Intermediate Physiological Dormancy Research Articles

Seed Dormancy Class and Germination Characteristics of Berberis amurensis var. latifolia Nakai, Native to Korea

Berberis amurensis var. latifolia Nakai is a plant native to the Ulleung Island in Korea. In this study, we aimed to identify seed dormancy-breaking and germination requirements of this species using water imbibition experiments, gibberellic acid (GA3) treatment (0, 10, 100, or 1000 mg/L), cold stratification (0, 2, 4, 8, or 12 weeks at 5 °C), move-along experiments, and phenological studies. In the water imbibition experiment, the seed weight increased by more than 120% after 24 h. Analysis of the internal morphological characteristics of the seeds revealed that the embryo in freshly matured seeds was fully grown and did not grow thereafter. The final germination percentages after 12 weeks of cold stratification at 5 °C were 49 ± 6.4% and 63 ± 3.4% under light and dark conditions, respectively. In move-along and phenological studies, a longer cold stratification treatment period resulted in a higher germination percentage; however, the warm stratification treatment did not affect germination significantly. The GA3 treatment had little effect on seed germination. Therefore, we concluded that B. amurensis var. latifolia seeds have intermediate physiological dormancy, and pre-treatment with cold stratification for 12 weeks and incubation in the dark are required for effective seed propagation.

Seed Dormancy Class and Germination Characteristics of Prunus spachiana (Lavallée ex Ed.Otto) Kitam. f. ascendens (Makino) Kitam Native to the Korean Peninsula.

Prunus spachiana (Lavallée ex Ed.Otto) Kitam. f. ascendens (Makino) Kitam leaves exert natural anti-inflammatory effects by inhibiting nitric oxide formation. P. spachiana flowers bloom earlier than other Prunus spp. and thus could serve as a valuable resource for the horticulture and pharmaceutical industries. However, its seed dormancy class and germination traits remain uncharacterized. Thus, this study aimed to characterize the seed dormancy and germination of P. spachiana. Imbibition, phenological, and move-along experiments were performed, and the effects of H2SO4 treatment, hormone soaking, warm/cold stratification, and endocarp removal on germination were explored. Observation revealed that ripe seeds of P. spachiana contain developed embryos and are water permeable. Radicle and shoot emergence began in March and April, respectively, under natural conditions in the year following production. No seed germination was observed after 30 days of incubation at 4, 15/6, 20/10, or 25/15 °C under light/dark conditions, indicating the physiological dormancy of the seeds. Germination increased with prolonged stratification and was affected by incubation temperature. Seed scarification by H2SO4 and soaking with gibberellic acid (GA3) and fluridone were ineffective in breaking dormancy. However, GA3 soaking of the seeds after endocarp removal effectively induced germination (100%). These results indicate that P. spachiana seeds exhibit intermediate physiological dormancy.

Effects of Pre-Treatments on Seed Dormancy and Germination of Endemic Muscari bourgaei Baker

M. bourgaei Baker is an endemic plant that grows in Türkiye. It has the potential to be an ornamental plant, so it is important to know its germination characteristics and seed morphological characteristics. We evaluated the effects of moist chilling (3 to 12 months) and application of gibberellic acid (GA3) (250 to 1000 mg/L−1) on seed germination under two different light regimes (light phase and dark phase) and four temperature regimes (20, 20/10, 25/15, and 15/10 °C). Seeds were collected from the subalpine belt of Mount Uludağ at an altitude between 2200 and 2300 m. M. bourgaei seeds were dormant and reached the highest germination percentage after 12 months of moist chilling. GA3 applications only have a limited effect on the breaking of dormancy in most cases. Maximum germination of 28 percent was obtained by the GA3 application of 1000 mg/L under dark phase with incubation at 15/10 °C. Scarification with sulfuric acid did not result in any germination. Seed germination of above 80 percent was obtained after 6 months of moist chilling and above 90 percent after 9 and 12 months of moist chilling. Intermediate physiological dormancy was determined as the type of dormancy. Our findings on seed germination and dormancy characteristics of M. bourgaei, which is an endemic alpine meadow plant, will contribute to the protection and development of the germplasm of this species.

