Rudimentary Embryos Research Articles

The rudimentary embryo: an early angiosperm invention that contributed to their dominance over gymnosperms

AbstractIn this review, we explore the origin of the rudimentary embryo, its relationship to other kinds of plant embryos and its role in the diversification of angiosperms. Rudimentary embryos have a length:width ratio of ≤2.0, and they have organs, including cotyledon(s) and a primary root. A literature survey failed to reveal rudimentary embryos in the pre-angiosperms, suggesting that this kind of embryo is an angiosperm invention. Although proembryos of some gymnosperms and angiosperms have a length:width ratio of ≤2.0, they have not formed meristems or organs. Thus, rudimentary embryos are not proembryos. During the development of rudimentary embryos in monocots and dicots (all non-monocots), the growth pattern of the epicotyledonary cells differs, resulting in differences in the placement of the shoot meristem and in one versus two cotyledons, respectively, but the embryo size is similar. Rudimentary embryos grow inside the seed prior to germination, which is true for linear-underdeveloped embryos, including those in some gymnosperms. Rudimentary embryos served as the starting point for the great diversification of embryos, and ultimately of seeds, in angiosperms, and they are still present in many families of extant angiosperms. The rudimentary embryo is part of the syndrome of changes, including increased speed of pollen germination and pollen tube growth, simplification of the female gametophyte, development of endosperm and elimination of multiple embryo production from each zygote, that distinguish angiosperm seed production from that of gymnosperms. We conclude that the rudimentary embryo was one of many new developments of angiosperms that contributed to their great success on earth.

Effect of different substrates on in vitro symbiotic seed germination for soilless production of Anacamptis laxiflora orchid

In recent years, the orchid species have become endangered due to overuse and habitat destruction. As with most flowering plants, seed production is the primary strategy for reproduction in orchids. Orchids produce tiny seeds consisting of a seed coat and a rudimentary embryo. However, it lacks the endosperm, which is generally required as the primary energy source during germination. The only way to germinate orchid seeds is to get nutrients from an external source. In nature, this is achieved by mycorrhizal symbiosis. This study used Ceratobasidium sp. inoculation of Anacamptis laxiflora (Lam.) seeds combined with media with various organic substrates to determine their effectiveness on germination and seedling development by in vitro culture. The highest germination rate (35.78%) was obtained in the medium with addition of young hazelnut leaves. Then, soilless ex vitro symbiotic germination was performed on young hazelnut leaves, the most effective organic substrate. Seed germination was determined to be 19.01% in this medium while 14.87% seedlings with developed leaves and roots were formed. For the first time, success was achieved by producing A. laxiflora from seed in ex vitro conditions without soil and adapting it to nature.

Comparison of the seed dormancy and germination characteristics of six Clematis species from South Korea

• Six Korean Clematis species display morphological or morphophysiological dormancy. • Germination indices are improved in Clematis seeds by 100 mg/L GA 4+7 treatment. • Dormancy is broken by temperature stratification in C. trichotoma and C. terniflora . Clematis species are perennial woody or herbaceous vines that are popular medicinal and ornamental horticultural plants. The seeds of six species were collected from five sites, and their germination characteristics and dormancy types were investigated. Seeds of all species had a typical achene morphology of a seed pod with a tail. Small, rudimentary embryos (0.14 to 0.29 E:S ratio) were observed, and the seeds showed sufficiently good water absorption (53.9–72.4%). Germination occurred within 30 days for C. apiifolia (light and dark conditions, 66.3% and 90.5%, respectively), C. heracleifolia var. urticifolia (77.0 and 92.5%), C. heracleifolia (37.3 and 88.3%), and C. serratifolia (1.0 and 96.5%). Germination was promoted using gibberellin treatments. Furthermore, the seeds of C. terniflora and C. trichotoma broke dormancy with short-term cold temperature stratification, and the embryos developed and germinated at warm temperatures. We concluded that the seeds of C. apiifolia, C. heracleifolia var. urticifolia, C. heracleifolia , and C. serratifolia are morphologically dormant whereas those of C. terniflora and C. trichotoma are morphophysiologically dormant. This study provides seed propagation and dormancy information for six Clematis species native to Korea.

