Seed longevity: survival and maintenance of high germination ability of dry seeds

Overexpression of protection of telomeres 1 (POT1), a single-stranded DNA-binding proteins in alfalfa (Medicago sativa), enhances seed vigor

Extensive bodies of research are dedicated to the study of seed aging with a particular focus on the roles of reactive oxygen species (ROS), and the ensuing oxidative damage during storage, as a primary cause of seed vigor decreasing. ROS diffuse to the nucleus and damage the telomeres, resulting in a loss of genetic integrity. Protection of telomeres 1 (POT1) is a telomeric protein that binds to the telomere region, and plays an essential role in maintaining genomic stability in plants. In this study, there were totally four MsPOT1 genes obtained from alfalfa genome. Expression analysis of four MsPOT1 genes in germinated seed presented the different expressions. Four MsPOT1 genes displayed high expression levels at the early stage of seed germination, Among the four POT1 genes, it was found that MS. gene040108 was significantly up-regulated in the early germination stage of CK seeds, but down-regulated in aged seeds. RT-qPCR assays and RNA-seq data revealed that MsPOT1-X gene was significantly induced by seed aging treatment. Transgenic seeds overexpressing MsPOT1-X gene in Arabidopsis thaliana and Medicago trunctula exhibited enhanced seed vigor, telomere length, telomerase activity associated with reduced H2O2 content. These results would provide a new way to understand aging stress-responsive MsPOT1 genes for genetic improvement of seed vigor. Although a key gene regulating seed vigor was identified in this study, the specific mechanism of MsPOT1-X gene regulating seed vigor needs to be further explored.

The role of oleosins and phosphatidylcholines on the membrane mechanics of oleosomes

HYPOTHESIS

Oilseeds use triacylglycerides as main energy source, and pack them into highly stable droplets (oleosomes) to facilitate the triacylglycerides' long-term storage in the aqueous cytosol. To prevent the coalescence of oleosomes, they are stabilized by a phospholipid monolayer and unique surfactant-shaped proteins, called oleosins. In this study, we use state-of-the-art interfacial techniques to reveal the function of each component at the oleosome interface.

EXPERIMENTS

We created model oil-water interfaces with pure oleosins, phosphatidylcholines, or mixtures of both components (ratios of 3:1, 1:1, 1:3), and applied large oscillatory dilatational deformations (LAOD). The obtained rheological response was analyzed with general stress decomposition (GSD) to get insights into the role of phospholipids and oleosins on the mechanics of the interface.

FINDINGS

Oleosins formed viscoelastic solid interfacial films due to network formation via in-plane interactions. Between adsorbed phosphatidylcholines, weak interactions were observed, suggesting the surface stress response upon dilatational deformations was dominated by density changes. In mixtures with 3:1 and 1:1 oleosin-to-phosphatidylcholine ratios, oleosins dominated the interfacial mechanics and formed a network, while phosphatidylcholines contributed to interfacial tension reduction. At higher phosphatidylcholine concentrations (1:3 oleosin-to-phosphatidylcholine), phosphatidylcholine dominated the interface, and no network formation occurred. Our findings improve the understanding of both components' role for oleosomes.

Integrated examination of the transcriptome and metabolome of the gene expression response and metabolite accumulation in soybean seeds for seed storability under aging stress

Soybean quality and production are determined by seed viability. A seed's capacity to sustain germination via dry storage is known as its seed life. Thus, one of the main objectives for breeders is to preserve genetic variety and gather germplasm resources. However, seed quality and germplasm preservation have become significant obstacles. In this study, four artificially simulated aging treatment groups were set for 0, 24, 72, and 120 hours. Following an aging stress treatment, the transcriptome and metabolome data were compared in two soybean lines with notable differences in seed vigor-R31 (aging sensitive) and R80 (aging tolerant). The results showed that 83 (38 upregulated and 45 downregulated), 30 (19 upregulated and 11 downregulated), 90 (52 upregulated and 38 downregulated), and 54 (25 upregulated and 29 downregulated) DEGs were differentially expressed, respectively. A total of 62 (29 upregulated and 33 downregulated), 94 (49 upregulated and 45 downregulated), 91 (53 upregulated and 38 downregulated), and 135 (111 upregulated and 24 downregulated) differential metabolites accumulated. Combining the results of transcriptome and metabolome investigations demonstrated that the difference between R31 and R80 responses to aging stress was caused by genes related to phenylpropanoid metabolism pathway, which is linked to the seed metabolite caffeic acid. According to this study's preliminary findings, the aging-resistant line accumulated more caffeic acid than the aging-sensitive line, which improved its capacity to block lipoxygenase (LOX) activity. An enzyme activity inhibition test was used to demonstrate the effect of caffeic acid. After soaking seeds in 1 mM caffeic acid (a LOX inhibitor) for 6 hours and artificially aging them for 24 hours, the germination rates of the R31 and R80 seeds were enhanced. In conclusion, caffeic acid has been shown to partially mitigate the negative effects of soybean seed aging stress and to improve seed vitality. This finding should serve as a theoretical foundation for future research on the aging mechanism of soybean seeds.

The association of protein-bound methionine sulfoxide with proteomic basis for aging in beech seeds

BACKGROUND

European beech (Fagus sylvatica L.) trees produce seeds irregularly; therefore, it is necessary to store beech seeds for forestation. Despite the acquisition of desiccation tolerance during development, beech seeds are classified as intermediate because they lose viability during long-term storage faster than typical orthodox seeds. In this study, beech seeds stored for short (3 years) or long (20 years) periods under optimal conditions and displaying 92 and 30% germination capacity, respectively, were compared.

RESULTS

Aged seeds displayed increased membrane damage, manifested as electrolyte leakage and lipid peroxidation levels. Analyses have been based on embryonic axes, which contained higher levels of reactive oxygen species (ROS) and higher levels of protein-bound methionine sulfoxide (MetO) in aged seeds. Using label-free quantitative proteomics, 3,949 proteins were identified, of which 2,442 were reliably quantified pointing to 24 more abundant proteins and 35 less abundant proteins in beech seeds under long-term storage conditions. Functional analyses based on gene ontology annotations revealed that nucleic acid binding activity (molecular function), ribosome organization or biogenesis and transmembrane transport (cellular processes), translational proteins (protein class) and membranous anatomical entities (cellular compartment) were affected in aged seeds. To verify whether MetO, the oxidative posttranslational modification of proteins that can be reversed via the action of methionine sulfoxide reductase (Msr) enzymes, is involved in the aging of beech seeds, we identified and quantified 226 MetO-containing proteins, among which 9 and 19 exhibited significantly up- and downregulated MetO levels, respectively, in beech seeds under long-term storage conditions. Several Msr isoforms were identified and recognized as MsrA1-like, MsrA4, MsrB5 and MsrB5-like in beech seeds. Only MsrA1-like displayed decreased abundance in aged seeds.

CONCLUSIONS

We demonstrated that the loss of membrane integrity reflected in the elevated abundance of membrane proteins had a higher impact on seed aging progress than the MetO/Msr system. Proteome analyses enabled us to propose protein Sec61 and glyceraldehyde-3-phosphate dehydrogenase as potential longevity modulators in beech seeds.

Identification of transcriptional modules linked to the drought response of Brassica napus during seed development and their mitigation by early biotic stress

In order to capture the drought impacts on seed quality acquisition in Brassica napus and its potential interaction with early biotic stress, seeds of the 'Express' genotype of oilseed rape were characterized from late embryogenesis to full maturity from plants submitted to reduced watering (WS) with or without pre-occurring inoculation by the telluric pathogen Plasmodiophora brassicae (Pb + WS or Pb, respectively), and compared to control conditions (C). Drought as a single constraint led to significantly lower accumulation of lipids, higher protein content and reduced longevity of the WS-treated seeds. In contrast, when water shortage was preceded by clubroot infection, these phenotypic differences were completely abolished despite the upregulation of the drought sensor RD20. A weighted gene co-expression network of seed development in oilseed rape was generated using 72 transcriptomes from developing seeds from the four treatments and identified 33 modules. Module 29 was highly enriched in heat shock proteins and chaperones that showed a stronger upregulation in Pb + WS compared to the WS condition, pointing to a possible priming effect by the early P. brassicae infection on seed quality acquisition. Module 13 was enriched with genes encoding 12S and 2S seed storage proteins, with the latter being strongly upregulated under WS conditions. Cis-element promotor enrichment identified PEI1/TZF6, FUS3 and bZIP68 as putative regulators significantly upregulated upon WS compared to Pb + WS. Our results provide a temporal co-expression atlas of seed development in oilseed rape and will serve as a resource to characterize the plant response towards combinations of biotic and abiotic stresses.

