications

We have prepared photoactive multifunctional nanofiber membranes via the simple electrospinning method. The antibacterial and photocatalytic properties of these materials are based on the generation of singlet oxygen formed by processes photosensitized by the tetraphenylporphyrin encapsulated in the nanofibers. The addition of magnetic features in the form of magnetic maghemite (γ-Fe₂O₃) nanoparticles stabilized by polyethylenimine enables additional functionalities, namely, the postirradiation formation of hydrogen peroxide and improved photothermal properties. This hybrid material allows for remote manipulation by a magnetic field, even in hazardous and/or highly microbial contaminant environments.

ROS and RNS Alterations in the Digestive Fluid of Nepenthes × ventrata Trap at Different Developmental Stages

The carnivorous pitcher plant, Nepenthes × ventrata (Hort. ex Fleming = N. ventricosa Blanco × N. alata Blanco), produces passive traps containing digestive fluid. Although reactive oxygen species (ROS) in the fluid were detected in some pitcher plants, the participation of reactive nitrogen species (RNS) in the digestion process has not yet been examined. The aim of this work was to investigate the production of superoxide anion (O2•-), nitric oxide (NO) and peroxynitrite (ONOO-) levels in the digestive fluid of traps throughout organ development. We revealed the ROS and RNS occurrence in the digestive fluid, linked to the ROS-scavenging capacity and total phenolics content. In digestive fluid from the fed traps, NO emission was higher than in the fluid from the developed unfed pitcher. The concentration of nitrite (NO2-) decreased in the fluid from the fed traps in comparison to the unfed ones, pointing at NO2- as the key source of NO. The enhanced emission of NO was associated with lowered content of ONOO- in the fluid, probably due to lower production of O2•-. At the same time, despite a decline in total phenolics, the maximum ROS scavenging capacity was detected. In addition, ROS and RNS were noted even in closed traps, suggesting their involvement not only in digestion per se but also their action as signaling agents in trap ontogeny.

Gallic acid induces constitutive resistance against Bactrocera dorsalis infestation in mango fruit by its dual action

The Oriental fruit fly, Bactrocera dorsalis (Hendel) is a major insect pest of mango fruit worldwide resulting in huge loss of fruit quality and productivity. However, there exist a few mango varieties resistant to B. dorsalis infestation. The objective of the present study was, therefore to identify the major fruit component imparting resistance to B. dorsalis. Principal Component Analysis of phenolic acids in pulp and peel tissues of two resistant varieties, viz., Langra and EC 95862, revealed that among the phenolic acids present in the fruit, gallic acid was the most abundant component in both fruit peel and pulp while laboratory studies revealed that gallic acid was acutely toxic to B. dorsalis with its dual action as antioxidant in the host and a prooxidant in the insect. Field study with the preharvest application of gallic acid on young developing fruits of B. dorsalis susceptible Alphonso mango showed that it could protect the fruit against insect damage confirming that gallic acid is essentially responsible for providing constitutive resistance against B. dorsalis in Langra and EC 95862. Thus, preharvest application of gallic acid to developing fruits could be used as part of an Integrated Pest Management strategy to control infestation by B. dorsalis. Future work on breeding / development of transgenes of susceptible mango varieties with high levels of gallic acid in fruit peel is likely to provide the simplest means of inducing constitutive resistance against B. dorsalis infestation.

Antagonistic potential of Trichoderma as a biocontrol agent against Sclerotinia asari

In the present study, the inhibitory potential of 14 Trichoderma strains (isolated from Asarum rhizosphere) was investigated against Sclerotinia asari using the plate dilution method. The activity of antioxidant enzymes viz; catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and malondialdehyde (MDA) in S. asari treated with the two Trichoderma strains was also evaluated. Untargeted metabolomic analysis by using LC/MS analysis was carried out to determine differential metabolites in T. hamatum (A26) and T. koningiopsis (B30) groups. Moreover, transcriptome analysis of S. asari during the inhibition of S. asari by B30, and A26 compared with the control (CK) was performed. Results indicated that inhibition rates of T. koningiopsis B30, and T. hamatum A26 were highest compared to other strains. Similarly, non-volatile metabolites extracted from the B30 strain showed a 100% inhibition of S. asari. The activity of CAT, SOD, and POD decreased after treatment with A26 and B30 strains while increasing MDA content of S. asari. Antifungal activity of differential metabolites like abamectin, eplerenone, behenic acid, lauric acid, josamycin, erythromycin, and minocycline exhibited the highest inhibition of S. asari. Transcriptome analysis showed that differentially expressed genes were involved in many metabolic pathways which subsequently contributed toward antifungal activity of Trichoderma. These findings suggested that both Trichoderma strains (B30 and A26) could be effectively used as biocontrol agents against Sclerotinia disease of Asarum.

Glucoraphanin and sulforaphane biosynthesis by melatonin mediating nitric oxide in hairy roots of broccoli (Brassica oleracea L. var. italica Planch): insights from transcriptome data

Glucoraphanin (GRA) is present in the seeds and nutrient organs of broccoli and is the precursor of the anti-cancer compound sulforaphane (SF). The hairy roots obtained by infecting broccoli (Brassica oleracea L. var. Italic Planch) leaves with Agrobacterium rhizogenes (ATCC15834) are phytohormonally autonomous, genetically stable, and can produce large amounts of the anti-cancer substance SF. Melatonin (MT) is a natural hormone widely found in plants. Studies have shown that melatonin can regulate the synthesis of secondary metabolites of downstream targets by mediating the synthesis of signal molecules. However, whether MT regulates the synthesis of NO and H₂O₂ and mediates the synthesis mechanism of secondary metabolites, GRA and SF, is not yet clear. In this study, the hairy roots of broccoli were treated with 500 μmol/L MT, and the genome of broccoli (Brassica oleracea L. var. botrytis L) was used as the reference genome for transcriptome analysis. By this approach, we found that MT regulates the synthesis of NO and H₂O₂ and mediates the synthesis of secondary metabolites GRA and SF. GO annotations indicated that DEGs involved in the MT treatment of broccoli hairy roots were mainly related to catalytic activity, cells, and metabolic processes; the KEGG pathway analysis indicated that MT treatment likely affects the hormone signal transduction process in broccoli hairy roots; broccoli hairy roots were treated with 500 μmol/L MT for 0, 6, 12, 20, and 32 h, respectively; compared with 0 h, the yield of GRA and SF increased under the other treatments. The highest yields of GRA and SF occurred at 12 h. The NO content was the highest at 12 h, and the H₂O₂ content was positively correlated with MT concentration. The content of NO and H₂O₂ were regulated, and the content of GRA and SF was increased under MT treatment. NO synthase inhibitor (L-NAME and TUN) could effectively inhibit the content of NO in broccoli hairy roots and reduce GRA and SF yield; MT could regulate NO levels by regulating NO synthesis-related enzymes and could alleviate the reduction of NO content in tissue cells caused by NO synthase inhibitor and promote NO synthesis. These results have important theoretical implications for understanding the regulation of GRA and SF synthesis events by NO and H₂O₂.

