Ascorbate-glutathione cycle of mitochondria in osmoprimed soybean cotyledons in response to imbibitional chilling injury

Effects of OsAOX1a Deficiency on Mitochondrial Metabolism at Critical Node of Seed Viability in Rice

Mitochondrial alternative oxidase 1a (AOX1a) plays an extremely important role in the critical node of seed viability during storage. However, the regulatory mechanism is still poorly understood. The aim of this study was to identify the regulatory mechanisms by comparing OsAOX1a-RNAi and wild-type (WT) rice seed during artificial aging treatment. Weight gain and time for the seed germination percentage decreased to 50% (P50) in OsAOX1a-RNAi rice seed, indicating possible impairment in seed development and storability. Compared to WT seeds at 100%, 90%, 80%, and 70% germination, the NADH- and succinate-dependent O₂ consumption, the activity of mitochondrial malate dehydrogenase, and ATP contents all decreased in the OsAOX1a-RNAi seeds, indicating that mitochondrial status in the OsAOX1a-RNAi seeds after imbibition was weaker than in the WT seeds. In addition, the reduction in the abundance of Complex I subunits showed that the capacity of the mitochondrial electron transfer chain was significantly inhibited in the OsAOX1a-RNAi seeds at the critical node of seed viability. The results indicate that ATP production was impaired in the OsAOX1a-RNAi seeds during aging. Therefore, we conclude that mitochondrial metabolism and alternative pathways were severely inhibited in the OsAOX1a-RNAi seeds at critical node of viability, which could accelerate the collapse of seed viability. The precise regulatory mechanism of the alternative pathway at the critical node of viability needs to be further analyzed. This finding might provide the basis for developing monitoring and warning indicators when seed viability declines to the critical node during storage.

Seed priming can enhance and retain stress tolerance in ensuing generations by inducing epigenetic changes and trans-generational memory

The significance of priming in enhancing abiotic stress tolerance is well-established in several important crops. Priming positively impacts plant growth and improves stress tolerance at multiple developmental stages, and seed priming is one of the most used methods. Seed priming influences the pre-germinative metabolism that ensures proper germination, early seedling establishment, enhanced stress tolerance and yield, even under unfavourable environmental conditions. Seed priming involves pre-exposure of seeds to mild stress, and this pre-treatment induces specific changes at the physiological and molecular levels. Interestingly, priming can improve the efficiency of the DNA repair mechanism, along with activation of specific signalling proteins and transcription factors for rapid and efficient stress tolerance. Notably, such acquired stress tolerance may be retained for longer duration, namely, later developmental stages or even subsequent generations. Epigenetic and chromatin-based mechanisms such as DNA methylation, histone modifications, and nucleosome positioning are some of the key molecular changes involved in priming/stress memory. Further, the retention of induced epigenetic changes may influence the priming-induced trans-generational stress memory. This review discusses known and plausible seed priming-induced molecular mechanisms that govern germination and stress memory within and across generations, highlighting their role in regulating the plant response to abiotic stresses. Understanding the molecular mechanism for activation of stress-responsive genes and the epigenetic changes resulting from seed priming will help to improve the resiliency of the crops for enhanced productivity under extreme environments.

Effect of Melatonin on Fruit Quality via Decay Inhibition and Enhancement of Antioxidative Enzyme Activities and Genes Expression of Two Mango Cultivars during Cold Storage

The postharvest deterioration of mango fruits is a critical issue limiting mango storage and preservation due to its climacteric nature. This study evaluated the storage behavior of two mango cultivars and their response to exogenous melatonin (MT, 1000 μmol L⁻¹) treatment in attenuating fruit decay and enhancing fruits’ physiological and metabolic processes and gene relative expression subjected to cold storage. MT treatment in both mango cultivars significantly delayed weight loss, firmness, respiration rate, and decay incidence. However, MT did not influence the TSS, TA, and TSS:TA ratio regardless of the cultivar. Moreover, MT inhibited the decrease in total phenol and flavonoid content and AsA content while delaying the increase in the MDA content of mango during storage in both cultivars. In addition, MT dramatically inhibited the enzyme activity of PPO. In contrast, an increase in the activities of antioxidant enzymes (SOD and APX) and PAL and their genes’ relative expression was noticed in MT-treated fruits versus control in both cultivars. However, MT treatment was cultivar dependent in most parameters under study. These results demonstrated that MT treatment could be an essential postharvest treatment in minimizing decay, maintaining fruit quality, and extending mango fruits’ postharvest shelf life by enhancing the physiological and metabolic processes during cold storage.

