NADPH Oxidase (Rboh) Activity is Up Regulated during Sweet Pepper (Capsicum annuum L.) Fruit Ripening

Polyphenol Mediated Suppression of Hepatocellular Carcinoma (HepG2) Cell Proliferation by Clerodendrum infortunatum L. Root

OBJECTIVE

Clerodendrum infortunatum L. has long been used in traditional medicine in Sri Lanka for tumours, cancer, and certain skin diseases. The present study aimed to assess the anticancer properties of the aqueous extract of C. infortunatum L. root (AECIR) through the activation of the apoptotic pathway on hepatocellular carcinoma (HepG2) and thus give it a scientific validation. Further, the contribution of polyphenols in antioxidant activity and cell cytotoxicity was investigated.

METHODS

Powdered plant material was boiled with water (100°C) to obtained AECIR.  The DPPH assay was used to determine the antioxidant potential. The activity of AECIR on HepG2 and normal rat fibroblast (CC1) cell growth was determined using MTT assay. The morphological changes related to apoptotic pathway was examined by Ethidium Bromide/Acridine Orange (EB/AO), Rhodamine 123 (Rh123) and DNA fragmentation assay.

RESULTS

The AECIR demonstrated antioxidant potential with an EC50 of 350.2 ± 1.5 ug/mL for DPPH assay. The HO•, H2O2 and •NO free radical scavenging activity was observed with EC50 of 19.7 ± 2.3, 11.7 ± 0.1 and 273.1 ± 0.9 ug/mL, respectively. The antiproliferative effect of AECIR on HepG2 cells was observed in a time and dose dependent manner with an EC50 of 239.1 ± 1.3 μg/mL while CC1 cells showed a nontoxic effect with an EC50 1062.7 ± 3.4 μg/mL after 24hrs treatment. A significant decrease in antioxidant activity (p<0.001) and 90% HepG2 cell viability was observed with polyphenol removed AECIR compared to the polyphenol present AECIR. The EB/AO uptake, depletion of mitochondrial transmembrane potential, and DNA fragmentation assay results revealed that the apoptosis was induced by AECIR.

CONCLUSION

The obtained result of the present study demonstrates that the antioxidant potential and antiproliferative activity of AECIR is attributed to the presence of polyphenols. Furthermore, the findings provide the scientific base for anti-cancer potential of AECIR.

Toxic effects of lead on plants: integrating multi-omics with bioinformatics to develop Pb-tolerant crops

MAIN CONCLUSION

Lead disrupts plant metabolic homeostasis and key structural elements. Utilizing modern biotechnology tools, it's feasible to develop Pb-tolerant varieties by discovering biological players regulating plant metabolic pathways under stress. Lead (Pb) has been used for a variety of purposes since antiquity despite its toxic nature. After arsenic, lead is the most hazardous heavy metal without any known beneficial role in the biological system. It is a crucial inorganic pollutant that affects plant biochemical and morpho-physiological attributes. Lead toxicity harms plants throughout their life cycle and the extent of damage depends on the concentration and duration of exposure. Higher levels of lead exposure disrupt numerous key metabolic activities of plants including oxygen-evolving complex, organelles integrity, photosystem II connectivity, and electron transport chain. This review summarizes the detrimental effects of lead toxicity on seed germination, crop growth, and yield, oxidative and ultra-structural alterations, as well as nutrient absorption, transport, and assimilation. Further, it discusses the Pb-induced toxic modulation of stomatal conductance, photosynthesis, respiration, metabolic-enzymatic activity, osmolytes accumulation, and antioxidant activity. It is a comprehensive review that reports on omics-based studies along with morpho-physiological and biochemical modifications caused by lead stress. With advances in DNA sequencing technologies, genomics and transcriptomics are gradually becoming popular for studying Pb stress effects in plants. Proteomics and metabolomics are still underrated and there is a scarcity of published data, and this review highlights both their technical and research gaps. Besides, there is also a discussion on how the integration of omics with bioinformatics and the use of the latest biotechnological tools can aid in developing Pb-tolerant crops. The review concludes with core challenges and research directions that need to be addressed soon.

Harmonized biochemical modification of cell walls to get permission for entrance of Azospirillum sp. to rice roots

Biological nitrogen-fixation is important in increasing crop efficiency. Azospirillum is a nitrogen-fixing microorganism that naturally coexists with grasses roots. The present study was undertaken to clarify the role of rice root cell walls in the acceptance of two Azospirillum species, alone or in combination with indole-3-acetic acid (IAA) and gibberellic acid (GA3) treatments. Rice seedlings were grown in Yoshida solution for 21 days and then inoculated with A. brasilense and A. irakens in the presence of 0, 0.57, and 1.14 mM of IAA or 0, 0.29, and 0.58 mM GA3 or a combination of 1.14 mM of IAA and 0.58 mM of GA3. The results showed that the amount of hydrogen peroxide, lipid peroxidation, total nitrogen and activity of ferulic acid peroxidase, NADPH oxidase, nitrate reductase, pectin methyl esterase, cellulase, mannanase, xylanase and pectinase were significantly increased in inoculated samples treated with or without phytohormones. The highest activity of these enzymes was observed in A. brasilense- inoculated rice roots in auxin+gibberellin treatment. In the latter, the activity of phenylalanine ammonia lyase and wall ferulic acid peroxidase enzymes, the content of cell wall polysaccharide, lignin, and total phenolic compounds were the least, compared to controls and also with those samples which were inoculated with A. irakens. The results indicate an active role of the wall and its enzymes in allowing bacteria to enter the roots. Understanding this mechanism can improve the methods of inoculating bacteria into plants and increase crop efficiency, which will result in reduced use of chemical fertilizers and their destructive environmental effects.

H2S-Generating Cytosolic L-Cysteine Desulfhydrase and Mitochondrial D-Cysteine Desulfhydrase from Sweet Pepper (Capsicum annuum L.) Are Regulated During Fruit Ripening and by Nitric Oxide

Aims: Pepper fruit is a horticultural product worldwide consumed that has great nutritional and economic relevance. Besides the phenotypical changes that undergo pepper fruit during ripening, there are many associated modifications at transcriptomic, proteomic, biochemical, and metabolic levels. Nitric oxide (NO) and hydrogen sulfide (H2S) are recognized signal molecules that can exert regulatory functions in diverse plant processes. This study aims at analyzing the interrelationship between NO and H2S during fruit ripening. Results: Our data indicate that the H2S-generating cytosolic L-cysteine desulfhydrase (LCD) and the mitochondrial D-cysteine desulfhydrase (DCD) activities are downregulated during ripening but this effect was reverted after NO treatment of fruits. Innovation and Conclusion: Using as a model the non-climacteric pepper fruits at different ripening stages and under an NO-enriched atmosphere, the activity of the H2S-generating LCD and DCD was analyzed. LCD and DCD activities were downregulated during ripening, but this effect was reverted after NO treatment of fruits. The analysis of LCD activity by non-denaturing polyacrylamide gel electrophoresis (PAGE) allowed identifying three isozymes designated CaLCD I to CaLCD III, which were differentially modulated by NO and strictly dependent on pyridoxal 5'-phosphate (PLP). In vitro analyses of green fruit samples in the presence of different compounds including NO donors, peroxynitrite (ONOO-), and reducing agents such as reduced glutathione (GSH) and L-cysteine (L-Cys) triggered an almost 100% inhibition of CaLCD II and CaLCD III. This redox adaptation process of both enzymes could be cataloged as a hormesis phenomenon. The protein tyrosine (Tyr) nitration (an NO-promoted post-translational modification) of the recombinant LCD was corroborated by immunoblot and by mass spectrometry (MS) analyses. Among the 11 Tyr residues present in this enzyme, MS of the recombinant LCD enabled us to identify that Tyr82 and Tyr254 were nitrated by ONOO-, this occurring near the active center on the enzyme, where His237 and Lys260 together with the cofactor PLP are involved. These data support the relationship between NO and H2S during pepper fruit ripening, since LCD and DCD are regulated by NO during this physiological event, and this could also be extrapolated to other plant species.

