Decrease in beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) seed viability caused by temperature and humidity conditions as related to membrane damage and lipid composition

The aim of this study was to determine if the loss of germinability and viability of beech (Fagus sylvatica L.) seeds stored at different variants of temperature (4, 20, and 30 °C) and relative humidity (RH: 45 and 75 %) is associated with a loss of membrane integrity and changes in lipid composition. Beech seeds stored for 9 weeks gradually lost viability at a rate dependent on temperature and humidity. The harmful effect of temperature increased with growing humidity. The loss of seed viability was strongly correlated with an increase in membrane permeability and with production of lipid hydroxyperoxides (LHPO), which was regarded as an indicator of peroxidation of unsaturated fatty acids. The condition of membranes was assessed on the basis of their permeability and the state of lipid components: phospholipids and fatty acids. During seed storage we observed a decline in concentration of individual phospholipids and fatty acids, proportional to the loss of seeds viability. We also detected a decrease in concentrations of α-tocopherol and sterols, which play an important role in protection of membranes against the harmful influence of the environment. Our results show that the germinability of beech seeds declines rapidly at temperature above 0 °C and growing humidity. This is due mainly to the loss of membrane integrity, caused by peroxidation of unsaturated fatty acids.     

The effect of the temperature of drying on viability and some factors affecting storability of <Emphasis Type="Italic">Fagus sylvatica</Emphasis> seeds

Beech (Fagus sylvatica L.) seeds, which are tolerant to desiccation, freshly harvested after shedding, were dried at 15 and 30 °C and at the similar rate, to 9% of water content. A slight decrease of germinability was observed in seeds dried at 30 °C. Moreover, there was a notably higher solute leakage and a higher level of lipid hydroperoxides. Seeds dried at 30 °C contained less PC and PE and a lower level of unsaturated fatty acids (18:2 and 18:3), sterols and α-tocopherol. These results as well as changes in ascorbate and glutathione contents provide conclusive evidence for the presence of oxidative stress in beech seeds desiccated at 30 °C, which damaged membranes due to increased lipid peroxidation and changed membrane structure leading to their enhanced sensibility to free radical attack during storage.     

Improving germination and vigour of aged and stored onion seeds by matriconditioning

Germination and vigour of accelerated aged (AA) and naturally stored onion seeds were examined. Accelerated ageing was conducted at 40 °C and 100 % relative humidity (RH). Non aged seeds were stored for 34 months at 3 or 15 °C and 40, 60 or 90 % RH. To restore seed viability, stored and aged seeds were matriconditioned with Micro-Cel E. A distinct loss of germination was observed after 5 days of accelerated ageing. Naturally stored seeds maintained high viability for 34 months, when stored at 3 °C and 40, 60 and 90 % RH or at 15 °C and 40 %. An increase of RH to 60 and 90 % at 15 °C caused loss of germination and vigour. Matriconditioning improved germination and increased endogenic ethylene release and in vivo ACC oxidase activity of both aged and stored seeds.     

Wet-dry cycling extends seed persistence by re-instating antioxidant capacity

Seeds in the field experience wet-dry cycling that is akin to the well-studied commercial process of seed priming in which seeds are hydrated and then re-dried to standardise their germination characteristics. To investigate whether the persistence (defined as in situ longevity) and antioxidant capacity of seeds are influenced by wet-dry cycling, seeds of the global agronomic weed Avena sterilis ssp. ludoviciana were subjected to (1) controlled ageing at 60% relative humidity and 53.5°C for 31 days, (2) controlled ageing then priming, or (3) ageing in the field in three soils for 21 months. Changes in seed viability (total germination), mean germination time, seedling vigour (mean seedling length), and the concentrations of the glutathione (GSH) / glutathione disulphide (GSSG) redox couple were recorded over time. As controlled-aged seeds lost viability, GSH levels declined and the relative proportion of GSSG contributing to total glutathione increased, indicative of a failing antioxidant capacity. Subjecting seeds that were aged under controlled conditions to a wet-dry cycle (to ?1 MPa) prevented viability loss and increased GSH levels. Field-aged seeds that underwent numerous wet-dry cycles due to natural rainfall maintained high viability and high GSH levels. Thus wet-dry cycles in the field may enhance seed longevity and persistence coincident with re-synthesis of protective compounds such as GSH.     

