Seed Collection in Temperate Trees-Clean, Fast, and Effective Extraction of Populus Seeds for Laboratory Use and Long-term Storage

Seeds ensure the growth of a new generation of plants and are thus central to maintaining plant populations and ecosystem processes. Nevertheless, much remains to be learned about seed biology and responses of germinated seedlings to environmental challenges. Experiments aiming to close these knowledge gaps critically depend on the availability of healthy, viable seeds. Here, we report a protocol for the collection of seeds from plants in the genus Populus. This genus comprises trees with a wide distribution in temperate forests and with economic relevance, used as scientific models for perennial plants. As seed characteristics can vary drastically between taxonomic groups, protocols need to be tailored carefully. Our protocol takes the delicate nature of Populus seeds into account. It uses P. deltoides as an example and provides a template to optimize bulk seed extraction for other Populus species and plants with similar seed characteristics. The protocol is designed to only use items available in most labs and households and that can be sterilized easily. The unique characteristics of this protocol allow for the fast and effective extraction of high-quality seeds. Here, we report on seed collection, extraction, cleaning, storage, and viability tests. Moreover, extracted seeds are well suited for tissue culture and experiments under sterile conditions. Seed material obtained with this protocol can be used to further our understanding of tree seed biology, seedling performance under climate change, or diversity of forest genetic resources. Key features • Populus species produce seeds that are small, delicate, non-dormant, with plenty of seed hair. Collection of seed material needs to be timed properly. • Processing, seed extraction, seed cleaning, and storage using simple, sterilizable laboratory and household items only. Obtained seeds are pure, high quality, close to 100% viability. • Seeds work well in tissue culture and in experiments under sterile conditions. • Extractability, speed, and seed germination were studied and confirmed for Populus deltoides as an example. • Can also serve as template for bulk seed collection from other Populus species and plant groups that produce delicate seeds (with no or little modifications). Graphical overview.

Metabolomics analysis of the nutraceutical diversity and physiological quality of Torreya yunnanensis seeds during cold storage

This study investigated how cold storage affects the nutraceutical diversity and physiological quality of Torreya yunnanensis seeds, using a widely targeted UPLC-MS/MS-based metabolomics analysis. The 373 identified metabolites were divided into nine categories: lipids, phenolic acids, amino acids and derivatives, organic acids, nucleotides, saccharides, vitamins and alcohols. Among them, 49 metabolites showed significant changes after 3 months of cold storage, affecting 28 metabolic pathways. The content of amino acid-related metabolites significantly increased, while the content of sugar-related metabolites decreased during storage. Notably, the content of proline acid, shikimic acid, α-linolenic acid and branched-chain amino acids showed significant changes, indicating their potential role in seed storage. This study deepens our understanding of the nutraceutical diversity and physiological quality of T. yunnanensis seeds during storage, providing insight for conservation efforts and habitat restoration.

Hermetic bags maintain soybean seed quality under high relative humidity environments

Soybean seed quality is affected by high relative humidity (r.h.) during storage in the humid tropics resulting in loss of germination. This study assessed the effectiveness of hermetic bags in preserving soybean seed quality when stored at high r.h. over three months. Treatments consisted of Purdue Improved Crop Storage (PICS) and control polypropylene (PP) woven bags kept at 30 and 80% r.h. Moisture content and germination were measured each month. Moisture content did not change, except in seed stored in PP bag at 80% r.h. where it more than doubled after one month. There was no significant difference in germination rates between soybean seed stored in PICS bags at 30 and 80% r.h. over three months. Soybean seed stored in PP bag at 30% r.h. had germination rates similar to those observed in PICS bags at 30 and 80% r.h., except after the third month where it significantly decreased compared to PICS bags at 30%. Germination rates of soybean seed stored in PICS at 30% and 80%, and PP bags at 30% decreased by about 3, 6, and 7%, respectively. However, the germination rates of soybean seed stored in PP bags at 80% r.h. dropped by 98% after three months. There was a significant negative correlation of -80.6% (Pearson correlation) between moisture content and seed germination. Farmers and seed producers/traders in the humid tropics can safely preserve soybean seed using commercially available hermetic bags.

Gaseous environment modulates volatile emission and viability loss during seed artificial ageing

Modulation of the gaseous environment using oxygen absorbers and/or silica gel shows potential for enhancing seed longevity through trapping toxic volatiles emitted by seeds during artificial ageing. Volatile profiling using non-invasive gas chromatography-mass spectrometry provides insight into the specific processes occurring during seed ageing. Production of alcohols, aldehydes and ketones, derived from processes such as alcoholic fermentation, lipid peroxidation and Maillard reactions, are known to be dependent on storage temperature and relative humidity, but little is known about the potential modulating role of the gaseous environment, which also affects seed lifespan, on volatile production. Seeds of Lolium perenne (Poaceae), Agrostemma githago (Caryophyllaceae) and Pisum sativum (Fabaceae) were aged under normal atmospheric oxygen conditions and in sealed vials containing either oxygen absorbers, oxygen absorbers and silica gel (equilibrated at 60% RH), or silica gel alone. Seeds of A. githago that were aged in the absence of oxygen maintained higher viability and produced fewer volatiles than seeds aged in air. In addition, seeds of A. githago and L. perenne aged in the presence of silica gel were longer lived than those aged without silica, with no effect on seed moisture content or oxygen concentration in the storage containers, but with silica gel acting as a volatile trap. These results indicate that the use of inexpensive oxygen absorbers and silica gel could improve seed longevity in storage for some species and suggests a potential, and previously unidentified, role for silica gel in ultra-dry storage.

