Towards a better monitoring of seed ageing under ex situ seed conservation

Low-Cost Imaging to Quantify Germination Rate and Seedling Vigor across Lettuce Cultivars

The survival and growth of young plants hinge on various factors, such as seed quality and environmental conditions. Assessing seedling potential/vigor for a robust crop yield is crucial but often resource-intensive. This study explores cost-effective imaging techniques for rapid evaluation of seedling vigor, offering a practical solution to a common problem in agricultural research. In the first phase, nine lettuce (Lactuca sativa) cultivars were sown in trays and monitored using chlorophyll fluorescence imaging thrice weekly for two weeks. The second phase involved integrating embedded computers equipped with cameras for phenotyping. These systems captured and analyzed images four times daily, covering the entire growth cycle from seeding to harvest for four specific cultivars. All resulting data were promptly uploaded to the cloud, allowing for remote access and providing real-time information on plant performance. Results consistently showed the 'Muir' cultivar to have a larger canopy size and better germination, though 'Sparx' and 'Crispino' surpassed it in final dry weight. A non-linear model accurately predicted lettuce plant weight using seedling canopy size in the first study. The second study improved prediction accuracy with a sigmoidal growth curve from multiple harvests (R2 = 0.88, RMSE = 0.27, p < 0.001). Utilizing embedded computers in controlled environments offers efficient plant monitoring, provided there is a uniform canopy structure and minimal plant overlap.

Cytological structures and physiological and biochemical characteristics of covered oat (Avena sativa L.) and naked oat (Avena nuda L.) seeds during high-temperature artificial aging

BACKGROUND

Seed aging, a natural and inevitable process occurring during storage. Oats, an annual herb belonging to the Gramineae family and pooideae. In addition to being a healthy food, oats serve as ecological pastures, combating soil salinization and desertification. They also play a role in promoting grassland agriculture and supplementing winter livestock feed. However, the high lipid and fat derivatives contents of oat seeds make them susceptible to deterioration, as fat derivatives are prone to rancidity, affecting oat seed production, storage, development, and germplasm resource utilization. Comparative studies on the effects of aging on physiology and cytological structure in covered and naked oat seeds are limited. Thus, our study aimed to determine the mechanism underlying seed deterioration in artificially aged 'LongYan No. 3' (A. sativa) and 'BaiYan No. 2' (A. nuda) seeds, providing a basis for the physiological evaluation of oat seed aging and serving as a reference for scientifically safe storage and efficient utilization of oats.

RESULTS

In both oat varieties, superoxide dismutase and catalase activities in seeds showed increasing and decreasing trends, respectively. Variance analysis revealed significant differences and interaction in all measured indicators of oat seeds between the two varieties at different aging times. 'LongYan No. 3' seeds, aged for 24-96 h, exhibited a germination rate of < 30%, Conductivity, malondialdehyde, soluble sugar, and soluble protein levels increased more significantly than the 'BaiYan No. 2'. With prolonged aging leading to cell membrane degradation, reactive oxygen species accumulation, disrupted antioxidant enzyme system, evident embryo cell swelling, and disordered cell arrangement, blocking the nutrient supply route. Simultaneously, severely concentrated chromatin in the nucleus, damaged mitochondrial structure, and impaired energy metabolism were noted, resulting in the loss of 'LongYan No. 3' seed vitality and value. Conversely, 'BaiYan No. 2' seeds showed a germination rate of 73.33% after 96 h of aging, consistently higher antioxidant enzyme activity during aging, normal embryonic cell shape, and existence of the endoplasmic reticulum.

CONCLUSIONS

ROS accumulation and antioxidant enzyme system damage in aged oat seeds, nuclear chromatin condensation, mitochondrial structure damage, nucleic acid metabolism and respiration weakened, oat seed vigor decreased. 'LongYan No. 3' seeds were more severely damaged under artificial aging than 'BaiYan No. 2' seeds, highlighting their heightened susceptibility to aging effects.

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.

Full-Length Transcriptome Sequencing Reveals the Molecular Mechanism of Metasequoia glyptostroboides Seed Responding to Aging

Metasequoia glyptostroboides, Hu and W. C. Cheng, as the only surviving relict species of the Taxodiaceae Metasequoia genus, is a critically endangered and protected species in China. There is a risk of extinction due to the low vigor of M. glyptostroboides seeds, and the physiological mechanism of seed aging in M. glyptostroboides is not yet clear. In order to investigate the physiological and molecular mechanisms underlying the aging process of M. glyptostroboides seeds, we analyzed the antioxidant system and transcriptome at 0, 2, 4, 6, and 8 days after artificial accelerated aging treatment at 40 °C and 100% relative humidity. It was found that the germination percentage of fresh dried M. glyptostroboides seeds was 54 ± 5.29%, and significantly declined to 9.33 ± 1.88% after 6 days of aging, and then gradually decreased until the seed died on day 8. Superoxide dismutase (SOD) activity, ascorbic acid (AsA), glutathione (GSH) content and superoxide anion (O₂^·-) content and production rate significantly decreased, while malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content and glutathione peroxidase (GPX) and catalase (CAT) activity gradually increased during the aging process. A total of 42,189 unigenes were identified in the whole transcriptome, and 40,446 (95.86%) unigenes were annotated in at least one protein database. A total of 15,376 differentially expressed genes (DEGs) were obtained; KEGG enrichment analysis results revealed that seed aging may be mainly involved in the protein-processing pathways in endoplasmic reticulum, oxidative phosphorylation, and ascorbate and aldarate metabolism. Weighted gene co-expression network analysis (WGCNA) revealed that the dark magenta, orange, and medium purple modules were highly correlated with physiological indicators such as SOD, CAT, and GSH and further identified 40 hub genes such as Rboh, ACO, HSF, and CML as playing important roles in the antioxidant network of M. glyptostroboides seeds. These findings provide a broader perspective for studying the regulatory mechanism of seed aging and a large number of potential target genes for the breeding of other endangered gymnosperms.

