The mechanisms involved in seed dormancy alleviation by hydrogen cyanide unravel the role of reactive oxygen species as key factors of cellular signaling during germination

Effects of Fe and Zn alone and combined treatment on Triticum aestivum L. seed germination

Seed germination represents a pivotal phase in crop production, exhibiting pronounced sensitivity to abiotic stresses. In this study, wheat seeds of the 'Ningchun 4' variety were subjected to treatments involving zinc (Zn) chloride and iron (Fe) chloride, both individually and in combination. The impacts of these treatments on Fe and Zn accumulation, starch mobilization, antioxidant responses, and nitric oxide (NO) metabolism during seed germination were thoroughly examined. Individual application of Fe or Zn significantly inhibited and delayed wheat seed germination, which was accompanied by elevated levels of starch, sucrose, and soluble sugars, as well as increased reactive oxygen species and malondialdehyde concentrations. Concurrently, total amylase and α-amylase activities were downregulated, while antioxidant enzyme activities and the expression of TaCAT, TaAPX, and TaGR were upregulated. Seeds treated solely with Fe exhibited excessive Fe accumulation, heightened Fe2+ content, and diminished Zn content. Conversely, these trends were reversed in seeds treated with Zn alone. Furthermore, reduced NO levels were associated with downregulated nitrate reductase and nitric oxide synthase activities, alongside decreased expression of their corresponding genes in response to Fe exposure. Notably, the above effects induced by Zn alone were less severe compared to those induced by Fe stress. Importantly, the addition of Zn (100 µM or 250 µM) significantly alleviated the detrimental effects of Fe on several parameters in germinating seeds. The results from NO fluorescent probe staining corroborated the quantitative NO measurements across different treatments. In conclusion, an appropriate concentration of Zn effectively promoted the germination of Fe-stressed wheat seeds by mitigating Fe accumulation, attenuating oxidative damage, and enhancing starch mobilization during seed germination.

Ecological risks of a biopesticide from marine-derived amino-oligosaccharides in agriculture: Food chain effects on non-target organisms Frankliniella occidentalis and its natural predator Neoseiulus barkeri

A biopesticide from marine-derived amino-oligosaccharides (AO) are extensively utilized in China, yet there is a lack of scientific literature on their potential ecological risks when transmitted through the food chain to Neoseiulus barkeri, a natural predator of Frankliniella occidentalis. In this study, we conducted a comprehensive investigation into the food chain effects of AO on both F. occidentalis and N. barkeri. Our findings indicate that AO-treated cucumber leaves facilitated the population growth of F. occidentalis but indirectly suppressed the fecundity of N. barkeri which fed on the first instar nymphs of F. occidentalis. Besides, F. occidentalis that ingested AO-treated cucumber leaves exhibited elevated levels of total protein and defense enzymes, including catalase (CAT) and peroxidase (POD), whereas the detoxification enzymes activity, such as carboxylesterase (CarE) and cytochrome P450 monooxygenase (P450), was diminished. Conversely, N. barkeri exhibited decreased levels of the defense enzymes superoxide dismutase (SOD) and POD, coupled with an elevated CarE activity, because of AO food chain transmission. In conclusion, the food chain effects of AO on non-target organisms F. occidentalis and N. barkeri may involve the modulation of defense and detoxification enzyme activities, leading to varying fitness costs. These findings provide critical insights for agricultural pest management strategies, highlighting the necessity of evaluating the effects of AO on non-target organisms within ecosystems, especially beneficial insects, during its application.

Redox Control of Seed Germination is Mediated by the Crosstalk of Nitric Oxide and Reactive Oxygen Species

Significance: Seed germination and seedling establishment are characterized by changes in the intracellular redox state modulated by accelerated production of nitric oxide (NO) and reactive oxygen species (ROS). Redox regulation and enhanced accumulation of NO and ROS, approaching excessively high levels during seed imbibition, are critically important for breaking endodormancy and inducing germination. Recent Advances: Upon depletion of oxygen under the seed coat, NO is produced anaerobically in the reductive pathway associated mainly with mitochondria, and it participates in the energy metabolism of the seed until radicle protrusion. NO turnover involves nitrate reduction to nitrite in the cytosol, nitrite reduction to NO in mitochondria, and NO oxygenation in the cytosol in the reaction involving the hypoxically induced class 1 phytoglobin. In postgerminative degradation of seed tissues, NO and ROS are involved in redox signaling via post-translational modification of proteins and mediation of phytohormonal responses. Critical Issues: The crosstalk between the cellular redox potential, NO, ROS, and phytohormones integrates major physiological processes related to seed germination. Intensive accumulation of NO and ROS during imbibition is critically important for breaking seed dormancy. Upon oxygen depletion, NO and other nitrous oxides (NOx) are produced anaerobically and support energy metabolism prior to radicle protrusion. Future Directions: The turnover of NOx and ROS is determined by the intracellular redox balance, and it self-controls redox and energy levels upon germination. The particular details, regulation of this process, and its physiological significance remain to be established. Antioxid. Redox Signal. 42, 442-461.

Nitric Oxide Pre-Treatment Advances Bulblet Dormancy Release by Mediating Metabolic Changes in Lilium

The lily is a globally popular cut flower, and managing dormancy in lily bulblets is essential for continuous, year-round production. While nitric oxide (NO) has been shown to influence seed dormancy and germination, its role in dormancy release in lilies was previously unconfirmed. In this study, we investigated the effects of NO on dormancy release in lily bulblets using SNP and c-PTIO. Results showed that SNP treatment promoted dormancy release, while c-PTIO inhibited it. Measurement of endogenous NO levels in the bulbs, along with enzyme activities of NOS-like and NR and gene expression levels of LoNOS-IP and LoNR, confirmed that NO plays a role in promoting dormancy release in lilies. To further elucidate the physiological mechanisms involved, we analyzed H2O2 levels, antioxidant enzyme activities, endogenous hormone levels, and carbohydrate metabolism in the bulbs. Findings demonstrated that NO facilitated dormancy release by increasing H2O2, gibberellins (GAs), indole-3-acetic acid (IAA), zeatin riboside (ZR), reducing sugars, and by accelerating the metabolism of abscisic acid (ABA) and starch. This study provides a foundation for deeper investigation into the mechanisms underlying dormancy release in lily bulbs.

Combination of maleic hydrazide and coumarin inhibits rice seed germination involving reactive oxygen species accumulation, ABA metabolism and starch degradation

Pre-harvest sprouting (PHS) in cereal crops is a prevalent phenomenon that impacts grain yield and quality. Several PHS inhibitory compounds were screened and identified in previous studies, such as eugenol (EUG), maleic hydrazide (MH), coumarin (COU), etc. However, few studies have focused on the combination of PHS inhibitors, and the inhibitory mechanism remains unclear. Here, through combination tests of EUG, MH, and COU, the optimal combination of PHS inhibitors was selected as MH 20 mg L-1 + COU 100 mg L-1, which presented the lowest germination percentages. The optimal combination treatment significantly decreased the germination rate, α-amylase activity, content of soluble sugar and soluble protein, enhanced ABA content and the activity of superoxide dismutase (SOD) and peroxidase (POD), inhibited the production of superoxide anion (O2-) and hydrogen peroxide, and reduced the content of malondialdehyde (MDA); conversely, this trend is precisely the opposite in normal germination. Furthermore, gene expression analysis revealed that the optimal combination of MH and COU significantly decreased the expression level of OsAmy1A and OsAmy3D at 12 and 48 h after imbibition (HAI); and promoted the expression of OsRbohs (OsRbohA, OsRbohC, OsRbohD, OsRbohE, OsRbohH) and ABA biosynthetic genes OsNCED1, OsNCED2, and OsNCED5, especially OsNCED2 at 12 HAI, but down-regulated expression of OsRbohs and ABA catabolic genes OsABA8ox1-3 at 48 HAI. These results demonstrated that the delay in seed germination induced by MH and COU involved in ROS, ABA, and sugars; the optimal combination of MH and COU inhibited the germination process by promoting ABA biosynthesis and reducing ABA catabolism, and restraining the α-amylase activity to lower soluble sugar content. Intriguingly, although the expression of OsRbohs, which play a crucial role in generating ROS, increased in early imbibition (12h), the activity of the antioxidant enzymes SOD and POD also increased with the optimal combination treatment of MH and COU, which lead to the delay in ROS accumulation and inhibition of germination. These results have deepened our understanding of the regulatory mechanism of PHS inhibitors and provided theoretical support for the application of MH and COU in preventing sprouting before crop harvesting.

