ROS production and lipid catabolism in desiccating Shorea robusta seeds during aging

Map-based cloning of Zmccr3 and its network construction and validation for regulating maize seed germination

KEY MESSAGE

Map-based cloning of Zmccr3 for regulate SG and its molecular regulatory pathway was performed and validated. WGCNA, target genes/pathways during the process of seed dormancy formation were obtained. Seed dormancy (SD) and pre-harvest sprouting (PHS) affect the grain yield and quality of grain in cereal and hybrid seed production. Although the benefits of studying SD and seed germination (SG) during seed development are well established, research into the genetic variation and molecular regulation of SD, particularly during the transition from SD to SG, remains very limited. In this study, bulked segregant analysis (BSA) and linkage analysis were used to map the QTL for the maize vp16 mutant of PHS. Using genetic and biological methods, the candidate gene was identified as Zmccr3, encoding cinnamoyl-CoA reductase 3 (ccr3), which is involved in the phenylalanine pathway of lignin metabolism and affects SG. Based on RNA-seq (RNA sequencing) at two stages of grain development with extreme PHS traits, a weighted gene coexpression network analysis (WGCNA) related to SD and SG formation was constructed, and ten target genes and three pathways during the transition from SD to SG were identified. Simultaneously, the Zmccr3 pathway was established and validated, involving upstream lipid metabolism, redox modification and degradation of cell wall oligosaccharides (as electrophilic compounds), regulation of GA signaling and intracellular ROS homeostasis, and downstream oxidation of cell wall lignin units and synthesis of phenolic compounds that affect endosperm weakening and cell wall loosening, ultimately regulating SG or SD. Therefore, we propose the Zmccr3 hypothesis to elucidate its possible functions. These findings have important theoretical and practical implications for understanding the genetic basis of PHS and SD in maize, increasing genetic resources and improving traits.

Rice seed storability: From molecular mechanisms to agricultural practices

The storability of rice seeds is crucial for ensuring flexible planting options, agricultural seed security, and global food safety. With the intensification of global climate change and the constant fluctuations in agricultural production conditions, enhancing the storability of rice seeds has become particularly important. Seed storability is a complex quantitative trait regulated by both genetic and environmental factors. This article reviews the main regulatory mechanisms of rice seed storability, including the accumulation of seed storage proteins, late embryogenesis abundant (LEA) proteins, heat shock proteins, sugar signaling, hormonal regulation by gibberellins and abscisic acid, and the role of the ubiquitination pathway. Additionally, this article explores the improvement of storability using wild rice genes, molecular marker-assisted selection, and gene editing techniques such as CRISPR/Cas9 in rice breeding. By providing a comprehensive scientific foundation and practical guidance, this review aims to promote the development of rice varieties with enhanced storability to meet evolving agricultural demands.

Exploring the lipid oxidation mechanisms during pumpkin seed kernels storage based on lipidomics: From phenomena, substances, and metabolic mechanisms

The study investigated the lipid oxidation of pumpkin seed kernels (PSK) under different storage conditions (room temperature, vacuum-room temperature, refrigeration, and vacuum-refrigeration) using HPLC-MS and GC-MS. Experimental results found the vacuum-refrigeration group showed the lowest PV (0.24 g/100 g), diene (8.68), hexanal (356.64 ± 16.06 ng/g), and nonanal (132.05 ± 8.38 ng/g) after a 9-month storage. A total of 586 lipids, including 6 classes and 27 subclasses, were detected, 46 of which showed significant differences. Refrigeration samples had the highest diacylglycerol content, while room temperature samples demonstrated the highest triacylglycerol and phosphatidylcholine content. Differential lipid metabolite analyses indicated that storage conditions mainly affected glycerolipid metabolism, glycerophospholipid metabolism, and sphingolipid metabolism pathways in PSK, while glycerolipid and glycerophospholipid metabolism were still dominant. It revealed that refrigeration was more effective than vacuum in inhibiting the oxidation of PSK. These findings could offer valuable references for the storage, transportation, preservation, and the development and utilization of PSK.

Relationship between Protein, MicroRNA Expression in Extracellular Vesicles and Rice Seed Vigor

Plant extracellular vesicles are non-self-replicating particles released by living plant cells and delimited by a lipid bilayer. They contain a large amount of lipids, RNA, and proteins. Seed vigor plays an important role in agricultural production and preservation of germplasm resources. Extracellular vesicles with cross-species communication with bioactive molecules can resist pathogens, exhibit anti-aging properties, and perform other functions; however, its potential influence on seed vigor has not been reported. In this study, rice seeds with different germination percentages were used to extract extracellular vesicles, endogenous proteins, and RNA. Protein qualitative identification and miRNA differential analysis were performed to analyze the regulatory mechanism of extracellular vesicles on seed vigor. Results: The profiles of four miRNA families were found to be significantly different: osa-miR164, osa-miR168, osa-miR166, and osa-miR159. Protein correlation analysis predicted that extracellular vesicles might mediate the synthesis of the seed cell wall; glyoxic acid cycle and tricarboxylic acid cycle; non-specific lipid transfer; mitochondrial quality control; and other biological processes to regulate rice seed viability. In addition, cupin protein, phospholipase D, aldehyde dehydrogenase, seven heat shock proteins (especially BiP1 and BiP2), protein disulfide isomerase-like (PDI), thioredoxin, calnexin and calreticulin, glutathione transferase, and other proteins found in extracellular vesicles were closely related to seed vigor. This provides a novel direction for the study of the regulation mechanism of seed vigor.

Serine Rejuvenated Degenerated Volvariella volvacea by Enhancing ROS Scavenging Ability and Mitochondrial Function

Serine is a functional amino acid that effectively regulates the physiological functions of an organism. This study investigates the effects of adding exogenous serine to a culture medium to explore a feasible method for the rejuvenation of V. volvacea degenerated strains. The tissue isolation subcultured strains T6, T12, and T19 of V. volvacea were used as test strains, and the commercially cultivated strain V844 (T0) was used as a control. The results revealed that the addition of serine had no significant effect on non-degenerated strains T0 and T6, but could effectively restore the production characteristics of degenerated strains T12 and T19. Serine increased the biological efficiency of T12 and even helped the severely degenerated T19 to regrow its fruiting body. Moreover, exogenous serine up-regulated the expression of some antioxidant enzyme genes, improved antioxidase activity, reduced the accumulation of reactive oxygen species (ROS), lowered malondialdehyde (MDA) content, and restored mitochondrial membrane potential (MMP) and mitochondrial morphology. Meanwhile, serine treatment increased lignocellulase and mycelial energy levels. These findings form a theoretical basis and technical support for the rejuvenation of V. volvacea degenerated strains and other edible fungi.

Functional analysis of a wheat class III peroxidase gene, TaPer12-3A, in seed dormancy and germination

BACKGROUND

Class III peroxidases (PODs) perform crucial functions in various developmental processes and responses to biotic and abiotic stresses. However, their roles in wheat seed dormancy (SD) and germination remain elusive.

RESULTS

Here, we identified a wheat class III POD gene, named TaPer12-3A, based on transcriptome data and expression analysis. TaPer12-3A showed decreasing and increasing expression trends with SD acquisition and release, respectively. It was highly expressed in wheat seeds and localized in the endoplasmic reticulum and cytoplasm. Germination tests were performed using the transgenic Arabidopsis and rice lines as well as wheat mutant mutagenized with ethyl methane sulfonate (EMS) in Jing 411 (J411) background. These results indicated that TaPer12-3A negatively regulated SD and positively mediated germination. Further studies showed that TaPer12-3A maintained H2O2 homeostasis by scavenging excess H2O2 and participated in the biosynthesis and catabolism pathways of gibberellic acid and abscisic acid to regulate SD and germination.