Ultrasound promotes germination of aging Pinus tabuliformis seeds is associated with altered lipid metabolism

Seed germination is an essential biological process for establishing new organisms of higher plants, it is especially significant for those aged seeds stored in gene banks for years. In this study, we investigated ultrasound treatment induced germination for aged Pinus tabuliformis seeds, which has been used in large scale aircraft sowing based afforestation in North China over 30 years' ago without knowing possible mechanisms. We showed certain strength of ultrasound could increase the germination rate of aged seeds for about 3 times compare with control. Interestingly, although our transcriptome and lipidome analysis showed the differences between control and ultrasound treatments can be observed 1 day after germination by partial least squares discriminant analysis (PLSDA) analysis, majority (75 % or 69 %) of the significantly altered genes or lipids were commonly shared between them. Further analysis for the commonly altered lipids between both treatments showed ultrasound provoked the variations of lipids during germination process. Our investigation also revealed large amount of ultrasound-related genes and lipids that might be involved in germination promotion process. We hypothesis ultrasound provokes seed lipidome which further increases seed germination of Pinus tabuliformis. Our study provides new insides into the role of ultrasound induced lipidome change in seed germination. Moreover, we provide a new method to improve germination of aged seeds which might benefit preservation of seeds in gene banks.

Seed Longevity-The Evolution of Knowledge and a Conceptual Framework

The lifespan or longevity of a seed is the time period over which it can remain viable. Seed longevity is a complex trait and varies greatly between species and even seed lots of the same species. Our scientific understanding of seed longevity has advanced from anecdotal 'Thumb Rules,' to empirically based models, biophysical explanations for why those models sometimes work or fail, and to the profound realisation that seeds are the model of the underexplored realm of biology when water is so limited that the cytoplasm solidifies. The environmental variables of moisture and temperature are essential factors that define survival or death, as well as the timescale to measure lifespan. There is an increasing understanding of how these factors induce cytoplasmic solidification and affect glassy properties. Cytoplasmic solidification slows down, but does not stop, the chemical reactions involved in ageing. Continued degradation of proteins, lipids and nucleic acids damage cell constituents and reduce the seed's metabolic capacity, eventually impairing the ability to germinate. This review captures the evolution of knowledge on seed longevity over the past five decades in relation to seed ageing mechanisms, technology development, including tools to predict seed storage behaviour and non-invasive techniques for seed longevity assessment. It is concluded that seed storage biology is a complex science covering seed physiology, biophysics, biochemistry and multi-omic technologies, and simultaneous knowledge advancement in these areas is necessary to improve seed storage efficacy for crops and wild species biodiversity conservation.

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.

Degradome sequencing reveals an integrative miRNA-mediated gene interaction network regulating rice seed vigor

BACKGROUND

It is well known that seed vigor is essential for agricultural production and rice (Oryza sativa L.) is one of the most important crops in the world. Though we previously reported that miR164c regulates rice seed vigor, but whether and how other miRNAs cooperate with miR164c to regulate seed vigor is still unknown.

RESULTS

Based on degradome data of six RNA samples isolated from seeds of the wild-type (WT) indica rice cultivar 'Kasalath' as well as two modified lines in 'Kasalath' background (miR164c-silenced line [MIM164c] and miR164c overexpression line [OE164c]), which were subjected to either no aging treatment or an 8-day artificial aging treatment, 1247 different target transcripts potentially cleaved by 421 miRNAs were identified. The miRNA target genes were functionally annotated via GO and KEGG enrichment analyses. By STRING database assay, a miRNA-mediated gene interaction network regulating seed vigor in rice was revealed, which comprised at least four interconnected pathways: the miR5075-mediated oxidoreductase related pathway, the plant hormone related pathway, the miR164e related pathway, and the previously reported RPS27AA related pathway. Knockout and overexpression of the target gene Os02g0817500 of miR5075 decreased and enhanced seed vigor, respectively. By Y2H assay, the proteins encoded by five seed vigor-related genes, Os08g0295100, Os07g0633100, REFA1, OsPER1 and OsGAPC3, were identified to interact with Os02g0817500.

CONCLUSIONS

miRNAs cooperate to regulate seed vigor in rice via an integrative gene interaction network comprising miRNA target genes and other functional genes. The result provided a basis for fully understanding the molecular mechanisms of seed vigor regulation.

Seed viability testing for research and conservation of epiphytic and terrestrial orchids

BACKGROUND

Seed viability testing is essential in plant conservation and research. Seed viability testing determines the success of ex-situ conservation efforts, such as seed banking but commonly testing protocols of orchids lack consistency and accuracy, therefore, there is a need to select an appropriate and reliable viability test, especially when conducting comparative studies. Here, we evaluated the suitability of three seed viability tests, Evans blue test (EB), Fluorescein diacetate test (FDA) and Tetrazolium test (TTC), with and without sterilization, on seeds of 20 orchid species, which included five epiphytes and fifteen terrestrials, using both fresh seeds and seeds stored at - 18 ºC for 6 to 8 years.

RESULTS

We found that sterilization and lifeform of seeds affected seed viability across all tests but the storage time was not an influential factor. Sterilization negatively affected seed viability under EB and FDA test conditions but increased the detection of viable seeds in the TTC test in both epiphytic and terrestrial species. The EB test, when administered without sterilization provided the highest viability results. Being non-enzymatic unlike TTC and FDA tests, as expected, the EB test was the most reliable with similar results between sterilized and not sterilized seeds for most epiphytic and terrestrial species as well as when compared between groups.