Seed dormancy break and germination by a rare relict of the Würmian glaciation in the Iberian Peninsula: Euonymus latifolius (Celastraceae)

AbstractSouthern European peninsulas have repeatedly played notable roles as refuges in the natural history of flora during periods of glaciation. Euonymus latifolius (Celastraceae) is a relict species from the last Würmian glaciation in the Iberian Peninsula. It still lives with isolated populations in favourable, cool mountainous microhabitats, being an extremely rare, critically endangered species. These Iberian populations are often high-priority targets for conservation due to their long-term persistence and unique evolutionary trajectory. Previously, it has not been feasible to promote significant programmes for reintroduction and/or population reinforcement of this singular plant species due to the great difficulties of conventional propagation. In this study, we analysed the effects of temperature, light and gibberellic acid (GA3) on the germination responses of E. latifolius to develop an effective protocol for seed germination as a main outcome. The results are coherent with the climatic temperature conditions recorded broadly in the Iberian Peninsula in the past and in the current refuge locations for the taxon. The germination responses of E. latifolius are compatible with those of seeds with intermediate physiological dormancy. In particular, the seeds required a 10-week warm period (20/7°C + 15/4°C) followed by 20 weeks of cold period (5 + 1.5°C) to break dormancy and achieve germination values over 90%. GA3 also promoted germination (80%). Therefore, we developed the first effective protocol for promoting E. latifolius seed germination and, thus, sexual propagation, to facilitate urgent ex situ actions in the current climate change context.

Physiological dormancy and dormancy release of Sassafras tzumu, a colored-leaf tree species with high landscape and economic value

Sassafras tzumu is one of the most valuable tree species in southern China. However, the dormancy of the seed limits its seedling quality. In order to improve the germination percentage of seeds, characteristics, causes of dormancy, changes in endogenous hormones and nutrients during storage were investigated. The results showed that seed viability was 78.11%, and the highest water absorption rate was 26.09%. The germination percentage of the embryo without cotyledon was 21.13%, but intact seed and embryo could not germinate on hormone-free medium. Seed embryo and coat extracts were found to have a significant inhibitory effect on seed germination. Germination percentage were significantly positively correlated to free amino content (p < 0.01) and negatively correlated to soluble sugar content (p < 0.05) during storage. The levels of GA3 and GA3/ABA had significant effects on the germination percentage of S. tzumu seed storage at 4°C. The results suggest that S. tzumu seeds are in intermediate physiological dormancy at maturity and are mainly caused by the presence of inhibitory substances in the seed tissues. Furthermore, changes in endogenous hormones and metabolism of nutrients at 4°C can significantly promote the release from dormancy of S. tzumu seeds.

Exogenous gibberellin can effectively and rapidly break intermediate physiological dormancy of Amsonia elliptica seeds.

Accelerated global warming is leading to the loss of plant species diversity, and ex situ preservation of seeds is becoming an increasingly important aspect of species conservation. However, information on dormancy and germination is lacking in many endangered species. Amsonia elliptica (Apocynaceae) is the only Amsonia species native to Korea, and the South Korean Ministry of Environment has designated it Class II endangered wildlife. Nevertheless, the dormancy class and the dormancy breaking method for seeds of this species for germination are not precisely known. We identified the structure of A. elliptica seeds and the causes of dormancy, which inhibits germination. In addition, we tried to develop an effective germination promotion method by testing the wet stratified condition, which breaks dormancy, and the form of gibberellin that can replace it. Fresh seeds of A. elliptica imbibe water, but the covering layers (endosperm and seed coat) inhibit germination by mechanically restricting the embryo. Initial germination tests confirmed low embryo growth potential and physiological dormancy (PD). Restriction due to the covering layer was eliminated by seed scarification, and abnormal germination was observed. After 12 weeks of cold moist stratification at 4°C, only 12% of seeds germinated. However, 68.8% of seeds subjected to 8 weeks of warm moist stratification followed by 12 weeks of cold stratification germinated, indicating that warm stratification pretreatment before cold stratification is effective in breaking dormancy. A. elliptica seeds exhibited intermediate PD. Furthermore, 61.3% of seeds soaked in 500 mg/L GA4+7 for 14 days and incubated at 25/15°C germinated. Therefore, GA4+7 rapidly broke the dormancy of A. elliptica seeds compared with warm plus cold stratification treatment, thus providing an efficient method for seedling production.

