Simple Morphophysiological Dormancy Research Articles

Conservation implications of seed germination studies of Aquilegia fragrans Benth.: A native and endangered medicinal plant species of Kashmir Himalaya

Insufficient investigation of seed germination studies of threatened plant species creates practical obstacles to their conservation efforts. Here, we investigate the seed germination of Aquilegia fragrans Benth.-an endangered medicinal plant species native to Himalaya. The effects of stratification conditions including time (10, 20, 30, and 40 days), temperature (−4, −10, and −20 °C), and hormone treatments (250 ppm GA3, 30 ppm BAP, and 30 ppm Zeatin) on germination of A. fragrans seeds collected from the alpine belt of Kashmir Himalaya were examined. Seeds of species exhibited non-deep simple morphophysiological dormancy (MPD). Seed germination showed significant differences among the various treatments. It was observed that the application of GA3, zeatin, and BAP significantly improved seed germination as compared with the control. The highest germination percentage (73 ± 1 %) along with maximum germination index (1.05 ± 0.05) was recorded in T30 (Seeds stratified for 30 days at −10 °C and treatment with Zeatin 30 ppm) followed by T19 (seeds stratified at −10 °C for 20 days and treatment with zeatin 30 ppm). The seed germination studies of A. fragrans have not been carried out before, and the information gathered in the present study may prove useful for the conservation of the target plant species. The present study will help in the conservation, sustainable development, and restoration of this prized medicinal plant species.

Seed dormancy, viability and germination of Illicium griffithii: A threatened medicinal plant of northeast India

Illicium griffithii Hook. f. & Thoms. is a threatened medicinal plant of North East India with low natural population. Field observation showed that the seeds remain dormant for 4–5 months and even after germination it fails to convert into saplings due to biotic interference. In the present study, various physical and chemical tests were conducted to overcome dormancy. The study revealed that the seeds of I. griffithii exhibited simple morpho-physiological dormancy reducing the germination percentage. Chemical scarification with 95 % H2SO4 for 5 min helped to overcome mechanical restriction of the endosperm and seed coat and resulted in high germination (80.5 %). Pre-treatment of the seeds with cold stratification for 60 days or application of gibberellic acid (GA3: 2000 mgl−1) effectively broke seed dormancy. Seeds stored at 5 °C (in moist sand) exhibited a minimum viability of 40 %, but all seeds stored dry at room temperatures and moist at 25 °C died. This study on seed germination would be helpful for mass multiplication of the species for reintroduction programmes including ex situ conservation that would aid in improving the subsistence economy of the local indigenous communities.

Seed Dormancy and Germination Requirements of Torilis scabra (Apiaceae)

The timing of seed germination significantly affects the fitness and life cycle of plants. Torilis scabra is a perennial medicinal herb occurring in mixed forests but the increasing use and modification of forestlands in recent decades has led to the degeneration of its natural habitat. Nonetheless, the requirements for germination in T. scabra remain unclear. The present study focused on identifying conditions necessary to break T. scabra seed dormancy and describing its seed dormancy type. By periodically collecting seeds that were sown in the field, germination phenology was studied. The impact of light, temperature, and warm/cold stratification on breaking seed dormancy and promoting germination was also determined through incubating seeds in laboratory conditions. Additionally, the effect of GA3 was explored to more accurately identify the type of dormancy present. The results demonstrated that the seeds of T. scabra possessed small, undeveloped embryos with physiological dormancy at the time of maturity. In the field, embryo growth initiated in early spring and the embryo–seed length ratio increased by ~300% before the radical emerged. In the laboratory, the embryo–seed length ratio increased from 0.24 to 0.82 when seeds were subjected to cold stratification at 4 °C and then transferred to 15/25 °C. Germination was observed across a broad temperature range after cold stratification. GA3 also helped to break dormancy but after-ripening did not. Taken together, the results suggest that seeds of T. scabra have non-deep simple morphophysiological dormancy.

