Effects of storage,mucilage presence,photoperiod, thermoperiod and salinity on germination of Farsetia aegyptia Turra (Brassicaceae) seeds: implications for restoration and seed banks in Arabian Desert

Seed viability and germination are key factors in the success of restoration efforts, especially when stored seeds are used. However, the effect of seed storage on germination of most of the native Arabian species is not well documented. We investigated the effect of storage time and role of the seed mucilage in regulating germination, dormancy, salinity tolerance and consequential survival strategy of F. aegyptia in an unpredictable arid desert setting. Effect of light and temperature during germination was studied under two photoperiods and two thermoperiods using intact and de-mucilaged seeds. Presence of mucilage and thermoperiod did not affect the germination. However, seed collection year and photoperiod had a highly significant effect on the germination. Increasing salinity levels decreased the germination of F. aegyptia but ungerminated seeds were able to germinate when salinity stress was alleviated. Seed storage at room temperature enhances the germination percentage, indicating that F. aegyptia seeds have physiological dormancy and it can be alleviated by after-ripening at dry storage. In addition, F. aegyptia seeds show ability to germinate at lower salinity concentration and remain viable even at higher saline conditions, indicating their adaptability to cope with such harsh environmental conditions.     

假酸浆种子发芽特性研究

在不同温度、不同贮藏时间和方法下,对来源于印度尼西亚的假酸浆种子发芽特性进行研究。结果表明:不同温度对假酸浆种子萌发的影响差异极显著,在15/25℃变温条件下种子发芽率最高,为84.3%,发芽快且整齐;假酸浆种子采收后立即播种其发芽率非常低,室温下贮藏6～9个月时在25℃恒温或15/25℃变温条件下均有较高发芽率,说明假酸浆种子有休眠性,通过延长贮藏时间能打破休眠,促进种子发芽;但室温贮藏15个月后,种子活力下降非常明显。低温冷藏在一定条件下能提高假酸浆种子萌发能力,能延长种子寿命。     

Psychotria hoffmansegiana (Willd ex Roem. & Schult.) Mull. Arg. and Palicourea marcagravii st. Hil. (Rubiaceae): potential for forming soil seed banks in a brazilian Cerrado.

The germinability of artificially buried Psychotria hoffmansegiana and Palicourea marcagravii seeds in Cerrado soil was tested, with the aim of evaluating whether dispersed seeds may be able to form a soil seed bank. The assays were carried out at a Cerrado Reserve in S?o Paulo State, Brazil. Seed samples were placed in nylon bags and buried at two different depths and in two different sites. Samples were periodically exhumed and germination tests were performed with both exhumed and dry stored seeds. In general, soil storage favoured seed survival and germination when compared to dry stored seeds. The seed germination was little affected by soil depth and by burial environment. Seeds of both species remained viable for at least 13 months, considering the time lapse between the collection and the end of the germination tests. It was suggested that both species can potentially form a persistent soil seed bank in Cerrado.     

Quantitative and qualitative consequences of reduced pollen loads in a mixed‐mating plant

Greater pollination intensity can enhance maternal plant fitness by increasing seed set and seed quality as a result of more intense pollen competition or enhanced genetic sampling. We tested experimentally these effects by varying the pollen load from a single pollen donor on stigmas of female flowers of Dalechampia scandens (Euphorbiaceae) and measuring the effects on seed number and seed mass. Seed set increased rapidly with pollen number at low to moderate pollen loads, and a maximum set of three seeds occurred with a mean pollen load of 19 pollen grains. We did not detect a trade‐off between the number of seeds and seed mass within a fruit. Seed mass increased with increasing pollen load, supporting the hypothesis of enhanced seed quality via increased pollen‐competition intensity or genetic sampling. These results suggest that maternal fitness increases with larger pollen loads, even when the fertilization success is already high. Our results further highlight the importance of high rates of pollen arrival onto stigmas, as mediated by reliable pollinators. Comparing the pollen‐to‐seed response curve obtained in this experiment with those observed in natural populations suggests that pollen limitation may be more severe in natural populations than predicted from greenhouse studies. These results also indicate that declines in pollinator abundance may decrease plant fitness through lowered seed quality before an effect on seed set is detected.     

