Desiccation Tolerance In Seeds Research Articles

Selecting Suitable Tree Species for Direct Seeding to Restore Forest Ecosystems in Northern Thailand

To upscale restoration of tropical forest ecosystems, direct seeding—sowing seeds directly into the ground—is potentially a more cost-effective technique than tree planting. However, its success is limited by seed predation, the harshness of environmental conditions on restoration sites and particularly by a lack of information about suitable tree species. Therefore, this study tested the suitability of 23 native forest tree species for direct seeding, to restore a biodiversity-rich, upland, evergreen forest in northern Thailand. Three replicate seed batches of each species were sown randomly in two degraded sites and in a tree nursery under controlled conditions. Seed removal and germination were monitored weekly until no further germination had occurred for more than a month. Subsequently, seedling yield, growth and species performance score were also monitored at appropriate intervals. Nine months after sowing, seed removal differed significantly among species but was generally low, with a cross-species average of 3.4% (±0.5 SE). Seed size was negatively correlated with seed removal. Eight species failed to germinate. Seed germination percentage varied widely among species. Cross-species average germination of the 15 species that germinated was 25% (±6.2 SE). Two species (Adenanthera microsperma and Alangium kurzii) were ranked as having high germination (>50%), five species (Choerospondias axillaris, Spondias pinnata, Diospyros glandulosa, Melia azedarach and Phyllanthus emblica) had medium germination (20–50%) and eight species had low germination (<20%). Following the first dry season, two of the fifteen germinated species failed to establish. Germination and establishment were influenced by seed size, seed storage behavior and successional status. A. microsperma, S. pinnata and C. axillaris are recommended for direct seeding based on their high species performance index values. This study further concluded that selecting desiccation-tolerant seeds, particularly those with medium-to-large sizes, could increase the chances of successful seedling establishment.

Imbibition and drying periods in desiccation tolerance of peanut seeds

Imbibition and drying periods in desiccation tolerance of peanut seeds

Seed Desiccation Sensitivity Varies with Geographic Distribution in Two New Zealand Native Pittosporum Species

Ex situ conservation involves the maintenance and reproduction of species in areas outside their natural habitats. Seed banking is a well-established ex situ approach used for plant conservation. Seed banking consists of collecting, drying, and storing seeds to preserve genetic diversity. The main limitation of this technique is that the seed must be desiccation tolerant. Seed storage behaviour can vary among species, and for some species, drying without loss of viability is not possible, meaning storage under conventional seed banking conditions (sub-zero temperatures and low relative humidity) is not possible. Understanding seed storage behaviour is an essential prerequisite for establishing whether conventional seed banking is an option for seed conservation. This study investigated the desiccation tolerance and sensitivity of mature seeds of two native New Zealand species of Pittosporum (P. eugenioides and P. crassifolium) from two geographic locations (Palmerston North and Wellington), with the aim of understanding their seed storage behaviour and thereby improving conservation outcomes. The variables measured were seed moisture content, viability, germination, and desiccation responses. We developed sorption isotherm for both species to support the future development of storage protocols. Our results show that both P. eugenioides and P. crassifolium display non-orthodox behaviour, i.e., are desiccation sensitive and cannot be stored under conventional seed banking conditions, but also suggest that seed desiccation responses vary with the geographical origin of the seeds. This study highlights the importance of exploring seed storage behaviour using different populations to optimize ex situ conservation strategies aimed at preserving the genetic diversity of New Zealand’s threatened and endangered species.