Evaluación del contenido de ácido carmínico con respecto al sacrificio y secado de Dactylopius coccus Costa en Nopaltepec, Estado de México

Digital images were obtained with the faxitron x-ray equipment in seed of: Pinus douglasiana, Pinus devoniana, Caesalpinia platyloba, Lisyloma divaricatum and Swetenia humilis. The correlation between morphological patterns of structures and the physiological development measured by EP germination analysis (ISTA), determination of pH of the exudate and electrical conductivity was established. The X-ray test turned out to be appropriate to analyze the development of embryos, internal physical damage, integuments damage, embryonic cavity filling, embryo alterations and insect attack. Pinus douglasiana showed correlation (-.88 *) between rudimentary embryos (ER) and normal seedlings (PN) and (.94 *) between embryo severe damage and abnormal seedlings; in Pinus devoniana, (-.75 *) for ER and PN; Caesalpinia platyloba and Lisyloma divaricatum They presented higher percentage of internal fissures and correlation (.89 **) of embryo with severe damage and dead seeds. Swetenia humilis in percentage of rudimentary embryos with dead seeds (.87 *). Regarding the external tonality, the electrical conductivity of the species P. devoniana, P. douglasiana S. humilis and C. platyloba, was higher on average in their seeds of dark testa than those of light tone suggesting a greater degree of deterioration.

Seed dormancy in ornamental plants: A review

Seed is the first input used in transfer of genetic traits in ornamental plants production. Seed dormancy is a physiological phenomenon in plants, which is caused by external or internal factors, and prevents seed germination, even in optimal conditions. Seed dormancy in flower crops impacts both seed production and germination. It can also complicate assessment of seed quality by the seed analyst who requires prompt germination to evaluate a seed lot. Flower crops display diverse mechanisms for seed dormancy like hard seed coat, immature, rudimentary embryo and inhibitors. It can be broken by soil melting and freezing, microorganism’s activity, forest fires, soil activity and being eaten by animals, in normal conditions. This review surveys and categorizes the different seed dormancy conditions found in flowering plants. Flower genera are listed according to dormancy type. Categories of dormancy include primary and secondary dormancy. Within primary dormancy, examples of flower genera can be found that display exogenous, endogenous and combinational dormancy. Secondary dormancy can be an important problem in selected flower seeds. Specific examples are given for each type of dormancy along with methods to alleviate dormancy.

Ambered Kernels in Stenospermocarpic Fruit of Eastern Black Walnut

“Ambers” is a term used to describe poorly filled, shriveled eastern black walnut (Juglans nigra L.) kernels with a dark brown or black-colored pellicle that are unmarketable. Studies were conducted to determine the incidence of ambered black walnut kernels and to ascertain when symptoms were apparent in specific tissues. The occurrence of ambered kernels was evaluated in fruit harvested from mature ‘Football’ trees growing at three sites within a commercial black walnut orchard in 2008 to 2010. Mature walnut fruit sampled from trees at Site 2 had greater odds for ambered kernels than those on trees at two other sites within the same orchard with 27% of the walnuts sampled exhibiting symptoms when examined in October. Also, black walnut fruit in 2010 had more ambered kernels than those examined in Oct. 2008 or 2009. Cropload, soil type, ambient temperatures, or precipitation was not apparently associated with a high incidence of ambered kernels. When black walnut fruit from trees at Site 2 were examined from 25 June to 6 Oct. 2011, embryos were visible in 50% of the fruit without discoloration on the first date. Stenospermocarpy (e.g., aborted or rudimentary embryos after fertilization) was observed in fruit with discolored or ambered kernels as early as 7 July. Stenospermocarpic fruit with ambered kernels had shorter embryo axis lengths (root apex to shoot apex) than fruit with non-ambered kernels on 7 July and at successive sampling dates. Cotyledon widths of ambered kernels in stenospermocarpic fruit were narrower than those of non-ambered kernels on 21 July, but symptomatic cotyledons continued to enlarge until 15 Sept. All fruit enlarged during the growing season and nut diameters varied by only 3.4 mm at harvest. Thus, visible embryo degeneration, which was associated with ambered kernels in black walnut fruit, was detected in early July when shell hardening occurs and kernel tissues are enlarging.

