Reactive Oxygen Species Scavenging System Research Articles

Water Deficit Severity during the Preceding Year Determines Plant Tolerance to Subsequent Year Drought Stress Challenges: A Case Study in Damask Rose

Water Deficit Severity during the Preceding Year Determines Plant Tolerance to Subsequent Year Drought Stress Challenges: A Case Study in Damask Rose

High-nitrogen fertilizer alleviated adverse effects of drought stress on the growth and photosynthetic characteristics of Hosta ‘Guacamole’

BackgroundSeveral plants are facing drought stress due to climate change in recent years. In this study, we aimed to explore the effect of varying watering frequency on the growth and photosynthetic characteristics of Hosta ‘Guacamole’. Moreover, we investigated the effect of high-nitrogen and -potassium fertilizers on alleviating the impacts of drought stress on the morphology, photosynthetic characteristics, chlorophyll fluorescence, fast chlorophyll a fluorescence transient, JIP-test parameters, and enzymatic and non-enzymatic scavenging system for reactive oxygen species (ROS) in this species.ResultsLeaf senescence, decreased chlorophyll contents, limited leaf area, and reduced photosynthetic characteristics and oxygen-evolving complex (OEC) activity were observed in Hosta ‘Guacamole’ under drought stress. However, high-nitrogen fertilizer (30-10-10) could efficiently alleviate and prevent the adverse effects of drought stress. High-nitrogen fertilizer significantly increased chlorophyll contents, which was higher by 106% than drought stress. Additionally, high-nitrogen fertilizer significantly improved net photosynthetic rate and water use efficiency, which were higher by 467% and 2900% than those under drought stress. It attributes that high-nitrogen fertilizer could reduce transpiration rate of leaf cells and stomatal opening size in drought stress. On the other hand, high-nitrogen fertilizer enhanced actual photochemical efficiency of PS II and photochemical quenching coefficient, and actual photochemical efficiency of PS II significantly higher by 177% than that under drought stress. Furthermore, high-nitrogen fertilizer significantly activated OEC and ascorbate peroxidase activities, and enhanced the performance of photosystem II and photosynthetic capacity compared with high-potassium fertilizers (15-10-30).ConclusionsHigh-nitrogen fertilizer (30-10-10) could efficiently alleviate the adverse effects of drought stress in Hosta ‘Guacamole’ via enhancing OEC activity and photosynthetic performance and stimulating enzymatic ROS scavenging system.

Synthetic modulation of ROS scavenging during host—Sclerotinia sclerotiorum interaction: a new strategy for the development of highly resistant plants

Sclerotinia sclerotiorum is a widespread fungal pathogen responsible for significant crop losses across the globe. The challenge of breeding resistant varieties is exacerbated by the fungus's sophisticated pathogenic mechanisms. A pivotal factor in the host-pathogen interaction is the regulation of reactive oxygen species (ROS) within both the fungi and the host plants. However, there is currently no efficient strategy to leverage this interaction mechanism for developing disease-resistant crop varieties. Here, we introduce an engineered ROS scavenging system designated as syn-ROS for impairing ROS neutralization in S. sclerotiorum while concurrently fortifying it in the host. The syn-ROS system comprises gene silencing constructs targeting the S. sclerotiorum Cu/Zn superoxide dismutase (SsSOD) and its copper chaperone (SsCCS), alongside overexpression constructs for the Arabidopsis thaliana AtSOD1 and AtCCS. Transgenic plants carrying the syn-ROS system demonstrated a marked enhancement in resistance to S. sclerotiorum. Upon infection, the expression of SsSOD and SsCCS was reduced, while the expression of AtSOD1 and AtCCS was enhanced in syn-ROS transgenic plants. Moreover, the infected syn-ROS plants showed decreased Cu/Zn SOD enzyme activity and elevated ROS concentrations within the fungal cells. In contrast, the cells of A. thaliana manifested increased Cu/Zn SOD enzyme activity and lowered ROS levels. Collectively, these findings suggest a novel and promising approach for contriving plants with robust resistance by synthetically manipulating ROS scavenging activities in the interaction between the host and S. sclerotiorum.