Seed traits and tropical arboreal species conservation: a case study of a highly diverse tropical humid forest region in Southern Costa Rica

Tropical areas are vital for conserving endangered tree species. However, barriers to the propagation and storage of plant material still limit preservation outcomes. Seed traits are essential in conservation but have rarely been applied in the tropics. In this work, we compile information about the germination and seed desiccation tolerance behaviour of 953 arboreal species from the Osa Peninsula, Costa Rica. We analysed how those traits are related to the growing strata, seed size, and dispersal mode and how they can be used to improve conservation initiatives based on the species distribution, abundance, extinction risk, and ex situ cultivation. Over a third of the species are probably recalcitrant but this number increase to almost half among the endangered and endemic ones. Most species have seeds dispersed by animals, but wind dispersal is usually orthodox and dominant in secondary forests. All species with tiny seeds and most understorey ones with small seeds are orthodox. Approximately half of the species have dormant seeds, while nearly one-third of nondormant species have cohorts with extended germination. Almost half of the species are conserved ex situ; however, several endangered, endemics could be expected to be considered exceptional. Seed traits could target orthodox species for seed banking in tropical forests, including the potential of secondary forests and a subset of oligarch species. For the recalcitrant ones, approaches based on the risk of extinction, distribution, abundance, and ex situ status allow for prioritizing collection and conservation strategies. Under this approach, we develop a list with priority species.

Mechanistic insights derived from re-establishment of desiccation tolerance in germinating xerophytic seeds: Caragana korshinskii as an example.

Germplasm conservation strongly depends on the desiccation tolerance (DT) of seeds. Xerophytic seeds have strong desiccation resistance, which makes them excellent models to study DT. Although some experimental strategies have been applied previously, most methods are difficult to apply to xerophytic seeds. In this review, we attempted to synthesize current strategies for the study of seed DT and provide an in-depth look at Caragana korshinskii as an example. First, we analyze congenital advantages of xerophytes in the study of seed DT. Second, we summarize several strategies used to study DT and illustrate a suitable strategy for xerophytic species. Then, based on our previous studies work with C. korshinskii, a feasible technical strategy for DT re-establishment is provided and we provide illustrate some special molecular mechanisms seen in xerophytic seeds. Finally, several steps to unveil the DT mechanism of xerophytic seeds are suggested, and three scientific questions that the field should consider are listed. We hope to optimize and utilize this strategy for more xerophytic species to more systematically decipher the physiological and molecular processes of seed DT and provide more candidate genes for molecular breeding.

Post-excision drying of immature Phalaenopsis seeds improves germination and desiccation tolerance

• Immature P halaenopsis seeds cannot tolerate drying and germinate poorly. • Incubation of excised immature seeds without free water increased germination. • Drying excised seeds slowly induced desiccation tolerance. • Excision of seeds induced two LEA protein genes regardless of drying. • Some LEA proteins may increase germinability. Long-term storage of many commercially valuable orchid seeds is uniquely challenging because they can only be germinated in aseptic culture, a practice requiring that fruits be prematurely excised before they dehisce to facilitate sterilization. The seeds from these fruits cannot tolerate the desiccation required for long-term storage, resulting in potential loss of valuable germplasm. Our aim is to develop methods to increase germinability and desiccation tolerance in immature orchid seeds to prepare them for long-term storage and to explore underlying biochemical factors. We assessed germinability, desiccation tolerance and expression of two typical L ate E mbryogenesis A bundant ( LEA) genes in Phalaenopsis amabilis, P. aphrodite and their hybrid seeds as a function of moisture content both during natural development and during experimental treatments of excised immature seeds. Germinability increased whenever excised seeds were incubated in the absence of free water at moisture contents high enough to permit protein synthesis, a treatment which resulted in the rapid (within 24 h) upregulation of two typical LEA genes. Whereas incubating excised seeds without free water at high moisture contents for 4 days improved germination and induced LEA genes, only drying of excised seeds over the course of 4 days induced tolerance to eventual moisture contents less than 10% moisture. In conclusion, our results suggest that the germination of seeds from orchid capsules excised prior to dehiscence (as for the green pod method) is improved by maintaining them for several days following excision at high relative humidity in the absence of free water. Such seeds can also be induced to tolerate desiccation - and thus potentially long term dry storage - by slowly drying them over the course of several days. Our results also support the hypothesis that some of the typical LEA proteins improve germinability but are alone insufficient for the development of desiccation tolerance.