Transcriptome profiling reveals ethylene production by reactive oxygen species in trichloroisocyanuric acid-treated rice seeds

Reactive oxygen species (ROS) have been extensively suggested to stimulate ethylene production. However, the molecular mechanism by which ROS stimulate ethylene production remains largely unclear. Here, transcriptome profiling was used to verify if ROS could stimulate ethylene production via direct formation of ethylene from ROS. Trichloroisocyanuric acid (TCICA) can stimulate seed germination in rice. When transcriptome profiling was performed to determine the molecular responsiveness of rice seeds to TCICA, TCICA was initially proven to be a ROS-generating reagent. A total of 300 genes potentially responsive to TCICA treatment were significantly annotated to cysteine, and the expression of these genes was significantly upregulated. Nonetheless, the levels of cystine did not exhibit significant changes upon TCICA exposure. Cystine was then proven to be a substrate that reacted with TCICA to form ethylene under FeSO4 conditions. Moreover, 7 of 22 genes responsive to TCICA were common with the hydrogen peroxide (H2O2)-responsive genes. Ethylene was then proven to be produced from cysteine or cystine by reacting with H2O2 under FeSO4 condition, and the hydroxyl radical (OH-) was proposed to be the free radical species responsible for ethylene formation under FeSO4 condition. These results provide the first line of evidence that ethylene can be produced from ROS in a non-enzymatic manner, thereby unveiling one new molecular mechanism by which ROS stimulate ethylene production and offering novel insights into the crosstalk between ethylene and ROS.

Regulation of seed germination: ROS, epigenetic, and hormonal aspects

BACKGROUND

The whole life of a plant is regulated by complex environmental or hormonal signaling networks that control genomic stability, environmental signal transduction, and gene expression affecting plant development and viability. Seed germination, responsible for the transformation from seed to seedling, is a key initiation step in plant growth and is controlled by unique physiological and biochemical processes. It is continuously modulated by various factors including epigenetic modifications, hormone transport, ROS signaling, and interaction among them. ROS showed versatile crucial functions in seed germination including various physiological oxidations to nucleic acid, protein, lipid, or chromatin in the cytoplasm, cell wall, and nucleus.

AIM

of review: This review intends to provide novel insights into underlying mechanisms of seed germination especially associated with the ROS, and considers how these versatile regulatory mechanisms can be developed as useful tools for crop improvement.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We have summarized the generation and elimination of ROS during seed germination, with a specific focus on uncovering and understanding the mechanisms of seed germination at the level of phytohormones, ROS, and epigenetic switches, as well as the close connections between them. The findings exhibit that ROS plays multiple roles in regulating the ethylene, ABA, and GA homeostasis as well as the Ca2+ signaling, NO signaling, and MAPK cascade in seed germination via either the signal trigger or the oxidative modifier agent. Further, ROS shows the potential in the nuclear genome remodeling and some epigenetic modifiers function, although the detailed mechanisms are unclear in seed germination. We propose that ROS functions as a hub in the complex network regulating seed germination.

Exploring fine tuning between phytohormones and ROS signaling cascade in regulation of seed dormancy, germination and seedling development

In higher plants, seed is a propagule which ensures dissemination and survival of species. Developmental phases of a seed comprise embryogenesis, maturation and germination paving a way to its final fate i.e. seedling establishment. The final stage of seed maturation is marked by dehydration, acquisition of dessication tolerance and induction of dormancy. A precise Abscisic acid (ABA) to Gibberellins (GA) ratio, accumulation of miRNA 156, low level of reactive oxygen species (ROS) and enzyme inactivity govern seed dormancy. This also prevent pre harvest sprouting of the seeds. Overtime, stored seed mRNAs and proteins are degraded through oxidation of specific nucleotides in response to ROS accumulation. This degradation alleviates seed dormancy and transforms a dormant seed into a germinating seed. At this stage, ABA catabolism and degradation accompanied by GA synthesis contribute to low ABA to GA ratio. GA as well as ROS acts downstream, to mobilize reserve food materials, rupture testa, enhance imbibition and protrude radicle. All these events mark seed germination. Further, seedling is established under the governance of auxin and light. ABA and GA are master regulators while auxin, cytokinins, ethylene, jasmonic acid, brassinosteroids act through interdependent pathways to tightly regulate seed dormancy, germination and seedling establishment. In this review, the role of phytohormones and ROS in accordance with environmental factors in governing seed dormancy, promoting seed germination and thus, establishing a seedling is discussed in detail.

The MKK3-MPK7 cascade phosphorylates ERF4 and promotes its rapid degradation to release seed dormancy in Arabidopsis

Seeds establish dormancy to delay germination until the arrival of a favorable growing season. In this study, we identify a fate switch comprised of the MKK3-MPK7 kinase cascade and the ethylene response factor ERF4 that is responsible for the seed state transition from dormancy to germination. We show that dormancy-breaking factors activate the MKK3-MPK7 module, which affects the expression of some α-EXPANSIN (EXPA) genes to control seed dormancy. Furthermore, we identify a direct downstream substrate of this module, ERF4, which suppresses the expression of these EXPAs by directly binding to the GCC boxes in their exon regions. The activated MKK3-MPK7 module phosphorylates ERF4, leading to its rapid degradation and thereby releasing its inhibitory effect on the expression of these EXPAs. Collectively, our work identifies a signaling chain consisting of protein phosphorylation, degradation, and gene transcription , by which the germination promoters within the embryo sense and are activated by germination signals from ambient conditions.

Transcription factor TERF1 promotes seed germination through HEXOKINASE 1 (HXK1)-mediated signaling pathway

Seed germination, a vital process for plant growth and development, is regulated by ethylene. Previously, we showed that Tomato Ethylene Responsive Factor 1 (TERF1), an ethylene-responsive factor (ERF) transcription factor, could significantly promote seed germination by increasing glucose content. As glucose can function as a signaling molecule to regulate plant growth and development through HEXOKINASE 1 (HXK1), we aim to illustrate how TERF1 promotes seed germination through the HXK1-mediated signaling pathway. We showed that seeds overexpressing TERF1 exhibited more resistance to N-acetylglucosamine (NAG), an inhibitor of the HXK1- mediated signaling pathway. We identified genes regulated by TERF1 through HXK1 based on transcriptome analysis. Gene expression and phenotype analysis demonstrated that TERF1 repressed the ABA signaling pathway through HXK1, which promoted germination through activating the plasma membrane (PM) H+-ATPase. TERF1 also alleviated the endoplasmic reticulum (ER) stress to accelerate germination by maintaining reactive oxygen species (ROS) homeostasis through HXK1. Our findings provide new insights into the mechanism regulated by ethylene through the glucose-HXK1 signaling pathway during seed germination.

MAN5, a Glycosyl Hydrolase Superfamily Protein, Is a Key Factor Involved in Cyanide-Promoted Seed Germination in Arabidopsis thaliana

Seed germination is the complex adaptive trait of higher plants influenced by a large number of genes and environmental factors. Numerous studies have been performed to better understand how germination is controlled by various environmental factors and applied chemicals, such as cyanide. However, still very little is known about the molecular mechanisms of how extrinsic signals regulate seed germination. Our and previous studies found that non-lethal cyanide treatment promotes seed germination, but the regulatory mechanism is unclear. In this study, we found that a low concentration of cyanide pretreatment significantly enhanced the expression of endo-β-mannanase 5 (MAN5) gene in Arabidopsis thaliana, and the mutation of this gene impaired cyanide-mediated seed germination. In contrast, overexpression of MAN5 gene enhanced Arabidopsis seed germination ability under both normal and salt stress conditions. Further studies showed that the expression of the MAN5 gene was negatively regulated by ABA insensitive 5 (ABI5); In abi5 mutant seeds, the expression of the MAN5 gene was increased and the seed germination rate was accelerated. Additionally, cyanide pretreatment markedly reduced the gene expression of ABI5 in Arabidopsis seeds. Taken together, our data support the involvement of MAN5 as a key gene in cyanide-mediated seed germination and confirm the role of ABI5 as a critical negative factor involved in cyanide-regulated MAN5 gene expression.

