Ascorbate and glutathione: the heart of the redox hub

Seed longevity and genome damage

Seeds are the mode of propagation for most plant species and form the basis of both agriculture and ecosystems. Desiccation tolerant seeds, representative of most crop species, can survive maturation drying to become metabolically quiescent. The desiccated state prolongs embryo viability and provides protection from adverse environmental conditions, including seasonal periods of drought and freezing often encountered in temperate regions. However, the capacity of the seed to germinate declines over time and culminates in the loss of seed viability. The relationship between environmental conditions (temperature and humidity) and the rate of seed deterioration (ageing) is well defined, but less is known about the biochemical and genetic factors that determine seed longevity. This review will highlight recent advances in our knowledge that provide insight into the cellular stresses and protective mechanisms that promote seed survival, with a focus on the roles of DNA repair and response mechanisms. Collectively, these pathways function to maintain the germination potential of seeds. Understanding the molecular basis of seed longevity provides important new genetic targets for the production of crops with enhanced resilience to changing climates and knowledge important for the preservation of plant germplasm in seedbanks.

Cold plasma treatment influences the physiological parameters of millet

In recent years, cold plasma treatment has emerged as a promising method to positively impact early seed growth. This study aimed to investigate the effects of cold plasma treatment on millet seeds with ambient air plasma discharge at pressures of 100 Pa and power ranging from 40 to 250 W. Results indicated that cold plasma treatment significantly increased radicle length by up to 112.5% (250 W) after 48 h and up to 57% (120 W) after 72 h compared to nontreated plants. The study also found that cold plasma treatment influenced electron transport during the primary phase of photosynthesis, with the effect varying with the power of discharge. However, high levels of discharge resulted in a significantly higher chlorophyll synthesis. These results suggest that cold plasma treatment may be used to reduce plant stress and improve growing properties.

Arbuscular mycorrhizal fungal contribution towards plant resilience to drought conditions

Climate changes cause altering rainfall patterns resulting in an increase in drought occurrences globally. These events are disrupting plants and agricultural productivity. To evade droughts, plants try to adapt and modify in the best capacities possible. The plants have adapted by structurally modifying roots, stems, and leaves, as well as modifying functions. Lately, the association of microbial communities with plants has also been proven to be an important factor in aiding resilience. The fungal representatives of the microbial community also help safeguard the plants against drought. We discuss how these fungi associate with plants and contribute to evading drought stress. We specifically focus on Arbuscular mycorrhizal fungi (AMF) mediated mechanisms involving antioxidant defenses, phytohormone mediations, osmotic adjustments, proline expressions, fungal water absorption and transport, morphological modifications, and photosynthesis. We believe understanding the mechanisms would help us to optimize the use of fungi in agricultural practices. That way we could better prepare the plants for the anticipated future drought events.

Multiple Physiological and Biochemical Functions of Ascorbic Acid in Plant Growth, Development, and Abiotic Stress Response

Ascorbic acid (AsA) is an important nutrient for human health and disease cures, and it is also a crucial indicator for the quality of fruit and vegetables. As a reductant, AsA plays a pivotal role in maintaining the intracellular redox balance throughout all the stages of plant growth and development, fruit ripening, and abiotic stress responses. In recent years, the de novo synthesis and regulation at the transcriptional level and post-transcriptional level of AsA in plants have been studied relatively thoroughly. However, a comprehensive and systematic summary about AsA-involved biochemical pathways, as well as AsA's physiological functions in plants, is still lacking. In this review, we summarize and discuss the multiple physiological and biochemical functions of AsA in plants, including its involvement as a cofactor, substrate, antioxidant, and pro-oxidant. This review will help to facilitate a better understanding of the multiple functions of AsA in plant cells, as well as provide information on how to utilize AsA more efficiently by using modern molecular biology methods.

Integrated metabolome and transcriptome analysis of differences in quality of ripe Lycium barbarum L. fruits harvested at different periods

BACKGROUND

Wolfberry is well-known for its high nutritional value and medicinal benefits. Due to the continuous ripening nature of Goji berries and the fact that they can be commercially harvested within a few weeks, their phytochemical composition may change during the harvesting process at different periods.

RESULT

The involved molecular mechanisms of difference in fruit quality of ripe Lycium barbarum L. harvested at four different periods were investigated by transcriptomic and metabolomics analyses for the first time. According to the results we obtained, it was found that the appearance quality of L. barbarum fruits picked at the beginning of the harvesting season was superior, while the accumulation of sugar substances in L. barbarum fruits picked at the end of the harvesting season was better. At the same time the vitamin C and carotenoids content of wolfberry fruits picked during the summer harvesting season were richer. Ascorbic acid, succinic acid, glutamic acid, and phenolic acids have significant changes in transcription and metabolism levels. Through the network metabolic map, we found that ascorbic acid, glutamic acid, glutamine and related enzyme genes were differentially accumulated and expressed in wolfberry fruits at different harvesting periods. Nevertheless, these metabolites played important roles in the ascorbate-glutathione recycling system. Ascorbic acid, phenolic substances and the ascorbate-glutathione recycling system have antioxidant effects, which makes the L. barbarum fruits harvested in the summer more in line with market demand and health care concepts.

CONCLUSION

This study laid the foundation for understanding the molecular regulatory mechanisms of quality differences of ripe wolfberry fruits harvested at different periods, and provides a theoretical basis for enhancing the quality of L. barbarum fruits.

Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 μmol photon m-2 s-1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 μmol photon m-2 s-1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Understanding the mechanistic basis of plant adaptation to salinity and drought

Plant growth and development is adversely affected by environmental constraints, particularly salinity and drought. Climate change has escalated the effect of salinity and drought on crops in varying ways, affecting agriculture and most importantly crop productivity. These stressors influence plants across a wide range of levels, including their morphology and physiological, biochemical, and molecular processes. Plant responses to salinity and drought stress have been the subject of intense research being explored globally. Considering the importance of the impact that these stresses can have on agriculture in the short term, novel strategies are being sought and adopted in breeding programs. Better understanding of the molecular, biochemical, and physiological responses of agriculturally important plants will ultimately help promote global food security. Moreover, considering the present challenges for agriculture, it is critical to consider how we can effectively transfer the knowledge generated with these approaches in the laboratory to the field, so as to mitigate these adversities. The present collection discusses how drought and salinity exert effects on plants.

New Prospects for Improving Microspore Embryogenesis Induction in Highly Recalcitrant Winter Wheat Lines

Among various methods stimulating biological progress, double haploid (DH) technology, which utilizes the process of microspore embryogenesis (ME), is potentially the most effective. However, the process depends on complex interactions between many genetic, physiological and environmental variables, and in many cases, e.g., winter wheat, does not operate with the efficiency required for commercial use. Stress associated with low-temperature treatment, isolation and transfer to in vitro culture has been shown to disturb redox homeostasis and generate relatively high levels of reactive oxygen species (ROS), affecting microspore vitality. The aim of this study was to investigate whether controlled plant growth, specific tiller pre-treatment and culture conditions could improve the potential of microspores to cope with stress and effectively induce ME. To understand the mechanism of the stress response, hydrogen peroxide levels, total activity and the content of the most important low-molecular-weight antioxidants (glutathione and ascorbate), as well as the content of selected macro- (Mg, Ca, NA, K) and micronutrients (Mn, Zn, Fe, Cu, Mo) were determined. These analyses, combined with the cytological characteristics of the microspore suspensions, allowed us to demonstrate that an increased microspore vitality and stronger response to ME induction were associated with higher stress resistance based on more efficient ROS scavenging and nutrient management. It was shown that a modified procedure, combining a low temperature with mannitol and sodium selenate tiller pre-treatment, reduced oxidative stress and improved the effectiveness of ME in winter wheat lines.