Control of postharvest soft rot of green peppers by Bacillus subtilis through regulating ROS metabolism

Soft rot caused by Pectobacterium carotovorum is one of the most serious postharvest bacterial diseases of green peppers. The present research aimed to determine the biocontrol effect of Bacillus subtilis on postharvest soft rot of green peppers and to further delve into biocontrol mechanisms by analyzing the metabolism of reactive oxygen species (ROS) in green peppers. As key results, soft rot occurrence of green peppers was alleviated with the increase of the concentration of B. subtilis, and the disease incidence and index of the fruits treated with 1 × 109 CFU/mL of B. subtilis for 4 d were 28.3% and 12.7%, respectively, which were significantly decreased compared with that of the control. B. subtilis could significantly increase NADPH oxidase (NOX) activity in green peppers to trigger ROS outbreaks, which induced defense response of the fruits. Furthermore, it promoted the enzymatic activities of the ROS scavenging system, including antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), ascorbic acid-glutathione (AsA-GSH) cycle-related enzymes (ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR)), glutathione peroxidase (GPX) cycle-related enzymes (GPX, GR and glutathione-s-transferase (GST)). Besides, B. subtilis increased the non-enzymatic ROS scavenging system contents, including ascorbate (AsA) and glutathione (GSH) in green peppers. Importantly, the levels of O2−·, H2O2 and malondialdehyde (MDA) in green peppers were reduced, thereby enhancing green pepper disease resistance. This study offers novel insights to advanced strategies in preventing and controlling postharvest soft rot in green peppers.

Understanding mechanisms for differential salinity tissue tolerance between quinoa and spinach: Zooming on ROS-inducible ion channels

Soil salinity is a worldwide issue and a major threat to global food security. Salinity tolerance is a complex mechanism that is conferred by numerous molecular, physiological, and biochemical traits. Of critical importance are plant’s ability to regulate redox balance without compromising reactive oxygen species (ROS) signalling and maintain cytosolic ion homeostasis. In this study, the mechanistic basis of K+ retention ability in leaf mesophyll (an important but highly sensitive plant tissue) was compared between halophytic quinoa and glycophytic spinach. Phenotypic data showed quinoa outperformed spinach under 100 to 500 mmol L−1 NaCl salinity. The major difference behind this differential salinity sensitivity was a differential K+ uptake in leaf mesophyll. Electrophysiological and molecular experiments revealed that a superior ability of mesophyll K+ retention in quinoa was conferred by three complementary mechanisms: (i) an intrinsically lower H+-ATPase activity in quinoa (potentially as an energy saving strategy); (ii) reduced sensitivity of K+ transporters to ROS; and (iii) increased sensitivity of ROS-inducible Ca2+-permeable channels. Moreover, the sensitivity of K+-transport systems to ROS was further examined in NaCl-acclimated quinoa and spinach plants. The key factors differentiating between K+ retention in acclimated leaf mesophyll was associated with the reduced sensitivity and gene expression of K+-permeable outward rectifying channel (GORK), Arabidopsis potassium transporter 1 (AKT1), and high affinity potassium transporter 5 (HAK5) to additional NaCl and ROS stress, along with the upregulation of ROS scavenging system. Taken together, our results showed that the tissue-specific and ROS-specific regulation of K+ retention are important for conferring salinity tolerant at least in the halophyte quinoa.

