Morphophysiological dormancy (MPD) is predominantly found in seeds of temperate regions and is uncommon in arid biomes. MPD has been reported in a number of Hibbertia (Dilleniaceae) species of temperate Australia, and in a single species of the arid zone, H. glaberrima. This study aimed to examine the dormancy and germination ecology of seeds of H. glaberrima. Seeds were subjected to temperature stratification treatments designed to mimic summer and autumn conditions in the Pilbara region of Western Australia. Seed germination and embryo growth were measured. We also tested the interaction between temperature stratification and cycles of drying and wetting designed to mimic sporadic rainfall events. All temperature and moisture treatments were tested in combination (+/–) with the smoke-derived chemical karrikinolide (KAR1). Exposing dormant seeds to temperatures suitable for warm stratification (35°C) for ≥ 8 weeks, followed by incubation at 25°C, resulted in significantly higher germination compared with non-stratified seeds. Exposing seeds to dry/wet cycling in conjunction with temperature stratification did not significantly increase germination. Exposure to KAR1 increased germination under most conditions. Once seeds are shed during October to December, they are exposed to hot and sporadically wet conditions over summer, allowing MPD to be overcome in a proportion of the seed population. Seeds may germinate in autumn (March to April), in conjunction with cooler temperatures. More deeply dormant individuals may require more than one summer to overcome dormancy. Similar to other species occurring in fire-prone ecosystems, fire also plays a crucial role in the germination ecology of H. glaberrima.

This study was conducted to evaluate the effect of a 12-h light, 12-h dark (12L : 12D) photoperiod of green light during day 1 to day 18 of incubation time, on embryo growth, hormone concentration and the hatch process. In the test group, monochromatic light was provided by a total of 204 green light-emitting diodes (522 nm) mounted in a frame which was placed above the top tray of eggs to give even spread of illumination. No light–dark cycle was used in the control group. Four batches of eggs (n=300/group per batch) from fertile Ross 308 broiler breeders were used in this experiment. The beak length and crown–rump length of embryos incubated under green light were significantly longer than that of control embryos at day 10 and day 12, respectively (P<0.01). Furthermore, green light-exposed embryos had a longer third toe length compared with control embryos at day 10, day 14 and day 17 (P=0.02). At group level (n=4 batches), light stimulation had no effect on chick weight and quality at take-off, the initiation of hatch and hatch window. However, the individual hatching time of the light exposure focal chicks (n=33) was 3.4 h earlier (P=0.49) than the control focal chicks (n=36) probably due to the change in melatonin rhythm of the light group. The results of this study indicate that green light accelerates embryo development and alters hatch-related hormones (thyroid and corticosterone), which may result in earlier hatching.

To increase our knowledge of the diversity of seed dormancy and germination in Rubiaceae, we investigated seed desiccation sensitivity and germination of three Psychotria species. Seeds of P. gardneri, P. nigra and P. zeylanica germinated to high percentages at <15% seed moisture content. Intact seeds of P. zeylanica and P. nigra imbibed water and thus do not have physical dormancy. More than 50% of the seeds of P. zeylanica, P. nigra and P. gardneri took 33, 53 and 110 d, respectively, at 25°C for the radicle to emerge, and embryo growth occurred before and after radicle emergence. Thus, seeds have morphophysiological dormancy. Shoot emergence of P. nigra and P. zeylanica seeds was delayed 50 and 80 d after radical emergence, respectively; thus, seeds have epicotyl morphophysiological dormancy (eMPD). This is the first report of eMPD in Rubiaceae. Since warm stratification promoted both radicle and shoot emergence in seeds of P. zeylanica and P. nigra, the level of eMPD is non-deep simple. Hence, dormancy of the studied Psychotria spp. can be described as C1bBb (radicle)–C1bBb (epicotyl), i.e. the embryo is underdeveloped and grows prior to radicle emergence and epicotyl emergence under warm temperatures (Bb), and both the radicle and epicotyl have non-deep simple physiological dormancy broken by warm temperatures (C1b). In two Psychotria species studied in detail, radicle emergence occurs at the beginning of the rainy season and plumule emergence at the peak rainy season when conditions are most favourable for rapid seedling development.

