Desiccation Sensitivity Research Articles

A classification system for germination in desiccation-sensitive Fagaceae acorns: with particular focus on physiological and epicotyl dormancy

Abstract Since the 17th century, understanding the germination ecology of Fagaceae fruits has attracted considerable interest. However, several questions remain, including: (i) How widespread is the coexistence of dormancy and desiccation-sensitivity (DS)? (ii) What kind of dormancy do Fagaceae fruits/acorns have? (iii) How common is epicotyl dormancy in Fagaceae fruits/acorns? (iv) What is the influence of embryonic axis position in Fagaceae fruits/acorns in relation to germination? Our literature synthesis shows that most—but not all—Fagaceae fruits/acorns are desiccation-sensitive. Many Quercus species have either physiological dormancy (PD) or epicotyl physiological dormancy (ePD), though the latter has been hitherto underestimated. Here, we propose a new classification system for Fagaceae species and identify two germination types: Type-I and Type-II. Further, we subdivide Type-I into Type-IA adjacent lingular (radicle extends through the apex and shoots develop close to the fruits/acorns) and Type-IS adjacent lingular (radicle extends near the scar and shoots develop close to the fruits/acorns), and Type-II into Type-IIA remote tubular, where the radicle extends through the apex or near the scar (Type-IIS), but shoots emerge at a distance from the fruits/acorns. Why the embryonic axis position varies between species cannot be explained based on phylogenetic relationships.

Desiccation sensitivity of fresh and germinating seeds of Tabebuia aurea: physiological and biochemical implications

Desiccation sensitivity of fresh and germinating seeds of Tabebuia aurea: physiological and biochemical implications

Dehydration and rehydration differently affect photosynthesis and volatile monoterpenes in bryophytes with contrasting ecological traits.

Bryophytes desiccate rapidly when relative humidity decreases. The capacity to withstand dehydration depends on several ecological and physiological factors. Volatile organic compounds (VOCs) may have a role in enhancing tolerance to desiccating bryophytes. However, the functions of VOCs in bryophytes have received little attention so far. We aimed to investigate the impact of a dehydration-rehydration treatment on primary carbon metabolism and volatile terpenes (VTs) in three bryophytes with contrasting ecological traits: Vessicularia dubyana, Porella platyphylla and Pleurochaete squarrosa. First, we confirmed the desiccation sensitivity gradient of the species. Under fully hydrated conditions, the photosynthetic rate (A) was inversely associated with stress tolerance, with a lower rate in more tolerant species. The partial recovery of A in P. platyphylla and P. squarrosa after rehydration confirmed the desiccation tolerance of these two species. On the other hand, A did not recover after rehydration in V. dubyana. Regarding VT, each species exhibited a distinct VT profile under optimum hydration, with the highest VT pool found in the more desiccation-sensitive species (V. dubyana). However, the observed species-specific VT pattern could be associated with the ecological habitat of each species. P. squarrosa, a moss of dry habitats, may synthesize mainly non-volatile secondary metabolites as stress-defensive compounds. On the other hand, V. dubyana, commonly found submerged, may need to invest photosynthetically assimilated carbon to synthesize a higher amount of VTs to cope with transient water stress occurrence. Further research on the functions of VTs in bryophytes is needed to deepen our understanding of their ecological significance.