Mechanism of Sugarbeet Seed Germination Enhanced by Hydrogen Peroxide

Seed germination is a critical first stage of plant development but can be arrested by factors including dormancy and environmental conditions. Strategies to enhance germination are of interest to plant breeders to ensure the ability to utilize the genetic potential residing inside a dormant seed. In this study, seed germination in two sugarbeet (Beta vulgaris ssp. vulgaris L.) lines F1004 and F1015 through incubating seeds in hydrogen peroxide (H₂O₂) solution was improved over 70% relative to germinating seeds through water incubation. It was further found that low germination from water incubation was caused by physical dormancy in F1015 seeds with initial seed imbibition blocked by the seed pericarp, and physiological dormancy in F1004 seeds with germination compromised due to the physiological condition of the embryo. To identify genes that are differentially expressed in response to cellular activities promoted by H₂O₂ during overcoming different type of dormancies, an RNA-Seq study was carried out and found H₂O₂ treatment during germination accelerated the degradation of seed stored mRNAs that were synthesized before or during seed storage to provide protections and maintain the dormant state. Comparison of transcripts in H₂O₂-treated seeds between the two sugarbeet lines identified differentially expressed genes (DEGs) that were higher in F1004 for alleviating physiological dormancy were known to relative to gene expression regulation. The research established that H₂O₂ overcomes both physical and physiological dormancies by hastening the transition of seeds from dormancy into germination. More DEGs related to gene expression regulation were involved in relieving physiological dormancy which provides new knowledge about the role of exogenous H₂O₂ as a signaling molecule for regulating gene activities during germination. Moreover, the protocol using H₂O₂ to promote germination will be useful for rescuing plant germplasms with poor germination.

Linking Reactive Oxygen Species (ROS) to Abiotic and Biotic Feedbacks in Plant Microbiomes: The Dose Makes the Poison

In nature, plants develop in complex, adaptive environments. Plants must therefore respond efficiently to environmental stressors to maintain homeostasis and enhance their fitness. Although many coordinated processes remain integral for achieving homeostasis and driving plant development, reactive oxygen species (ROS) function as critical, fast-acting orchestrators that link abiotic and biotic responses to plant homeostasis and development. In addition to the suite of enzymatic and non-enzymatic ROS processing pathways that plants possess, they also rely on their microbiota to buffer and maintain the oxidative window needed to balance anabolic and catabolic processes. Strong evidence has been communicated recently that links ROS regulation to the aggregated function(s) of commensal microbiota and plant-growth-promoting microbes. To date, many reports have put forth insightful syntheses that either detail ROS regulation across plant development (independent of plant microbiota) or examine abiotic–biotic feedbacks in plant microbiomes (independent of clear emphases on ROS regulation). Here we provide a novel synthesis that incorporates recent findings regarding ROS and plant development in the context of both microbiota regulation and plant-associated microbes. Specifically, we discuss various roles of ROS across plant development to strengthen the links between plant microbiome functioning and ROS regulation for both basic and applied research aims.

Biosynthesis and beneficial effects of microbial gibberellins on crops for sustainable agriculture

Soil microbes promote plant growth through several mechanisms such as secretion of chemical compounds including plant growth hormones. Among the phytohormones, auxins, ethylene, cytokinins, abscisic acid and gibberellins are the best understood compounds. Gibberellins were first isolated in 1935 from the fungus Gibberella fujikuroi and are synthesized by several soil microbes. The effect of gibberellins on plant growth and development has been studied, as has the biosynthesis pathways, enzymes, genes and their regulation. This review revisits the history of gibberellin research highlighting microbial gibberellins and their effects on plant health with an emphasis on the early discoveries and current advances that can find vital applications in agricultural practices.

The antioxidant defense and glyoxalase systems contribute to the thermotolerance of Heliotropium thermophilum

This study focused on the impact of the antioxidant defence and glyoxalase systems on extreme heat tolerance of the thermophilic plant Heliotropium thermophilum L. For this purpose, plants were exposed to 20, 40, 60 and 80±5°C soil temperature gradually for 15days under laboratory conditions. Our results showed that the hydrogen peroxide and superoxide levels of H. thermophilum were lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Some antioxidant enzyme activities tended to increase in plants at 40, 60 and 80±5°C compared with those at 20±5°C and the protein contents responsible for the antioxidant enzymes were in parallel with these enzyme activities. The contents of both reduced and oxidised ascorbate and glutathione rose with increasing temperature. Methylglyoxal level was lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Glyoxalase activities highly increased with rising of soil temperature from 20±5°C to 80±5°C. The results of this study suggest that differential modulations of enzymatic antioxidants and the increase in non-enzymatic antioxidants and glyoxalase activities can contribute to the development of the thermotolerance of H. thermophilum through the detoxification of reactive oxygen species and methylglyoxal.

Thermotherapy and Storage Temperature Manipulations Limit the Production of Reactive Oxygen Species in Stored Pedunculate Oak Acorns

For many species, seed storage protocols are still being improved to provide viable seeds of the highest quality. Seed storage is extremely problematic for short-lived seeds categorized as recalcitrant, including pedunculate oak (Quercus robur L.), for which the optimal seed storage protocol involves a temperature of –3 °C and 40% acorn moisture content recommendations. The sensitivity of pedunculated oak seeds to temperature manipulations under preparation for long-term storage has been poorly investigated, particularly in terms of the production of reactive oxygen species (ROS), which are assumed to be determinants of seed longevity. Thermotherapy, the pathogen elimination procedure, did not increase the level of three types of ROS: hydrogen peroxide (H2O2), superoxide anion radical and hydroxyl radical (•OH). The temporal heat stress of thermotherapy resulted in slightly reduced levels of H2O2, indicating activation of the antioxidant systems in acorn preparation for storage. The effect of constant storage temperatures (−3, −5, −7 °C) and their combinations (−3 → −5 °C or −3 → −5 →−7 °C) on ROS levels and seed viability was investigated in three provenances. The highest ROS levels were detected in acorns stored at −7 °C, whereas three-step cold acclimation was beneficial for reducing ROS levels. Interestingly, the levels of H2O2 were not affected by temperature in thermotherapized acorns. In contrast, decreasing storage temperature caused a linear increase in •OH levels in all provenances. The effect of heat stress and cold stress on ROS levels in relation to long-term seed storage of pedunculate oak is discussed here in relation to the seed viability evidenced via germination rates, seedling emergence and electrolyte leakage. Thermotherapy and cold acclimation of acorns can improve their viability after storage by decreasing ROS levels.