CONCLUSIONS

The lifeform of the species and seed sterilization prior to testing are important influential factors in orchid seed viability testing. Since EB test was found to be reliable we recommend the EB test for seed viability assessment in orchids rather than the less reliable but commonly used TTC test, or the FDA test, which require more expensive and sophisticated instrumentation. Since storage time was not an influential factor in orchid seed viability testing, the recommendations of this study can be used for both fresh as well as long-term stored orchid seeds. This is helpful for research and especially for conservation measures such as seed banking. However, due to the species specificity of the bio-physiology of orchids, we call for comprehensive viability test assessment in the hyper diverse orchid family to be extended to a greater number of species to facilitate efficient conservation and research.

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.

Volatile signature indicates viability of dormant orthodox seeds

All seeds eventually die even under optimal storage conditions. The moment of viability loss is difficult to predict and detect. In order to differentiate between dead and viable dormant orthodox seeds, GC-MS analysis was used to non-invasively evaluate the volatile signature of seeds of Pyrus communis L. and Sorbus aucuparia L. Dormant seeds are capable of extended metabolic depression. However, their low metabolic rate remains largely unquantified, and there are no measurements of metabolites, i.e. volatile organic compounds (VOC) for physiologically dormant seeds during storage. Therefore, to address this issue, seeds were stored at a broad range of moisture content (MC) ranging from 2 to 30% under cryogenic (-196°C), cool (5°C) and elevated (40°C) temperatures. Volatile emission was highly dependent on seed MC and storage temperature and was higher under conditions associated with seed viability loss. However, changes in the emission of volatiles entrapped in seeds and released during 24 h after storage were detected for all conditions, providing insight into the processes occurring in dry dormant seeds. Among the 36 volatiles identified, three (acetaldehyde, ethanol, ethyl acetate) were highly correlated with seed germinability and show potential for the non-invasive screening of viability. Significantly, all three VOC are derived mostly from glycolysis and peroxidation and were detected even under very low moisture and temperature storage conditions. This is the first study to report on VOC accumulation and emission from physiologically dormant seeds and provide a broader view into their viability.

Relationship between mitochondrial changes and seed aging as a limitation of viability for the storage of beech seed (Fagus sylvatica L.)

Aging is one of the most fundamental biological processes occurring in all forms of eukaryotic life. Beech trees (Fagus sylvatica L.) produce seeds in intervals of 5–10 years. Its yearly seed yield is usually very low, so there is a need for long-term seed storage to enable propagation of this species upon demand. Seeds for sowing must be of high quality but they are not easy to store without viability loss. Understanding the mechanism responsible for seed aging is therefore very important. We observed the generation of reactive oxygen species (ROS) in mitochondria of embryonic axes and cotyledons of beech seeds during natural aging. The presence of ROS led to changes in compromised mitochondrial membrane integrity and in mitochondrial metabolism and morphology. In this study, we pointed to the involvement of mitochondria in the natural aging process of beech seeds, but the molecular mechanisms underlying this involvement are still unknown.

Nanotechnology: an efficient approach for rejuvenation of aged seeds

Modern agricultural efforts are now in search of an efficient, eco-friendly and sustainable approach for enhanced crop production. Nearly 50-60% of seeds lost occurs due to improper technical handling. Seed deterioration manifests itself as reduction in the rate of germination and growth with increased susceptibility to biotic and abiotic stresses. Furthermore, seed ageing is another economic and scientific issue that is associated with an array of internal (structural, physiological and genetic) and external (storage temperature and relative humidity) factors. Reactive oxygen species (ROS) are believed to be a key player in ageing phenomenon. However, hydrated storage, or ROS blockers are a few of the conventionally used methods to minimize the ageing process. Recently, exogenous applications of different inorganic nanoparticles (metal and metal oxide) are suggested to revitalize and revive aged seeds. Owing to their special properties of nano-size with high surface area they easily penetrate the seed coat. Exposure of nanoparticles has been suggested to neutralize the excess of ROS to a level that initiates hormonal signaling to support early emergence of radicles from the seeds. Nanotechnology has been well explored to enhance the crops nutritional quality, livestock productivity, plant protection from various stressors and in enhancement of seed quality via nanopesticides and nanofertilizers. Aiming at sustainable agriculture practices with fewer inputs, maximum benefits, ecologically safe and compatible technique the nanotechnology is an efficient approach to counteract problems of seed ageing incurring during storage, which is relatively less explored and unresolved conventionally, in general.

Changes in Proline Levels during Seed Development of Orthodox and Recalcitrant Seeds of Genus Acer in a Climate Change Scenario

In the present study, we examined the utility of proline usage as a biochemical indicator of metabolic changes caused by climate change (mean temperature and precipitation) during seed development of two Acer species differing in desiccation tolerance: Norway maple (Acer platanoides L.—desiccation tolerant—orthodox) and sycamore (Acer pseudoplatanus L.—desiccation sensitive—recalcitrant). In plants, proline is an element of the antioxidant system, which has a role in response to water loss and high temperatures. Our study considered whether proline could be treated as an indicator of tree seed viability, crucial for genetic resources conservation. Proline content was measured biweekly in developing seeds (between 11 and 23 weeks after flowering) collected in consecutive years (2017, 2018, and 2019). We showed that proline concentrations in recalcitrant seeds were positively correlated with mean two-week temperature. In contrast, in orthodox seeds no such relationship was found. Proline content proved to be sensitive to thermal-moisture conditions changes, which makes it a promising biochemical marker of seed desiccation tolerance in different climatic conditions.

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.