Dynamics of chromosomal instability in Welsh onion (Allium fistulosum L.): Influence of seed storage temperature

The age-related dynamics of chromosomal instability in cells of the root meristem of seedlings and germination capacity of seeds of Welsh onion (Allium fistulosum L.) in two storage temperature regimes in the course of six years following collection of the seeds are investigated. Seeds that had been stored at room temperature (14–28°C) lost germination capacity after six years of storage. The frequency of aberrant anaphases in these seeds grew from 2% in the first month of storage of the seeds to 80% in the 75th month. The germination capacity of seeds that had been stored at reduced temperatures (4–9°C) amounted to 73–77% in the sixth year, while the frequency of aberrant anaphases in these seeds remained within the range 2–4% throughout the six years. Thus, storage of Welsh onion seeds for six years at reduced temperatures tends to preserve the germination capacity of the seeds and prevents the development of chromosomal instability in the root meristem cells of the seedlings over this period.     

Effects of seed maturation time and dry storage on light and temperature requirements during germination in invasive Prosopis juliflora

The effects of time of seed maturation and dry seed storage and of light and temperature requirements during seed incubation on final germination percentage and germination rate were assessed for the invasive shrub Prosopis juliflora (Sw.) D.C., grown under desert environmental conditions of the United Arab Emirates (UAE). Seeds were collected from Fujira on the northern coast of the UAE at different times during the growing seasons (autumn, winter and spring) and were germinated immediately and after 8 months of dry storage under room temperature (20±3 °C). Seeds were germinated at three temperatures (15, 25 and 40 °C) in both continuous light and darkness. The results showed significant effects for time of seed collection, seed storage, light and temperature of seed incubation and many of their interactions on both germination percentage and rate. Fresh seeds matured during autumn and winter germinated significantly greater at 40 °C and in light than at lower temperatures and in dark. Storage significantly increased germination percentage and rate; the increase was greater for seeds matured during winter than for seeds matured during spring. This indicates that dormancy breakage was greater in seeds of winter than seeds of spring. The need for high temperature to achieve greater germination was significantly reduced after seed storage, especially for seeds matured in autumn and winter.     

Biological fitness of Trichoderma atroviride during long-term storage,after production in different culture conditions

Identification of the production and storage factors that affect conidium germination and bioactivity (fitness) will assist the success of biological control agents. Effects of culturing conditions on conidium fitness of Trichoderma atroviride LU132 were examined in different storage conditions over time. Abiotic factors (temperature, nutrients, water activity and pH) during production were studied. Conidia from the culturing regimes which resulted in greatest and least bioactivity against Rhizoctonia solani in dual culture were selected to assess effects of storage conditions on conidium fitness. Fitness of the test conidia was examined after storage at 30°C and at 0% or 50% relative humidity (RH) over 6 months. Fitness declined over time, and the decline was greater for 50% RH than 0% RH, probably through reduced metabolic activity of conidia during long-term storage. Stored conidia were probably affected by dehydration, temperature and other factors such as oxidation, before and during storage, and also by rehydration after storage. The greatest number of conidia and germination percentage resulted from production at 25°C, but greatest bioactivity resulted from those produced at 30°C. No significant effects on bioactivity were detected between the conidium production treatments C?:?N 5?:?1 and C?:?N 160?:?1, indicating that C?:?N ratio in culture medium is not important for conidium survival of T. atroviride.     

Systematic overestimation of Salicaceae seed survival using radicle emergence in response to drying and storage: implications for ex situ seed banking