Oryza coarctata PROTEIN L-ISOASPARTYL METHYLTRANSFERASE (PIMT) repairs isoaspartyl modification to antioxidative enzymes and is implicated in seed traits in rice

PROTEIN L -ISOASPARTYL METHYLTRANSFERASE (PIMT) is a protein repairing enzyme, which is highly abundant in orthodox seeds, and plays an important role in seed vigor and longevity. PIMT essentially repairs isoaspartyl modification in proteins. Despite PIMT has been characterized from several orthodox seed producing plant species, role and regulation of PIMTs in recalcitrant seed producing plants are still limited. In the present study, PIMT from Oryza coarctata, which produces recalcitrant seeds and possess both enzymatically active ( Oc PIMT1–1 and Oc PIMT2–1) and inactive ( Oc PIMT1–2 and Oc PIMT2–2) PIMT isoforms , are functionally characterized through biochemical and genetic approach. We show that PIMT isoforms are differentially localized in Oryza sativa and Oryza coarctata. We also report that enzymatically active OcPIMTs isoforms, but not enzymatically inactive OcPIMTs isoforms, could impart seed vigor, viability and longevity in A. thaliana . Likewise, rice transgenic lines were also generated, and ectopic overexpression of enzymatically active OcPIMT isoforms resulted in increased seed length and weight with improved seed vigor and longevity. Subsequent analysis revealed that antioxidant enzymes ( Os APX and Os CAT) are susceptible to isoAsp modification, which negatively influences their biological functions; however, OcPIMT s physically interact, repairs and protect their function from harmful isoAsp modification, and thereby modulate ROS homeostasis in seeds during aging. Collectively, our results highlight the mechanisms and importance of ectopic expression of OcPIMT isoforms in seed desiccation tolerance and subsequent vigor, viability and longevity in rice. • O. coarctata encodes functionally active and inactive PIMT isoforms. • Ectopic over-expression of functionally active PIMT isoforms improves seed vigor and longevity in rice. • Antioxidative enzymes are susceptible to isoAsp damage during aging and seed storage. • OcPIMT isoforms interacts and repairs antioxidant enzymes from isoAsp damage and maintains its enzymatic properties. • Overall PIMT mediated repair is important to maintain seed vigor and viability.

A seed‐specific transcription factor, HSFA9, anticipates UV‐B light responses by mimicking the activation of the UV‐B receptor in tobacco

SUMMARYSunflower heat shock factor A9 (HSFA9, hereafter A9) is a transcription factor involved in seed desiccation tolerance and longevity. A9 also links the regulation of seed maturation with that of seedling photomorphogenesis through visible light receptors. Analyses in transgenic Nicotiana tabacum (tobacco) indicated that A9 also affects responses mediated by NtUVR8, the receptor of ultraviolet light B (UV‐B). We compared the effects of A9 and UV‐B illumination on the nuclear localization of GFP‐NtUVR8 in Nicotiana benthamiana leaves. We also used co‐immunoprecipitation and limited proteolysis for analyzing the interaction between A9 and NtUVR8. We found that A9, by binding to NtUVR8, induced structural changes that resulted in enhancing the nuclear localization of NtUVR8 by hindering its nuclear export. The localization of UVR8 is crucial for receptor activation and function in Arabidopsis, where UV‐B‐activated nuclear UVR8 binds the E3 ubiquitin ligase COP1, leading to enhanced UV‐B responses and photoprotection. A9 similarly activated NtUVR8 by enhancing COP1 binding without UV‐B light. Seedlings and dark‐germinated seeds that overexpress A9 showed primed UV‐B light stress protection. Our results unveil a UV‐B‐independent activation mechanism and a role for UVR8 in plant seeds that might contribute to early stress protection, facilitating seedling establishment.

What affects the desiccation tolerance threshold of Brazilian Eugenia (Myrtaceae) seeds?