Non-deep simple and deep simple morphophysiological dormancy in seeds of three species of Ilex from subtropical and tropical regions of Taiwan

AbstractDormancy-breaking requirements and level of morphophysiological dormancy (MPD) were determined for seeds of Ilex formosana and I. uraiensis from the subtropical region, and seeds of I. rotunda from both the subtropical and tropical regions of Taiwan. We hypothesized that some Ilex species would have deep simple MPD broken by warm stratification. Germination of seeds and embryo growth was monitored at 30/20, 25/15, 20/10, 15/5°C and at 25°C. Seeds were cold-stratified and then incubated at 25/15°C, and seeds treated with GA3 and GA4 were incubated at 25/15°C. Fresh seeds reached 50% germination after 11–45 weeks of warm stratification. Pre-treatment with GA increased germination percentages of I. formosana and I. rotunda (tropical) but not I. uraiensis and I. rotunda (subtropical), while cold stratification did not promote germination of either species but increased the germination rate of I. rotunda (tropical). Embryo length in seeds of all species increased ≥710% prior to root emergence, and growth occurred during warm stratification. The positive response to GA and relatively short time for beginning of germination and to reach 50% germination indicate non-deep simple MPD in seeds of I. formosana and I. rotunda (tropical). The negative response to GA and long time for beginning of germination and to reach 50% germination indicate deep simple MPD in seeds of I. uraiensis and I. rotunda (subtropical). Thus, in both the subtropical and tropical regions of Taiwan, the seeds of Ilex species have non-deep simple and deep simple MPD that are broken by warm stratification. Furthermore, GA treatment increases the germination rate and percentage of Ilex seeds with non-deep simple MPD, and cold stratification promotes the seed germination rate of Ilex species with non-deep simple MPD in tropical region.

Embryo maturation, dormancy and seed storage behaviour of Gymnacranthera canarica (King) Warb., a threatened endemic tree species of Southern Western Ghats

Gymnacranthera canarica is a severely endangered endemic tree species found in the Myristica swamps of the Southern Western Ghats. Seed storage behaviour is an essential factor to consider when developing effective conservation methods for plant genetic resources whose ex-situ preservation is unclear. The seed storage behaviour, seed dormancy state, dormancy breaking treatments, germination, and phytohormonal analysis of G. canarica were explored in this work. G. canarica seed moisture at shedding was 28.86%, germinated to 34% at 25ºC, and had a low germination rate in natural conditions. Germination was considerably aided by Gibberellic acid pretreatment and drying stratification. G. canarica seeds may have non-deep simple morphophysiological dormancy, as evidenced by the fact that their embryos grew at temperatures between 20 and 25ºC (MPD). Seeds can be stored for up to 60 days at 20ºC after being desiccated to 19.37% suggest that G. canarica seeds are recalcitrant, with non-deep simple morphophysiological dormancy, and that seed pretreatment with Gibberellic acid prior to germination could be a viable approach for mass propagation and long term ex-situ conservation could be the potential storage of this critically endangered species.

Seed germination ecology of common bladderwort (Utricularia vulgaris L.)

Generative reproduction of the carnivorous aquatic plant Utricularia vulgaris (Lentibulariaceae) from seeds may be a critical process in the recovery of natural populations following temporary drying of habitat, and in the colonisation of new potential sites through dispersal of seeds by water birds. However, little is presently known about the seed ecology and germination biology of this species. We tested the germination response of seeds under various temperature and seed storage regimes, to examine the processes required for seed dormancy alleviation and the effects of different germination solution and temperature on germination probability. Seeds likely possess non-deep simple morphophysiological dormancy alleviated by warm stratification. Highest germination success was recorded for warm-stratified seeds and seeds exposed to ethylene. Seeds were photophilous, with germination more successful at 21 °C than at 25 °C and greatest in slightly alkaline (pH 8) germination solution containing KHCO3, CaCl2 and MgSO4 mimicking the mesotrophic humic waters in which the species naturally occurs. In the alkaline solution, 97 % of seeds rose to the surface prior to germination. In natural habitats, this effect may facilitate seedlings reaching the warmer and irradiated water surface. As seed germination success appears linked to light availability, water chemistry, and seed position in the water column, careful management and ecological restoration of remnant habitats harbouring this species may need to ensure positive conservation outcomes.