Biodiversity conservation programmes are underpinned by seed banking following drying to low water contents (WC), and supported by both the assessment and prediction of seed viability over time. The means of judging viability is thus crucial to the comprehension of seed vigour. We selected seeds of three species and one hybrid in the Salicaceae likely to have variation in tolerance to drying, processing and storage, including in relation to cryobanking, and compared survival growth as radicle emergence (germination) and normal seedling production. With three seed lots of Salix gracilistyla, air-drying to 8–10 % WC enhanced seed survival after 40 days’ storage at 5 °C as compared with non-treated seeds at 14–20 % WC. Four seed lots of Populus alba × P. glandulosa showed equally high germination (88–100 %) and proportions of normal seedlings (81–99 %) when stored at 5 °C for 7–10 weeks. Among seven seed lots of S. gracilistyla, two groups with different storage behaviour could be statistically distinguished with normal seedling production ranging from 0 to 45 % after storage at 5 °C for 13 weeks. Seed tolerance to WC manipulation and cryopreservation was very variable among species and seed lots. Seed lots of S. hallaisanensis and S. gracilistyla with ~80 % germination survived cryopreservation at 10 % WC, but were sensitive to lower WCs. In contrast, Populus seeds had greater desiccation tolerance combined with cryopreservation capability. With seed lots of all species and hybrids, cryopreservation had little effect on viability unless the high moisture freezing limit had been exceeded (~10–20 % WC, depending on seed lot). However, under all conditions of handling (drying, rehydration, storage at 5 °C or cryopreservation) using germination as the only indicator of viability over-estimated survival compared with normal seedling production.     

Seed germinability and longevity influences regeneration of <Emphasis Type="Italic">Acacia gerrardii</Emphasis>

Acacia gerrardii is the only native tree species of the Kuwaiti desert ecosystem. However, anthropogenic disturbances and harsh arid climate have contributed towards the disappearance of this keystone species from its habitat. In this study, effects of different seed pretreatments to break dormancy, water entry pathway, and ecology (seasonal timing) of dormancy loss and germination of A. gerrardii were investigated. Effects of mechanical scarification, hot water treatment (30 s, 1, 2, and 5 min), and concentrated acid scarification (10, 20, and 30 min) on germination percentage and rate (time to 50% germination and final germination) were also examined. Pretreatment with mechanical scarification produced the highest germination in the least time and 20 °C, 40% RH with 12 h of light (2370 Lux) were found to provide the best germination environment. Seeds were rapidly aged at 60% RH and 45 or 50 °C to determine longevity, and the results were analyzed using probit analysis. Times taken for viability of A. gerrardii seeds aged at 45 and 50 °C to fall to 50% (p₅₀) were 38.6 and 9.3 days, respectively, and therefore the seeds can be considered to have medium longevity. Experiments to find the water entry pathway in A. gerrardii indicated that the micropyle region was the primary point of water entry into the seed. Seed burial experiments indicated that though seed retention decreased over time, there was no significant decrease in number of viable seeds after 31 weeks. The findings of this study are important to nursery managers, seed banks, and those involved in conservation and restoration activities.     

Ageing of tomato seeds involves glutathione oxidation

The effect of seed ageing on the oxidation of reduced glutathione (GSH) and the role of GSH oxidation in ageing-induced deterioration were studied in seeds of tomato ( Lycopersicon esculentum Mill. cv. Lerica, Moneymaker and Cromco). Both long-term storage at 15°C/30% relative humidity (RH) and artificial ageing at 20°C/75% RH, 30°C/45% RH and 60°C/45% RH resulted in a marked loss of GSH and a simultaneous, though not proportional, increase in its oxidized form GSSG. The glutathione thiol-disulfide status shifted towards a highly oxidized form, while the total glutathione pool decreased. The extent of GSH oxidation differed between ageing conditions and was not directly related to the extent of seed deterioration. Thiobarbituric acid-reactive substances did not increase in ageing tomato seeds, suggesting that lipid peroxidation did not take place. Hydration of seeds, either upon imbibition in water or by priming in an osmotic solution, resulted in a rapid decrease in GSSG, a shift of the glutathione redox couple to a mainly reduced status and an increase in the glutathione pool, in both control and aged seeds. The results indicate that, in tomato seeds, (1) seed ageing involves GSH oxidation into GSSG, which is indicative of oxidative stress, (2) ageing does not affect the GSSG reduction capacity upon subsequent imbibition, and (3) the lowered viability of aged seeds cannot directly be ascribed to the decreased GSH pool or To the highly oxidized glutathione redox status.     

