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Deterioration of seed during dry storage is a major problem for genebanks and seed companies. Germination tests are the gold standard to monitor seed viability; however, these prove to be insensitive during the early stage of storage when viability changes are subtle. Recent findings demonstrate that decline in RNA integrity may be an early indicator of seed longevity during dry storage. The goal of this study was to determine the sensitivity of RNA integrity, measured as RNA integrity number (RIN), regarding how soon changes can be detected and how many seeds are required. We compared the statistical power of germination and RIN assays using a well‐characterized collection of 'Williams 82' soybean seeds, with cohorts harvested between 1989 and 2019 and stored at 5 °C. Germination was monitored in 1‐ to 3‐yr intervals since 1989, and RIN was monitored in 1‐ to 2‐yr intervals since 2016 providing an extensive dataset to conduct statistical power analyses. Decline in RIN can be detected in soybean seeds within 10 yr with a RNA monitor test that consumes approximately 30 seeds. In contrast, a germination test detects deterioration in 16 yr using approximately 50 seeds, and by this time, the seed lot is near the limit of longevity and has entered the phase of rapid mortality. Work from this study indicates that early detection of aging using RIN decline can be used to predict the longevity threshold to optimize viability monitoring and regeneration times, preventing loss of valuable samples by overtesting or missing the longevity threshold. Core Ideas: We calculate the statistical power of RNA integrity assays (RIN) for monitoring seed aging during storage.RIN detects changes in stored seeds earlier and with fewer seeds compared with traditional germination assays.Monitoring RIN presents a method to predict seed longevity with increased efficiency in seed storage operations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent evidence points to relationships between intra-specific seed mass variation and viability loss in response to ageing stress. However, little is known about how seed quality may change temporally in response to such stress. Here we examined seed–water relations of mass-separated Rudbeckia mollis seeds to better understand physiological status among mass classes. We then evaluated seed viability and vigour changes in response to various storage conditions or post-storage vigour tests (a 41°C, 75% RH stress for up to 45 d). We found similar pre-storage physiology among mass classes. However, seeds of lower mass deteriorated up to 1.5-fold faster than heavier seeds under certain conditions. Stressing seeds after storage resulted in distinct vigour differences among mass classes. For example, vigour in lower mass seeds tended to decline more compared to heavier seeds following storage in a climate-controlled room. Alternatively, vigour loss varied among mass classes following storage in a non-climate-controlled shed. Our results highlight the importance of distinguishing between pre-sowing storage and post-storage vigour effects when quantifying relative levels of viability loss among seeds of different mass. Furthermore, differential responses to storage and ageing stress among mass classes may have important implications for post-storage regeneration and subsequent population dynamics. [ABSTRACT FROM AUTHOR]

Main conclusion: Discrete categories of seed physiology can be explained through a unified concept of the structural and molecular mobility responses within cells to drying. Tolerance of desiccation is typically described by a threshold or low water content limit to survival. This convention provides fairly good distinction between orthodox and recalcitrant seeds, which show thresholds of less than about 0.07 and greater than about 0.2 g HO g DW, respectively. Threshold water contents, however, are not direct measures of the intensity of water stress tolerated by seeds, nor are they measures of cell response to water stress. More direct criteria, that accommodate both spatial and temporal effects of water loss, are required to explain variation of desiccation tolerance and longevity in seeds from diverse genetic backgrounds and growth conditions. This essay presents the argument that changes in cellular volume directly quantify primary responses to desiccating stress in a context that also links damage, as cellular constituents compress, and protection, as compressed molecules form stabilizing structure. During desiccation, fluid cytoplasm solidifies, and the newly formed spatial relationships among molecules determine whether and how long viability is maintained. The diversity of seed behaviors suggests complexity and opportunity to discover molecules and mechanisms that regulate survival and perception of time in cells that lack metabolic function. [ABSTRACT FROM AUTHOR]

Summary Slow movement of molecules in glassy matrices controls the kinetics of chemical and physical reactions in dry seeds. Variation in physiological activity among seeds suggests that there are differences in mobility among seed glasses. Testing this hypothesis is difficult because few tools are available to measure molecular mobility within dry seeds. Here, motional properties within dry pea cotyledons were assessed using dynamic mechanical analysis. The technique detected several molecular relaxations between −80 and +80°C and gave a more detailed description of water content-temperature effects on molecular motion than previously understood from studies of glass formation in seeds at glass transition (Tg). Diffusive movement is delimited by the α relaxation, which appears to be analogous to Tg. β and γ relaxations were also detected at temperatures lower than α relaxations, clearly demonstrating intramolecular motion within the glassy matrix of the pea cotyledon. Glass transitions, or the mechanical counterpart α relaxation, appear to be less relevant to seed aging during dry storage than previously thought. On the other hand, β relaxation occurs at temperature and moisture conditions typically used for seed storage and has established importance for physical aging of synthetic polymer glasses. Our data show that the nature and extent of molecular motion varies considerably with moisture and temperature, and that the hydrated conditions used for accelerated aging experiments and ultra-dry conditions sometimes recommended for seed storage give greater molecular mobility than more standard seed storage practices. We believe characterization of molecular mobility is critical for evaluating how dry seeds respond to the environment and persist through time. [ABSTRACT FROM AUTHOR]

Abstract: Seeds die inevitably but unexpectedly during storage and current understanding of seed quality and storage conditions do not allow reliable means to predict or prevent this critical problem. Chemical degradation of seed components likely occurs through oxidative damage, but the rate of these reactions is dominated by properties of seed that are affected by temperature and moisture. These visco-elastic properties contribute to the structure of seeds as amorphous solids. This paper presents the perspective of seed maturation and post-harvest treatment as an exercise in engineering design for a structure that must persist through time and fluctuating conditions. Structural analyses are engineering tools used to select proper composition of materials and predict their behavior under a range of circumstances and are applicable to measurement within seeds. Thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) measure structural deformation and stress–strain relationships, providing sensitive and universal parameters that detect differences in structural stability in materials with subtle compositional differences or processing methods. When applied to seeds, TMA and DMA techniques provide information consistent with existing information on glass and first order transitions. The depth of additional information obtainable about the behavior of the glass and interactions with lipid structure suggests that these techniques will be able to quantify differences among seed structures that contribute to their tendency to age. [ABSTRACT FROM AUTHOR]

The article discusses the effectiveness of cryogenic freezing technology for the preservation of recalcitrant, or water requiring, seeds for plant biodiversity germplasm seed banks, with particular focus on storage of plant species endemic to humid tropical regions. It is noted that larger recalcitrant seeds can be preserved by removal and in vitro germination of the embryonic axis prior to cryopreservation. Other topics include the use of cryoprotectant agents, the estimation of the production of recalcitrant seeds in rare and endangered plants in various global regions, and the challenges of preventing hybridization to protect diversity in tree species.