The great diversity in kinds of seed dormancy: a revision of the Nikolaeva–Baskin classification system for primary seed dormancy

AbstractThis review provides a revised and expanded word-formula system of whole-seed primary dormancy classification that integrates the scheme of Nikolaeva with that of Baskin and Baskin. Notable changes include the following. (1) The number of named tiers (layers) in the classification hierarchy is increased from three to seven. (2) Formulae are provided for the known kinds of dormancy. (3) Seven subclasses of class morphological dormancy are designated: ‘dust seeds’ of mycoheterotrophs, holoparasites and autotrophs; diaspores of palms; and seeds with cryptogeal germination are new to the system. (4) Level non-deep physiological dormancy (PD) has been divided into two sublevels, each containing three types, and Type 6 is new to the system. (5) Subclass epicotyl PD with two levels, each with three types, has been added to class PD. (6) Level deep (regular) PD is divided into two types. (7) The simple and complex levels of class morphophysiological dormancy (MPD) have been expanded to 12 subclasses, 24 levels and 16 types. (8) Level non-deep simple epicotyl MPD with four types is added to the system. (9) Level deep simple regular epicotyl MPD is divided into four types. (10) Level deep simple double MPD is divided into two types. (11) Seeds with a water-impermeable seed coat in which the embryo-haustorium grows after germination (Canna) has been added to the class combinational dormancy. The hierarchical division of primary seed dormancy into many distinct categories highlights its great diversity and complexity at the whole-seed level, which can be expressed most accurately by dormancy formulae.

Non-Deep Simple Morphophysiological Dormancy and Germination Characteristics of Gentiana triflora var. japonica (Kusn.) H. Hara (Gentianaceae), a Rare Perennial Herb in Korea

This study investigated the kind of seed dormancy and seed germination of Gentiana triflora var. japonica (Kusn.) H. Hara for developing a seed propagation method. The seeds were collected in October 2020 from plants at Mt. Sobaeksan, Korea. In a water imbibition experiment, seed weights increased by >101.9% of their initial masses over 12 h. Effects of incubation temperature (5, 15, 20, 25, 15/6, or 25/15 °C), cold stratification period (5 °C; 0, 4, 8, or 12 weeks), and gibberellic acid (GA3; 0, 10, 100, or 1000 mg∙L−1) and potassium nitrate treatment (KNO3; 0, 1000, 2000, or 4000 mg∙L−1) on seed germination were investigated to characterize seed dormancy. These seeds exhibited underdeveloped embryos during seed dispersal. The seeds failed to reach the final germination of 15.0% after treatment at 5, 15, 20, 25, 15/6, or 25/15 °C. After cold stratification for 8 weeks, the germination increased dramatically by >90.0% compared to that at 0 weeks. After the GA3 treatment, the germination reached >80.0% within 5 days. The final germination was 90.0% in the 100 mg∙L−1 GA3 treatment group. However, the KNO3 treatment had no effect on seed germination. Therefore, the G. triflora var. japonica seeds exhibited non-deep simple morphophysiological dormancy.

Seed dormancy, germination and storage behavior of Magnolia sinica, a plant species with extremely small populations of Magnoliaceae

Magnolia sinica is one of the most endangered Magnoliaceae species in China. Seed biology information concerning its long-term ex situ conservation and utilization is insufficient. This study investigated dormancy status, germination requirements and storage behavior of M. sinica. Freshly matured seeds germinated to ca. 86.5% at 25/15 °C but poorly at 30 °C; GA3 and moist chilling promoted germination significantly at 20 °C. Embryos grew at temperatures (alternating or constant) between 20 °C and 25 °C, but not at 5 °C or 30 °C. Our results indicate that M. sinica seeds possibly have non-deep simple morphophysiological dormancy (MPD). Seeds survived desiccation to 9.27% and 4.85% moisture content (MC) as well as a further 6-month storage at −20 °C and in liquid nitrogen, including recovery in vitro as excised embryos. The established protocol ensured that at least 58% of seedlings were obtained after both cold storage and cryopreservation. These results indicate that both conventional seed banking and cryopreservation have potential as long-term ex situ conservation methods, although further optimized approaches are recommended for this critically endangered magnolia species.