Effects of microhabitat,light and temperature on seed germination of a critically endangered Himalayan medicinal herb,Swertia chirayita: Conservation implications

Abstract

Swertia chirayita, a critically endangered medicinal herb, is being over-harvested in the wild. Understanding seed germination is a pre-requisite to ensure species conservation. The germination of seeds collected from six microhabitats was studied at 20°C, 25°C, and 30°C, both under a 14/10 h light/dark photoperiod and in continuous darkness. Two-way ANOVA indicated that microhabitat and temperature significantly affect seed germination, germination rate, germination recovery (GR), and GR rate. Overall, the seeds collected from under canopy showed a significantly (p < 0.05) higher germination than those from open habitats, at 20°C, 25°C, and 30°C (14/10 h light/dark photoperiod). Germination was negligible in continuous darkness but after transfer to a 14/10 h light/dark photoperiod, the seeds from under canopy significantly recovered at 20°C and at 25°C (p < 0.05), and showed the highest germination percentage compared to seeds collected from tree base, stump base, shrubberies, and grassy slope. Similarly, at 30°C, seeds from under canopy recorded the highest GR percentage. In general, seed germination, mean germination rate, seed GR, and GR rate were significantly greater (p < 0.05) at 25°C. Among the microhabitats tested, variation in GR rate was significant (p < 0.05). Seeds were confirmed to be positively photoblastic.     

The deterioration of <Emphasis Type="Italic">Moringa oleifera</Emphasis> Lam. seeds in the course of storage involves reserve degradation

Seed deterioration in the course of storage may involve hydrolytic reactions. Hence, we aimed to evaluate viability, vigour, contents of reserves and metabolites, and activities of hydrolytic enzymes in Moringa oleifera Lam. seeds during storage under controlled conditions. Seeds were packaged in semipermeable plastic and maintained in a growth chamber (27 ± 2 °C and RH 60–65%) and under refrigeration (4 ± 2 °C and RH 20–25%) for 18 months. Samples were taken at the start of the experiment and every 3 months. During the first 12 months, water content, viability, and vigour remained almost unaffected, while the content of neutral lipids, starch, soluble sugars and free amino acids did not reduce in the seeds kept under refrigeration. After this period, the loss of viability and vigour was accompanied by the degradation of storage lipids, storage proteins, and non-reducing sugars associated with the increase of lipase and acid protease activity in both environmental conditions. As the seed water content remained below 8% in the course of the experiment, we suggest that non-enzymatic hydrolysis might play a role in the deterioration of M. oleifera seeds during storage. At least for planting, we recommend that M. oleifera seeds be kept at low relative humidity under refrigeration for up to 12 months.     

Adenine nucleotides and energy charge during dormancy breaking in embryo axes of <Emphasis Type="Italic">Acer platanoides</Emphasis> and <Emphasis Type="Italic">Fagus sylvatica</Emphasis> seeds

We analysed changes in AMP, ADP, and ATP concentrations and adenylate energy charge in Norway maple (Acer platanoides L.) and European beech (Fagus sylvatica L.) seeds during dormancy breaking (at 3 °C) and in the control variant at 15 °C. Values of the studied indicators in stratified beech seeds were generally higher at 15 °C, at least until germination (+3 °C). By contrast, in maple seeds, the values recorded during dormancy breaking by cold stratification were much higher than at 15 °C. Three peaks (usually in weeks 3, 6, and 8) were observed in maple seeds at 3 °C, but not at 15 °C. Among adenine nucleotides, AMP reached the highest levels in both species in both variants of the experiment.     

A continental-scale study of seed lifespan in experimental storage examining seed,plant, and environmental traits associated with longevity

Management of seed banks conserving the biodiversity of phylogenetically diverse species requires insight into seed longevity. This study determined the seed longevity of 172 species sourced from across the mega-diverse flora of the Australia continent. Seeds were aged via a controlled ageing experiment through storage at 45 °C and 60 % RH, or 60 °C and 60 % RH, and regularly tested for germination. Relative seed longevity between species was determined by comparing the time to 50 % viability loss (p ₅₀), calculated via probit analysis of seed survival curves. Seed, plant, and environmental traits were examined for associations with longevity. The p ₅₀ values varied between species from 3.0 to 588.6 days. Serotinous species, and woody trees and shrubs, had significantly longer-lived seeds than geosporous species, and species of herbaceous habit. Seeds that possess physical dormancy, and seeds with large embryos with little endosperm, were also long-lived. There was a weak, but significant, positive correlation between seed mass and longevity. Seeds sourced from regions of higher mean annual temperature and rainfall were significantly longer-lived than seeds from cooler and drier regions, although both environmental factors were weakly associated with longevity. Compared with species from other regions of the world, prolonged longevity is a feature of many Australian species. Nevertheless, seed life-spans vary substantially between species and close consideration of seed traits along with biotic and abiotic components of the plants and their environment can assist to differentiate between potentially long- and short-lived seeds.     