CONCLUSION

These findings not only provide new insights for future functional analysis of TaPer12-3A in regulating wheat SD and germination but also provide a target gene for breeding wheat varieties with high pre-harvest sprouting resistance by gene editing technology.

The metabolic profiles of Eugenia astringens and E. uniflora (Myrtaceae) sensitive seeds affect desiccation

Myrtaceae species are abundant in tropical Atlantic rainforests, but 41% of the 5500 species of this family are of extreme conservation concern. Eugenia astringens and E. uniflora are native Brazilian Myrtaceae species that occur in the same habitats and produce desiccation-sensitive (DS) seeds. We hypothesized that their seed desiccation-sensitivity degree is associated with specific metabolic signatures. To test it, we analyzed the germination and metabolic profiles of fresh and desiccated seeds. The water content (WC) at which at least half of the seeds survived desiccation was lower in E. astringens (0.17 g H2 O g-1 DW) than in E. uniflora (0.41 g H2 O g-1 DW). We identified 103 annotated metabolites from 3261 peaks in both species, which differed in their relative contents between E. astringens and E. uniflora seeds. The main differences in seed metabolic profiles include several protective molecules in the group of carbohydrates and organic acids and amino acid contents. The relative contents of monosaccharides and disaccharides, malic and quinic acids, amino acids and saturated fatty acids may have taken part in the distinct DS behaviour of E. astringens and E. uniflora seeds. Our study provides evidence of the relationship between desiccation sensitivity, seed viability and metabolic profile of tropical seeds by comparing two closely related Eugenia species with different DS degrees.

Nuclear factor OsNF-YC5 modulates rice seed germination by regulating synergistic hormone signaling

Regulation of seed dormancy/germination is of great importance for seedling establishment and crop production. Nuclear factor-Y (NF-Y) transcription factors regulate plant growth and development, as well as stress responses; however, their roles in seed germination remain largely unknown. In this study, we reported that NF-Y gene OsNF-YC5 knockout increased, while its overexpression reduced, the seed germination in rice (Oryza sativa L.). ABA-induced seed germination inhibition assays showed that the osnf-yc5 mutant was less sensitive but OsNF-YC5-overexpressing lines were more sensitive to exogenous ABA than the wild type. Meanwhile, MeJA treatment substantially enhanced the ABA sensitivity of OsNF-YC5-overexpressing lines during seed germination. Mechanistic investigations revealed that the interaction of OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (SAPK9) with OsNF-YC5 enhanced the stability of OsNF-YC5 by protein phosphorylation, while the interaction between JASMONATE ZIM-domain protein 9 (OsJAZ9) and OsNF-YC5 repressed OsNF-YC5 transcriptional activity and promoted its degradation. Furthermore, OsNF-YC5 transcriptionally activated ABA catabolic gene OsABA8ox3, reducing ABA levels in germinating seeds. However, the transcriptional regulation of OsABA8ox3 by OsNF-YC5 was repressed by addition of OsJAZ9. Notably, OsNF-YC5 improved seed germination under salinity conditions. Further investigation showed that OsNF-YC5 activated the high-affinity K+ transporter gene (OsHAK21) expression, and addition of SAPK9 could increase the transcriptional regulation of OsHAK21 by OsNF-YC5, thus substantially reducing the ROS levels to enhance seed germination under salt stress. Our findings establish that OsNF-YC5 integrates ABA and JA signaling during rice seed germination, shedding light on the molecular networks of ABA-JA synergistic interaction.

Oxidative damage from repeated tissue isolation for subculturing causes degeneration in Volvariella volvacea

The fungal fruiting body is the organized mycelium. Tissue isolation and mycelium succession are common methods of fungal species purification and rejuvenation in the production of edible mushrooms. However, repeated succession increases strain degeneration. In this study, we examined the effect of repeated tissue isolation from Volvariella volvacea fruitbodies on the occurrence of degeneration. The results showed that less than four times in succession improved production capacity, however, after 12 successions, the traits indicating strain degeneration were apparent. For instance, the density of aerophytic hyphae, hyphal growth rate and hyphal biomass were gradually reduced, while the hyphae branching was increased. Also, other degenerative traits such as prolonged production cycles and decreased biological efficiency became evident. In particular, after 19 successions, the strain degeneration became so severe no fruiting bodies were produces anymore. Meanwhile, with the increase in successions, the antioxidant enzyme activity decreased, reactive oxygen species (ROS) increased, the number of nuclei decreased, and the mitochondrial membrane potential decreased along with morphological changes in the mitochondria. This study showed that repeated tissue isolation increased oxidative damage in the succession strain due to the accumulation of ROS, causing cellular senescence, in turn, degeneration in V. volvacea strain.

Genome-wide identification and expression pattern analysis of lipoxygenase genes of chickpea (Cicer arietinum L.) in response to accelerated aging

Seed aging is a major problem which is caused by various factors such as unfavorable physiological, biochemical, and metabolic alterations in seed cells. Lipoxygenase (LOXs), an oxidoreductase enzyme that catalyzes the oxidation of polyunsaturated fatty acids, acts as a negative regulator in seed viability and vigour during storage. In this study, we identified ten putative LOX gene family members in the chickpea genome, designated as "CaLOX" which are mainly located in the cytoplasm and chloroplast. These genes share different physiochemical properties and similarities in their gene structures and conserved functional regions. The promoter region contained the cis-regulatory elements and transcription binding factors, which were mainly linked to biotic and abiotic stress, hormones, and light responsiveness. In this study, chickpea seeds were treated with accelerated aging treatment for 0, 2, and 4 days at 45°C and 85 % relative humidity. Increased level of reactive oxygen species, malondialdehyde, electrolyte leakage, proline, lipoxygenase (LOX) activity, and decreased catalase activity indicates cellular dysfunction and demonstrated seed deterioration. Quantitative real-time analysis reveals that 6 CaLOX genes were upregulated, and 4 CaLOX genes were downregulated during the seed aging process in chickpea. This comprehensive study will reveal the role of the CaLOX gene in response to aging treatment. The identified gene may be used to develop better-quality seeds in chickpea.

The lipoxygenase OsLOX10 affects seed longevity and resistance to saline-alkaline stress during rice seedlings

Prolonged storage of rice seeds can lead to a decrease in seed vigor and seedling quality. The Lipoxygenase (LOX) gene family is widely distributed in plants, and LOX activity is closely related to seed viability and stress tolerance. In this study, the lipoxygenase OsLOX10 gene from the 9-lipoxygenase metabolic pathway was cloned from rice, and its roles in determining seed longevity and tolerance to saline-alkaline stress caused by Na₂CO₃ in rice seedlings were mainly investigated. CRISPR/Cas9 knockout of OsLOX10 increased seed longevity compared with the wild-type and OsLOX10 overexpression lines in response to artificial aging. The expression levels of other 9-lipoxygenase metabolic pathway related genes, such as LOX1, LOX2 and LOX3, were increased in the LOX10 overexpression lines. Quantitative real-time PCR and histochemical staining analysis showed that the expression of LOX10 was highest in seed hulls, anthers and the early germinating seeds. KI-I₂ staining of starch showed that LOX10 could catalyze the degradation of linoleic acid. Furthermore, we found that the transgenic lines overexpressing LOX10 showed better tolerance to saline-alkaline stress than the wild-type and knockout mutant lines. Overall, our study demonstrated that the knockout LOX10 mutant increased seed longevity, whereas overexpression of LOX10 enhanced tolerance to saline-alkaline stress in rice seedlings.