条叶百合种子萌发的研究

研究了不同光、温对条叶百合(Lilium callosum)种子萌发的影响。研究结果表明:(1)避光条件下温度对栽培4年生条叶百合种子萌发影响最大,其种子萌发最适宜温度为25℃, 4~5天开始萌动, 1~2周萌发完全。随着温度的升高或降低其种子萌发率下降。但在5℃时萌发率又有大幅升高, 35℃种子萌发完全受到抑制。(2)同一果序不同位置果实的种子萌发以最下部果实为好,中间果实次之,上部最差。(3)同一果实内中部种子萌发最好,下部种子次之,上部种子最差,上、中、下三部分种子萌发率与其千粒重呈正相关。(4)在相同实验条件下,野生条叶百合与栽培4年生条叶百合种子萌发率一致,但萌发完全时间比栽培条叶百合多14天。(5)贮藏一年后条叶百合种子萌发率没有下降。     

DIFFERENTIAL SUCCESS OF POLLEN DONORS IN A SELF-COMPATIBLE LILY

If pollen donors are equally effective at siring seeds, the presence of equal proportions of pollen from two pollen donors on a stigma will lead to equal proportions of seeds sired by each pollen donor. Variation in germination rates, pollen-tube growth, and embryo viability may cause one donor to sire more seed than another. We looked for differential donor success in the field by simultaneously applying equal amounts of pollen from two pollen donors. We simultaneously applied equal amounts of self and outcross pollen to receptive stigmas and simultaneously applied pollen from two donors at different physical distances from the recipient. Following simultaneous application of self and outcross pollen, significantly more of the seeds were sired by outcross pollen donors. Seed set following simultaneous application of two outcross donors was also nonrandom. Pollen donors from 100 m were more likely to sire seeds when competing with pollen from plants nearby (1 m). To determine whether pollen-tube growth rates were responsible for these patterns of paternity, we varied the timing of deposition of outcross pollen allowing self pollen tubes a head start on the stigma. Outcross pollen was applied 3 or 24 h after self pollen. In spite of this time delay, the majority of the seeds were again sired by outcross pollen. There was no significant difference in the amount of seeds sired by self pollen between the two delay treatments. This result suggests that mechanisms operating after ovule fertilization may contribute to the discordance between the proportions of the pollen present and the proportions of seeds sired.     

Seed viability and seed dormancy of non-native Phragmites australis in suburbanized and forested watersheds of the Chesapeake Bay, USA

The non-native, invasive haplotype of Phragmites australis is rapidly invading tidal and non-tidal wetlands across North America. Phragmites has the potential to spread by seeds and rhizomes. Seed viability and dormancy differences were quantified among 18 patches of non-native Phragmites in subestuarine wetlands in developed (i.e., suburbanized) vs. forested watersheds of the Chesapeake Bay. We used tetrazolium and germination assays to assess seed viability and compared germination percentages and rate of germination among fresh seeds, cold–moist treated seeds, and warm–dry treated seeds to evaluate seed dormancy. Seed viability was <1% in most patches but a few patches produced abundant viable seeds (5–21%). Seed viability, however, did not differ significantly between wetlands in forested vs. developed watersheds. Contrary to studies of Phragmites seed dormancy in European populations, some Phragmites seeds were dormant at maturity; cold–moist treated seeds germinated faster and to higher percentages than fresh seeds or warm–dry treated seeds.     