Nitric Oxide Regulates Seed Germination by Integrating Multiple Signalling Pathways

Seed germination is of great significance for plant development and crop yield. Recently, nitric oxide (NO) has been shown to not only serve as an important nitrogen source during seed development but also to participate in a variety of stress responses in plants to high salt, drought, and high temperature. In addition, NO can affect the process of seed germination by integrating multiple signaling pathways. However, due to the instability of NO gas activity, the network mechanism for its fine regulation of seed germination remains unclear. Therefore, this review aims to summarize the complex anabolic processes of NO in plants, to analyze the interaction mechanisms between NO-triggered signaling pathways and different plant hormones such as abscisic acid (ABA) and gibberellic acid (GA), ethylene (ET) and reactive oxygen species (ROS) signaling molecules, and to discuss the physiological responses and molecular mechanisms of seeds during the involvement of NO in abiotic stress, so as to provide a reference for solving the problems of seed dormancy release and improving plant stress tolerance.

Imbibitional redox and hormonal priming revealed regulation of oxidative window as a key factor for progression of germination of indica rice cultivars

In the present investigation we have manipulated seeds of two indica rice cultivars, differing in sensitivity towards salinity stress (Oryza sativa L. cv. IR29 and Pokkali), with different combination of germination influencing hormones and redox modulating agents [500 µM Gibberellic acid (GA) + 20 mM H2O2, 500 µM GA + 100 µM Diphenyleneiodonium chloride (DPI), 500 µM GA + 500 µM N,N-dimethylthiourea (DMTU), 30 µM Triadimefon (TDM) + 100 µM DPI, 30 µM TDM + 500 µM DMTU] during early imbibition for exploring significance of regulation of oxidative window during germination. Reactive oxygen species (ROS)-antioxidant (AOX) interaction dynamics, assessed through redox metabolic fingerprints revealed significant changes in oxidative window of germinating tissue under redox and hormonal priming. GA (500 µM) + H2O2 (20 mM) priming formed favorable redox cue and opened the oxidative window for germination, whereas GA (500 µM) + DPI (100 µM), GA (500 µM) + DMTU (500 µM) and TDM (30 µM) + DPI (100 µM) combination failed to generate redox cue for opening the oxidative window at metabolic interface. Assessment of transcript abundance of genes of enzymes of central redox hub (RBOH-SOD-ASC-GSH/CAT pathway) further confirmed the transcriptional reprogramming of genes (Osrboh, OsSodCc2, OsCatA, OsAPx2, OsGRase) necessary for antioxidant-coupled origin of redox cue for germination. Assessment of pool of gibberellic acid, abscisic acid and jasmonic acid revealed a close connection between the hormonal homeostasis and internal redox cue. Role of oxidative window generated during metabolic reactivation phase for successful progression of germination is suggested.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01303-x.

Gasotransmitter H2S accelerates seed germination via activating AOX mediated cyanide-resistant respiration pathway

Hydrogen sulfide (H₂S) has been witnessed as a crucial gasotransmitter involving in various physiological processes in plants. H₂S signaling has been reported to involve in regulating seed germination, but the underlying mechanism remains poorly understood. Here, we found that endogenous H₂S production was activated in germinating Arabidopsis seeds, correlating with upregulated both the transcription and the activity of L-cysteine desulfhydrase (EC 4.4.1.28, LCD and DES1) responsible for H₂S production. Moreover, seed germination could be significantly accelerated by exogenous NaHS (the H₂S donor) fumigation and over-expressing DES1, while H₂S-generation defective (lcd/des1) seeds exhibited decreased germination speed. We also confirmed that the alternative oxidase (AOX), a cyanide-insensitive terminal oxidase, can be stimulated by imbibition. Furthermore, exogenous H₂S fumigation and over-expressing DES1 could significantly reinforced imbibition induced increase of both the AOX1A expression and AOX protein abundance, while this increase could be obviously weakened in lcd/des1. Additionally, exogenous H₂S fumigation mediated post-translational modification to keep AOX in its reduced and active state, which might involve H₂S induced improvement of the reduced GSH content and the cell reducing power. The promotive effect of H₂S on germination was clearly impaired by inducing aox1a mutation, indicating that AOX acts downstream of H₂S signaling to accelerate seed germination. Consequently, H₂S signaling was activated during germination then acted as a trigger to induce AOX mediated cyanide-resistant respiration to accelerate seed germination. Our study correlates H₂S signaling to cyanide-resistant respiration, providing evidence for more extensive studies of H₂S signaling.

Genetic mechanisms of aging in plants: What can we learn from them?

Plants hold all records in longevity. Their aging is a complex process. In the presented review, we analyzed published data on various aspects of plant aging with focus on any inferences that could shed a light on aging in animals and help to fight it in human. Plant aging can be caused by many factors, such as telomere depletion, genomic instability, loss of proteostasis, changes in intercellular interaction, desynchronosis, autophagy misregulation, epigenetic changes and others. Plants have developed a number of mechanisms to increase lifespan. Among these mechanisms are gene duplication ("genetic backup"), the active work of telomerases, abundance of meristematic cells, capacity of maintaining the meristems permanently active and continuous activity of phytohormones. Plant aging usually occurs throughout the whole perennial life, but could be also seasonal senescence. Study of causes for seasonal aging can also help to uncover the mechanisms of plant longevity. The influence of different factors such as microbiome communities, glycation, alternative oxidase activity, mitochondrial dysfunction on plant longevity was also reviewed. Adaptive mechanisms of long-lived plants are considered. Further comparative study of the mechanisms underlying longevity of plants is necessary. This will allow us to reach a potentially new level of understanding of the aging process of plants.

Intracellular reactive oxygen species trafficking participates in seed dormancy alleviation in Arabidopsis seeds

Reactive oxygen species (ROS) release seed dormancy through an unknown mechanism. We used different seed dormancy-breaking treatments to decipher the dynamics and localization of ROS production during seed germination. We studied the involvement of ROS in the breaking of Arabidopsis seed dormancy by cold stratification, gibberellic acid (GA₃ ) and light. We characterized the effects of these treatments on abscisic acid and gibberellins biosynthesis and signalling pathways. ROS, mitochondrial redox status and peroxisomes were visualized and/or quantified during seed imbibition. Finally, we performed a cytogenetic characterization of the nuclei from the embryonic axes during seed germination. We show that mitochondria participate in the early ROS production during seed imbibition and that a possible involvement of peroxisomes in later stages should still be analysed. At the time of radicle protrusion, ROS accumulated within the nucleus, which correlated with nuclear expansion and chromatin decompaction. Taken together, our results provide evidence of the role of ROS trafficking between organelles and of the nuclear redox status in the regulation of seed germination by dormancy.

Insights into the Genomic Architecture of Seed and Pod Quality Traits in the U.S. Peanut Mini-Core Diversity Panel

Traits such as seed weight, shelling percent, percent sound mature kernels, and seed dormancy determines the quality of peanut seed. Few QTL (quantitative trait loci) studies using biparental mapping populations have identified QTL for seed dormancy and seed grade traits. Here, we report a genome-wide association study (GWAS) to detect marker–trait associations for seed germination, dormancy, and seed grading traits in peanut. A total of 120 accessions from the U.S. peanut mini-core collection were evaluated for seed quality traits and genotyped using Axiom SNP (single nucleotide polymorphism) array for peanut. We observed significant variation in seed quality traits in different accessions and different botanical varieties. Through GWAS, we were able to identify multiple regions associated with sound mature kernels, seed weight, shelling percent, seed germination, and dormancy. Some of the genomic regions that were SNP associated with these traits aligned with previously known QTLs. For instance, QTL for seed dormancy has been reported on chromosome A05, and we also found SNP on the same chromosome associated with seed dormancy, explaining around 20% of phenotypic variation. In addition, we found novel genomic regions associated with seed grading, seed germination, and dormancy traits. SNP markers associated with seed quality and dormancy identified here can accelerate the selection process. Further, exploring the function of candidate genes identified in the vicinity of the associated marker will assist in understanding the complex genetic network that governs seed quality.