Influence of Pasteurisation (Conventional vs. Radiofrequency) and Chill Storage on Retention of Ascorbic Acid, Tocopherol and Carotenoids in Salmorejo

Salmorejo, a Mediterranean tomato-oil puree, is considered a dietary source of antioxidant vitamins C and E and carotenoids lycopene and β-carotene, the latter endowed with provitamin A activity. However, these antioxidants can be degraded in oxidation reactions catalysed or not by enzymes during pasteurisation and storage treatments used to stabilise the salmorejo before consumption. Due to its better penetration, the use of dielectric heating by radiofrequency (RF) may improve results of pasteurisation in this product. The objective was to assess the effects of pasteurisation temperature (70-100 °C, at 5 °C intervals) and storage time (0-5 months, at one-month intervals) on levels of ascorbic acid, α-tocopherol and carotenoids and antioxidant capacity (AC) in salmorejo pasteurised (over 10 s) by conventional (CH) or RF continuous heating. Two successive experiments were conducted to select an adequate pasteurisation temperature for use in the shelf-life study. Pasteurisation upon tested conditions allows a good retention of salmorejo antioxidants. Either CH or RF pasteurisers can be used with similar results. Vitamin C (L-ascorbic + dehydroascorbic acids) was more abundant (15-19 mg 100 g-1) than carotenoids (0.9-2.6 mg 100 g-1) (all-trans + cis lycopene and β-carotene) and α-tocopherol (0.8-1.2 mg 100 g-1) in the pasteurised product. Using excessively low temperatures (70 °C) resulted in partial losses of the three antioxidants, possibly due to oxidase residual activities. Intensifying thermal treatment improved this issue with minor losses of the thermolabile vitamin C and increased carotenoid content. Using a suitable temperature (80 °C) did not prevent most vitamin C from being degraded by the first month, while α-tocopherol, and, to a lesser extent, carotenoids, showed good retention levels during shelf life under refrigeration. Vitamins C and E and carotenoids, either by degradation, regeneration or releasing, likely contribute to the AC in salmorejo. Phenolic antioxidant response, radical-scavenging activities and redox potential values confirmed this finding. The pasteurised-chilled salmorejo shows good antioxidant properties with potential health implications, a positive nutritional aspect for consumers of this tomato-oil homogenate. The losses of antioxidants and AC due to pasteurization would be of little relevance compared to the losses accumulated during shelf life.

Growth, Physiological, and Biochemical Variations in Tomatoes after Infection with Different Density Levels of Meloidogyne enterolobii

Meloidogyne enterolobii is an extremely important plant parasitic nematode. Tomato (Solanum lycopersicum) is an essential worldwide vegetable, and M. enterolobii poses a major threat to its production. The present research investigated the effects of different levels of inoculum density of M. enterolobii (100, 500, 1000, 1500, and 2000 second-stage juveniles (J2s)/plant) on tomato growth, physiological, and biochemical changes at 7, 14, 21, and 28 days post-inoculation (dpi). The negative impact of M. enterolobii on plants gradually increased when the inoculum level increased. Therefore, M. enterolobii population densities (500-2000 J2s/plant) significantly (p < 0.05) reduced plant growth, photosynthetic pigmentation, gas exchange, and chlorophyll fluorescence compared to control plants, while the low population density (100 J2s/plant) showed very little influence. Furthermore, plants with the highest M. enterolobii inoculum (2000 J2s/plant) exhibited a greater number of egg masses and galls. The inoculum densities of M. enterolobii exhibited a notable correlation with the significant elevation of both malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, which are recognized as very detrimental stresses in plants. Similarly, a rise in the activity of several defensive antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), indicates the defensive mechanism used to combat the oxidative destruction produced by M. enterolobii. The specific activity of glutathione (GSH) and ascorbate (ASA) increased as potent antioxidant defense molecules in response to induced oxidative damage. In addition, our findings also demonstrated that the highest population density (2000 J2s/plant) increased the secondary metabolites responsible for scavenging oxidative stress in the plants. However, further research is required to explore the underlying reasons for this phenomenon and to develop efficient chemical or biocontrol strategies for managing M. enterolobii.

Exogenous melatonin induces salt and drought stress tolerance in rice by promoting plant growth and defense system

Due to global climate change, crops are certainly confronted with a lot of abiotic and biotic stress factors during their growth that cause a serious threat to their development and overall productivity. Among different abiotic stresses, salt and drought are considered the most devastating stressors with serious impact on crop's yield stability. Here, the current study aimed to elucidate how melatonin works in regulating plant biomass, oxidative stress, antioxidant defense system, as well as the expression of genes related to salt and drought stress in rice plants. Eight groups of rice plants (3 replicates, 5 plants each) underwent varied treatments: control, melatonin, salt, drought, salt + drought, salt + melatonin, drought + melatonin, and salt + drought + melatonin. Melatonin (100 µM) was alternately applied a week before stress exposure; salt stress received 100 mM NaCl every 3 days for 3 weeks, and drought stress involved 10% PEG. Young leaves were randomly sampled from each group. The results showed that melatonin treatment markedly reduces salt and drought stress damage by promoting root, shoot length, fresh and dry weight, increasing chlorophyll contents, and inhibiting excessive production of oxidative stress markers. Salt and drought stress significantly decreased the water balance, and damaged cell membrane by reducing relative water contents and increasing electrolyte leakage. However, melatonin treated rice plants showed high relative water contents and low electrolyte leakage. Under salt and drought stress conditions, exogenous application of melatonin boosted the expression level of salt and drought stress responsive genes like OsSOS, OsNHX, OsHSF and OsDREB in rice plants. Taken together, our results reveal that melatonin treatment significantly increases salt and drought tolerance of rice plants, by increasing plant biomass, suppressing ROS accumulation, elevating antioxidants defense efficiency, and up-regulating the expression of salt and drought stress responsive genes.

Transcriptomic and metabolomic profiling reveals the drought tolerance mechanism of Illicium difengpi (Schisandraceae)

Illicium difengpi (Schisandraceae), an endangered medicinal plant endemic to karst areas, is highly tolerant to drought and thus can be used as an ideal material for investigating adaptive mechanism to drought stress. The understanding of the drought tolerance of I. difengpi, especially at the molecular level, is lacking. In the present study, we aimed to clarify the molecular mechanism underlying drought tolerance in endemic I. difengpi plant in karst regions. The response characteristics of transcripts and changes in metabolite abundance of I. difengpi subjected to drought and rehydration were analyzed, the genes and key metabolites responsive to drought and rehydration were screened, and some important biosynthetic and secondary metabolic pathways were identified. A total of 231,784 genes and 632 metabolites were obtained from transcriptome and metabolome analyses, and most of the physiological metabolism in drought-treated I. difengpi plants recovered after rehydration. There were more upregulated genes than downregulated genes under drought and rehydration treatments, and rehydration treatment induced stable expression of 65.25% of genes, indicating that rehydration alleviated drought stress to some extent. Drought and rehydration treatment generated flavonoids, phenolic acids, flavonols, amino acids and their derivatives, as well as metabolites such as saccharides and alcohols in the leaves of I. difengpi plants, which alleviated the injury caused by excessive reactive oxygen species. The integration of transcriptome and metabolome analyses showed that, under drought stress, I. difengpi increased glutathione, flavonoids, polyamines, soluble sugars and amino acids, contributing to cell osmotic potential and antioxidant activity. The results show that the high drought tolerance and recovery after rehydration are the reasons for the normal growth of I. difengpi in karst mountain areas.

Uncovering the wide protective responses in Coffea spp. leaves to single and superimposed exposure of warming and severe water deficit

Climate changes boosted the frequency and severity of drought and heat events, with aggravated when these stresses occur simultaneously, turning crucial to unveil the plant response mechanisms to such harsh conditions. Therefore, plant responses/resilience to single and combined exposure to severe water deficit (SWD) and heat were assessed in two cultivars of the main coffee-producing species: Coffea arabica cv. Icatu and C. canephora cv. Conilon Clone 153 (CL153). Well-watered plants (WW) were exposed to SWD under an adequate temperature of 25/20°C (day/night), and thereafter submitted to a gradual increase up to 42/30°C, and a 14-d recovery period (Rec14). Greater protective response was found to single SWD than to single 37/28°C and/or 42/30°C (except for HSP70) in both cultivars, but CL153-SWD plants showed the larger variations of leaf thermal imaging crop water stress index (CWSI, 85% rise at 37/28°C) and stomatal conductance index (IG, 66% decline at 25/20°C). Both cultivars revealed great resilience to SWD and/or 37/28°C, but a tolerance limit was surpassed at 42/30°C. Under stress combination, Icatu usually displayed lower impacts on membrane permeability, and PSII function, likely associated with various responses, usually mostly driven by drought (but often kept or even strengthened under SWD and 42/30°C). These included the photoprotective zeaxanthin and lutein, antioxidant enzymes (superoxide dismutase, Cu,Zn-SOD; ascorbate peroxidase, APX), HSP70, arabinose and mannitol (involving de novo sugar synthesis), contributing to constrain lipoperoxidation. Also, only Icatu showed a strong reinforcement of glutathione reductase activity under stress combination. In general, the activities of antioxidative enzymes declined at 42/30°C (except Cu,Zn-SOD in Icatu and CAT in CL153), but HSP70 and raffinose were maintained higher in Icatu, whereas mannitol and arabinose markedly increased in CL153. Overall, a great leaf plasticity was found, especially in Icatu that revealed greater responsiveness of coordinated protection under all experimental conditions, justifying low PIChr and absence of lipoperoxidation increase at 42/30°C. Despite a clear recovery by Rec14, some aftereffects persisted especially in SWD plants (e.g., membranes), relevant in terms of repeated stress exposure and full plant recovery to stresses.