Thallium-mediated NO signaling induced lipid accumulation in microalgae and its role in heavy metal bioremediation

Thallium (Tl⁺) is a trace metal with extreme toxicity and is highly soluble in water, posing a great risk to ecological and human safety. This work aimed to investigate the role played by Tl⁺ in regulating lipid accumulation in microalgae and the removal efficiency of Tl⁺. The effect of Tl⁺ on the cell growth, lipid production and Tl⁺ removal efficiency of Parachlorella kessleri R-3 was studied. Low concentrations of Tl⁺ had no significant effect on the biomass of microalgae. When the Tl⁺ concentration exceeded 5 μg L^-1, the biomass of microalgae showed significant decrease. The highest lipid content of 63.65% and lipid productivity of 334.55 mg L^-1 d^-1 were obtained in microalgae treated with 10 and 5 μg L^-1 Tl⁺, respectively. Microalgae can efficiently remove Tl⁺ and the Tl⁺ removal efficiency can reach 100% at Tl⁺ concentrations of 0-25 μg L^-1. The maximum nitric oxide (NO) level of 470.48 fluorescence intensity (1 × 10⁶ cells)^-1 and glutathione (GSH) content of 343.51 nmol g^-1 (fresh alga) were obtained under 5 μg L^-1 Tl⁺ stress conditions. Furthermore, the exogenous donor sodium nitroprusside (SNP) supplemented with NO was induced in microalgae to obtain a high lipid content (59.99%), lipid productivity (397.99 mg L^-1 d^-1) and GSH content (430.22 nmol g^-1 (fresh alga)). The corresponding analysis results indicated that NO could participate in the signal transduction pathway through modulation of reactive oxygen species (ROS) signaling to activate the antioxidant system by increasing the GSH content to eliminate oxidative damage induced by Tl⁺ stress. In addition, NO regulation of ROS signaling may enhance transcription factors associated with lipid synthesis, which stimulates the expression of genes related to lipid synthesis, leading to increased lipid biosynthesis in microalgae. Moreover, it was found that the change in Tl⁺ had little effect on the fatty acid components and biodiesel properties. This study showed that Tl⁺ stress can promote lipid accumulation in microalgae for biodiesel production and simultaneously effectively remove Tl⁺, which provided evidence that NO was involved in signal transduction and antioxidant defense, and improved the understanding of the interrelation between NO and ROS to regulate lipid accumulation in microalgae.

Class III Peroxidases (POD) in Pepper (Capsicum annuum L.): Genome-Wide Identification and Regulation during Nitric Oxide (NO)-Influenced Fruit Ripening

The class III peroxidases (PODs) catalyze the oxidation of several substrates coupled to the reduction of H₂O₂ to water, and play important roles in diverse plant processes. The POD family members have been well-studied in several plant species, but little information is available on sweet pepper fruit physiology. Based on the existing pepper genome, a total of 75 CaPOD genes have been identified, but only 10 genes were found in the fruit transcriptome (RNA-Seq). The time-course expression analysis of these genes showed that two were upregulated during fruit ripening, seven were downregulated, and one gene was unaffected. Furthermore, nitric oxide (NO) treatment triggered the upregulation of two CaPOD genes whereas the others were unaffected. Non-denaturing PAGE and in-gel activity staining allowed identifying four CaPOD isozymes (CaPOD I-CaPOD IV) which were differentially modulated during ripening and by NO. In vitro analyses of green fruit samples with peroxynitrite, NO donors, and reducing agents triggered about 100% inhibition of CaPOD IV. These data support the modulation of POD at gene and activity levels, which is in agreement with the nitro-oxidative metabolism of pepper fruit during ripening, and suggest that POD IV is a target for nitration and reducing events that lead to its inhibition.

The captivating role of calcium in plant-microbe interaction

Plant immune response is fascinating due to the complete absence of a humoral system. The adaptive immune response in plants relies on the intracellular orchestration of signalling molecules or intermediates associated with transcriptional reprogramming. Plant disease response phenomena largely depend on pathogen recognition, signal perception, and intracellular signal transduction. The pathogens possess specific pathogen-associated molecular patterns (PAMP) or microbe-associated molecular patterns (MAMP), which are first identified by pattern recognition receptors (PRRs) of host plants for successful infection. After successful pathogen recognition, the defence response is initiated within plants. The first line of non-specific defence response is called PAMP-triggered immunity (PTI), followed by the specific robust signalling is called effector-triggered immunity (ETI). Calcium plays a crucial role in both PTI and ETI. The biphasic induction of reactive oxygen species (ROS) is inevitable in any plant-microbe interaction. Calcium ions play crucial roles in the initial oxidative burst and ROS induction. Different pathogens can induce calcium accumulation in the cytosol ([Ca²⁺]_Cyt), called calcium signatures. These calcium signatures further control the diverse defence-responsive proteins in the intracellular milieu. These calcium signatures then activate calcium-dependent protein kinases (CDPKs), calcium calmodulins (CaMs), calcineurin B-like proteins (CBLs), etc., to impart intricate defence signalling within the cell. Decoding this calcium ionic map is imperative to unveil any plant microbe interplay and modulate defence-responsive pathways. Hence, the present review is unique in developing concepts of calcium signature in plants and their subsequent decoding mechanism. This review also intends to articulate early sensing of calcium oscillation, signalling events, and comprehensive mechanistic roles of calcium within plants during pathogenic ingression. This will accumulate and summarize the exciting roles of calcium ions in plant immunity and provide the foundation for future research.

Insights into the Mechanism of Flavor Loss in Strawberries Induced by Two Fungicides Integrating Transcriptome and Metabolome Analysis

Consumers have been complaining about the deterioration of the flavor of strawberries. The use of pesticides could have potential impacts on fruit flavor but the mechanisms are unclear. Here, we spayed boscalid and difenoconazole on the small green fruit of strawberries to investigate their effect on fruit flavor quality and the mechanism. The results indicated that both fungicides decreased the contents of soluble sugar and nutrients but increased acids in mature fruits, changed the levels of volatiles, and caused oxidative damage, which ultimately reduced the flavor quality of strawberries, and the negative effect of boscalid was greater. Combined with transcriptome and metabolome, boscalid altered the genes in sugar-acid metabolism (SUT, SPS, and INV), volatiles (FaQR, FaOMT, FaLOX, and FaAAT), and amino acid synthesis pathways and metabolites. This study elaborated on the effects of fungicides on the flavor quality of strawberries from physiological-biochemical and molecular levels and laid the foundation for improving the strawberry flavor quality.

Small Heat Shock Protein (sHSP) Gene Family from Sweet Pepper (Capsicum annuum L.) Fruits: Involvement in Ripening and Modulation by Nitric Oxide (NO)

Small heat shock proteins (sHSPs) are usually upregulated in plants under diverse environmental stresses. These proteins have been suggested to function as molecular chaperones to safeguard other proteins from stress-induced damage. The ripening of pepper (Capsicum annuum L.) fruit involves important phenotypic, physiological, and biochemical changes, which have associated endogenous physiological nitro-oxidative stress, but they can also be significantly affected by environmental conditions, such as temperature. Based on the available pepper genome, a total of 41 sHSP genes were identified in this work, and their distributions in the 12 pepper chromosomes were determined. Among these genes, only 19 sHSP genes were found in the transcriptome (RNA-Seq) of sweet pepper fruits reported previously. This study aims to analyze how these 19 sHSP genes present in the transcriptome of sweet pepper fruits are modulated during ripening and after treatment of fruits with nitric oxide (NO) gas. The time-course expression analysis of these genes during fruit ripening showed that 6 genes were upregulated; another 7 genes were downregulated, whereas 6 genes were not significantly affected. Furthermore, NO treatment triggered the upregulation of 7 sHSP genes and the downregulation of 3 sHSP genes, whereas 9 genes were unchanged. These data indicate the diversification of sHSP genes in pepper plants and, considering that sHSPs are important in stress tolerance, the observed changes in sHSP expression support that pepper fruit ripening has an associated process of physiological nitro-oxidative stress, such as it was previously proposed.