Reproductive resilience: putting pollen grains in two baskets

To ensure reproductive success, flowering plants produce an excess of pollen to fertilize a limited number of ovules. Pollen grains mature into two distinct subpopulations - those that display high metabolic activity and elevated reactive oxygen species (ROS) levels immediately after hydration (high-ROS/active), and those that maintain an extended period of dormancy with low metabolic activity (low-ROS/inactive/arrested/dormant). We propose that the dormant pollen serves as a backup to provide a second chance for successful fertilization when the 'first wave' of pollen encounters an unpredictable growth condition such as heat stress. This model provides a framework for considering the role of dormancy in reproductive stress tolerance as well as strategies for mitigating pollen thermovulnerability to daytime and night-time warming that is associated with global climate change.

Advances in the Understanding of Reactive Oxygen Species-Dependent Regulation on Seed Dormancy, Germination, and Deterioration in Crops

Reactive oxygen species (ROS) play an essential role in the regulation of seed dormancy, germination, and deterioration in plants. The low level of ROS as signaling particles promotes dormancy release and triggers seed germination. Excessive ROS accumulation causes seed deterioration during seed storage. Maintaining ROS homeostasis plays a central role in the regulation of seed dormancy, germination, and deterioration in crops. This study highlights the current advances in the regulation of ROS homeostasis in dry and hydrated seeds of crops. The research progress in the crosstalk between ROS and hormones involved in the regulation of seed dormancy and germination in crops is mainly summarized. The current understandings of ROS-induced seed deterioration are reviewed. These understandings of ROS-dependent regulation on seed dormancy, germination, and deterioration contribute to the improvement of seed quality of crops in the future.

Combined Transcriptome and Metabolome Analysis of Musa nana Laur. Peel Treated With UV-C Reveals the Involvement of Key Metabolic Pathways

An increasing attention is being given to treat fruits with ultraviolet C (UV-C) irradiation to extend shelf-life, senescence, and protection from different diseases during storage. However, the detailed understanding of the pathways and key changes in gene expression and metabolite accumulation related to UV-C treatments are yet to be explored. This study is a first attempt to understand such changes in banana peel irradiated with UV-C. We treated Musa nana Laur. with 0.02 KJ/m2 UV-C irradiation for 0, 4, 8, 12, 15, and 18 days and studied the physiological and quality indicators. We found that UV-C treatment reduces weight loss and decay rate, while increased the accumulation of total phenols and flavonoids. Similarly, our results demonstrated that UV-C treatment increases the activity of defense and antioxidant system related enzymes. We observed that UV-C treatment for 8 days is beneficial for M. nana peels. The peels of M. nana treated with UV-C for 8 days were then subjected to combined transcriptome and metabolome analysis. In total, there were 425 and 38 differentially expressed genes and accumulated metabolites, respectively. We found that UV-C treatment increased the expression of genes in secondary metabolite biosynthesis related pathways. Concomitant changes in the metabolite accumulation were observed. Key pathways that were responsive to UV-C irradiation include flavonoid biosynthesis, phenylpropanoid bios6ynthesis, plant-pathogen interaction, MAPK signaling (plant), and plant hormone signal transduction pathway. We concluded that UV-C treatment imparts beneficial effects on banana peels by triggering defense responses against disease, inducing expression of flavonoid and alkaloid biosynthesis genes, and activating phytohormone and MAPK signaling pathways.

New insights into the role of cyanide in the promotion of seed germination in tomato

BACKGROUND

Cyanide is a natural metabolite that exists widely in plants, and it is speculated to be involved in the regulation of various growth and development processes of plants in addition to being regarded as toxic waste. Previous studies have shown that exogenous cyanide treatment helps to improve seed germination, but the mechanism is still unclear. In this study, tomato (Solanum lycopersicum cv. Alisa Craig) was used as the material, and the effects of cyanide pretreatment at different concentrations on tomato seed germination were investigated.

RESULTS

The results showed that exogenous application of a lower concentration of cyanide (10 μmol/L KCN) for 12 h strongly increased the tomato seed germination rate. RNA-Seq showed that compared with the control, a total of 15,418 differentially expressed genes (P<0.05) were obtained after pretreatment with KCN for 12 h, and in the next 12 h, a total of 13,425 differentially expressed genes (P<0.05) were regulated. GO and KEGG analyses demonstrated that exogenous KCN pretreatment was involved in regulating the expression (mainly downregulation) of seed storage proteins, thereby accelerating the degradation of stored proteins for seed germination. In addition, KCN pretreatment was also involved in stimulating glycolysis, the TCA cycle and oxidative phosphorylation. Notably, it is shown that KCN acted on the regulation of plant hormone biosynthesis and perception, i.e., down-regulated the gene expression of ABA biosynthesis and signal transduction, but up-regulated the expression of genes related to GA biosynthesis and response. Consistent with this, plant hormone measurements confirmed that the levels of ABA were reduced, but GA levels were induced after pretreatment with KCN.

CONCLUSION

These findings provide new insights into the regulation of seed germination by cyanide, that is cyanide-mediated seed germination occurs in a time- and dose-dependent manner, and is related to the mobilization of energy metabolism and the regulation of some plant hormone signals.

Transcriptomic Changes in Internode Explants of Stinging Nettle during Callogenesis

Callogenesis, the process during which explants derived from differentiated plant tissues are subjected to a trans-differentiation step characterized by the proliferation of a mass of cells, is fundamental to indirect organogenesis and the establishment of cell suspension cultures. Therefore, understanding how callogenesis takes place is helpful to plant tissue culture, as well as to plant biotechnology and bioprocess engineering. The common herbaceous plant stinging nettle (Urtica dioica L.) is a species producing cellulosic fibres (the bast fibres) and a whole array of phytochemicals for pharmacological, nutraceutical and cosmeceutical use. Thus, it is of interest as a potential multi-purpose plant. In this study, callogenesis in internode explants of a nettle fibre clone (clone 13) was studied using RNA-Seq to understand which gene ontologies predominate at different time points. Callogenesis was induced with the plant growth regulators α-napthaleneacetic acid (NAA) and 6-benzyl aminopurine (BAP) after having determined their optimal concentrations. The process was studied over a period of 34 days, a time point at which a well-visible callus mass developed on the explants. The bioinformatic analysis of the transcriptomic dataset revealed specific gene ontologies characterizing each of the four time points investigated (0, 1, 10 and 34 days). The results show that, while the advanced stage of callogenesis is characterized by the iron deficiency response triggered by the high levels of reactive oxygen species accumulated by the proliferating cell mass, the intermediate and early phases are dominated by ontologies related to the immune response and cell wall loosening, respectively.

Metabolic Changes in Seed Embryos of Hypoxia-Tolerant Rice and Hypoxia-Sensitive Barley at the Onset of Germination

Rice (Oryza sativa L.) and barley (Hordeum vulgare L.) are the cereal species differing in tolerance to oxygen deficiency. To understand metabolic differences determining the sensitivity to low oxygen, we germinated rice and barley seeds and studied changes in the levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), activities of the enzymes involved in their scavenging, and measured cell damage parameters. The results show that alcohol dehydrogenase activity was higher in rice than in barley embryos providing efficient anaerobic fermentation. Nitric oxide (NO) levels were also higher in rice embryos indicating higher NO turnover. Both fermentation and NO turnover can explain higher ATP/ADP ratio values in rice embryos as compared to barley. Rice embryos were characterized by higher activity of S-nitrosoglutathione reductase than in barley and a higher level of free thiols in proteins. The activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase) in imbibed embryos were higher in rice than in barley, which corresponded to the reduced levels of ROS, malonic dialdehyde and electrolyte leakage. The observed differences in metabolic changes in embryos of the two cereal species differing in tolerance to hypoxia can partly explain the adaptation of rice to low oxygen environments.