Foliar application of ascorbic acid enhances growth and yield of lettuce (Lactuca sativa) under saline conditions by improving antioxidant defence mechanism

Lettuce (Lactuca sativa L.) production is low because of different environmental stresses. Salt stress significantly reduces lettuce growth and yield. Foliar application of ascorbic acid is considered as a possible way to mitigate the adverse salinity effects on plants. This current study investigated the effect of foliar spray of ascorbic acid (control, 100, 200, 300 and 400mg/L) to mitigate negative effects of salinity (0, 50, 100 and 150mMNaCl) in lettuce plants in 2019 and 2020. Salinity level of 200mMNaCl significantly reduced growth and yield traits; i.e. leaf length and diameter, number of leaves, fresh plant weight, number of roots, root length and root dry weight and these traits increased under foliar application of ascorbic acid concentration of 400mg/L. Two salinity levels (150 and 200mMNaCl)×400mg/L ascorbic acid enhanced superoxide dismutase (SOD) content in lettuce plants. Peroxidase (POD) content increased in 200mMNaCl and 400mg/L ascorbic acid. Catalase (CAT) content increased in 100, 150 and 200mMNaCl and 400mg/L ascorbic acid. Ascorbic acid was significantly greater in 200mMNaCl and 400mg/L ascorbic acid. Phenolic content was the maximum in 200mMNaCl and 300mg/L and 400mg/L ascorbic acid. Titratable acidity was higher in 0, 50, 100, 150 and 200mMNaCl and control of ascorbic acid. We conclude that ascorbic acid had potential to mitigate the adverse effects of salinity by reducing oxidative injury in agricultural crops especially lettuce.

Biochemical dynamics during postharvest: Highlighting the interplay of stress during storage and maturation of fresh produce

The lifecycle of fresh produce involves a sequence of biochemical events during their ontology, and these events are particularly significant for climacteric fruits. A high demand during ripening is observed in these plant products, which is reflected in a high rate of respiration and ethylene production. Increased respiratory demand triggers the activation of secondary pathways such as alternate oxidase, which do not experience critical increases in energy consumption in non-climacteric fruit. In addition, biochemical events produced by external factors lead to compensatory responses in fresh produce to counteract the oxidative stress caused by the former. The dynamics of these responses are accompanied by signaling, where reactive oxygen species play a pivotal role in fresh product cell perception. This review aims to describe the protection mechanisms of fresh produce against environmental challenges and how controlled doses of abiotic stressors can be used to improve quality and prolong their shelf-life through the interaction of stress and defense mechanisms.

Melatonin-regulated heat shock proteins and mitochondrial ATP synthase induce drought tolerance through sustaining ROS homeostasis in H2S-dependent manner

Drought is thought to be one of the major global hazards to crop production. Understanding the role of melatonin (Mel) during plant adaptive responses to drought stress (DS) was the aim of the current investigation. Involvement of hydrogen sulfide (H2S) was also explored in Mel-regulated mechanisms of plants' tolerance to DS. A perusal of the data shows that exposure of tomato plants to DS elevated the activity of mitochondrial enzymes viz. pyruvate dehydrogenase, malate dehydrogenase, and citrate synthase. Whereas the activity of ATP synthase and ATPase was downregulated under stress conditions. Under DS, an increase in the expression level of heat shock proteins (HSPs) and activation level of antioxidant defense system was observed as well. On the other hand, an increase in the activity of NADPH oxidase and glycolate oxidase was observed along with the commencement of oxidative stress and accompanying damage. Application of 30 μM Mel to drought-stressed plants enhanced H2S accumulation and further elevated the activity of mitochondrial enzymes, activation level of the defense system, and expression of HSP17.6 and HSP70. Positive effect of Mel on these attributes was reflected by reduced level of ROS and related damage. However, application of H2S biosynthesis inhibitor DL-propargylglycine reversed the effect of Mel on the said attributes and again the damaging effects of drought were observed even in presence of Mel. This observation led us to conclude that Mel-regulated defense mechanisms operate through endogenous H2S under DS conditions.

Mitigating Salinity Stress in Quinoa (Chenopodium quinoa Willd.) with Biochar and Superabsorber Polymer Amendments

In agriculture, soil amendments are applied to improve soil quality by increasing the water retention capacity and regulating the pH and ion exchange. Our study was carried out to investigate the impact of a commercial biochar (Bc) and a superabsorbent polymer (SAP) on the physiological and biochemical processes and the growth performance of Chenopodium quinoa (variety ICBA-5) when exposed to high salinity. Plants were grown for 25 days under controlled greenhouse conditions in pots filled with a soil mixture with or without 3% Bc or 0.2% SAP by volume before the initiation of 27 days of growth in hypersaline conditions, following the addition of 300 mM NaCl. Without the Bc or soil amendments, multiple negative effects of hypersalinity were detected on photosynthetic CO2 assimilation (Anet minus 70%) and on the production of fresh matter from the whole plant, leaves, stems and roots (respectively, 55, 46, 64 and 66%). Moreover, increased generation of reactive oxygen species (ROS) was indicated by higher levels of MDA (plus 142%), antioxidant activities and high proline levels (plus 311%). In the pots treated with 300 mM NaCl, the amendments Bc or SAP improved the plant growth parameters, including fresh matter production (by 10 and 17%), an increased chlorophyll content by 9 and 13% and Anet in plants (by 98 and 115%). Both amendments (Bc and SAP) resulted in significant salinity mitigation effects, decreasing proline and malondialdehyde (MDA) levels whilst increasing both the activity of enzymatic antioxidants and non-enzymatic antioxidants that reduce the levels of ROS. This study confirms how soil amendments can help to improve plant performance and expand the productive range into saline areas.

Nucleotide Limitation Results in Impaired Photosynthesis, Reduced Growth and Seed Yield Together with Massively Altered Gene Expression

Nucleotide limitation and imbalance is a well-described phenomenon in animal research but understudied in the plant field. A peculiarity of pyrimidine de novo synthesis in plants is the complex subcellular organization. Here, we studied two organellar localized enzymes in the pathway, with chloroplast aspartate transcarbamoylase (ATC) and mitochondrial dihydroorotate dehydrogenase (DHODH). ATC knock-downs were most severely affected, exhibiting low levels of pyrimidine nucleotides, a low energy state, reduced photosynthetic capacity and accumulation of reactive oxygen species. Furthermore, altered leaf morphology and chloroplast ultrastructure were observed in ATC mutants. Although less affected, DHODH knock-down mutants showed impaired seed germination and altered mitochondrial ultrastructure. Thus, DHODH might not only be regulated by respiration but also exert a regulatory function on this process. Transcriptome analysis of an ATC-amiRNA line revealed massive alterations in gene expression with central metabolic pathways being downregulated and stress response and RNA-related pathways being upregulated. In addition, genes involved in central carbon metabolism, intracellular transport and respiration were markedly downregulated in ATC mutants, being most likely responsible for the observed impaired growth. We conclude that impairment of the first committed step in pyrimidine metabolism, catalyzed by ATC, leads to nucleotide limitation and by this has far-reaching consequences on metabolism and gene expression. DHODH might closely interact with mitochondrial respiration, as seen in delayed germination, which is the reason for its localization in this organelle.

