Search

Summary: Seed size shapes plant evolution and ecosystems, and may be driven by plant size and architecture, dispersers, habitat and insularity. How these factors influence the evolution of giant seeds is unclear, as are the rate of evolution and the biogeographical consequences of giant seeds.We generated DNA and seed size data for the palm tribe Borasseae (Arecaceae) and its relatives, which show a wide diversity in seed size and include the double coconut (Lodoicea maldivica), the largest seed in the world. We inferred their phylogeny, dispersal history and rates of change in seed size, and evaluated the possible influence of plant size, inflorescence branching, habitat and insularity on these changes.Large seeds were involved in 10 oceanic dispersals. Following theoretical predictions, we found that: taller plants with fewer‐branched inflorescences produced larger seeds; seed size tended to evolve faster on islands (except Madagascar); and seeds of shade‐loving Borasseae tended to be larger.Plant size and inflorescence branching may constrain seed size in Borasseae and their relatives. The possible roles of insularity, habitat and dispersers are difficult to disentangle. Evolutionary contingencies better explain the gigantism of the double coconut than unusually high rates of seed size increase. [ABSTRACT FROM AUTHOR]

We argue that the need for a quality seed supply chain is a major bottleneck for the restoration of Chile's native ecosystems, thus supplementing the list of bottlenecks proposed by Bannister et al. in 2018. Specifically, there is a need for defining seed transfer zones, developing standards and capacities for properly collecting and storing seeds, reducing information gaps on seed physiology and longevity, and implementing an efficient seed supply chain with certification of seed origin and quality. Without such capacities, countries are unlikely to meet their restoration commitments. Although we focus on bottlenecks in Chile, the issues we raise are relevant to other countries and thus the global agenda for ecological restoration. [ABSTRACT FROM AUTHOR]

Summary: Much is known about the inter‐specific distribution of life span in a wide diversity of vertebrates and in adult plants, but not for seeds, yet the functional trait seed life span underpins global agriculture, plant species conservation and seed persistence in the soil. We sourced data for five storage conditions (soil seed bank; high temperature – high humidity accelerated ageing; temperate, cooler, open storage; cool, dry, refrigerator; and cold, dry, freezer); and analysed the distribution of orthodox seed life span amongst crop and wild species. In all cases, whether for maximum known in situ life span in the soil seed bank (417 species), or for half‐lives (P50s) ex situ (732 species), the distribution is right‐skewed. The finding that seeds of > 50% of species are likely to have life spans ≤ 20% of the longest recorded under the same conditions has implications for future research on the evolution of seed traits and gene bank collections management. [ABSTRACT FROM AUTHOR]

Plant persistence and migration in face of climate change depends on successful reproduction by seed, a central aspect of plant life that drives population dynamics, community assembly and species distributions. Plant reproduction by seed is a chain of physiological processes, the rates of which are a function of temperature, and can be modelled using thermal time models. Importantly, while seed reproduction responds to its instantaneous thermal environment, there is also evidence of phenotypic plasticity in response to the thermal history experienced by the plant's recent ancestors, by the reproducing plant since seedling establishment, and by its seeds both before and after their release. This phenotypic plasticity enables a thermal memory of plant reproduction, which allows individuals to acclimatise to their surroundings. This review synthesises current knowledge on the thermal memory of plant reproduction by seed, and highlights its importance for modelling approaches based on physiological thermal time. We performed a comprehensive search in the Web of Science and analysed 533 relevant articles, of which 81 provided material for a meta‐analysis of thermal memory in reproductive functional traits based on the effect size Zr. The articles encompassed the topics of seed development, seed yield (mass and number), seed dormancy (physiological, morphological and physical), germination, and seedling establishment. The results of the meta‐analysis provide evidence for a thermal memory of seed yield, physiological dormancy and germination. Seed mass and physiological dormancy appear to be the central hubs of this memory. We argue for integrating thermal memory into a predictive framework based on physiological time modelling. This will provide a quantitative assessment of plant reproduction, a complex system that integrates past and present thermal inputs to achieve successful reproduction in changing environments. The effects of a warming environment on plant reproduction cannot be reduced to a qualitative interpretation of absolute positives and negatives. Rather, these effects need to be understood in terms of changing rates and thresholds for the physiological process that underlie reproduction by seed. [ABSTRACT FROM AUTHOR]