A New Role for Plastid Thioredoxins in Seed Physiology in Relation to Hormone Regulation

In Arabidopsis seeds, ROS have been shown to be enabling actors of cellular signaling pathways promoting germination, but their accumulation under stress conditions or during aging leads to a decrease in the ability to germinate. Previous biochemical work revealed that a specific class of plastid thioredoxins (Trxs), the y-type Trxs, can fulfill antioxidant functions. Among the ten plastidial Trx isoforms identified in Arabidopsis, Trx y1 mRNA is the most abundant in dry seeds. We hypothesized that Trx y1 and Trx y2 would play an important role in seed physiology as antioxidants. Using reverse genetics, we found important changes in the corresponding Arabidopsis mutant seeds. They display remarkable traits such as increased longevity and higher and faster germination in conditions of reduced water availability or oxidative stress. These phenotypes suggest that Trxs y do not play an antioxidant role in seeds, as further evidenced by no changes in global ROS contents and protein redox status found in the corresponding mutant seeds. Instead, we provide evidence that marker genes of ABA and GAs pathways are perturbed in mutant seeds, together with their sensitivity to specific hormone inhibitors. Altogether, our results suggest that Trxs y function in Arabidopsis seeds is not linked to their previously identified antioxidant roles and reveal a new role for plastid Trxs linked to hormone regulation.

Chitosan (CTS) Alleviates Heat-Induced Leaf Senescence in Creeping Bentgrass by Regulating Chlorophyll Metabolism, Antioxidant Defense, and the Heat Shock Pathway

Chitosan (CTS) is a deacetylated derivative of chitin that is involved in adaptive response to abiotic stresses. However, the regulatory role of CTS in heat tolerance is still not fully understood in plants, especially in grass species. The aim of this study was to investigate whether the CTS could reduce heat-induced senescence and damage to creeping bentgrass associated with alterations in antioxidant defense, chlorophyll (Chl) metabolism, and the heat shock pathway. Plants were pretreated exogenously with or without CTS (0.1 g L-1) before being exposed to normal (23/18 °C) or high-temperature (38/33 °C) conditions for 15 days. Heat stress induced detrimental effects, including declines in leaf relative water content and photochemical efficiency, but significantly increased reactive oxygen species (ROS) accumulation, membrane lipid peroxidation, and Chl loss in leaves. The exogenous application of CTS significantly alleviated heat-induced damage in creeping bentgrass leaves by ameliorating water balance, ROS scavenging, the maintenance of Chl metabolism, and photosynthesis. Compared to untreated plants under heat stress, CTS-treated creeping bentgrass exhibited a significantly higher transcription level of genes involved in Chl biosynthesis (AsPBGD and AsCHLH), as well as a lower expression level of Chl degradation-related gene (AsPPH) and senescence-associated genes (AsSAG12, AsSAG39, Asl20, and Ash36), thus reducing leaf senescence and enhancing photosynthetic performance under heat stress. In addition, the foliar application of CTS significantly improved antioxidant enzyme activities (SOD, CAT, POD, and APX), thereby effectively reducing heat-induced oxidative damage. Furthermore, heat tolerance regulated by the CTS in creeping bentgrass was also associated with the heat shock pathway, since AsHSFA-6a and AsHSP82 were significantly up-regulated by the CTS during heat stress. The potential mechanisms of CTS-regulated thermotolerance associated with other metabolic pathways still need to be further studied in grass species.

Abnormal Mitochondrial Physiology in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by abnormalities within the innate and adaptive immune systems. Activation and proliferation of a wide array of immune cells require significant up-regulation in cellular energy metabolism, with the mitochondria playing an essential role in the initiation and maintenance of this response. This article highlights how abnormal mitochondrial function may occur in SLE and focuses on how energy metabolism, oxidative stress, and impaired mitochondrial repair play a role in the pathogenesis of the disease. How this may represent an appealing novel therapeutic target for future drug therapy in SLE also is discussed.

Effects of exogenous ascorbic acid on the mycelia growth and primordia formation of Pleurotus ostreatus

Primordia formation is the first and most critical step in the development of fruiting bodies of edible fungi. In this study, the effects of exogenous ascorbic acid (ASA) on the Pleurotus ostreatus mycelia growth and primordia formation were researched and the results showed that the growth rate of P. ostreatus mycelia was accelerated and the time of primordia formation was advanced. The protein content and ascorbate oxidase (AAO) activity analysis showed that with the increase of ASA concentration, the protein content of mycelia first decreased and then increased, and in a certain concentration range, exogenous ASA could significantly promote the activity of AAO. Further expression analysis of the development regulating genes (Pofst3 and Pofst4) as well as blue light receptor coding genes (PoWC-1 and PoWC-2) showed the expression levels of those four genes all changed after the exogenous ASA addition, which indicated that the expression changes of PoWC-1 and PoWC-2, two key genes in the light morphogenesis, might affect the expression levels of development regulating genes Pofst3 and Pofst4, so as to lead to the formation of primordia in advance.

The novel galactosyl transferase-like (SbGalT) gene from Salicornia brachiata maintains photosynthesis and enhances abiotic stress tolerance in transgenic tobacco

We hereby report in planta function characterization of a novel galactosyl transferase-like (SbGalT) gene from Salicornia brachiata for enhanced abiotic stress tolerance. The SbGalT gene had an open reading frame of 1563 bp. The ectopic expression of SbGalT gene in tobacco improved the seed germination, seedling growth, biomass accumulation and potassium/sodium ratio under salt and osmotic stress. The SbGalT over-expression delayed stress-induced senescence, pigment break-down and ion induced cytotoxicity in tobacco. Higher contents of organic solutes and potassium under stress maintained the osmotic homeostasis and relative water content in tobacco. Higher activity of antioxidant enzymes under stress in transgenic tobacco curtailed the accumulation of reactive oxygen species (ROS) and maintained the membrane integrity. The chlorophyll a fluorescence transient indicated no effects of the imposed strengths of stress on basal state of photosystem (PS) I in transgenic tobacco over-expressing the SbGalT gene. Due to improved membrane integrity, the transgenic tobacco exhibited improved photosynthesis, stomatal conductance, intercellular CO2, transpiration, maximum quantum yield and operating efficiency of PSII, electron transport, photochemical and non-photochemical quenching. In agreement with photosynthesis, physiological health, tolerance index and growth parameters, transgenic tobacco accumulated higher contents of sugar, starch, amino acid, polyphenol and proline under stress conditions. The multivariate data analysis exhibited significant statistical distinctions among osmotic adjustment, physiological health and growth, and photosynthetic responses in control and SbGalT transgenic tobacco under stress conditions. The results strongly indicated novel SbGalT gene as a potential candidate for developing the smart agriculture.