The reproductive biology of Fagaceae acorns in the current and future climate

Fagaceae is an iconic plant family with 1000+ species distributed predominantly in the northern hemisphere. The reproductive ecology of the Fagaceae species is highly complex, and in the past three centuries, understanding the fruit masting strategies, dispersal, pathogen pressure, and storage has enjoyed steady research interest. However, the interrelationship between these factors is surprisingly less explored, undermining how acorns survive the post-dispersal period. The ability of fruits (acorns, nuts) to survive post-dispersal conditions starts during the maturation drying stage. Successful fruit production depends on the maternal environment, with a ‘good fruit production year’ occurring every few years. This phenomenon might out-maneuver predators by providing sufficient numbers to be consumed but still leaving enough for germination. Because most Fagaceae species have desiccation-sensitive (DS) fruits, survival after dispersal is challenging due to frequent dry spells. Fruit size is not phylogenetically conserved within the genus, with the average fruit mass of Castanea being 50 times higher than the desiccation-tolerant genus Fagus. Larger fruit size may be an adaptation in dry areas because prolonged drying continuously desiccates large-sized cotyledons before desiccating embryos. For species adapted to dry environments, synchronizing dispersal with the growing season could be beneficial, but exceptions exist. Many consumers, such as rodents, aid in the dispersal of fruits, but some fruits are killed in the process, especially those predated late. Upon settling on a site, the pericarp protects the embryo to a certain extent; if drying occurs, the cotyledons become the first site of water loss. However, under extreme drying, survival depends on sporadic rainfall, i.e., wet-dry cycle, which aids in maintaining the critical moisture content required by the fruits for survival. Nonetheless, these adaptive mechanisms are challenged by climate change, which affects the maturation, persistence, and seedling establishment of numerous Fagaceae species.

Utjecaj osjetljivosti na isušivanje i kritičnog sadržaja vlage na žirove vrste Quercus cerris, Quercus petraea i Quercus robur

In this study, critical moisture contents and desiccation sensitivity of Quercus cerris (Turkey oak), Quercus petraea (Sessile oak), Quercus robur (Pedunculate oak) seeds were determined to see how desiccation affects acorn moisture content and germination behaviour. The moisture content of the harvested acorns was found to be 41% for Q. cerris, 46% for Q. petraea and 45% for Q. robur. The acorns were separated into sublots, sprayed with distilled water to reach their maximum moisture content and then left to dry for 18 days. There were statistically significant differences in germination as a function of desiccation time and decreasing moisture content. Initial germination was delayed. The highest moisture contents were 48% for Q. cerris, 51% for Q. petraea and 49% for Q. robur acorns. The highest water uptake was 17% in Q. cerris, 11% in Q. petraea and the lowest was 9% in Q. robur. The moisture content with a germination percentage below 50% was considered as the critical moisture content. In a period of 12-15 days after the beginning of the drying process, the acorns reached the critical moisture content. The germination percentage decreased from 83% to 43% for Q. cerris, from 100% to 44% for Q. petraea and from 97% to 43% for Q. robur as the moisture content decreased from the maximum to the critical moisture content. For Q. cerris, Q. petraea and Q. robur, the critical moisture contents at which acorns begin to lose viability were between 28-31%, 31-36% and 32-37%, respectively. The results of the present study provide guidance for nursery practices carried out on oak species, from acorn harvesting to seeding and post-seeding care.

Variation of sugar compounds in Phoebe chekiangensis seeds during natural desiccation.

To investigate the role of sugar metabolism in desiccation-sensitive seeds, we performed a natural desiccation treatment on Phoebe chekiangensis seeds in a room and systematically analyzed the changes in seed germination, sugar compounds, malondialdehyde, and relative electrical conductivity during the seed desiccation. The results revealed that the initial moisture content of P. chekiangensis seed was very high (37.06%) and the seed was sensitive to desiccation, the germination percentage of the seed decreased to 5.33% when the seed was desiccated to 22.04% of moisture content, therefore, the seeds were considered recalcitrant. Based on the logistic model, we know that the moisture content of the seeds is 29.05% when the germination percentage drops to 50% and that it is desirable to keep the seed moisture content above 31.74% during ambient transportation. During seed desiccation, sucrose and trehalose contents exhibited increasing trends, and raffinose also increased during the late stage of desiccation, however, low levels of the non-reducing sugar accumulations may not prevent the loss of seed viability caused by desiccation. Glucose and fructose predominated among sugar compounds, and they showed a slight increase followed by a significant decrease. Their depletion may have contributed to the accumulation of sucrose and raffinose family oligosaccharides. Correlation analysis revealed a significant relationship between the accumulation of sucrose, trehalose, and soluble sugars, and the reduction in seed viability. Sucrose showed a significant negative correlation with glucose and fructose. Trehalose also exhibited the same pattern of correlation. These results provided additional data and theoretical support for understanding the mechanism of sugar metabolism in seed desiccation sensitivity.