Analysis of Plant L-Cysteine Desulfhydrase (LCD) Isozymes by Non-denaturing Polyacrylamide Gel Electrophoresis

Hydrogen sulfide (H₂S) is a signaling molecule that achieves different regulatory functions in animal and plant cells. The cytosolic enzyme L-cysteine desulfhydrase (LCD; EC 4.4.1.28) catalyzes the conversion of cysteine (L-Cys) to pyruvate and ammonium with the concomitant generation of H₂S, this enzyme being considered one of the main sources of H₂S in higher plants. Using non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with a specific assay for LCD activity, the present protocol allows identifying diverse LCD isozymes present in different organs (roots, shoots, leaves, and fruits) and plant species including pea, garlic, Arabidopsis, and pepper.

Hormetic activation of nano-sized rare earth element terbium on growth, PSII photochemistry, antioxidant status and phytohormone regulation in Lemnaminor

Soils contaminated with rare earth elements (REEs) can damage agriculture by causing physiological disorders in plants which are evaluated as the main connection of the human food chain. A biphasic dose response with excitatory responses to low concentrations and inhibitory/harmful responses to high concentrations has been defined as hormesis. However, not much is clear about the ecological effects and potential risks of REEs to plants. For this purpose, here we showed the impacts of different concentrations of nano terbium (Tb) applications (5-10-25-50-100-250-500 mg L^-1) on the accumulation of endogeneous certain ions and hormones, chlorophyll fluoresence, photochemical reaction capacity and antioxidant activity in duckweed (Lemna minor). Tb concentrations less than 100 mg L^-1 increased the contents of nitrogen (N), phosphate (P), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), manganese (Mn²⁺) and iron (Fe²⁺). Chlorophyll fluorescence (F_v/F_m and F_v/F_o) was suppressed under 250-500 mg L^-1 Tb. In addition, Tb toxicity affected the trapped energy adversely by the active reaction center of photosystem II (PSII) and led to accumulation of inactive reaction centers, thus lowering the detected level of electron transport from photosystem II (PSII) to photosystem I (PSI). On the other hand, 5-100 mg L^-1 Tb enhanced the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), NADPH oxidase (NOX), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione S-transferase (GST). Tb (5-50 mg L^-1) supported the maintenance of cellular redox status by promoting antioxidant pathways involved in the ascorbate-glutathione (AsA-GSH) cycle. In addition to the antioxidant system, the contents of some hormones such as indole-3-acetic acid (IAA), gibberellic acid (GA), cytokinin (CK) and salicylic acid (SA) were also induced in the presence of 5-100 mg L^-1 Tb. In addition, the levels of hydrogen peroxide (H₂O₂) and lipid peroxidation (TBARS) were controlled through ascorbate (AsA) regeneration and effective hormonal modulation in L. minor. However, this induction in the antioxidant system and phytohormone contents could not be resumed after applications higher than 250 mg L^-1 Tb. TBARS and H₂O₂, which indicate the level of lipid peroxidation, increased. The results in this study showed that Tb at appropriate concentrations has great potential to confer tolerance of duckweed by supporting the antioxidant system, protecting the biochemical reactions of photosystems and improving hormonal regulation.

Rare earth element scandium mitigates the chromium toxicity in Lemna minor by regulating photosynthetic performance, hormonal balance and antioxidant machinery

Chromium (Cr) toxicity is a serious problem that threatens the health of living organisms and especially agricultural production. The presence of excess Cr leads to biomass loss by causing the imbalance of biochemical metabolism and inhibiting photosynthetic activity. A new critical approach to cope with Cr toxicity is the use of the rare earth elements (REEs) as an antioxidant defence system enhancer in plants. However, the effect of scandium (Sc), which is one of the REEs, is not clear enough in Lemna minor exposed to Cr toxicity. For this purpose, the photosynthetic and biochemical effects of scandium (50 μM and 200 μM Sc) treatments were investigated in Lemna minor under Cr stress (100 μM, 200 μM and 500 μM Cr). Parameters related to photosynthesis (F_v/F_m, F_v/F_o) were suppressed under Cr stress. Stress altered antioxidant enzymes activities and hormone contents. Sc applications against stress increased the activities of superoxide dismutase (SOD), NADPH oxidase (NOX), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and glutathione S-transferase (GST). In addition to the antioxidant system, the contents of indole-3-acetic acid (IAA), abscisic acid (ABA) and jasmonic acid (JA) were also rearranged. However, in all treatment groups, with the provision of ascorbate (AsA) regeneration and effective hormone signaling, reactive oxygen species (ROS) retention which result in high hydrogen peroxide (H₂O₂) content and lipid peroxidation (TBARS) were effectively removed. Sc promoted the maintenance of cellular redox state by regulating antioxidant pathways included in the AsA-GSH cycle. Our results showed that Sc has great potential to confer tolerance to duckweed by reducing Cr induced oxidative damage, protecting the biochemical reactions of photosynthesis, and improving hormone signaling.

Lipoxygenase (LOX) in Sweet and Hot Pepper (Capsicum annuum L.) Fruits during Ripening and under an Enriched Nitric Oxide (NO) Gas Atmosphere

Lipoxygenases (LOXs) catalyze the insertion of molecular oxygen into polyunsaturated fatty acids (PUFA) such as linoleic and linolenic acids, being the first step in the biosynthesis of a large group of biologically active fatty acid (FA)-derived metabolites collectively named oxylipins. LOXs are involved in multiple functions such as the biosynthesis of jasmonic acid (JA) and volatile molecules related to the aroma and flavor production of plant tissues, among others. Using sweet pepper (Capsicum annuum L.) plants as a model, LOX activity was assayed by non-denaturing polyacrylamide gel electrophoresis (PAGE) and specific in-gel activity staining. Thus, we identified a total of seven LOX isozymes (I to VII) distributed among the main plant organs (roots, stems, leaves, and fruits). Furthermore, we studied the FA profile and the LOX isozyme pattern in pepper fruits including a sweet variety (Melchor) and three autochthonous Spanish varieties that have different pungency levels (Piquillo, Padrón, and Alegría riojana). It was observed that the number of LOX isozymes increased as the capsaicin content increased in the fruits. On the other hand, a total of eight CaLOX genes were identified in sweet pepper fruits, and their expression was differentially regulated during ripening and by the treatment with nitric oxide (NO) gas. Finally, a deeper analysis of the LOX IV isoenzyme activity in the presence of nitrosocysteine (CysNO, a NO donor) suggests a regulatory mechanism via S-nitrosation. In summary, our data indicate that the different LOX isozymes are differentially regulated by the capsaicin content, fruit ripening, and NO.

Review of the Mechanisms by Which Transcription Factors and Exogenous Substances Regulate ROS Metabolism under Abiotic Stress

Reactive oxygen species (ROS) are signaling molecules that regulate many biological processes in plants. However, excess ROS induced by biotic and abiotic stresses can destroy biological macromolecules and cause oxidative damage to plants. As the global environment continues to deteriorate, plants inevitably experience abiotic stress. Therefore, in-depth exploration of ROS metabolism and an improved understanding of its regulatory mechanisms are of great importance for regulating cultivated plant growth and developing cultivars that are resilient to abiotic stresses. This review presents current research on the generation and scavenging of ROS in plants and summarizes recent progress in elucidating transcription factor-mediated regulation of ROS metabolism. Most importantly, the effects of applying exogenous substances on ROS metabolism and the potential regulatory mechanisms at play under abiotic stress are summarized. Given the important role of ROS in plants and other organisms, our findings provide insights for optimizing cultivation patterns and for improving plant stress tolerance and growth regulation.