Dormancy cycles in Aquilegia oxysepala Trautv. et Mey. (Ranunculaceae), a species with non-deep simple morphophysiological dormancy

Seed dormancy and the formation of a soil seed bank is important plant regeneration strategies, especially if the environment is unpredictable. The present research explores how environmental factors control seed dormancy release, and how seed dormancy is related to the soil seed bank and regeneration of the perennial Aquilegia oxysepala. The effects of incubation temperature, light, cold and warm stratification, gibberellic acid (GA3) along with the germination phenology of A. oxysepala in the field were used to determine the type of seed dormancy. Seasonal change of seed dormancy was determined by regularly exhuming buried seeds and incubating them in laboratory conditions. A. oxysepala seeds has underdeveloped (small) embryos along with physiological dormancy at dispersal. With the increased amounts of cold stratification, the germination of A. oxysepala increased gradually. GA3 served as a substitute for cold stratification. Breaking of physiological dormancy under natural temperatures in the field occurred in winter, while growth of embryos and germination of seeds occurred in early spring. Viable seeds that had not germinated in early spring were induced into secondary dormancy by high soil temperatures. A. oxysepala provides one of a few examples of dormancy cycling in seeds with morphophysiological dormancy. Freshly matured seeds of A. oxysepala seeds have non-deep simple morphophysiological dormancy. The annual dormancy–non-dormancy cycle maintains the coordination between timing of seedling emergence with favorable seasons, thus increasing the survival chances of seedlings in environments with seasonal changes.

Dormancy-breaking and germination requirements of Thalictrum squarrosum Stephan ex Willd. seeds with underdeveloped embryos

The timing of seed germination has a significant effect on the life cycles and fitness of plants. Thalictrum squarrosum is a perennial herb with medical and ornamental value. However, the dormancy type and the regeneration strategy it uses to adapt to the natural habitat have yet to be investigated. The present study determined the seed germination requirements of T. squarrosum seeds and characterized the type of seed dormancy observed in this species. The results indicate that seeds of T. squarrosum had differentiated but underdeveloped embryos. After 30 days of incubation under 5/15, 10/20, 15/25, and 20/30 °C in light/dark conditions, no seed germination was observed, which indicated that the seeds had a morphophysiological type of dormancy. After 12 weeks of cold stratification, > 90 % seeds germinated at 5/15 and 10/20 °C. In addition, a gibberellic acid (GA3) treatment can substitute for the need for cold stratification and successfully broke dormancy in T. squarrosum seed. Seeds treated with 1000 mg/L GA3 had higher germination rates than those treated with 10 or 100 mg/L GA3. Embryo growth and germination began in February under natural conditions of the year following production. We conclude that T. squarrosum seed exhibits non-deep simple morphophysiological dormancy. These findings will enhance our understanding of the regeneration strategy of T. squarrosum that allows it to adapt to the environment and will offer a reference to horticulturalists and seed ecologists in understanding the germination processes of T. squarrosum.

Different levels of morphophysiological seed dormancy in Ribes alpinum and R. uva-crispa (Grossulariaceae) facilitate adaptation to differentiated habitats

Aim of the study: To study the germination ecology of two species of the genus Ribes to reveal their levels of morphophysiological dormancy (MPD) and to facilitate the production of plants from seeds, a key tool for population reinforcement.Area of study: Experiments were carried out both outdoors and in the laboratory in Albacete (Spain) with seeds from the Meridional Iberian System mountain range.Material and methods: Seeds from one population of Ribes alpinum and from other of Ribes uva-crispa were collected during several years. Embryo length, radicle and seedling emergence, and effects on germination of stratification and GA3 were analysed to determine the level of MPD.Main results: In R. alpinum, embryo length in fresh seeds was 0.49 mm, needing to grow to 1.30 mm to germinate. Warm stratification (25/10ºC) promoted embryo length enlargement to 0.97 mm. Afterwards, seeds germinated within a wide temperature range. Embryo growth and seedling emergence occur late summer-early autumn. In R. uva-crispa, embryo length in fresh seeds was 0.52 mm, being 2.10 mm the minimal size to germinate. Embryos exposed to a moderately warm stratification (20/7ºC + 15/4ºC) followed by cold (5ºC) grew to 2.30 mm. Then, seeds germinated ≥ 80% when incubated at temperatures ≥ 15/4ºC. Embryos grew in autumn/early winter, and seedlings emerged late winter-early spring.Research highlights: These results showed that R. alpinum seeds have a nondeep simple MPD while R. uva-crispa seeds have a nondeep complex MPD. Moreover, the different germinative models found for each species help explain their installation in distinct habitats.Keywords: Ribes; seed dormancy break; radicle emergence; seedling emergence; nondeep simple and nondeep complex MPD.Abbreviations used: Morphophysiological dormancy (MPD), morphological dormancy (MD), Gibberellic acid (GA3), months (m).