The anatomy of the stigma and style from Cyclamen persicum (Mill.) cv. "pure white" and its relation to pollination success

Old flowers of Cyclamen generate few or no seeds. To understand the pollination problems of Cyclamen we investigate the general anatomy of the stigma and the style of Cyclamen persicum by scanning electron microscopy at different stages of floral maturity. Our investigations confirm that there is a hollow style. Against data commonly found in the literature, we present evidence of pollen germination and tube growth that show the stigma is not outside the style but inside it. Furthermore the maturation process of the style during the flowering time indicates a mechanism by which the stigma becomes shut off through closure at the terminal aperture of the style. At 3 to 5 days after anthesis there was the beginning closure of the style which was nearly completed at 21 days. The substance which leads to the closure is still unknown. The closure of the hollow style is a probable cause for failure of seed set in flowers not pollinated early in anthesis.     

The breeding system of Fumana ericifolia: first evidence of autogamy in woody Cistaceae

Fumana ericifolia belongs to the family Cistaceae, in which all perennial species previously studied have been reported to be self-incompatible and xenogamous. Here we show that F. ericifolia is self-compatible and autogamous. Its flowers last only four to eight hours and produce a small amount of pollen and ovules. Self-pollination depends on changes in the relative position of the stigma and the anthers, triggered by the abscission of the petals; this in turn causes closing of the sepals, which push the anthers onto the stigma. Pollen remains highly viable and germinable, and the stigma keeps its receptivity several hours after the loss of the petals. Hand pollination treatments revealed that fruits are produced both in selfed and crossed flowers. The germination of pollen grains on the stigma, the rate of pollen tube growth along the style, and the penetration into the ovules were similar in self-and cross-pollinations; also, there were no significant differences in fruit set, seed set and weight of seeds. Thus, we report the first evidence of autogamy in a woody Cistaceae and suggest that selfing may ensure reproductive success when pollinators are limited.     

Pollen flow,self-pollination and gender specialization: Factors affecting seed-set in the tristylous speciesLythrum salicaria (Lythraceae)

Some of the factors governing seed-set in three populations ofLythrum salicaria are examined during two seasons. Plants spatially segregated from legitimate neighbours by distances exceeding 1m set few seeds. Plants with small inflorescences set fewer seeds than those with medium or large inflorescences. Flowers having self pollen applied to the stigma before legitimate pollination set fewer seed per flower than those pollinated with legitimate pollen only. Seeds of the mid-style morph germinated more effectively than those of the long style morph and seeds of the short-style morph showed very low levels of germination.     

POLLEN TUBE ATTRITION IN ERYTHRONIUM GRANDIFLORUM

Seed set after selfing in E. grandiflorum is often reduced relative to seed set after crossing; however, the compatibility patterns seen are not due to genes of major effect (i.e., S alleles). There is quantitative variation in the proportion of pollen tubes reaching the base of the style after both self- and cross-pollinations. Pollen tubes require between 24 and 72 hr to reach the ovary, but pollen tube growth ceases after 72 hr. When styles were removed from the ovaries 5 days after pollination, between 10 and 80% of the pollen tubes in the stigma had not reached the base of the style. The number of pollen tubes at the base of the style is a much better predictor of seed set than is the number of pollen tubes in the stigma. Pollen tube attrition is not affected by the age of the recipient flower or by the number of pollen donors contributing to the stigmatic pollen pool. The number of pollen tubes reaching the base of the style is dependent upon the source of the pollen and appears to be a decelerating function of the number of pollen tubes present in the stigma.     

Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.     