Reduction of desiccation sensitivity in seeds of tree species

ABSTRACT: Desiccation sensitivity is a condition present in seeds of several tree species of economic and ecological importance, which makes such seeds unable to tolerate drying and storage. Thus, studies that seek strategies to maintain the viability of such seeds after being subjected to drying are necessary. An alternative for this purpose is the use of priming in solutions of known osmotic potential. Solutions of polyethylene glycol (PEG), glycerol, as well as phytohormones such as abscisic acid (ABA) and salicylic acid (SA) are related to stress tolerance in seeds. The objective of this work was to study desiccation sensitive seeds of Inga vera, Eugenia uniflora and Tapirira guianensis, using solutions of PEG, SA, sucrose, glycerol and combinations of SA+PEG in an attempt of reducing seed desiccation sensitivity. The responses varied according to the species, but in general, successful results in maintaining the viability of the seeds after drying were obtained from the treatmen of seed with sucrose, glycerol and combinations of PEG and SA. Treatment of seeds with these compounds is promising in reducing the desiccation sensitivity of seeds of tree species.

The metabolic profiles of Eugenia astringens and E. uniflora (Myrtaceae) sensitive seeds affect desiccation.

Myrtaceae species are abundant in tropical Atlantic rainforests, but 41% of the 5500 species of this family are of extreme conservation concern. Eugenia astringens and E. uniflora are native Brazilian Myrtaceae species that occur in the same habitats and produce desiccation-sensitive (DS) seeds. We hypothesized that their seed desiccation-sensitivity degree is associated with specific metabolic signatures. To test it, we analyzed the germination and metabolic profiles of fresh and desiccated seeds. The water content (WC) at which at least half of the seeds survived desiccation was lower in E. astringens (0.17 g H2 O g-1 DW) than in E. uniflora (0.41 g H2 O g-1 DW). We identified 103 annotated metabolites from 3261 peaks in both species, which differed in their relative contents between E. astringens and E. uniflora seeds. The main differences in seed metabolic profiles include several protective molecules in the group of carbohydrates and organic acids and amino acid contents. The relative contents of monosaccharides and disaccharides, malic and quinic acids, amino acids and saturated fatty acids may have taken part in the distinct DS behaviour of E. astringens and E. uniflora seeds. Our study provides evidence of the relationship between desiccation sensitivity, seed viability and metabolic profile of tropical seeds by comparing two closely related Eugenia species with different DS degrees.

The Co-Occurrence of Physiological and Epicotyl Physiological Dormancy in Three Desiccation-Sensitive Castanopsis (Fagaceae) Acorns from China with Specific Reference to the Embryonic Axis Position

Ecological significance of dormancy in desiccation-sensitive seeds is poorly understood. Quercus exhibits mutually exclusive occurrence of physiological (PD) and epicotyl dormancy (ePD), with no reported co-occurrence or dormancy class in other genera. We aimed to understand the dormancy in three Castanopsis species and document desiccation sensitivity and germination patterns concerning the embryonic axis position. We hypothesized that Castanopsis acorns are recalcitrant and potentially dormant. Fresh and cold-stratified acorns of Castanopsis chinensis, Castanopsis purpurella, and Castanopsis sclerophylla were subjected to desiccation and germination. Seedling emergence and internal morphology was monitored following cold (CS) and warm (WS) stratification. Fresh acorns had radicles emerge only after CS but require WS for shoot emergence. Drying to 20% moisture content led to complete death. In C. purpurella and C. sclerophylla, the embryonic axis was near the scar, and germination occurred by cracking the pericarp near the scar, which contrasts with C. chinensis. Moderate drying relieved dormancy due to the mechanical resistance of the pericarp. All three acorns were desiccation-sensitive and dormant. This is the first explicit report on PD and ePD co-occurrence in desiccation-sensitive seeds, but literature surveys allow for inference of such coexistence. CS alleviated PD and WS relieved ePD. Winter temperatures break PD, and acorns germinate during spring, but shoot emergence is delayed until summer. Our results are instructive for research on the dormancy of desiccation-sensitive species and the reproduction of Fagaceae species in subtropical forests.