Nucleoporin 50 proteins affect longevity and salinity stress tolerance in seeds

Nucleoporin 50 (Nup50) is an evolutionarily conserved protein that is a constituent of the nuclear pore complex (NPC); however, its physiological role in plants is unclear. Arabidopsis has two Nup50 proteins, Nup50a and Nup50b, which are highly expressed in developing seeds. Green fluoresceent protein (GFP)-fused Nup50a and Nup50b are localized exclusively in the nucleopolasm, implying an additional function beyond the NPC in the nuclear envelope. To investigate the function of Nup50s, we employed the CRISPR/Cas9 [clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9] system to generate a nup50a nup50b double mutant, which exhibited premature translation termination of both Nup50 proteins. While the mutant showed no significant abnormal phenotype during vegetative growth, the nup50a nup50b seeds had an abnormal shape compared with the wild type. Comparative transcriptomics using immature seeds revealed that Nup50s regulate the expression of various genes, including cell wall-related genes. The nup50a nup50b seeds exhibited reduced seed longevity and salinity stress tolerance. Tetrazolium uptake and mucilage release assays implied that the nup50a nup50b seeds had greater water permeability than the wild type. Taken together, our results imply that Nup50s play a critical role in seed formation by regulating gene expression.

Seed Longevity and Ageing: A Review on Physiological and Genetic Factors with an Emphasis on Hormonal Regulation

Upon storage, seeds inevitably age and lose their viability over time, which determines their longevity. Longevity correlates with successful seed germination and enhancing this trait is of fundamental importance for long-term seed storage (germplasm conservation) and crop improvement. Seed longevity is governed by a complex interplay between genetic factors and environmental conditions experienced during seed development and after-ripening that will shape seed physiology. Several factors have been associated with seed ageing such as oxidative stress responses, DNA repair enzymes, and composition of seed layers. Phytohormones, mainly abscisic acid, auxins, and gibberellins, have also emerged as prominent endogenous regulators of seed longevity, and their study has provided new regulators of longevity. Gaining a thorough understanding of how hormonal signalling genes and pathways are integrated with downstream mechanisms related to seed longevity is essential for formulating strategies aimed at preserving seed quality and viability. A relevant aspect related to research in seed longevity is the existence of significant differences between results depending on the seed equilibrium relative humidity conditions used to study seed ageing. Hence, this review delves into the genetic, environmental and experimental factors affecting seed ageing and longevity, with a particular focus on their hormonal regulation. We also provide gene network models underlying hormone signalling aimed to help visualize their integration into seed longevity and ageing. We believe that the format used to present the information bolsters its value as a resource to support seed longevity research for seed conservation and crop improvement.

The role of the biochemical composition of soybean seeds in the tolerance to deterioration under natural and artificial aging

The fast decline in the physiological quality of seeds during storage is a serious problem. It is known that the reduction of seed quality may be related to its biochemical constitution. However, the relationship between the composition and the mechanisms linked to the loss of vigor of soybean seeds during aging has not been elucidated yet. Thus, the aim of this work was to analyze the role of the biochemical composition of soybean seeds in the physiological quality and in the tolerance to deterioration due to natural and artificial aging. Seeds of six soybean genotypes were analyzed initially and after being submitted to natural aging, storage for eight months, and artificial aging, using the temperature of 41 °C and 100 % relative humidity for 96 h. Moisture content, germination and vigor tests were carried out. Also, there were measured the content of oil, total protein, soluble protein, malonaldehyde, and fatty acids palmitic, stearic, oleic, linoleic, and linolenic. It was verified that the physiological quality of soybean seeds decreased with both kinds of aging. However, the deterioration process occurs by distinct mechanisms. The biochemical composition of the seeds is associated with the physiological quality and their storage potential is changed by natural and artificial aging. The tolerance of the seed to deterioration is related to soluble protein and fatty acids content. Oleic fatty acid and soluble protein can be used as indicators of physiological quality in soybean seeds.

The orchid seed coat: a developmental and functional perspective

Orchid seeds are 'dust-like.' The seed coat is usually thin, with only one to a few cell layers. It originates from the integuments formed during ovule development. In orchids, the outer integument is primarily responsible for forming a mature seed coat. The inner integument usually fails to develop after fertilization, becomes compressed, and collapses over the expanding embryo. Hence, the seed coat is formed from the funiculus, chalaza, and outer integumentary cells. The outermost layer of the seed coat, the testa, is lignified, usually at the radial and inner tangential walls. The subepidermal thin-walled layer(s), the tegmen, subsequently cold, resulting in seeds having only a single layer of seed coat cells. In some species, cells of the inner integument remain alive with the ability to synthesize and accumulate lipidic and or phenolic compounds in their walls covering the embryo. This cover is called the 'carapace,' a protective shield contributing to the embryo's added protection. A developmental and functional perspective of the integuments and seed coat during seed development and germination is presented in this review.

Investigating the impact of terminal heat stress on contrasting wheat cultivars: a comprehensive analysis of phenological, physiological, and biochemical traits

Terminal heat stress has become one of the major threats due to global climate change which is significantly affecting the production and productivity of wheat crop. Therefore, it is necessary to identify key traits and genotypes to breed heat-tolerant wheat. The present study was undertaken with the objective of comparing the effects of heat stress (HSE) and extended heat stress (EHSE) on phenological-physio-biochemical traits of contrasting heat-tolerant and heat-susceptible genotypes during the reproductive phase. Phenological traits exhibited significant reduction under EHSE compared to HSE. Heat-tolerant genotypes maintained balanced phenological-physio-biochemical traits, while heat-sensitive genotypes showed significant reductions under both stress regimes. Among phenological traits, DM (R2 = 0.52) and BY (R2 = 0.44) have shown a positive effect on seed yield, indicating that biomass and crop duration contributed to the yield advantage under stress. During the grain filling stage, both the normalized difference vegetation index (NDVI) and chlorophyll (Chl) exhibited consistently positive impacts on grain yield under both HSE and EHSE conditions. This could be attributed to the enhanced photosynthesis resulting from delayed senescence and improved assimilate remobilization under terminal heat stress. The biochemical activity of superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX) was induced in tolerant genotypes under HSE. The correlation of canopy temperature with phenological-physio-biochemical traits remained static under HSE and EHSE, suggesting CT as the best selection parameter for heat tolerance. The traits showing a positive association with yield and that are less affected under stress could be used for selecting tolerant genotypes under stress environments. These tolerant genotypes can be used to develop mapping populations to decipher the genes conferring tolerance as well as to study the molecular basis of tolerance.

Ultrasonic treatment to enhance seed germination and vigour of wheat (Triticum durum) in association with γ-aminobutyric acid (GABA) shunt pathway

Treatments of wheat (Triticum durum L.) seeds with sonication or hydropriming may enhance seed germination and vigour in association with γ-aminobutyric acid (GABA). Therefore, the objective of this study is to examine the effect of sonication and hydropriming treatments on seed germination of wheat through the characterisation of seed germination performance, GABA shunt metabolite level (GABA, glutamate, and alanine), and the level of glutamate decarboxylase (GAD) mRNA transcription. Wheat seeds were exposed to three treatments for 0, 5, 10, 15, and 20min: (1) sonication with water; (2) sonication without water; and (3) hydropriming without sonication. Treated seeds were evaluated for germination percentage, mean time to germinate, germination rate index in the warm germination test, and seedling emergence and shoot length in the cold test. GABA shunt metabolites level (GABA, glutamate, and alanine), and the level of GAD mRNA transcription were measured for the seeds after treatments and for seedlings during germination and cold tests. Seeds treated with sonication or hydropriming treatments had a higher germination rate index (faster germination) in the standard germination test, and higher seedling emergence and shoot length in the cold test. Seeds treated with sonication or hydropriming treatments showed an enhancement in GABA shunt and their metabolites (alanine and glutamate), and GAD mRNA transcription level compared to untreated-control seeds. In conclusion, the sonication or hydropriming treatments significantly improved the germination performance of wheat and enhanced GABA metabolism to maintain the C:N metabolic balance, especially under cold stress.

Isopropylmalate synthase NtIPMS as a potential molecular marker for seed vigor in tobacco

Seed vigor is an important trait for tobacco production. However, the evaluation of seed vigor using molecular biomarkers is scarcely reported in tobacco. In this study, the development of molecular marker isopropylmalate synthase NtIPMS was conducted to detect seed ageing degree and seed priming effect in tobacco. Quantitative real-time PCR (qRT-PCR) analysis showed that the expression of NtIPMS was significantly induced at the initial imbibition stage during seed germination. The NtIPMS expression was positively correlated with the degree of seed ageing in non-pelleted and pelleted seeds. The mRNA level of NtIPMS was gradually increased with the increasing degree of seed ageing. The early best effect of gibberellin priming was observed in 30-h primed seeds, and the highest expression of NtIPMS was observed in 12-h primed seeds. The best stop time-point of seed priming is likely at the time 18 h after the relatively higher NtIPMS expression occurred during seed priming process. The NtIPMS mRNA detection has the potential usage as a potential molecular marker for the evaluation of seed vigor in tobacco.