Distinct toxic effects, gene expression profiles, and phytohormone responses of Polygonatum cyrtonema exposed to two different antibiotics

The excessive usage of veterinary antibiotics has raised significant concerns regarding their environmental hazard and agricultural impact when entering surface water and soil. Animal waste serves as a primary source of organic fertilizer for intensive large-scale agricultural cultivation, including the widely utilized medicinal and edible plant, Polygonatum cyrtonem. In this study, we employed a novel plant stress tissue culture technology to investigate the toxic effects of tetracycline hydrochloride (TCH) and sulfadiazine (SDZ) on P. cyrtonema. TCH and SDZ exhibited varying degrees of influence on plant growth, photosynthesis, and the reactive oxygen species (ROS) scavenging system. Flavonoid levels increased following exposure to TCH and SDZ. The biosynthesis and signaling pathways of the growth hormones auxin and gibberellic acid were suppressed by both antibiotics, while the salicylic acid-mediated plant stress response was specifically induced in the case of SDZ. Overall, the study unveiled both common and unique responses at physiological, biochemical, and molecular levels in P. cyrtonema following exposure to two distinct types of antibiotics, providing a foundational framework for comprehensively elucidating the precise toxic effects of antibiotics and the versatile adaptive mechanisms in plants.

Rejuvenating Aged Bone Repair through Multihierarchy Reactive Oxygen Species-Regulated Hydrogel.

Aging exacerbates the dysfunction of tissue regeneration at multiple levels and gradually diminishes individual's capacity to withstand stress, damage, and disease. The excessive accumulation of reactive oxygen species (ROS) is considered a hallmark feature of senescent stem cells, which causes oxidative stress, deteriorates the host microenvironment, and eventually becomes a critical obstacle for aged bone defect repair. Till now, the strategies cannot synchronously and thoroughly regulate intracellular and extracellular ROS in senescent cells. Herein, a multihierarchy ROS scavenging system for aged bone regeneration is developed by fabricating an injectable PEGylated poly(glycerol sebacate) (PEGS-NH2 )/poly(γ-glutamic acid) (γ-PGA) hydrogel containing rapamycin-loaded poly(diselenide-carbonate) nanomicelles (PSeR). This PSeR hydrogel exhibits highly sensitive ROS responsiveness to the local aged microenvironment and dynamically releases drug-loaded nanomicelles to scavenge the intracellular ROS accumulated in senescent bone mesenchymal stem cells. The PSeR hydrogel effectively tunes the antioxidant function and delays senescence of bone mesenchymal stem cells by safeguarding DNA replication in an oxidative environment, thereby promoting the self-renewal ability and enhancing the osteogenic capacity for aged bone repair in vitro and in vivo. Thus, this multihierarchy ROS-regulated hydrogel provides a new strategy for treating degenerative diseases.

Nanocatalytic theranostics with intracellular mutual promotion for ferroptosis and chemo-photothermal therapy

The reactive oxygen species (ROS) produced through the Fenton reaction, induces lipid peroxide (LPO), causing cellular structural damage and ultimately triggering ferroptosis. However, the generation of ROS in the tumor microenvironment (TME) is limited by the catalytic efficiency of the Fenton reaction. Herein, a novel hollow mesoporous silica nanoparticle (HMSN) combined with multi-metal sulfide-doped mesoporous silica nanocatalyzers (NCs) was developed, namely MxSy-HMSN NCs (M represents Cu Mn and Fe, S denotes sulfur). The MxSy-HMSN can dramatically enhanced the ferroptosis by: (1) facilitating the conversion of H2O2 to ·OH through Fenton or Fenton-like reactions through co-catalysis; (2) weakening ROS scavenging systems by depleting the over expressed glutathione (GSH) in TME; (3) providing exceptional photothermal therapy to augment ferroptosis. The MxSy-HMSN can also act as smart cargos for anticancer drug-doxorubicin (DOX). The release of DOX is responsive to GSH/pH/Near-infrared Light (NIR) irradiation at the tumor lesion, significantly improving therapeutic outcomes while minimizing side effects. Additionally, the MxSy-HMSN has demonstrated excellent magnetic resonance imaging (MRI) potential. This smart MxSy-HMSN offer a synergetic approach combining ferroptosis with chemo-photothermal therapy and magnetic resonance imaging (MRI) diagnose, which could be an informative guideline for the design of future NCs.