Desiccation sensitive (DS) seeds are shed at high water contents (WC) and metabolically active, but WC thresholds vary broadly among species even in the same genus. Eugenia is an important ecological genus that has high occurrence in several Brazilian morphoclimatic domains. In this study, we assessed seed desiccation tolerance of five Eugenia species collected in specific meteorological conditions. We reported the species geographical ranges and verified the rainfall and temperature of species sites in the year prior to seed collection. We also assessed initial WC, seed germination and vigor and seedling growth upon desiccation. Eugenia uniflora was the widest spread among the five species, while E. astringens was the most restricted. In this specific study, widespread species showed a higher WC threshold than restricted species. In the same way, the WC of fresh seeds was not correlated to the desiccation tolerance threshold. Seed desiccation tolerance was species dependent and correlated with the environmental status of seed collection sites. Wetter and warmer conditions were correlated to the E. uniflora higher DS threshold. Low rainfall and temperature corresponded to a lower desiccation sensitivity of E. astringens seeds. Seeds of the five species lost half viability between 0.44 and 0.25g H2O g DW- 1 and after 65-270h of desiccation. Our results indicate that abiotic factors impact plant populations during the seed production season and can drive seed desiccation tolerance threshold and physiological behavior. These results should be taken into account in ex-situ plant conservation programs and tropical species management.

ABI transcription factors and PROTEIN L-ISOASPARTYL METHYLTRANSFERASE module mediate seed desiccation tolerance and longevity in Oryza sativa.

In contrast to desiccation-tolerant orthodox seeds, recalcitrant seeds are desiccation sensitive and are unable to survive for a prolonged time. Here, our analyses of Oryza species with contrasting seed desiccation tolerance reveals that PROTEIN L-ISOASPARTYL METHYLTRANSFERASE (PIMT), an enzyme that repairs abnormal isoaspartyl (isoAsp) residues in proteins, acts as a key player that governs seed desiccation tolerance to orthodox seeds but is ineffective in recalcitrant seeds. We observe that, unlike the orthodox seed of Oryza sativa, desiccation intolerance of the recalcitrant seeds of Oryza coarctata are linked to reduced PIMT activity and increased isoAsp accumulation due to the lack of coordinated action of ABA and ABI transcription factors to upregulate PIMT during maturation. We show that suppression of PIMT reduces, and its overexpression increases, seed desiccation tolerance and seed longevity in O. sativa. Our analyses further reveal that the ABI transcription factors undergo isoAsp formation that affect their functional competence; however, PIMT interacts with and repairs isoAsp residues and facilitates their functions. Our results thus illustrate a new insight into the mechanisms of acquisition of seed desiccation tolerance and longevity by ABI transcription factors and the PIMT module.

Oxidant system and ABA drive germination in seeds of palm species with differences in desiccation tolerance

AbstractWe investigated the thermal thresholds to seed germination and the variations in abscisic acid (ABA) levels and oxidative metabolism during seed dormancy-breaking and germination in two palm species with differences in desiccation tolerance. We used Mauritia flexuosa (buriti palm, desiccation-sensitive seeds) from swampy habitats (Veredas) and Attalea speciosa (babassu, desiccation-tolerant seeds) from the transition zone between the forest and semi-arid region (drained soils). Germination was evaluated at 15–40°C after dormancy-breaking (operculum removal). At optimal temperature for both species (30°C), embryos were sampled in distinct germination phases – dry, imbibed, after operculum removal and at early germination – and used for quantifying ABA and hydrogen peroxide (H2O2) content, antioxidant enzyme activities and for histolocalization of superoxide anion (O2−). Seeds of M. flexuosa germinated only in a narrow temperature range (25–35°C), while A. speciosa seeds germinated between 15 and 40°C. After operculum removal, reduced ABA levels in embryos of M. flexuosa were accompanied by constant H2O2 levels, while in A. speciosa, similar levels of ABA and H2O2 were maintained throughout all germination phases. The presence of O2− was restricted to the haustorium, and an increase in O2− accumulation was observed in both species after operculum removal. Similarities were noted between both species regarding enzyme activities; however, the activities were higher in embryos from M. flexuosa. The presence of O2− only in the haustorium indicates that this region of the embryo is an active structure following imbibition and is involved in germination itself, not just functioning in reserve mobilization.