Convallariamajalis has double dormancy and hypogeal germination, but no information is available on embryo growth or on the effects of light and gibberellic acid (GA3) on germination in this genus. Therefore, we investigated embryo growth and other germination features in seeds of C. keiskei and compared the data with those of Trillium camschatcense in another study. Until now, in seeds with double dormancy, embryo growth and germination (epigeal) have been studied in detail only for seeds of T. camschatcense. Phenology of embryo growth and emergence of cotyledonary petiole/root (hereafter root) and shoot in seeds of C. keiskei were monitored outdoors. Effects of temperature, light and GA3 on embryo growth and root and shoot emergence were tested under laboratory conditions. Roots emerged the first spring following seed dispersal in autumn. The embryo grew soon after root emergence, and germination was hypogeal. Seeds with an emerged root formed buds from which a shoot (leaf) emerged above ground during the second spring. Alternating temperatures and light had negative effects on root emergence, and GA3 did not substitute for cold stratification in root emergence. Seeds of C. keiskei have double dormancy, but it differs from that in T. camschatcense. Based on differences in embryo growth before (T. camschatcense) versus after (C. keiskei) root emergence, and on epigeal (T. camschatcense) versus hypogeal (C. keiskei) germination, we suggest that two types of deep simple double morphophysiological dormancy (MPD) be recognized. Since embryo growth in C. keiskei does not fit the standard definition of MPD, we propose to expand this definition.

The Araliaceae is known to have seeds with underdeveloped embryos that must grow prior to radicle emergence, and thus they have morphological (MD) or morphophysiological (MPD) dormancy. Araliaceae is one of about 15 families with woody species in the tropical montane zone, and in Hawaii 15 species occur in the montane. Our purpose was to determine if seeds of the Hawaiian Araliaceae species Cheirodendron trigynum subsp. trigynum have MD or MPD and, if MPD, what level. In a move-along experiment, some seeds were incubated continuously at 15/6, 20/10 or 25/15°C, while others were moved sequentially from low to high or from high to low temperature regimes. Germination percentages and embryo growth were monitored. Also, the effects of cold and warm stratification on dormancy break were determined. Seeds had physiological dormancy (PD) in addition to small embryos that grew prior to germination, and thus MPD. PD was broken slowly ( ≥ 12 weeks), after which embryos grew rapidly, followed by root and shoot emergence. Embryos grew at temperatures suitable for warm stratification; thus, seeds have Type 1 non-deep simple MPD; the dormancy formula is C1bBb. Seeds from Oahu germinated to 94–100% at 15/6, 20/10 and 25/15°C, while those from the Big Island germinated to high percentages only at 15/6 and 20/10°C. Temperature shifts improved germination of seeds from the Big Island, and movement from either low to high or from high to low temperature regimes was effective in promoting germination. This is the first report of non-deep simple MPD in the Araliaceae.

Narcissus longispathus (Amaryllidaceae) is a perennial geophyte and a Mediterranean narrowly endemic species. At dispersal time, N. longispathus seeds are dormant and have underdeveloped embryos. This work aimed to determine requirements for dormancy break and germination and to compare dormancy traits with those of the two endemic Iberian congeners. Phenology of embryo growth and germination were studied by regularly exhuming seeds sown in near-natural conditions. Temperature and light requirements for embryo growth, breaking of dormancy and germination were determined by incubating seeds under controlled laboratory conditions. Mean embryo length in fresh seeds was 1.50 mm, and embryos had to grow to 3.80 mm before radicle emergence. Embryos grew to full size and seeds germinated when they were warm stratified for 2 months (optimum 1 month at 20/7°C+1 month at 15/4°C), then cold stratified at 5°C for 2 months, and finally incubated at cool temperatures (15/4°C) for 30 d. However, in seeds only subjected to either warm or cold stratification, the embryos hardly grew and did not germinate. In natural conditions, the embryos elongate in autumn–winter, and in late winter–early spring (March) almost all radicles and seedlings emerged. Velocity of embryo growth and germination percentages increased with seed storage duration. Seeds of N. longispathus have non-deep complex morphophysiological dormancy (MPD). This is the first report of such a level of MPD in Narcissus. Our data suggest that non-deep complex MPD may have been derived from intermediate complex MPD in the section Pseudonarcissi.