Mimicking the natural thermal environments experienced by seeds to break physiological dormancy to enhance seed testing and seedling production

Physiological dormancy (PD) is the most common class of seed dormancy on earth. It is highly variable and is an important part of the adaptation of many species to their habitat. Often, two questions are asked about seeds that failed to germinate in a germination test: (1) are they non-viable or dormant, and (2) if dormant do they have PD and how is it broken? We provide an overview on how to approach studies of species with PD for which few or no data are available. Information about habitat environmental conditions during the seed stage can be used to formulate hypotheses on dormancy-breaking and germination requirements. These hypotheses can be tested by a move-along experiment. There are three levels of PD, and they are distinguished by the conditions required to break PD and promote germination. Seeds with non-deep PD (the most common level of PD) require different conditions for dormancy-break and germination, i.e.a change in the season, while those with intermediate and deep PD germinate at the dormancy-breaking conditions, e.g.during a long period of cold stratification. Knowing how to break PD enhances testing for seed viability and helps ensure high germination percentages of viable seeds.

Intermediate Physiological Dormancy in Seeds of Prunus maackii Native to Korea

Intermediate Physiological Dormancy in Seeds of Prunus maackii Native to Korea

Germination biology of dimorphic seeds of the annual halophyte common seepweed (Suaeda glauca)

AbstractCommon seepweed [Suaeda glauca (Bunge) Bunge] is a common salt-tolerant weed species distributed across the agricultural regions of northern China. It produces dimorphic seeds with different phenotypic characteristics and seed sizes. However, there is no information regarding the germination biology of these dimorphic seeds. Studies were conducted to evaluate the effects of ecological factors such as temperature, light, pH, osmotic stress, salt concentration, and planting depth on seed germination and seedling emergence. The results showed that brown seeds were nondormant, whereas black seeds had an intermediate physiological dormancy. The germination percentage of brown seeds was more than 80% at all temperature regimes and light conditions, but the optimum germination occurred at the cold thermoperiod of 20/10 C. In contrast, less than 6% of black seeds germinated at all temperature regimes and light conditions. Eight weeks of cold stratification did not break the dormancy of black seeds, whereas low concentrations of gibberellic acid (0.1 and 1.0 mM) significantly increased seed germination. Removal of the testa of black seeds also promoted germination and produced normal seedlings. Brown seeds showed moderate tolerance to salt stress, with 16% germination percentage at a salt concentration of 600 mM NaCl. The germination of brown seeds was 38% at an osmotic potential stress of −0.8 MPa; above that, no germination was obtained. Brown seeds germinated well in a wide pH range (4 to 10), with a germination percentage higher than 95%. Seedling emergence percentage was higher than 90% at burial depths of 0 to 2 cm, while germination percentage severely decreased for brown seeds with burial depths &gt;2 cm, indicating that shallow tillage could be an effective measure to minimize seed germination. Information gathered from this study will help to develop an effective protocols for controlling S. glauca.

Seed germination of woody and shrubby introduced species

The article presents the research results of seed germination of woody and shrubby introduced species. Depending on the depth of dormancy, the studied plant species were divided into 3 groups. The first group includes plants with the absence of dormancy or with a short dormancy; the seeds of these species do not need stratification. The second group includes plants whose seeds are in a state of a rather long intermediate physiological dormancy; they need cold stratification. The organic dormancy period of plant seeds of the second group is different – from 25 to 160 days. As a rule, these are plants with a well-formed seed bud. The physiological dormancy of the seed bud and the inhibitory effect of its covers can be an obstacle to its formation. The third group includes plants whose seeds may not germinate for several years. As a rule, the seeds of these plants are in a state of a deep physiological or morphophysiological dormancy; multi-stage stratification is recommended for their germination. The introduced species of the third group are the most difficult to study since their seeds can belong to different variants of deep dormancy, which combines the physiological immaturity of different structures of the seed bud with the incomplete morphological maturity and exogenous dormancy.