Application of the MSAP Technique to Evaluate Epigenetic Changes in Plant Conservation

Epigenetic variation, and particularly DNA methylation, is involved in plasticity and responses to changes in the environment. Conservation biology studies have focused on the measurement of this variation to establish demographic parameters, diversity levels and population structure to design the appropriate conservation strategies. However, in ex situ conservation approaches, the main objective is to guarantee the characteristics of the conserved material (phenotype and epi-genetic). We review the use of the Methylation Sensitive Amplified Polymorphism (MSAP) technique to detect changes in the DNA methylation patterns of plant material conserved by the main ex situ plant conservation methods: seed banks, in vitro slow growth and cryopreservation. Comparison of DNA methylation patterns before and after conservation is a useful tool to check the fidelity of the regenerated plants, and, at the same time, may be related with other genetic variations that might appear during the conservation process (i.e., somaclonal variation). Analyses of MSAP profiles can be useful in the management of ex situ plant conservation but differs in the approach used in the in situ conservation. Likewise, an easy-to-use methodology is necessary for a rapid interpretation of data, in order to be readily implemented by conservation managers.

Variation in Seed Metabolites between Two Indica Rice Accessions Differing in Seed Longevity

For a better understanding of germination after seed storage, metabolite profiling was conducted using hybrid triple quadrupole time-of-flight (QTOF) mass spectrometry. After moisture content (MC) equilibration, seeds of "WAS170" (short-lived) and "IR65483" (long-lived) were stored at 10.9% MC and 45 °C. Samples for metabolite analysis were taken after 0 and 20 days of storage. Among 288 metabolites, two flavonoids (kaempferide and quercetin-3-arabinoside), one amino acid (S-sulfocysteine) and one sugar (D-glucose) increased in "IR65483" seeds after storage but were not detected in "WAS170" seeds. Based on the genome sequence database, we identified clear allelic differences with non-synonymous mutations on the six flavonol synthase genes regulating the accumulation of kaempferol- and quercetin-metabolites. On the other hand, two metabolites (thiamine monophosphate and harmaline) increased in short-lived seeds after storage; these metabolites could be potential biochemical indicators of seed deterioration.

Timing for antioxidant-priming against rice seed ageing: optimal only in non-resistant stage

Seed deterioration due to ageing strongly affects both germplasm preservation and agricultural production. Decelerating seed deterioration and boosting seed viability become increasingly urgent. The loss of seed viability is inevitable even under cold storage. For species with short-lived seed or for regions with poor preservation infrastructure where cold storage is not readily available, seed enhancement is more reliable to increase seed viability and longevity. Antioxidant priming as a way of seed enhancement usually improves seed germination. As for post-priming survival, however, significant uncertainty exists. The controversy lies particularly on seeds of high germination percentage (GP > 95%) whose viability is hardly improvable and the benefits of priming depend on prolonging seed longevity. Therefore, this study timed antioxidant priming to prolong the longevity of high-viability seeds under artificially accelerated ageing (AAA). Rice (Nipponbare) seeds (GP > 97%) under room-temperature-storage (RTS) for 6 months. were resistant to AAA first with little viability loss for a certain period, the resistant stage. This resistance gradually vanished without GP change, during a prolonged RTS period which was named the vulnerable stage. According to the results, although antioxidant priming severely curtailed the resistant stage for seeds with a long plateau in the survival curve, it decelerated viability loss for seeds in the vulnerable stage. In complement to seed storage, priming potentially retains high seed GP which would decrease without seed enhancement. To maximize the benefits of priming for high-GP seeds, two time points are advised as the start of a time window for priming: (1) just at the end of the resistant stage without notable viability loss, which is hard to grasp by GP monitoring; (2) slight but identifiable GP decline.

Biochemical Profile of the Soybean Seed Embryonic Axis and Its Changes during Accelerated Aging

Seed deterioration is an important topic in plant science, as the majority of cultivated species use seeds as their means of propagation; however, due to its complexity, the process of seed deterioration has not yet been completely elucidated. Three soybean cultivars (BMX Raio, BMX Zeus, and DM 53i54) exposed to four distinct periods of accelerated aging (0, 3, 6 and 9 days) in a fully randomized experimental design. Initially, vigor and germination tests were performed. The activity of superoxide dismutase, catalase, ascorbate peroxidase enzymes, hydrogen peroxide, malonaldehyde, DNA oxidation, macromolecules and mineral content, and Maillard reactions were quantified in the embryonic axis. Results showed that DNA did not suffer degradation or oxidation. In terms of consumption of reserves, only sugars were consumed, while levels of protein, starch, and triglycerides were maintained. The Maillard reaction did show potential as an indicator of buffer capacity of protein to ROS. Additionally, levels of catalase and ascorbate peroxidase decreased during the aging process. Moreover, nutrient analysis showed that a high magnesium level in the cultivar bestowed greater resilience to deterioration, which can indicate a potential function of magnesium in the cell structure via reflex in seed aging through seed respiration.

A rapid and sensitive method to assess seed longevity through accelerated aging in an invasive plant species

BACKGROUND

Seed longevity and vigor assessment is crucial for efficient ex situ biodiversity conservation in genebanks but may also have potential applications for the understanding of ecological processes and in situ biodiversity conservation. In fact, one of the factors determining the persistence of invasive species, a main threat to global biodiversity, is the generation of soil seed banks where seeds may remain viable for several years. Artificial seed aging tests using high temperatures and high relative humidity have been described for seed longevity estimation but have been mainly optimized for species with commercial interest. Thus, the aim of the study is to define a rapid and sensitive method to assess seed longevity and vigor through accelerated aging in the worldwide distributed invasive species Carpobrotus edulis to provide tools to biodiversity managers to evaluate invasive potential and develop effective post-eradication plans.