Interactions of melatonin, reactive oxygen species, and nitric oxide during fruit ripening: an update and prospective view

Fruit ripening is a physiological process that involves a complex network of signaling molecules that act as switches to activate or deactivate certain metabolic pathways at different levels, not only by regulating gene and protein expression but also through post-translational modifications of the involved proteins. Ethylene is the distinctive molecule that regulates the ripening of fruits, which can be classified as climacteric or non-climacteric according to whether or not, respectively, they are dependent on this phytohormone. However, in recent years it has been found that other molecules with signaling potential also exert regulatory roles, not only individually but also as a result of interactions among them. These observations imply the existence of mutual and hierarchical regulations that sometimes make it difficult to identify the initial triggering event. Among these 'new' molecules, hydrogen peroxide, nitric oxide, and melatonin have been highlighted as prominent. This review provides a comprehensive outline of the relevance of these molecules in the fruit ripening process and the complex network of the known interactions among them.

Multiwalled Carbon Nanotubes Alter the PSII Photochemistry, Photosystem-Related Gene Expressions, and Chloroplastic Antioxidant System in Zea mays under Copper Toxicity

A critical approach against copper (Cu) toxicity is the use of carbon nanomaterials (CNMs). However, the effect of CNMs on Cu toxicity-exposed chloroplasts is not clear. The photosynthetic, genetic, and biochemical effects of multiwalled carbon nanotubes (50-100-250 mg L^-1 CNT) were investigated under Cu stress (50-100 μM CuSO₄) in Zea mays chloroplasts. F_v/F_m and F_v/F_o were suppressed under stress. Stress altered the antioxidant system and the expression of psaA, psaB, psbA, and psbD. The chloroplastic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione S-transferase (GST), and glutathione peroxidase (GPX) increased under CNT + stress, and those of hydrogen peroxide (H₂O₂) and lipid peroxidation decreased. CNTs were promoted to the maintenance of the redox state by regulating enzyme/non-enzyme activity/contents involved in the AsA-GSH cycle. Furthermore, CNTs inverted the negative effects of Cu by upregulating the transcriptions of photosystem-related genes. However, the high CNT concentration had adverse effects on the antioxidant capacity. CNT has great potential to confer tolerance by reducing Cu-induced damage and protecting the biochemical reactions of photosynthesis.

Phenolic-rich beverages reduce bacterial TMA formation in an ex vivo-in vitro colonic fermentation model

The production of pro-atherogenic trimethylamine N-oxide (TMAO) is dependent on the gut microbiota metabolism of quaternary amines (i.e., choline) into trimethylamine (TMA). Nutritional strategies that target microbial conversion of choline into TMA could reduce cardiovascular disease and atherosclerosis burden by reducing subsequent formation of TMAO. This study aimed to evaluate (1) whether beverages rich in known inhibitors of TMA production (chlorogenic acid, catechin and epicatechin) can reduce TMA formation and (2) the effect of upper gastrointestinal digestion on efficacy. To do this, either raw or digested coffee, tea and cocoa beverages were evaluated for their TMA-d₉ production inhibition in our ex vivo-in vitro fermentation model with human fecal slurries and choline-d₉ substrate. Results showed that digestion was required to unlock the TMA-d₉ production inhibition potential of coffee and cocoa beverages, and that teas did not possess a strong inhibition potential either digested or undigested. By fractionating digested bioactive beverages, we determined that those fractions rich in chlorogenic acid were the most bioactive. Overall, this study suggests that regular cocoa and coffee consumption could be a nutritional strategy able to reduce TMAO levels. In vivo studies should be carried out to confirm the potential of these beverages as strategies to inhibit TMA production.

Ethylene signaling increases reactive oxygen species accumulation to drive root hair initiation in Arabidopsis

Root hair initiation is a highly regulated aspect of root development. The plant hormone ethylene and its precursor, 1-amino-cyclopropane-1-carboxylic acid, induce formation and elongation of root hairs. Using confocal microscopy paired with redox biosensors and dyes, we demonstrated that treatments that elevate ethylene levels lead to increased hydrogen peroxide accumulation in hair cells prior to root hair formation. In the ethylene-insensitive receptor mutant, etr1-3, and the signaling double mutant, ein3eil1, the increase in root hair number or reactive oxygen species (ROS) accumulation after ACC and ethylene treatment was lost. Conversely, etr1-7, a constitutive ethylene signaling receptor mutant, has increased root hair formation and ROS accumulation, similar to ethylene-treated Col-0 seedlings. The caprice and werewolf transcription factor mutants have decreased and elevated ROS levels, respectively, which are correlated with levels of root hair initiation. The rhd2-6 mutant, with a defect in the gene encoding the ROS-synthesizing RESPIRATORY BURST OXIDASE HOMOLOG C (RBOHC), and the prx44-2 mutant, which is defective in a class III peroxidase, showed impaired ethylene-dependent ROS synthesis and root hair formation via EIN3EIL1-dependent transcriptional regulation. Together, these results indicate that ethylene increases ROS accumulation through RBOHC and PRX44 to drive root hair formation.

Mitochondrial protein expression during sweet pepper (Capsicum annuum L.) fruit ripening: iTRAQ-based proteomic analysis and role of cytochrome c oxidase

The physiological process of fruit ripening is associated with the late developmental stages of plants in which mitochondrial organelles play an important role in the final success of this whole process. Thus, an isobaric tag for relative and absolute quantification (iTRAQ)-based analysis was used to quantify the mitochondrial proteome in pepper fruits in this study. Analysis of both green and red pepper fruits identified a total of 2284 proteins, of which 692 were found to be significantly more abundant in unripe green fruits as compared to red fruits, while 497 showed lower levels as the ripening process proceeded. Of the total number of proteins identified, 2253 (98,6%) were found to share orthologs with Arabidopsis thaliana. Proteomic analysis identified 163 proteins which were categorized as cell components, the major part assigned to cellular, intracellular space and other subcellular locations such as cytosol, plastids and, to a lesser extent, to mitochondria. Of the 224 mitochondrial proteins detected in pepper fruits, 78 and 48 were more abundant in green and red fruits, respectively. The majority of these proteins which displayed differential abundance in both fruit types were involved in the mitochondrial electron transport chain (mETC) and the tricarboxylic acid (TCA) cycle. The abundance levels of the proteins from both pathways were higher in green fruits, except for cytochrome c (CYC2), whose abundance was significantly higher in red fruits. We also investigated cytochrome c oxidase (COX) activity during pepper fruit ripening, as well as in the presence of molecules such as nitric oxide (NO) and hydrogen peroxide (H₂O₂), which promote thiol-based oxidative post-translational modifications (oxiPTMs). Thus, with the aid of in vitro assays, cytochrome c oxidase (COX) activity was found to be potentially inhibited by the PTMs nitration, S-nitrosation and carbonylation. According to protein abundance data, the final segment of the mETC appears to be a crucial locus with regard to fruit ripening, but also because in this location the biosynthesis of ascorbate, an antioxidant which plays a major role in the metabolism of pepper fruits, occurs.