COI1 dependent jasmonic acid signalling positively modulates ROS scavenging system in transgenic hairy root culture of tomato

Reactive oxygen species (ROS) production is a routine event in plants. ROS function as signalling molecules in regulating plant development and defence. However, their accumulation beyond threshold leads to toxicity. Hence, plants are evolved with specialized ROS scavenging system involving phytohormones (synthesis and signalling), enzymes and metabolites. To understand the role of phytohormone jasmonic acid (JA) signalling in ROS scavenging, tomato coronatine insensitive 1 (SlCOI1), a key gene in JA signalling, was silenced and overexpressed in tomato transgenic hairy roots (HR) under the constitutive promoter. Targeted metabolomics of transgenic HR revealed accumulation of phenolic acids including ferulic acid, coumaric acid, vanillic acid, and flavonoid catechin in SlCOI1 overexpressed line. Moreover, osmolyte amino acids proline, asparagine, and glutamine showed a positive co-relation with transgenic overexpression of SlCOI1. Ascorbic acid-glutathione, a crucial antioxidant system was found to be influenced by COI1-mediated JA signalling. The expression of genes encoding enzymes superoxide dismutase 1, ascorbate peroxidase 1, and dehydroascorbate reductase 2 was found to be down and upregulated in SlCOI1 silenced and overexpressed lines, respectively. Methyl jasmonate and Fusarium oxysporum f.sp. lycopersici crude extract treatment further confirmed the regulatory role of COI1-mediated JA signalling in regulation of enzymatic components involved in ROS scavenging. The COI1-mediated JA signalling could also elevate the expression of RESPIRATORY BURST OXIDASE HOMOLOG-B gene which is involved in ROS wave signal generation. The present study underscores the role of COI1-mediated JA signalling in modulating enzymatic and non-enzymatic components of ROS scavenging system and pathogen associated molecular pattern triggered immunity.

Transcriptome and photosynthetic analyses provide new insight into the molecular mechanisms underlying heat stress tolerance in Rhododendron × pulchrum Sweet.

Rhododendron species provide excellent ornamental use worldwide, yet heat stress (HS) is one of the major threats to their cultivation. However, the intricate mechanisms underlying the photochemical and transcriptional regulations associated with the heat stress response in Rhododendron remain relatively unexplored. In this study, the analyses of morphological characteristics and chlorophyll fluorescence (ChlF) kinetics showed that HS (40°C/35°C) had a notable impact on both the donor's and acceptor's sides of photosystem II (PSII), resulting in reduced PSII activity and electron transfer capacity. The gradual recovery of plants observed following a 5-day period of culture under normal conditions indicates the reversible nature of the HS impact on Rhododendron × pulchrum. Analysis of transcriptome data unveiled noteworthy trends: four genes associated with photosynthesis-antenna protein synthesis (LHCb1, LHCb2 and LHCb3) and the antioxidant system (glutamate-cysteine ligase) experienced significant down-regulation in the leaves of R. × pulchrum during HS. Conversely, aseorbate peroxidase and glutathione S-transferase TAU 8 demonstrated an up-regulated pattern. Furthermore, six down-regulated genes (phos-phoenolpyruvate carboxylase 4, sedoheptulose-bisphosphatase, ribose-5-phosphate isomerase 2, high cyclic electron flow 1, beta glucosidase 32 and starch synthase 2) and two up-regulated genes (beta glucosidase 2 and UDP-glucose pyrophosphorylase 2) implicated in photosynthetic carbon fixation and starch/sucrose metabolism were identified during the recovery process. To augment these insights, a weighted gene co-expression network analysis yielded a co-expression network, pinpointing the hub genes correlated with ChlF dynamics' variation trends. The cumulative results showed that HS inhibited the synthesis of photosynthesis-antenna proteins in R.×pulchrum leaves. This disruption subsequently led to diminished photochemical activities in both PSII and PSI, albeit with PSI exhibiting heightened thermostability. Depending on the regulation of the reactive oxygen species scavenging system and heat dissipation, photoprotection sustained the recoverability of R. × pulchrum to HS.