Seed Hardening: A Way to Tolerate Against Abiotic Stress in Rainfed Areas

Pre-sowing hardening or priming of seeds is one of the best methods for altering the biochemical and physiological process of seeds for favourable condition to induce drought tolerance in emerging seedlings. The recurrent phenomenon in rainfed areas i.e. soil moisture stress immediately after sowing affects seeds germination and their establishment. Under sub-optimal environmental conditions like rainfed farming, poor seed germination followed by poor field establishment is a common phenomenon. Seed hardening enables seedlings to survive this early moisture stress. hydration of seeds for short term before planting greatly benefits stand establishment along with the uses of chemicals like potassium or sodium phosphate would give additional advantage. It is defined as the process of soaking seeds in chemical solution for specified time and then drying to induce tolerance to drought. Various seed priming/hardening techniques have been developed including hydro-priming, halo-priming, osmo-priming and hormonal priming. Micronutrient seed treatments, which include seed priming and seed coating, are an attractive and easy alternative. Seed hardening promotes early establishment provides more strengthen to plant and it became competitive against infections and diseases is related to gene regulation and expression under stress conditions. The discovery of plant hormones in the 1920s underlined the crucial role of these compounds in seed desiccation tolerance, reserve mobilization, as well as cell division and cell elongation occurring during germination. The seed hardening is considered as low cost technology and is the most important requirement for pre-monsoon sowing. Seed hardening offer an attractive option for resource poor farmers. During seed hardening, seeds are subjected to partial hydration followed by dehydration before sowing.

Differential Influx of Natural Plant Growth Regulators during Embryogeny in the Recalcitrant Seeds of Syzygium cumini (L) Skeels

Background: The hormonal up-regulation and down-regulation in recalcitrant seeds, on the other hand, has received little research. We tested fou plant growth regulators from distinct families of phytohormones at the same time to better understand their differential input from maternal tissues to growing Syzygium cumini seeds. Methods: During April-June 2020, seeds were collected in their native habitats in the Western Ghats. Seeds were chosen at random from each treatment. The embryonic tissues of seeds were chopped up and frozen for LC-MS/MS hormonal profiling. Result: Except for ABA, the dynamics of key plant hormones in this recalcitrant seed were identical to that of desiccation-tolerant orthodox seeds. When compared to other conventional seeds, SA was shown to accumulate at an unusually high level in mature embryonic tissues, demonstrating the highly hydrated seed’s defense mechanism against fungal attack following seed shedding.

Defining exceptional species—A conceptual framework to expand and advance ex situ conservation of plant diversity beyond conventional seed banking

The multiple, complex risks to plant species survival are increasing, and conservation strategies that include ex situ as well as in situ approaches are needed now more than ever. Seed banking (drying at c.15% relative humidity and then storing at −20 °C) is the most efficient and effective ex situ method for long-term conservation for a majority of plant species. However, some plant species are not amenable to this practice, and such species have been labeled exceptional. Critical limitations to conventional seed banking include: 1) the unavailability of sufficient seed for storage; 2) seeds that are completely intolerant of the drying process (recalcitrant); 3) fully or partially desiccation tolerant seeds that are short-lived or sensitive to storage in a conventional freezer; and 4) seeds exhibiting complex dormancies that significantly hinder post-storage germination. Here we describe species examples to illustrate the key features of these four factors of exceptionality. This definition of exceptionality will provide the foundation for identifying exceptional species and directing resources to the appropriate approaches needed for their conservation. The long-term ex situ conservation of exceptional species will require living collections, as well as technologies involving expertise in cryobiotechnology, seed biology, plant physiology, plant ecology, and horticulture, emphasizing the importance of fully integrating multi-disciplinary conservation actions underpinned by training and knowledge exchange. Given that the number of known exceptional species is anticipated to increase substantially with further research, we call for immediate, concerted, and focused international action to address the conservation needs of the world's exceptional plant species.