Recent progress in molecular genetics and omics-driven research in seed biology

Elucidating the mechanisms that control seed development, metabolism, and physiology is a fundamental issue in biology. Michel Caboche had long been a catalyst for seed biology research in France up until his untimely passing away last year. To honour his memory, we have updated a review written under his coordination in 2010 entitled "Arabidopsis seed secrets unravelled after a decade of genetic and omics-driven research". This review encompassed different molecular aspects of seed development, reserve accumulation, dormancy and germination, that are studied in the lab created by M. Caboche. We have extended the scope of this review to highlight original experimental approaches implemented in the field over the past decade such as omics approaches aimed at investigating the control of gene expression, protein modifications, primary and specialized metabolites at the tissue or even cellular level, as well as seed biodiversity and the impact of the environment on seed quality.

Seed nanopriming: How do nanomaterials improve seed tolerance to salinity and drought?

Salt and drought stress are major environmental issues world-widely. These stresses can result in failures of seed germination, limiting agricultural production. New approaches are needed to increase crop production, ensuring food safety, quality, and agriculture sustainability. Nanopriming (priming seeds with nanomaterials) is an emerging seed technology improving crop production under the drastic climate change associated with stress factors. The present review not only provided an overview of nanopriming achieved salt and drought tolerance but also tried to discuss the behind mechanisms. We argued that the physico-chemical properties of the nanomaterials are key factors affecting their negative or positive effects on seed germination in terms of seed nanopriming. Furthermore, we highlighted the possible critical role of seed coat anatomy in effective nanopriming, in terms of saving costs and reducing biosafety issues. This review aims to help researchers to better understand and follow this fast-developing, cost-effective, and environmentally friendly research area.

Identification and Functional Analysis of Long Non-Coding RNA (lncRNA) in Response to Seed Aging in Rice

Many lncRNAs have been shown to play a vital role in aging processes. However, how lncRNAs regulate seed aging remains unknown. In this study, we performed whole transcriptome strand-specific RNA sequencing of samples from rice embryos, analyzed the differences in expression of rice seed lncRNAs before and after artificial aging treatment (AAT), and systematically screened 6002 rice lncRNAs. During the AAT period, the expression levels of most lncRNAs (454) were downregulated and only four were upregulated among the 458 differentially expressed lncRNAs (DELs). Cis- or trans-regulated target genes of the four upregulated lncRNAs were mainly related to base repair, while 454 downregulated lncRNAs were related to plant-pathogen interaction, plant hormones, energy metabolism, and secondary metabolism. The pathways of DEL target genes were similar with those of differentially expressed mRNAs (DEGs). A competing endogenous RNA (ceRNA) network composed of 34 lncRNAs, 24 microRNAs (miRNA), and 161 mRNAs was obtained. The cDNA sequence of lncRNA LNC_037529 was obtained by rapid amplification of cDNA ends (RACE) cloning with a total length of 1325 bp, a conserved 5' end, and a non-conserved 3' end. Together, our findings indicate that genome-wide selection for lncRNA downregulation was an important mechanism for rice seed aging. LncRNAs can be used as markers of seed aging in rice. These findings provide a future path to decipher the underlying mechanism associated with lncRNAs in seed aging.

Comparative Seeds Storage Transcriptome Analysis of Astronium fraxinifolium Schott, a Threatened Tree Species from Brazil

Astronium fraxinifolium Schott (Anacardiaceae), also known as a 'gonçalo-alves', is a tree of the American tropics, with distribution in Mexico, part of Central America, Argentina, Bolivia, Brazil and Paraguay. In Brazil it is an endangered species that occurs in the Cerrado, Caatinga and in the Amazon biomes. In support of ex situ conservation, this work aimed to study two accessions with different longevity (p50) of A. fraxinifolium collected from two different geographic regions, and to evaluate the transcriptome during aging of the seeds in order to identify genes related to seed longevity. Artificial ageing was performed at a constant temperature of 45 °C and 60% relative humidity. RNA was extracted from 100 embryonic axes exposed to control and aging conditions for 21 days. The transcriptome analysis revealed differentially expressed genes such as Late Embryogenesis Abundant (LEA) genes, genes involved in the photosystem, glycine rich protein (GRP) genes, and several transcription factors associated with embryo development and ubiquitin-conjugating enzymes. Thus, these results contribute to understanding which genes play a role in seed ageing, and may serve as a basis for future functional characterization of the seed aging process in A. fraxinifolium.

Raffinose family oligosaccharides (RFOs): role in seed vigor and longevity

Seed vigor and longevity are important agronomic attributes, as they are essentially associated with crop yield and thus the global economy. Seed longevity is a measure of seed viability and the most essential property in gene bank management since it affects regeneration of seed recycling. Reduced seed life or storability is a serious issue in seed storage since germplasm conservation and agricultural enhancement initiatives rely on it. The irreversible and ongoing process of seed deterioration comprises a complex gene regulatory network and altered metabolism that results in membrane damage, DNA integrity loss, mitochondrial dysregulation, protein damage, and disrupted antioxidative machinery. Carbohydrates and/or sugars, primarily raffinose family oligosaccharides (RFOs), have emerged as feasible components for boosting or increasing seed vigor and longevity in recent years. RFOs are known to perform diverse functions in plants, including abiotic and biotic stress tolerance, besides being involved in regulating seed germination, desiccation tolerance, vigor, and longevity. We emphasized and analyzed the potential impact of RFOs on seed vigor and longevity in this review. Here, we comprehensively reviewed the molecular mechanisms involved in seed longevity, RFO metabolism, and how RFO content is critical and linked with seed vigor and longevity. Further molecular basis, biotechnological approaches, and CRISPR/Cas applications have been discussed briefly for the improvement of seed attributes and ultimately crop production. Likewise, we suggest advancements, challenges, and future possibilities in this area.

Comparative changes in sugars and lipids show evidence of a critical node for regeneration in safflower seeds during aging

During seed aging, there is a critical node (CN) where the population viability drops sharply. Exploring the specific locations of the CN in different species of plants is crucial for understanding the biological storage properties of seeds and refining seed life span management. Safflower, a bulk oil crop that relies on seeds for propagation, has a short seed life. However, at present, its biological characteristics during storage are not clear, especially the changes in metabolic capability and cell structures. Such knowledge is needed to improve the management of safflower seed life span and effective preservation in gene banks. Here, the seed survival curve of oilseed safflower under the controlled deterioration conditions of 60% relative humidity and 50°C was detected. The seed population showed an inverted S shape for the fall in germination. In the first 12 days of aging, germination remained above 86%. Prior to the CN at approximately day 10 (C10), when viability was in the "plateau" interval, seed vigor reduced at the same imbibition time point. Further analysis of the changes in sugar concentration found that the sucrose content decreased slowly with aging and the content of raffinose and two monosaccharides decreased abruptly at C10. Differentially metabolized lipids, namely lysophospholipids [lyso-phosphatidylcholine (LPC) and lyso-phosphatidylethanolamines (LPE)] and PMeOH, increased at day 3 of aging (C3). Fatty acid content increased by C6, and the content of phospholipids [phosphatidylcholines (PC), phosphatidylethanolamines (PE), and phosphatidylinositols (PI) and glycolipids [digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulphoquinovosyl diglycerides (SQDG)] decreased significantly from C10. In addition, the activities of raffinose hydrolase alpha-galactosidase and the glyoxylate key enzyme isocitrate lyase decreased with seed aging. Confocal microscopy and transmission electron microscopy revealed shrinkage of the seed plasma membrane at C10 and the later fragmentation. Seedling phenotypic indicators and 2,3,5-triphenyltetrazolium chloride activity assays also verified that there were significant changes in seeds quality at the CN. In summary, the time point C10 is a CN during seed population aging. Before the CN, sugar and lipid metabolism, especially fatty acid metabolism into sugar, can make up for the energy consumed by aging. After this point, the seeds were irreversibly damaged, and their viability was greatly and rapidly reduced as the cell structure became increasingly destroyed.