Exogenous 2,4-Epibrassinolide Treatment Maintains the Quality of Carambola Fruit Associated With Enhanced Antioxidant Capacity and Alternative Respiratory Metabolism

Brassinosteroids act by delaying fruit ripening. The effects of different concentrations of 2,4-epibrassinolide (eBL) treatments on carambola fruit ripening were investigated. The results show that treatment of 2.8 mg L-1, eBL with 10 min effectively delays ripening and maintains the quality of carambola fruit. This is achieved by retarding color changes and firmness losses while maintaining high level of soluble protein content and vitamin C, and low organic acid content. eBL-delayed senescence may be due to the inhibition of respiration rate and enhanced antioxidant system. It is noteworthy that eBL treatment markedly reduces the content of fructose-6-phosphate (6-P-F) and enhances the activity of cytochrome oxidase (CCO), and the total activity of glucose-6-phosphate dehydrogenase (G-6-PDH) and 6-phosphate gluconate dehydrogenase (6-PGDH). eBL treatment induces the IAA and GA contents but reduces that of ABA. In general, senescence retardation and quality improvement by eBL treatment may be due to the enhanced antioxidant capacity and altered respiratory pathways.

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.

Retrograde signalling from the mitochondria to the nucleus translates the positive effect of ethylene on dormancy breaking of Arabidopsis thaliana seeds

Ethylene and reactive oxygen species (ROS) regulate seed dormancy alleviation, but the molecular basis of their action and crosstalk remains largely unknown. Here we studied the mechanism of Arabidopsis seed dormancy release by ethylene using cell imaging, and genetic and transcriptomics approaches, in order to tackle its possible interaction with ROS homeostasis. We found that the effect of ethylene on seed germination required ROS production by the mitochondrial electron transport chain. Seed response to ethylene involved a mitochondrial retrograde response (MRR) through nuclear ROS production and upregulation of the MRR components AOX1a and ANAC013, but also required the activation of the ethylene canonical pathway. Together our data allowed deciphering of the mode of action of ethylene on seed germination and the associated dynamics of ROS production. Our findings highlight the occurrence of retrograde signalling in seed germination.

Roles of Reactive Oxygen Species and Mitochondria in Seed Germination

Seed germination is crucial for the life cycle of plants and maximum crop production. This critical developmental step is regulated by diverse endogenous [hormones, reactive oxygen species (ROS)] and exogenous (light, temperature) factors. Reactive oxygen species promote the release of seed dormancy by biomolecules oxidation, testa weakening and endosperm decay. Reactive oxygen species modulate metabolic and hormone signaling pathways that induce and maintain seed dormancy and germination. Endosperm provides nutrients and senses environmental signals to regulate the growth of the embryo by secreting timely signals. The growing energy demand of the developing embryo and endosperm is fulfilled by functional mitochondria. Mitochondrial matrix-localized heat shock protein GhHSP24.7 controls seed germination in a temperature-dependent manner. In this review, we summarize comprehensive view of biochemical and molecular mechanisms, which coordinately control seed germination. We also discuss that the accurate and optimized coordination of ROS, mitochondria, heat shock proteins is required to permit testa rupture and subsequent germination.

In vivo light-sheet microscopy resolves localisation patterns of FSD1, a superoxide dismutase with function in root development and osmoprotection

Superoxide dismutases (SODs) are enzymes detoxifying superoxide to hydrogen peroxide while temporal developmental expression and subcellular localisation are linked to their functions. Therefore, we aimed here to reveal in vivo developmental expression, subcellular, tissue- and organ-specific localisation of iron superoxide dismutase 1 (FSD1) in Arabidopsis using light-sheet and Airyscan confocal microscopy. FSD1-GFP temporarily accumulated at the site of endosperm rupture during seed germination. In emerged roots, it showed the highest abundance in cells of the lateral root cap, columella, and endodermis/cortex initials. The largest subcellular pool of FSD1-GFP was localised in the plastid stroma, while it was also located in the nuclei and cytosol. The majority of the nuclear FSD1-GFP is immobile as revealed by fluorescence recovery after photobleaching. We found that fsd1 knockout mutants exhibit reduced lateral root number and this phenotype was reverted by genetic complementation. Mutant analysis also revealed a requirement for FSD1 in seed germination during salt stress. Salt stress tolerance was coupled with the accumulation of FSD1-GFP in Hechtian strands and superoxide removal. It is likely that the plastidic pool is required for acquiring oxidative stress tolerance in Arabidopsis. This study suggests new developmental and osmoprotective functions of SODs in plants.

Shifting paradigms and novel players in Cys-based redox regulation and ROS signaling in plants - and where to go next

Cys-based redox regulation was long regarded a major adjustment mechanism of photosynthesis and metabolism in plants, but in the recent years, its scope has broadened to most fundamental processes of plant life. Drivers of the recent surge in new insights into plant redox regulation have been the availability of the genome-scale information combined with technological advances such as quantitative redox proteomics and in vivo biosensing. Several unexpected findings have started to shift paradigms of redox regulation. Here, we elaborate on a selection of recent advancements, and pinpoint emerging areas and questions of redox biology in plants. We highlight the significance of (1) proactive H₂O₂ generation, (2) the chloroplast as a unique redox site, (3) specificity in thioredoxin complexity, (4) how to oxidize redox switches, (5) governance principles of the redox network, (6) glutathione peroxidase-like proteins, (7) ferroptosis, (8) oxidative protein folding in the ER for phytohormonal regulation, (9) the apoplast as an unchartered redox frontier, (10) redox regulation of respiration, (11) redox transitions in seed germination and (12) the mitochondria as potential new players in reductive stress safeguarding. Our emerging understanding in plants may serve as a blueprint to scrutinize principles of reactive oxygen and Cys-based redox regulation across organisms.

Ascorbate glutathione-dependent H2O2 scavenging is an important process in axillary bud outgrowth in rosebush

BACKGROUND AND AIMS

Branching is an important mechanism of plant shape establishment and the direct consequence of axillary bud outgrowth. Recently, hydrogen peroxide (H2O2) metabolism, known to be involved in plant growth and development, has been proposed to contribute to axillary bud outgrowth. However, the involvement of H2O2 in this process remains unclear.

METHODS

We analysed the content of H2O2 during bud outgrowth and characterized its catabolism, both at the transcriptional level and in terms of its enzymatic activities, using RT-qPCR and spectrophotometric methods, respectively. In addition, we used in vitro culture to characterize the effects of H2O2 application and the reduced glutathione (GSH) synthesis inhibitor l-buthionine sulfoximine (BSO) on bud outgrowth in relation to known molecular markers involved in this process.

KEY RESULTS

Quiescent buds displayed a high content of H2O2 that declined when bud outgrowth was initiated, as the consequence of an increase in the scavenging activity that is associated with glutathione pathways (ascorbate-glutathione cycle and glutathione biosynthesis); catalase did not appear to be implicated. Modification of bud redox state after the application of H2O2 or BSO prevented axillary bud outgrowth by repressing organogenesis and newly formed axis elongation. Hydrogen peroxide also repressed bud outgrowth-associated marker gene expression.

CONCLUSIONS

These results show that high levels of H2O2 in buds that are in a quiescent state prevents bud outgrowth. Induction of ascorbate-glutathione pathway scavenging activities results in a strong decrease in H2O2 content in buds, which finally allows bud outgrowth.

Plant-Derived Smoke Affects Biochemical Mechanism on Plant Growth and Seed Germination

The role of plant-derived smoke, which is changed in mineral-nutrient status, in enhancing germination and post-germination was effectively established. The majority of plant species positively respond to plant-derived smoke in the enhancement of seed germination and plant growth. The stimulatory effect of plant-derived smoke on normally growing and stressed plants may help to reduce economic and human resources, which validates its candidature as a biostimulant. Plant-derived smoke potentially facilitates the early harvest and increases crop productivity. Karrikins and cyanohydrin are the active compound in plant-derived smoke. In this review, data from the latest research explaining the effect of plant-derived smoke on morphological, physiological, biochemical, and molecular responses of plants are presented. The pathway for reception and interaction of compounds of plant-derived smoke at the cellular and molecular level of plant is described and discussed.