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.

Water permeability/impermeability in seeds of 15 species of Caragana (Fabaceae)

Majority legumes in the temperate and arctic zones have water-impermeable seeds (physical dormancy, PY). However, various authors have reported that seeds of some Caragana species are water-permeable and thus non-dormant. We (1) tested seeds of 15 species of Caragana matured in the same site in 2014, 2016 and/or 2017 for presence of PY, (2) determined if dry storage decreased or increased the percentage of seeds with PY and (3) located the site on the seed coat of 11 species where water enters the seed. Sixty-three percent and 45% of the seeds of C. roborovskyi had PY in 2016 and 2017, respectively, but only 0-14% of the seeds of the other 14 species had PY. The palisade layer in the seed coat of water impermeable seeds had no cracks in it, whereas cracks were present in the palisade layer of water-permeable seeds. Year of collection and dry storage had significant effects on imbibition of two species (C. acanthophylla and C. roborovskyi). In two (C. acanthophylla and C. roborovskyi) of the 11 species tested, the hilum was the site of water entry into seeds (control seeds, not any dormant broken treatments), but for the other nine species tested water entered through all parts of the seed coat.

Mapping of QTL associated with seed longevity in durum wheat (Triticum durum Desf.)

Regeneration cycle of seeds kept at genebanks is determined by seed longevity. Information about longevity of species is important for storage periods, germination test intervals, and reproduction cycles. Seed longevity is different between species and depends on the storage conditions. It also differs between genotypes of a species providing the basis of genetic analyses of seed longevity. Studies in hexaploid wheat and barley have identified numerous quantitative trait locus (QTL) linked to the trait. Seed longevity in durum wheat, however, has not been attempted so far. Here, we present the first report of genetic analysis of grain longevity in durum wheat using a bi-parental mapping population composed of 114 recombinant inbred lines. QTL analysis identified three highly significant and one significant QTL for initial germination (on chromosomes 4B, 5A (2 QTL), and 6B), three significant QTL for germination after accelerated aging treatment (on chromosomes 5A and 7B (2 QTL)), and five significant QTL determining relative germination and distributed on chromosomes 3A, 3B, 5A, 6B, and 7B. This study confirms the results of previous investigations in bread wheat and provides a baseline for further research in durum wheat.

Effects of temperature and salinity on Ruppia sinensis seed germination, seedling establishment, and seedling growth

As typical submerged aquatic vegetation, Ruppia species are facing population reductions due to anthropogenic impacts. In this study, we investigated the effects of temperature and salinity on seed germination and seedling establishment of Ruppia sinensis seeds collected from northern China. The effects of seven salinities (0-50) and six water temperatures (0-30°C) on seed germination were investigated to identify the environmental conditions that could potentially limit survival and growth. We found that: 1) optimum seed germination was salinity 5 at 30°C; 2) high salinity (salinity 40-50) and low temperature (0°C) significantly inhibited seed germination; 3) seed germination with increasing temperature showed a bimodal pattern at suitable salinities (5-10); 4) storing seeds at high salinities (40-50) or low temperature (0°C) promoted germination after transferal to optimal germination conditions. These findings may serve as useful information for R. sinensis habitat establishment and restoration programs.

The production, localization and spreading of reactive oxygen species contributes to the low vitality of long-term stored common beech (Fagus sylvatica L.) seeds

The common beech (Fagus sylvatica L.) is propagated by seeds, but the seed set is irregular with five to ten years in between crops. It is therefore necessary to store the seeds. However, beech seeds lose germinability during long-term storage. In this study, beech seeds were stored at -10°C under controlled conditions for 2, 5, 8, 11 and 13 years. Our results show that beech seeds lose germinability during storage in proportion to the duration of storage. The decrease in germinability correlated with increased electrolyte leakage and accumulation of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. Furthermore, a strong positive correlation was observed among the releases of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. In situ localization showed that superoxide anion radicals and hydrogen peroxide were first detectable in root cap cells. When the seed storage time was extended, the reactive oxygen species fluorescence expanded to more areas of the radicle, reaching the root apical meristem. A storage time-dependent decrease in catalase activity, observed in both embryonic axes and cotyledons, was also positively correlated with germinability. DNA fragmentation was observed in beech seeds during storage and occurred predominantly in embryonic axes stored for 5 years and more. Altogether, these results suggest that the loss of germinability in beech seeds during long-term storage depends on several factors, including strong of reactive oxygen species accumulation accompanied by reduced catalase activity as well as membrane injury and DNA alternations, which may be aging-related and ROS-derived. We suggest that the accumulating reactive oxygen species that spread to the root apical meristem are key factors that affect seed germinability after long-term storage.