Seed dormancy and germination in Cardiocrinum giganteum var. yunnanense, a perennial herb in China with post-dispersal embryo growth

Seeds of Cardiocrinum giganteum var. yunnanense, which is native to China, has underdeveloped embryos when dispersed from parent plants that did not grow until the second autumn and winter after exposure to summer temperatures. Radicles and cotyledons emerged in late winter and spring. Thus, a 15–16 month period was required from dispersal to seed germination. Under laboratory conditions, this period could be shortened to 5–6 months in a 25°C/15°C (60 days) → 15°C/5°C (60 days) → 5°C (60 days) temperature sequence. Based on dormancy-breaking requirements, the seeds have deep simple morphophysiological dormancy (MPD). This is practical knowledge for propagation of the species from seeds.

Seed dormancy and germination of Epimedium koreanum Nakai

Epimedium species are shade-tolerant perennials with flowers and leaves that vary in color, making them valuable groundcover plants. We investigated the dormancy of E. koreanum seeds and their requirements for embryo growth and germination. First, the phenology of embryo growth, germination, and seedling emergence under field conditions were observed. Then, the effects of temperature sequences and gibberellic acid (GA3) treatment on dormancy and germination were evaluated in two laboratory experiments. Under field conditions, the underdeveloped embryos grew very little from June to early September, while rapid growth of the embryos was observed from late September to November. Embryo growth was completed by early December, resulting of 16-fold increase of the initial length of the embryo. The seeds had germinated in March of the following year, and the germination percentage reached 84.4 %. In the laboratory experiments, embryos hardly grew when the seeds were incubated at a constant temperature of 20 or 15 °C. When the seeds were warm stratified at 25 °C and then moved to lower temperatures of 20 and 15 °C, the embryo grew rapidly. Germination then occurred after cold stratification at 5 °C for 12 weeks. However, if seeds were subjected to cold stratification first, the embryo did not grow, and no seeds germinated. GA3 treatment increased embryo growth in the seeds, but few seeds germinated less than 10 %. Based on these results, seed dormancy of E. koreanum can be broken through warm followed by cold stratification. Therefore, the seeds can be classified as having deep simple morphophysiological dormancy. This is the first report of the ecophysiology of seed dormancy and germination in the genus Epimedium in the Korean peninsula.

Seed dormancy in Campanulaceae: morphological and morphophysiological dormancy in six species of Hawaiian lobelioids

We determined the requirements for dormancy break/germination and kind of dormancy in seeds of the Hawaiian lobelioids Cyanea kunthiana, Delissea rhytidoperma, Lobelia grayana, L. hypoleuca, Trematolobelia grandifolia, and T. singularis. Fresh seeds were incubated in light/dark at 15/6, 20/10, and 25/15 °C, and germination monitored at two-week intervals for 14 weeks. For each species, the mean embryo length (E): seed (S) length ratio was determined for freshly matured seeds and for seeds at the time the seed coat split but before radicle emergence (germination). The embryo in seeds of all six species incubated at 25/15 °C grew inside the seed prior to germination (42%–148% increase in E:S ratio, depending on species). Seeds of L. grayana and L. hypoleuca have morphological dormancy (MD); they germinated to 82%–98% at the three temperature regimes in 4 weeks. Seeds of the other species have nondeep simple morphophysiological dormancy (MPD) and require >4 weeks for maximum germination to occur. Our results add to the growing body of knowledge about the kind (class) of seed dormancy in Campanulaceae, which suggests that seeds of members of this family have either MD or MPD and embryos grow at warm (≥15 °C) temperatures.