Morphological and Morphophysiological Dormancy in Seeds of Two Genera (Heloniopsis and Thalictrum) Native to Korea

Abstract: This study was conducted to find basic information for the research of morphological dormancy in seeds of two genera (Heloniopsis and Thalictrum) native to Korea. Seeds of Heloniopsis koreana, Heloniopsis tubiflora, Thalictrum rochenbrunianum,Thalictrum uchiyamai , and Thalictrum coreanum were collected, and embryo morphology and seed germination were investi gated. All seeds of five species had underdeveloped embryos which occupied about 10-20% of the full seed length at maturity. The seeds of H. koreana and H. tubiflora had rudimentary embryos. The seeds of T. rochenbrunianum , T. uchiyamai, and T. coreanum had intermediate type between rudimentary and linear embryo. The small embryos of all seeds of five species grew to a critical length before radicles emerge from the seeds. At 30 days after sowing, the seeds of H. koreana and H. tubiflora germinated to 22.7% and 40.7%, respectively. On the other hand, the seeds of T. rochenbrunianum , T. uchiyamai, and T. coreanum germinated to 12.5%, 3.3%, and 0%, respectively. If embryo growth and germination in seeds are completed in approximately 30 da ys, the seed are said to have morphological dormancy (MD). However, if the seeds require > 30 days for germination, they are considered to have morphophysiological dormancy (MPD). Thus, the seeds of H. koreana and H. tubiflora had about 78% and 60% MPD, respectively. On the other hand, the seeds of T. rochenbrunianum, T. uchiyamai, amd T. coreanum had about 87%, 96%, and 100% MPD, respectively. There was a different level of dormancy (MD and MPD) within the same seed population examined. Therefore, germination of the seeds was delayed due to the underdeveloped embryos. This result could contribute to determine morphological seed dormancy and germination mechanism in seeds of the Korean Peninsula.Additional key words:

A new approach to highly sensitive determination of retinoic acid isomers by preconcentration with CdSe quantum dots

Unusual amounts of retinoic acid (RA) isomers play an important role in abnormal morphological development of mammals; such as rat embryos. Each isomer of RA has a unique function in first steps of embryonic life. In the current study, a new method for preconcentration and simultaneous determination of all-trans retinoic acid, 13-cis retinoic acid, 9-cis retinoic acid and 9,13-di-cis retinoic acid in rat whole rudimentary embryo culture (RWEC) has been developed. RA isomers were extracted from samples by conjugation to appropriate amount of surface modified CdSe quantum dots (QDs) prior to HPLC/UV determination. In order to quickly release of the analytes with unchanged form, separated RA-QD conjugation were irradiated by intensive near infrared wavelength (NIR). Low energy NIR irradiation results in maintaining the primary forms of RA isomers during the release. The conjugation and release mechanisms were described and experimental parameters were investigated in detail. Under optimized conditions, the method was linear in the range of 0.040-34.600 pmol g(-1) for all-trans RA (R(2)=0.9996), 0.070-34.200 pmol g(-1) for 13-cis RA (R(2)=0.9992), 0.050-35.300 pmol g(-1) for 9,13-di-cis RA (R(2)=0.9998) and 0.050-32.900 pmol g(-1) for 9-cis RA (R(2)=0.9990). The present method can be useful for retinoic acid monitoring in clinical studies.