Differential Impact of Nitric Oxide and Abscisic Acid on the Cellular and Physiological Functioning of sub1A QTL Bearing Rice Genotype under Salt Stress

Hydroponic culture containing 200 mM NaCl was used to induce oxidative stress in seedlings of cultivars initially primed with 1 mM SNP and 10 µM ABA. Exogenous application of sodium nitroprusside (SNP - a nitric oxide donor) and abscisic acid (ABA) was well sensitized more in cv. Swarna Sub1 than cv. Swarna and also reflected in different cellular responses. The major effects of salinity, irrespective of the cultivar, were lowering the water relation, including relative water content and osmotic potential, and decreasing the compatible solutes like alanine, gamma-aminobutyric acid, and glycine betaine. The accumulated polyamines were reduced more in cv. Swarna with a concomitant decrease in photosynthetic reserves. NADP-malic enzyme activity, sucrose accumulation, ascorbate peroxidase, and glutathione S-transferase activities gradually declined under NaCl stress and the catabolizing enzymes like invertase (both wall and cytosolic forms) also declined. On the contrary, plants suffered from oxidative stress through superoxide, hydrogen peroxide, and their biosynthetic enzymes like NADP(H) oxidase. Moderation of Na⁺/K⁺ by both SNP and ABA were correlated with other salt sensitivities in the plants. The maximum effects of SNP and ABA were found in the recovery of antioxidation pathways, osmotic tolerance, and carbohydrate metabolism. Findings predict the efficacy of SNP and ABA either independently or cumulatively in overcoming NaCl toxicity in rice.

Nitric Oxide (NO) Differentially Modulates the Ascorbate Peroxidase (APX) Isozymes of Sweet Pepper (Capsicum annuum L.) Fruits

Nitric oxide (NO) is a free radical which modulates protein function and gene expression throughout all stages of plant development. Fruit ripening involves a complex scenario where drastic phenotypical and metabolic changes take place. Pepper fruits are one of the most consumed horticultural products worldwide which, at ripening, undergo crucial phenotypical and biochemical events, with NO and antioxidants being implicated. Based on previous transcriptomic (RNA-Seq), proteomics (iTRAQ), and enzymatic data, this study aimed to identify the ascorbate peroxidase (APX) gene and protein profiles in sweet peppers and to evaluate their potential modulation by NO during fruit ripening. The data show the existence of six CaAPX genes (CaAPX1–CaAPX6) that encode corresponding APX isozymes distributed in cytosol, plastids, mitochondria, and peroxisomes. The time course expression analysis of these genes showed heterogeneous expression patterns throughout the different ripening stages, and also as a consequence of treatment with NO gas. Additionally, six APX isozymes activities (APX I–APX VI) were identified by non-denaturing PAGE, and they were also differentially modulated during maturation and NO treatment. In vitro analyses of fruit samples in the presence of NO donors, peroxynitrite, and glutathione, showed that CaAPX activity was inhibited, thus suggesting that different posttranslational modifications (PTMs), including S-nitrosation, Tyr-nitration, and glutathionylation, respectively, may occur in APX isozymes. In silico analysis of the protein tertiary structure showed that residues Cys32 and Tyr235 were conserved in the six CaAPXs, and are thus likely potential targets for S-nitrosation and nitration, respectively. These data highlight the complex mechanisms of the regulation of APX isozymes during the ripening process of sweet pepper fruits and how NO can exert fine control. This information could be useful for postharvest technology; NO regulates H₂O₂ levels through the different APX isozymes and, consequently, could modulate the shelf life and nutritional quality of pepper fruits.

Nitric oxide regulation of plant metabolism

Nitric oxide (NO) has emerged as an important signal molecule in plants, having myriad roles in plant development. In addition, NO also orchestrates both biotic and abiotic stress responses, during which intensive cellular metabolic reprogramming occurs. Integral to these responses is the location of NO biosynthetic and scavenging pathways in diverse cellular compartments, enabling plants to effectively organize signal transduction pathways. NO regulates plant metabolism and, in turn, metabolic pathways reciprocally regulate NO accumulation and function. Thus, these diverse cellular processes are inextricably linked. This review addresses the numerous redox pathways, located in the various subcellular compartments that produce NO, in addition to the mechanisms underpinning NO scavenging. We focus on how this molecular dance is integrated into the metabolic state of the cell. Within this context, a reciprocal relationship between NO accumulation and metabolite production is often apparent. We also showcase cellular pathways, including those associated with nitrate reduction, that provide evidence for this integration of NO function and metabolism. Finally, we discuss the potential importance of the biochemical reactions governing NO levels in determining plant responses to a changing environment.

Induction of Metabolic Changes in Amino Acid, Fatty Acid, Tocopherol, and Phytosterol Profiles by Exogenous Methyl Jasmonate Application in Tomato Fruits

Methyl jasmonate hormone can stimulate the production of several metabolites responsible for improving fruit quality and nutritional attributes related to human health. In this context, efforts to manipulate tomatoes, such as using hormonal treatment to increase metabolite levels essential to plant growth and human nutrition, have received considerable attention. The aim of this study was to show the impact of metabolic profile on fruit quality and nutritional properties under exogenous methyl jasmonate during fruit ripening. The treatments were performed using 100 ppm of methyl jasmonate and 100 ppm of gaseous ethylene over 24 h. Ethylene emission, fruit surface color and metabolomics analysis were measured at 4, 10, and 21 days after harvest, considering the untreated fruits as control group. Methyl jasmonate induced the production of amino acids—mainly glutamine, glutamic acid and γ-aminobutyric acid (at least 14-fold higher)—and fatty acids—mainly oleic, linoleic, and linolenic acids (at least three-fold higher than untreated fruits); while exogenous ethylene predominantly affected sugar metabolism, increasing the levels of fructose, mannose and glucose to at least two-fold that levels in the untreated fruits. Additionally, methyl jasmonate significantly affected secondary metabolites, inducing by at least 80% the accumulation of α-tocopherol and β-sitosterol in fully ripe fruits. Our results suggest that the postharvest application of the hormone methyl jasmonate can contribute to the sensory characteristics and increase the nutritional value of the fruits since important changes related to the tomato metabolome were associated with compounds responsible for the fruit quality and health benefits.

Peroxisomal Proteome Mining of Sweet Pepper (Capsicum annuum L.) Fruit Ripening Through Whole Isobaric Tags for Relative and Absolute Quantitation Analysis

Peroxisomes are ubiquitous organelles from eukaryotic cells characterized by an active nitro-oxidative metabolism. They have a relevant metabolic plasticity depending on the organism, tissue, developmental stage, or physiological/stress/environmental conditions. Our knowledge of peroxisomal metabolism from fruits is very limited but its proteome is even less known. Using sweet pepper (Capsicum annuum L.) fruits at two ripening stages (immature green and ripe red), it was analyzed the proteomic peroxisomal composition by quantitative isobaric tags for relative and absolute quantitation (iTRAQ)-based protein profiling. For this aim, it was accomplished a comparative analysis of the pepper fruit whole proteome obtained by iTRAQ versus the identified peroxisomal protein profile from Arabidopsis thaliana. This allowed identifying 57 peroxisomal proteins. Among these proteins, 49 were located in the peroxisomal matrix, 36 proteins had a peroxisomal targeting signal type 1 (PTS1), 8 had a PTS type 2, 5 lacked this type of peptide signal, and 8 proteins were associated with the membrane of this organelle. Furthermore, 34 proteins showed significant differences during the ripening of the fruits, 19 being overexpressed and 15 repressed. Based on previous biochemical studies using purified peroxisomes from pepper fruits, it could be said that some of the identified peroxisomal proteins were corroborated as part of the pepper fruit antioxidant metabolism (catalase, superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductaseglutathione reductase, 6-phosphogluconate dehydrogenase and NADP-isocitrate dehydrogenase), the β-oxidation pathway (acyl-coenzyme A oxidase, 3-hydroxyacyl-CoA dehydrogenase, enoyl-CoA hydratase), while other identified proteins could be considered "new" or "unexpected" in fruit peroxisomes like urate oxidase (UO), sulfite oxidase (SO), 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase (METE1), 12-oxophytodienoate reductase 3 (OPR3) or 4-coumarate-CoA ligase (4CL), which participate in different metabolic pathways such as purine, sulfur, L-methionine, jasmonic acid (JA) or phenylpropanoid metabolisms. In summary, the present data provide new insights into the complex metabolic machinery of peroxisomes in fruit and open new windows of research into the peroxisomal functions during fruit ripening.