RESULTS

Slow seed deterioration rate was obtained when C. edulis seeds were subjected to common accelerated aging temperatures (43-45 °C). This contrasts with the rapid viability decay between 24-72 h when seeds were subjected to temperatures superior to 55 °C, a strong inflection point for this species' thermosensitivity. Relative humidity also played a role in defining seed survival curves, but only at high temperatures, speeding up the deterioration process. The selected aging conditions, 55 °C at 87% relative humidity were tested over two C. edulis populations and three measures were proposed to parametrize the differential sigmoidal seed survival curves, defining the seed resistance to deterioration (L₅, aging time where 95% of seeds maintain their viability), medium longevity (L₅₀, 50% of seeds lose their viability) and lethal aging time (L₉₅, 95% of viability loss).

CONCLUSIONS

An accelerated aging test at 55 °C and 87% relative humidity constitutes a rapid and sensitive method that can be performed within a working week, allowing managers to easily test seed vigor and longevity. This test may contribute to assess invasive potential, design effective monitoring programs and soil seed bank eradication treatments.

Does Storage under Gene Bank Conditions Affect Seed Germination and Seedling Growth? The Case of Senecio morisii (Asteraceae), a Vascular Plant Exclusive to Sardinian Water Meadows

Understanding seed viability under long-term storage conditions provides basic and useful information to investigate the effectiveness of seed banking. Besides the germination success, seedling establishment is also an important requirement, and a decisive step to ensure plant propagation. We used comparative data of germination, seedling growth, and survival percentage between fresh and 10-years-stored seeds of Senecio morisii, a narrow endemic and vulnerable species of Sardinia (Italy), in order to evaluate if differences exist in these traits between fresh and 10-years-stored seeds. Stored seeds showed higher germination percentages than fresh ones, whereas seedling growth and survival did not present significant differences between them, except for seedling growth in plants produced from seeds germinated at 25 °C. This study allowed us to assess if seeds of S. morisii were able to germinate under controlled conditions, and if they maintained their viability and germination capacity for at least 10 years of long-term storage in the seed bank. In addition, the high seedling survival detected in both fresh and stored seeds suggests that stored seeds of S. morisii can be used to support reinforcement or reintroduction actions when fresh materials are not available.

The History of Domestication and Selection of Lucerne: A New Perspective From the Genetic Diversity for Seed Germination in Response to Temperature and Scarification

Lucerne (Medicago sativa), a major perennial pasture legume, belongs to a species complex that includes several subspecies with wild and cultivated populations. Stand establishment may be compromised by poor germination. Seed scarification, deterioration and temperature have an impact on germination. The objective of this study was to analyse the genetic diversity of lucerne germination in response to three factors: (1) temperature, with seven constant temperatures ranging from 5 to 40°C, was tested on 38 accessions, (2) seed scarification was tested on the same accessions at 5 and 22°C, (3) seed deterioration was tested on two accessions and two seed lots at the seven temperatures. The germination dynamics of seed lots over time was modelled and three parameters were analysed: germinability (germination capacity), maximum germination rate (maximum% of seeds germinating per time unit), and lag time before the first seed germinates. Seed scarification enhanced germinability at both temperatures and its effect was much higher on falcata and wild sativa accessions. Incomplete loss of the hardseededness trait during domestication and selection is hypothesised, indicating that the introduction of wild material in breeding programmes should be followed by the selection for germinability without scarification. Seed lots with altered germinability had low germination at extreme temperatures, both cold and hot, suggesting that mild temperatures are required to promote germination of damaged seed lots. A large genetic diversity was revealed for germination (both capacity and rate) in response to temperature. All accessions had an optimal germination at 15 or 22°C and a poor germination at 40°C. The sativa varieties and landraces had a high germination from 5 to 34°C while the germination of falcata and the wild sativa accessions were weakened at 5 or 34°C, respectively. These differences are interpreted in terms of adaptation to the climate of their geographical origin regions in order to escape frost or heat/drought risks. These new findings give insights on adaptation and domestication of lucerne in its wide geographic area. They suggest further improvement of germination is needed, especially when introducing wild material in breeding pools to remove scarification requirements and to limit differences in response to temperature.

Effect of Nitrogen Reactive Compounds on Aging in Seed

Reactive nitrogen species (RNS) are universal compounds that are constantly present in plant cells. RNS function depends on their actual level (the "nitrosative door" concept), duration of plant exposure to RNS and the context of the exposure. RNS are involved in the nitration of nucleic acids and fatty acids, posttranslational protein modifications (nitration and S-nitrosylation), and modulation of reactive oxygen species metabolism. RNS are regulatory molecules of various physiological processes in plants, including seed formation, maturation, dormancy and germination. The free radical theory of aging, well documented for animals, indicated that RNS participate in the regulation of the life span. Some data point to RNS contribution in preservation of seed vigor and/or regulation of seed longevity. Seed aging is a problem for biologists and agriculture, which could be solved by application of RNS, as a factor that may potentially expand seed vitality resulting in increased germination rate. The review is focused on RNS, particularly nitric oxide contribution to regulation of seed aging.

Reframing conservation physiology to be more inclusive, integrative, relevant and forward-looking: reflections and a horizon scan

Applying physiological tools, knowledge and concepts to understand conservation problems (i.e. conservation physiology) has become commonplace and confers an ability to understand mechanistic processes, develop predictive models and identify cause-and-effect relationships. Conservation physiology is making contributions to conservation solutions; the number of 'success stories' is growing, but there remain unexplored opportunities for which conservation physiology shows immense promise and has the potential to contribute to major advances in protecting and restoring biodiversity. Here, we consider how conservation physiology has evolved with a focus on reframing the discipline to be more inclusive and integrative. Using a 'horizon scan', we further explore ways in which conservation physiology can be more relevant to pressing conservation issues of today (e.g. addressing the Sustainable Development Goals; delivering science to support the UN Decade on Ecosystem Restoration), as well as more forward-looking to inform emerging issues and policies for tomorrow. Our horizon scan provides evidence that, as the discipline of conservation physiology continues to mature, it provides a wealth of opportunities to promote integration, inclusivity and forward-thinking goals that contribute to achieving conservation gains. To advance environmental management and ecosystem restoration, we need to ensure that the underlying science (such as that generated by conservation physiology) is relevant with accompanying messaging that is straightforward and accessible to end users.