Enhanced Seed Germination of Ilex dumosa R. (Aquifoliaceae) through In Vitro Culture of Cut Pyrenes

An in vitro culture protocol was developed that increased the germination percentage and decreased the lag time to germination for Ilex dumosa R. pyrenes as a tool for replacing the laborious task of embryo rescue technique. This method involves transversely cutting surface-sterilized pyrenes with a scalpel blade, then placing the micropylar one-third end with the rudimentary embryo (≈0.25 mm long) on solidified (agar 0.65%) quarter-strength salts and vitamins of Murashige and Skoog, 1962 medium with 3% sucrose, and incubating in a growth room at 27 ± 2 °C with a 14-h photoperiod (116 μmol·m−2·s−1). Most of the cut pyrenes (greater than 50%) germinated within the first month after inoculation and achieved maximum germination (≈70%) in 2 months compared with whole pyrenes, which began to germinate 3 months after sowing and required more than 8 months for maximum germination (37%). Moreover, the germination percentage of cut pyrenes was significantly higher than the germination of isolated embryos (34%). Thus, the cut pyrenes culture is a simpler and more effective technique than embryo rescue. Easily, on average, a trained operator is able to culture ≈1000 cut pyrenes per day instead of ≈100 isolated embryos.

Nondeep simple morphophysiological dormancy in seeds of Ilex maximowicziana from northern (subtropical) and southern (tropical) Taiwan

AbstractIn this study, we show that seeds of Ilex maximowicziana collected from northern and southern Taiwan differ in germination responses to temperature. Seeds produced by plants growing in the tropical environment of southern Taiwan were more responsive (in a positive way) to higher incubation temperatures than those produced by plants growing in the subtropical environment of northern Taiwan. On the other hand, seeds produced in northern Taiwan were more responsive (in a positive way) to low incubation temperatures and to cold stratification than those from southern Taiwan. Germination percentages and rates of seeds from northern Taiwan were higher at 20/10°C than at 30/20°C, reaching a plateau of >80% germination after 12 weeks incubation, whereas germination of seeds from southern Taiwan reached >80% at 30/20 and 25°C but not at 20/10°C. Gibberellic acid (GA3) increased germination rate but not germination percentage of seeds from both southern and northern Taiwan. Freshly matured seeds of I. maximowicziana have rudimentary embryos. During dormancy break, embryo length increased 11.5‐ and 8.0‐fold in northern and southern seeds, respectively, before radicle emergence. Thus, seeds of Ilex maximowicziana have nondeep simple morphophysiological dormancy. This is the first detailed study of the germination requirements of a subtropical/tropical species of the large cosmopolitan genus Ilex.

A cryopreservation protocol for immature zygotic embryos of species of Ilex (Aquifoliaceae)

Tropical Ilex species have recalcitrant seeds. This work describes experiments demonstrating the feasibility of long-term conservation of Ilex brasiliensis, I. brevicuspis, I. dumosa, I. intergerrima, I. paraguariensis, I. pseudoboxus, I. taubertiana, and I. theezans through cryopreservation of zygotic rudimentary embryos at the heart developmental stage. The embryos were aseptically removed from the seeds and precultured (7 days) in the dark, at 27 +/- 2 degrees C on solidified (0.8% agar) 1/4MS medium, [consisting of quarter-strength salts and vitamins of Murashige and Skoog (1962) medium] with 3% sucrose and 0.1 mg/l Zeatin. The embryos were then encapsulated in 3% calcium alginate beads and pretreated at 24 h intervals in liquid medium supplemented with progressively increasing sucrose concentrations (0.5, 0.75 and 1 M). Beads were dehydrated for 5 h with silicagel to 25% water content (fresh weight basis) and then placed in sterile 5 ml cryovials. Then the beads were either plunged rapidly in liquid nitrogen were they were kept for 1 h (rapid cooling) or cooled at 1 degrees C min(-1) to -30 degrees C. Then the beads were immersed in liquid nitrogen for 1 h (slow cooling). The beads were rewarmed by immersion of the cryovials for 1 min in a water bath thermostated at 30 degrees C. Finally, beads were transferred onto culture medium (1/4MS, 3% sucrose, 0.1 mg/l zeatin, solidified with 0.8% agar) and incubated in a growth room at 27 +/- 2 degrees C under a 14 h light (116 micromol. m(-2) x s(-1))/ 10 h dark photoperiod. Maximum recovery percentages between 15 and 83% (depending on de the species and the treatment) were obtained with the cryopreserved embryos.