Although it has been speculated that seeds of the gymnosperm family Podocarpaceae have an underdeveloped embryo, no detailed studies have been done to definitively answer this question. Our purpose was to determine if embryos in seeds of two species of Podocarpaceae, Podocarpus costalis and Nageia nagi, from Taiwan are underdeveloped and to examine the kind of dormancy the seeds have. Embryos in fresh seeds of P. costalis were 4.6 ± 0.5 mm long, and they increased in length by about 54% before radicle emergence (germination), demonstrating that the embryo is underdeveloped at seed maturity. Seeds germinated to >90% at 30/20, 25/15 and 25°C in light in ≤ 4 weeks, without any cold stratification pretreatment. Thus, seeds of P. costalis have morphological dormancy (MD). Embryos in fresh seeds of N. nagi were 7.4 ± 0.8 mm long and they increased in length by about 39% before radicle emergence (germination) occurred, indicating that the embryo is underdeveloped at seed maturity. Seeds germinated to < 25% at 30/20 and 25°C in light in 4 weeks but to >90% at the same temperatures in 12 weeks. Thus, most seeds of N. nagi have morphophysiological dormancy (MPD). Although underdeveloped embryos are considered to be a primitive condition in seed plants, they also occur in the most advanced orders. The occurrence of underdeveloped embryos in Podocarpaceae documents that they are not restricted to a basal clade in gymnosperms.

Heretofore, no detailed account was available on seed dormancy and germination of a member of the Colchicaceae (Liliales). Thus, the primary aim of this study was to do an in-depth investigation of the temperature requirements for dormancy break and germination in seeds of Merendera montana (Colchicaceae) at the embryo and whole-seed levels under near-natural temperatures in a non-heated frame shade-house and under controlled conditions in the laboratory. Mean embryo length in fresh seeds was c. 0.57 mm and embryos had to grow to at least 1.30 mm before radicle emergence. Embryos grew to full size and seeds completed germination (radicles emerged) when they were stratified at 28/14°C for 60 d followed by a cool temperature for 60 d and then incubated at a cool temperature for 30 d. The optimum cool stratification temperature for dormancy-break was 10°C. Thus, after the moist pretreatment at 28/14°C+10°C, radicle emergence was>93% at all incubation temperatures (5, 15/4 and 20/7°C). In its natural habitat, M. montana seeds are dispersed in June, the embryo elongates to full size in autumn and radicles emerge from early November to early February. Although the shoot does not emerge until March and April, it is not physiologically dormant. The shoot emerged from 80% of the radicle-emerged seeds in 13 d at 20/7°C without a previous cold pretreatment. Seeds of M. montana have non-deep complex morphophysiological dormancy, C1b1aB-C1a. This is the first study on seeds with complex MPD to show a delay in shoot emergence following root emergence despite the shoot being physiologically non-dormant.

Fritillaria tubiformis subsp. moggridgei (Liliaceae) is a rare, endemic species that inhabits open mountains and alpine grasslands of the Ligurian Alps. At the time of seed dispersal, the underdeveloped embryos were 27% the length of the seed. Here we report the results of laboratory experiments carried out to determine the temperature preferences for embryo growth and radicle emergence. Embryo growth commenced immediately after sowing at 4°C. Once the embryo had grown the length of the seed, the radicle emerged. The time required for embryo growth and radicle emergence was longer when seeds were placed through a seasonal sequence of temperatures, commencing with late summer (10/20°C), compared with seeds immediately placed at a temperature to simulate winter conditions (4°C). Prematurely transferring seeds from winter to spring temperatures (5/10°C) also slowed the progress of germination. Radicle emergence did not occur at 10 or − 5°C and less than 20% germination occurred in seeds placed at constant 0°C. Addition of gibberellic acid (GA3) did not promote embryo growth of seeds placed at 20°C. Overall, the temperature preferences for embryo growth and subsequent radicle emergence are such that, in situ, seed germination may occur during the winter under snow cover or at the end of winter to coincide with snow melt and warming temperatures.