Torrid Panicgrass Dormancy Relief Through Exogenous Chemical Treatments and Seed Storage Optimization of Temperature and Relative Humidity Parameters

Seed dormancy is an evolutionary adaptation for increasing seedling survival by delaying germination and is found in many families of seed plants. Although dormancy is ecologically important, it becomes problematic during agronomic production and restoration. Torrid panicgrass (Panicum torridum) is a native Hawaiian annual grass that has been identified as a re-vegetation candidate for seasonally dry areas. Torrid panicgrass seed appears to possess a nondeep to intermediate physiological dormancy. This research aimed to characterize dormancy relief parameters by 1) evaluating exogenous hormonal, reactive oxygen intermediates, and simulated combustion product treatments; and 2) determining optimized storage conditions of relative humidity (RH) and temperature over a 10-month duration. Results indicate that all exogenous chemical treatments tested were not effective at relieving the dormancy present in torrid panicgrass. Optimal storage conditions to relieve dormancy were found with seeds equilibrated to 12% RH, stored at 30 °C for a period of 8 months resulting in 55% germination. Maintenance of viability for long-term storage up to 10 months was best achieved with seeds stored at 12% RH at 10, 20, or 30 °C.

Proteomic analysis of Zanthoxylum nitidum seeds dormancy release: Influence of stratification and gibberellin

Zanthoxylum nitidum (Roxb.) DC. is one of the most important economic crops on account of its value as a Chinese herbal medicine (Zanthoxyli radix), health product and daily chemical raw materials. Zanthoxylum nitidum seeds are characterized to be an intermediate physiological dormancy that requires three months of cold stratification (4 °C) or gibberellin (GA) treatment (300 mg L−1, soaking for two days) to relieve seed dormancy and promote germination. Exploring the changes of proteins and related biosynthetic and metabolic pathways during seed dormancy release will contribute to expand our knowledge of this process. In this study, mature Zanthoxylum nitidum seeds from Pingyuan County, Guangdong province were treated with cold stratification and GA solution. The differently expressed proteins after treatments were characterized by iTRAQ coupled LC–MS/MS. In total, 484 proteins showed that at least 1.3-fold differences in abundance were detected after treatments; a majority of the differently abundant proteins are involved in the respiration-related metabolism processes, biosynthesis of amino acids and translation during the dormancy release of Zanthoxylum nitidum seeds. This study is the first to use the iTRAQ-based proteomics approach to analyse the proteome of Zanthoxylum nitidum seeds, pointing out the direction for our further research on the pathways and even the key genes and proteins associated with the dormancy release of Zanthoxylum nitidum seeds.

Seed germination requirements of Buck’s beard [Aruncus dioicus (Walter) Fernald (Rosaceae)

Aruncus dioicus (Walter) Fernald (Rosaceae) is a perennial herbaceous plant whose young shoots are traditionally collected in the wild and consumed as a food in NE Italy. The aim of this study was to determine the germination requirements of its seeds in order to start its cultivation, and to assess the germination of six accessions of the species. Viability of seeds ranged from 86 to 97% in the various accessions. Germination rate was almost null in seeds of two accessions, and ranged from 10.5 to 37.3 in the other ones. The seed coat was permeable to water. Treatments with GA3, KNO3 and mechanical scarification did not enhance the germination, while the cold stratification treatment at 2 °C for different periods improved the germination rate and the mean germination time as compared with the untreated seeds. With 45 days of cold stratification, the germination rate and mean germination time (respectively, 90.1% and 7.7 dd) of seeds were different from those of the untreated seeds. Cold stratified seeds germinated under artificial light and did not germinate in the dark. Seeds of A. dioicus displayed an intermediate physiological dormancy, removable by a cold stratification treatment, requiring both light and cold conditions.