Changes in nutritional quality-related traits of quinoa seeds under different storage conditions

Within the context of climate change and its impact on global food security, seed storage has become key, as it ensures long-term food and next-season seed preservation. Aiming at evaluating quality-related changes in quinoa seeds over storage time, different storage temperatures (–20, 4, 12, 25, and 37°C) and humidity conditions (use of silica gel or not) were studied and different seed nutritional parameters were evaluated at different points during a year of storage. Also, to determine if these variations could be conditioned by the genotype used, two quinoa cultivars were compared. The results proved that quinoa seed quality is highly dependent on the storage temperature but is not consistently affected by the use of silica gel if the seed moisture content (SMC) is kept between 5 and 12%. Furthermore, quality can be maintained and even improved by keeping SMC lower than 12% and storage temperatures low (4°C). Under these conditions (at 4°C in hermetic packaging with or without silica gel), and after 12 months of storage, there was an increase in amino acids like isoleucine, serine, arginine, glycine, and glutamic acid and in seed viability and germination. On the contrary, quinoa seeds stored at 37°C showed an accumulation of reactive oxygen species (ROS) which was related to a lower antioxidant capacity and a reduction in the contents of essential amino acids like isoleucine, lysine, histidine, and threonine, resulting in a delayed and reduced germination capacity, and, therefore, lower seed quality. Besides, quality-related differences appeared between cultivars highlighting differences linked to the genotype. Overall, this work demonstrates that optimal storage temperatures and SMC can preserve or even improve quinoa seed nutritional quality, which in turn can impact food safety and agriculture.

Assessing Seedbank Longevity and Seed Persistence of the Invasive Tussock Grass Nassella trichotoma Using in-Field Burial and Laboratory-Controlled Ageing

The ability to produce highly dense and persistent seedbanks is a major contributor to the successful widespread establishment of invasive plants. This study seeks to identify seed persistence and seedbank longevity for the invasive tussock grass Nassella trichotoma (Nees.) Hack. ex Arechav in order to recommend management strategies for preventing re-emergence from the seedbank. To determine the seedbank longevity and persistence, two experiments were conducted: (i) seeds were buried at four depths (0, 1, 2, and 4 cm) and collected and assessed for viability, seed decay, and in-field germination after 6, 9, 12, 15, and 18 months of field burial; and (ii) seeds were exposed to artificial ageing conditions (60% RH and 45 °C) for 1, 2, 5, 9, 20, 30, 50, 75, 100, and 120 days, and viability was determined through germination tests and tetrazolium tests. Less than 10% of the seeds collected after 12 months of in-field burial were viable. The artificial ageing treatment found germination declined to 50% after 5.8 days, further suggesting that N. trichotoma seeds are short lived. The results from both experiments indicate that N. trichotoma has a transient seedbank, with less than 10% of the seeds demonstrating short-term persistence. It is likely the persistent seeds beyond 12 months were exhibiting secondary dormancy as viable seeds did not germinate under optimal germination conditions. The "Best Practice Guidelines" recommend monitoring for seedbank recruitment for at least three years after treating N. trichotoma infestations. The results of this study support this recommendation as a small proportion of the seeds demonstrated short-term persistence.

Nitric oxide-an antidote to seed aging modifies meta-tyrosine content and expression of aging-linked genes in apple embryos

Short-term (3 h) treatment of embryos isolated from accelerated aged apple seeds (Malus domestica Borkh.) with nitric oxide (NO) partially reduced the effects of aging. The study aimed to investigate the impact of the short-term NO treatment of embryos isolated from apple seeds subjected to accelerated aging on the expression of genes potentially linked to the regulation of seed aging. Apple seeds were artificially aged for 7, 14, or 21 days. Then, the embryos were isolated from the seeds, treated with NO, and cultured for 48 h. Progression of seed aging was associated with the decreased transcript levels of most of the analyzed genes (Lea1, Lea2a, Lea4, Hsp70b, Hsp20a, Hsp20b, ClpB1, ClpB4, Cpn60a, Cpn60b, Raptor, and Saur). The role of NO in the mitigation of seed aging depended on the duration of the aging. After 7 and 14 days of seed aging, a decreased expression of genes potentially associated with the promotion of aging (Tor, Raptor, Saur) was noted. NO-dependent regulation of seed aging was associated with the stimulation of the expression of genes encoding chaperones and proteins involved in the repair of damaged proteins. After NO application, the greatest upregulation of ClpB, Pimt was noted in the embryos isolated from seeds subjected to 7-day long accelerated aging, Hsp70b, Hsp70c, and Cpn in the embryos of seeds aged for 14 days, and Lea2a in the embryos of seeds after 21 days of aging. We also demonstrated the increased meta-tyrosine concentration depending or in respect the progression of artificial aging, and the NO-induced increased phenylalanine content in seeds artificially aged for 21 days. In the NO-treated embryos of seeds aged for 7 and 21 days, the level of tyrosine was almost doubled compared to the aged tissue. Our data confirmed the usage of meta-tyrosine as a marker of seed aging and indicated that the increased meta-tyrosine/tyrosine ratio could be related to the loss of seed viability.

Deterioration in the Quality of Recalcitrant Quercus robur Seeds during Six Months of Storage at Subzero Temperatures: Ineffective Activation of Prosurvival Mechanisms and Evidence of Freezing Stress from an Untargeted Metabolomic Study

Pedunculate oak (Quercus robur L.) is an economically important forest-forming species in Poland that produces seeds that are sensitive to desiccation; therefore, short-lived seeds are classified as recalcitrant. Such seeds display active metabolism throughout storage. Acorns stored under controlled conditions (moisture content of 40%, temperature -3 °C) maintain viability for up to 1.5-2 years. Meanwhile, oaks only produce large numbers of seeds every few years during so-called mast years. This results in a scarcity of good-quality seeds for continuous nursery production and restoration. The recalcitrant storage behavior and the requirements of foresters make it necessary to develop a new protocol for longer acorn storage at lower temperatures. Two storage temperatures were tested: -3 °C (currently used in forest practice) and -7 °C. Our results showed that acorns stored for six months exhibited deterioration and reduced germination capacity, as well as reduced seedling performance, particularly when acorns were stored at -7 °C. To elucidate the decrease in quality during storage, an untargeted metabolomics study was performed for the first time and supported with the analysis of carbohydrates and percentages of carbon (C) and nitrogen (N). Embryonic axes were characterized by a lower C:N ratio and higher hydration. A total of 1985 metabolites were detected, and 303 were successfully identified and quantified, revealing 44 known metabolites that displayed significantly up- or downregulated abundance. We demonstrated for the first time that the significant deterioration of seed germination potential, particularly in seeds stored at -7 °C, was accompanied by an increased abundance of phenolic compounds and carbohydrates but also amino acids and phosphorylated monosaccharides, particularly in the embryonic axes. The increased abundance of defense-related metabolites (1,2,4-Benzenetriol; BTO), products of ascorbic acid degradation (threonic and isothreonic acid), as well as antifreezing compounds (sugar alcohols, predominantly threitol), was reported in seed stored at -7 °C. We hypothesize that seed deterioration was caused by freezing stress experienced during six months of storage at -7 °C, a decline in antioxidative potential and the unsuccessful rerouting of the energy-production pathways. Additionally, our data are a good example of the application of high-throughput metabolomic tools in forest management.

SK, Sheoran S, K. UB, K. BN, Kumar S, Singh AN, Singh HV. Seed Longevity in Legumes: Deeper Insights Into Mechanisms and Molecular Perspectives

Sustainable agricultural production largely depends upon the viability and longevity of high-quality seeds during storage. Legumes are considered as rich source of dietary protein that helps to ensure nutritional security, but associated with poor seed longevity that hinders their performance and productivity in farmer's fields. Seed longevity is the key determinant to assure proper seed plant value and crop yield. Thus, maintenance of seed longevity during storage is of prime concern and a pre-requisite for enhancing crop productivity of legumes. Seed longevity is significantly correlated with other seed quality parameters such as germination, vigor, viability and seed coat permeability that affect crop growth and development, consequently distressing crop yield. Therefore, information on genetic basis and regulatory networks associated with seed longevity, as well as molecular dissection of traits linked to longevity could help in developing crop varieties with good storability. Keeping this in view, the present review focuses towards highlighting the molecular basis of seed longevity, with special emphasis on candidate genes and proteins associated with seed longevity and their interplay with other quality parameters. Further, an attempt was made to provide information on 3D structures of various genetic loci (genes/proteins) associated to seed longevity that could facilitate in understanding the interactions taking place within the seed at molecular level. This review compiles and provides information on genetic and genomic approaches for the identification of molecular pathways and key players involved in the maintenance of seed longevity in legumes, in a holistic manner. Finally, a hypothetical fast-forward breeding pipeline has been provided, that could assist the breeders to successfully develop varieties with improved seed longevity in legumes.