Melatonin-mediated postharvest quality and antioxidant properties of fresh fruits: A comprehensive meta-analysis

At postharvest, fruits have a short shelf life. Recently, there has been much literature on the effects of melatonin on the postharvest quality of horticultural crops. However, reports of various findings comprise mixed claims and product-specific conclusions. Therefore, a meta-analysis systematically dissects the comprehensive effect on several fruits. In this meta-analysis, standard mean difference (SMD) was adopted using a random-effect model. The study used 36 articles and isolated 24 indicator parameters of postharvest quality and antioxidant properties based on the inclusion criteria. As exhibited in the forest plot, melatonin reduced chilling injury, weight loss, respiration rate, and ethylene content (SMD -0.90, 95% CI [-1.14, -0.65]; I²  = 81%; p < .00001). Similarly, the application of melatonin significantly suppressed electrolyte leakage, malondialdehyde (MDA), hydrogen peroxide, superoxide anion, lipoxygenase, and polyphenol oxidase (SMD -0.89, 95% CI [-1.09, -0.69]; I²  = 70%; p < .00001). In addition, exogenous melatonin application induced endogenous melatonin content, phenolic content, and flavonoid and anthocyanin contents (SMD 1.15, 95% CI [0.91, 1.39]; I²  = 71%; p = .01). Moreover, melatonin treatment enhanced antioxidant activities (catalase, superoxide dismutase, peroxidase, ascorbate peroxidase, and phenylalanine ammonia-lyse) (SMD 1.37, 95% CI [1.03, 1.71]; I²  = 86%; p < .00001). Thus, in the whole study, the overall effect was significantly high in treated fruit (p < .0001), and the overall heterogeneity was above (I² ) > 70%. In addition, the funnel plot showed symmetry in the most selected studies. To sum up, the result gives a further understanding of melatonin's capabilities in reducing postharvest losses and maintaining the quality of fresh fruits.

Influence of exogenous ascorbic acid and glutathione priming on mitochondrial structural and functional systems to alleviate aging damage in oat seeds

BACKGROUND

Loss of vigor caused by seed aging adversely affects agricultural production under natural conditions. However, priming is an economical and effective method for improving the vigor of aged seeds. The objective of this study was to test the effectiveness of exogenous ascorbic acid (ASC) and glutathione (GSH) priming in the repairing of aged oat (Avena sativa) seeds, and to test the hypothesis that structural and functional systems in mitochondria were involved in this process.

RESULTS

Oat seeds were artificially aged for 20 days at 45 °C, and were primed with solutions (1 mmol L^- 1) of ASC, GSH, or ASC + GSH at 20 °C for 0.5 h before or after their aging. Seed germination, antioxidant enzymes in the ASC-GSH cycle, cytochrome c oxidase (COX) and mitochondrial malate dehydrogenase (MDH) activities, and the mitochondrial ultrastructures of the embryonic root cells were markedly improved in aged oat seeds through post-priming with ASC, GSH, or ASC + GSH, while their malondialdehyde and H₂O₂ contents decreased significantly (P < 0.05).

CONCLUSION

Our results suggested that priming with ASC, GSH, or ASC + GSH after aging could effectively alleviate aging damage in oat seeds, and that the role of ASC was more effective than GSH, but positive effects of post-priming with ASC and GSH were not superior to post-priming with ASC in repairing aging damage of aged oat seeds. However, pre-priming with ASC, GSH, or ASC + GSH was not effective in oat seeds, suggesting that pre-priming with ASC, GSH, or ASC + GSH could not inhibit the occurrence of aging damage in oat seeds.

PtomtAPX, a mitochondrial ascorbate peroxidase, plays an important role in maintaining the redox balance of Populus tomentosa Carr

Plant mitochondria are important energy-producing structure and ROS are generated as byproducts. APX is one enzyme of the AsA-GSH cycle to reduces H₂O₂ to water. We identified both PtomtAPX and PtosAPX are located in mitochondria of Populus tomentosa Carr. PtomtAPX is specifically targeted to mitochondria, while PtosAPX is dual targeted to both chloroplast and mitochondria. The expression of PtomtAPX in mitochondria was 60-fold that of PtosAPX by ELISA and qPCR analysis. Under high light stress, the expression levels of PtosAPX increased, while that of PtomtAPX only slightly changed. Compared to the WT, the antisense transgenic PtomtAPX cell lines showed slowed growth, smaller cells impaired mitochondria in MS medium under normal growth. RNA-seq results showed 3121 genes significantly altered expression in the antisense cells, and most of them are important for mitochondrial function, particularly in oxidative phosphorylation. Our findings demonstrates a mitochondrial location for one APX isoform, and provide valuable insight into the mechanism which ROS balance is modulated by AsA-GSH cycle in mitochondria.