Desiccation Tolerance and germination of Psidium guajava seeds from different regions of Brazil

Background: The germination ecology of P. guajava seeds collected in two regions of Brazil was investigated aiming to (1) characterize the seed batches; (2) determine the best temperature for germination; and (3) assess variations in seed desiccation tolerance (DT). For each batch, we determined seed water content and initial germination. To evaluate temperature effects, we tested seed germination. After, we generated the imbibition curves for the two provenance. To evaluate the loss of DT, the seeds were left to germinate along different time intervals. We monitored water loss by regularly weighing the seeds until achieving stabilization, keeping them under these conditions for 72 hours. After drying, the seeds were pre-hydrated and submitted to the germination test. Results:We identified variations in physiological characteristics between the seeds from north and southeast batches. At the temperature extremes, the seeds from both provenance failed to germinate. The highest germination percentages were observed at 20 and 25 °C (constant) and between 20-30 °C (alternating) for the two batches and, for the southeast batch specifically, at 30 °C. The imbibition curve displayed a triphasic pattern with a rapid increase in seed fresh weight in the first 48 hours. Conclusion: The southeast provenance seeds lost DT abruptly, until its complete loss after radicle protrusion, which occurred in both batches. The highest values of germination speed index (GSI) of both provenance were observed after a 9-day imbibition period, suggesting seed hydration memory. Drying resulted in necrosis of the root tissue and death of the seeds with visible roots.

Active metabolism during desiccation of the desiccation tolerant short-lived seeds of Poincianella pluviosa (DC.) L. P. Queiroz

Abstract: During embryogenesis and seed filling, developing seeds are metabolically highly active, while at the desiccation stage of tolerant seeds a decreased metabolism is expected. Seeds of Poincianella pluviosa present an extensive maturation cycle (11 months), longer than seed storability at room temperature (8 months). The metabolic profile of these seeds was characterized during maturation and drying, focusing in their role on seed behavior after shedding. Distinct responses of the embryonic axes and cotyledons to drying were observed depending on the developmental stage. Low proportions of tricarboxylic acids intermediaries until maturity indicated a low respiratory metabolism prior to the desiccation stage. Changes in shikimate, 4-coumarate, and quinate proportions suggest a metabolic shift towards the synthesis of chlorogenate isomers, found in high proportions in dispersed seeds. High proportions of lactate and glycerol were observed in immature seeds after artificial drying, but also in naturally dried axes of dispersed seeds. This suggests an active metabolism prior to drying and an osmotic stress under hypoxia, mechanisms that were never described before in desiccation-tolerant seeds. The results indicated that P. pluviosa seeds are dispersed with an incomplete metabolic switch-off, which can be related to their short lifespan.

Capacidade antioxidante equivalente ao trolox em sementes de Coffea arabica L.

ABSTRACT The causes of the low desiccation tolerance and low longevity of coffee seeds have not yet been fully elucidated, and a full understanding of their complex physiology is of great interest. Among several alternatives, the loss of antioxidant capacity in seeds may be related to their rapid loss in quality during storage. The objective of this study was to determine the total antioxidant capacity of coffee harvested at different ripeness stages before and after the storage of seeds with different water contents and to relate antioxidant capacity to physiological quality. Seeds in the greenish-yellow or cherry stages, recently harvested or stored for nine months at 10 °C with 40, 30, 20 and 12% water content (wet basis - wb), were submitted to physiological and biochemical quality evaluations, and the Trolox equivalent antioxidant capacity (TEAC) was determined. The germination and root protrusion of coffee seeds from greenish-yellow and cherry fruits were not affected by drying, but seeds harvested at physiological maturity had greater vigor when the moisture content was lower. The quality of coffee seeds decreased during storage, and this decrease was greater in seeds stored with higher water contents. Coffee seeds in the greenish-yellow stage had a higher antioxidant capacity than those in the cherry stage when recently harvested, but there was a substantial reduction in this capacity during storage at both maturation stages. Coffee seed deterioration is related to a reduction in antioxidant capacity, and the isoenzymatic profiles of the antioxidant process are little affected by the seed maturation stage. The deterioration of coffee seeds during storage is related to a reduction in their total antioxidant capacity, regardless of their maturation stage, being more pronounced in the greenish-yellow stage.

Seed production and storage for endangered Morus boninensis using an ex-situ living collection.