A cadmium-tolerant endophytic bacterium reduces oxidative stress and Cd uptake in KDML105 rice seedlings by inducing glutathione reductase-related activity and increasing the proline content

The effect of the endophytic Cupriavidus taiwanensis KKU2500-3 on the Cd toxicity of KDML105 rice seedlings was investigated in a 10 μM CdCl2 hydroponic system. As demonstrated after bacterial inoculation of germinating rice seeds, KKU2500-3 colonized all rice plant parts. In RB (Rice + KKU2500-3) and RBC (Rice + KKU2500-3+Cd), KKU2500-3 effectively colonized and was detected at a markedly higher number in the root surface and interior than in shoots and leaves. The activities of antioxidant enzymes ascorbate peroxidase (APOX), glutathione reductase (GR), and superoxide dismutase (SOD) and the proline content in inoculated rice were higher in roots and aboveground tissues. RBC exhibited a higher reduced-to-oxidized glutathione ratio in roots and leaves (3-55%) but a lower malondialdehyde content (8-78%). Phytochelatins (PCs) were detected in all rice tissues, but their levels in RBC were 13-70% lower than those in RC (Rice + Cd), demonstrating that the induction of PCs in rice was unrelated to KKU2500-3. The Cd levels in roots and shoots were lower in RBC than RC, and the root-to-shoot Cd translocation factor was 0.6-62.2% lower. At 30 DAT, the Cd levels in RBC roots and shoots were 30.2% and 73.7% lower, respectively, than those in RC. Colonized KKU2500-3 activated GR and increased the proline content to overcome rice Cd toxicity. These effects may trap Cd in plant cells and reduce its translocation. Hence, KKU2500-3 synergistically interacts with rice to detoxify Cd at early growth stages, and KDML105 rice grains with low Cd accumulation could be produced if this interaction is maintained until late growth stages.

Changes in the chemical, physical, and sensory properties of rice according to its germination rate

This study aimed to decipher the association among the physicochemical properties, sensory quality, and germination rate of rice samples stored at different storage conditions and for different durations (stored at 10, 20, and 30 °C for 8 months). The germination rate of the samples varied from 0.3 to 98.7%. A reduced germination rate increased the lipid oxidation, hardness, and most pasting properties of rice, whereas seed viability, moisture content, and adhesiveness were reduced. Amylose and protein contents were not influenced by the changes in germination rate. However, with a decrease in germination rate, the surface endosperm cells were aggregated, whereas the sizes of inner endosperm cells in cooked rice were reduced. Several metabolites involved in rice sensory quality were also altered, and a related pathway was proposed. Collectively, these results suggest that germination rate could serve as a potential indicator to track the changes in rice quality.

Impacts of Rapid Desiccation on Oxidative Status, Ultrastructure and Physiological Functions of Syzygium maire (Myrtaceae) Zygotic Embryos in Preparation for Cryopreservation

Syzygium maire is a highly threatened Myrtaceae tree species endemic to New Zealand. Due to its recalcitrant seed storage behaviour, cryopreservation is the only viable long-term ex situ conservation option for this species. This study investigated viability, oxidative stress, thermal properties, and ultrastructure of zygotic embryo axes (EAs) desiccated to various moisture contents (MC). Fresh EAs had a MC of c. 1.9 g/g with 100% viability but rapid desiccation to MC < 0.3 g/g significantly reduced viability and decreased the activities of the enzymatic antioxidants superoxide dismutase, catalase and glutathione peroxidase, with a sevenfold increase in the production of protein carbonyls and lipid peroxides. Differential Scanning Calorimetry analysis showed no thermal events in EAs desiccated to a MC of <0.2 g/g, indicating that all freezable water had been removed, but this was lethal to both EAs and enzymatic antioxidants. The ultrastructure of desiccated EAs showed signs of plasmolysis, while fully hydrated EAs exposed to cryogenic temperature had ultrastructural disintegration and membrane damage. The decline in enzymatic antioxidant activities and the increase in lipid peroxidation suggest that S. maire EA viability loss is due to oxidative stress rather than structural impacts.

iTRAQ and RNA-seq analyses provide an insight into mechanisms of recalcitrance in a medicinal plant Panax notoginseng seeds during the after-ripening process

Panax notoginseng (Burk) F.H. Chen is an important economic and medicinal plant from the family of Araliaceae, and its seed is characterised by the recalcitrance and after-ripening process. However, the molecular mechanism on the dehydration sensitivity is not clear in recalcitrant seeds. In the present study, isobaric tag for relative and absolute quantification (iTRAQ) and RNA-seq were used to analyse the proteomic and transcriptomic changes in seeds of P. notoginseng in days after-ripening (DAR). A total of 454 differentially expressed proteins (DEPs) and 12000 differentially expressed genes (DEGs) were obtained. The activity of enzymes related to antioxidant system were significantly increased, and the late embryogenesis abundant (LEA) protein family and most members of glutathione metabolism enzymes have been downregulated during the after-ripening process. The lack or inadequate accumulation of LEA proteins in the embryo and the low activity of antioxidant defense in glutathione metabolism might be the key factors leading to the dehydration sensitivity in recalcitrant seeds of P. notoginseng. In addition, the increased activity of elycolysis (EMP), citric acid cycle (TCA) and pentose phosphate pathway (PPP) pathways might be one of important signals to complete the after-ripening process. Overall, our study might provide a new insight into the molecular mechanism on dehydration sensitivity of recalcitrant seeds.

Role of miR164 in the growth of wheat new adventitious roots exposed to phenanthrene

Polycyclic aromatic hydrocarbons (PAHs), ubiquitous organic pollutants in the environment, can accumulate in humans via the food chain and then harm human health. MiRNAs (microRNAs), a kind of non-coding small RNAs with a length of 18-30 nucleotides, regulate plant growth and development and respond to environmental stress. In this study, it is demonstrated that miR164 can regulate root growth and adventitious root generation of wheat under phenanthrene exposure by targeting NAC (NAM/ATAF/CUC) transcription factor. We observed that phenanthrene treatment accelerated the senescence and death of wheat roots, and stimulated the occurrence of new roots. However, it is difficult to compensate for the loss caused by old root senescence and death, due to the slower growth of new roots under phenanthrene exposure. Phenanthrene accumulation in wheat roots caused to generate a lot of reactive oxygen species, and enhanced lipoxygenase activity and malonaldehyde concentration, meaning that lipid peroxidation is the main reason for root damage. MiR164 was up-regulated by phenanthrene, enhancing the silence of NAC1, weakening the association with auxin signal, and inhibiting the occurrence of adventitious roots. Phenanthrene also affected the expression of CDK (the coding gene of cyclin-dependent kinase) and CDC2 (a gene regulating cell division cycle), the key genes in the cell cycle of pericycle cells, thereby affecting the occurrence and growth of lateral roots. In addition, NAM (a gene regulating no apical meristem) and NAC23 may also be related to the root growth and development in wheat exposed to phenanthrene. These results provide not only theoretical basis for understanding the molecular mechanism of crop response to PAHs accumulation, but also knowledge support for improving phytoremediation of soil or water contaminated by PAHs.

The uncoupling of respiration in plant mitochondria: keeping reactive oxygen and nitrogen species under control

Plant mitochondrial respiration involves the operation of various alternative pathways. These pathways participate, both directly and indirectly, in the maintenance of mitochondrial functions though they do not contribute to energy production, being uncoupled from the generation of an electrochemical gradient across the mitochondrial membrane and thus from ATP production. Recent findings suggest that uncoupled respiration is involved in reactive oxygen species (ROS) and nitric oxide (NO) scavenging, regulation, and homeostasis. Here we discuss specific roles and possible functions of uncoupled mitochondrial respiration in ROS and NO metabolism. The mechanisms of expression and regulation of the NDA-, NDB- and NDC-type non-coupled NADH and NADPH dehydrogenases, the alternative oxidase (AOX), and the uncoupling protein (UCP) are examined in relation to their involvement in the establishment of the stable far-from-equilibrium state of plant metabolism. The role of uncoupled respiration in controlling the levels of ROS and NO as well as inducing signaling events is considered. Secondary functions of uncoupled respiration include its role in protection from stress factors and roles in biosynthesis and catabolism. It is concluded that uncoupled mitochondrial respiration plays an important role in providing rapid adaptation of plants to changing environmental factors via regulation of ROS and NO.