Plant subcellular proteomics: Application for exploring optimal cell function in soybean

Plants have evolved complicated responses to developmental changes and stressful environmental conditions. Subcellular proteomics has the potential to elucidate localized cellular responses and investigate communications among subcellular compartments during plant development and in response to biotic and abiotic stresses. Soybean, which is a valuable legume crop rich in protein and vegetable oil, can grow in several climatic zones; however, the growth and yield of soybean are markedly decreased under stresses. To date, numerous proteomic studies have been performed in soybean to examine the specific protein profiles of cell wall, plasma membrane, nucleus, mitochondrion, chloroplast, and endoplasmic reticulum. In this review, methods for the purification and purity assessment of subcellular organelles from soybean are summarized. In addition, the findings from subcellular proteomic analyses of soybean during development and under stresses, particularly flooding stress, are presented and the proteins regulated among subcellular compartments are discussed. Continued advances in subcellular proteomics are expected to greatly contribute to the understanding of the responses and interactions that occur within and among subcellular compartments during development and under stressful environmental conditions.

BIOLOGICAL SIGNIFICANCE

Subcellular proteomics has the potential to investigate the cellular events and interactions among subcellular compartments in response to development and stresses in plants. Soybean could grow in several climatic zones; however, the growth and yield of soybean are markedly decreased under stresses. Numerous proteomics of cell wall, plasma membrane, nucleus, mitochondrion, chloroplast, and endoplasmic reticulum was carried out to investigate the respecting proteins and their functions in soybean during development or under stresses. In this review, methods of subcellular-organelle enrichment and purity assessment are summarized. In addition, previous findings of subcellular proteomics are presented, and functional proteins regulated among different subcellular are discussed. Subcellular proteomics contributes greatly to uncovering responses and interactions among subcellular compartments during development and under stressful environmental conditions in soybean.

Hypobaric Treatment Effects on Chilling Injury, Mitochondrial Dysfunction, and the Ascorbate-Glutathione (AsA-GSH) Cycle in Postharvest Peach Fruit

In this study, hypobaric treatment effects were investigated on chilling injury, mitochondrial dysfunction, and the ascorbate-glutathione (AsA-GSH) cycle in peach fruit stored at 0 °C. Internal browning of peaches was dramatically reduced by applying 10-20 kPa pressure. Hypobaric treatment markedly inhibited membrane fluidity increase, whereas it kept mitochondrial permeability transition pore (MPTP) concentration and cytochrome C oxidase (CCO) and succinic dehydrogenase (SDH) activity relatively high in mitochondria. Similarly, 10-20 kPa pressure treatment reduced the level of decrease observed in AsA and GSH concentrations, while it enhanced ascorbate peroxidase (APX), glutathione reductase (GR), and monodehydroascorbate reductase (MDHAR) activities related to the AsA-GSH cycle. Furthermore, comparative transcriptomic analysis showed that differentially expressed genes (DEGs) associated with the metabolism of glutathione, ascorbate, and aldarate were up-regulated in peaches treated with 10-20 kPa for 30 days at 0 °C. Genes encoding GR, MDHAR, and APX were identified and exhibited higher expression in fruits treated with low pressure than in fruits treated with normal atmospheric pressure. Our findings indicate that the alleviation of chilling injury by hypobaric treatment was associated with preventing mitochondrial dysfunction and triggering the AsA-GSH cycle by the transcriptional up-regulation of related enzymes.

Different Modes of Hydrogen Peroxide Action During Seed Germination

Hydrogen peroxide was initially recognized as a toxic molecule that causes damage at different levels of cell organization and thus losses in cell viability. From the 1990s, the role of hydrogen peroxide as a signaling molecule in plants has also been discussed. The beneficial role of H2O2 as a central hub integrating signaling network in response to biotic and abiotic stress and during developmental processes is now well established. Seed germination is the most pivotal phase of the plant life cycle, affecting plant growth and productivity. The function of hydrogen peroxide in seed germination and seed aging has been illustrated in numerous studies; however, the exact role of this molecule remains unknown. This review evaluates evidence that shows that H2O2 functions as a signaling molecule in seed physiology in accordance with the known biology and biochemistry of H2O2. The importance of crosstalk between hydrogen peroxide and a number of signaling molecules, including plant phytohormones such as abscisic acid, gibberellins, and ethylene, and reactive molecules such as nitric oxide and hydrogen sulfide acting on cell communication and signaling during seed germination, is highlighted. The current study also focuses on the detrimental effects of H2O2 on seed biology, i.e., seed aging that leads to a loss of germination efficiency. The dual nature of hydrogen peroxide as a toxic molecule on one hand and as a signal molecule on the other is made possible through the precise spatial and temporal control of its production and degradation. Levels of hydrogen peroxide in germinating seeds and young seedlings can be modulated via pre-sowing seed priming/conditioning. This rather simple method is shown to be a valuable tool for improving seed quality and for enhancing seed stress tolerance during post-priming germination. In this review, we outline how seed priming/conditioning affects the integrative role of hydrogen peroxide in seed germination and aging.