Physiologic alterations in orthodox seeds due to deterioration processes

Seed deterioration is a partially elucidated phenomenon that happen during the life of the seed. This review describes the processes that lead to seed deterioration, including loss of seed protection capacity against reactive oxygen species (ROS), damage to the plasma membrane, consumption of reserves, and damage to genetic material. A hypothesis of how seed deterioration occurs was also addressed; in this hypothesis, seed deterioration was divided into three phases. The first is the beginning of deterioration, with a slight reduction of vigor caused by the reactions of reducing sugars with antioxidant enzymes and genetic material. In the second, the cell shows oxidative damages, causing lipid peroxidation, which leads to the leaching of solutes, the formation of malondialdehyde, and, consequently, an increase in damages to genetic material. In the third phase, there is cell collapse with mitochondrial membrane deconstruction and a high accumulation of reactive oxygen species, malondialdehyde, and reducing sugars.

Loss of genetic integrity in artificially aged seed lots of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.)

Loss of genetic integrity can occur during the long-term conservation of seeds. We have studied these effects in seeds of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) exposed to accelerated aging (elevated temperature and moisture) conditions. Tests of first count, germination, and germination speed index were performed to measure physiological quality; cytogenetic tests and comet assay were used to evaluate genetic integrity. With aging, we observed a decrease in mitotic index and an increase in the frequency of chromosomal alterations in root cells of imbibed seeds, as well as increased DNA damage (comet assay) in dry and imbibed seed embryos of both species. The comet assay can be a useful technique for measuring genetic integrity in seed conservation programs.

Regulation of thiol metabolism as a factor that influences the development and storage capacity of beech seeds

Seeds are the basis of propagation for the common beech (Fagus sylvatica L.), but the seed set of the beech is unsteady, with 5-10 years between abundant crops. Beech seeds are very difficult to store and lose their viability quickly even in optimum storage conditions. To date, it has not been possible to determine factors indicative of the aging process and the loss of viability of beech seeds during storage. To address this important economic challenge and interesting scientific problem, we analyzed the adjustment of the redox state during the development and storage of seeds. Many metabolic processes are based on reduction and oxidation reactions. Thiol proteins control and react to the redox state in the cells. The level of thiol proteins increased during seed maturation and decreased during storage. Gel-based redox proteomics identified 17 proteins in beech seeds during development. The proteins could be assigned to processes like metabolism and antioxidant functions. During storage, the number of proteins decreased to only six, i.e., oxidoreductases, peptidases, hydrolases and isomerases. The occurrence of peroxiredoxins (PRX) as thiol peroxidases and redox regulators indicates an important role of cytosolic 1CysPRX and PRXIIC, mitochondrial PRXIIF, and plastidic PRXIIE, 2CysPRX, and PRXQ in beech seeds during development and storage. Particularly, 2CysPRX was present in beech seeds during development and storage and may perform an important function in regulation of the redox state during both seed development and storage. The role of thiol proteins in the regulation of the redox state during the development and storage of beech seeds is discussed.

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.

Mitochondria Are Important Determinants of the Aging of Seeds

Seeds enable plant survival in harsh environmental conditions, and via seeds, genetic information is transferred from parents to the new generation; this stage provides an opportunity for sessile plants to settle in new territories. However, seed viability decreases over long-term storage due to seed aging. For the effective conservation of gene resources, e.g., in gene banks, it is necessary to understand the causes of decreases in seed viability, not only where the aging process is initiated in seeds but also the sequence of events of this process. Mitochondria are the main source of reactive oxygen species (ROS) production, so they are more quickly and strongly exposed to oxidative damage than other organelles. The mitochondrial antioxidant system is also less active than the antioxidant systems of other organelles, thus such mitochondrial 'defects' can strongly affect various cell processes, including seed aging, which we discuss in this paper.

Arabidopsis Seed Stored mRNAs are Degraded Constantly over Aging Time, as Revealed by New Quantification Methods

How plant seeds age remains poorly understood and effective tools for monitoring seed aging are lacking. Dry seeds contain various stored mRNAs which are believed to be required for protein synthesis during early stages of seed germination. We reasoned that seed stored mRNAs would undergo degradation during seed aging, based on the propensity of mRNAs to degrade. We performed RT-PCR and qPCR analyses to study the changes in stored mRNA levels of Arabidopsis seeds during aging. All stored mRNAs analyzed were gradually degraded in both naturally and artificially aged seeds. The difference in Ct values between aged and control seeds (ΔCt value) was highly correlated with the mRNA fragment size and seed aging time. We derived mathematical equations for estimating the relative amount of undamaged stored mRNAs and frequency of the breakdown at one nucleotide level for individual mRNAs. Stored mRNAs were found to break down randomly. The frequency of breaks per nucleotide per day, which we named β value, remained fairly constant under the same aging conditions over aging time. This parameter should allow the effects of different conditions on the degradation of stored mRNAs to be quantitatively compared. Also, we showed that the change in stored mRNA levels could serve as a more precise biomarker for seed aging assessment than three existing methods. These methods and findings will advance the studies of stored mRNAs and seed ageing in plants, and likely slow RNA degradation in non-plant systems.