Germination of <Emphasis Type="Italic">Sedum oxypetalum</Emphasis> (Crassulaceae) in a primary lava-field shrubland

Sedum oxypetalum is one of the dominant species in the xerophilous shrublands in the lava fields of the Basin of Mexico. Germination of this species was evaluated to understand its ecological response. We tested the effects of different pre-germination treatments (cold, and dry and wet heat) and storage time, as well as those of natural priming in two microhabitats with different disturbance levels. Experiments were performed in laboratory conditions under constant (25 °C) and fluctuating (20/30 °C) temperatures. Seeds did not germinate during burial and proved to be positively photoblastic. Under pre-germination treatments, final germination percentage was higher at 20/30 °C in seeds after four or more months of storage. None of the pre-germination treatments favored germination. Seeds can survive for more than 1 year and form a seed bank. Thus, seeds underwent natural priming that favored final germination percentage; however, germination rate and lag time were not affected by this process. In natural conditions, germination is delayed until the rainy season, improving the success of seedling establishment and growth. We discuss the role of fluctuating temperature in germination processes and the adaptations of seeds to their seasonal environment.     

Wheat seed ageing viewed through the cellular redox environment and changes in pH

To elucidate biochemical mechanisms leading to seed deterioration, we studied 23 wheat genotypes after exposure to seed bank storage for 6–16 years compared to controlled deterioration (CD) at 45?°C and 14 (CD14) and 18% (CD18) moisture content (MC) for up to 32 days. Under two seed bank storage conditions, seed viability was maintained in cold storage (CS) at 0?°C and 9% seed MC, but significantly decreased in ambient storage (AS) at 20?°C and 9% MC. Under AS and CS, organic free radicals, most likely semiquinones, accumulated, detected by electron paramagnetic resonance, while the antioxidant glutathione (GSH) was partly lost and partly converted to glutathione disulphide (GSSG), detected by HPLC. Under AS the glutathione half-cell reduction potential (E_GSSG/2GSH) shifted towards more oxidising conditions, from ?186 to ?141?mV. In seeds exposed to CD14 or CD18, no accumulation of organic free radicals was observed, GSH and seed viability declined within 32 and 7 days, respectively, GSSG hardly changed (CD14) or decreased (CD18) and E_GSSG/2GSH shifted to ?116?mV. The pH of extracts prepared from seeds subjected to CS, AS and CD14 decreased with viability, and remained high under CD18. Across all treatments, E_GSSG/2GSH correlated significantly with seed viability (r?=?0.8, p<.001). Data are discussed with a view that the cytoplasm is in a glassy state in CS and AS, but during the CD treatments, underwent transition to a liquid state. We suggest that enzymes can be active during CD but not under the seed bank conditions tested. However, upon CD, enzyme-based repair processes were apparently outweighed by deteriorative reactions. We conclude that seed ageing by CD and under seed bank conditions are accompanied by different biochemical reactions.     

Germination behaviour of seeds of Withania somnifera (L.) Dunal: a high value medicinal plant

In order to evolve a quick method for smooth and optimum germination for Withania somnifera- a medicinally efficacious multipurpose plant, present investigation was carried to study the effect of physico-chemical treatments, storage, temperature, photoperiod and growth regulators (GA₃, IAA, IBA, 2–4 D and BA) on germinability. The most effective treatment is GA₃ at 150 μg/ml concentration at 25 °C. The optimal temperature for germination is 25 °C and continuous light favored germination showing that photoperiod has a significant role. The seedlings derived from seeds performed well when grown in a glasshouse. The data have implications for conservation and cultivation of the species studied.     