Kiwifruit Monodehydroascorbate Reductase 3 Gene Negatively Regulates the Accumulation of Ascorbic Acid in Fruit of Transgenic Tomato Plants

Ascorbic acid is a potent antioxidant and a crucial nutrient for plants and animals. The accumulation of ascorbic acid in plants is controlled by its biosynthesis, recycling, and degradation. Monodehydroascorbate reductase is deeply involved in the ascorbic acid cycle; however, the mechanism of monodehydroascorbate reductase genes in regulating kiwifruit ascorbic acid accumulation remains unclear. Here, we identified seven monodehydroascorbate reductase genes in the genome of kiwifruit (Actinidia eriantha) and they were designated as AeMDHAR1 to AeMDHAR7, following their genome identifiers. We found that the relative expression level of AeMDHAR3 in fruit continued to decline during development. The over-expression of kiwifruit AeMDHAR3 in tomato plants improved monodehydroascorbate reductase activity, and, unexpectedly, ascorbic acid content decreased significantly in the fruit of the transgenic tomato lines. Ascorbate peroxidase activity also increased significantly in the transgenic lines. In addition, a total of 1781 differentially expressed genes were identified via transcriptomic analysis. Three kinds of ontologies were identified, and 106 KEGG pathways were significantly enriched for these differently expressed genes. Expression verification via quantitative real-time PCR analysis confirmed the reliability of the RNA-seq data. Furthermore, APX3, belonging to the ascorbate and aldarate metabolism pathway, was identified as a key candidate gene that may be primarily responsible for the decrease in ascorbic acid concentration in transgenic tomato fruits. The present study provides novel evidence to support the feedback regulation of ascorbic acid accumulation in the fruit of kiwifruit.

A Specific Protective Mechanism Against Chloroplast Photo-Reactive Oxygen Species in Phosphate-Starved Rice Plants

Phosphorus (Pi) starvation prevents a good match between light energy absorption and photosynthetic carbon metabolism, generating photo-reactive oxygen species (photo-ROS) in chloroplasts. Plants have evolved to withstand photo-oxidative stress, but the key regulatory mechanism underlying it remains unclear. In rice (Oryza sativa), DEEP GREEN PANICLE1 (DGP1) is robustly up-regulated in response to Pi deficiency. DGP1 decreases the DNA-binding capacities of the transcriptional activators GLK1/2 on the photosynthetic genes involved in chlorophyll biosynthesis, light harvesting, and electron transport. This Pi-starvation-induced mechanism dampens both electron transport rates through photosystem I and II (ETRI and ETRII) and thus mitigates the electron-excessive stress in mesophyll cells. Meanwhile, DGP1 hijacks glycolytic enzymes GAPC1/2/3, redirecting glucose metabolism toward the pentose phosphate pathway with superfluous NADPH production. Phenotypically, light irradiation induces O2 - production in Pi-starved WT leaves but is observably accelerated in dgp1 mutant and impaired in GAPCsRNAi and glk1glk2 lines. Interestingly, overexpressed DGP1 in rice caused hyposensitivity to ROS-inducers (catechin and methyl viologen), but the dgp1 mutant shows a similar inhibitory phenotype with the WT seedlings. Overall, the DGP1 gene serves as a specific antagonizer against photo-ROS in Pi-starved rice plants, which coordinates light-absorbing and anti-oxidative systems by orchestrating transcriptional and metabolic regulations, respectively.

Integrated transcriptome and proteome analyses unravel a series of early defence responses in Sarcandra glabra against Colletotrichum gloeosporioides

Anthracnose caused by Colletotrichum gloeosporioides critically threatens the growth and commercial cultivation of Sarcandra glabra . However, the defence responses and underlying mechanisms remain unclear. Herein, we aimed to investigate the molecular reprogramming in S. glabra leaves infected with C. gloeosporioides . Leaf tissues at 0, 24 and 48h post-inoculation (hpi) were analysed by combining RNA sequencing and Tandem Mass Tag-based liquid chromatography with tandem mass spectrometry. In total, 18 441 and 25 691 differentially expressed genes were identified at 24 and 48hpi compared to 0hpi (uninoculated control), respectively. In addition, 1240 and 1570 differentially abundant proteins were discovered at 24 and 48hpi compared to 0hpi, respectively. Correlation analysis revealed that transcription and translation levels were highly consistent regarding repeatability and expression. Analyses using databases KEGG and iPATH revealed tricitric acid cycle, glycolysis/gluconeogenesis and phenylpropanoid biosynthesis were induced, whereas photosynthesis and tryptophan were suppressed. Enzymatic activity assay results were consistent with the upregulation of defence-related enzymes including superoxide dismutases, catalases, peroxidases and chitinases. The transcriptome expression results were additionally validated by quantitative real-time polymerase chain reaction analyses. This study provides insights into the molecular reprogramming in S. glabra leaves during infection, which lay a foundation for investigating the mechanisms of host-Colletotrichum interactions and breeding disease-resistant plants.

The comparison of antioxidant properties and nutrigenomic redox-related activities of vitamin C, C-vitamers, and other common ascorbic acid derivatives

The term 'vitamin C' describes a group of compounds with antiscorbutic activity of l-ascorbic acid (AA). Despite AA's omnipresence in plant-derived foods, its derivatives have also been successfully implemented in the food industry as antioxidants, including the D-isomers, which lack vitamin C activity. This study aimed to determine the relationship between redox-related activities for five derivatives of AA using electrochemical, chemical, and biological approaches. Here we report that AA, C-vitamers, and other commonly consumed AA derivatives differ in their redox-related activities. As long as the physiological range of concentrations was maintained, there was no simple relationship between their redox properties and biological activity. Clear distinctions in antioxidant activity were observed mostly at high concentrations, which were strongly correlated with electrochemical and kinetic parameters describing redox-related properties of the studied compounds. Despite obvious similarities in chemical structures and antioxidant activity, we showed that C-vitamers may exhibit different nutrigenomic effects. Together, our findings provide a deeper insight into so far underinvestigated area combining chemical properties with biological activities of commonly applied AA derivatives.

Effects of low nitrogen on seedling growth, photosynthetic characteristics and antioxidant system of rice varieties with different nitrogen efficiencies

Nitrogen plays a significant role in influencing various physiological processes in plants, thereby impacting their ability to withstand abiotic stresses. This study used hydroponics to compare the effects of three nitrogen supply levels (1N, 1/2N and 1/4N) on the antioxidant capacity of rice varieties JJ88 (nitrogen efficient) and XN999 (nitrogen inefficient) with different nitrogen use efficiencies. The results show that compared with the XN999 variety, the JJ88 variety has stronger adaptability to low-nitrogen conditions, which is mainly reflected in the relatively small decrease in dry weight and net photosynthetic rate (Pn); In the early stage of low-nitrogen treatment (0-7 d), the [Formula: see text] production rate, hydrogen peroxide (H2O2) and malondialdehyde (MDA) content of JJ88 variety increased relatively slightly, but the superoxide dismutase (SOD), peroxide The activity of enzyme (POD) and catalase (CAT) increased significantly; After low-nitrogen treatment, the ASA-GSH cycle enzyme activity of JJ88 variety was relatively high, and the dehydroascorbate reductase (DHAR) activity after 14 days of low-nitrogen treatment was higher than that of 1N treatment; The content of reduced ascorbic acid (ASA) in non-enzymatic antioxidants was lower than that of 1N treatment after 14 days of low nitrogen treatment; The contents of oxidized dehydroascorbic acid (DHA) and carotenoids (Car) were higher than those of 1N treatment after 21d and 14d of low nitrogen treatment respectively; The contents of reduced glutathione (GSH), oxidized glutathione (GSSG) and proline (Pro) showed a larger upward trend during the entire low-nitrogen treatment period. In summary, the JJ88 rice variety has a strong ability to regulate oxidative stress and osmotic damage under low nitrogen conditions. It can slow down plant damage by regulating antioxidant enzyme activity and antioxidant content. This provides a basis for achieving nitrogen reduction and efficiency improvement in rice and the breeding of nitrogen-efficient varieties.