MePOD12 participates the regulation to postharvest physiological deterioration by ROS scavenging and lignin accumulation in cassava tuberous roots

Cassava tuberous root, as a staple food crop and industrial raw material worldwide, is highly sensitive to postharvest physiological deterioration (PPD) caused by wound. However, the molecular mechanism underlying PPD tolerance remains elusive in cassava. The reactive oxygen species (ROS) scavenging system is activated at the preliminary stage of PPD and peroxidase (POD) can effectively eliminate ROS. The expression level of MePOD12 and POD enzymatic activity in cassava tuberous roots was considerably up-regulated with PPD occurrence. Yeast two-hybrid and luciferase reporter assay showed that MePOD12 physically interacted with lignin-related cinnamyl alcohol dehydrogenase 15 (MeCAD15) in vitro and in vivo. The MePOD12-silenced tuberous roots decayed more than control, especially stored at room temperature for 3 and 5 days after harvesting. The total antioxidant capacity, activities of POD, SOD, CAT, CAD and lignin content were lower than those of control. Particularly, after harvest for 3 days, the accumulation of hydrogen peroxide and superoxide anion substantially increased compared to control. In addition, a proposed model was generated to elaborate the response mechanism of MePOD12 participating in PPD regulation via ROS elimination and lignin accumulation. It provides a new clue for breeding cassava PPD-tolerant varieties.

An ABA-inducible gene IbTSJT1 positively regulates drought tolerance in transgenic sweetpotato

The TSJT1 protein belongs to the superfamily of class-II glutamine amidotransferases (GATase). There is little research on the functions and underlying mechanisms of TSJT1 in plants. In this study, an abscisic acid (ABA)-inducible gene IbTSJT1 was isolated from drought-tolerant sweetpotato line ‘Xushu55-2’. Its expression was strongly induced by PEG6000 and ABA. The IbTSJT1 protein was localized in the nucleus and cell membrane. The IbTSJT1-overexpressing sweetpotato plants exhibited significantly enhanced drought tolerance. Their ABA and proline contents and superoxide dismutase (SOD) and peroxidase (POD) activities were increased and reactive oxygen species (ROS) scavenging-related genes were upregulated under drought stress. The stomatal aperture assay confirmed that the IbTSJT1-overexpressing plants increased the sensitivity to ABA. Yeast one-hybrid (Y1H) assay, electrophoretic mobility shift assay (EMSA), luciferase reporter assay and ChIP-qPCR assay indicated that IbABF2 could directly bind to the cis-acting ABA-responsive element (ABRE) in the IbTSJT1 promoter to activate the expression of IbTSJT1. These findings suggest that IbTSJT1 mediates ABA-dependent drought stress responses and enhances drought tolerance by inducing stomatal closure and activating ROS scavenging system in transgenic sweetpotato. Our study provides a novel gene for improving drought tolerance of sweetpotato and other plants.

PtAPX9-PtLTPG14 modulates the AsA-GSH cycle for lipid mechanisms in poplar

Ascorbate peroxidase (APX) is an essential antioxidant enzyme participating in cellular homeostasis by scavenging reactive oxygen species (ROS). Nevertheless, few reports were involved in the roles of poplar APX in lipid mechanism, especially in lipid peroxidation. This study identified 11 PtAPX genes from the poplar genome, and PtAPXs were clustered into five clades. The exon/intron distribution and conserved motif analysis showed that PtAPXs exhibit a comparatively well-preserved gene structure and motif composition in the same Clade. Collinearity investigation indicated segmental duplication is considered the main duplication form during the evolutionary process of PtAPX genes. Also, the superoxide dismutase (SOD), monodehydroascorbate reductase (MDHAR), and glutathione-disulfide reductase (GSR) involved in the redox metabolism were discovered from the interaction network with PtAPXs. In addition, a series of transcription factors (TFs), such as MYB, bHLH, WRKY, and NAC, were identified from the TF network with PtAPX genes. Gene expression patterns revealed that PtAPXs have different expression levels in various tissues and organs and are significantly affected by various abiotic stresses, including ABA, NaCl, and H2O2. The luciferase (LUC) complementation assay gave new visions into the PtAPX9-PtLTPG14 complex participating in lipid metabolism, especially in lipid peroxidation, thus maintaining cellular homeostasis. These discoveries provided a novel perspective for further functional study on the roles of PtAPX9 in lipid metabolism and ROS scavenging system.