Temporal Dynamics of Endogenous Bacterial Composition in Rice Seeds During Maturation and Storage, and Spatial Dynamics of the Bacteria During Seedling Growth

Seed endophytes are of interest because they are believed to affect seed quality, and ultimately, plant growth and fitness. A comprehensive understanding of the assembly of the seed microbiome during seed development and maturation, the fate of microbes during storage, and the migration of microbes during seedling growth are still lacking. In this study, to understand the assembly and fate of endogenous bacteria in rice seeds from the ripening stage to the storage and seedling stages, we employed culture-dependent and metagenomic analyses. Bacterial communities in rice seeds were composed of a few dominant taxa that were introduced at the milky and dough stages, and they persisted during seed maturation. The culturable bacterial population gradually increased during the ripening stage, whereas there was a gradual decrease during storage. Bacteria that persisted during storage proliferated after imbibition and were distributed and established in the shoots and roots of rice seedlings. The storage temperature influenced the abundance of bacteria, which consequently changed the bacterial composition in the shoots and roots of seedlings. Pantoea, Pseudomonas, and Allorhizobium were consistently abundant from seed development to the germination stage. Some endogenous bacterial strains significantly promoted the growth of Arabidopsis and rice plants. Overall, our results indicate that rice seeds are colonized by a few bacterial taxa during seed development, and their relative abundance fluctuates during storage and contributes significantly to the establishment of endophytes in the stems and roots of rice plants. The selected bacterial isolates can be used to improve the growth and health of rice plants. To the best of our knowledge, this is the first study to reveal the dynamics of bacterial populations during storage of rice seeds at different temperatures. The temporal dynamics of the bacterial community during seed storage provide clues for the manipulation of endogenous bacteria in rice plants.

OsGLYI3, a glyoxalase gene expressed in rice seed, contributes to seed longevity and salt stress tolerance

The glyoxalase pathway plays a vital role in the chemical detoxification of methylglyoxal (MG) in biological systems. Our previous study suggested that OsGLYI3 may be effective in seed natural aging. In this study, the rice OsGLYI3 gene was cloned and characterized as specifically expressed in the seed. The accelerated aging (AA) treatment results indicated significant roles of OsGLYI3 in seed longevity and vigor, as the seeds of the transgenic lines with overexpressed and knocked-out OsGLYI3 exhibited higher and lower germination, respectively. The AA treatment also increased the superoxide dismutase (SOD) activity in the overexpressed transgenic seeds compared to the wild-type seeds yet lowered the SOD activity in the CRISPR/Cas9-derived transgenic rice lines. Rice OsGLYI3 was markedly upregulated in response to NaCl induced stress conditions. Compared to wild-type plants, overexpressed transgenic rice lines exhibited increased GLYI activity, decreased MG levels and improved salt stress tolerance, while CRISPR/Cas9 knockout transgenic rice lines showed decreased glyoxalase I activity, increased MG levels, and greater sensitivity to stress treatments with NaCl. Collectively, our results confirmed for the first time that OsGLYI3 is specifically expressed in rice seeds and contributes to seed longevity and salt stress tolerance.

Transcription Factor DOF4.1 Regulates Seed Longevity in Arabidopsis via Seed Permeability and Modulation of Seed Storage Protein Accumulation

Seed longevity is modulated by multiple genetic factors in Arabidopsis thaliana. A previous genome-wide association study using the Elevated Partial Pressure of Oxygen (EPPO) aging assay pinpointed a genetic locus associated with this trait. Reverse genetics identified the transcription factor DOF4.1 as a novel seed longevity factor. dof4.1 loss-of-function plants generate seeds exhibiting higher germination after accelerated aging assays. DOF4.1 is expressed during seed development and RNAseq data show several putative factors that could contribute to the dof4.1 seed longevity phenotype. dof4.1 has reduced seed permeability and a higher levels of seed storage proteins mRNAs (cruciferins and napins) in developing seeds, as compared to wild-type seeds. It has been reported that mutant lines defective in cruciferins or napins present reduced seed longevity. The improved longevity of dof4.1 is totally lost in the quadruple mutant dof4.1 cra crb crc, but not in a dof4.1 line depleted of napins, suggesting a prominent role for cruciferins in this process. Moreover, a negative regulation of DOF4.1 expression by the transcription factor DOF1.8 is suggested by co-inoculation assays in Nicotiana benthamiana. Indeed, DOF1.8 expression anticorrelates with that of DOF4.1 during seed development. In summary, modulation of DOF4.1 levels during seed development contributes to regulate seed longevity.

Transcriptome-Wide Characterization of Seed Aging in Rice: Identification of Specific Long-Lived mRNAs for Seed Longevity

Various long-lived mRNAs are stored in seeds, some of which are required for the initial phase of germination and are critical to seed longevity. However, the seed-specific long-lived mRNAs involved in seed longevity remain poorly understood in rice. To identify these mRNAs in seeds, we first performed aging experiment with 14 rice varieties, and categorized them as higher longevity (HL) and lower longevity (LL) rice varieties in conventional rice and hybrid rice, respectively. Second, RNA-seq analysis showed that most genes showed similar tendency of expression changes during natural and artificial aging, suggesting that the effects of these two aging methods on transcription are comparable. In addition, some differentially expressed genes (DEGs) in the HL and LL varieties differed after natural aging. Furthermore, several specific long-lived mRNAs were identified through a comparative analysis of HL and LL varieties after natural aging, and similar sequence features were also identified in the promoter of some specific long-lived mRNAs. Overall, we identified several specific long-lived mRNAs in rice, including gibberellin receptor gene GID1, which may be associated with seed longevity.

Assessment of the Effects of Seed Storage Time on Germination Rate and Performance Evaluation of Ethiopian Faba Bean (Vicia faba L.) Varieties for Yield and Related Traits

In Ethiopia, faba bean (Vicia faba L.) varieties are important and widely used as a source of food and cash source to large number of subsistence farmers. However, their production and productivity is below the world's average partly because of lack of their sustainable performance in the current scenario of climate change. Therefore, the present study was designed to test the effects of seed storage time and to evaluate the performance of 31 faba bean varieties collected from Holeta, Kulumsa and Sinana agricultural research systems, Ethiopia. The study involved germination test and field experiment that was laid out using randomized complete block design (RCBD) and conducted at multiple test locations. Data were collected on qualitative and quantitative traits and analyzed using SAS version 9.0, and MINITAB® Release 19. Accordingly, most of the varieties showed a promising germination rate regardless of their storage duration suggesting their sustainable performance under suitable storage conditions. Most of the qualitative and quantitative traits showed a wide range of variations revealing their stable performance and better chance for further improvement. Analysis of variance also revealed a highly significant (p < 0.001) variation for several of the traits suggesting maintenance of the original diversity that could be important in further selection breeding. Likewise, high genetic advance coupled with high heritability and genotypic coefficient of variation together with wide range of variations in both PCV and GCV observed in several of the quantitative traits suggest their sustainable performance and significance in further effective selection. Moreover, a promising high yielding varieties such as Dida1, Welki, Hachalu, Ashebeka and Obse have been identified for further use. Clustering grouped the varieties into three clusters implying significant amount of genetic variability among them. Overall, the results generated could be used as a baseline information for improving faba bean production and productivity. However, to exploit more and determine the actual performance of the varieties more markers such as molecular markers (DNA based) are recommended.

Does oxygen affect ageing mechanisms of Pinus densiflora seeds? A matter of cytoplasmic physical state

During desiccation, the cytoplasm of orthodox seeds solidifies into an intracellular glass with highly restricted diffusion and molecular mobility. Temperature and water content govern seed ageing rates, while oxygen (O2) can promote deteriorative reactions. However, whether the cytoplasmic physical state affects involvement of O2 in seed ageing remains unresolved. We aged Pinus densiflora seeds by controlled deterioration (CD) at 45 °C and distinct relative humidity (RH), resulting in cells with a glassy (11% and 30% RH) or fluid (60% and 80% RH) cytoplasm. Hypoxic conditions (0.4% O2) during CD delayed seed deterioration, lipid peroxidation, and decline of antioxidants (glutathione, α-tocopherol, and γ-tocopherol), but only when the cytoplasm was glassy. In contrast, when the cytoplasm was fluid, seeds deteriorated at the same rate regardless of O2 availability, while being associated with limited lipid peroxidation, detoxification of lipid peroxide products, substantial loss of glutathione, and resumption of glutathione synthesis. Changes in metabolite profiles provided evidence of other O2-independent enzymatic reactions in a fluid cytoplasm, including aldo-keto reductase and glutamate decarboxylase activities. Biochemical profiles of seeds stored under seed bank conditions resembled those obtained after CD regimes that maintained a glassy cytoplasm. Overall, O2 contributed more to seed ageing when the cytoplasm was glassy, rather than fluid.