Unraveling the impact of arsenic on the redox response of peanut plants inoculated with two different Bradyrhizobium sp. strains

Arsenic (As) can be present naturally in groundwater from peanut fields, constituting a serious problem, as roots can accumulate and mobilize the metalloid to their edible parts. Understanding the redox changes in the legume exposed to As may help to detect potential risks to human health and recognize tolerance mechanisms. Thirty-days old peanut plants inoculated with Bradyrhizobium sp. strains (SEMIA6144 or C-145) were exposed to a realistic arsenate concentration, in order to unravel the redox response and characterize the oxidative stress indexes. Thus, root anatomy, reactive oxygen species detection by fluorescence microscopy and, ROS histochemical staining along with the NADPH oxidase activity were analyzed. Besides, photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress indicators. Results showed that at 3 μM As^V, the cross-section areas of peanut roots were augmented; NADPH oxidase activity was significantly increased and O₂˙¯and H₂O₂ accumulated in leaves and roots. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant regardless the inoculated strain, while chlorophylls and carotenes were increased only in those inoculated with Bradyrhizobium sp. C-145. Interestingly, the oxidative burst, mainly induced by the NADPH oxidase activity, and the consequent oxidative stress was strain-dependent and organ-differential. Additionally, As modifies the root anatomy, acting as a possibly first defense mechanism against the metalloid entry. All these findings allowed us to conclude that the redox response of peanut is conditioned by the rhizobial strain, which contributes to the importance of effectively formulating bioinoculants for this crop.

Os4BGlu14, a monolignol β-Glucosidase, negatively affects seed longevity by influencing primary metabolism in rice

Os4BGlu14, a monolignol β-glucosidase, plays a negative role in seed longevity by affecting primary metabolism during seed development and aging. Seed longevity is a crucial trait in agriculture and in the conservation of germplasm resources. β-Glucosidases (BGlus) are multifunctional enzymes that affect plant growth and their adaptation to the environment. The function of rice BGlus in seed longevity, however, remains unknown. We report here that Os4BGlu14, a rice β-Glucosidase, negatively affected seed longevity during accelerated aging. Os4BGlu14 was highly expressed in rice embryos and induced by accelerated aging. Compared to the wild type, rice lines overexpressing Os4BGlu14 had significantly greater grain length, but smaller grain width and thickness. Overexpressing (OE) lines also showed lower starch but higher glucose contents. After accelerated aging treatment, OE lines displayed a significantly lower germination percentage than the wild type. Additionally, these lines had higher lignin accumulation before and after accelerated aging. Metabolome analysis detected 217 metabolites in untreated and aged rice seeds. Comparison of the differential metabolites between WT and OE5 revealed that ten key metabolites, four of which (e.g., uridine 5'-diphosphoglucose-glucose, UDPG) were increased, while the other six (e.g., γ-aminobutyric acid and methionine) were decreased, might be the crucial factors that lead to seed deterioration. Further analysis confirmed higher UDPG levels and more severe programmed cell death in OE lines than in the wild type. Furthermore, OE lines presented a lower germination rate after abscisic acid and paclobutrazol treatment during germination, compared to the wild type. Our study provides a basis for understanding the function of Os4BGlu14 in seed longevity in rice.

Comparative Physiological and Proteomic Analysis Reveals Different Involvement of Proteins during Artificial Aging of Siberian Wildrye Seeds

Seed aging has an important effect on the germplasm preservation and industrialized production of Siberian wildrye (Elymus sibiricus) in the Qinghai-Tibet Plateau. However, so far its underlying molecular mechanisms still largely remain unknown. To shed light on this topic, one-year stored seeds of E. sibiricus were exposed to artificial aging treatments (AAT), followed by seed vigor characteristics and physiological status monitoring. Then global proteomics analysis was undertaken by the tandem mass tags (TMT) technique, and the proteins were quantified with liquid chromatography-tandem mass spectrometry on three aging time points (0 h, 36 h and 72 h). Finally, we verified the expression of related proteins by parallel reaction monitoring (PRM). Our results demonstrated that the seed vigor decreased remarkably in response to artificial aging, but the relative ion-leakage and malondialdehyde content, superoxide anion and hydrogen peroxide showed the opposite situation. Proteomic results showed that a total of 4169 proteins were identified and quantified. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that a series of key pathways including carbohydrate metabolism, lipid metabolism, and antioxidant activity were severely damaged by aging treatments. Numerous key proteins such as glyceraldehyde triphosphate glyceraldehyde dehydrogenase, succinate dehydrogenase, lipoxygenase, peroxidase, glutathione-s-transferase and late embryogenesis abundant proteins were significantly down-regulated. However, the up-regulation of the heat shock protein family has made a positive contribution to oxidative stress resistance in seeds. This study provides a useful catalog of the E. sibiricus proteomes with insights into the future genetic improvement of seed storability.

Effects of Inorganic Salt Solutions on Vigour, Viability, Oxidative Metabolism and Germination Enzymes in Aged Cabbage and Lettuce Seeds

This study assessed the potential of pre-hydration treatment with aqueous solutions (electrolysed [cathodic water; CW] and non-electrolysed) prepared from four different inorganic ion combinations: 1 mM CaCl2, 1 µm CaCl2 and 1 mM MgCl2 (CaMg, hereafter), 1 mM MgCl2 and 1 mM NaCl to invigorate controlled deteriorated (CDd) Brassicaoleracea (cabbage) and Lactucasativa (lettuce) seeds by assessing germination, vigour and biochemical markers (electrolyte leakage, lipid peroxidation products, protein carbonylation, and defence and germination associated enzymes) of oxidative stress. Additionally, the possible effects of pH of electrolysed CaMg and NaCl solutions were assessed. The inorganic salt solutions were applied to fresh seeds and seeds deteriorated to 75% viability (P75), 50% viability (P50) and 25% viability (P25); deionised water served as control. The pre-hydration treatment did not enhance normal seedling production in cabbage. However, Ca-containing and CW hydration treatments (CaCl2 CW, CaMg and CaMg CW [6.5], MgCl2 CW, NaCl CW and NaCl CW [6.5]) promoted normal seedling production of CDd lettuce seeds, while seedling vigour was enhanced by CaMg, CaMg CW (6.5), NaCl CW and NaCl CW (6.5) in CDd cabbage seeds, and CaCl2, CaCl2 CW, CaMg, CaMg CW (6.5), MgCl2 CW, NaCl CW and NaCl CW (6.5) in CDd lettuce seeds. The supplementation of Ca, a component of the ionised solutes, and/or the reducing potential of CW contributed to increased normal seedling production in lettuce seeds irrespective of the pH of treatment solutions or degree of deterioration. Overall, the pre-hydration treatments enhanced endogenous antioxidants leading to reduced levels of electrolyte leakage, lipid peroxidation, protein carbonylation, and enhanced germination enzyme activities in lettuce seeds. The study concluded that pre-hydration with selected inorganic salt solutions can invigorate debilitated lettuce seeds.

What Do We Know About the Genetic Basis of Seed Desiccation Tolerance and Longevity?