Suppression of LOX activity enhanced seed vigour and longevity of tobacco (Nicotiana tabacum L.) seeds during storage

The preservation of seed viability and quality in storage is an important trait both for commercial and germplasm usage. To better explore potential mechanisms of tobacco seed deterioration, seed packed in cloth bag (C) and vacuum bag (V) were stored under room temperature (RT) and low temperature (LT, 18°C), and sampled periodically for laboratory testing. Seed stored in low temperature with vacuum bag (LT/V) owned the highest seed vigour after 25 months of storage and in room temperature with cloth bag (RT/C) lost seed vigour and germination ability after 20-month storage. Meanwhile, seed in RT/C notably increased about 5-fold endogenous hydrogen peroxide (H₂O₂), 4-fold malondialdehyde (MDA) contents, 12-fold Lipoxygenases (LOX) activity and 2-fold the expression of NtLOX3 comparing with LT/V at the end of 15-month storage. In addition, regression analysis indicated that LOX activity was strongly negatively correlated with seed vigour as the R ² value reached 0.970 in RT/C. Furthermore, caffeic acid and catechin, the inhibitors of LOX activity, were applied to tobacco seeds pre-treatment and followed with artificial accelerated aging. Seeds pretreated with inhibitors, especially caffeic acid, reduced LOX activity by 50%, MDA and H₂O₂ contents by 40% and 20%, respectively, and increased more than 1.2-fold seed vigour and seedling quality comparing with seeds pretreated with H₂O after 6-day artificial aging, indicating a better seed storability after artificial accelerated aging. These results suggest that LOX accelerated seed aging, and suppression of LOX activity enhanced seed vigour and viability in accelerated aging tobacco seed, opening new opportunities for effective management of seed germplasm under long-term storage and conservation.

TUNEL Assay and DAPI Staining Revealed Few Alterations of Cellular Morphology in Naturally and Artificially Aged Seeds of Cultivated Flax

In a search for useful seed aging signals as biomarkers for seed viability prediction, we conducted an experiment using terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and 4&prime;,6-diamidino-2-phenylindole (DAPI) staining to analyze morphological and molecular changes in naturally aged (NA) and artificially aged (AA) flax (Linum usitatissimum L.) seeds. A total of 2546 sections were performed from 112 seeds of 12 NA and AA seed samples with variable germination rates. Analyzing 1384 micrographs generated from TUNEL assay and DAPI staining revealed few alterations of the cellular morphology of the NA and AA seeds. Also, the revealed DNA degradations in the aged flax seeds appeared to be associated with seed samples of low germination rates. These results suggest that oily flax seed aging may alter the cellular morphology differently than starchy wheat seed aging. The results also imply that the TUNEL assay and DAPI staining may not yield informative assessments on cellular alterations and DNA degradation after the aging of oily seeds.

An integrative insight on dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga, a tropical grass with great economic and ecological impact

Even though exhaustively studied, dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga remains a mystery. To clarify this, we asked the following question: could dormancy alleviation in diaspores of this species be associated with ageing, GA/ABA balance and remaining structures of the panicoid spikelet? We answer this question using diaspores of U. humidicola cv. BRS Tupi as a biological model, a cultivar with a wide edaphoclimatic range in Neotropical areas and whose diaspores possess 'deep dormancy' when dispersed. We analysed both germination and early plant development using a split-plot model. Our findings demonstrate that dormancy alleviation in diaspores of U. humidicola is a synergic phenomenon driven by crosstalk between age, GA/ABA balance and remaining structures of the panicoid spikelet covering caryopses, since this interaction acts on the dynamics of germination and early plant development. We demonstrate that: (i) spreading germination time is a maternal survival mechanism of this species, which has repercussions for occupational aggressiveness of the species; (ii) remaining structures of the panicoid spikelet covering caryopses are the main modulator of embryo development. These structures control the after-ripening process, which is modulated by some molecular factor. We also highlight that it is necessary to review concepts about dormancy of dispersal units in this grass species.

Dehiscence method: a seed-saving, quick and simple viability assessment in rice

BACKGROUND

Seed viability monitoring is very important in ex situ germplasm preservation to detect germplasm deterioration. This requires seed-, time- and labor- saving methods with high precision to assess seed germination as viability. Although the current non-invasive, rapid, sensing methods (NRSs) are time- and labor-saving, they lack the precision and simplicity which are the virtues of traditional germination. Moreover, they consume a considerable amount of seeds to adjust sensed signals to germination percentage, which disregards the seed-saving objective. This becomes particularly severe for rare or endangered species whose seeds are already scarce. Here we propose a new method that is precise, low-invasive, simple, and quick, which involves analyzing the pattern of dehiscence (seed coat rupture), followed by embryonic protrusion.

RESULTS

Dehiscence proved simple to identify. After the trial of 20 treatments from 3 rice varieties, we recognized that dehiscence percentage at the 48th hour of germination (D(48)) correlates significantly with germination rate for tested seed lots. In addition, we found that the final germination percentage corresponded to D(48) plus 5. More than 70% of the seeds survived post-dehiscence desiccation for storage. Hydrogen peroxide (1 mM) as the solution for imbibition could further improve the survival. The method also worked quicker than tetrazolium which is honored as a fast, traditional method, in detecting less vigorous but viable seeds.

CONCLUSION

We demonstrated the comprehensive virtues of dehiscence method in assessing rice seed: it is more precise and easier to use than NRSs and is faster and more seed-saving than traditional methods. We anticipate modifications including artificial intelligence to extend our method to increasingly diverse circumstances and species.