Germination of Triticum aestivum L.: Effects of Soil–Seed Interaction on the Growth of Seedlings

Seed size, sowing depth, and seed disinfection can affect seed germination and seedling establishment, which, in turn, can directly affect crop growth and yield. The current study was comprised of two experiments, the first of which was conducted in the laboratory, and a second which was performed under glasshouse conditions. The objective of these experiments was to investigate the effects of seed size, sowing depth, and seed disinfection on seed germination and initial seedling growth of selected wheat (Triticum aestivum L.) cultivars. The treatments in laboratory experiment were arranged in a completely randomized design, which included: (Ι) four wheat cultivars (Pishgam, Haydari, Soissons, and Mihan), (ΙΙ) two seed size classes (x < 2.25 mm, and x > 2.25 mm), and two disinfection treatments (no-disinfection and disinfection), (ΙΙΙ) with five replicates. In addition to the aforementioned treatments, the effect of planting depth (4, 6, and 8 cm) was also investigated in the subsequent glasshouse experiment. The best results were obtained at a sowing depth of 4 cm, in the non-disinfected treatment, using large seeds. In contrast, the lowest percentage and speed of seed germination and vigor index were observed in seeds sown at 8 cm depth, in the disinfected seed treatment, using small seeds. Large seeds contain larger nutrient stores which may improve seed germination indices, which would therefore result in improved percentage and speed of seed germination, followed by faster coleoptile and seedling growth, higher seedling dry weight and seed vigor. These data also illustrated that seed disinfection in the Pishgam and Haydari cultivars had inhibitory effects upon coleoptile growth and seedling length, which could be related to the fungicide’s chemical composition. Unlike other cultivars, disinfection did not show a significant effect on the Soissons cultivar. Based on our data, in order to improve both the speed of wheat seed germination and subsequent plant growth and development; it is necessary to select high-quality, large seeds, planted at a specific planting depth, which have been treated with an effective disinfectant; all of which will be specific for the wheat cultivar in question. Overall, the current study has provided useful information on the effect size seed, sowing depth, and disinfection have upon germination characteristics and seedling growth of wheat cultivars, which can form the basis for future field scale trails.

Ultrasonic Waves Regulate Antioxidant Defense and Gluconeogenesis to Improve Germination From Naturally Aged Soybean Seeds

Soybean seeds contain substantial triacylglycerols and fatty acids that are prone to oxidation during storage, contributing to the dramatic deterioration of seed vigor. This study reports an ultrasonic waves treatment (UWT), which is a physical method capable of promoting the germination ability of the aged soybean seeds by regulating the antioxidant defense and gluconeogenesis. Germination test revealed that UWT significantly increased the germination rate and seedlings' establishment of the soybean seeds stored for 12 months, although insignificantly impacting the vigor of fresh (stored for 1 month) and short-term stored (for 6 months) seeds. Further biochemical analysis revealed that UWT decreased the hydrogen peroxide (H₂O₂), O₂⋅^-, and malondialdehyde contents in the aged soybean seeds during early germination. Consistently, UWT prominently elevated the activities of superoxide dismutase, catalase, and acetaldehyde dehydrogenase, and also the corresponding gene expressions. Besides, the soluble sugar content of UWT was significantly higher than that of the untreated aged seeds. Analysis of enzyme activity showed UWT significantly upregulated the activities of several key enzymes in gluconeogenesis and the transcription levels of corresponding genes. Moreover, UWT enhanced the invertase activity within aged seeds, which was responsible for catalyzing sucrose hydrolysis for forming glucose and fructose. In summary, UWT improved germination and seedlings establishment of aged soybean seeds by regulating antioxidant defense and gluconeogenesis. This study expands the application of ultrasonication in agricultural production and further clarifies the physiological and molecular mechanisms of the aged seed germination, aiming to provide theoretical and practical guidance for seed quality and safety.

Seed coat lignification level is crucial in Capsicum spp seed longevity

Capsicum (pepper) is known for its poor seed germination, particularly seed longevity is usually much shorter than other Solanaceae. However, the molecular mechanisms involved are mostly unknown in these species. The present study examines the differences in seed longevity among Capsicum species and varietal types. Feral or less domesticated species, such as Capsicum chinense and particularly Capsicum frutescens, showed higher germination rates than the more domesticated Capsicum annuum after accelerated seed aging treatments. In addition, variability was detected in the expression of genes involved in the response to seed deterioration. The differences observed in ASPG1 expression led us to study the seed protein profile in dry and germinating seeds. Seed storage protein mobilization during germination was faster in seed aging-resistant genotypes. Similarly, the transcriptional change observed for the orthologous gene of the trans-species regulator AtHB25 prompted us to study the structure and molecular components of the seed coat in peppers. All the Capsicum pepper accessions analyzed presented very lignified testa and we observed a positive correlation between the amount of lignin and seed viability. Our results provide essential information to explain the poor germination observed in pepper seeds and provide an experimental framework for future improvements in this important character.

Nitric Oxide as a Remedy against Oxidative Damages in Apple Seeds Undergoing Accelerated Ageing

Seed ageing is associated with a high concentration of reactive oxygen species (ROS). Apple (Malus domestica Borkh.) seeds belong to the orthodox type. Due to a deep dormancy, they may be stored in dry condition at 5 °C for a long time, without viability loss. In the laboratory, artificial ageing of apple seeds is performed by imbibition in wet sand at warm temperature (33 °C). The aim of the work was to study nitric oxide (NO) as a seed vigour preservation agent. Embryos isolated from apple seeds subjected to accelerated ageing for 7, 14, 21 or 40 days were fumigated with NO. Embryo quality was estimated by TTC and MDA tests. ROS level was confirmed by NBT staining. We analysed the alteration in transcript levels of CAT, SOD and POX. NO fumigation of embryos of seeds aged for 21 days stimulated germination and increased ROS level which correlated to the elevated expression of RBOH. The increased total antioxidant capacity after NO fumigation was accompanied by the increased transcript levels of genes encoding enzymatic antioxidants, that could protect against ROS overaccumulation. Moreover, post-aged NO application diminished the nitro-oxidative modification of RNA, proving NO action as a remedy in oxidative remodelling after seeds ageing.

Relationship between the Characteristics of Bread Wheat Grains, Storage Time and Germination

Seed storage is important to farmers, breeders and for germplasm preservation. During storage, seeds accumulate damage at the structural and metabolic level, which disrupt their function and reduce resistance to adverse external conditions. In this regard, issues related to seed aging prove to be relevant for maintaining the viability of genetic collections. We analyzed morphological characteristics of grains and their coat color for 44 recombinant inbred lines (RILs) of bread wheat grown in four different seasons, 2003, 2004, 2009 and 2014. Our investigations were performed in 2020. For 19 RILs from the same seasons germination was evaluated. Our results demonstrate that genotype significantly affects the variability of all seed traits, and the year of harvesting affects about 80% of them (including all the traits of shape and size). To identify the trend between changes in grain characteristics and harvesting year, we estimated correlation coefficients between them. No significant trend was detected for the grain shape/size traits, while 90% of the color traits demonstrated such a trend. The most significant negative correlations were found between the harvesting year and the traits of grain redness: the greater the storage time, the more intensive is red color component for the grains. At the same time, it was shown that grains of longer storage time (earlier harvesting year) have lighter coat. Analysis of linear correlations between germination of wheat seeds of different genotypes and harvesting years and their seed traits revealed a negative linear relationship between the red component of coat color and germination: the redder the grains, the lower their germination rate. The results obtained demonstrate manifestations of metabolic changes in the coat of grains associated with storage time and their relationship with a decrease of seed viability.

Quantitative Trait Locus Mapping of Seed Vigor in Soybean under -20 °C Storage and Accelerated Aging Conditions via RAD Sequencing

Due to its fast deterioration, soybean (Glycine max L.) has an inherently poor seed vigor. Vigor loss occurring during storage is one of the main obstacles to soybean production in the tropics. To analyze the genetic background of seed vigor, soybean seeds of a recombinant inbred line (RIL) population derived from the cross between Zhonghuang24 (ZH24, low vigor cultivar) and Huaxia3hao (HX3, vigorous cultivar) were utilized to identify the quantitative trait loci (QTLs) underlying the seed vigor under -20 °C conservation and accelerated aging conditions. According to the linkage analysis, multiple seed vigor-related QTLs were identified under both -20 °C and accelerated aging storage. Two major QTLs and eight QTL hotspots localized on chromosomes 3, 6, 9, 11, 15, 16, 17, and 19 were detected that were associated with seed vigor across two storage conditions. The indicators of seed vigor did not correlate well between the two aging treatments, and no common QTLs were detected in RIL populations stored in two conditions. These results indicated that deterioration under accelerated aging conditions was not reflective of natural aging at -20 °C. Additionally, we suggest 15 promising candidate genes that could possibly determine the seed vigor in soybeans, which would help explore the mechanisms responsible for maintaining high seed vigor.