Long-term seed storage is important for protecting both economic interests and biodiversity. The extraordinary properties of seeds allow us to store them in the right conditions for years. However, not all types of seeds are resilient, and some do not tolerate extreme desiccation or low temperature. Seeds can be divided into three categories: (1) orthodox seeds, which tolerate water losses of up to 7% of their water content and can be stored at low temperature; (2) recalcitrant seeds, which require a humidity of 27%; and (3) intermediate seeds, which lose their viability relatively quickly compared to orthodox seeds. In this article, we discuss the genetic bases for desiccation tolerance and longevity in seeds and the differences in gene expression profiles between the mentioned types of seeds.

Desiccation Tolerance: Avoiding Cellular Damage During Drying and Rehydration

Desiccation of plants is often lethal but is tolerated by the majority of seeds and by vegetative tissues of only a small number of land plants. Desiccation tolerance is an ancient trait, lost from vegetative tissues following the appearance of tracheids but reappearing in several lineages when selection pressures favored its evolution. Cells of all desiccation-tolerant plants and seeds must possess a core set of mechanisms to protect them from desiccation- and rehydration-induced damage. This review explores how desiccation generates cell damage and how tolerant cells assuage the complex array of mechanical, structural, metabolic, and chemical stresses and survive.Likewise, the stress of rehydration requires appropriate mitigating cellular responses. We also explore what comparative genomics, both structural and responsive, have added to our understanding of cellular protection mechanisms induced by desiccation, and how vegetative desiccation tolerance circumvents destructive, stress-induced cell senescence.

Inhibition of the mitochondrial respiratory components (Complex I and Complex III) as stimuli to induce oxidative damage in Oryza sativa L. under thiocyanate exposure

Repression of the electron transport in mitochondria can result in an increase of reactive oxygen species (ROS) in plant cells. This study was to clarify inhibition of the mitochondrial respiratory components (Complex I and Complex III) as stimuli to induce oxidative damage in Oryza sativa L. under exogenous SCN^- exposure with special emphasis on lipid peroxidation, protein modification, and DNA damage at the biochemical and molecular levels. Our results showed that enzymatic activity and gene expression of cytochrome c reductase (Complex III) in roots and shoots of rice seedlings were significantly repressed by SCN^- exposure, where significant inhibition of NADH dehydrogenase (Complex I) was only detected in shoots, suggesting that Complex III was the main target attacked by SCN^- ligand in rice roots, and both components were arrested in shoots. ROS analysis in tissues indicated that SCN^- exposure caused significant accumulation of H₂O₂ and O₂^-•, increased malondialdehyde (MDA) and carbonyl content in rice materials in a dose-dependent manner. Similarly, a remarkable elevation of electrolyte leakage was observed in rice tissue samples. The comet assay indicated a positive correlation between DNA damage and external SCN^- exposure. In conclusion, oxidative burst generated from the inhibitions of the electron transport in mitochondria in rice seedlings under SCN^- exposure can cause lipid peroxidation, protein modification and DNA damage, eventually decreasing fresh weight of rice seedlings.

Quantitative proteomic analyses of two soybean low phytic acid mutants to identify the genes associated with seed field emergence

BACKGROUND

Seed germination is essential to crop growth and development, and ultimately affects its harvest. It is difficult to breed soybeans low in phytic acid with a higher seed field emergence. Although additional management and selection could overcome the phytate reduction, the mechanisms of seed germination remain unknown.

RESULTS

A comparative proteomic analysis was conducted between two low phytic acid (LPA) soybean mutants (TW-1-M and TW-1), both of which had a deletion of 2 bp in the GmMIPS1 gene. However, the TW-1 seeds showed a significantly lower field emergence compared to the TW-1-M. There were 282 differentially accumulated proteins (DAPs) identified between two mutants at the three stages. Among these DAPs, 80 were down-accumulated and 202 were up-accumulated. Bioinformatic analysis showed that the identified proteins were related to functional categories of oxidation reduction, response to stimulus and stress, dormancy and germination processes and catalytic activity. KEGG analysis showed that these DAPs were mainly involved in energy metabolism and anti-stress pathways. Based upon the conjoint analysis of DAPs with the differentially expressed genes (DEGs) previously published among three germination stages in two LPA mutants, 30 shared DAPs/DEGs were identified with different patterns, including plant seed protein, beta-amylase, protein disulfide-isomerase, disease resistance protein, pyrophosphate-fructose 6-phosphate 1-phosphotransferase, cysteine proteinase inhibitor, non-specific lipid-transfer protein, phosphoenolpyruvate carboxylase and acyl-coenzyme A oxidase.

CONCLUSIONS

Seed germination is a very complex process in LPA soybean mutants. The TW-1-M and TW-1 showed many DAPs involved in seed germination. The differential accumulation of these proteins could result in the difference of seed field emergence between the two mutants. The high germination rate in the TW-1-M might be strongly attributed to reactive oxygen species-related and plant hormone-related genes. All these findings would help us further explore the germination mechanisms in LPA crops.

Reactive Oxygen Species as Potential Drivers of the Seed Aging Process

Seeds are an important life cycle stage because they guarantee plant survival in unfavorable environmental conditions and the transfer of genetic information from parents to offspring. However, similar to every organ, seeds undergo aging processes that limit their viability and ultimately cause the loss of their basic property, i.e., the ability to germinate. Seed aging is a vital economic and scientific issue that is related to seed resistance to an array of factors, both internal (genetic, structural, and physiological) and external (mainly storage conditions: temperature and humidity). Reactive oxygen species (ROS) are believed to initiate seed aging via the degradation of cell membrane phospholipids and the structural and functional deterioration of proteins and genetic material. Researchers investigating seed aging claim that the effective protection of genetic resources requires an understanding of the reasons for senescence of seeds with variable sensitivity to drying and long-term storage. Genomic integrity considerably affects seed viability and vigor. The deterioration of nucleic acids inhibits transcription and translation and exacerbates reductions in the activity of antioxidant system enzymes. All of these factors significantly limit seed viability.

A quantitative trait locus, qSE3, promotes seed germination and seedling establishment under salinity stress in rice

Seed germination is a complex trait determined by both quantitative trait loci (QTLs) and environmental factors and also their interactions. In this study, we mapped one major QTLqSE3 for seed germination and seedling establishment under salinity stress in rice. To understand the molecular basis of this QTL, we isolated qSE3 by map-based cloning and found that it encodes a K⁺ transporter gene, OsHAK21. The expression of qSE3 was significantly upregulated by salinity stress in germinating seeds. Physiological analysis suggested that qSE3 significantly increased K⁺ and Na⁺ uptake in germinating seeds under salinity stress, resulting in increased abscisic acid (ABA) biosynthesis and activated ABA signaling responses. Furthermore, qSE3 significantly decreased the H₂ O₂ level in germinating seeds under salinity stress. All of these seed physiological changes modulated by qSE3 might contribute to seed germination and seedling establishment under salinity stress. Based on analysis of single-nucleotide polymorphism data of rice accessions, we identified a HAP3 haplotype of qSE3 that was positively correlated with seed germination under salinity stress. This study provides important insights into the roles of qSE3 in seed germination and seedling establishment under salinity stress and facilitates the practical use of qSE3 in rice breeding.