Chemical Applications, Scarification and Stratification Effects on Seed Germination of Rare Endemic Verbascum calycosum Hausskn. ex Murb. (Scrophulariaceae)

Verbascum calycosum is an endemic plant species having considerable narrow distribution in Erzincan (Turkey) region. This species is known from only a single population and its habitats are highly threatened due to intensive human activities and soil erosion. In this study, the germination behavior of V. calycosum under different concentrations of NaCl, HCl, KNO3, GA3 (100 and 200 μM), hot-cold stratification and mechanical scarification were investigated. Seeds were exposed to a photoperiod of 8 h light/16 h dark with a 23/18 °C thermoperiod. Germination rates increased with GA3-100 µM (39%), GA3-200 µM (54.5%), mechanical scarification (34.5%) and cold stratification treatments (+4 °C, 23.25%; -20 °C, 18.25%) on the other hand, KNO3, NaCl, HCl and stratification with hot water treatments have decreased germination rates significantly when compared to the control (12.25%). Increased germination after GA3 application and mechanical scarification indicated that seeds of V. calycosum exhibited both non-deep and intermediate physiological dormancy as well as physical dormancy due to its hard seed coat. The highest speed of germination index was obtained at cold stratification of +4 °C and -20 °C (10.3). This study represents first report about seed dormancy and germination characteristics of V. calycosum. Overall, these results will provide valuable data for ex situ conservation of this rare endemic plant.

Effect of Seed Position on Parental Plant on Proportion of Seeds Produced with Nondeep and Intermediate Physiological Dormancy.

The position in which seeds develop on the parental plant can have an effect on dormancy-break and germination. We tested the hypothesis that the proportion of seeds with intermediate physiological dormancy (PD) produced in the proximal position on a raceme of Isatis violascens plants is higher than that produced in the distal position, and further that this difference is related to temperature during seed development. Plants were watered at 3-day intervals, and silicles and seeds from the proximal (early) and distal (late) positions of racemes on the same plants were collected separately and tested for germination. After 0 and 6 months dry storage at room temperature (afterripening), silicles and seeds were cold stratified for 0–16 weeks and tested for germination. Mean daily maximum and minimum temperatures during development/maturation of the two groups of seeds did not differ. A higher proportion of seeds with the intermediate level than with the nondeep level of PD was produced by silicles in the proximal position than by those in the distal position, while the proportion of seeds with nondeep PD was higher in the distal than in the proximal position of the raceme. The differences were not due only to seed mass. Since temperature and soil moisture conditions were the same during development of the seeds in the raceme, differences in proportion of seeds with intermediate and nondeep PD are attributed to position on parental plant. The ecological consequence of this phenomenon is that it ensures diversity in dormancy-breaking and germination characteristics within a seed cohort, a probable bet-hedging strategy. This is the first demonstration of position effects on level of PD in the offspring.

Seed dormancy in Camellia sinensis L. (Theaceae): effects of cold-stratification and exogenous gibberellic acid application on germination

There are several different opinions regarding dormancy in tea (Camellia sinensis L.), but there is no strong evidence available to conclude whether or not these seeds are dormant. Freshly matured tea seeds collected from Hangzhou, China, at the natural dispersal time did not germinate in light at daily alternative temperature regimes of 10/15, 15/20, 20/25, or 25/35 °C, or at a constant temperature of 25 °C. Seeds were permeable to water and the embryos did not grow prior to radicle emergence, thus, the seeds have no physical, morphological, or morphophysiological dormancy. When cold-stratified at 4 °C for 1, 2, and 3 months, 64%, 88%, and 93% of the seeds germinated, respectively. Intact fresh seeds failed to germinate after treatment with 0, 10, 500, and 1000 ppm GA3, whereas 3%, 4%, 61%, and 86% of cracked seeds germinated, respectively. Thus, the seeds have nondeep and intermediate physiological dormancy. Seeds cold-stratified for 2 months that were buried at soil depths of 0, 1, and 5 cm in pots showed that seeds at 1 cm depth established significantly higher number of seedlings (P &lt; 0.05) than at other two depths. Because tea seeds are susceptible to summer temperature drying, these seeds do not establish a persistent seed bank.

Classification of seed dormancy and treatment of gibberellic acid to improve germination of arrowleaf balsamroot

With its perennial showy flower, soil-stabilizing taproot, and energy-rich winter foliage, arrowleaf balsamroot ( Balsamorhiza sagittata (Pursh) Nutt. [Asteraceae]) has several traits that lend it to ornamental and conservation applications, if it can be propagated successfully and cost efficiently. Percent germination remains low, however, because of its unknown seed dormancy classification and dormancy-release mechanism. Based on a series of germination tests, seeds exhibit nondeep physiological dormancy, type 2; intermediate physiological dormancy, type 2; and deep physiological dormancy, types 1 and 3 according to the Baskin and Baskin (2004) classification. In the Schwienbacher and others (2011) reclassification, seeds exhibit the class and level, physiological deep dormancy. Gibberellic acid (GA3) followed by cold-moist incubation at 5°C (41 °F) significantly increased percent final germination, with a maximum final germination of 81 ±2%.