Thermotherapy and Storage Temperature Manipulations Limit the Production of Reactive Oxygen Species in Stored Pedunculate Oak Acorns

For many species, seed storage protocols are still being improved to provide viable seeds of the highest quality. Seed storage is extremely problematic for short-lived seeds categorized as recalcitrant, including pedunculate oak (Quercus robur L.), for which the optimal seed storage protocol involves a temperature of –3 °C and 40% acorn moisture content recommendations. The sensitivity of pedunculated oak seeds to temperature manipulations under preparation for long-term storage has been poorly investigated, particularly in terms of the production of reactive oxygen species (ROS), which are assumed to be determinants of seed longevity. Thermotherapy, the pathogen elimination procedure, did not increase the level of three types of ROS: hydrogen peroxide (H2O2), superoxide anion radical and hydroxyl radical (•OH). The temporal heat stress of thermotherapy resulted in slightly reduced levels of H2O2, indicating activation of the antioxidant systems in acorn preparation for storage. The effect of constant storage temperatures (−3, −5, −7 °C) and their combinations (−3 → −5 °C or −3 → −5 →−7 °C) on ROS levels and seed viability was investigated in three provenances. The highest ROS levels were detected in acorns stored at −7 °C, whereas three-step cold acclimation was beneficial for reducing ROS levels. Interestingly, the levels of H2O2 were not affected by temperature in thermotherapized acorns. In contrast, decreasing storage temperature caused a linear increase in •OH levels in all provenances. The effect of heat stress and cold stress on ROS levels in relation to long-term seed storage of pedunculate oak is discussed here in relation to the seed viability evidenced via germination rates, seedling emergence and electrolyte leakage. Thermotherapy and cold acclimation of acorns can improve their viability after storage by decreasing ROS levels.

Spatially Resolved Metabolomics and Lipidomics Reveal Salinity and Drought-Tolerant Mechanisms of Cottonseeds

In the current era of global climate change, environmental stresses, especially drought and salt, have impaired the growth and productivity of crops, e.g., cotton. Understanding the mechanisms of plants' adaptation to these abiotic stresses is crucial to breed stress-tolerant crop species. In the present study, integrated metabolomics, lipidomics, and mass spectrometry imaging (MSI) were used to discover the spatial distribution of differential metabolites and lipids in two cottonseed cultivars with contrasting drought and salt tolerance properties. Seventeen differential metabolites and 125 differential lipids were identified. Their possible roles in augmenting stress tolerance were illustrated, which were involved in reactive oxygen species scavenging, osmotic adjustment, and cell membrane structure reconstruction. MSI analysis provided a visualization of nine differential lipids and four differential metabolites in cottonseeds with varied abundances and distributions. The results may help understand cottonseeds' convictive metabolic and lipidomic regulatory networks in coping with salinity and drought stresses and give new insights into the stress-tolerance traits relevant to other crops.

Seed bank persistence of a South American cordgrass in invaded northern Atlantic and Pacific Coast estuaries

Invasive alien plant species impart considerable impacts that contribute to the decline of biodiversity worldwide. The ability of an invasive species to overcome barriers to establish and spread in new environments, and the long-term effects of plant invasions supporting their persistence are keys to invasion success. The capacity of introduced species to form soil seed banks can contribute to their invasiveness, yet few studies of invaders have addressed seed bank dynamics. Improved knowledge of this recruitment process can improve conservation management. We studied temporal and spatial changes in soil seed bank characteristics of the cordgrass Spartina densiflora from two continental invaded ranges. In the Odiel Marshes (Southwest Iberian Peninsula), S. densiflora formed transient seed banks (<1 year). At Humboldt Bay Estuary (California), viable seeds persisted for at least 4 years though the germination percentage fell abruptly after the first year from 29 % to less than 5 % of remaining viable seeds. Total soil seed bank density increased with S. densiflora above-ground cover in both estuaries, pointing to the transient component of the seed bank as a critical component of vegetation dynamics during S. densiflora invasion. Even so, seed densities as high as c. 750 seeds m-2 in Odiel Marshes and c. 12 400 seeds m-2 in Humboldt Bay were recorded in some plots without fruiting S. densiflora plants. S. densiflora spikelet (dispersal unit) density was more than double close to the sediment surface than deeper within soil. Our study shows the importance of evaluating seed banks during the design of invasive species management since seed bank persistence may vary among invaded sites, and can affect the timing and duration required for desired management outcomes.

OsGRETCHENHAGEN3-2 modulates rice seed storability via accumulation of abscisic acid and protective substances

Seed storability largely determines the vigor of seeds during storage and is significant in agriculture and ecology. However, the underlying genetic basis remains unclear. In the present study, we report the cloning and characterization of the rice (Oryza sativa) indole-3-acetic acid (IAA)-amido synthetase gene GRETCHEN HAGEN3-2 (OsGH3-2) associated with seed storability. OsGH3-2 was identified by performing a genome-wide association study in rice germplasms with linkage mapping in chromosome substitution segment lines, contributing to the wide variation of seed viability in the populations after long periods of storage and artificial ageing. OsGH3-2 was dominantly expressed in the developing seeds and catalyzed IAA conjugation to amino acids, forming inactive auxin. Transgenic overexpression, knockout, and knockdown experiments demonstrated that OsGH3-2 affected seed storability by regulating the accumulation level of abscisic acid (ABA). Overexpression of OsGH3-2 significantly decreased seed storability, while knockout or knockdown of the gene enhanced seed storability compared with the wild-type. OsGH3-2 acted as a negative regulator of seed storability by modulating many genes related to the ABA pathway and probably subsequently late embryogenesis-abundant proteins at the transcription level. These findings shed light on the molecular mechanisms underlying seed storability and will facilitate the improvement of seed vigor by genomic breeding and gene-editing approaches in rice.

Is protein carbonylation a biomarker of seed priming and ageing?

For a long time, it has been known that seed priming allows the improvement of plant production and tolerance to abiotic stresses. However, a negative effect on the longevity of the seeds thus primed was observed; these mechanisms are still poorly understood. In addition, it has been shown by several authors that seed ageing is associated with the oxidation and particularly with carbonylation of protein. Our work consisted in studying the AOPP and carbonyl protein at the different parts of the embryo from freshly primed seeds and from those that have been primed for 4 years (after storage). We subjected Vigna unguiculata (L.) Walp. seeds to a single or double hydropriming. Our study showed that hydropriming, and more particularly a double cycle of hydration-dehydration, makes it possible to attenuate the oxidation of the protein while it favours a certain threshold of carbonylation in the freshly dehydrated seeds in order to better trigger the germination process. On the other hand, after a storage period of 4 years, these dehydrated seeds are characterised by a strong accumulation of the products of oxidation and especially carbonylated protein, compared with the untreated seeds, which could explain the decrease of the longevity of these seeds.

Genome-Wide Association Study Reveals the QTLs for Seed Storability in World Rice Core Collections

Seed storability is a main agronomically important trait to assure storage safety of grain and seeds in rice. Although many quantitative trait loci (QTLs) and associated genes for rice seed storability have been identified, the detailed genetic mechanisms of seed storability remain unclear in rice. In this study, a genome-wide association study (GWAS) was performed in 456 diverse rice core collections from the 3K rice genome. We discovered the new nine QTLs designated as qSS1-1, qSS1-2, qSS2-1, qSS3-1, qSS5-1, qSS5-2, qSS7-1, qSS8-1, and qSS11-1. According to the analysis of the new nine QTLs, our results could well explain the reason why seed storability of indica subspecies was superior to japonica subspecies in rice. Among them, qSS1-2 and qSS8-1 were potentially co-localized with a known associated qSS1/OsGH3-2 and OsPIMT1, respectively. Our results also suggest that pyramiding breeding of superior alleles of these associated genes will lead to new varieties with improved seed storability in the future.

Ageing beautifully: can the benefits of seed priming be separated from a reduced lifespan trade-off?

Germination performance is affected following seed exposure to a combination of temperature fluctuations and cycles of hydration and dehydration. This has long been exploited in a seed technology termed priming, which increases germination speed and seedling vigour, but these benefits have often been associated with effects on seed lifespan, or longevity, with conflicting evidence for positive and negative effects. Seed longevity is a key seed trait influencing not only the storage of commercial stocks but also in situ and ex situ seed conservation. In the context of increasingly variable environmental conditions faced by both crops and wild species, this has led to renewed interest in understanding the molecular factors that underlie priming. Here, we provide an overview of the literature relating to the effect of priming on seed lifespan, and catalogue the different parameters used for priming treatments and their consequences on longevity for a range of species. Our current limited understanding of the molecular basis for priming effects is also outlined, with an emphasis on recent advances and promising approaches that should lead towards the application and monitoring of the priming process in a less empirical manner.