Hydrogen-rich water alleviates programmed cell death induced by GA in wheat aleurone layers by modulation of reactive oxygen species metabolism

Hydrogen gas (H₂) has been recently regarded as a novel gaseous signaling molecule that performs multiple functional roles in plant. Here, we demonstrate that hydrogen rich water (HRW)-an experimentally tractable reagent to assess the effects of the H₂ significantly delays wheat aleurone layer programmed cell death (PCD) induced by gibberellic acid (GA). Endogenous H₂ production exhibited lower level in aleurone layers under GA treatment, whereas the H₂ production was apparently increased under abscisic acid (ABA) treatment. HRW not only increased H₂ production but also delayed GA-induced PCD. We further observed that application of HRW substantially prevented the increases of hydrogen peroxide (H₂O₂) and superoxide anion radical (O₂^.-) triggered by GA. HRW also directly react with hydroxyl radical (·OH) to delay GA-induced PCD. Quantitative real-time PCR (qRT-PCR) and biochemical assays showed that HRW induced the transcripts and enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) that metabolize reactive oxygen species (ROS); these increases coincided with the observed changes in O₂^.-, H₂O₂ and ·OH accumulation upon GA treatment. Our study therefore suggests that HRW-triggered alleviation of wheat aleurone layer PCD induced by GA results from a combination of H₂-mediated decreases of ROS levels, including O₂^.-, H₂O₂, and ·OH.

Analysis of Curcumin as a Radiosensitizer in Cancer Therapy with Serum Survivin Examination: Randomised Control Trial

OBJECTIVE

One of the important treatments for cervical cancer is radiation therapy. This study sought to determine the role of curcumin as a radio-sensitizing agent for use with radiation therapy for cervical cancer. To accomplish this, we assessed the levels of survivin, which is an anti-apoptotic protein that plays a role in cell division and apoptosis inhibition.

METHOD

This study used a quasi-experimental design, including a pretest-posttest control group design approach. The study subjects included cervical carcinoma stage IIB-IIIB patients who were scheduled to undergo surgery at the Hasan Sadikin Hospital Bandung during the research period. The advanced cervical cancer patients were assigned to two groups: i) those who received curcumin + radiation therapy and ii) those who received placebo + radiation therapy.

RESULTS

In the group treated with curcumin + radiation, 15 (75%) patients showed decreased survivin levels and 5 (25%) showed increased survivin levels. Whereas, in the placebo + radiation group, there were 8 (40%) patients who showed decreased survivin levels and 12 (60%) who showed increased survivin levels.

CONCLUSION

In conclusion, curcumin is an effective, alternative radiosensitizer agent for application in cervical cancer treatment.
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In vivo light-sheet microscopy resolves localisation patterns of FSD1, a superoxide dismutase with function in root development and osmoprotection

Superoxide dismutases (SODs) are enzymes detoxifying superoxide to hydrogen peroxide while temporal developmental expression and subcellular localisation are linked to their functions. Therefore, we aimed here to reveal in vivo developmental expression, subcellular, tissue- and organ-specific localisation of iron superoxide dismutase 1 (FSD1) in Arabidopsis using light-sheet and Airyscan confocal microscopy. FSD1-GFP temporarily accumulated at the site of endosperm rupture during seed germination. In emerged roots, it showed the highest abundance in cells of the lateral root cap, columella, and endodermis/cortex initials. The largest subcellular pool of FSD1-GFP was localised in the plastid stroma, while it was also located in the nuclei and cytosol. The majority of the nuclear FSD1-GFP is immobile as revealed by fluorescence recovery after photobleaching. We found that fsd1 knockout mutants exhibit reduced lateral root number and this phenotype was reverted by genetic complementation. Mutant analysis also revealed a requirement for FSD1 in seed germination during salt stress. Salt stress tolerance was coupled with the accumulation of FSD1-GFP in Hechtian strands and superoxide removal. It is likely that the plastidic pool is required for acquiring oxidative stress tolerance in Arabidopsis. This study suggests new developmental and osmoprotective functions of SODs in plants.

Involvement of the MetO/Msr System in Two Acer Species That Display Contrasting Characteristics during Germination

The levels of methionine sulfoxide (MetO) and the abundances of methionine sulfoxide reductases (Msrs) were reported as important for the desiccation tolerance of Acer seeds. To determine whether the MetO/Msrs system is related to reactive oxygen species (ROS) and involved in the regulation of germination in orthodox and recalcitrant seeds, Norway maple and sycamore were investigated. Changes in water content, MetO content, the abundance of MsrB1 and MsrB2 in relation to ROS content and the activity of reductases depending on nicotinamide adenine dinucleotides were monitored. Acer seeds differed in germination speed-substantially higher in sycamore-hydration dynamics, levels of hydrogen peroxide, superoxide anion radicals (O2•-) and hydroxyl radicals (•OH), which exhibited peaks at different stages of germination. The MetO level dynamically changed, particularly in sycamore embryonic axes, where it was positively correlated with the levels of O2•- and the abundance of MsrB1 and negatively with the levels of •OH and the abundance of MsrB2. The MsrB2 abundance increased upon sycamore germination; in contrast, it markedly decreased in Norway maple. We propose that the ROS-MetO-Msr redox system, allowing balanced Met redox homeostasis, participates in the germination process in sycamore, which is characterized by a much higher speed compared to Norway maple.

Carbon dot induces tolerance to arsenic by regulating arsenic uptake, reactive oxygen species detoxification and defense-related gene expression in Cicer arietinum L

The scientific and technological applications of one of the nanomaterials viz.; carbon dot (C-dots), having extraordinary properties, is becoming an emerging and ongoing research area in recent times. In the present study, we have evaluated the effectiveness of C-dots in reducing arsenic (As) toxicity by analyzing physiological, biochemical and molecular parameters in Cicer arietinum L. The results revealed that As decreased the germination rate, growth, biomass, and membrane stability of the cell to a significant extent. Further, As was taken up by the growing seeds which eventually caused cell death. Levels of reactive oxygen species (ROS), stress markers (malondialdehyde), activities of defensive enzymes (glutathione-S-transferase and pyrroline-5-carboxylate synthetase) and non-enzymatic antioxidant contents (proline and glutathione) were increased under As stress. Moreover, As treatment resulted in the up-regulation of expressions of NADPH oxidase and defense-related genes in Cicer arietinum L. However, application of C-dots along with As improved the germination and growth of Cicer arietinum L. Exogenous application of C-dots, enhanced the expressions of defense-related genes and, contents of proline and glutathione, thereby causing considerable reductions in ROS, and malondialdehyde levels. Overall, this study suggests the possible involvement of C-dots in lowering the toxic effects of As on biomass by reducing As uptake and, inducing the activities/gene expressions and contents of enzymatic and non-enzymatic antioxidants.