Transcription Factor GmERF105 Negatively Regulates Salt Stress Tolerance in Arabidopsis thaliana.

The Ethylene Response Factor (ERF) transcription factors form a subfamily of the AP2/ERF family that is instrumental in mediating plant responses to diverse abiotic stressors. Herein, we present the isolation and characterization of the GmERF105 gene from Williams 82 (W82), which is rapidly induced by salt, drought, and abscisic acid (ABA) treatments in soybean. The GmERF105 protein contains an AP2 domain and localizes to the nucleus. GmERF105 was selectively bound to GCC-box by gel migration experiments. Under salt stress, overexpression of GmERF105 in Arabidopsis significantly reduced seed germination rate, fresh weight, and antioxidant enzyme activity; meanwhile, sodium ion content, malonic dialdehyde (MDA) content, and reactive oxygen species (ROS) levels were markedly elevated compared to the wild type. It was further found that the transcription levels of CSD1 and CDS2 of two SOD genes were reduced in OE lines. Furthermore, the GmERF105 transgenic plants displayed suppressed expression of stress response marker genes, including KIN1, LEA14, NCED3, RD29A, and COR15A/B, under salt treatment. Our findings suggest that GmERF105 can act as a negative regulator in plant salt tolerance pathways by affecting ROS scavenging systems and the transcription of stress response marker genes.

Effects of ROS pathway inhibitors and NADH and FADH2 linked substrates on mitochondrial bioenergetics and ROS emission in the heart and kidney cortex and outer medulla

Mitochondria are major sources of reactive oxygen species (ROS), which play important roles in both physiological and pathological processes. However, the specific contributions of different ROS production and scavenging components in the mitochondria of metabolically active tissues such as heart and kidney cortex and outer medulla (OM) are not well understood. Therefore, the goal of this study was to determine contributions of different ROS production and scavenging components and provide detailed comparisons of mitochondrial respiration, bioenergetics, ROS emission between the heart and kidney cortex and OM using tissues obtained from the same Sprague-Dawley rat under identical conditions and perturbations. Specifically, data were obtained using both NADH-linked substrate pyruvate + malate and FADH2-linked substrate succinate followed by additions of inhibitors of different components of the electron transport chain (ETC) and oxidative phosphorylation (OxPhos) and other ROS production and scavenging systems. Currently, there is limited data available for the mitochondria of kidney cortex and OM, the two major energy-consuming tissues in the body only next to the heart, and scarce quantitative information on the interplay between mitochondrial ROS production and scavenging systems in the three tissues. The findings from this study demonstrate significant differences in mitochondrial respiratory and bioenergetic functions and ROS emission among the three tissues. The results quantify the rates of ROS production from different complexes of the ETC, identify the complexes responsible for variations in mitochondrial membrane depolarization and regulations of ROS production, and quantify the contributions of ROS scavenging enzymes towards overall mitochondrial ROS emission. These findings advance our fundamental knowledge of tissue-specific and substrate-dependent mitochondrial respiratory and bioenergetic functions and ROS emission. This is important given the critical role that excess ROS production, oxidative stress, and mitochondrial dysfunction in the heart and kidney cortex and OM play in the pathogenesis of cardiovascular and renal diseases, including salt-sensitive hypertension.

The Sweet Potato K+ Transporter IbHAK11 Regulates K+ Deficiency and High Salinity Stress Tolerance by Maintaining Positive Ion Homeostasis.