Seeds of tomato (Lycopersicon esculentum Mill.) which develop in a fully hydrated environment in the fruit switch from a developmental to a germinative mode without a requirement for desiccation

Seed water content is high during early development of tomato seeds (10–30 d after pollination (DAP)), declines at 35 DAP, then increases slightly during fruit ripening (following 50 DAP). The seed does not undergo maturation drying. Protein content during seed development peaks at 35 DAP in the embryo, while in the endosperm it exhibits a triphasic accumulation pattern. Peaks in endosperm protein deposition correspond to changes in endosperm morphology (i.e. formation of the hard endosperm) and are largely the consequence of increases in storage proteins. Storage-protein deposition commences at 20 DAP in the embryo and endosperm; both tissues accumulate identical proteins. Embryo maturation is complete by 40 DAP, when maximum embryo protein content, size and seed dry weight are attained. Seeds are tolerant of premature drying (fast and slow drying) from 40 DAP.Thirty-and 35-DAP seeds when removed from the fruit tissue and imbibed on water, complete germination by 120 h after isolation. Only seeds which have developed to 35 DAP produce viable seedlings. The inability of isolated 30-DAP seed to form viable seedlings appears to be related to a lack of stored nutrients, since the germinability of excised embryos (20 DAP and onwards) placed on Murashige and Skoog (1962, Physiol. Plant. 15, 473–497) medium is high. The switch from a developmental to germinative mode in the excised 30- and 35-DAP imbibed seeds is reflected in the pattern of in-vivo protein synthesis. Developmental and germinative proteins are present in the embryo and endosperm of the 30- and 35-DAP seeds 12 h after their isolation from the fruit. The mature seed (60 DAP) exhibits germinative protein synthesis from the earliest time of imbibition. The fruit environment prevents precocious germination of developing seeds, since the switch from development to germination requires only their removal from the fruit tissue.Abbreviations DAP days after pollination - kDa kilodaltons - SP1-4 storage proteins 1–4 - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis - HASI hours after seed isolation - MS medium Murashige and Skoog (1962) medium This work is supported by National Science and Engineering Research Council of Canada grant A2210 to J.D.B.     

Pollen-pistil interactions in Hermodactylus tuberosus Mill. (Iridaceae)

ABSTRACT

Hermodactylus tuberosus Mill. (Iridaceae) is a species with a very short style and a tricarpellar unilocular ovary. For ornamental purposes it is usually reproduced by means of tubers, although both vegetative and seed reproduction occur in nature. However, its capsules do not contain many seeds in comparison to the high number of ovules inside the ovary. To understand this conflicting process a study on H. tuberosus pollen-pistil interaction was carried out. Pollen viability was evaluated by different techniques. Germination rate was tested in vitro and in vivo after stigma, intrastylar and intraovarian pollinations. A high percentage of the pollen grains were found to be viable resulting in a high percentage of in vitro germination and a low rate of germination on the stigma. Indeed, many pollen tubes developed after intrastylar and intraovarian pollinations. Several anomalies characterized pollen germination and pollen tube growth in vitro and in vivo. Observations from field trials indicated that capsules were only produced from open or hand, cross- pollinated flowers, confirming that the plant is self- incompatible and not apomictic. In addition, all the mature capsules contained only a few mature seeds suggesting the existence of pre- and postzygotic seed set inhibition.     

Dormancy Breaking and Storage Behavior of Garcinia cowa Roxb. (Guttiferae) Seeds: Implications for Ecological Function and Germplasm Conservation