Regulation of Seed Dormancy and Germination Mechanisms in a Changing Environment

Environmental conditions are the basis of plant reproduction and are the critical factors controlling seed dormancy and germination. Global climate change is currently affecting environmental conditions and changing the reproduction of plants from seeds. Disturbances in germination will cause disturbances in the diversity of plant communities. Models developed for climate change scenarios show that some species will face a significant decrease in suitable habitat area. Dormancy is an adaptive mechanism that affects the probability of survival of a species. The ability of seeds of many plant species to survive until dormancy recedes and meet the requirements for germination is an adaptive strategy that can act as a buffer against the negative effects of environmental heterogeneity. The influence of temperature and humidity on seed dormancy status underlines the need to understand how changing environmental conditions will affect seed germination patterns. Knowledge of these processes is important for understanding plant evolution and adaptation to changes in the habitat. The network of genes controlling seed dormancy under the influence of environmental conditions is not fully characterized. Integrating research techniques from different disciplines of biology could aid understanding of the mechanisms of the processes controlling seed germination. Transcriptomics, proteomics, epigenetics, and other fields provide researchers with new opportunities to understand the many processes of plant life. This paper focuses on presenting the adaptation mechanism of seed dormancy and germination to the various environments, with emphasis on their prospective roles in adaptation to the changing climate.

The efficacy of different seed priming agents for promoting sorghum germination under salt stress

Sorghum [Sorghum bicolor (L.) Moench] seed germination is sensitive to salinity, and seed priming is an effective method for alleviating the negative effects of salt stress on seed germination. However, few studies have compared the effects of different priming agents on sorghum germination under salt stress. In this study, we quantified the effects of priming with distilled water (HP), sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl₂), and polyethylene glycol (PEG) on sorghum seed germination under 150 mM NaCl stress. The germination potential, germination rate, germination index, vigor index, root length, shoot length, root fresh weight, shoot fresh weight, root dry weight, and shoot dry weight were significantly reduced by salt stress. Different priming treatments alleviated the germination inhibition caused by salt stress to varying degrees, and 50 mM CaCl₂ was the most effective treatment. In addition, the mitigation effect of priming was stronger on root traits than on shoot traits. Mitigation efficacy was closely related to both the type of agent and the concentration of the solution. Principal component analysis showed that all concentrations of CaCl₂ had higher scores and were clearly distinguished from other treatments based on their positive effects on all germination traits. The effects of the other agents varied with concentration. The priming treatments were divided into three categories based on their priming efficacy, and the 50, 100, and 150 mM CaCl₂ treatments were placed in the first category. The 150 mM KCl, 10% PEG, HP, 150 mM NaCl, 30% PEG, and 50 mM KCl treatments were placed in the second category, and the 100 mM NaCl, 100 mM KCl, 20% PEG, and 50 mM NaCl treatments were least effective and were placed in the third category. Choosing appropriate priming agents and methods for future research and applications can ensure that crop seeds germinate healthily under saline conditions.

Desiccation Tolerance as the Basis of Long-Term Seed Viability

Desiccation tolerance appeared as the key adaptation feature of photoautotrophic organisms for survival in terrestrial habitats. During the further evolution, vascular plants developed complex anatomy structures and molecular mechanisms to maintain the hydrated state of cell environment and sustain dehydration. However, the role of the genes encoding the mechanisms behind this adaptive feature of terrestrial plants changed with their evolution. Thus, in higher vascular plants it is restricted to protection of spores, seeds and pollen from dehydration, whereas the mature vegetative stages became sensitive to desiccation. During maturation, orthodox seeds lose up to 95% of water and successfully enter dormancy. This feature allows seeds maintaining their viability even under strongly fluctuating environmental conditions. The mechanisms behind the desiccation tolerance are activated at the late seed maturation stage and are associated with the accumulation of late embryogenesis abundant (LEA) proteins, small heat shock proteins (sHSP), non-reducing oligosaccharides, and antioxidants of different chemical nature. The main regulators of maturation and desiccation tolerance are abscisic acid and protein DOG1, which control the network of transcription factors, represented by LEC1, LEC2, FUS3, ABI3, ABI5, AGL67, PLATZ1, PLATZ2. This network is complemented by epigenetic regulation of gene expression via methylation of DNA, post-translational modifications of histones and chromatin remodeling. These fine regulatory mechanisms allow orthodox seeds maintaining desiccation tolerance during the whole period of germination up to the stage of radicle protrusion. This time point, in which seeds lose desiccation tolerance, is critical for the whole process of seed development.

Analysis of Stored mRNA Degradation in Acceleratedly Aged Seeds of Wheat and Canola in Comparison to Arabidopsis

Seed aging has become a topic of renewed interest but its mechanism remains poorly understood. Our recent analysis of stored mRNA degradation in aged Arabidopsis seeds found that the stored mRNA degradation rates (estimated as the frequency of breakdown per nucleotide per day or β value) were constant over aging time under stable conditions. However, little is known about the generality of this finding to other plant species. We expanded the analysis to aged seeds of wheat (Triticum aestivum) and canola (Brassica napus). It was found that wheat and canola seeds required much longer periods than Arabidopsis seeds to lose seed germination ability completely under the same aging conditions. As what had been observed for Arabidopsis, stored mRNA degradation (∆Ct value in qPCR) in wheat and canola seeds correlated linearly and tightly with seed aging time or mRNA fragment size, while the quality of total RNA showed little change during seed aging. The generated β values reflecting the rate of stored mRNA degradation in wheat or canola seeds were similar for different stored mRNAs assayed and constant over seed aging time. The overall β values for aged seeds of wheat and canola showed non-significant differences from that of Arabidopsis when aged under the same conditions. These results are significant, allowing for better understanding of controlled seed aging for different species at the molecular level and for exploring the potential of stored mRNAs as seed aging biomarkers.

PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT) in plants: regulations and functions

Proteins are essential molecules that carry out key functions in a cell. However, as a result of aging or stressful environments, the protein undergoes a range of spontaneous covalent modifications, including the formation of abnormal l-isoaspartyl residues from aspartyl or asparaginyl residues, which can disrupt the protein's inherent structure and function. PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT: EC 2.1.1.77), an evolutionarily conserved ancient protein repairing enzyme (PRE), converts such abnormal l-isoaspartyl residues to normal l-aspartyl residues and re-establishes the protein's native structure and function. Although originally discovered in animals as a PRE, PIMT emerged as a key PRE in plants, particularly in seeds, in which PIMT plays a predominant role in preserving seed vigor and viability for prolonged periods of time. Interestingly, higher plants encode a second PIMT (PIMT2) protein which possesses a unique N-terminal extension, and exhibits several distinct features and far more complexity than non-plant PIMTs. Recent studies indicate that the role of PIMT is not restricted to preserving seed vigor and longevity but is also implicated in enhancing the growth and survivability of plants under stressful environments. Furthermore, expression studies indicate the tantalizing possibility that PIMT is involved in various physiological processes apart from its role in seed vigor, longevity and plant's survivability under abiotic stress. This review article particularly describes new insights and emerging interest in all facets of this enzyme in plants along with a concise comparative overview on isoAsp formation, and the role and regulation of PIMTs across evolutionary diverse species. Additionally, recent methods and their challenges in identifying isoaspartyl containing proteins (PIMT substrates) are highlighted.

Elucidation of the miR164c-Guided Gene/Protein Interaction Network Controlling Seed Vigor in Rice

MicroRNAs (miRNAs) play important roles in various aspects of plant physiology and metabolism. The expression level of miR164c is negatively correlated with seed vigor in rice (Oryza sativa L.); however, the mechanism of seed vigor regulation by miR164c remains unknown. Anti-aging capacity is an important indicator of seed vigor. Here, we report an miR164c-guided gene/protein interaction network that regulates the anti-aging ability of rice seeds. Seeds of the wild-type (WT) rice cultivar "Kasalath" and its transgenic derivatives, miR164c-silenced line (MIM164c) and miR164c overexpression line (OE164c), with significant differences in anti-aging capacity, showed significant differences in gene and protein expression levels. The differentially expressed genes (DEGs) or proteins were significantly enriched in six metabolic functional categories related to seed vigor, including "stress response," "protein processing in endoplasmic reticulum (ER)," "embryo development," "serine-type endopeptidase inhibitor," "energy metabolism," and "other." Differences in the expression levels of genes or proteins related to energy metabolism, serine endopeptidase, and stress response in seeds under normal storage conditions may be associated with anti-aging capacity. The results of gene/protein interaction analyses suggest that miR164c first targets PSK5, and the PSK5 protein then interacts with the ubiquitin-associated gene RPS27AA, which simultaneously impacts the genes/proteins in the six above-mentioned functional categories. Expression levels of some of the key genes and proteins in the interaction network were verified by real-time fluorescence quantitative PCR (RT-qPCR) and multiple reaction monitoring mass spectrometry (MRM-MS), respectively. Thus, the present study provides new insights into the miRNA-mediated gene and protein interaction network that regulates seed vigor.

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.