Seeds of Aconitum napellus subsp. castellanum were physiologically dormant at maturity in early autumn, with underdeveloped embryos. Thus they have morphophysiological dormancy (MPD). Embryos in fresh seeds were on average 1.01 mm long, and they had to grow to 3.60 mm before radicle emergence. Cold stratification at 5°C for 5 months with light enhanced the mean embryo length to 2.73 mm (SE = 0.13) and seed germination to 20%. However, with higher temperatures (15/4, 20/7, 25/10, 28/14 and 32/18°C) embryo growth was small, with no seeds germinating. Optimal germination was achieved after 4 months of cold stratification at 5°C followed by incubation at 20/7°C for 1 month with light, when germination ranged between 70 and 79%, depending on seed age, locality and year of collection. Cold stratification could be substituted by the application of GA3 solution, since mean embryo length in seeds incubated at 25/10°C for 1 month with light was 3.52 mm and the germination was 80%. Since cold stratification was the only requirement for the loss of MPD, the longest embryo growth occurred during this treatment, and GA3 promoted MPD loss, we concluded that A. napellus seeds have intermediate complex MPD. Germination was higher in 4-month stored than in freshly matured seeds. A pronounced variability in germinative patterns at inter-annual and inter-population level was recorded.

This study examined whether the restricted habitat preference of the spring-flowering woodland geophyte Anemone ranunculoides L., compared with that of A. nemorosa growing in the same woodlands in northern Italy, could be explained by subtle differences in germination preference and emergence phenology. Immediately after harvest, seeds of A. ranunculoides were either sown on agar in the laboratory under simulated seasonal temperatures or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of seed dispersal, grew during summer in the laboratory and in the wild, culminating in radicle emergence in the autumn, when temperatures fell to c. 15°C. Shoot emergence was delayed under natural conditions until soil temperature had dropped further to c. 10°C. Compared with populations of the closely related Anemone nemorosa L. occupying the same woodland habitat, which have been reported to have non-dormant radicles, A. ranunculoides displayed a narrower temperature tolerance for radicle emergence and high levels of germination were possible only after prolonged exposure to summer conditions, indicating physiological dormancy. However, unlike A. nemorosa, shoot emergence in A. ranunculoides was not dependent on winter temperatures, suggesting weaker epicotyl morphophysiological dormancy. Under a regime of diurnal temperature alternation, simulating the microclimate where there is little plant cover, germination failed almost completely; this could explain the absence of A. ranunculoides in open habitats.

Although various aspects of the biology of Anemone nemorosa have been examined, few studies present data on seed germination, and even then information tends to be rather contradictory. A. nemorosa L. is a spring-flowering, woodland geophyte, widely distributed across much of Europe. Germination phenology, including embryo development and radicle and shoot emergence, were investigated in one mountain and three lowland populations from northern Italy. Immediately after harvest, seeds were either sown on agar in the laboratory under simulated seasonal temperatures, or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of dispersal, grew under summer conditions in the laboratory and in the wild. However, seeds did not germinate under continuous summer conditions. Radicle emergence in the field was first recorded at the beginning of autumn, when soil temperatures had dropped to c. 15°C in the case of the three lowland populations, and to c. 10°C at the mountain site. Shoot emergence was delayed under natural conditions until late autumn/early winter, when soil temperatures had dropped to c. 10°C in the lowlands and c. 6°C at the mountain site. In the laboratory, a period of cold stratification was required for shoot emergence, and this requirement was more pronounced in the mountain population. Seeds of the mountain population completed embryo development, radicle emergence and shoot emergence at cooler temperatures compared with the lowland populations. These results suggest that germination in A. nemorosa is highly adapted and finely tuned to local climate. We conclude that seeds of A. nemorosa display deep, simple epicotyl, morphophysiogical dormancy, and this is the first report of such dormancy for the genus Anemone. However, the continuous development and growth of embryos from the time of natural dispersal, and the lack of evidence of developmental arrest under natural conditions, suggests that radicles are non-dormant.

Torilis japonica (Apiaceae) has a widespread distribution, extending from western Europe to eastern Asia. In Europe, it usually behaves as a spring-germinating biennial species. Ripe seeds of T. japonica have an underdeveloped embryo and can persist in the soil for several years. The aim of this research was to reveal the mechanisms regulating the seasonal emergence pattern of seedlings. Experiments in a natural environment were performed to study phenology of seedling emergence and embryo growth. Seasonal changes in the dormancy status of T. japonica seeds were examined by regularly exhuming buried seeds and incubating them in controlled conditions. The action of temperature and light in regulating dormancy, embryo growth and germination was studied in the laboratory. Results showed that seeds of T. japonica have non-deep, simple morphophysiological dormancy (MPD), whereby physiological dormancy is broken by moist chilling (5°C). Once MPD was broken, embryo growth and subsequent germination started in spring, when appropriate temperature and light conditions were present. Seeds buried at a depth where light could not reach them showed cyclic changes in their dormancy status; embryo growth in these seeds could not be initiated because of the lack of a light stimulus. As far as we know, this is the first extensive study of seasonal dormancy cycles in a spring-germinating species of the Apiaceae. T. japonica occurs in a temperate climate with cool winters and warm, moist summers. In this climate, spring is often the most favourable season for seedling establishment.