Meaningful conservation techniques for the endangered Morus boninensis require seed production and storage, since insitu purebred seed production is infrequent in Ogasawara Islands (World Natural Heritage Site) in Japan. Ex situ living M. boninensis specimens produced seeds by open- and artificial-pollination in a greenhouse. Seed desiccation tolerance and storage characteristics were examined. Open-pollinated seeds were dried at 75, 33 and 8% relative humidity (RH) for 5days then cryopreserved at -170°C. Artificially pollinated seeds were dried at 8% RH then stored cryogenically at -170°C and in freezers at -80 or -20°C for 6months. Germination rates were compared among seeds before and after drying and storage. Germination rates of undried seeds were 83% for open-pollinated seeds and 65% for artificially pollinated seeds. M. boninensis seeds exhibited the characteristic high desiccation tolerance of orthodox seeds and maintained a high germination rate after drying to a moisture content of approximately 4%. Cryopreservation of open-pollinated dry seeds with moisture contents of ca. 12, 7 and 4% maintained germination rates, while cryopreservation of undried seeds (moisture content ca. 44%) resulted in no germinability. Cryogenic and freezer storage of artificially pollinated dry seeds for 6months resulted in maintenance of germination rates comparable to undried seeds before storage. Seed production was enabled by ex situ M. boninensis collection. The present study also developed a method for low temperature seed storage. Ex situ living tree collection represents a feasible seed resource for reintroduction and restoration programmes for M. boninensis.

Characterization of physiological traits during development of the recalcitrant seeds of Quercus serrata.

We investigated how developmental stage affects seed traits, including the relative level of desiccation tolerance of Quercus serrata. We tested the hypothesis that the relative level of desiccation tolerance is a quantitative trait associated with seed development and that a maximum relative level of desiccation tolerance is reached during development. Seed growth and physiological traits of Q. serrata from a subtropical forest were examined in detail during the developmental process. During seed development, the relative level of desiccation tolerance and other seed traits of Q. serrata varied. Dry matter accumulation in seed components increased rapidly beginning in mid-August, and moisture content declined. At the peak period of seed dispersal in late September, seeds were fully mature, with 100% germination. Relative level of desiccation tolerance increased up to the point of peak dispersal; however, at this time seeds were still recalcitrant. Post-mature development was accompanied by further increases in seed dry matter and decreases in moisture content, which led to a decrease in seed germination and relative level of desiccation tolerance. Our results suggest that in species with recalcitrant seeds, the relative level of desiccation tolerance and other seed traits are quantitative at the intraspecific level. The relative level of desiccation tolerance for recalcitrant seeds does not increase infinitely during phase II of development. There is a maximum relative level of desiccation tolerance in recalcitrant seeds within a species.

Assessing the storage potential of Australian rainforest seeds: a decision-making key to aid rapid conservation

Seed banking of rainforest species is hindered by lack of knowledge as to which species are tolerant of desiccation and freezing. We assessed 313 Australian rainforest species for seed banking suitability by comparing the germination percentage of fresh seeds to seeds dried at 15% RH and seeds stored at −20 °C after drying. We then compared desiccation responses to environmental, habit, fruit and seed characteristics to identify the most useful predictors of desiccation sensitivity. Of 162 species with ≥ 50% initial germination, 22% were sensitive to desiccation, 64% were tolerant and 10% were partially tolerant; the responses of 4% were uncertain. Of 107 desiccation tolerant species tested for response to freezing, 24% were freezing sensitive or short-lived in storage at −20 °C. Median values for fresh seed moisture content (SMC), oven dry weight (DW) and the likelihood of desiccation sensitivity (PD-S) were significantly greater for desiccation sensitive than desiccation tolerant seeds. Ninety-four to 97% of seeds with SMC < 29%, DW < 20 mg or PD-S < 0.01 were desiccation tolerant. Ordinal logistic regression of desiccation response against environmental, habit, fruit and seed characteristics indicated that the likelihood of desiccation sensitivity was significantly increased by a tree habit, fleshy fruit, increasing fresh SMC and increasing PD-S. The responses observed in this study were combined with earlier studies to develop a simple decision key to aid prediction of desiccation responses in untested rainforest species.