Nymphaeaceae: a basal angiosperm family (ANITA grade) with a fully developed embryo

AbstractRudimentary, broad and small linear embryos occur among members of the most primitive (basal) extant angiosperms, collectively called the ANITA grade (i.e.Amborella,NymphaealesandAustrobaileyales).Amborella(rudimentary) andAustrobaileyales(rudimentary inAustrobaileyaceae,IlliciaceaeandSchisandraceaeand small linear inTrimeniaceae) have kinds of embryos that are known to be underdeveloped; consequently, they must grow inside the seed prior to radicle emergence (germination). On the other hand, it is not known if broad embryos need to grow before radicles can emerge, and whether they are underdeveloped or fully developed. Thus, we addressed the question: ‘Is the broad embryo ofNymphaealesalso underdeveloped?’. Although the embryo length : seed length ratios inNymphaeaAlbert Greenburg,N.capensisvar.zanzibariensisandN.immutabiliswere 0.311, 0.349 and 0.234, respectively, embryos did not grow prior to radicle emergence. Thus, they are fully developed at seed maturity. IfAmborellaandNymphaealesare equally the most basal angiosperms, as some molecular phylogenetic studies indicate, then we must conclude that the broad and rudimentary embryos are equally primitive.

Temperatures affecting embryo development and seed germination of Christmas rose ( Helleborus niger) after sowing

Embryo development followed by seed germination was investigated in seeds of Christmas rose ( Helleborus niger) held under different temperature conditions. The seeds had a heart-shaped embryo when dispersed from parent plants. That embryo developed rapidly to the torpedo stage at 25 °C, after which no further development occurred. When seeds with a torpedo-stage embryo were held at 15 °C, the embryos developed to the cotyledon stage, but no further germination occurred. Similar phenomena in the course of embryo development were observed in seeds held in a non-heated polyethylene house, in which the embryos developed to the torpedo stage at 20 °C or more, while further development to the cotyledon stage was attained only at temperatures of 15 °C or less. Seeds with a cotyledon-stage embryo rarely germinated until they were treated at 4 °C for more than 8 weeks. These results suggest that seeds of H. niger have a deep, simple morphophysiological dormancy caused by the combination of rudimentary embryos and a physiological dormancy that can be broken by cycles of warming and chilling.

Endo-β-mannanase activity is associated with the completion of embryogenesis in imbibed carrot (Daucus carota L.) seeds

AbstractDevelopment of the rudimentary embryo in mature carrot (Daucus carota) seed during imbibition was characterized. The small embryo in the carrot seed, located in the micropylar region, elongated into the lateral part during imbibition and attained about two-thirds the length of the seed before radicle protrusion. Developing embryos excised from imbibed seeds were only capable of germinating in both water and Murashige–Skoog (MS) medium when they reached maximum size. The corrosion cavity into which the embryo grew enlarged concomitantly with endosperm degradation. The expression of endo-β-mannanase (EC 3.2.1.78), which is assumed to be involved in endosperm degradation, was characterized. A cDNA encoding an endo-β-mannanase was obtained by reverse transcription polymerase chain reaction (RT-PCR) using total RNA extracted from 24-h-imbibed carrot seeds. The full-length cDNA (DcMAN1) exhibited 64% deduced amino acid sequence identity with tomato (Lycopersicon esculentum) seed germination-associated mannanase (LeMAN2). DcMAN1 mRNA and endo-β-mannanase activity were first detected in the micropylar-half seed and then in the lateral-half seed. The timing of the appearance of DcMAN1 mRNA and endo-β-mannanase activity in the lateral-half seed corresponded with that of embryo development into this region. These results suggest that the expression of DcMAN1 and endo-β-mannanase activity in imbibed carrot seeds is associated with the enlargement of the corrosion cavity, which accompanies embryogenesis.