Cytosolic Glucose-6-Phosphate Dehydrogenase Is Involved in Seed Germination and Root Growth Under Salinity in Arabidopsis

Glucose-6-phosphate dehydrogenase (G6PDH or G6PD) is the key regulatory enzyme in the oxidative pentose phosphate pathway (OPPP). The cytosolic isoforms including G6PD5 and G6PD6 account for the major part of the G6PD total activity in plant cells. Here, we characterized the Arabidopsis single null mutant g6pd5 and g6pd6 and double mutant g6pd5/6. Compared to wild type, the mutant seeds showed a reduced germination rate and root elongation under salt stress. The seeds and seedlings lacking G6PD5 and G6PD6 accumulate more reactive oxygen species (ROS) than the wild type under salt stress. Cytosolic G6PD (cy-G6PD) affected the expression of NADPH oxidases and the G6PD enzymatic activities in the mutant atrbohD/F, in which the NADPH oxidases genes are disrupted by T-DNA insertion and generation of ROS is inhibited, were lower than that in the wild type. The NADPH level in mutants was decreased under salt stress. In addition, we found that G6PD5 and G6PD6 affected the activities and transcript levels of various antioxidant enzymes in response to salt stress, especially the ascorbate peroxidase and glutathione reductase. Exogenous application of ascorbate acid and glutathione rescued the seed and root phenotype of g6pd5/6 under salt stress. Interestingly, the cytosolic G6PD negatively modulated the NaCl-blocked primary root growth under salt stress in the root meristem and elongation zone.

Combined QTL mapping, physiological and transcriptomic analyses to identify candidate genes involved in Brassica napus seed aging

Seed aging is an inevitable problem in the germplasm conservation of oil crops. Thus, clarifying the genetic mechanism of seed aging is important for rapeseed breeding. In this study, Brassica napus seeds were exposed to an artificial aging environment (40 °C and 90% relative humidity). Using a population of 172 recombinant inbred lines, 13 QTLs were detected on 8 chromosomes, which explained ~ 9.05% of the total phenotypic variation. The QTLs q2015AGIA-C08 and q2016AGI-C08-2 identified in the two environments were considered the same QTL. After artificial aging, lower germination index, increased relative electrical conductivity, malondialdehyde and proline content, and reduced soluble sugar, protein content and antioxidant enzyme activities were detected. Furthermore, seeds of extreme lines that were either left untreated (R0 and S0) or subjected to 15 days of artificial aging (R15 and S15) were used for transcriptome sequencing. In total, 2843, 1084, 429 and 1055 differentially expressed genes were identified in R15 vs. R0, S15 vs. S0, R0 vs. S0 and R15 vs. S15, respectively. Through integrated QTL mapping and RNA-sequencing analyses, seven genes, such as BnaA03g37460D, encoding heat shock transcription factor C1, and BnaA03g40360D, encoding phosphofructokinase 4, were screened as candidate genes involved in seed aging. Further researches on these candidate genes could broaden our understanding of the regulatory mechanisms of seed aging.

Comparative metabolomic analysis of seed metabolites associated with seed storability in rice (Oryza sativa L.) during natural aging

Seed storability is an important trait for crop breeding, however, the mechanism underlying seed storability remains largely unknown. Here, a mass spectrometry-based comparative metabolomic study was performed for rice seeds before and after 24-month natural storage between two hybrid rice cultivars, IIYou 998 (IIY) with low storability and BoYou 998 (BY) with relative high storability. A total of 48 metabolites among 90 metabolite peaks detected were conclusively identified, and most of them are involved in the primary metabolism. During the 24-month storage, 19 metabolites with significant changes in abundance were found in the storage-sensitive IIY seeds, but only 8 in the BY seeds, most of which are free amino acids and soluble sugars. The observed changes of the metabolites in IIY seeds that are consistent with our protoemics results are likely to be involved in its sensitivity to storage. Levels of all identified 18 amino acid-related metabolites and most sugar-related metabolites were significantly higher in IIY seeds both before and after storage. However the level of raffinose was lower in IIY seeds before and after storage, and did not change significantly throughout the storage period in both two cultivars, suggesting its potential role in seed storability. Taken together, these results may help to improve our understanding of seed storability.

Desiccation-induced ROS accumulation and lipid catabolism in recalcitrant Madhuca latifolia seeds

Loss of viability in desiccation-sensitive seeds of Madhuca latifolia (Roxb.) J. F. Macbr., an important multipurpose tropical tree, was correlated with seed water content (WC). WC declined from 0.59 to 0.19 g g-1 fresh mass, 35 days after harvest from mother plant, at ambient conditions (temperature 25 ± 2 °C, relative humidity 50 ± 2%). The desiccation-induced reduction in viability was related with an accumulation of reactive oxygen species (ROS) that promoted lipid peroxidation associated loss of membrane integrity. Conducted study revealed 1.6-19 folds rise in lipid peroxidized products in desiccated M. latifolia seeds, and was found to be linked inversely with WC and germination percentage. Additionally, increased activities (7 and 13 folds) of lipid hydrolyzing enzymes; lipase (EC 3.1.1.3) and lipoxygenase (EC 1.13.11.12) respectively, were discernible in desiccating M. latifolia seeds. In summary, increased ROS, lipid oxidation, lipase and lipoxygenase were strongly correlated with viability loss in desiccating M. latifolia seeds.

Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects

Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.

In-depth proteomic analysis of Glycine max seeds during controlled deterioration treatment reveals a shift in seed metabolism

Seed aging is one of the major events, affecting the overall quality of agricultural seeds. To analyze the effect of seed aging, soybean seeds were exposed to controlled deterioration treatment (CDT) for 3 and 7days, followed by their physiological, biochemical, and proteomic analyses. Seed proteins were subjected to protamine sulfate precipitation for the enrichment of low-abundance proteins and utilized for proteome analysis. A total of 14 differential proteins were identified on 2-DE, whereas label-free quantification resulted in the identification of 1626 non-redundant proteins. Of these identified proteins, 146 showed significant changes in protein abundance, where 5 and 141 had increased and decreased abundances, respectively while 352 proteins were completely degraded during CDT. Gene ontology and KEGG analyses suggested the association of differential proteins with primary metabolism, ROS detoxification, translation elongation and initiation, protein folding, and proteolysis, where most, if not all, had decreased abundance during CDT. Western blotting confirmed reduced level of antioxidant enzymes (DHAR, APx1, MDAR, and SOD) upon CDT. This in-depth integrated study reveals a major downshift in seed metabolism upon CDT. Reported data here serve as a resource for its exploitation to metabolic engineering of seeds for multiple purposes, including increased seed viability, vigor, and quality.

BIOLOGICAL SIGNIFICANCE

Controlled deterioration treatment (CDT) is one of the major events that negatively affects the quality and nutrient composition of agricultural seeds. However, the molecular mechanism of CDT is largely unknown. A combination of gel-based and gel-free proteomic approach was utilized to investigate the effects of CDT in soybean seeds. Moreover, we utilized protamine sulfate precipitation method for enrichment of low-abundance proteins, which are generally masked due to the presence of high-abundance seed storage proteins. Reported data here serve as resource for its exploitation to metabolic engineering of seeds for multiple purposes, including increased seed viability, vigor, and quality.

The Seed Semipermeable Layer and Its Relation to Seed Quality Assessment in Four Grass Species

The existence of a semipermeable layer in grass seeds has been extensively reported, yet knowledge of its influence on tests for seed viability and vigor that depend upon measurement of electrical conductivity (EC) is limited. This study determined the presence and location of the semipermeable layer, and its relation to seed viability and vigor assessment, in seeds of four important grass species-Elymus nutans Griseb., Lolium perenne L., Leymus chinensis (Trin.) Tzvel., and Avena sativa L. Intact seeds of E. nutans, Lolium perenne, and Leymus chinensis exhibited little staining with triphenyl tetrazolium chloride (TTC), and there were no differences in EC between seeds with different germination percentage (GP) (P > 0.05). After piercing the seed coat, however, all three species displayed positive staining with TTC, along with a significant negative correlation between EC and GP (E. nutans: R² = 0.7708; Lolium perenne: R²= 0.8414; Leymus chinensis: R² = 0.859; P < 0.01). In contrast, both intact and pierced seeds of A. sativa possessed a permeable seed coat that showed positive staining with TTC and EC values that were significantly negatively correlated with GP [R² = 0.9071 (intact) and 0.9597 (pierced); P < 0.01]. In commercial seed lots of A. sativa, a field emergence test indicated that EC showed a significant negative correlation with field emergence at two sowing dates (R²= 0.6069, P < 0.01 and 0.5316, P < 0.05). Analysis of seed coat permeability revealed the presence of a semipermeable layer located in the seed coat adjacent to the endosperm in E. nutans, Lolium perenne, and Leymus chinensis; however, no semipermeable layer was observed in A. sativa. This is the first report of the absence of a semipermeable layer in a grass species. The existence of a semipermeable layer is one of the most important factors affecting seed viability and vigor testing (based on EC measurement) in E. nutans, Lolium perenne, and Leymus chinensis. Increasing the permeability of the semipermeable layer, e.g., by piercing the seed coat, may permit the use of EC measurement to assess seed vigor in species that possess such a layer.