A UK seed conservation collection of Anemone nemorosa L. seeds held at the Millennium Seed Bank (MSB) showed low viability in its first post-storage test. Because achenes of A. nemorosa are naturally dispersed when they are green, we tested the hypothesis that seeds may not be fully desiccation tolerant and storable at the time of natural dispersal, and that a post-harvest treatment could increase the proportion of desiccation-tolerant seeds. Achenes harvested at the point of natural dispersal in late May in 2003 and 2004 were either placed immediately on 1% water agar at 20°C (‘laboratory’ treatment), or placed in nylon sachets and buried in leaf litter among plants growing in the wild (‘field’ treatment). Samples were withdrawn at intervals over a period of 168 d and tested for desiccation tolerance (drying to 0.059 g H2O (g DW)− 1) and longevity (controlled ageing at 60% relative humidity and 45°C). An initial increase, followed by a decline, in the proportion of seeds surviving desiccation and in the longevity of both laboratory- and field-treated samples coincided with the development of embryos from globular to heart- and then torpedo-shaped. Developmental arrest was not required for the acquisition of desiccation tolerance, and continued growth and development of the embryo resulted in a loss of desiccation tolerance, similar to that seen in orthodox seeds upon radicle emergence. Furthermore, while A. nemorosa seeds, like many from the Ranunculaceae family, might be described as having morphological or morphophysiological dormancy, this lack of developmental arrest does not fit with the usual concept of dormancy. The implications of these results for the classification systems of seed-storage behaviour and dormancy, and for the long-term conservation of seeds of A. nemorosa, are discussed.

There are two ideas regarding changes in the physiological and ecological tolerances and requirements within plant lineages through geological time. One is that these attributes have changed very little, or not at all (trait stasis), and the other is that they have undergone considerable change (adaptation), as plants shifted to new climatic and vegetation zones. We tested these ideas for seed dormancy-breaking and germination requirements of four species in a subclade of Aristolochia subgenus Siphisia: the three temperate species, A. macrophylla and A. tomentosa (the basal species in the subclade) of eastern USA and A. manshuriensis of East Asia, and the Mediterranean-climate species A. californica endemic to California, USA. A long period at cold-stratifying temperatures was required for growth of the underdeveloped embryo and seed germination in A. californica, whereas embryos grew and seeds germinated in the other three species at warm temperatures, either before or after they were cold stratified. Thus, seeds of A. californica have either intermediate or deep complex morphophysiological dormancy (MPD), whereas those of the three temperate species have either morphological dormancy or non-deep simple MPD. Further, there were quantitative differences in temperature requirements for dormancy-break and germination between the Appalachian A. macrophylla, which did not differ from its sister species A. manshuriensis, and the lowland A. tomentosa. Thus, within this lineage there has been both trait stasis and divergence (adaptation) in the physiology and ecology of seed dormancy and germination.