Non-deep simple morphophysiological dormancy in seeds of Angelica keiskei (Apiaceae)

Angelica keiskei is a vegetable and medicinal plant with high economic value. Growing demands for market and unprecedented anthropogenic damage to forests has caused severe degeneration of its populations. Moreover, the germination protocol for seeds of A. keiskei is complex, leading to a high cost of propagation and seed wastage. The primary aim of present study was to determine the requirements for seed dormancy break and germination and to characterize the class of seed dormancy in A. keiskei. The effects of temperature, light, cold stratification, dry storage, gibberellic acid (GA3) on dormancy break and germination were tested combined with move-along experiments and a germination phenology study. The results showed that seeds of A. keiskei had embryos that were differentiated but underdeveloped (small) and had physiological dormancy (PD) at maturity in autumn. Before the emergence of radicles, the embryo/seed length ratio increased from 0.20 to 0.85, a 425% increase. Germination of A. keiskei gradually increased following increased amounts of cold stratification. After 8 weeks of cold stratification, seeds germinated to 75, 78, 63 and 14% at 5/15, 10/20, 15/25 and 20/30 °C, respectively, in light. GA3 substituted for cold stratification. After 8 weeks of cold stratification, > 80% of seeds treated with ≥10 mg·L-1 GA3 germinated across the temperature range. In the move-along experiments, little or no embryo growth and germination occurred at 5 °C. However, after breaking PD by cold stratification at 5 °C, the rate of embryo growth increased rapidly at warm temperatures (5/15 °C) and reached the critical length for germination within 2 weeks of incubation. We identified that seeds of A. keiskei exhibited non-deep simple morphophysiological dormancy. Natural cold stratification broke PD during winter and allowed the germination of seeds and the production of seedlings at the start of the growing season.

Radicle emergence with increased temperatures following summer dispersal in Trillium camschatcense: A species with deep simple double morphophysiological dormancy in seeds

AbstractSeeds with deep simple double morphophysiological dormancy (MPD) need cold stratification during the first winter after dispersal for radicle emergence, followed by the summer for root and bud development and finally a second winter for shoot emergence. In a previous study, we demonstrated that Trillium camschatcense seeds have this type of dormancy with radicles emerging from most seeds after the first winter. However, radicles also emerged from a few seeds in autumn during the same year as dispersal. We thought that temperatures after seed dispersal played a role in radicle emergence before the first winter. To confirm our idea, we investigated germination phenology outdoors, relationships between temperatures after seed dispersal and radicle emergence in the first year outdoors, radicle emergence in the first winter under varied temperatures using incubators, and shoot emergence from seeds with an emerged radicle in the first year outdoors. Our phenology study confirmed that T. camschatcense seeds have deep simple double MPD. Over 7 years, 0.2–7.5% of radicles emerged in the first year before winter and these percentages were moderately positively correlated with temperatures, especially minimum temperatures. Increasing August and September temperatures increased radicle emergence in the laboratory. Shoots emerged from seeds with an emerged radicle in the first year after the first winter. With increased autumn temperatures in warmer regions or with global warming, we predict that germination phenology may shift: increased radicle emergence in the first year and shoot emergence following the first (and not second) winter.