Tomato SlIDA has a critical role in tomato fertilization by modifying reactive oxygen species homeostasis

Anther development and pollen tube elongation are key steps for pollination and fertilization. The timing and spatial distribution of reactive oxygen species (ROS) and programmed cell death are central to these processes, but the regulatory mechanism of ROS production is not well understood. Inflorescence deficient in abscission (IDA) is implicated in many plant development and responses to environmental stimuli. However, their role in reproductive development is still unknown. We generated tomato knockout lines (CR-slida) of an IDA homolog (SlIDA), which is expressed in the tapetum, septum and pollen tube, and observed a severe defect in male gametes. Further analysis indicated that there was a programmed cell death defect in the tapetum and septum and a failure of anther dehiscence in the CR-slida lines, likely related to insufficient ROS signal. Liquid chromatography-tandem mass spectrometry identified mature SlIDA as a 14-mer EPIP peptide, which was shown to be secreted, and a complementation experiment showed that application of a synthetic 14-mer EPIP peptide rescued the CR-slida defect and enhanced the ROS signal. Moreover, the application of the ROS scavengers diphenyleneiodonium or Mn-TMPP suppressed peptide function. Collectively, our results revealed that SlIDA plays an essential role in pollen development and pollen tube elongation by modulating ROS homeostasis.

Coordination of five class III peroxidase-encoding genes for early germination events of Arabidopsis thaliana

The Class III peroxidases (CIII Prxs) belong to a plant-specific multigene family. Thanks to their double catalytic cycle they can oxidize compounds or release reactive oxygen species (ROS). They are either involved in different cell wall stiffening processes such as lignification and suberization, in cell wall loosening or defense mechanisms. Germination is an important developmental stage requiring specific peroxidase activity. However, little is known about which isoforms are involved. Five CIII Prx encoding genes: AtPrx04, AtPrx16, AtPrx62, AtPrx69, and AtPrx71 were identified from published microarray data mining. Delayed or induced testa and endosperm rupture were observed for the corresponding CIII Prx mutant lines indicating either a gene-specific inducing or repressing role during germination, respectively. Via in situ hybridization AtPrx16, AtPrx62, AtPrx69 and AtPrx71 transcripts were exclusively localized to the micropylar endosperm facing the radicle, and transcriptomic data analysis enabled positioning the five CIII Prxs in a co-expression network enriched in germination, cell wall, cell wall proteins and xyloglucan hits. Evidence were produced showing that the five CIII Prxs were cell wall-targeted proteins and that the micropylar endosperm displayed a complex cell wall domain topochemistry. Finally, we drew a spatio-temporal model highlighting the fine sequential gene expression and the possible involvement of micropylar endosperm cell wall domains to explain the non-redundant cell wall stiffening and loosening functions of the CIII Prxs in a single cell type. We also highlighted the necessity of a peroxidase homeostasis to accurately control the micropylar endosperm cell wall dynamics during Arabidopsis germination events.

The NADPH-oxidase LsRbohC1 plays a role in lettuce (Lactuca sativa) seed germination

Reactive oxygen species (ROS) are increasingly recognized as non-enzymatic players in the processes of radicle elongation growth and endosperm weakening during seed germination. NADPH oxidases (EC 1.6.3.1), also known as respiratory burst oxidase homologues (Rbohs), are key enzymes for the production of ROS. We previously reported that ROS are involved in the radicle elongation growth and endosperm weakening during lettuce seed germination. However, the function of the gene(s) encoding Rbohs during lettuce seed germination remains to be elucidated. In this study, one lettuce Rboh gene LsRbohC1 was cloned, and over-expression and RNAi-lines of this gene were generated. It was found that LsRbohC1 was abundantly expressed in germinating seeds, especially in the endosperm cap and hypocotyl. Over-expression/knock-down of this gene observably increased/decreased the production of superoxide radicals in the radicle and endosperm cap, and significantly promoted/delayed the germination process. The results suggest that LsRbohC1 plays a role in lettuce seed germination.

The signalling role of ROS in the regulation of seed germination and dormancy

Reactive oxygen species (ROS) are versatile compounds which can have toxic or signalling effects in a wide range living organisms, including seeds. They have been reported to play a pivotal role in the regulation of seed germination and dormancy but their mechanisms of action are still far from being fully understood. In this review, we sum-up the major findings that have been carried out this last decade in this field of research and which altogether shed a new light on the signalling roles of ROS in seed physiology. ROS participate in dormancy release during seed dry storage through the direct oxidation of a subset of biomolecules. During seed imbibition, the controlled generation of ROS is involved in the perception and transduction of environmental conditions that control germination. When these conditions are permissive for germination, ROS levels are maintained at a level which triggers cellular events associated with germination, such as hormone signalling. Here we propose that the spatiotemporal regulation of ROS production acts in concert with hormone signalling to regulate the cellular events involved in cell expansion associated with germination.

The Apoplast: A Key Player in Plant Survival

The apoplast comprises the intercellular space, the cell walls, and the xylem. Important functions for the plant, such as nutrient and water transport, cellulose synthesis, and the synthesis of molecules involved in plant defense against both biotic and abiotic stresses, take place in it. The most important molecules are ROS, antioxidants, proteins, and hormones. Even though only a small quantity of ROS is localized within the apoplast, apoplastic ROS have an important role in plant development and plant responses to various stress conditions. In the apoplast, like in the intracellular cell compartments, a specific set of antioxidants can be found that can detoxify the different types of ROS produced in it. These scavenging ROS components confer stress tolerance and avoid cellular damage. Moreover, the production and accumulation of proteins and peptides in the apoplast take place in response to various stresses. Hormones are also present in the apoplast where they perform important functions. In addition, the apoplast is also the space where microbe-associated molecular Patterns (MAMPs) are secreted by pathogens. In summary, the diversity of molecules found in the apoplast highlights its importance in the survival of plant cells.

Oxidation processes related to seed storage and seedling growth of Malus sylvestris, Prunus avium and Prunus padus

Seeds stored in controlled conditions in gene banks, faster or slower lose their viability. The effects of seed moisture content levels (ca. 5, 8, 11%) combined with storage temperatures (-3°, -18°, -196°C) were investigated in terms of the description of seeds defined as orthodox under oxidative stress after seed storage, during germination, and initial seedling growth. Hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) and ascorbate (Asc) were analyzed in relation to seed germinability and seedlings emergence in three species: Malus sylvestris L., Prunus avium L. and Prunus padus L. The effect of seed storage conditions on H2O2 levels appeared in germinated seeds after the third year of storage in each species. The H2O2 levels were negatively correlated with the germination and seedling emergence of P. avium seeds after three years of storage under all examined combinations. The emergence of P. padus seedlings was not linked to any of the stress markers tested. The P. padus seed biochemical traits were least altered by storage conditions, and the seeds produced tolerant seedlings of relatively high levels of H2O2 and TBARS. To cope with different H2O2 levels, TBARS levels, and Asc levels in seeds of three species varying storage conditions different molecular responses, i.e. repairing mechanisms, were applied during stratification to compensate for the storage conditions and, as a result, seeds remained viable and seedlings were successfully established.