Proteome changes associated with dormancy release of Dongxiang wild rice seeds

Seed dormancy provides optimum timing for seed germination and subsequent seedling growth, but the mechanism of seed dormancy is still poorly understood. Here, we used Dongxiang wild rice (DXWR) seeds to investigate the dormancy behavior and the differentially changed proteome in embryo and endosperm during dormancy release. DXWR seed dormancy was caused by interaction of embryo and its surrounding structure, and was an intermediate physiological dormancy. During seed dormancy release, a total of 109 and 97 protein spots showed significant change in abundance and were successfully identified in embryo and endosperm, respectively. As a result of dormancy release, the abundance of nine proteins involved in storage protein, cell defense and rescue and energy changed in the same way in both embryo and endosperm, while 67 and 49 protein spots changed differentially in embryo and endosperm, respectively. Dormancy release of DXWR seeds was closely associated with degradation of storage proteins in both embryo and endosperm. At the same time, the abundance of proteins involved in metabolism, glycolysis and TCA cycle, cell growth and division, protein synthesis and destination and signal transduction increased in embryos while staying constant or decreasing in endosperms.

Effects of germination season on life history traits and on transgenerational plasticity in seed dormancy in a cold desert annual.

The maternal environment can influence the intensity of seed dormancy and thus seasonal germination timing and post-germination life history traits. We tested the hypotheses that germination season influences phenotypic expression of post-germination life history traits in the cold desert annual Isatis violascens and that plants from autumn- and spring-germinating seeds produce different proportions of seeds with nondeep and intermediate physiological dormancy (PD). Seeds were sown in summer and flexibility in various life history traits determined for plants that germinated in autumn and in spring. A higher percentage of spring- than of autumn-germinating plants survived the seedling stage, and all surviving plants reproduced. Number of silicles increased with plant size (autumn- > spring-germinating plants), whereas percent dry mass allocated to reproduction was higher in spring- than in autumn-germinating plants. Autumn-germinating plants produced proportionally more seeds with intermediate PD than spring-germinating plants, while spring-germinating plants produced proportionally more seeds with nondeep PD than autumn-germinating plants. Flexibility throughout the life history and transgenerational plasticity in seed dormancy are adaptations of I. violascens to its desert habitat. Our study is the first to demonstrate that autumn- and spring-germinating plants in a species population differ in proportion of seeds produced with different levels of PD.

Seed Germination Ecology of the Cold Desert Annual Isatis violascens (Brassicaceae): Two Levels of Physiological Dormancy and Role of the Pericarp

The occurrence of various species of Brassicaceae with indehiscent fruits in the cold deserts of NW China suggests that there are adaptive advantages of this trait. We hypothesized that the pericarp of the single-seeded silicles of Isatis violascens restricts embryo expansion and thus prevents germination for 1 or more years. Thus, our aim was to investigate the role of the pericarp in seed dormancy and germination of this species. The effects of afterripening, treatment with gibberellic acid (GA3) and cold stratification on seed dormancy-break were tested using intact silicles and isolated seeds, and germination phenology was monitored in an experimental garden. The pericarp has a role in mechanically inhibiting germination of fresh seeds and promotes germination of nondormant seeds, but it does not facilitate formation of a persistent seed bank. Seeds in silicles in watered soil began to germinate earlier in autumn and germinated to higher percentages than isolated seeds. Sixty-two percent of seeds in the buried silicles germinated by the end of the first spring, and only 3% remained nongerminated and viable. Twenty to twenty-five percent of the seeds have nondeep physiological dormancy (PD) and 75–80% intermediate PD. Seeds with nondeep PD afterripen in summer and germinate inside the silicles in autumn if the soil is moist. Afterripening during summer significantly decreased the amount of cold stratification required to break intermediate PD. The presence of both nondeep and intermediate PD in the seed cohort may be a bet-hedging strategy.