Dormancy-breaking requirements and types of dormancy were determined for seeds of Lonicera fragrantissima Lindl. & Paxt., L. japonica Thunb., L. maackii (Rupr.) Maxim. and L. morrowii A. Gray. Seeds of all four species have underdeveloped spatulate embryos that are about 20–40%fully developed (elongated) when dispersed. Embryos in freshly matured, intact seeds grew better at 25/15°C than at 5°C. Gibberellic acid (GA3) (tested only in the light) was more effective in breaking dormancy in L. maackii and L. morrowii than in L. fragrantissima and L. japonica. Warm- followed by cold stratification was required to break dormancy in seeds of L. fragrantissima, whereas seeds of L. japonica required cold stratification only. Thus, seeds of L. fragrantissima have deep simple morphophysiological dormancy (MPD) and those of L. japonica nondeep simple MPD. About 50%of the seeds of L. maackii required warm- or cold stratification only to come out of dormancy and 50% of those of L. morrowii required warm stratification only, whereas the other 50% did not require stratification to germinate. Thus, about half of the seeds of the two species has nondeep simple MPD, and the other half has morphological dormancy (MD). In these laboratory tests, seeds of L. japonica, L. maackii, and L. morrowii generally germinated to significantly higher percentages in light than in darkness; seeds of L. fragrantissima were not tested in darkness. Peaks of germination for seeds of L. fragrantissima, L. japonica, L. maackii and L. morrowii sown on a soil surface and covered with Quercus leaves under near-natural temperature conditions shortly after seed maturity and dispersal in late June 1997, late November 1997, early November 1996 and late June 1998, respectively, occurred in early March 1998, late February 1998, late March 1997 and early October 1998, respectively. The germination phenologies of seeds of the same species and seed lots buried in soil were similar to those of seeds under leaf litter. High percentages of seeds of all four species germinated both under litter (78–96%) and beneath the soil surface (78–97%). These germination patterns correspond closely with the requirements for embryo growth and dormancy break in the four Lonicera species.

The effects of temperature on embryo growth, radicle emergence and cotyledon emergence of Gagea lutea (Liliaceae), a perennial herb widely distributed in Europe, eastern Siberia, the Kurile Islands, Sakhalin and the Far East, were monitored outdoors and in laboratory tests. In Japan, this species inhabits open secondary grasslands and deciduous forests. Seeds with an underdeveloped embryo are dispersed in late May/early June in Hokkaido. The embryo elongates in autumn, and the radicle emerges from the seed in mid-October to mid-November, at temperatures of about 15/4°C. However, cotyledons do not emerge until April, after seeds with an emerged radicle are covered with snow (near 0°C) for about 4 months. In laboratory experiments, temperatures of 25/15°C or 20/10°C followed by 5–10°C were required for embryo growth and radicle emergence. Rate and percentage of cotyledon emergence were promoted by keeping seeds with an emerged radicle under snow. The optimum temperature for cotyledon emergence after 81 d under snow was 15/5°C. Thus, G. lutea has deep simple epicotyl morphophysiological dormancy, and this is the first report of epicotyl dormancy in the genus.

Many maternally derived factors may be involved in the regulation of embryonic growth but the control mechanisms involved are poorly understood. Human placental lactogen (hPL) has been implicated in playing a role in the control of embryonic growth. Several investigators suggested that there may be a possible link between the effects of this hormone and insulin-like growth factors (IGFs). In order to determine the growth promoting potential of hPL and involvement of IGFs in the mechanism of action of the hormone, 9.5 d rat embryos were cultured in vitro for 48 h in depleted serum in the presence and absence of hPL with additional IGF antisera. The growth supporting capacity of the serum was reduced by removal of low molecular weight molecules by prolonged filtration of the serum using filters with a molecular weight exclusion of 30 kDa. Addition of hPL (3.2–25.6 ng/ml) to depleted serum significantly improved embryonic growth and development, suggesting that the developing embryo may utilise hPL. The presence of antisera against hPL, IGF-I and -II abolished the hPL-induced increase in the development in all parameters suggesting that there may be a possible link between the IGFs and the effects of hPL on rat embryonic development and this hormone may achieve its growth promoting effects via IGFs.

To determine whether sperm membrane components, rSMP-B and YWK-II, are suitable candidates as immunocontraceptives in humans, antifertility activities of the antibodies to the peptide fragments, rSMP-229 and rSMP-230 of rSMP-B and YAL-198 of YWK-II, were examined. In a previous report, anti-rSMP-230 antibody was shown to immobilise human sperm and to block human fertilisation, and the antigen (rSMP-230) to interact with antisperm antibodies found in sera of infertile women. Antibody to the second synthetic peptide, rSMP-229, corresponding to a different segment of rSMP-B, mimicked the biological activities of the anti-rSMP-230 antibody. Anti-YAL-198 antibody significantly, although weakly, inhibited human fertilisation. In the murine model, the anti-rSMP-B antibodies blocked in vitro fertilisation of mouse eggs but had no influence on embryo growth. Anti-YAL-198 antibody, however, arrested the growth of zygotes. In conclusion, rSMP-B, a human sperm protein, is a promising candidate in the development of an immunocontraceptive for human application. A second sperm protein, YWK-II, is effective as an antifertility immunogen in experimental animals.