Modulation of Aleurone Peroxidases in Kernels of Insect-Resistant Maize (Zea mays L.; Pob84-C3R) After Mechanical and Insect Damage

Peroxidases (PODs) have many biological functions during the plant life cycle. In maize kernels, endosperm PODs have been identified as biochemical contributors to resistance against Sitophilus zeamais, but their identities have not been determined. In this study, we identified these PODs and determined whether their contributions are basal or inducible. Semi-purification and LC-MS/MS analyses showed that the protein ZmPrx35 is the predominant soluble endosperm POD from kernels of Pob84-C3R. Subsequent time-course analyses after mechanical damage showed that POD activity was regulated in a fluctuating kinetics pattern and that zmprx35 mRNA expression levels reflected this pattern. After 48 h of infestation with S. zeamais or Prostephanus truncatus, soluble endosperm POD activities were 1.38- or 0.85-fold, respectively. Under the same conditions, zmprx35 expression was induced 1.61-fold (S. zeamais infestation) and 1.17-fold (P. truncatus infestation). These findings suggest that ZmPrx35 contributes to the protective responses of aleurone cells against wounding and pest attacks, which could be enhanced/repressed by insect factors. Our data also provide evidence that the mechanisms of resistance of maize Pob84-C3R kernels toward the insect pests S. zeamais and P. truncatus are independent.

Peptide-Bound Methionine Sulfoxide (MetO) Levels and MsrB2 Abundance Are Differentially Regulated during the Desiccation Phase in Contrasted Acer Seeds

Norway maple and sycamore produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Drying affects reduction and oxidation (redox) status in seeds. Oxidation of methionine to methionine sulfoxide (MetO) and reduction via methionine sulfoxide reductases (Msrs) have never been investigated in relation to seed desiccation tolerance. MetO levels and the abundance of Msrs were investigated in relation to levels of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical and hydroxyl radical (•OH), and the levels of ascorbate and glutathione redox couples in gradually dried seeds. Peptide-bound MetO levels were positively correlated with ROS concentrations in the orthodox seeds. In particular, •OH affected MetO levels as well as the abundance of MsrB2 solely in the embryonic axes of Norway maple seeds. In this species, MsrB2 was present in oxidized and reduced forms, and the latter was favored by reduced glutathione and ascorbic acid. In contrast, sycamore seeds accumulated higher ROS levels. Additionally, MsrB2 was oxidized in sycamore throughout dehydration. In this context, the three elements •OH level, MetO content and MsrB2 abundance, linked together uniquely to Norway maple seeds, might be considered important players of the redox network associated with desiccation tolerance.

High post-anthesis temperature effects on bread wheat (Triticum aestivum L.) grain transcriptome during early grain-filling

BACKGROUND

High post-anthesis (p.a) temperatures reduce mature grain weights in wheat and other cereals. However, the causes of this reduction are not entirely known. Control of grain expansion by the maternally derived pericarp of the grain has previously been suggested, although this interaction has not been investigated under high p.a. temperatures. Down-regulation of pericarp localised genes that regulate cell wall expansion under high p.a. temperatures may limit expansion of the encapsulated endosperm due to a loss of plasticity in the pericarp, reducing mature grain weight. Here the effect of high p.a. temperatures on the transcriptome of the pericarp and endosperm of the wheat grain during early grain-filling was investigated via RNA-Seq and is discussed alongside grain moisture dynamics during early grain development and mature grain weight.

RESULTS

High p.a. temperatures applied from 6-days after anthesis (daa) and until 18daa reduced the grain's ability to accumulate water, with total grain moisture and percentage grain moisture content being significantly reduced from 14daa onwards. Mature grain weight was also significantly reduced by the same high p.a. temperatures applied from 6daa for 4-days or more, in a separate experiment. Comparison of our RNA-Seq data from whole grains, with existing data sets from isolated pericarp and endosperm tissues enabled the identification of subsets of genes whose expression was significantly affected by high p.a. temperature and predominantly expressed in either tissue. Hierarchical clustering and gene ontology analysis resulted in the identification of a number of genes implicated in the regulation of cell wall expansion, predominantly expressed in the pericarp and significantly down-regulated under high p.a. temperatures, including endoglucanase, xyloglucan endotransglycosylases and a β-expansin. An over-representation of genes involved in the 'cuticle development' functional pathway that were expressed in the pericarp and affected by high p.a. temperatures was also observed.

CONCLUSIONS

High p.a. temperature induced down-regulation of genes involved in regulating pericarp cell wall expansion. This concomitant down-regulation with a reduction in total grain moisture content and grain weight following the same treatment period, adds support to the theory that high p.a. temperatures may cause a reduction in mature grain weight as result of decreased pericarp cell wall expansion.

Responses of tropical tree species to urban air pollutants: ROS/RNS formation and scavenging

Air pollution in an urban environment is the major stress factor for vegetation due to the direct generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). To quantify urban air pollution-induced ROS/RNS formation, damage and detoxification, nine different biochemical parameters related to free radical formation, scavenging and membrane damage were estimated in twelve tropical tree species. The experiment was performed in three different seasons at four distinct urban environments in Varanasi city located in the Indo-Gangetic plain of India. Redundancy analysis was performed to statistically assess the relationship between air pollutants (PM_2.5, NO₂, SO₂ and O₃) and temperature with ROS/RNS generation and their detoxification. Significant effects of air pollution exposure and temperature on ROS/RNS formation, scavenging and membrane damage were recorded with increasing pollution load in the city for all the tree species. The extent of variability (47-87%) in responses of different tree species was due to their intrinsic ability to scavenge free radicals which minimized the membrane damage. PM_2.5, NO₂ and O₃ were identified as major pollutants that influenced trees to different extents in regulating ROS/RNS. However, the response was maximum against NO₂ (34-72%) followed by PM_2.5 (16-64%) and O₃ (3-31%), indicating that under urban environment, trees are considerably sensitive to the combined effects of both particulate and gaseous pollutants. Reactive oxygen intermediate release, total free radical scavenging activity, NO scavenging activity and membrane stability index were identified as major parameters which showed distinct responses with increasing pollution load. Caesalpinia sappan, Ficus religiosa and Albizia lebbeck were identified as most tolerant tree species having higher ROS/RNS scavenging potential resulted in lower membrane damage. Thus responses of urban trees to air pollution are governed by their intrinsic defence mechanisms to scavenge ROS/RNS by maintaining the membrane integrity through integrated cross-talk between different antioxidative pathways.