Analysis and Identification of Genes Associated with the Desiccation Sensitivity of Panax notoginseng Seeds.

Panax notoginseng (Burk.) F. H. Chen, a species of the genus Panax, radix has been traditionally used to deal with various hematological diseases and cardiovascular diseases since ancient times in East Asia. P. notoginseng produces recalcitrant seeds which are sensitive to desiccation and difficult to store for a long time. However, few data are available on the mechanism of the desiccation sensitivity of P. notoginseng seeds. To gain a comprehensive perspective of the genes associated with desiccation sensitivity, cDNA libraries from seeds under control and desiccation processes were prepared independently for Illumina sequencing. The data generated a total of 70,189,896 reads that were integrated and assembled into 55,097 unigenes with a mean length of 783 bp. In total, 12,025 differentially expressed genes (DEGs) were identified during the desiccation process. Among these DEGs, a number of central metabolism, hormonal network-, fatty acid-, and ascorbate-glutathione-related genes were included. Our data provide a comprehensive resource for identifying the genes associated with the desiccation sensitivity of P. notoginseng seeds.

A horizontal view of primary metabolomes in vegetative desiccation tolerance.

Vegetative desiccation tolerance (VDT), the ability of such tissues to survive the near complete loss of cellular water, is a rare but polyphyletic phenotype. It is a complex multifactorial trait, typified by universal (core) factors but with many and varied adaptations due to plant architecture, biochemistry and biotic/abiotic dynamics of particular ecological niches. The ability to enter into a quiescent biophysically stable state is what ultimately determines desiccation tolerance. Thus, understanding the metabolomic complement of plants with VDT gives insight into the nature of survival as well as evolutionary aspects of VDT. In this study, we measured the soluble carbohydrate profiles and the polar, TMS-derivatisable metabolomes of 7 phylogenetically diverse species with VDT, in contrast with two desiccation sensitive (DS) species, under conditions of full hydration, severe water deficit stress, and desiccation. Our study confirmed the existence of core mechanisms of VDT systems associated with either constitutively abundant trehalose or the accumulation of raffinose family oligosaccharides and sucrose, with threshold ratios conditioned by other features of the metabolome. DS systems did not meet these ratios. Considerable chemical variations among VDT species suggest that co-occurring but distinct stresses (e.g., photooxidative stress) are dealt with using different chemical regimes. Furthermore, differences in the timing of metabolic shifts suggest there is not a single "desiccation programme" but that subprocesses are coordinated differently at different drying phases. There are likely to be constraints on the composition of a viable dry state and how different adaptive strategies interact with the biophysical constraints of VDT.

Diversity of seed storage behavior of tree species from tropical lowland rainforests in Sri Lanka, a global biodiversity hotspot

AbstractTropical lowland rainforests are considered to be ecologically important refugia of national and global significance, yet wide‐scale deforestation and degradation of tropical lowland rainforests lead to losses in biodiversity. Seed storage behavior information is required for the effective restoration of these forests. Here, we studied the seed storage behavior of 42 selected tropical lowland rainforest tree species from Sri Lanka with the aim to test the reliability of current experimental methods and predictive models to predict the desiccation sensitivity of seeds. Seed storage behavior was experimentally determined through the 100 seed method and the results were compared with three predictive models; thousand seed weight–moisture content (TSW–MC), seed coat ratio–seed mass (SCR–SM), and phylogenetic affiliation models. Based on the 100 seed method, 28 species were identified as desiccation sensitive and 14 species were identified as desiccation tolerant. Compared to the 100 seed method, the predictability of the SCR–SM model was 70%, whereas the TSW–MC and phylogenetic affiliation models showed 52% and 58% predictability, respectively. Due to its higher predictability, the SCR–SM model has a high potential to be an effective predictive tool of seed storage behavior. This study revealed that tropical lowland rainforests are dominated by trees producing desiccation‐sensitive seeds. Further, species dispersing seeds in the peak rainy season have desiccation‐sensitive seeds, while those dispersing seeds in the normal wet season have desiccation‐tolerant seeds. Another key finding was that 100% of the subcanopy species produce nonorthodox, that is, desiccation‐sensitive seeds, which gradually decrease from subcanopy to understory.