With the need to meet ambitious restoration targets, an improved native seed sector for the production of herbaceous species with a practical and supportive policy framework is recognized. We evaluated the current “ready‐made” policy frameworks in Europe regarding the native seed supply of herbaceous species and found them to be, generally, unsatisfactory for both producers and users. Initially, such policies were designed for fodder seed and relate to distinctness, uniformity, and stability, traits that do not reflect the genetic heterogeneity of native species required for ecological restoration. Until recently, more suitable certification standards were designed to multiply fodder seed for preservation of the natural environment; however, due to the disparateness of the seed market in Europe, this policy is rarely practical and fails to encompass all herbaceous native species often resulting in unregulated seed sales. We recommend a new or adapted native seed policy constructed through a participatory or bottom‐up approach and supported through the formation of widely based trade associations. Such a policy could stimulate the native seed trade with concomitant impacts on the speed of improving ecosystem services. [ABSTRACT FROM AUTHOR]

Abstract: Globally, annual expenditure on ecological restoration of degraded areas for habitat improvement and biodiversity conservation is approximately $18bn. Seed farming of native plant species is crucial to meet restoration goals, but may be stymied by the disconnection of academic research in seed science and the lack of effective policies that regulate native seed production/supply. To illustrate this problem, we identified 1,122 plant species important for European grasslands of conservation concern and found that only 32% have both fundamental seed germination data available and can be purchased as seed. The “restoration species pool,” or set of species available in practice, acts as a significant biodiversity selection filter for species use in restoration projects. For improvement, we propose: (1) substantial expansion of research and development on native seed quality, viability, and production; (2) open‐source knowledge transfer between sectors; and (3) creation of supportive policy intended to stimulate demand for biodiverse seed. [ABSTRACT FROM AUTHOR]

High sensitivity of seeds to water loss is a widespread phenomenon in the world's plant species. The molecular basis of this trait is poorly understood but thought to be associated with critical changes in membrane function. We profiled membrane lipids of seeds in eight species with varying levels of desiccation tolerance and found a close association between reducing seed viability and increasing phosphatidic acid (PA). We applied hydration-dehydration cycles to Arabidopsis seeds, which are normally desiccation tolerant, to mimic the onset of desiccation sensitivity with progression towards germination and examined the role of phospholipase D (PLD) in desiccation stress-induced production of PA. We found that PLDα1 became more abundant and migrated from the cytosol to the membrane during desiccation, whereas PLDδ did not change, and that all desiccation-induced PA was derived from PLDα1 hydrolysis. When PLDα1 was suppressed, the germination level after each hydration-dehydration cycle improved significantly. We further demonstrated that PLDα1-mediated PA formation modulates desiccation sensitivity as applying its inhibitor improved seed desiccation tolerance and its suppression in protoplasts enhanced survival under dehydration. The insights provided by comparative lipidomics enable us to propose a new membrane-based model for seed desiccation stress and survival. [ABSTRACT FROM AUTHOR]

Understanding the key aspects of plant regeneration from seeds is crucial in assessing species assembly to their habitats. However, the regenerative traits of seed dormancy and germination are underrepresented in this context. In the alpine zone, the large species and microhabitat diversity provide an ideal context to assess habitat-related regenerative strategies. To this end, seeds of 53 species growing in alpine siliceous and calcareous habitats (6230 and 6170 of EU Directive 92/43, respectively) were exposed to different temperature treatments under controlled laboratory conditions. Germination strategies in each habitat were identified by clustering with k-means. Then, phylogenetic least squares correlations (PGLS) were fitted to assess germination and dormancy differences between species' main habitat (calcareous and siliceous), microhabitat (grasslands, heaths, rocky, and species with no specific microhabitats), and chorology (arctic-alpine and continental). Calcareous and siliceous grasslands significantly differ in their germination behaviour with a slow, mostly overwinter germination and high germination under all conditions, respectively. Species with high overwinter germination occurs mostly in heaths and have an arctic-alpine distribution. Meanwhile, species with low or high germinability in general inhabit in grasslands or have no specific microhabitat (they belong to generalist), respectively. Alpine species use different germination strategies depending on habitat provenance, species' main microhabitat, and chorotype. Such differences may reflect adaptations to local environmental conditions and highlight the functional role of germination and dormancy in community ecology. [ABSTRACT FROM AUTHOR]

Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo-referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum ( Tb), optimum ( To) and ceiling ( Tc) temperature for germination and the thermal time (θ50) for each species based on the linearity of germination rate with temperature. Species with the highest Tb and lowest Tc germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ50, varied tenfold. A left-skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at To. For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century. [ABSTRACT FROM AUTHOR]