Seed Transcriptome Annotation Reveals Enhanced Expression of Genes Related to ROS Homeostasis and Ethylene Metabolism at Alternating Temperatures in Wild Cardoon

The association among environmental cues, ethylene response, ABA signaling, and reactive oxygen species (ROS) homeostasis in the process of seed dormancy release is nowadays well-established in many species. Alternating temperatures are recognized as one of the main environmental signals determining dormancy release, but their underlying mechanisms are scarcely known. Dry after-ripened wild cardoon achenes germinated poorly at a constant temperature of 20, 15, or 10 °C, whereas germination was stimulated by 80% at alternating temperatures of 20/10 °C. Using an RNA-Seq approach, we identified 23,640 and annotated 14,078 gene transcripts expressed in dry achenes and achenes exposed to constant or alternating temperatures. Transcriptional patterns identified in dry condition included seed reserve and response to dehydration stress genes (i.e., HSPs, peroxidases, and LEAs). At a constant temperature, we observed an upregulation of ABA biosynthesis genes (i.e., NCED9), ABA-responsive genes (i.e., ABI5 and TAP), as well as other genes previously related to physiological dormancy and inhibition of germination. However, the alternating temperatures were associated with the upregulation of ethylene metabolism (i.e., ACO1, 4, and ACS10) and signaling (i.e., EXPs) genes and ROS homeostasis regulators genes (i.e., RBOH and CAT). Accordingly, the ethylene production was twice as high at alternating than at constant temperatures. The presence in the germination medium of ethylene or ROS synthesis and signaling inhibitors reduced significantly, but not completely, germination at 20/10 °C. Conversely, the presence of methyl viologen and salicylhydroxamic acid (SHAM), a peroxidase inhibitor, partially increased germination at constant temperature. Taken together, the present study provides the first insights into the gene expression patterns and physiological response associated with dormancy release at alternating temperatures in wild cardoon (Cynara cardunculus var. sylvestris).

Dynamic transcriptome and metabolome analyses of two types of rice during the seed germination and young seedling growth stages

Background

Seed germination and young seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice. Previous studies have focused on the identification of QTLs. However, there are few studies on the metabolome or transcriptome of germination and young seedling growth in rice.

Results

Here, an indica rice and a japonica rice were used as materials, and the transcripts and metabolites were detected during the germination and young seedling growth periods on a large scale by using RNA sequencing and a widely targeted metabolomics method, respectively. Fourteen shared transcripts and 15 shared metabolites that were continuously differentially expressed in the two materials were identified and may be essential for seed germination and young seedling growth. Enrichment analysis of differentially expressed genes in transcriptome expression profiles at different stages indicated that cell wall metabolism, lipid metabolism, nucleotide degradation, amino acid, etc., were enriched at 0–2 days, and most of the results are consistent with those of previous reports. Specifically, phenylpropanoid biosynthesis and glutathione metabolism were continuously enriched during the seed germination and young seedling growth stages. Next, KO enrichment analysis was conducted by using the differentially expressed genes of the two materials at 2, 3 and 4 days. Fourteen pathways were enriched. Additionally, 44 differentially expressed metabolites at 2, 3 and 4 days were identified. These metabolites may be responsible for the differences in germination and young seedling growth between the two materials. Further attention was focused on the ascorbate–glutathione pathway, and it was found that differences in ROS-scavenging abilities mediated by some APX, GPX and GST genes may be directly involved in mediating differences in the germination and young seedling growth speed of the two materials.

Conclusions

In summary, these results may enhance the understanding of the overall mechanism of seed germination and young seedling growth, and the outcome of this study is expected to facilitate rice breeding for direct seeding.

Molecular genetic bases of seed resistance to oxidative stress during storage

Conservation of plant genetic diversity, including economically important crops, is the foundation for food safety. About 90 % of the world’s crop genetic diversity is stored as seeds in genebanks. During storage seeds suffer physiological stress consequences, one of which is the accumulation of free radicals, primarily reactive oxygen species (ROS). An increase in ROS leads to oxidative stress, which negatively affects the quality of seeds and can lead to a complete loss of their viability. The review summarizes data on biochemical processes that affect seed longevity. The data on the destructive effect of free radicals towards plant cell macromolecules are analyzed, and the ways to eliminate excessive ROS in plants, the most important of which is the glutathioneascorbate pathway, are discussed. The relationship between seed dormancy and seed longevity is examined. Studying seeds of different plant species revealed a negative correlation between seed dormancy and longevity, while various authors who researched Arabidopsis seeds reported both positive and negative correlations between dormancy and seed longevity. A negative correlation between seed dormancy and viability probably means that seeds are able to adapt to changing environmental conditions. This review provides a summary of Arabidopsis genes associated with seed viability. By now, a significant number of loci and genes affecting seed longevity have been identified. This review contains a synopsis of modern studies on the viability of barley seeds. QTLs associated with barley seed longevity were identified on chromosomes 2H, 5H and 7H. In the QTL regions studied, the Zeo1, Ale, nud, nadp-me, and HvGR genes were identified. However, there is still no definite answer as to which genes would serve as markers of seed viability in a certain plant species.

Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects

Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

The signalling role of ROS in the regulation of seed germination and dormancy

Reactive oxygen species (ROS) are versatile compounds which can have toxic or signalling effects in a wide range living organisms, including seeds. They have been reported to play a pivotal role in the regulation of seed germination and dormancy but their mechanisms of action are still far from being fully understood. In this review, we sum-up the major findings that have been carried out this last decade in this field of research and which altogether shed a new light on the signalling roles of ROS in seed physiology. ROS participate in dormancy release during seed dry storage through the direct oxidation of a subset of biomolecules. During seed imbibition, the controlled generation of ROS is involved in the perception and transduction of environmental conditions that control germination. When these conditions are permissive for germination, ROS levels are maintained at a level which triggers cellular events associated with germination, such as hormone signalling. Here we propose that the spatiotemporal regulation of ROS production acts in concert with hormone signalling to regulate the cellular events involved in cell expansion associated with germination.

Reactive Oxygen Species (ROS) and Nucleic Acid Modifications During Seed Dormancy

The seed is the propagule of higher plants and allows its dissemination and the survival of the species. Seed dormancy prevents premature germination under favourable conditions. Dormant seeds are only able to germinate in a narrow range of conditions. During after-ripening (AR), a mechanism of dormancy release, seeds gradually lose dormancy through a period of dry storage. This review is mainly focused on how chemical modifications of mRNA and genomic DNA, such as oxidation and methylation, affect gene expression during late stages of seed development, especially during dormancy. The oxidation of specific nucleotides produced by reactive oxygen species (ROS) alters the stability of the seed stored mRNAs, being finally degraded or translated into non-functional proteins. DNA methylation is a well-known epigenetic mechanism of controlling gene expression. In Arabidopsis thaliana, while there is a global increase in CHH-context methylation through embryogenesis, global DNA methylation levels remain stable during seed dormancy, decreasing when germination occurs. The biological significance of nucleic acid oxidation and methylation upon seed development is discussed.

Evidence for the Involvement of Vernalization-related Genes in the Regulation of Cold-induced Ripening in 'D'Anjou' and 'Bartlett' Pear Fruit

European pear (Pyrus communis L.) cultivars require a genetically pre-determined duration of cold-temperature exposure to induce autocatalytic system 2 ethylene biosynthesis and subsequent fruit ripening. The physiological responses of pear to cold-temperature-induced ripening have been well characterized, but the molecular mechanisms underlying this phenomenon continue to be elucidated. This study employed previously established cold temperature conditioning treatments for ripening of two pear cultivars, 'D'Anjou' and 'Bartlett'. Using a time-course transcriptomics approach, global gene expression responses of each cultivar were assessed at four stages of developmental during the cold conditioning process. Differential expression, functional annotation, and gene ontology enrichment analyses were performed. Interestingly, evidence for the involvement of cold-induced, vernalization-related genes and repressors of endodormancy release was found. These genes have not previously been described to play a role in fruit during the ripening transition. The resulting data provide insight into cultivar-specific mechanisms of cold-induced transcriptional regulation of ripening in European pear, as well as a unique comparative analysis of the two cultivars with very different cold conditioning requirements.