Neuronal expression in Drosophila of an evolutionarily conserved metallophosphodiesterase reveals pleiotropic roles in longevity and odorant response.

Evolutionarily conserved genes often play critical roles in organismal physiology. Here, we describe multiple roles of a previously uncharacterized Class III metallophosphodiesterase in Drosophila, an ortholog of the MPPED1 and MPPED2 proteins expressed in the mammalian brain. dMpped, the product of CG16717, hydrolyzed phosphodiester substrates including cAMP and cGMP in a metal-dependent manner. dMpped is expressed during development and in the adult fly. RNA-seq analysis of dMppedKO flies revealed misregulation of innate immune pathways. dMppedKO flies showed a reduced lifespan, which could be restored in Dredd hypomorphs, indicating that excessive production of antimicrobial peptides contributed to reduced longevity. Elevated levels of cAMP and cGMP in the brain of dMppedKO flies was restored on neuronal expression of dMpped, with a concomitant reduction in levels of antimicrobial peptides and restoration of normal life span. We observed that dMpped is expressed in the antennal lobe in the fly brain. dMppedKO flies showed defective specific attractant perception and desiccation sensitivity, correlated with the overexpression of Obp28 and Obp59 in knock-out flies. Importantly, neuronal expression of mammalian MPPED2 restored lifespan in dMppedKO flies. This is the first description of the pleiotropic roles of an evolutionarily conserved metallophosphodiesterase that may moonlight in diverse signaling pathways in an organism.

Desiccation Sensitivity Characteristics and Low-Temperature Storage of Recalcitrant Quercus variabilis Seed

This study aims to investigate the desiccation sensitivity characteristics and the critical moisture content of the recalcitrant Quercus variabilis seed. Additionally, cryopreservation of the recalcitrant seeds were studied. Wild-collected Q. variabilis seeds were used in this research. Differential scanning calorimetry (DSC) was employed to evaluate the critical moisture content and germination indices at different moisture contents were measured. The initial moisture content of the seeds and embryonic axes decreased from 33.1% and 40.9%, respectively, to 10.0%, accompanied by a germination rate decrease of 95.6% and 90.0% to 6.3% and 60.0%, respectively. The theoretical critical moisture content of the embryonic axis was calculated to be 11.55%. As dehydration progressed, drastic changes were observed in the antioxidant enzyme system. Initially, the levels of PRO and SOD in the seeds increased and then decreased, while the levels of POD and MDA consistently increased. The cryopreservation of the embryonic axis was achieved using vitrification. The embryonic axis with a moisture content of 10% had a 15% survival rate when pretreated with PVS2 for 60 min prior to cryopreservation. The results demonstrated that the cryopreservation of the Q. variabilis embryonic axis is possible, but the method needs adjustment to increase the recovery survival rate.

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.

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.

Climate drives patterns of seed traits in Quercus species across China.

Traits enabling seeds to survive post-dispersal desiccation and subsequently germinate are important aspects of plant regeneration for species with desiccation-sensitive seeds. However, how desiccation and germination-related traits co-vary and relate to patterns of climate variation are unknown. We investigated physiological traits related to desiccation and germination of desiccation-sensitive seeds from 19 Quercus species, which typically dominate subalpine, subtropical and temperate forests in China. The results demonstrate a strong relationship between climate and seed traits consistent with a hypothesis of minimizing seed death from desiccation. Seeds of subalpine species were most desiccation sensitive and died fastest when dried. These species avoided drought and cold by germinating rapidly. Subtropical and temperate oaks had more variable strategies to minimize the risk of mortality reflecting a continuum between traits that facilitate rapid germination (with the risk of rapid desiccation) and slow germination (and slow desiccation). Across the Quercus species, the relative level of seed desiccation sensitivity, which we predicted to be important for reducing the risk of drying related mortality, was independent of climate. For desiccation-sensitive seeds this suggests a more diverse range of strategies for minimizing desiccation risk than reported previously.