How membranes organize during seed germination: three patterns of dynamic lipid remodelling define chilling resistance and affect plastid biogenesis

Imbibitional chilling injury during germination causes agricultural losses, but this can be overcome by osmopriming. It remains unknown how membranes reorganize during germination. Herein, we comparatively profiled changes of membrane lipids during imbibition under normal and chilling temperatures in chilling-tolerant and -sensitive soybean seeds. We found three patterns of dynamic lipid remodelling during the three phases of germination. Pattern 1 involved a gradual increase in plastidic lipids during phases I and II, with an abrupt increase during phase III. This abrupt increase was associated with initiation of photosynthesis. Pattern 3 involved phosphatidic acid (PA) first decreasing, then increasing, and finally decreasing to a low level. Patterns 1 and 3 were interrupted in chilling-sensitive seeds under low temperature, which lead a block in plastid biogenesis and accumulation of harmful PA, respectively. However, they were rescued and returned to their status under normal temperature after polyethylene glycol osmopriming. We specifically inhibited phospholipase D (PLD)-mediated PA formation in chilling-sensitive seeds of soybean, cucumber, and pea, and found their germination under low temperature was significantly improved. These results indicate that membranes undergo specific and functional reorganization of lipid composition during germination and demonstrate that PLD-mediated PA causes imibibitional chilling injury.

Deciphering priming-induced improvement of rapeseed (Brassica napus L.) germination through an integrated transcriptomic and proteomic approach

Rape seeds primed with -1.2 MPa polyethylene glycol 6000 showed improved germination performance. To better understand the beneficial effect of osmopriming on seed germination, a global expression profiling method was used to compare, for the first time, transcriptomic and proteomic data for osmoprimed seeds at the crucial phases of priming procedure (soaking, drying), whole priming process and subsequent germination. Brassica napus was used here as a model to dissect the process of osmopriming into its essential components. A total number of 952 genes and 75 proteins were affected during the main phases of priming and post-priming germination. Transcription was not coordinately associated with translation resulting in a limited correspondence between mRNAs level and protein abundance. Soaking, drying and final germination of primed seeds triggered distinct specific pathways since only a minority of genes and proteins were involved in all phases of osmopriming while a vast majority was involved in only one single phase. A particular attention was paid to genes and proteins involved in the transcription, translation, reserve mobilization, water uptake, cell cycle and oxidative stress processes.

Effect of glutathione reductase knockdown in response to UVB-induced oxidative stress in human lung adenocarcinoma

Background

Glutathione reductase (GR) plays a critical role in the maintenance of physiological redox status in cells. However, the comprehensive investigations of GR-modulated oxidative stress have not been reported.

Methods

In the present study, we cultured a human lung adenocarcinoma line CL1-0 and its GR-knockdown derivative CL1-0ΔGR to evaluate their differential responses to UVB-irradiation.

Results

We identified 18 proteins that showed significant changes under UVB-irradiation in CL1-0ΔGR cells rather than in CL1-0 cells. Several proteins involving protein folding, metabolism, protein biosynthesis and redox regulation showed significant changes in expression.

Conclusions

In summary, the current study used a comprehensive lung adenocarcinoma-based proteomic approach for the identification of GR-modulated protein expression in response to UVB-irradiation. To our knowledge, this is the first global proteomic analysis to investigate the role of GR under UVB-irradiation in mammalian cell model.