Germination of Aristolochia Seeds (Aristolochiaceae)

We studied the seed morphology and germination of 17 Aristolochia species (A. arborea, A. baetica, A. inflata, A. gigantea, A. gracilis, A. clematitis, A. contorta, A. fimbriata, A. labiata, A. littoralis, A. macrophylla, A. manshuriensis, A. maxima, A. rotunda, A. sempervirens, A. tomentosa, A. trilobata). The seeds of A. clematitis, A. contorta, A. trilobata, A. labiata, and A. maxima, as well as all species of Siphisia section (seeds with no wings), have the higher seed morphometric parameters. The seed weight characteristics of species typical of tropical climatic zones (the Gymnolobus section) were lower by ten or more times than those of the species of the other two sections, which are typical of a temperate climate. The greater weight of seeds studied for the species of Siphisia and Diplolobus sections is associated with the presence of a voluminous endosperm, which is required for the embryo development after a long period of time between dissemination and seedlings emergence. The period from sowing to the beginning of germination and the length of the germination period differ between species; the duration of germination is from 1 month to 3.5 years. The seeds of the species from temperate climatic zones (sections Diplolobus and Siphisia) have a non-deep simple morphophysiological dormancy, and the germination starts 1–11 months after seed sowing. We observed intervals in germination from 2 to 12 months in the species of the Diplolobus section; after the intervals, the germination process was continued. The seeds of most of the Gymnolobus section species from tropical zones have a morphological type of dormancy and germinate without intervals. The prolonged germination period and the type of morphophysiological dormancy of seeds have an adaptive value for the species conservation and survival in situ and ex situ.

Three levels of simple morphophysiological dormancy in seeds ofIlex(Aquifoliaceae) species from Argentina

AbstractAs a contribution to understanding the world biogeography of seed dormancy in the cosmopolitan genusIlex, we studied seeds ofI.argentina,I. brasiliensis,I. brevicuspis,I. dumosa,I. paraguariensisandI. theezansfrom the subtropical region of Argentina. We hypothesized that seeds of these species have non-deep simple morphophysiological dormancy (MPD). Effects of temperature, cold stratification and gibberellic acid (GA3) on seed germination and embryo growth were tested. Regardless of incubation temperature, little or no germination occurred for any species until ≥6 weeks. There was an up to 3-fold increase in embryo length to seed length (E:S) ratio before seeds germinated, and embryos grew only during warm-stratifying conditions. Seeds ofI. brasiliensis,I. brevicuspisandI. theezanshad non-deep simple MPD and germinated to ≥80% after 12, 24 and 16 weeks, respectively. Cold stratification increased germination ofI. brasiliensisandI. brevicuspis, and GA3increased the rate but not final germination percentage ofI. brasiliensisandI. theezans. Fresh seeds ofI. dumosarequired 40 weeks of warm stratification to germinate to 53%, while those after-ripened for 2 months germinated to 81% after 30 weeks; this species has intermediate simple MPD. Seeds ofI. argentinaandI. paraguariensisgerminated to 15 and 21%, respectively, after 40 weeks of warm stratification and did not after-ripen or respond to GA3; these seeds have deep simple MPD. This is the first report of intermediate and deep simple MPD that is broken by warm stratification, thereby increasing our knowledge of seed dormancy inIlexand in subtropical regions.

Morphophysiological dormancy, germination, and cryopreservation in Aristolochia contorta seeds

Background and aims – Aristolochia contorta is a valuable medicinal plant, a relict of the Tertiary flora. Little is known about the germination biology of Aristolochia. The specific objectives of the present study were to (1) determine the type of dormancy in seeds of A. contorta, (2) describe the embryo development, and (3) explore the influence of deep freezing of the seeds in liquid nitrogen on their germinability.Methods – Seeds were germinated in Petri dishes in sand previously sterilised at high temperature; germination experiments were carried out at 27±2°C under natural light. All measurements of seeds and embryos were done using light microscopy (LM). For cryopreservation, fresh seeds were placed in aluminium foil bags, immersed into liquid nitrogen (-196°С), and stored for twelve months.Key results – The seeds of Aristolochia contorta have non-deep simple morphophysiological dormancy. A variety of embryo forms were revealed for Aristolochia species for the first time. Two cases of polyembryony were noted in A. contorta. The seeds of A. contorta are resistant to cryopreservation in liquid nitrogen.Conclusions – High variability in dormancy depth and the extended germination period of A. contorta seeds can be considered as adaptive strategies for survival in unfavourable conditions and renewal of germination under optimal conditions. Cryopreservation helped maintain the viability of A. contorta seeds but did not lead to the breaking of the dormancy; hence, for successful germination, it is necessary to use methods of breaking dormancy after freezing.