Silicon-Solubilizing Media and Its Implication for Characterization of Bacteria to Mitigate Biotic Stress

Silicon (Si), the second most abundant element on earth, remains unavailable for plants' uptake due to its poor solubility. Microbial interventions to convert it in soluble forms are well documented. However, studies on discrimination of Si and P solubilizing microbes due to common estimation method and sharing of solubilization mechanism are still obscure. A defined differential media, i.e. silicon-solubilizing media (NBRISSM) is developed to screen Si solubilizers. NBRISN13 (Bacillus amyloliquefaciens), a Si solubilizer, exhibiting antagonistic property against Rhizoctonia solani, was further validated for disease resistance. The key finding of the work is that NBRISSM is a novel differential media for screening Si solubilizers, distinct from P solubilizers. Dominance of Pseudomonas and Bacillus spp. for the function of Si solubilization was observed during diversity analysis of Si solubilizers isolated from different rhizospheres. Sphingobacterium sp., a different strain has been identified for silicon solubilization other than Pseudomonas and Bacillus sp. Role of acidic phosphatase during Si solubilization has been firstly reported in our study in addition to other pH dependent phenomenon. Study also showed the combinatorial effect of feldspar and NBRISN13 on elicited immune response through (i) increased Si uptake, (ii) reduced disease severity, (iii) modulation of cell wall degrading and antioxidative enzyme activities, and (iv) induced defense responsive gene expression.

Interplay between turgor pressure and plasmodesmata during plant development

Plasmodesmata traverse cell walls, generating connections between neighboring cells. They allow intercellular movement of molecules such as transcription factors, hormones, and sugars, and thus create a symplasmic continuity within a tissue. One important factor that determines plasmodesmal permeability is their aperture, which is regulated during developmental and physiological processes. Regulation of aperture has been shown to affect developmental events such as vascular differentiation in the root, initiation of lateral roots, or transition to flowering. Extensive research has unraveled molecular factors involved in the regulation of plasmodesmal permeability. Nevertheless, many plant developmental processes appear to involve feedbacks mediated by mechanical forces, raising the question of whether mechanical forces and plasmodesmal permeability affect each other. Here, we review experimental data on how one of these forces, turgor pressure, and plasmodesmal permeability may mutually influence each other during plant development, and we discuss the questions raised by these data. Addressing such questions will improve our knowledge of how cellular patterns emerge during development, shedding light on the evolution of complex multicellular plants.

Ozone effects on plants in natural ecosystems

Tropospheric ozone (O₃ ) is an important stressor in natural ecosystems, with well-documented impacts on soils, biota and ecological processes. The effects of O₃ on individual plants and processes scale up through the ecosystem through effects on carbon, nutrient and hydrologic dynamics. Ozone effects on individual species and their associated microflora and fauna cascade through the ecosystem to the landscape level. Systematic injury surveys demonstrate that foliar injury occurs on sensitive species throughout the globe. However, deleterious impacts on plant carbon, water and nutrient balance can also occur without visible injury. Because sensitivity to O₃ may follow coarse physiognomic plant classes (in general, herbaceous crops are more sensitive than deciduous woody plants, grasses and conifers), the task still remains to use stomatal O₃ uptake to assess class and species' sensitivity. Investigations of the radial growth of mature trees, in combination with data from many controlled studies with seedlings, suggest that ambient O₃ reduces growth of mature trees in some locations. Models based on tree physiology and forest stand dynamics suggest that modest effects of O₃ on growth may accumulate over time, other stresses (prolonged drought, excess nitrogen deposition) may exacerbate the direct effects of O₃ on tree growth, and competitive interactions among species may be altered. Ozone exposure over decades may be altering the species composition of forests currently, and as fossil fuel combustion products generate more O₃ than deteriorates in the atmosphere, into the future as well.

AtPER1 enhances primary seed dormancy and reduces seed germination by suppressing the ABA catabolism and GA biosynthesis in Arabidopsis seeds

Seed is vital to the conservation of germplasm and plant biodiversity. Seed dormancy is an adaptive trait in numerous seed-plant species, enabling plants to survive under stressful conditions. Seed dormancy is mainly controlled by abscisic acid (ABA) and gibberellin (GA) and can be classified as primary and secondary seed dormancy. The primary seed dormancy is induced by maternal ABA. Here we found that AtPER1, a seed-specific peroxiredoxin, is involved in enhancing primary seed dormancy. Two loss-of-function atper1 mutants, atper1-1 and atper1-2, displayed suppressed primary seed dormancy accompanied with reduced ABA and increased GA contents in seeds. Furthermore, atper1 mutant seeds were insensitive to abiotic stresses during seed germination. The expression of several ABA catabolism genes (CYP707A1, CYP707A2, and CYP707A3) and GA biosynthesis genes (GA20ox1, GA20ox3, and KAO3) in atper1 mutant seeds was increased compared to wild-type seeds. The suppressed primary seed dormancy of atper1-1 was completely reduced by deletion of CYP707A genes. Furthermore, loss-of-function of AtPER1 cannot enhance the seed germination ratio of aba2-1 or ga1-t, suggesting that AtPER1-enhanced primary seed dormancy is dependent on ABA and GA. Additionally, the level of reactive oxygen species (ROS) in atper1 mutant seeds was significantly higher than that in wild-type seeds. Taken together, our results demonstrate that AtPER1 eliminates ROS to suppress ABA catabolism and GA biosynthesis, and thus improves the primary seed dormancy and make the seeds less sensitive to adverse environmental conditions.

Quaternary Ammonium Salts of Iminofullerenes: Fabrication and Effect on Seed Germination

In this study, novel water-soluble quaternary ammonium salts of iminofullerenes (IFQA) were synthesized by nitrene chemistry in combination with quaternization and identified as [C₆₀(NCH₂CH₂NH₃⁺·CF₃COO^-)₄·10H₂O]_n by various spectroscopies. Maize and Arabidopsis seeds were used to test the bioactivity of IFQA in seed germination. Compared with the control, maize seed exposure to 50 mg/L IFQA (normal: 73.1% vs 58.7%; drought: 66.7% vs 50.0% at the second day) and Arabidopsis seed exposure to 20 mg/L IFQA (normal: 77.5% vs 58.8%; drought: 63.3% vs 36.7% at the second day) had higher germination rates and quicker germination. The results of two-dimensional gel electrophoresis combined with mass spectroscopy showed that the abundance of 21 proteins in embryo proteome of maize seeds was significantly changed (>1.5 fold). The downregulated six storage proteins and upregulated four proteins induced by IFQA for energy production and sugar metabolism indicated a faster metabolic activity of maize seed germination. The upregulated eight stress-related proteins and antioxidant enzymes suggested that the role of IFQA was to activate the metabolic processes in seed germination and also increase seed stress response. The results provide important information to understand the mechanism of seed germination enhancement by carbon nanomaterials.