Identification and characterization of a novel chloroplast/mitochondria co-localized glutathione reductase 3 involved in salt stress response in rice

Glutathione reductases (GRs) are important components of the antioxidant machinery that plants use to respond against abiotic stresses. In rice, one cytosolic and two chloroplastic GR isoforms have been identified. In this work, we describe the cloning and characterization of the full-length cDNA encoding OsGR3, a chloroplast-localized GR that up to now was considered as a non-functional enzyme because of assumed lack of N-terminal conserved domains. The expression of OsGR3 in E. coli validated that it can be translated as a protein with GR activity. OsGR3 shows 76 and 53 % identity with OsGR1 (chloroplastic) and OsGR2 (cytosolic), respectively. Phylogenetic analysis revealed 2 chloroplastic GRs in Poaceae species, including rice, sorghum and brachypodium, but only one chloroplastic GR in dicots. A plastid transit peptide is located at the N terminus of OsGR3, and genetic transformation of rice with a GR3-GFP fusion construct further confirmed its localization in chloroplasts. Furthermore, OsGR1 and OsGR3 are also targeted to mitochondria, which suggest a combined antioxidant mechanism in both chloroplasts and mitochondria. However, both isoforms showed a distinct response to salinity: the expression of OsGR3 but not OsGR1 was induced by salt stress. In addition, the transcript level of OsGR3 was greatly increased with salicylic acid treatment but was not significantly affected by methyl jasmonate, dehydration or heat shock stress. Our results provide new clues about the possible roles of functional OsGR3 in salt stress and biotic stress tolerance.

Glutathione and glutathione reductase: a boon in disguise for plant abiotic stress defense operations

Abiotic stresses such as salinity, drought, clilling, heavy metal are the major limiting factors for crop productivity. These stresses induce the overproduction of reactive oxygen species (ROS) which are highly reactive and toxic, which must be minimized to protect the cell from oxidative damage. The cell organelles, particularly chloroplast and mitochondria are the major sites of ROS production in plants where excessive rate of electron flow takes place. Plant cells are well equipped to efficiently scavenge ROS and its reaction products by the coordinated and concerted action of antioxidant machinery constituted by vital enzymatic and non-enzymatic antioxidant components. Glutathione reductase (GR, EC 1.6.4.2) and tripeptide glutathione (GSH, γ-Glutamyl-Cysteinyl-Glycine) are two major components of ascorbate-glutathione (AsA-GSH) pathway which play significant role in protecting cells against ROS and its reaction products-accrued potential anomalies. Both GR and GSH are physiologically linked together where, GR is a NAD(P)H-dependent enzymatic antioxidant and efficiently maintains the reduced pool of GSH - a cellular thiol. The differential modulation of both GR and GSH in plants has been widely implicated for the significance of these two enigmatic antioxidants as major components of plant defense operations. Considering recent informations gained through molecular-genetic studies, the current paper presents an overview of the structure, localization, biosynthesis (for GSH only), discusses GSH and GR significance in abiotic stress (such as salinity, drought, clilling, heavy metal)-exposed crop plants and also points out unexplored aspects in the current context for future studies.

Seed germination and vigor

Germination vigor is driven by the ability of the plant embryo, embedded within the seed, to resume its metabolic activity in a coordinated and sequential manner. Studies using "-omics" approaches support the finding that a main contributor of seed germination success is the quality of the messenger RNAs stored during embryo maturation on the mother plant. In addition, proteostasis and DNA integrity play a major role in the germination phenotype. Because of its pivotal role in cell metabolism and its close relationships with hormone signaling pathways regulating seed germination, the sulfur amino acid metabolism pathway represents a key biochemical determinant of the commitment of the seed to initiate its development toward germination. This review highlights that germination vigor depends on multiple biochemical and molecular variables. Their characterization is expected to deliver new markers of seed quality that can be used in breeding programs and/or in biotechnological approaches to improve crop yields.

Enhanced activity of galactono-1,4-lactone dehydrogenase and ascorbate-glutathione cycle in mitochondria from complex III deficient Arabidopsis

The mitochondrial antioxidant homeostasis was investigated in Arabidopsis ppr40-1 mutant, which presents a block of electron flow at complex III. The activity of the ascorbate biosynthetic enzyme, L-galactono-1,4-lactone dehydrogenase (EC 1.3.2.3) (GLDH) was elevated in mitochondria isolated from mutant plants. In addition increased activities of the enzymes of Foyer-Halliwell-Asada cycle and elevated glutathione (GSH) level were observed in the mutant mitochondria. Lower ascorbate and ascorbate plus dehydroascorbate contents were detected at both cellular and mitochondrial level. Moreover, the more oxidized mitochondrial redox status of ascorbate in the ppr40-1 mutant indicated that neither the enhanced activity of GLDH nor Foyer-Halliwell-Asada cycle could compensate for the enhanced ascorbate consumption in the absence of a functional respiratory chain.