Structure and Ecological Function of Fungal Endophytes from Stems of Different Mulberry Cultivars

To explore the microbial community structure and ecological function of mulberry and their potential relationship with the resistance of mulberry, the community structure and function of endophytic fungi in 18 mulberry cultivars were analyzed and predicted by using high-throughput sequencing technology and the FUNGuild database. A total of 352 operational taxonomic units of fungi were observed at a 97% similarity level, representing six phyla of fungi, Fungi_unclassified, Ascomycota, Basidiomycota, Zygomycota, Rozellomycota, and Chytridiomycota. Fungi_unclassified was dominant, and Ascomycota was relatively dominant in all cultivars. At the genus level, Ascomycota_unclassified was dominant, and Ampelomyces was relatively dominant, with a richness in TAIWANCHANGGUOSANG 16.47-8975.69 times that in the other cultivars. Classified Ascomycota_unclassified was 4.75-296.65 times more common in NANYUANSIJI than in the other cultivars. Based on the FUNGuild analysis method, we successfully annotated six nutrient types, namely, pathotroph, pathotroph-saprotroph, pathotroph-saprotroph-symbiotroph, saprotroph, saprotroph-symbiotroph, and symbiotroph, among which saprophytic-symbiotic accounted for the largest proportion and was absolutely dominant in TWC. This research suggests that community composition differs among cultivars and that the diversity and richness of endophytic fungi in resistant cultivars are higher than those in susceptible cultivars. The ecological functions of cultivars with different resistances are quite different.

Ammonium to total nitrogen ratio affects the purslane (Portulaca oleracea L.) growth, nutritional, and antioxidant status

Purslane (Portulaca oleracea L.) is a widespread weed, which is greatly appreciated for its high nutritional value. The present work evaluated the effect of different ammonium/total nitrogen ratios (NH4/Total N: Nr 0.01-0.15) on growth, physiological and biochemical parameters, and nutrient accumulation in different plant parts of hydroponically grown purslane, under two growing seasons, spring and autumn. Young seedlings of purslane were transferred to a Nutrient Film Technique (NFT) system and they were exposed to different Nr levels. The pH and the electrical conductivity of the nutrient solution were kept constant at 5.8 and 2.3 mS cm-1, respectively. After the end of the cultivation periods (19 days for spring and 22 days for autumn), a series of assessments (growth parameters, mineral content in different plant organs, antioxidant status of the plant, etc.) were done. Plant height, leaf number, root fresh weight and plant biomass revealed decreased trends at the higher NH4/total N ratios, especially during the autumn growing season. Total phenols, flavonoids and antioxidant capacity appeared increased at Nr ≤ 0.10 during both seasons (autumn and spring), revealing higher nitrogen accumulation rates and increased water and nutrient use efficiency. Purslane plants grown in Nr 0.05-0.10 revealed a less intense oxidative stress, with decreased lipid peroxidation levels that was the result of the activation of both enzymatic (superoxide dismutase, catalase and peroxidase) and non-enzymatic (ascorbic acid) antioxidant capacity of the plant. Increased Nr resulted in the accumulation of potassium, while calcium and magnesium levels in leaves were decreased. Additionally, the greater water use efficiency was measured for plants grown under Nr 0.01-0.05. Therefore, the recommended ammonium/total nitrogen ratio for purslane production of increased yield, improved nutritional value and efficient use of water and nitrogen sources is to employ Nr of 0.05, while additional care should be addressed during autumn periods as plants are subjected to greater impacts of the Nr ratio.

Desalination brine effects beyond excess salinity: Unravelling specific stress signaling and tolerance responses in the seagrass Posidonia oceanica

Desalination has been proposed as a global strategy for tackling freshwater shortage in the climate change era. However, there is a concern regarding the environmental effects of high salinity brines discharged from desalination plants on benthic communities. In this context, seagrasses such as the Mediterranean endemic and ecologically important Posidonia oceanica have shown high vulnerability to elevated salinities. Most ecotoxicological studies regarding desalination effects are based on salinity increments using artificial sea salts, although it has been postulated that certain additives within the industrial process of desalination may exacerbate a negative impact beyond just the increased salinities of the brine. To assess the potential effect of whole effluent brines on P. oceanica, mesocosm experiments were conducted within 10 days, simulating salinity increment with either artificial sea salts or brines from a desalination plant (at 43 psμ, 6 psμ over the natural 37 psμ). Morphometrical (growth and necrosis), photochemical (PSII chlorophyll a fluorometry), metabolic, such as hydrogen peroxide (H2O2), thiobarbituric reactive substances (TBARS) and ascorbate/dehydroascorbate (ASC/DHA), and molecular (expression of key tolerance genes) responses were analyzed in each different treatment. Although with a still positive leaf growth, associated parameters decreased similarly for both artificial sea salt and brine treatments. Photochemical parameters did not show general patterns, although only P. oceanica under brines demonstrated greater energy release through heat (NPQ). Lipid peroxidation and upregulation of genes related to oxidative stress (GR, MnSOD, and FeSOD) or ion exclusion (SOS3 and AKT2/3) were similarly incremented on both hypersalinity treatments. Conversely, the ASC/DHA ratio was significantly lower, and the expression of SOS1, CAT, and STRK1 was increased under brine influence. This study revealed that although metabolic and photochemical differences occurred under both hypersalinity treatments, growth (the last sign of physiological detriment) was similarly compromised, suggesting that the potential effects of desalination are mainly caused by brine-associated salinities and are not particularly related to other industrial additives.

CysQuant: Simultaneous quantification of cysteine oxidation and protein abundance using data dependent or independent acquisition mass spectrometry

Protein cysteinyl thiols are susceptible to reduction-oxidation reactions that can influence protein function. Accurate quantification of cysteine oxidation is therefore crucial for decoding protein redox regulation. Here, we present CysQuant, a novel approach for simultaneous quantification of cysteine oxidation degrees and protein abundancies. CysQuant involves light/heavy iodoacetamide isotopologues for differential labeling of reduced and reversibly oxidized cysteines analyzed by data-dependent acquisition (DDA) or data-independent acquisition mass spectrometry (DIA-MS). Using plexDIA with in silico predicted spectral libraries, we quantified an average of 18% cysteine oxidation in Arabidopsis thaliana by DIA-MS, including a subset of highly oxidized cysteines forming disulfide bridges in AlphaFold2 predicted structures. Applying CysQuant to Arabidopsis seedlings exposed to excessive light, we successfully quantified the well-established increased reduction of Calvin-Benson cycle enzymes and discovered yet uncharacterized redox-sensitive disulfides in chloroplastic enzymes. Overall, CysQuant is a highly versatile tool for assessing the cysteine modification status that can be widely applied across various mass spectrometry platforms and organisms.

Glutathione and peroxisome redox homeostasis

Despite intensive research on peroxisome biochemistry, the role of glutathione in peroxisomal redox homeostasis has remained a matter of speculation for many years, and only recently has this issue started to be experimentally addressed. Here, we summarize and compare data from several organisms on the peroxisome-glutathione topic. It is clear from this comparison that the repertoire of glutathione-utilizing enzymes in peroxisomes of different organisms varies widely. In addition, the available data suggest that the kinetic connectivity between the cytosolic and peroxisomal pools of glutathione may also be different in different organisms, with some possessing a peroxisomal membrane that is promptly permeable to glutathione whereas in others this may not be the case. However, regardless of the differences, the picture that emerges from all these data is that glutathione is a crucial component of the antioxidative system that operates inside peroxisomes in all organisms.

Ascorbate Peroxidase 2 (APX2) of Chlamydomonas Binds Copper and Modulates the Copper Insertion into Plastocyanin

Recent phylogenetic studies have unveiled a novel class of ascorbate peroxidases called "ascorbate peroxidase-related" (APX-R). These enzymes, found in green photosynthetic eukaryotes, lack the amino acids necessary for ascorbate binding. This study focuses on the sole APX-R from Chlamydomonas reinhardtii referred to as ascorbate peroxidase 2 (APX2). We used immunoblotting to locate APX2 within the chloroplasts and in silico analysis to identify key structural motifs, such as the twin-arginine transport (TAT) motif for lumen translocation and the metal-binding MxxM motif. We also successfully expressed recombinant APX2 in Escherichia coli. Our in vitro results showed that the peroxidase activity of APX2 was detected with guaiacol but not with ascorbate as an electron donor. Furthermore, APX2 can bind both copper and heme, as evidenced by spectroscopic, and fluorescence experiments. These findings suggest a potential interaction between APX2 and plastocyanin, the primary copper-containing enzyme within the thylakoid lumen of the chloroplasts. Predictions from structural models and evidence from 1H-NMR experiments suggest a potential interaction between APX2 and plastocyanin, emphasizing the influence of APX2 on the copper-binding abilities of plastocyanin. In summary, our results propose a significant role for APX2 as a regulator in copper transfer to plastocyanin. This study sheds light on the unique properties of APX-R enzymes and their potential contributions to the complex processes of photosynthesis in green algae.