Did selection for seed traits across the Cretaceous/Paleogene boundary sort plants based on ploidy?

Paleobotanists debate whether the Cretaceous/Paleogene boundary (KPB) event was selective. As the hypothesis that the KPB event selected for plants with fast-return leaf economic traits (e.g. deciduousness) has lost empirical support in recent investigations, researchers have turned to alternative hypotheses to explain an abrupt decline in primary productivity across the KPB. Two contemporary hypotheses designed to explain selectivity among plants across the KPB are that (1) polyploids exhibited greater survivorship than their diploid progenitors or counterparts (i.e. the KPB-whole genome duplication or WGD hypothesis) and that (2) plants with desiccation-tolerant (DT), i.e. orthodox, seeds exhibited greater survivorship than plants with desiccationsensitive (DS), also known as recalcitrant, seeds. Late embryogenesis abundant (LEA) protein gene families are perceived to confer DT and seed longevity among vascular plants. Non-parametric Wilcoxon signed-rank test for matched pairs and a Mann-Whitney U test reveal that plant lineages perceived to have undergone WGD across the KPB exhibit significantly greater numbers of LEA genes than those that did not. On the basis of these data, this investigation elicits a merger between the KPB-WGD and KPB-seed traits concepts. However, emphasis is shifted from the concept of WGD as an immediate adaptation to climatic stress at the KPB (the KPB-WGD hypothesis) to the concept that WGD was an exaptation, which, by definition, fortuitously enhanced the survival of vascular plants across the KPB but that probably evolved initially in other climatic contexts.

Comparative Transcriptome Analysis Revealed Candidate Genes Potentially Related to Desiccation Sensitivity of Recalcitrant Quercus variabilis Seeds.

Chinese cork oak (Quercus variabilis) is a widely distributed and highly valuable deciduous broadleaf tree from both ecological and economic perspectives. Seeds of this species are recalcitrant, i.e., sensitive to desiccation, which affects their storage and long-term preservation of germplasm. However, little is known about the underlying molecular mechanism of desiccation sensitivity of Q. variabilis seeds. In this study, the seeds were desiccated with silica gel for certain days as different treatments from 0 (Control) to 15 days (T15) with a gradient of 1 day. According to the seed germination percentage, four key stages (Control, T2, T4, and T11) were found. Then the transcriptomic profiles of these four stages were compared. A total of 4,405, 4,441, and 5,907 differentially expressed genes (DEGs) were identified in T2 vs. Control, T4 vs. Control, and T11 vs. Control, respectively. Among them, 2,219 DEGs were overlapped in the three comparison groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that these DEGs were enriched into 124 pathways, such as “Plant hormone signal transduction” and “Glycerophospholipid metabolism”. DEGs related to hormone biosynthesis and signal transduction (ZEP, YUC, PYR, ABI5, ERF1B, etc.), stress response proteins (LEA D-29, HSP70, etc.), and phospholipase D (PLD1) were detected during desiccation. These genes and their interactions may determine the desiccation sensitivity of seeds. In addition, group specific DEGs were also identified in T2 vs. Control (PP2C62, UNE12, etc.), T4 vs. Control (WRKY1-like, WAK10, etc.), and T11 vs. Control (IBH1, bZIP44, etc.), respectively. Finally, a possible work model was proposed to show the molecular regulation mechanism of desiccation sensitivity in Q. variabilis seeds. This is the first report on the molecular regulation mechanism of desiccation sensitivity of Q. variabilis seeds using RNA-Seq. The findings could make a great contribution to seed storage and long-term conservation of recalcitrant seeds in the future.

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.