Identification of Compounds with Potential Therapeutic Uses from Sweet Pepper (Capsicum annuum L.) Fruits and Their Modulation by Nitric Oxide (NO)

Plant species are precursors of a wide variety of secondary metabolites that, besides being useful for themselves, can also be used by humans for their consumption and economic benefit. Pepper (Capsicum annuum L.) fruit is not only a common food and spice source, it also stands out for containing high amounts of antioxidants (such as vitamins C and A), polyphenols and capsaicinoids. Particular attention has been paid to capsaicin, whose anti-inflammatory, antiproliferative and analgesic activities have been reported in the literature. Due to the potential interest in pepper metabolites for human use, in this project, we carried out an investigation to identify new bioactive compounds of this crop. To achieve this, we applied a metabolomic approach, using an HPLC (high-performance liquid chromatography) separative technique coupled to metabolite identification by high resolution mass spectrometry (HRMS). After chromatographic analysis and data processing against metabolic databases, 12 differential bioactive compounds were identified in sweet pepper fruits, including quercetin and its derivatives, L-tryptophan, phytosphingosin, FAD, gingerglycolipid A, tetrahydropentoxylin, blumenol C glucoside, colnelenic acid and capsoside A. The abundance of these metabolites varied depending on the ripening stage of the fruits, either immature green or ripe red. We also studied the variation of these 12 metabolites upon treatment with exogenous nitric oxide (NO), a free radical gas involved in a good number of physiological processes in higher plants such as germination, growth, flowering, senescence, and fruit ripening, among others. Overall, it was found that the content of the analyzed metabolites depended on the ripening stage and on the presence of NO. The metabolic pattern followed by quercetin and its derivatives, as a consequence of the ripening stage and NO treatment, was also corroborated by transcriptomic analysis of genes involved in the synthesis of these compounds. This opens new research perspectives on the pepper fruit’s bioactive compounds with nutraceutical potentiality, where biotechnological strategies can be applied for optimizing the level of these beneficial compounds.

Loss of function of the chloroplast membrane K+/H+ antiporters AtKEA1 and AtKEA2 alters the ROS and NO metabolism but promotes drought stress resilience

Potassium (K⁺) exerts key physiological functions such as osmoregulation, stomatal movement, membrane transport, protein synthesis and photosynthesis among others. Previously, it was demonstrated in Arabidopsis thaliana that the loss of function of the chloroplast K⁺Efflux Antiporters KEA1 and KEA2, located in the inner envelope membrane, provokes inefficient photosynthesis. Therefore, the main goal of this study was to evaluate the potential impact of the loss of function of those cation transport systems in the metabolism of reactive oxygen and nitrogen species (ROS and RNS). Using 14-day-old seedlings from Arabidopsis double knock-out kea1kea2 mutants, ROS metabolism and NO content in roots and green cotyledons were studied at the biochemical level. The loss of function of AtKEA1 and AtKEA2 did not cause oxidative stress but it provoked an alteration of the ROS homeostasis affecting some ROS-generating enzymes. These included glycolate oxidase (GOX) and NADPH-dependent superoxide generation activity, enzymatic and non-enzymatic antioxidants and both NADP-isocitrate dehydrogenase and NADP-malic enzyme activities. NO content, analyzed by confocal laser scanning microscopy (CLSM), was negatively affected in both photosynthetic and non-photosynthetic organs in kea1kea2 mutant seedlings. Furthermore, the S-nitrosoglutathione reductase (GSNOR) protein expression and activity were downregulated in kea1kea2 mutants, whereas the tyrosine nitrated protein profile, analyzed by immunoblot, was unaffected but the relative expression of each immunoreactive band changed. Moreover, kea1kea2 mutants showed an increased photorespiratory pathway and stomata closure, thus promoting a higher resilience to drought stress. Data suggest that the chloroplast osmotic balance and integrity maintained by AtKEA1 and AtKEA2 are necessary to keep the balance of ROS/RNS metabolism. Moreover, these data open new questions about how endogenous NO generation might be affected by the K⁺/H⁺ transport located in the chloroplasts.

Nitric oxide, other reactive signalling compounds, redox, and reductive stress

Nitric oxide (NO) and other reactive nitrogen species (RNS) are key signalling molecules in plants, but they do not work in isolation. NO is produced in cells, often increased in response to stress conditions, but many other reactive compounds used in signalling are generated and accumulate spatially and temporally together. This includes the reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), and hydrogen sulfide (H2S). Here, the interactions with such other reactive molecules is briefly reviewed. Furthermore, along with ROS and H2S, NO will potentially contribute to the overall intracellular redox of the cell. However, RNS will exist in redox couples and therefore the influence of the cellular redox on such couples will be explored. In discussions of the aberrations in intracellular redox it is usually oxidation, so-called oxidative stress, which is discussed. Here, we consider the notion of reductive stress and how this may influence the signalling which may be mediated by NO. By getting a more holistic view of NO biology, the influence on cell activity of NO and other RNS can be more fully understood, and may lead to the elucidation of methods for NO-based manipulation of plant physiology, leading to better stress responses and improved crops in the future.

Effect of Engineered Nickel Oxide Nanoparticle on Reactive Oxygen Species-Nitric Oxide Interplay in the Roots of Allium cepa L

Scientists anxiously follow instances of heavy metals augmenting in the environment and undergoing bioaccumulation and trace their biomagnification across food webs, wary of their potent toxicity on biological entities. Engineered nanoparticles supplement natural pools of respective heavy metals and can mimic their effects, exerting toxicity at higher concentrations. Thus, a thorough understanding of the underlying mechanism of this precarious interaction is mandatory. Most urban and industrial environments contain considerable quantities of nickel oxide nanoparticles. These in excess can cause considerable damage to plant metabolism through a significant increase in cellular reactive oxygen species and perturbation of its cross-talk with the reactive nitrogen species. In the present work, the authors have demonstrated how the intrusion of nickel oxide nanoparticles (NiO-NP) affected the exposed roots of Allium cepa: starting with disruption of cell membranes, before being interiorized within cell organelles, effectively disrupting cellular homeostasis and survival. A major shift in the reactive oxygen species (ROS) and nitric oxide (NO) equanimity was also observed, unleashing major altercations in several crucial biochemical profiles. Altered antioxidant contents and upregulation of stress-responsive genes, namely, Catalase, Ascorbate peroxidase, Superoxide dismutase, and Rubisco activase, showing on average 50-250% rise across NiO-NP concentrations tested, also entailed increased cellular hydrogen peroxide contents, with tandem rise in cellular NO. Increased NO content was evinced from altered concentrations of nitric oxide synthase and nitrate reductase, along with NADPH oxidase, when compared with the negative control. Though initially showing a dose-dependent concomitant rise, a significant decrease of NO was observed at higher concentrations of NiO-NP, while cellular ROS continued to increase. Modified K/Na ratios, with increased proline concentrations and GABA contents, all hallmarks of cellular stress, correlated with ROS-NO perturbations. Detailed studies showed that NiO-NP concentration had a significant role in inducing toxicity, perturbing the fine balance of ROS-NO, which turned lethal for the cell at higher dosages of the ENP precipitating in the accumulation of stress markers and an inevitable shutdown of cellular mechanisms.

Beyond Ethylene: New Insights Regarding the Role of Alternative Oxidase in the Respiratory Climacteric

Climacteric fruits are characterized by a dramatic increase in autocatalytic ethylene production that is accompanied by a spike in respiration at the onset of ripening. The change in the mode of ethylene production from autoinhibitory to autostimulatory is known as the System 1 (S1) to System 2 (S2) transition. Existing physiological models explain the basic and overarching genetic, hormonal, and transcriptional regulatory mechanisms governing the S1 to S2 transition of climacteric fruit. However, the links between ethylene and respiration, the two main factors that characterize the respiratory climacteric, have not been examined in detail at the molecular level. Results of recent studies indicate that the alternative oxidase (AOX) respiratory pathway may play an essential role in mediating cross-talk between ethylene response, carbon metabolism, ATP production, and ROS signaling during climacteric ripening. New genomic, metabolic, and epigenetic information sheds light on the interconnectedness of ripening metabolic pathways, necessitating an expansion of the current, ethylene-centric physiological models. Understanding points at which ripening responses can be manipulated may reveal key, species- and cultivar-specific targets for regulation of ripening, enabling superior strategies for reducing postharvest wastage.