Algal Bio-Stimulants Enhance Salt Tolerance in Common Bean: Dissecting Morphological, Physiological, and Genetic Mechanisms for Stress Adaptation

Salinity adversely affects the plant's morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3',5'-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

Redox regulation, thioredoxins, and glutaredoxins in retrograde signalling and gene transcription

Integration of reactive oxygen species (ROS)-mediated signal transduction pathways via redox sensors and the thiol-dependent signalling network is of increasing interest in cell biology for their implications in plant growth and productivity. Redox regulation is an important point of control in protein structure, interactions, cellular location, and function, with thioredoxins (TRXs) and glutaredoxins (GRXs) being key players in the maintenance of cellular redox homeostasis. The crosstalk between second messengers, ROS, thiol redox signalling, and redox homeostasis-related genes controls almost every aspect of plant development and stress response. We review the emerging roles of TRXs and GRXs in redox-regulated processes interacting with other cell signalling systems such as organellar retrograde communication and gene expression, especially in plants during their development and under stressful environments. This approach will cast light on the specific role of these proteins as redox signalling components, and their importance in different developmental processes during abiotic stress.

L-Cysteine hydrochloride inhibits Aspergillus flavus growth and AFB1 synthesis by disrupting cell structure and antioxidant system balance

Aflatoxin B1 (AFB1) is the most potent known naturally occurring carcinogen and pose an immense threat to food safety and human health. L-Cysteine hydrochloride (L-CH) is a food additive often used as a fruit and vegetable preservative and also to approved bread consistency. In this study, we investigated the effects and mechanisms of L-CH as an antimicrobial on the growth of Aspergillus flavus (A. flavus) and AFB1 biosynthesis. L-CH significantly inhibited A. flavus mycelial growth, affected mycelial morphology and AFB1 synthesis. Furthermore, L-CH induced glutathione (GSH) synthesis which scavenged intracellular reactive oxygen species (ROS). RNA-Seq indicated that L-CH inhibited hyphal branching, and spore and sclerotia formation by controlling cell wall and spore development-related genes. Activation of the GSH metabolic pathway eliminated intracellular ROS, leading to hyphal dwarfing. L-CH treatment downregulated most of the Aflatoxin (AF) cluster genes and aflS, aflR, AFLA_091090 transcription factors. This study provides new insights into the molecular mechanism of L-CH control of A. flavus and AFB1 foundation. We believe that L-CH could be used as a food additive to control AFB1 in foods and also in the environment.

Alsherif E, Magdy Korany S, Hassan AHA, AbdElgawad H. Potassium Nitrate and Ascorbic Acid Priming Improved Tissue Chemical Composition and Antioxidant and Antimicrobial Activities of Linseed (Linum usitatissimum L.) Sprouts

Potassium nitrate (KNO3) and ascorbic acid (AsA) priming can effectively boost biomass accumulation and nutritional value of plants; nevertheless, few studies investigated their effects on seed sprouting. Thus, we aimed to explore the effects of KNO3 and AsA priming on linseed (Linum usitatissimum L.) sprout growth and assess the changes in bioactive compound levels, which provide valuable insights into the potential benefits of these priming treatments on sprout quality and nutritional value. To this end, germination, biomass accumulation, photosynthetic pigments, primary and secondary metabolites, and mineral profiles in the primed sprouts were evaluated. Moreover, to assess the impact on biological value, we determined the antioxidant and antimicrobial activities of the treated sprout extract. A marked enhancement was observed in germination and pigment levels of KNO3- and AsA-primed sprouts. These increases were in line with induced primary metabolites (e.g., carbohydrate and amino acid contents), particularly under KNO3 treatment. There was also an increase in amino acid metabolism (e.g., increased GS, GDH, and GOGAT enzyme activities), nitrogen level, and nitrate reductase (NR) activity. The linseed sprouts primed with AsA exhibited strong antioxidant and antibacterial activities. Consistently, high levels of polyphenols, flavonoids, total AsA, and tocopherols, as well as improved activity of antioxidant enzymes [peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD)], were recorded. This study proposes KNO3 and AsA priming as an innovative approach to improving the nutritional and health-promoting properties of linseed sprouts. This knowledge will contribute to a better understanding of the biochemical processes involved in improving the nutritional quality and functional benefits of linseed sprouts.

Titanium dioxide nanoparticles require K+ and hydrogen sulfide to regulate nitrogen and carbohydrate metabolism during adaptive response to drought and nickel stress in cucumber

Crop plants face severe yield losses worldwide owing to their exposure to multiple abiotic stresses. The study described here, was conducted to comprehend the response of cucumber seedlings to drought (induced by 15% w/v polyethylene glycol 8000; PEG) and nickel (Ni) stress in presence or absence of titanium dioxide nanoparticle (nTiO2). In addition, it was also investigated how nitrogen (N) and carbohydrate metabolism, as well as the defense system, are affected by endogenous potassium (K+) and hydrogen sulfide (H2S). Cucumber seedlings were subjected to Ni stress and drought, which led to oxidative stress and triggered the defense system. Under the stress, N and carbohydrate metabolism were differentially affected. Supplementation of the stressed seedlings with nTiO2 (15 mg L-1) enhanced the activity of antioxidant enzymes, ascorbate-glutathione (AsA-GSH) system and elevated N and carbohydrates metabolism. Application of nTiO2 also enhanced the accumulation of phytochelatins and activity of the enzymes of glyoxalase system that provided additional protection against the metal and toxic methylglyoxal. Osmotic stress brought on by PEG and Ni, was countered by the increase of proline and carbohydrates levels, which helped the seedlings keep their optimal level of hydration. Application nTiO2 improved the biosynthesis of H2S and K+ retention through regulating Cys biosynthesis and H+-ATPase activity, respectively. Observed outcomes lead to the conclusion that nTiO2 maintains redox homeostasis, and normal functioning of N and carbohydrates metabolism that resulted in the protection of cucumber seedlings against drought and Ni stress. Use of 20 mM tetraethylammonium chloride (K+- channel blocker), 500 μM sodium orthovanadate (PM H+-ATPase inhibitor), and 1 mM hypotaurine (H2S scavenger) demonstrate that endogenous K+ and H2S were crucial for the nTiO2-induced modulation of plants' adaptive responses to the imposed stress.

Enzyme-based kinetic modelling of ASC-GSH cycle during tomato fruit development reveals the importance of reducing power and ROS availability

The ascorbate-glutathione (ASC-GSH) cycle is at the heart of redox metabolism, linking the major redox buffers with central metabolism through the processing of reactive oxygen species (ROS) and pyridine nucleotide metabolism. Tomato fruit development is underpinned by changes in redox buffer contents and their associated enzyme capacities, but interactions between them remain unclear. Based on quantitative data obtained for the core redox metabolism, we built an enzyme-based kinetic model to calculate redox metabolite concentrations with their corresponding fluxes and control coefficients. Dynamic and associated regulations of the ASC-GSH cycle throughout the whole fruit development were analysed and pointed to a sequential metabolic control of redox fluxes by ASC synthesis, NAD(P)H and ROS availability depending on the developmental phase. Furthermore, we highlighted that monodehydroascorbate reductase and the availability of reducing power were found to be the main regulators of the redox state of ASC and GSH during fruit growth under optimal conditions. Our kinetic modelling approach indicated that tomato fruit development displayed growth phase-dependent redox metabolism linked with central metabolism via pyridine nucleotides and H2 O2 availability, while providing a new tool to the scientific community to investigate redox metabolism in fruits.