The K+ transporter KT/HAK/KUP (K+ transporter/high-affinity K+/K+ uptake) family has a critical effect on K+ uptake and translocation in plants under different environmental conditions. However, the functional analysis of KT/HAK/KUP members in sweet potatoes is still limited. The present work reported the physiological activity of a new gene, IbHAK11, in the KT/HAK/KUP family in sweet potatoes. IbHAK11 expression increased significantly in the low K+-tolerant line compared with the low K+-sensitive line following treatment with low K+ concentrations. IbHAK11 upregulation promoted root growth in Arabidopsis under low K+ conditions. Under high saline stress, transgenic lines had superior growth and photosynthetic characteristics compared with the wild-type (WT). As for IbHAK11-overexpressing plants, activation of both the non-enzymatic and enzymatic reactive oxygen species (ROS) scavenging systems was observed. Therefore, IbHAK11-overexpressing plants had lower malondialdehyde (MDA) and ROS levels (including H2O2 and O2-) compared with WT under salt-induced stress. We also found that under both low K+ and high salinity conditions, overexpression of IbHAK11 enhanced K+ translocation from the root to the shoot and decreased Na+ absorption in Arabidopsis. Consequently, IbHAK11 positively regulated K+ deficiency and high salinity stresses by regulating K+ translocation and Na+ uptake, thus maintaining K+/Na+ homeostasis in plants.

Selenium enhances ROS scavenging systems and sugar metabolism increasing growth of sugarcane plants

Selenium (Se) beneficial effect on plants is related to an increase in nitrogen (N) assimilation and its role as an abiotic stress mitigator by reactive oxygen species (ROS) scavenging enhanced by antioxidant metabolism. This study aimed to evaluate sugarcane (Saccharum spp.) growth, photosynthetic and antioxidant responses, and sugar accumulation in response to Se supply. The experimental design was a factorial scheme 2 × 4: two sugarcane varieties (RB96 6928 and RB86 7515) and four Se application rates (0; 5; 10 and 20 μmol L−1) applied as sodium selenate in the nutrient solution. Leaf Se concentration increased under Se application in both varieties. The enzymes SOD (EC 1.15.1.1) and APX (EC 1.11.1.11) showed increase activities under Se application on variety RB96 6928. Nitrate reductase activity increased in both varieties resulting in the conversion of nitrate into higher total amino acids concentration indicating an enhanced N assimilation. This led to an increased concentration of chlorophylls and carotenoids, increased CO2 assimilation rate, stomatal conductance, and internal CO2 concentration. Selenium provided higher starch accumulation and sugar profiles in leaves boosting plant growth. This study shows valuable information regarding the role of Se on growth, photosynthetic process, and sugar accumulation in sugarcane leaves, which could be used for further field experiments. The application rate of 10 μmol Se L−1 was the most adequate for both varieties studied considering the sugar concentration and plant growth.

Ascorbate peroxidase plays an important role in photoacclimation in the extremophilic red alga Cyanidiococcus yangmingshanensis.

Acidothermophilic cyanidiophytes in natural habitats can survive under a wide variety of light regimes, and the exploration and elucidation of their long-term photoacclimation mechanisms promises great potential for further biotechnological applications. Ascorbic acid was previously identified as an important protectant against high light stress in Galdieria partita under mixotrophic conditions, yet whether ascorbic acid and its related enzymatic reactive oxygen species (ROS) scavenging system was crucial in photoacclimation for photoautotrophic cyanidiophytes was unclear. The significance of ascorbic acid and related ROS scavenging and antioxidant regenerating enzymes in photoacclimation in the extremophilic red alga Cyanidiococcus yangmingshanensis was investigated by measuring the cellular content of ascorbic acid and the activities of ascorbate-related enzymes. Accumulation of ascorbic acid and activation of the ascorbate-related enzymatic ROS scavenging system characterized the photoacclimation response after cells were transferred from a low light condition at 20 μmol photons m-2 s-1 to various light conditions in the range from 0 to 1000 μmol photons m-2 s-1. The activity of ascorbate peroxidase (APX) was most remarkably enhanced with increasing light intensities and illumination periods among the enzymatic activities being measured. Light-dependent regulation of the APX activity was associated with transcriptional regulation of the chloroplast-targeted APX gene. The important role of the APX activity in photoacclimation was evidenced by the effect of the APX inhibitors on the photosystem II activity and the chlorophyll a content under the high light condition at 1000 μmol photons m-2 s-1. Our findings provide a mechanistic explanation for the acclimation of C. yangmingshanensis to a wide range of light regimes in natural habitats.