Nitric oxide: A radical molecule with potential biotechnological applications in fruit ripening

Nitric oxide (NO) is a short-life and free radical molecule involved in a wide range of cellular, physiological and stressful processes in higher plants. In recent years it has been observed that exogenous NO application can palliate adverse damages against abiotic and biotic stresses. Conversely, there is accumulating information indicating that endogenous NO participates significantly in the mechanism of modulation of the ripening in climacteric and non-climacteric fruits. Even more, when NO is exogenously applied, it can mediate beneficial effects during ripening and postharvest storage being one of the main effects the increase of antioxidant systems. Consequently, NO could be a promising biotechnological tool to improve crops through ameliorating nutritional indexes and to alleviate damages during fruit ripening and postharvest management. Thus, this approach should be complementary to previous strategies to allow preserving the quality and healthiness of fruits with a view of enhancing their added value. The present mini-review aims to provide an overview of NO biochemistry in plants and updated information on the relevance of NO in fruit ripening and postharvest stages with a view to its biotechnological applications.

Genome-wide identification and characterization of Respiratory Burst Oxidase Homolog genes in six Rosaceae species and an analysis of their effects on adventitious rooting in apple

Adventitious root formation is essential for plant propagation, development, and response to various stresses. Reactive oxygen species (ROS) are essential for adventitious root formation. However, information on Respiratory Burst Oxidase Homolog (RBOH), a key enzyme that catalyzes the production ROS, remains limited in woody plants. Here, a total of 44 RBOH genes were identified from six Rosaceae species (Malus domestica, Prunus avium, Prunus dulcis 'Texas’, Rubus occidentalis, Fragaria vesca and Rosa chinensis), including ten from M. domestica. Their phylogenetic relationships, conserved motifs and gene structures were analyzed. Exogenous treatment with the RBOH protein inhibitor diphenyleneiodonium (DPI) completely inhibited adventitious root formation, whereas exogenous H₂O₂ treatment enhanced adventitious root formation. In addition, we found that ROS accumulated during adventitious root primordium inducing process. The expression levels of MdRBOH-H, MdRBOH-J, MdRBOH-A, MdRBOH-E1 and MdRBOH-K increased more than two-fold at days 3 or 9 after auxin treatment. In addition, cis-acting element analysis revealed that the MdRBOH-E1 promoter contained an auxin-responsive element and the MdRBOH-K promoter contained a meristem expression element. Based on the combined results from exogenous DPI and H₂O₂ treatment, spatiotemporal expression profiling, and cis-element analysis, MdRBOH-E1 and MdRBOH-K appear to be candidates for the control of adventitious rooting in apple.

Antioxidant Profile of Pepper (Capsicum annuum L.) Fruits Containing Diverse Levels of Capsaicinoids

Capsicum is the genus where a number of species and varieties have pungent features due to the exclusive content of capsaicinoids such as capsaicin and dihydrocapsaicin. In this work, the main enzymatic and non-enzymatic systems in pepper fruits from four varieties with different pungent capacity have been investigated at two ripening stages. Thus, a sweet pepper variety (Melchor) from California-type fruits and three autochthonous Spanish varieties which have different pungency levels were used, including Piquillo, Padrón and Alegría riojana. The capsaicinoids contents were determined in the pericarp and placenta from fruits, showing that these phenyl-propanoids were mainly localized in placenta. The activity profiles of catalase, total and isoenzymatic superoxide dismutase (SOD), the enzymes of the ascorbate–glutathione cycle (AGC) and four NADP-dehydrogenases indicate that some interaction with capsaicinoid metabolism seems to occur. Among the results obtained on enzymatic antioxidants, the role of Fe-SOD and the glutathione reductase from the AGC is highlighted. Additionally, it was found that ascorbate and glutathione contents were higher in those pepper fruits which displayed the greater contents of capsaicinoids. Taken together, all these data indicate that antioxidants may contribute to preserve capsaicinoids metabolism to maintain their functionality in a framework where NADPH is perhaps playing an essential role.

Cross-Species Comparison of Fruit-Metabolomics to Elucidate Metabolic Regulation of Fruit Polyphenolics Among Solanaceous Crops

Many solanaceous crops are an important part of the human daily diet. Fruit polyphenolics are plant specialized metabolites that are recognized for their human health benefits and their defensive role against plant abiotic and biotic stressors. Flavonoids and chlorogenates are the major polyphenolic compounds found in solanaceous fruits that vary in quantity, physiological function, and structural diversity among and within plant species. Despite their biological significance, the elucidation of metabolic shifts of polyphenols during fruit ripening in different fruit tissues, has not yet been well-characterized in solanaceous crops, especially at a cross-species and cross-cultivar level. Here, we performed a cross-species comparison of fruit-metabolomics to elucidate the metabolic regulation of fruit polyphenolics from three representative crops of Solanaceae (tomato, eggplant, and pepper), and a cross-cultivar comparison among different pepper cultivars (Capsicum annuum cv.) using liquid chromatography-mass spectrometry (LC-MS). We observed a metabolic trade-off between hydroxycinnamates and flavonoids in pungent pepper and anthocyanin-type pepper cultivars and identified metabolic signatures of fruit polyphenolics in each species from each different tissue-type and fruit ripening stage. Our results provide additional information for metabolomics-assisted crop improvement of solanaceous fruits towards their improved nutritive properties and enhanced stress tolerance.

Superoxide Radical Metabolism in Sweet Pepper (Capsicum annuum L.) Fruits Is Regulated by Ripening and by a NO-Enriched Environment

Superoxide radical (O2 •-) is involved in numerous physiological and stress processes in higher plants. Fruit ripening encompasses degradative and biosynthetic pathways including reactive oxygen and nitrogen species. With the use of sweet pepper (Capsicum annuum L.) fruits at different ripening stages and under a nitric oxide (NO)-enriched environment, the metabolism of O2 •- was evaluated at biochemical and molecular levels considering the O2 •- generation by a NADPH oxidase system and its dismutation by superoxide dismutase (SOD). At the biochemical level, seven O2 •--generating NADPH-dependent oxidase isozymes [also called respiratory burst oxidase homologs (RBOHs) I-VII], with different electrophoretic mobility and abundance, were detected considering all ripening stages from green to red fruits and NO environment. Globally, this system was gradually increased from green to red stage with a maximum of approximately 2.4-fold increase in red fruit compared with green fruit. Significantly, breaking-point (BP) fruits with and without NO treatment both showed intermediate values between those observed in green and red peppers, although the value in NO-treated fruits was lower than in BP untreated fruits. The O2 •--generating NADPH oxidase isozymes I and VI were the most affected. On the other hand, four SOD isozymes were identified by non-denaturing electrophoresis: one Mn-SOD, one Fe-SOD, and two CuZn-SODs. However, none of these SOD isozymes showed any significant change during the ripening from green to red fruits or under NO treatment. In contrast, at the molecular level, both RNA-sequencing and real-time quantitative PCR analyses revealed different patterns with downregulation of four genes RBOH A, C, D, and E during pepper fruit ripening. On the contrary, it was found out the upregulation of a Mn-SOD gene in the ripening transition from immature green to red ripe stages, whereas a Fe-SOD gene was downregulated. In summary, the data reveal a contradictory behavior between activity and gene expression of the enzymes involved in the metabolism of O2 •- during the ripening of pepper fruit. However, it could be concluded that the prevalence and regulation of the O2 •- generation system (NADPH oxidase-like) seem to be essential for an appropriate control of the pepper fruit ripening, which, additionally, is modulated in the presence of a NO-enriched environment.