Transcriptomic and genetic approaches reveal that low-light-induced disease susceptibility is related to cellular oxidative stress in tomato

The impact of low light intensities on plant disease outbreaks represents a major challenge for global crop security, as it frequently results in significant yield losses. However, the underlying mechanisms of the effect of low light on plant defense are still poorly understood. Here, using an RNA-seq approach, we found that the susceptibility of tomato to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) under low light was associated with the oxidation-reduction process. Low light conditions exacerbated Pst DC3000-induced reactive oxygen species (ROS) accumulation and protein oxidation. Analysis of gene expression and enzyme activity of ascorbate peroxidase 2 (APX2) and other antioxidant enzymes revealed that these defense responses were significantly induced by Pst DC3000 inoculation under normal light, whereas these genes and their associated enzyme activities were not responsive to pathogen inoculation under low light. Additionally, the reduced ascorbate to dehydroascorbate (AsA/DHA) ratio was lower under low light compared with normal light conditions upon Pst DC3000 inoculation. Furthermore, the apx2 mutants generated by a CRISPR-Cas9 gene-editing approach were more susceptible to Pst DC3000 under low light conditions. Notably, this increased susceptibility could be significantly reduced by exogenous AsA treatment. Collectively, our findings suggest that low-light-induced disease susceptibility is associated with increased cellular oxidative stress in tomato plants. This study sheds light on the intricate relationship between light conditions, oxidative stress, and plant defense responses, and may pave the way for improved crop protection strategies in low light environments.

Electron Transport in Chloroplasts: Regulation and Alternative Pathways of Electron Transfer

This work represents an overview of electron transport regulation in chloroplasts as considered in the context of structure-function organization of photosynthetic apparatus in plants. Main focus of the article is on bifurcated oxidation of plastoquinol by the cytochrome b6f complex, which represents the rate-limiting step of electron transfer between photosystems II and I. Electron transport along the chains of non-cyclic, cyclic, and pseudocyclic electron flow, their relationships to generation of the trans-thylakoid difference in electrochemical potentials of protons in chloroplasts, and pH-dependent mechanisms of regulation of the cytochrome b6f complex are considered. Redox reactions with participation of molecular oxygen and ascorbate, alternative mediators of electron transport in chloroplasts, have also been discussed.

Effect of Eco-Friendly Application of Bee Honey Solution on Yield, Physio-Chemical, Antioxidants, and Enzyme Gene Expressions in Excessive Nitrogen-Stressed Common Bean (Phaseolus vulgaris L.) Plants

Excessive use of nitrogen (N) pollutes the environment and causes greenhouse gas emissions; however, the application of eco-friendly plant biostimulators (BSs) can overcome these issues. Therefore, this paper aimed to explore the role of diluted bee honey solution (DHS) in attenuating the adverse impacts of N toxicity on Phaseolus vulgaris growth, yield quality, physio-chemical properties, and defense systems. For this purpose, the soil was fertilized with 100, 125, and 150% of the recommended N dose (RND), and the plants were sprayed with 1.5% DHS. Trials were arranged in a two-factor split-plot design (N levels occupied main plots × DH- occupied subplots). Excess N (150% RND) caused a significant decline in plant growth, yield quality, photosynthesis, and antioxidants, while significantly increasing oxidants and oxidative damage [hydrogen peroxide (H2O2), superoxide (O2•-), nitrate, electrolyte leakage (EL), and malondialdehyde (MDA) levels]. However, DHS significantly improved antioxidant activities (glutathione and nitrate reductases, catalase, ascorbate peroxidase, superoxide dismutase, proline, ascorbate, α-tocopherol, and glutathione) and osmoregulatory levels (soluble protein, glycine betaine, and soluble sugars). Enzyme gene expressions showed the same trend as enzyme activities. Additionally, H2O2, O2•-, EL, MDA, and nitrate levels were significantly declined, reflecting enhanced growth, yield, fruit quality, and photosynthetic efficiency. The results demonstrate that DHS can be used as an eco-friendly approach to overcome the harmful impacts of N toxicity on P. vulgaris plants.

GhIMP10D, an inositol monophosphates family gene, enhances ascorbic acid and antioxidant enzyme activities to confer alkaline tolerance in Gossypium hirsutum L

BACKGROUND

Inositol monophosphates (IMP) are key enzymes in the ascorbic acid (AsA) synthesis pathways, which play vital roles in regulating plant growth and development and stresses tolerance. To date, no comprehensive analysis of the expression profile of IMP genes and their functions under abiotic stress in cotton has been reported.

RESULTS

In this study, the genetic characteristics, phylogenetic evolution, cis-acting elements and expression patterns of IMP gene family in cotton were systematically analyzed. A total of 28, 27, 13 and 13 IMP genes were identified in Gossypium hirsutum (G. hirsutum), Gossypium barbadense (G. barbadense), Gossypium arboreum (G. arboreum), and Gossypium raimondii (G. raimondii), respectively. Phylogenetic analysis showed that IMP family genes could cluster into 3 clades. Structure analysis of genes showed that GhIMP genes from the same subgroup had similar genetic structure and exon number. And most GhIMP family members contained hormone-related elements (abscisic acid response element, MeJA response element, gibberellin response element) and stress-related elements (low temperature response element, defense and stress response element, wound response element). After exogenous application of abscisic acid (ABA), some GhIMP genes containing ABA response elements positively responded to alkaline stress, indicating that ABA response elements played an important role in response to alkaline stress. qRT-PCR showed that most of GhIMP genes responded positively to alkaline stress, and GhIMP10D significantly upregulated under alkaline stress, with the highest up-regulated expression level. Virus-induced gene silencing (VIGS) experiment showed that compared with 156 plants, MDA content of pYL156:GhIMP10D plants increased significantly, while POD, SOD, chlorophyII and AsA content decreased significantly.

CONCLUSIONS

This study provides a thorough overview of the IMP gene family and presents a new perspective on the evolution of this gene family. In particular, some IMP genes may be involved in alkaline stress tolerance regulation, and GhIMP10D showed high expression levels in leaves, stems and roots under alkaline stress, and preliminary functional verification of GhIMP10D gene suggested that it may regulate tolerance to alkaline stress by regulating the activity of antioxidant enzymes and the content of AsA. This study contributes to the subsequent broader discussion of the structure and alkaline resistance of IMP genes in cotton.

Interrogating bioinspired ESIPT/PCET-based Ir(iii)-complexes as organelle-targeted phototherapeutics: a redox-catalysis under hypoxia to evoke synergistic ferroptosis/apoptosis

Installing proton-coupled electron transfer (PCET) in Ir-complexes is indeed a newly explored phenomenon, offering high quantum efficiency and tunable photophysics; however, the prospects for its application in various fields, including interrogating biological systems, are quite open and exciting. Herein, we developed various organelle-targeted Ir(iii)-complexes by leveraging the photoinduced PCET process to see the opportunities in phototherapeutic application and investigate the underlying mechanisms of action (MOAs). We diversified the ligands' nature and also incorporated a H-bonded benzimidazole-phenol (BIP) moiety with π-conjugated ancillary ligands in Ir(iii) to study the excited-state intramolecular proton transfer (ESIPT) process for tuning dual emission bands and to tempt excited-state PCET. These visible or two-photon-NIR light activatable Ir-catalysts generate reactive hydroxyl radicals (˙OH) and simultaneously oxidize electron donating biomolecules (1,4-dihydronicotinamide adenine dinucleotide or glutathione) to disrupt redox homeostasis, downregulate the GPX4 enzyme, and amplify oxidative stress and lipid peroxide (LPO) accumulation. Our homogeneous photocatalytic platform efficiently triggers organelle dysfunction mediated by a Fenton-like pathway with spatiotemporal control upon illumination to evoke ferroptosis poised with the synergistic action of apoptosis in a hypoxic environment leading to cell death. Ir2 is the most efficient photochemotherapy agent among others, which provided profound cytophototoxicity to 4T1 and MCF-7 cancerous cells and inhibited solid hypoxic tumor growth in vitro and in vivo.

Jasmonic Acid Effect on Cucumis sativus L. Growth Is Related to Inhibition of Plasma Membrane Proton Pump and the Uptake and Assimilation of Nitrates

When plants are exposed to environmental stress, their growth is inhibited. Under such conditions, controlled inhibition of growth is beneficial for plant survival. Jasmonic acid (JA) is a well-known phytohormone that limits plant growth, which has been confirmed in several species. However, its role in cucumber seedlings has not yet been comprehensively investigated. For this reason, we aimed to determine the involvement of JA in the regulation of proteins crucial for growth including plasma membrane proton pump (PM H+-ATPase), PM nitrate transporters, and nitrate reductase (NR). Treatment of cucumber seedlings with JA not only limited their growth but also increased the H2O2 content in their roots. The main sources of ROS generated for signalling purposes are PM NADPH oxidase (RBOH) and superoxide dismutase (SOD). Exposure of seedlings to JA induced the expression of some CsRBOH and SOD encoding genes, suggesting that ROS signalling can be activated by JA. As a consequence of JA exposure, the activity of all analysed proteins was inhibited and the expression of their genes was modified. The results indicate that reduction of PM H+-ATPase activity and the related decrease in nitrate uptake and assimilation are responsible for the root growth retardation of JA-treated plants.