Decline in RNA integrity of dry-stored soybean seeds correlates with loss of germination potential

This study investigates the relationship between germination ability and damage to RNA in soybean seeds (cv 'Williams 82') stored dry at 5 °C for 1-27 years. Total germination of 14 age cohorts harvested between 2015 and 1989 ranged from 100% to 3%. Germination decline followed classic seed viability kinetics, with symptomatic seed aging beginning after 17 years of storage. RNA integrity was assessed in dry seeds by electrophoresis of total RNA, followed by calculation of the RNA integrity number (RIN, Agilent Bioanalyzer software), which evaluates RNA fragment size distributions. Analysis of RNA extracted from cotyledons, embryonic axes, plumules, and seed coats across the range of age cohorts showed consistent RNA degradation: older seeds had over-representation of small RNAs compared with younger seeds, which had nearly a 2:1 ratio of 25S and 18S rRNAs. RIN values for cotyledons and embryonic axes from the same seed were correlated. Decline in RIN tracked reduced germination, with a pronounced decrease in RIN after 17 years of storage. This led to a high correlation between the mean RIN of cotyledon RNA and the total germination percentage (R2=0.91, P<0.0001). Despite this relationship, germinable and non-germinable seeds within cohorts could not be distinguished unless the RIN was <3.5, indicating substantial deterioration. Our work demonstrates that seed RNA incurs damage over time, observable in fragment size distributions. Under the experimental conditions used here, RIN appears to be a promising surrogate for germination tests used to monitor viability of stored seeds.

Rethinking the approach to viability monitoring in seed genebanks

Seed viability monitoring, usually through a germination test, is a key aspect of genebank management; a low viability result triggers the regeneration of an accession in order to ensure that the genetic diversity of the accession is conserved and available for distribution. However, regular viability monitoring of large collections is costly in terms of seeds, labour and other resources. Genebanks differ in how they conduct their viability monitoring and how they collect, manage and store the data that are generated. In this article, we propose alternatives to the current norm of conducting an initial germination test soon after arrival at the genebank and then testing after regular, set storage intervals, as recommended in the Food and Agriculture Organization's Genebank Standards for Plant Genetic Resources for Food and Agriculture. We use real data from the International Rice Genebank (held at the International Rice Research Institute) to illustrate some of the issues regarding the accuracy and reliability of germination test results, in particular when they are used to predict the longevity of a seed lot in storage and to set viability monitoring intervals. We suggest the use of seed storage experiments on samples of seeds to identify which seed lots from a particular crop season to test first. We also give advice on the use of sequential testing schemes potentially to reduce the number of seeds used for viability testing; the use of tolerance tables to identify unlikely results when samples are subdivided into replicates; and what data to include in a genebank management database to improve the management of seed collections.

Molecular approaches for genetic improvement of seed quality and characterization of genetic diversity in soybean: a critical review

Soybean is an economically important leguminous crop. Genetic improvements of soybeans have focused on enhancement of seed and oil yield, development of varieties suited to different cropping systems, and breeding resistant/tolerant varieties for various biotic and abiotic stresses. Plant breeders have used conventional breeding techniques for the improvement of these traits in soybean. The conventional breeding process can be greatly accelerated through the application of molecular and genomic approaches. Molecular markers have proved to be a new tool in soybean breeding by enhancing selection efficiency in a rapid and time-bound manner. An overview of molecular approaches for the genetic improvement of soybean seed quality parameters, considering recent applications of marker-assisted selection and 'omics' research, is provided in this article.

Different Modes of Hydrogen Peroxide Action During Seed Germination

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

A Belated Green Revolution for Cannabis: Virtual Genetic Resources to Fast-Track Cultivar Development

Cannabis is a predominantly diecious phenotypically diverse domesticated genus with few if any extant natural populations. International narcotics conventions and associated legislation have constrained the establishment, characterization, and use of Cannabis genetic resource collections. This has resulted in the underutilization of genepool variability in cultivar development and has limited the inclusion of secondary genepools associated with genetic improvement strategies of the Green Revolution. The structured screening of ex situ germplasm and the exploitation of locally-adapted intraspecific traits is expected to facilitate the genetic improvement of Cannabis. However, limited attempts have been made to establish the full extent of genetic resources available for pre-breeding. We present a thorough critical review of Cannabis ex situ genetic resources, and discuss recommendations for conservation, pre-breeding characterization, and genetic analysis that will underpin future cultivar development. We consider East Asian germplasm to be a priority for conservation based on the prolonged historical cultivation of Cannabis in this region over a range of latitudes, along with the apparent high levels of genetic diversity and relatively low representation in published genetic resource collections. Seed cryopreservation could improve conservation by reducing hybridization and genetic drift that may occur during Cannabis germplasm regeneration. Given the unique legal status of Cannabis, we propose the establishment of a global virtual core collection based on the collation of consistent and comprehensive provenance meta-data and the adoption of high-throughput DNA sequencing technologies. This would enable representative core collections to be used for systematic phenotyping, and so underpin breeding strategies for the genetic improvement of Cannabis.

The Associative Changes in Scutellum Nuclear Content and Morphology with Viability Loss of Naturally Aged and Accelerated Aging Wheat (Triticum aestivum) Seeds

Timely prediction of seed viability loss over long-term storage represents a challenge in management and conservation of ex situ plant genetic resources. However, little attention has been paid to study the process of seed deterioration and seed aging signals under storage. An attempt was made here to investigate morphological and molecular changes in the scutellum and aleurone sections of naturally or artificially aged wheat seeds using TUNEL assay and DAPI staining. Twelve wheat genotypes or samples exposed to natural ageing (NA) or accelerated ageing (AA) were assayed and these samples had germination rates ranging from 11 to 93%. The assayed samples showed substantial changes in scutellum, but not aleurone. The nuclei observed in the majority of the scutellum cells of the NA seed samples of lower germination rates were longer in size and less visible, while the scutellum cell morphology or arrangement remained unchanged. In contrast, longer AA treatments resulted in the loss of scutellum cell structure, collapse of cell layers, and disappearance of honey comb arrangements. These nuclei and structural changes were consistent with the DNA assessments of nuclear alternations for the selected wheat samples. Interestingly, the sample seed germination loss was found to be associated with the reductions in the scutellum nuclear content and with the increases in the scutellum nuclei length to width ratio. These findings are significant for understanding the process of wheat seed deterioration and are also useful for searching for sensitive seed aging signals for developing tools to monitor seed viability under storage.