Human sperm DNA damage inhibition and antioxidant activity of T. arjuna bark: an in vitro study

Complimentary or natural antioxidant type of alternative medicine is developed worldwide to treat male infertility. The aim of this study is to the extraction of T. arjuna bark and activity against human sperm DNA damage in asthenoteratospermic smoker's subjects-an in vitro study. All preliminary and antioxidant assays (DPPH, H₂O₂, and total antioxidant, reducing power activity) were done. T. arjuna bark metal analysis was done with AAS. On the other hand, patients were asked to fill a direct questionnaire about smoking history; 25 infertile smokers were identified as asthenoteratospermic; 34 fertile non-smokers (control) were assessed for semen parameters by CASA, seminal plasma Zinc analysis by AAS, DNA fragmentation by colorimetric method and semen genomic DNA damage inhibition by modified non-enzymatic salting out extraction method. Most of the antioxidants are highly present in the aqueous extract; meanwhile, the major content in this extract is zinc 16 µg/g (Ca = 0.5 µg/g; Se = 2.2 µg/g and Mg = 1.6 µg/g) along with FT-IR peaks which also confirmed the metal presence. The semen parameters in smokers that were noticed are low sperm count and morphological changes. Meanwhile, in the seminal plasma of smokers, zinc and DNA fragmentation results were positively correlated with sperm morphology (p < 0.001). Repaired DNA bands were noticed in the in vitro study of aqueous T. arjuna bark, in smokers' semen. T. arjuna bark will act as cryo protector as well as great zinc supplementary to maintain sperm motility and morphology in smokers.

Whole genome-wide transcript profiling to identify differentially expressed genes associated with seed field emergence in two soybean low phytate mutants

BACKGROUND

Seed germination is important to soybean (Glycine max) growth and development, ultimately affecting soybean yield. A lower seed field emergence has been the main hindrance for breeding soybeans low in phytate. Although this reduction could be overcome by additional breeding and selection, the mechanisms of seed germination in different low phytate mutants remain unknown. In this study, we performed a comparative transcript analysis of two low phytate soybean mutants (TW-1 and TW-1-M), which have the same mutation, a 2 bp deletion in GmMIPS1, but show a significant difference in seed field emergence, TW-1-M was higher than that of TW-1 .

RESULTS

Numerous genes analyzed by RNA-Seq showed markedly different expression levels between TW-1-M and TW-1 mutants. Approximately 30,000-35,000 read-mapped genes and ~21000-25000 expressed genes were identified for each library. There were ~3900-9200 differentially expressed genes (DEGs) in each contrast library, the number of up-regulated genes was similar with down-regulated genes in the mutant TW-1and TW-1-M. Gene ontology functional categories of DEGs indicated that the ethylene-mediated signaling pathway, the abscisic acid-mediated signaling pathway, response to hormone, ethylene biosynthetic process, ethylene metabolic process, regulation of hormone levels, and oxidation-reduction process, regulation of flavonoid biosynthetic process and regulation of abscisic acid-activated signaling pathway had high correlations with seed germination. In total, 2457 DEGs involved in the above functional categories were identified. Twenty-two genes with 20 biological functions were the most highly up/down- regulated (absolute value Log2FC >5) in the high field emergence mutant TW-1-M and were related to metabolic or signaling pathways. Fifty-seven genes with 36 biological functions had the greatest expression abundance (FRPM >100) in germination-related pathways.

CONCLUSIONS

Seed germination in the soybean low phytate mutants is a very complex process, which involves a series of physiological, morphological and transcriptional changes. Compared with TW-1, TW-1-M had a very different gene expression profile, which included genes related to plant hormones, antioxidation, anti-stress and energy metabolism processes. Our research provides a molecular basis for understanding germination mechanisms, and is also an important resource for the genetic analysis of germination in low phytate crops. Plant hormone- and antioxidation-related genes might strongly contribute to the high germination rate in the TW-1-M mutant.

Genetic Modification for Improving Seed Vigor Is Transitioning from Model Plants to Crop Plants

Although seed vigor is a complex physiological trait controlled by quantitative trait loci, technological advances in the laboratory are being translated into applications for enhancing seed vigor in crop plants. In this article, we summarize and discuss pioneering work in the genetic modification of seed vigor, especially through the over-expression of protein L-isoaspartyl methyltransferase (PIMT, EC 2.1.1.77) in seeds. The impressive success in improving rice seed vigor through the over-expression of PIMT provides a valuable reference for engineering high-vigor seeds for crop production. In recent decades, numerous genes/proteins associated with seed vigor have been identified. It is hoped that such potential candidates may be used in the development of genetically edited crops for a high and stable yield potential in crop production. This possibility is very valuable in the context of a changing climate and increasing world population.

Imperative roles of salicylic acid and nitric oxide in improving salinity tolerance in Pisum sativum L

This study was undertaken to scrutinize efficacy of salicylic acid (SA) and/or sodium nitroprusside [SNP, source of nitric oxide (NO)] to mitigate injury symptoms of saline stress in Pisum sativum L. Exposure to sodium chloride (NaCl) was found to be injurious to germinating P. sativum L. (var. Shubhra IM-9101) and a direct correlation between severity of toxicity and NaCl-concentrations could be discernible. Both SA and NO serves as signal molecules in plant stress responses, and play crucial roles in key regulatory pathways of growth, development and metabolism. The limiting effects of salinity on radicle length and biomass accumulation were considerably released by SA and/or SNP and among which their combined application was found to be the most promising. Supplemented SA and/or SNP, particularly their cocktail, resulted in a substantial decline in reactive oxygen species accumulation, which later caused reduced accumulations of malondialdehyde, 4-hydroxy-2-nonenal and protein carbonyl, in NaCl subjected germinating P. sativum L. seeds. SA and/or SNP had significant inducing effects on activities of superoxide dismutase, catalase, guaiacol peroxidase and ascorbate peroxidase. Additionally, exogenous SA and/or SNP led to the higher proline, sugar and glycinebetaine contents, than that of the control. On the basis of accumulated results, it could be concluded that the cocktail of SA and SNP may be efficiently used to overcome the adverse signatures of salinity stress.

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.

Mitochondrial structural and antioxidant system responses to aging in oat (Avena sativa L.) seeds with different moisture contents

We observed the relationship between lifespan and mitochondria, including antioxidant systems, ultrastructure, and the hydrogen peroxide and malondialdehyde contents in 4 h imbibed oat (Avena sativa L.) seeds that were aged with different moisture contents (4%, 10% and 16%) for 0 (the control), 8, 16, 24, 32 and 40 d at 45 °C. The results showed that the decline in the oat seed vigor and in the integrity of the mitochondrial ultrastructure occurred during the aging process, and that these changes were enhanced by higher moisture contents. Mitochondrial antioxidants in imbibed oat seeds aged with a 4% moisture content were maintained at higher levels than imbibed oat seeds aged with a 10% and 16% moisture content. These results indicated that the levels of mitochondrial antioxidants and malondialdehyde after imbibition were related to the integrity of the mitochondrial membrane in aged oat seeds. The scavenging role of mitochondrial superoxide dismutase was inhibited in imbibed oat seeds aged at the early stage. Monodehydroascorbate reductase and dehydroascorbate reductase played more important roles than glutathione reductase in ascorbate regeneration in aged oat seeds during imbibition.