The dormancy breaking and storage behavior of Garcinia cowa Roxb. seeds were investigated.The seeds of G. cowa had 8-11 months dormancy in their natural habitat. Seeds were matured and dispersed at the end of the rainy season (mid-late August to late September) and were scatter-hoarded by rodents as food for winter after the seeds had fallen to the ground. Seedlings often emerged in the forest during the rainy season (May to August) the following year. Intact seeds of G. cowa failed to germinate after being sown at 30 ℃ for 120 d and the mean germination time (MGT) of seeds cultured in a shade (50% sunlight)nursery was 252 d. The most effective method of breaking dormancy was to remove the seed coat totally,which reduced the MGT to 13 d at 30 ℃. Germination was also promoted by partial removal of the seed coat (excising the hilum and exposing the radicle) and chemical scarification (immersion in 1% H2O2 for 1 d).Unscarified seeds take up water rapidly in the first 96 h, but water was absorbed by the outside seed coat,without penetrating through it. The moisture content (MC) of G. cowa seeds was high (50% in fresh weight)at shedding. The seeds could tolerate desiccation to some extent, until the MC reached approximately 40%;below that, the viability decreases rapidly and all seeds died at approximately 17% of MC. Seed viability decreased rapidly when seeds were chilled at 4 ℃; germination was 2% after storage for 1 week. Even stored at 10 ℃, seeds began to be damaged after 4 weeks. Seed storage for 1 yr revealed that in both dry (relative humidity (35 ± 5)%) and moist (wet sand) storage conditions, seed viability declined, but germination percentages for seeds stored under moist conditions are better than for seed stored under dry conditions.Because of their low tolerance to desiccation, marked chilling sensitivity and relatively short lifespan, G.cowa seeds should be classified into the tropical recalcitrant category. The ecological implications of dormant recalcitrant seeds and cues on storing recalcitrant seeds were discussed.     

REPRODUCTIVE PROFICIENCY IN PAEONIA CALIFORNICA (PAEONIACEAE)

Study of three populations of geophytic Paeonia californica in southern California revealed considerable variation, within and between populations, in both potential and in realized seed output. Plants are weakly self-compatible, but natural seed set (x = 4.2 seeds per carpel) is closer to seed set produced in hand cross-pollinations (x = 4.5) than in self pollinations (x = 1.4). Flowers are protogynous, nectariferous, and scented; 17 species of bees in four families, and one species of melyrid beetle were found in them and probably account for pollinations at these sites. Counts of reproductive parts show greatest inter-population variation in mean numbers per plant, of flowers (population means ranged from 16.2 to 21.2), ovules (744 to 1142), pollen grains (23 million to 38 million), and % viable pollen (26.6 to 81.4). Seed set also varied significantly, with only 11.4 to 26.8 % of the ovules maturing into seeds. This low reproductive success is probably correlated with the genetic anomalies studied by others—particularly the translocation heterozygosity that causes lowered production of viable gametes. The relatively few seeds produced are heavy (x = 0.184 g per seed), and germination percentages are high (x = 80%). The elongation of cotyledon bases during hypogeal germination seems to permit optimal germination at soil depths of only 2–3 cm, but environmental factors such as drought stress and herbivore pressure promote high seedling mortality.     

Diversity in seed germination behavior in relation to heterocarpy inSalsola komarovii Iljin

Seed germination behavior in two types of dimorphic fruits inSalsola komarovii Iljin (Chenopodiaceae) was studied. The germination percentage was much higher in the long-winged type than in the short-winged type when the fruits were tested for germinability. If lignified perianths were removed from the fruits, seeds of both types germinated at higher percentages and the difference in the germination percentage between two types decreased. The extract of the perianths inhibited the seed germination. Abscisic acid was detected in the extract of the perianths by enzyme-linked immunosorbent assay and its level was higher in the short-winged type than in the long-winged type. Germinability in both types was lost one year after harvest when the fruits were stored at room temperature and the germination was tested with fruits. When the seeds were tested, however, the short-winged type germinated even two years after the harvest; the germinability of the short-winged type lasted one year longer than that of the long-winged type. Light irradiation was not required for the seed germination in either type regardless of presence or absence of the perianths. No clear difference between the two types was observed either in optimal temperature for the germination or in strength of the resistance to salinity.     