Spatiotemporal variations in salicylic acid and hydrogen peroxide in sunflower seeds during transition from dormancy to germination

Phytohormones and reactive oxygen species mediate processes such as germination and dormancy. The elucidation of the physiological and biochemical events implicated in the transition from dormancy to germination in different plant species such as sunflower becomes a topic of interest. In this study, we investigated the spatiotemporal variation of salicylic acid (SA), hydrogen peroxide (H₂ O₂ ) and the activity of two antioxidant enzymes (catalase, CAT - EC 1.11.1.6 and ascorbate peroxidase - EC 1.11.1.11) in embryonic axis and cotyledons of dry and imbibed seeds of dormant (B123) and non-dormant (B91) sunflower lines. The results showed that embryonic axis had higher level of SA and H₂ O₂ than cotyledons in both lines. In dry seeds, B123 embryo (embryonic axis + cotyledons) showed a higher SA content than B91. After dry storage at room temperature, SA decreased in B123 embryos to a value close to that registered in B91 embryos. B123 embryonic axis of dry seeds presented higher H₂ O₂ levels than B91. Dry storage led to an increase of H₂ O₂ levels and a decrease of CAT activity in B123 embryonic axis. During imbibition, B123 seeds stored for 33 days displayed an increase in SA level in the embryonic axis (3 h of imbibition) and this lower level correlated with a decrease in H₂ O₂ (6 h of imbibition). Thus, the embryo-imposed dormancy in B123 dry seeds was associated with high levels of SA and low H₂ O₂ , whereas the dormancy release was linked with SA decrease and increase of H₂ O₂ as a consequence of lower CAT activity.

Arabidopsis GLR3.5-modulated seed germination involves GA and ROS signaling

Seed germination, a crucial developmental step, is regulated by multiple plant endogenous signals, among which phytohormones absisic acid (ABA) and gibberellin (GA) act antagonistically. Reactive oxygen species (ROS) interact with the two hormones to coordinate germination. We have previously reported that Arabidopsis glutamate receptor homolog3.5 (AtGLR3.5) modulates calcium signal to attenuate the repression effect of ABA on seed germination and that amino acid L-methionine functions upstream of AtGLR3.5, resulting in calcium influx. Here, we show that AtGLR3.5 modulates GA and ROS signaling during seed germination. Our findings provide a more complete picture as to the molecular mechanisms of AtGLR3.5 in seed germination control.

Molecular dynamics of pre-germinative metabolism in primed eggplant (Solanum melongena L.) seeds

Seed priming, a pre-sowing technique that enhances the antioxidant/DNA repair activities during the pre-germinative metabolism, still retains empirical features. We explore for the first time the molecular dynamics of pre-germinative metabolism in primed eggplant (Solanum melongena L.) seeds in order to identify hallmarks (expression patterns of antioxidant/DNA repair genes combined with free radical profiles) useful to discriminate between high- and low-quality lots. The hydropriming protocol hereby developed anticipated (or even rescued) germination, when applied to lots with variable quality. ROS (reactive oxygen species) raised during hydropriming and dropped after dry-back. Upregulation of antioxidant/DNA repair genes was observed during hydropriming and the subsequent imbibition. Upregulation of SmOGG1 (8-oxoguanine glycosylase/lyase) gene detected in primed seeds at 2 h of imbibition appeared as a promising hallmark. On the basis of these results, the investigation was restricted within the first 2 h of imbibition, to verify whether the molecular landscape was reproducible in different lots. A complex pattern of antioxidant/DNA repair gene expression emerged, reflecting the preponderance of seed lot-specific profiles. Only the low-quality eggplant seeds subjected to hydropriming showed enhanced ROS levels, both in the dry and imbibed state, and this might be a useful signature to discriminate among lots. The plasticity of eggplant pre-germinative metabolism stimulated by priming imposes a plethora of heterogeneous molecular responses that might delay the search for quality hallmarks. However, the information hereby gained could be translated to eggplant wild relatives to speed-up their use in breeding programs or other agronomical applications.

NO and ABA Interaction Regulates Tuber Dormancy and Sprouting in Potato

In plants, nitric oxide synthase (NOS)-like or nitrate reductase (NR) produces nitric oxide (NO), which is involved in releasing seed dormancy. However, its mechanism of effect in potato remains unclear. In this study, spraying 40 μM sodium nitroprusside (SNP), an exogenous NO donor, quickly broke tuber dormancy and efficiently promoted tuber sprouting, whereas 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), an NO scavenger, repressed the influence of NO on tuber sprouting. Compared with the control (distilled water), SNP treatment led to a rapid increase in NO content after 6 h and a decreased abscisic acid (ABA) content at 12 and 24 h. c-PTIO treatment significantly inhibited increase of NO levels and increased ABA production. In addition, N ^G -nitro-L-arginine methyl ester, an NOS inhibitor, clearly inhibited the NOS-like activity, whereas tungstate, an NR inhibitor, inhibited the NR activity. Furthermore, NO promoted the expression of a gene involved in ABA catabolism (StCYP707A1, encoding ABA 8'-hydroxylase) and inhibited the expression of a gene involved in ABA biosynthesis (StNCED1, encoding 9-cis-epoxycarotenoid dioxygenase), thereby decreasing the ABA content, disrupting the balance between ABA and gibberellin acid (GA), and ultimately inducing dormancy release and tuber sprouting. The results demonstrated that NOS-like or NR-generated NO controlled potato tuber dormancy release and sprouting via ABA metabolism and signaling in tuber buds.

Metabolism of Stone Fruits: Reciprocal Contribution Between Primary Metabolism and Cell Wall

Cell wall turnover and modification in its composition are key factors during stone fruit development and patterning. Changes in cell wall disassembly and reassembly are essential for fruit growth and ripening. Modifications in cell wall composition, resulting in the formation of secondary cell walls, are necessary for producing the most distinctive trait of drupes: the lignified endocarp. The contribution of primary metabolism to cell wall synthesis has been investigated in detail, while the knowledge on the contribution of the cell wall to primary metabolites and related processes is still fragmented. In this review, starting from peculiarities of cell wall of drupes cells (in mesocarp and endocarp layers), we discuss the structure and composition of cell wall, processes related to its modification and contribution to the synthesis of primary metabolites. In particular, our attention has been focused on the ascorbate synthesis cell wall-related and on the potential role of cyanogenic compounds in the deposition of the secondary cell wall.

Alleviating dormancy in Brassica oleracea seeds using NO and KAR1 with ethylene biosynthetic pathway, ROS and antioxidant enzymes modifications

BACKGROUND

Seed dormancy is a prevailing condition in which seeds are unable to germinate, even under favorable environmental conditions. Harvested Brassica oleracea (Chinese cabbage) seeds are dormant and normally germinate (poorly) at 21 °C. This study investigated the connections between ethylene, nitric oxide (NO), and karrikin 1 (KAR1) in the dormancy release of secondary dormant Brassica oleracea seeds.

RESULTS

NO and KAR1 were found to induce seed germination, and stimulated the production of ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC), and both ethylene biosynthesis enzyme ACC oxidase (ACO) [1] and ACC synthase (ACS) [2]. In the presence of NO and KAR1, ACS and ACO activity reached maximum levels after 36 and 48 h, respectively. The inhibitor of ethylene 2,5-norbornadiene (NBD) had an adverse effect on Brassica oleracea seed germination (inhibiting nearly 50% of germination) in the presence of NO and KAR1. The benefits from NO and KAR1 in the germination of secondary dormant Brassica oleracea seeds were also associated with a marked increase in reactive oxygen species (ROS) (H₂O₂ and O₂˙-) and antioxidant enzyme activity at early germination stages. Catalase (CAT) and glutathione reductase (GR) activity increased 2 d and 4 d, respectively, after treatment, while no significant changes were observed in superoxide dismutase (SOD) activity under NO and KAR1 applications. An increase in H₂O₂ and O₂˙- levels were observed during the entire incubation period, which increasing ethylene production in the presence of NO and KAR1. Abscisic acid (ABA) contents decreased and glutathione reductase (GA) contents increased in the presence of NO and KAR1. Gene expression studies were carried out with seven ethylene biosynthesis ACC synthases (ACS) genes, two ethylene receptors (ETR) genes and one ACO gene. Our results provide more evidence for the involvement of ethylene in inducing seed germination in the presence of NO and KAR1. Three out of seven ethylene biosynthesis genes (BOACS7, BOACS9 and BOACS11), two ethylene receptors (BOETR1 and BOETR2) and one ACO gene (BOACO1) were up-regulated in the presence of NO and KAR1.