The conditional mitochondrial protein complexome in the Arabidopsis thaliana root and shoot

Protein complexes are important for almost all biological processes. Hence, to fully understand how cells work, it is also necessary to characterize protein complexes and their dynamics in response to various cellular cues. Moreover, the dynamics of protein interaction play crucial roles in regulating the (dis)association of protein complexes and, in turn, regulating biological processes such as metabolism. Here, mitochondrial protein complexes were investigated by blue native PAGE and size-exclusion chromatography under conditions of oxidative stress in order to monitor their dynamic (dis)associations. Rearrangements of enzyme interactions and changes in protein complex abundance were observed in response to oxidative stress induced by menadione treatment. These included changes in enzymatic protein complexes involving γ-amino butyric acid transaminase (GABA-T), Δ-ornithine aminotransferase (Δ-OAT), or proline dehydrogenase 1 (POX1) that are expected to affect proline metabolism. Menadione treatment also affected interactions between several enzymes of the tricarboxylic acid (TCA) cycle and the abundance of complexes of the oxidative phosphorylation pathway. In addition, we compared the mitochondrial complexes of roots and shoots. Considerable differences between the two tissues were observed in the mitochondrial import/export apparatus, the formation of super-complexes in the oxidative phosphorylation pathway, and specific interactions between enzymes of the TCA cycle that we postulate may be related to the metabolic/energetic requirements of roots and shoots.

Multi-omics data provide insight into the adaptation of the glasshouse plant Rheum nobile to the alpine subnival zone

Subnival glasshouse plants provide a text-book example of high-altitude adaptation with reproductive organs enclosed in specialized semi-translucent bracts, monocarpic reproduction and continuous survival under stress. Here, we present genomic, transcriptomic and metabolomic analyses for one such plant, the Noble rhubarb (Rheum nobile). Comparative genomic analyses show that an expanded number of genes and retained genes from two recent whole-genome duplication events are both relevant to subnival adaptation of this species. Most photosynthesis genes are downregulated within bracts compared to within leaves, and indeed bracts exhibit a sharp reduction in photosynthetic pigments, indicating that the bracts no longer perform photosynthesis. Contrastingly, genes related to flavonol synthesis are upregulated, providing enhanced defense against UV irradiation damage. Additionally, anatomically abnormal mesophyll combined with the downregulation of genes related to mesophyll differentiation in bracts illustrates the innovation and specification of the glass-like bracts. We further detect substantial accumulation of antifreeze proteins (e.g. AFPs, LEAs) and various metabolites (e.g. Proline, Protective sugars, procyanidins) in over-wintering roots. These findings provide new insights into subnival adaptation and the evolution of glasshouse alpine plants.

Selenate triggers diverse oxidative responses in Astragalus species with diverse selenium tolerance and hyperaccumulation capacity

Selenium (Se) hyperaccumulators are capable of uptake and tolerate high Se dosages. Excess Se-induced oxidative responses were compared in Astragalus bisulcatus and Astragalus cicer. Plants were grown on media supplemented with 0, 25 or 75 μM selenate for 14 days. Both A. bisulcatus and A. cicer accumulated >2000 μg/g dry weight Se to the shoot but the translocation factors of A. cicer were below 1 suggesting its non hyperaccumulator nature. A. cicer showed Se sensitivity indicated by reduced seedling fresh weight, root growth and root apical meristem viability, altered element homeostasis in the presence of Se. In Se-exposed A. bisulcatus, less toxic organic Se forms (mainly MetSeCys, γ-Glu-MetSeCys, and a selenosugar) dominated, while these were absent from A. cicer suggesting that the majority of the accumulated Se may be present as inorganic forms. The glutathione-dependent processes were more affected, while ascorbate levels were not notably influenced by Se in either species. Exogenous Se triggered more intense accumulation of malondialdehyde in the sensitive A. cicer compared with the tolerant A. bisulcatus. The extent of protein carbonylation in the roots of the 75 μM Se-exposed A. cicer exceeded that of A. bisulcatus indicating a correlation between selenate sensitivity and the degree of protein carbonylation. Overall, our results reveal connection between oxidative processes and Se sensitivity/tolerance/hyperaccumulation and contribute to the understanding of the molecular responses to excess Se.

Coated Hematite Nanoparticles Alleviate Iron Deficiency in Cucumber in Acidic Nutrient Solution and as Foliar Spray

Micronutrient iron (Fe) deficiency poses a widespread agricultural challenge with global implications. Fe deficiency affects plant growth and immune function, leading to reduced yields and contributing to the global "hidden hunger." While conventional Fe-based fertilizers are available, their efficacy is limited under certain conditions. Most recently, nanofertilizers have been shown as promising alternatives to conventional fertilizers. In this study, three nanohematite/nanoferrihydrite preparations (NHs) with different coatings were applied through the roots and shoots to Fe-deficient cucumber plants. To enhance Fe mobilization to leaves during foliar treatment, the plants were pre-treated with various acids (citric acid, ascorbic acid, and glycine) at a concentration of 0.5 mM. Multiple physiological parameters were examined, revealing that both root and foliar treatments resulted in improved chlorophyll content, biomass, photosynthetic parameters, and reduced ferric chelate reductase activity. The plants also significantly accumulated Fe in their developing leaves and its distribution after NHs treatment, detected by X-ray fluorescence mapping, implied long-distance mobilization in their veins. These findings suggest that the applied NHs effectively mitigated Fe deficiency in cucumber plants through both modes of application, highlighting their potential as nanofertilizers on a larger scale.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

How do barley plants with impaired photosynthetic light acclimation survive under high-light stress?

MAIN CONCLUSION

WHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione. Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley (Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α-tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.

A chromosome-scale Rhubarb (Rheum tanguticum) genome assembly provides insights into the evolution of anthraquinone biosynthesis

Rhubarb is the collective name for various perennial plants from the genus Rheum L. and the Polygonaceae family. They are one of the most ancient, commonly used, and important herbs in traditional Chinese medicine. Rhubarb is a major source of anthraquinones, but how they are synthesized remains largely unknown. Here, we generate a genome sequence assembly of one important medicinal rhubarb R. tanguticum at the chromosome level, with 2.76 Gb assembled into 11 chromosomes. The genome is shaped by two recent whole-genome duplication events and recent bursts of retrotransposons. Metabolic analyses show that the major anthraquinones are mainly synthesized in its roots. Transcriptomic analysis reveals a co-expression module with a high correlation to anthraquinone biosynthesis that includes key chalcone synthase genes. One CHS, four CYP450 and two BGL genes involved in secondary metabolism show significantly upregulated expression levels in roots compared with other tissues and clustered in the co-expression module, which implies that they may also act as candidate genes for anthraquinone biosynthesis. This study provides valuable insights into the genetic bases of anthraquinone biosynthesis that will facilitate improved breeding practices and agronomic properties for rhubarb in the future.

Methane formation driven by light and heat prior to the origin of life and beyond

Methane is a potent greenhouse gas, which likely enabled the evolution of life by keeping the early Earth warm. Here, we demonstrate routes towards abiotic methane and ethane formation under early-earth conditions from methylated sulfur and nitrogen compounds with prebiotic origin. These compounds are demethylated in Fenton reactions governed by ferrous iron and reactive oxygen species (ROS) produced by light and heat in aqueous environments. After the emergence of life, this phenomenon would have greatly intensified in the anoxic Archean by providing methylated sulfur and nitrogen substrates. This ROS-driven Fenton chemistry can occur delocalized from serpentinization across Earth's humid realm and thereby substantially differs from previously suggested methane formation routes that are spatially restricted. Here, we report that Fenton reactions driven by light and heat release methane and ethane and might have shaped the chemical evolution of the atmosphere prior to the origin of life and beyond.