Changes in germinability,lipid peroxidation,and antioxidant enzyme activities in pear stock (<Emphasis Type="Italic">Pyrus betulaefolia</Emphasis> Bge.) seeds during room- and low-temperature storage

The aim of this study was to determine if loss of germinability in Pyrus betulaefolia seeds stored at 4°C and at room temperature is associated with a loss of membrane lipid peroxidation or changes in antioxidant enzyme activities. The results indicated that germination percentage clearly decreased when seeds were stored at room temperature rather than at 4°C from 6 to 12 months. Room-temperature storage of the pear stock seed for 12 months decreased germination to 15.52%, but germination percentage was not changed when seed was stored at 4°C for 12 months. MDA, a marker for membrane lipid peroxidation, increased significantly under room-temperature storage conditions. Antioxidant enzyme (SOD, POD, and CAT) activities were a good indicator of germination percentage in pear stock seeds. Antioxidant enzyme activities of pear stock seeds at 4°C were higher than antioxidant enzyme activities in seeds stored at room temperature from 6 to 12 months. Antioxidant enzyme activities of the pear stock seed decreased markedly under conditions of room-temperature storage from 6 to 12 months. The results of this study showed that long-term room-temperature storage was detrimental for maintaining the vigor of P. betulaefolia seeds. The mechanisms responsible for this outcome are a higher level of membrane lipid peroxidation and a lower level of activity of antioxidant enzymes.     

Seed Dormancy,Seedling Establishment and Dynamics of the Soil Seed Bank of Stipa bungeana (Poaceae) on the Loess Plateau of Northwestern China

Studying seed dormancy and its consequent effect can provide important information for vegetation restoration and management. The present study investigated seed dormancy, seedling emergence and seed survival in the soil seed bank of Stipa bungeana, a grass species used in restoration of degraded land on the Loess Plateau in northwest China. Dormancy of fresh seeds was determined by incubation of seeds over a range of temperatures in both light and dark. Seed germination was evaluated after mechanical removal of palea and lemma (hulls), chemical scarification and dry storage. Fresh and one-year-stored seeds were sown in the field, and seedling emergence was monitored weekly for 8 weeks. Furthermore, seeds were buried at different soil depths, and then retrieved every 1 or 2 months to determine seed dormancy and seed viability in the laboratory. Fresh seeds (caryopses enclosed by palea and lemma) had non-deep physiological dormancy. Removal of palea and lemma, chemical scarification, dry storage (afterripening), gibberellin (GA₃) and potassium nitrate (KNO₃) significantly improved germination. Dormancy was completely released by removal of the hulls, but seeds on which hulls were put back to their original position germinated to only 46%. Pretreatment of seeds with a 30% NaOH solution for 60 min increased germination from 25% to 82%. Speed of seedling emergence from fresh seeds was significantly lower than that of seeds stored for 1 year. However, final percentage of seedling emergence did not differ significantly for seeds sown at depths of 0 and 1 cm. Most fresh seeds of S. bungeana buried in the field in early July either had germinated or lost viability by September. All seeds buried at a depth of 5 cm had lost viability after 5 months, whereas 12% and 4% seeds of those sown on the soil surface were viable after 5 and 12 months, respectively.     

The effects of stigma age on receptivity in Silene alba (Caryophyllaceae)

Silene alba, a perennial, dioecious plant, produces flowers that open in the evening and can remain open and receptive to pollination for up to 5 d, though in hot and dry conditions the flowers will wilt during the day only to reopen night after night. In the field, it is visited by two different kinds of pollinators with differential success: moths visit the flowers at night, and their movements result in broad pollen dispersal and large seed production, whereas bees, wasps, and flies visit the flowers in the mornings and have decreased pollination effectiveness. However, this differential success may be due to a decrease in stigmatic receptivity soon after the flowers open. We performed controlled pollinations to determine the effect of stigma age on pollen germination and seed set. We pollinated flowers at 12-h intervals up to 120 h and divided these into two sets: from one set, we removed stigmas 24 h after pollination to examine percentage of pollen germination. The second set of flowers was allowed to produce fruits, and the seeds were counted and weighed. Pollen germination declined significantly with stigma age, but there was no significant effect of stigma age at pollination on the number or mass of resulting seeds. Thus, the decreased pollination success of bees is not due to a decrease in stigmatic receptivity but is most likely a result of pollinator inefficiency.