CONCLUSION

Consequently, ACS activity, ACO activity and the expression of different ethylene related genes increased, modified the ROS level, antioxidant enzyme activity, and ethylene biosynthesis pathway and successfully removed (nearly 98%) of the seed dormancy of secondary dormant Brassica olereace seeds after 7 days of NO and KAR1 application.

The Long-Standing Paradox of Seed Dormancy Unfolded?

There has been a long-standing question in seed research, why cyanide, a respiration inhibitor, breaks seed dormancy. While the alternative respiratory pathway and reactive oxygen species have been suggested to be part of the mechanism, the cell biological and mechanistic significance of this paradox remains unclear. The outcomes of recent research on mitochondrial RNA processing for the subunits of the electron transport chain complexes seem to offer a logical explanation. This opinion article attempts to integrate the accumulating evidence of mitochondrial involvement in ABA signaling with the frontier of seed research on DELAY OF GERMINATION1, a master regulator of dormancy, to present a coherent model for ABA signaling in seeds, which could also address the old paradox in seed research.

iTRAQ-based mitochondrial proteome analysis of the molecular mechanisms underlying postharvest senescence of Zizania latifolia

To explore the molecular mechanisms underlying postharvest senescence of Zizania latifolia, the changes in the mitochondrial proteome of plants treated with or without (control) 1-methyleyelopropene and ethylene during storage at room temperature for 0, 3 and 6 days were investigated using isobaric tags for relative and absolute quantitation (iTRAQ) labeling combined with two-dimensional liquid chromatography-tandem mass spectrometry. A total of 1,390 proteins with two or more peptides were identified, of which 211 showed a significant (p < .05) change (at least twofold) in relative abundance. Monitoring the parallel reaction validated the reliability and accuracy of the iTRAQ results. Bioinformatics and functional analysis of these differentially expressed proteins (DEPs) revealed that postharvest senescence of Z. latifolia could be attributed to (a) strengthened pentose phosphate pathway, (b) imbalanced protein, amino acid, organic acid, and fatty acid metabolism, (c) disordered energy homeostasis, (d) exacerbated oxidative damage, (e) RNA degradation, (f) activation of the Ca²⁺ , mitogen-activated protein kinase, and jasmonic acid signaling pathways, (g) programed cell death, (h) excessive biosynthesis of secondary metabolites, or (i) degradation of cell structure. Our findings provide integrated insight into the molecular mechanisms of postharvest senescence during storage as well as the DEPs that show promise as targets for controlling senescence-induced quality deterioration of Z. latifolia. PRACTICAL APPLICATIONS: Postharvest senescence is the most important factor that causes fast quality deterioration of Zizania latifolia. The understanding of the processes leading to postharvest senescence of Z. latifolia is essential in enhancing the commercial value and extending the shelf life of the product. It is currently believed that the mitochondrial metabolism is closely related to postharvest senescence. For this, the changes of proteome in Z. latifolia mitochondria treated with or without (control) 1-MCP and ETH during storage at room temperature were investigated. Results showed that a variety of physiobiochemical responses occur during postharvest senescence of Z. latifolia. 1-MCP treatment significantly inhibited the changes of these physiobiochemical processes, finally, retarding the postharvest senescence of Z. latifolia. ETH treatment had opposite effects on proteome changes compared with 1-MCP treatment. Taken together, these results enrich the understanding of the molecular mechanisms of postharvest senescence of Z. latifolia.

Does integrative effects of glyphosate, gibberellin and hydrogen peroxide ameliorate the deleterious effects of the herbicide on sorghum seed through its germination?

We investigated the interconnected roles of reactive oxygen species (ROS) generated upon seed exposure to glyphosate and/or gibberellic acid (GA3), and the possible interaction between the herbicide and the plant hormone during germination of sorghum seeds. GA3 decreased antioxidant enzyme activity in embryos, and the over accumulation of hydrogen peroxide (H2O2) in 1000 mM GA3-treated seeds resulted in the lowest germinability among treatments. The deleterious effects of glyphosate on germination rate, in contrast, were not related to H2O2 accumulation, but to its interference with the mitochondrial electron transport chain. However, interactions among glyphosate, GA3 and H2O2 during seed germination were observed. Similar to paclobutrazol, glyphosate appears to interfere with the de novo synthesis of gibberellin, which modulates seed germination through oxidative metabolism. Seeds experiencing increased oxidative status due to GA3 (100 mM) or H2O2 (50 mM) applications had the effects of glyphosate on germination rate reversed. Since decreased ATP synthesis is a secondary effect of glyphosate, increased H2O2 concentrations in embryos must facilitate germination by decreasing the energy required by ATP-demanding metabolism. Our results showed that glyphosate affect seed germination of sorghum, and that the herbicide interacts with oxidative and gibberellin metabolisms.

Redox metabolism and cell wall modifications as global and local targets respectively, of cyanide induced dormancy release of walnut kernels

The HCN-induced seed dormancy release necessitates alterations in reactive oxygen species (ROS) metabolism and radicle cell wall loosening. Little is known about the interaction of ROS metabolism with cell wall hydrolytic enzymes during HCN-induced seed dormancy release. Thus dormant walnut (Juglans regia L.) kernels were exposed to HCN (4 h) and studied for redox metabolism and cell wall-modifying enzymes during 10 days of incubation (DI) i.e. before radicle emergence. HCN increased ROS especially in the embryonic axes (EAs) but decreased ROS-generating NADPH oxidase and ROS scavenging superoxide dismutase (SOD) and peroxidase (POX) with no effects on catalase (CAT), ascorbate peroxidase (APX) and cell wall-modifying enzymes activities in short term up to 2 DI. In long term roughly from 4 DI onwards, HCN-exposed EA displayed greater superoxide anions and enhanced activities of POX, APX, NADPH oxidase, cell wall peroxidase (CW-POX), β- 1, 4-D glucanase, mannanase, polygacturonase and xylanase. Meanwhile HCN increased greater expression of POX and mannanase isoforms as revealed by in-gel activity assay. Except for higher activities of CAT, POX and APX, cotyledonary activities of CW-POX, mannanase and polygacturonase and to some extent β- 1, 4-D glucanase remained unaffected by HCN. Thus short term ROS accumulation in HCN-treated EA is due to declined SOD and POX activities. In long term the enhanced activities of both NADPH oxidase: CW-POX couple and cell wall-modifying enzymes in EA bring about wall loosening in preparation for radicle emergence. Evidences for the simultaneous operation of both mechanisms are provided in walnut EAs during dormancy release.

OoNAC72, a NAC-Type Oxytropis ochrocephala Transcription Factor, Conferring Enhanced Drought and Salt Stress Tolerance in Arabidopsis

The NAC proteins form one of the largest families of plant-specific transcription factors (TFs) and play essential roles in developmental processes and stress responses. In this study, we characterized a NAC domain transcription factor, OoNAC72, from a legume Oxytropis ochrocephala. OoNAC72 was proved to be localized in the nuclei in tobacco lower epidermal cells and had transcriptional activation activity in yeast, confirming its transcription activity. OoNAC72 expression could be induced by drought, salinity and exogenous abscisic acid (ABA) in O. ochrocephala seedlings. Furthermore, over-expression of OoNAC72 driven by CaMV35S promoter in Arabidopsis resulted in ABA hypersensitivity and enhanced tolerance to drought and salt stresses during seed germination and post-germinative growth periods. In addition, over-expression of OoNAC72 enhanced the expression of stress-responsive genes such as RD29A, RD29B, RD26, LEA14, ANACOR19, ZAT10, PP2CA, and NCED3. These results highlight the important regulatory role of OoNAC72 in multiple abiotic stress tolerance, and may provide an underlying reason for the spread of O. ochrocephala.

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.