Earlier Degraded Tapetum1 (EDT1) Encodes an ATP-Citrate Lyase Required for Tapetum Programmed Cell Death

In flowering plants, the tapetum cells in anthers undergo programmed cell death (PCD) at the late meiotic stage, providing nutrients for further development of microspores, including the formation of the pollen wall. However, the molecular basis of tapetum PCD remains elusive. Here we report a tapetum PCD-related mutant in rice (Oryza sativa), earlier degraded tapetum 1 (edt1), that shows complete pollen abortion associated with earlier-than-programmed tapetum cell death. EDT1 encodes a subunit of ATP-citrate lyase (ACL), and is specifically expressed in the tapetum of anthers. EDT1 localized in both the nucleus and the cytoplasm as observed in rice protoplast transient assays. We demonstrated that the A and B subunits of ACL interacted with each other and might function as a heteromultimer in the cytoplasm. EDT1 catalyzes the critical steps in cytosolic acetyl-CoA synthesis. Our data indicated a decrease in ATP level, energy charge, and fatty acid content in mutant edt1 anthers. In addition, the genes encoding secretory proteases or lipid transporters, and the transcription factors known to regulate PCD, were downregulated. Our results demonstrate that the timing of tapetum PCD must be tightly regulated for successful pollen development, and that EDT1 is involved in the tapetum PCD process. This study furthers our understanding of the molecular basis of pollen fertility and fecundity in rice and may also be relevant to other flowering plants.

Dehydration Sensitivity at the Early Seedling Establishment Stages of the European Beech (Fagus sylvatica L.)

Shortage of water is a limiting factor for the growth and development of plants, particularly at early developmental stages. We focused on the European beech (Fagus sylvatica L.), which produces seeds and further seedlings in large intervals of up to ten years. To explore the beech seedling establishment process, six stages referring to embryo expansion were studied to determine sensitivity to dehydration. The characterization of the response of elongating embryonic axes and cotyledons included a viability test before and after dehydration and measurement of the amounts of electrolyte leakage, concentration, and arrangement of storage materials, changes in chaperone proteins related to water deficit, and accumulation of hydrogen peroxide and superoxide anion radicals. Elongating embryonic axes and cotyledons differed in water content, dehydration rates, membrane permeability before and after dehydration, protein, and lipid decomposition pattern, and amount of 44-kDa dehydrin and 22-kDa small heat shock protein (sHSP). Protruding embryonic axes were more sensitive to dehydration than cotyledons, although dehydration caused transient reinduction of three dehydrin-like proteins and sHSP synthesis, which accompany desiccation tolerance. Extended deterioration, including overproduction of hydrogen peroxide and depletion of superoxide anion radicals, was reported in dehydrated embryonic axes longer than 10 mm characterized by highly elevated cellular leakage. The apical part elongating embryonic axes consisting of the radicles was the most sensitive part of the seed to dehydration, and the root apical meristem area was the first to become inviable. The effects of severe dehydration involving ROS imbalance and reduced viability in beech seedlings with embryonic axes longer than 10 mm might help to explain the difficulties in beech seedling establishment observed in drought-affected environments. The conversion of environmental drought into climate-originated oxidative stress affecting beech seedling performance is discussed in this report.

Redox metabolism and cell wall modifications as global and local targets respectively, of cyanide induced dormancy release of walnut kernels

The HCN-induced seed dormancy release necessitates alterations in reactive oxygen species (ROS) metabolism and radicle cell wall loosening. Little is known about the interaction of ROS metabolism with cell wall hydrolytic enzymes during HCN-induced seed dormancy release. Thus dormant walnut (Juglans regia L.) kernels were exposed to HCN (4 h) and studied for redox metabolism and cell wall-modifying enzymes during 10 days of incubation (DI) i.e. before radicle emergence. HCN increased ROS especially in the embryonic axes (EAs) but decreased ROS-generating NADPH oxidase and ROS scavenging superoxide dismutase (SOD) and peroxidase (POX) with no effects on catalase (CAT), ascorbate peroxidase (APX) and cell wall-modifying enzymes activities in short term up to 2 DI. In long term roughly from 4 DI onwards, HCN-exposed EA displayed greater superoxide anions and enhanced activities of POX, APX, NADPH oxidase, cell wall peroxidase (CW-POX), β- 1, 4-D glucanase, mannanase, polygacturonase and xylanase. Meanwhile HCN increased greater expression of POX and mannanase isoforms as revealed by in-gel activity assay. Except for higher activities of CAT, POX and APX, cotyledonary activities of CW-POX, mannanase and polygacturonase and to some extent β- 1, 4-D glucanase remained unaffected by HCN. Thus short term ROS accumulation in HCN-treated EA is due to declined SOD and POX activities. In long term the enhanced activities of both NADPH oxidase: CW-POX couple and cell wall-modifying enzymes in EA bring about wall loosening in preparation for radicle emergence. Evidences for the simultaneous operation of both mechanisms are provided in walnut EAs during dormancy release.

ROS management is mediated by ascorbate-glutathione-α-tocopherol triad in co-ordination with secondary metabolic pathway under cadmium stress in Withania somnifera

Being static, plants are frequently exposed to various essential and non-essential heavy metals from the surroundings. This exposure results in considerable ROS generation leading to oxidative stress, the primary response of the plants under heavy metal stress. Withania somnifera is a reputed Indian medicinal plant in Ayurveda, having various pharmacological activities due to the presence of withanolides. The present study deals with the understanding endurance of oxidative stress caused by heavy metal exposure and its management through antioxidant partners in synchronization with secondary metabolites in W. somnifera. The quantitative assessment of enzymatic/non-enzymatic antioxidants revealed significant participation of ascorbate-glutathione-α-tocopherol triad in ROS management. Higher activities of glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) resulted in glutathione and ascorbate accumulation. In addition, superoxide dismutase (SOD), glutathione peroxidase (GPX) and peroxidase (POD) were contributed considerably in ROS homeostasis maintenance. In-situ localization and assays related to ROS generation/scavenging revealed key management of ROS status under Cd stress. Higher antioxidative and reducing power activity attributed to the tolerance capability to the plant. Increased expression of withanolide biosynthetic pathway genes such as WsHMGR, WsDXS, WsDXR and WsCAS correlated with enhanced withanolides. The present study indicated the crucial role of the ascorbate-glutathione-α-tocopherol triad in co-ordination with withanolide biosynthesis in affording the oxidative stress, possibly through a cross-talk between the antioxidant machinery and secondary metabolite biosynthesis. The knowledge may be useful in providing the guidelines for developing abiotic stress resistance in plants using conventional and molecular approaches.

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.