The role of oxidative stress in determining the level of viability of black poplar (Populus nigra) seeds stored at different temperatures

Black poplar (Populus nigra L.) is one of the most threatened tree species in Europe since up to 99% of its natural habitat has disappeared. Black poplar seeds are characterised by short longevity. It was recently demonstrated that black poplar seeds can be successfully stored at -10°C, -20°C and -196°C for at least 2 years but not at higher temperatures. In the present study, the role of oxidative stress in determining the level of viability of black poplar seeds stored at -196°C, -20°C, -10°C, -3°C and 3°C for 3 months, 1 year and 2 years was monitored. The superoxide anion radicals (O2-•) and hydrogen peroxide (H2O2) increased during storage and had an impact on membrane integrity as determined by changes in the content of fatty acids and phospholipids and increases in electrolyte leakage. The level of non-enzymatic and enzymatic components of the ascorbate-glutathione (AsA-GSH) cycle was also investigated. The level of O2-• was strongly correlated with the level of seed germination after 1 and 2 years of storage. This was accompanied by changes in the redox potential, as well as changes in the content of linoleic acid and phosphatydiloglycerol over the same period of time. In particular, the deleterious effect of H2O2 was observed after 2 years of storage when its accumulation was highly correlated with changes in the composition of fatty acids and phospholipids. Despite increased activity of AsA-GSH cycle enzymes, the level of reducing agents was insufficient and seeds exhibited large increases in the redox potential when stored at -3°C and still higher when stored at 3°C. Overall, the results of the study demonstrate that oxidative stress increases during seed storage, especially at the warmer temperatures and injures seed tissues; resulting in a loss of viability.

Antisense suppression of LOX3 gene expression in rice endosperm enhances seed longevity

Lipid peroxidation plays a major role in seed longevity and viability. In rice grains, lipid peroxidation is catalyzed by the enzyme lipoxygenase 3 (LOX3). Previous reports showed that grain from the rice variety DawDam in which the LOX3 gene was deleted had less stale flavour after grain storage than normal rice. The molecular mechanism by which LOX3 expression is regulated during endosperm development remains unclear. In this study, we expressed a LOX3 antisense construct in transgenic rice (Oryza sativa L.) plants to down-regulate LOX3 expression in rice endosperm. The transgenic plants exhibited a marked decrease in LOX mRNA levels, normal phenotypes and a normal life cycle. We showed that LOX3 activity and its ability to produce 9-hydroperoxyoctadecadienoic acid (9-HPOD) from linoleic acid were significantly lower in transgenic seeds than in wild-type seeds by measuring the ultraviolet absorption of 9-HPOD at 234 nm and by high-performance liquid chromatography. The suppression of LOX3 expression in rice endosperm increased grain storability. The germination rate of TS-91 (antisense LOX3 transgenic line) was much higher than the WT (29% higher after artificial ageing for 21 days, and 40% higher after natural ageing for 12 months). To our knowledge, this is the first report to demonstrate that decreased LOX3 expression can preserve rice grain quality during storage with no impact on grain yield, suggesting potential applications in agricultural production.

Increased rate of drying reduces metabolic inequity and critical water content in radicles of Cicer arietinum L

Orthodox seed serves as easily accessible model to study desiccation-sensitivity in plant tissues because once they undergo germination, they become sensitive to desiccation imposed injuries. In the proposed study, effects of rate of drying on the viability, electrolyte leakage, superoxide accumulation, lipid-protein oxidation and antioxidant enzymes were explored in excised radicles of Cicer arietinum L. under dehydration and wet storage. For both the drying conditions, desiccation could be explained by exponential and inverse functions. Under rapid drying tissue viability as scored by germination efficiency and tetrazolium staining remained 100 % all through the analysis (24 h) but declined remarkably after 0.30 g g(-1) fresh mass water content (4 days) under slow drying. Moreover, precipitous fall in tissue viability was observed after 2 weeks of wet storage. Rapid drying was also accompanied with limited amounts of electrolyte leakage, superoxide radical, malondialdehyde and protein hydroperoxide, together with enhanced level of protein. Additionally, activities of both superoxide dismutase and ascorbate peroxidase were increased in rapidly dried radicles, but guaiacol peroxidase was declined. In contrary, above referred biomarkers were observed to perform either inversely or poorly during slow drying and wet storage suggesting that above documented alterations might be the resultant of ageing and not desiccation. Gathered data demonstrated that increased drying lowers the critical water content for tissue survival and also reduces the risk of damage resulting from aqueous-based deleterious reactions. Additionally, it also showed that growing radicles are a popular model to explore desiccation-sensitivity in plant tissues and/or seeds.

The production, localization and spreading of reactive oxygen species contributes to the low vitality of long-term stored common beech (Fagus sylvatica L.) seeds

The common beech (Fagus sylvatica L.) is propagated by seeds, but the seed set is irregular with five to ten years in between crops. It is therefore necessary to store the seeds. However, beech seeds lose germinability during long-term storage. In this study, beech seeds were stored at -10°C under controlled conditions for 2, 5, 8, 11 and 13 years. Our results show that beech seeds lose germinability during storage in proportion to the duration of storage. The decrease in germinability correlated with increased electrolyte leakage and accumulation of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. Furthermore, a strong positive correlation was observed among the releases of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. In situ localization showed that superoxide anion radicals and hydrogen peroxide were first detectable in root cap cells. When the seed storage time was extended, the reactive oxygen species fluorescence expanded to more areas of the radicle, reaching the root apical meristem. A storage time-dependent decrease in catalase activity, observed in both embryonic axes and cotyledons, was also positively correlated with germinability. DNA fragmentation was observed in beech seeds during storage and occurred predominantly in embryonic axes stored for 5 years and more. Altogether, these results suggest that the loss of germinability in beech seeds during long-term storage depends on several factors, including strong of reactive oxygen species accumulation accompanied by reduced catalase activity as well as membrane injury and DNA alternations, which may be aging-related and ROS-derived. We suggest that the accumulating reactive oxygen species that spread to the root apical meristem are key factors that affect seed germinability after long-term storage.

Physiological and proteomic analyses on artificially aged Brassica napus seed

Plant seeds lose their viability when they are exposed to long term storage or controlled deterioration treatments, by a process known as seed aging. Based on previous studies, artificially aging treatments have been developed to accelerate the process of seed aging in order to understand its underlying mechanisms. In this study, we used Brassica napus seeds to investigate the mechanisms of aging initiation. B. napus seeds were exposed to artificially aging treatment (40°C and 90% relative humidity) and their physio-biochemical characteristics were analyzed. Although the treatment delayed germination, it did not increase the concentration of cellular reactive oxygen species (ROS). Comparative proteomic analysis was conducted among the control and treated seeds at different stages of germination. The proteins responded to the treatment were mainly involved in metabolism, protein modification and destination, stress response, development, and miscellaneous enzymes. Except for peroxiredoxin, no changes were observed in the accumulation of other antioxidant enzymes in the artificially aged seeds. Increased content of abscisic acid (ABA) was observed in the artificially treated seeds which might be involved in the inhibition of germination. Taken together, our results highlight the involvement of ABA in the initiation of seed aging in addition to the ROS which was previously reported to mediate the seed aging process.