RNAi mediated silencing of lipoxygenase gene to maintain rice grain quality and viability during storage

Lipoxygenase (LOX) is a common enzyme which catalyzes lipid peroxidation of seeds and consequently enhances seed quality deterioration and decreases seed viability. During seed storage, peroxidation of unsaturated fatty acids occur due to enhancement of LOX activity which directly leads to reduction in seed vigour and deterioration of grain nutritional quality. This study was undertaken to overcome these problem during rice seed storage by attenuating LOX activity using RNAi technology. To improve seed storage stability, we down regulated LOX gene activity by using a functional fragment of the LOX gene under the control of both constitutive (CaMV35S) and aleurone-specific (Oleosin-18) promoter separately. To understand the storage stability, RNAi–LOX seeds and non-transgenic control seeds were subjected to accelerated aging at 45 °C and 85 % relative humidity for 14 days. Our studies demonstrate that down regulation of LOX activity reduces the seed quality deterioration under storage condition. In addition GC–MS analysis revealed that reduction of fatty acid level in non-transgenic seeds during storage was higher when compared with that of transgenic rice seeds. Furthermore, the transgenic rice seeds with reduced LOX activity exhibited enhanced seed germination efficiency after storage than that of non-transgenic rice seeds. This study will have direct impact on nutritional stability of quality rice grains.     

Different plant provenance same seed tolerance to abiotic stress: implications for <Emphasis Type="Italic">ex situ</Emphasis> germplasm conservation of a widely distributed coastal dune grass (<Emphasis Type="Italic">Uniola paniculata</Emphasis> L.)

Preservation of genetic diversity within germplasm repositories represents an important tool for plant conservation. However, seeds must tolerate extreme levels of post-harvest desiccation and cold to realize benefits of ex situ storage. Factors including local climate and habitat impact expression of desiccation and freezing tolerance especially for widely distributed species. Our aim here was to understand the influence of a latitudinal gradient on seed desiccation and cryo-freezing tolerance. We sampled mature U. paniculata seeds from two geographically and genetically distinct populations then examined seed-water relations and germination following desiccation via equilibrium drying assays (0.5 to 91% RH; ?797 to ?12.9 MPa). Germination ability after drying and subsequent cryo-freezing treatments (?196?°C, 1 to 1440 min) was also evaluated. Seeds of both populations displayed similar reverse sigmoid moisture sorption isotherms characteristic of desiccation tolerant tissues. Furthermore, initial seed water potential (?63 and ?90 MPa) was considerably lower than the lethal limit (?20 MPa) identified for desiccation sensitive tissues. Final germination (range 58–93%) and temporal patterns differed significantly between populations following desiccation and cryo-freezing stress, but these germination responses were similar to initial germination. A higher proportion of non-germinated, yet viable seeds remained for the northern compared to southern population. Location does influence germination response, but differential germination is related to seed dormancy rather than desiccation or cryo-freezing sensitivity. Ex situ conservation of U. paniculata is therefore feasible across the latitudinal gradient studied here.     

Seed ecology of the geophyte Conopodium majus (Apiaceae), indicator species of ancient woodland understories and oligotrophic meadows

• Conopodium majus is a geophyte with pseudomonocotyly, distributed in Atlantic Europe. It is an indicator of two declining European habitats: ancient woodland understories and oligotrophic hay meadows. Attempts to reintroduce it by seed have been hindered by scarce seedling emergence and limited knowledge of its seed biology.
• Micro‐CT scanning was used to assess pseudomonocotyly. Embryo growth and germination were studied in the laboratory and the field, using dissection and image analysis. The effects of temperature, light, nitrate and GA₃ on germination were tested. Seed desiccation tolerance was investigated by storage at different RHs and by drying seeds at different stages of embryo growth.
• Seeds possess morphological but not physiological dormancy. Embryo growth and germination were promoted by temperatures between 0 and 5 °C, arrested above 10 °C, and indifferent to alternating temperatures, light, nitrate and GA₃. Pseudomonocotyly appears to result from cotyledon fusion. While seeds tolerated drying to 15% RH and storage for 1 year at 20 °C, viability was lost when storage was at 60% RH. Seeds imbibed at 5 °C for 84 days had significant internal embryo growth but were still able to tolerate drying to 15% RH.
• Reproduction by seed in C. majus follows a strategy shared by geophytes adapted to deciduous temperate forests. The evolution of fused cotyledons may enable the radicle and the hypocotyl to reach deeper into the soil where a tuber can develop. The embryo is capable of growth within the seed at low temperatures so that germination is timed for early spring.