Previous studies have shown that controlled deterioration treatment ( CDT) induces programmed cell death in elm ( Ulmus pumila L.) seeds, which undergo certain fundamental processes that are comparable to apoptosis in animals. In this study, the essential characteristics of mitochondrial physiology in elm seeds during CDT were identified by cellular ultrastructural analysis, whole-body optical imaging, Western blotting and semi-quantitative RT- PCR. The alteration in mitochondrial morphology was an early event during CDT, as indicated by progressive dynamic mitochondrial changes and rupture of the mitochondrial outer membrane; loss of mitochondrial transmembrane potential (Δψm) ensued, and mitochondrial ATP levels decreased. The mitochondrial permeability transition pore inhibitor cyclosporine A effectively suppressed these changes during ageing. The in situ localization of production of reactive oxygen species (ROS), and evaluation of the expression of voltage-dependent anion-selective channel and cyclophilin D indicated that the levels of mitochondrial permeability transition pore components were positively correlated with ROS production, leading to an imbalance of the cellular redox potential and ultimately to programmed cell death. Pre-incubation with ascorbic acid slowed loss of mitochondrial Δψm, and decreased the effect of CDT on seed viability. However, there were no significant changes in multiple antioxidant elements or chaperones in the mitochondria during early stages of ageing. Our results indicate that CDT induces dynamic changes in mitochondrial physiology via increased ROS production, ultimately resulting in an irreversible loss of seed viability. [ABSTRACT FROM AUTHOR]

ABSTRACT Seed deterioration is poorly understood and remains an active area for research. Seeds of elm ( Ulmus pumila L.) were aged at 37 °C above water [controlled deterioration treatment (CDT)] for various lengths of time to assess programmed cell death (PCD) and reactive oxygen species (ROS) product in embryonic tissues during a 5 d period. The hallmarks of PCD were identified in the elm seeds during CDT including TUNEL experiments, DNA laddering, cytochrome c (cyt c) leakage and enzymatic activities. These analyses indicated that PCD occurred systematically and progressively in deteriorated elm seeds. Cyt c release and increase in caspase-3-like/DEVDase activity occurred during CDT, which could be suppressed by ascorbic acid (AsA) and caspase-3 inhibitor Ac-DEVD-CHO, respectively. In situ localization of ROS production indicated that the distinct spatial-temporal signature of ROS during CDT coincided with the changes in PCD hallmark features. Multiple antioxidant elements were activated during the first few days of CDT, but were subsequently depleted as PCD progressed. Taken together, our findings identify PCD as a key mechanism that occurs asymmetrically during elm seeds CDT and suggest an important role for PCD in seeds deterioration. [ABSTRACT FROM AUTHOR]

The geographical distribution of existing populations of horse chestnut ( Aesculus hippocastanum L.) in Europe is determined by past demographic events during the Quaternary. In the present study we evaluate the imprints that northward expansions originated from common ancestry at southern Europe may have left on the present patterns of genetic variation for horse chestnut across the continent. Genetic diversity and levels of population structure in a European south-north gradient, ranging from the Balkans to the Scandinavian Peninsula, were determined with Amplified Fragment Length Polymorphism (AFLP) markers in 159 loci. A family of rarefaction techniques for the estimation of gene diversity was used to exclude potential confounding effects as a result of the unequal sample sizes. The results indicate that northern populations are not more genetically depleted than southern populations, thus suggesting that diversity for this species is not correlated with latitudinal distribution. Detailed hypotheses based on prediction models for different historical events associated with human-mediated spread of cultivation are examined for a better understanding of the current genetic patterns of regional differentiation. [ABSTRACT FROM AUTHOR]