Differences in Physiological Responses of Two Tomato Genotypes to Combined Waterlogging and Cadmium Stresses.

Waterlogging and heavy mental (e.g., cadmium) stress are two primary threats to crop growth. The combination of abiotic stresses was common and frequent, especially in the field condition. Even though the effects of individual waterlogging and cadmium on tomato plants have been widely investigated, the response of tomatoes under combined waterlogging and cadmium stress remains unclear. This study aimed to clarify and compare physiological, biochemical characteristics and plant growth of two tomato genotypes under individual and combined stress. Two tomato genotypes ('MIX-002' and 'LA4440') were treated under control, waterlogging, cadmium stress and their combination. The results showed that chloroplast ultrastructure of tomatoes under individual and combined stress was damaged with disordered stroma and grana lamellae. The H2O2 (hydrogen peroxide) content and O2·- (superoxide anion radical) production rate of plants under all the three stresses was not significantly higher than the control except for 'LA4440' under the combined stress. Antioxidant enzymes actively responded in the two tomato genotypes, as shown by significant increase in SOD activity from 'MIX-002' under waterlogging and combined stress and from 'LA4440' under cadmium. Meanwhile, CAT activity of 'MIX-002' under waterlogging and 'LA4440' under combined stress significantly decreased, and the POD activity of 'MIX-002' under combined stress significantly increased as compared with the respective control. The APX activity of 'MIX-002' and 'LA4440' under combined stress was significantly lower and higher than the respective controls. This indicated that tomato plants were able to secure redox homeostasis and protect plants from oxidative damage through the synergetic regulation of antioxidant enzymes. Plant height and biomass of the two genotypes under individual and combined stress significantly decreased, which could be a direct result from the chloroplast alteration and resource re-allocation. Overall, the effects of combined waterlogging and cadmium stress were not simply the sum of individual effects on two tomato genotypes. Distinct ROS (reactive oxygen species) scavenging systems of two tomato genotypes under stresses suggest a genotype-dependent antioxidant enzymes regulation.

Calcium-dependent protein kinase GhCDPK4 plays a role in drought and abscisic acid stress responses

Drought is an important factor limiting the yield and quality of cotton. In the present study, the gene encoding the cotton calcium-dependent protein kinase GhCDPK4 was identified and characterized in the transcriptome of cotton under PEG-induced drought stress. In RT-qPCR experiments, GhCDPK4 expression was found to be up-regulated under drought and abscisic acid (ABA) stress. Under drought conditions, heterologous overexpression of GhCDPK4 in tobacco showed a better phenotypic status, higher antioxidant enzyme activity, and lower relative electrolyte leakage (REL) and malondialdehyde (MDA) content. Meanwhile, ghcdpk4-silenced cotton plants, which were extremely sensitive to drought, exhibited higher levels of O2-，H2O2, and MDA contents compared to the control. Meanwhile, silenced lines showed impaired stomatal closure under drought stress, resulting in increased water loss from transpiration in silenced lines. GhCDPK4 expression was induced by ABA, and there are five ABA-responsive elements in its promoter. and C2-DOMAIN ABA-RELATED 4(CAR4, Gh_D09G1653) were found to interact and be co-expressed in the GhCDPK4 interaction network. Therefore, GhCDPK4 may reduce the extent of water loss and oxidative damage in cotton under drought by positively regulating ABA-controlled stomatal closure and reactive oxygen species (ROS) scavenging systems. This study demonstrates the great potential of GhCDPK4 in improving drought resistance in crops.