Inhibition of NADP-malic enzyme activity by H2 S and NO in sweet pepper (Capsicum annuum L.) fruits

NADPH is an essential cofactor in many physiological processes. Fruit ripening is caused by multiple biochemical pathways in which, reactive oxygen and nitrogen species (ROS/RNS) metabolism is involved. Previous studies have demonstrated the differential modulation of nitric oxide (NO) and hydrogen sulfide (H₂ S) content during sweet pepper (Capsicum annuum L.) fruit ripening, both of which regulate NADP-isocitrate dehydrogenase activity. To gain a deeper understanding of the potential functions of other NADPH-generating components, we analyzed glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), which are involved in the oxidative phase of the pentose phosphate pathway (OxPPP) and NADP-malic enzyme (NADP-ME). During fruit ripening, G6PDH activity diminished by 38%, while 6PGDH and NADP-ME activity increased 1.5- and 2.6-fold, respectively. To better understand the potential regulation of these NADP-dehydrogenases by H₂ S, we obtained a 50-75% ammonium-sulfate-enriched protein fraction containing these proteins. With the aid of in vitro assays, in the presence of H₂ S, we observed that, while NADP-ME activity was inhibited by up to 29-32% using 2 and 5 mM Na₂ S as H₂ S donor, G6PDH and 6PGDH activities were unaffected. On the other hand, NO donors, S-nitrosocyteine (CysNO) and DETA NONOate also inhibited NADP-ME activity by 35%. These findings suggest that both NADP-ME and 6PGDH play an important role in maintaining the supply of NADPH during pepper fruit ripening and that H₂ S and NO partially modulate the NADPH-generating system.

Assessment of Subcellular ROS and NO Metabolism in Higher Plants: Multifunctional Signaling Molecules

Reactive oxygen species (ROS) and nitric oxide (NO) are produced in all aerobic life forms under both physiological and adverse conditions. Unregulated ROS/NO generation causes nitro-oxidative damage, which has a detrimental impact on the function of essential macromolecules. ROS/NO production is also involved in signaling processes as secondary messengers in plant cells under physiological conditions. ROS/NO generation takes place in different subcellular compartments including chloroplasts, mitochondria, peroxisomes, vacuoles, and a diverse range of plant membranes. This compartmentalization has been identified as an additional cellular strategy for regulating these molecules. This assessment of subcellular ROS/NO metabolisms includes the following processes: ROS/NO generation in different plant cell sites; ROS interactions with other signaling molecules, such as mitogen-activated protein kinases (MAPKs), phosphatase, calcium (Ca²⁺), and activator proteins; redox-sensitive genes regulated by the iron-responsive element/iron regulatory protein (IRE-IRP) system and iron regulatory transporter 1(IRT1); and ROS/NO crosstalk during signal transduction. All these processes highlight the complex relationship between ROS and NO metabolism which needs to be evaluated from a broad perspective.

Sweet Pepper (Capsicum annuum L.) Fruits Contain an Atypical Peroxisomal Catalase That is Modulated by Reactive Oxygen and Nitrogen Species

During the ripening of sweet pepper (Capsicum annuum L.) fruits, in a genetically controlled scenario, enormous metabolic changes occur that affect the physiology of most cell compartments. Peroxisomal catalase gene expression decreases after pepper fruit ripening, while the enzyme is also susceptible to undergo post-translational modifications (nitration, S-nitrosation, and oxidation) promoted by reactive oxygen and nitrogen species (ROS/RNS). Unlike most plant catalases, the pepper fruit enzyme acts as a homodimer, with an atypical native molecular mass of 125 to 135 kDa and an isoelectric point of 7.4, which is higher than that of most plant catalases. These data suggest that ROS/RNS could be essential to modulate the role of catalase in maintaining basic cellular peroxisomal functions during pepper fruit ripening when nitro-oxidative stress occurs. Using catalase from bovine liver as a model and biotin-switch labeling, in-gel trypsin digestion, and nanoliquid chromatography coupled with mass spectrometry, it was found that Cys377 from the bovine enzyme could potentially undergo S-nitrosation. To our knowledge, this is the first report of a cysteine residue from catalase that can be post-translationally modified by S-nitrosation, which makes it especially important to find the target points where the enzyme can be modulated under either physiological or adverse conditions.

Nitric oxide and hydrogen sulfide in plants: which comes first?

Nitric oxide (NO) is a signal molecule regarded as being involved in myriad functions in plants under physiological, pathogenic, and adverse environmental conditions. Hydrogen sulfide (H2S) has also recently been recognized as a new gasotransmitter with a diverse range of functions similar to those of NO. Depending on their respective concentrations, both these molecules act synergistically or antagonistically as signals or damage promoters in plants. Nevertheless, available evidence shows that the complex biological connections between NO and H2S involve multiple pathways and depend on the plant organ and species, as well as on experimental conditions. Cysteine-based redox switches are prone to reversible modification; proteomic and biochemical analyses have demonstrated that certain target proteins undergo post-translational modifications such as S-nitrosation, caused by NO, and persulfidation, caused by H2S, both of which affect functionality. This review provides a comprehensive update on NO and H2S in physiological processes (seed germination, root development, stomatal movement, leaf senescence, and fruit ripening) and under adverse environmental conditions. Existing data suggest that H2S acts upstream or downstream of the NO signaling cascade, depending on processes such as stomatal closure or in response to abiotic stress, respectively.

Nitric oxide-dependent regulation of sweet pepper fruit ripening

Ripening is a complex physiological process that involves changes in reactive nitrogen and oxygen species that govern the shelf-life and quality of fruits. Nitric oxide (NO)-dependent changes in the sweet pepper fruit transcriptome were determined by treating fruits at the initial breaking point stage with NO gas. Fruits were also harvested at the immature (green) and ripe (red) stages. Fruit ripening in the absence of NO resulted in changes in the abundance of 8805 transcripts whose function could be identified. Among these, functional clusters associated with reactive oxygen/nitrogen species and lipid metabolism were significantly modified. NO treatment resulted in the differential expression of 498 genes framed within these functional categories. Biochemical analysis revealed that NO treatment resulted in changes in fatty acid profiling, glutathione and proline contents, and the extent of lipid peroxidation, as well as increases in the activity of ascorbate peroxidase and lipoxygenase. These data provide supporting evidence for the crucial role of NO in the ripening of pepper fruit.

Nitric oxide in the physiology and quality of fleshy fruits

Fruits are unique to flowering plants and confer a selective advantage as they facilitate seed maturation and dispersal. In fleshy fruits, development and ripening are associated with numerous structural, biochemical, and physiological changes, including modifications in the general appearance, texture, flavor, and aroma, which ultimately convert the immature fruit into a considerably more attractive and palatable structure for seed dispersal by animals. Treatment with exogenous nitric oxide (NO) delays fruit ripening, prevents chilling damage, promotes disease resistance, and enhances the nutritional value. The ripening process is influenced by NO, which operates antagonistically to ethylene, but it also interacts with other regulatory molecules such as abscisic acid, auxin, jasmonic acid, salicylic acid, melatonin, and hydrogen sulfide. NO content progressively declines during fruit ripening, with concomitant increases in protein nitration and nitrosation, two post-translational modifications that are promoted by reactive nitrogen species. Dissecting the intimate interactions of NO with other ripening-associated factors, including reactive oxygen species, antioxidants, and the aforementioned phytohormones, remains a challenging subject of research. In this context, integrative 'omics' and gene-editing approaches may provide additional knowledge of the impact of NO in the regulatory processes involved in controlling physiology and quality traits in both climacteric and non-climacteric fruits.