Introduction: The quantity and composition of seed oil affects seed viability and storability and hence the value of a species as a resource for nutrition and plant conservation. Supercritical fluid extraction with carbon dioxide (SFE-CO2) offers a rapid, environmentally friendly alternative to traditional solvent extraction. Objective: To develop a method using SFE-CO2 to quantify the seed oil content in a broad range of species with high to low oil contents. Methodology: Seed oil was extracted using SFE-CO2 from four crop species representing high, medium and low oil content: Helianthus annuus, Asteraceae, with ca. 55% oil; Brassica napus, Brassicaceae, with ca. 50% oil; Glycine max, Fabaceae, with ca. 20% oil; and Pisum sativum, Fabaceae, with ca. 2% oil. Extraction pressures of 5000, 6000 and 7500 psi and temperatures of 40, 60 and 80°C were examined and a second step using 15% ethanol as a modifier included. Oil yields were compared with that achieved from Smalley Butt extraction. The optimised SFE-CO2 method was validated on six species from taxonomically distant families and with varying oil contents: Swietenia humilis (Meliaceae), Stenocereus thurberi (Cactaceae), Sinapis alba (Brassicaceae), Robinia pseudoacacia (Fabaceae), Poa pratensis (Poaceae) and Trachycarpus fortunei (Arecaceae). Results: The two-step extraction at 6000 psi and 80°C produced oil yields equivalent to or higher than Smalley Butt extraction for all species, including challenging species from the Brassicaceae family. Conclusion: SFE-CO2 enables the rapid analysis of seed oils across a broad range of seed oil contents. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recalcitrant seeds are intolerant of desiccation and cannot be stored in conventional seed banks. Cryopreservation allows storage of the germplasm of some recalcitrant seeded species, but application to a wide range of plant diversity is still limited. The present work aimed at understanding the stresses that accompany the first steps in cryopreservation protocols, wounding and desiccation, both of which are likely to lead to the formation of reactive oxygen species (ROS). Extracellular ROS production was studied in isolated embryonic axes of sweet chestnut ( Castanea sativa). Axis excision was accompanied by a burst of superoxide (O2·−), demonstrated by a colorimetric assay using epinephrine, electron spin resonance and staining with nitroblue tetrazolium. Superoxide was immediately produced on the cut surface after isolation of the axis from the seed, with an initial ‘burst’ in the first 5 min. Isolated axes subjected to variable levels of desiccation stress showed a decrease in viability and vigour and increased electrolyte leakage, indicative of impaired membrane integrity. The pattern of O2·− production showed a typical Gaussian pattern in response to increasing desiccation stress. The results indicate a complex interaction between excision and subsequent drying and are discussed with a view of manipulating ROS production for optimisation of cryopreservation protocols. [ABSTRACT FROM AUTHOR]

In the tropics, species with recalcitrant or desiccation-sensitive, Type III seeds are largely restricted to regions with comparatively high rainfall, because desiccation-induced seed death will be minimal in these environments. However, species with recalcitrant seeds do occur in drylands, although little is known about ecological adaptations to minimize seed death in these environments. Here we present data for the seed desiccation tolerance of 10 African dryland species and examine the relationships between seed size, rainfall at the time of seed shed, and desiccation tolerance for these and a further 70 species from the scientific literature. The combined data set encompasses species from 33 families. Three species (Syzygium cumini, Trichilia emetica, and Vitellaria paradoxa) had desiccation-sensitive seeds, and the remaining seven species investigated were desiccation-tolerant. The desiccation-sensitive species had large (>0.5 g) seeds, germinated rapidly, and had comparatively small investments in seed physical defenses. Furthermore, seed was shed in months of high rainfall (>60 mm). In comparison, for species with desiccation-tolerant seeds, seed mass varied across five orders of magnitude, and seed was shed in wet and dry months. Although infrequent in dryland environments (approximately 11% of the species examined here), species with desiccation-sensitive seeds do occur; large size, rapid germination, and the timing of dispersal all reduce the likelihood of seed drying. Furthermore, desiccation-sensitivity may be advantageous for large-seeded species by increasing the efficiency of resource use in seed provisioning. [ABSTRACT FROM AUTHOR]

The effect of moist stratification at cool temperatures on Aesculus hippocastanum (horse chestnut) seed dormancy release and subsequent thermal time requirement for germination has been investigated. Germination performance following over 50 different treatments, each varying in time and temperature of stratification and germination to a total test time of over 3 yr, was used to develop a predictive model for dormancy release and germination. Stratification at 2–16°C caused a reduction in base (minimum) temperature for germination (Tb), being fastest at the colder temperatures. Using the sigmoid relationship between rate of reduction in Tb and stratification temperature, seed germination can be predicted in relation to thermal time accumulation above a gradually reducing Tb. Newly shed unstratified seeds, seeds with reduced viability, and seeds on the brink of germination because of Tb being close to stratification temperature, did not conform to the model. Tb is not constant during dormancy release in horse chestnut seeds. A reduction in Tb in response to cold stratification may be characteristic of summer annuals, suggesting future applications for this approach in seed ecology studies. [ABSTRACT FROM AUTHOR]