Subnivean embryo development in the alpine herb Caltha leptosepala (Ranunculaceae)

Caltha leptosepala D.C. (Ranunculaceae) is a perennial herb of alpine wet meadows. Seeds of this species have morphophysiological dormancy; they contain a rudimentary embryo that must undergo further development prior to germination. The embryo itself is also dormant and requires a physiological cue for resumption of development. We ask how C. leptosepala can break embryo dormancy and complete embryo development, germination, and seedling growth under the constraint of the extremely short alpine wet meadow growing season. Seeds were stratified at 2.5°C and collected at regular intervals for germination trials and histological analysis. At dispersal, the embryo occupies approximately 7% of the length of the seed and is dormant. Embryo development resumes within 1 month of stratification. Embryos grow to fill the seed over a 4- to 7-month period. Germination rates are positively correlated with stratification time and reach 50% at 4 months and 70% at 7 months. Because embryo development requires a time period longer than the snow-free period prior to germination in the alpine wet meadow, we conclude that embryo development in C. leptosepala takes place beneath alpine snowbanks. Morphophysiological dormancy in Caltha is not uniquely derived, but the ability of Caltha embryos to develop and germinate at low temperatures may be an adaptation to their environment.Key words: alpine, rudimentary embryo, Ranunculaceae, seed, dormancy, germination.

イチゴ属の種間交雑Ｆｒａｇａｒｉａ ｘ ａｎａｎａｓｓａ×Ｆ．ｖｅｓｃａにおける花粉の発芽異常およびはいの発育停止と交雑不和合性の関係

To investigate why the interspecific cross Fragaria x ananassa (8x) × F. vesca (2x) gives a lower rate of viable hybrid achenes and seedlings, emasculated flowers of F. x ananassa 'Honeoye' (8x) were pollinated with pollen of 'Changsen', a clone of F. vesca (2x) originally from Changbaishan, Jilin Province, China. The intraspecific cross F. x ananassa 'Honeoye' × 'Hokowase' was used as the control. In the interspecific cross, 6 out of 10 pollinated flowers produced 303 developed achenes of which 167 seedlings were grown ; 84 were hybrids (5x) and 83 were apomicts. The germination of F. vesca pollens on the stigmas of F. x ananassa was rarely observed and the elongation of pollen tubes in the style was irregular. For the interspecific cross, in addition to normal growth of embryos with endosperm, delayed fertilization was observed as well as the suspended growth of embryos at the globular stage. Such abnormal embryos lacked endosperm development. These results indicate that abnormality in pollen germination and pollen tube elongation, and aberrant growth of embryos and endosperm could be the basis of incompatibility in the interspecific cross of F. x ananassa × F. vesca. Embryo rescue culture which prevents abortion of rudimentary embryos, which can occur in the interspecific cross in strawberries, may be the means to develop new hybrids.

In Vitro Culture of Rudimentary Embryos of Ilex paraguariensis: Responses to Exogenous Cytokinins

The effects of benzyladenine (BAP), kinetin (KIN), zeatin (ZEA), isopentenyladenine (2iP), and thidiazuron (TDZ) were studied on in vitro growth of rudimentary embryos of Ilex paraguariensis St. Hil. Heart stage zygotic embryos were removed from seeds of immature, light green fruits and cultured aseptically on quarter-strength Murashige and Skoog medium containing 3% sucrose, 0.65% agar, and supplemented with or without three concentrations of BAP, KIN, ZEA, 2iP, or TDZ. Cultures were incubated in darkness at 27 ± 2°C. Media containing 4.4 × 10−6m BAP, 4.6 × 10−6m KIN, or 4.9 × 10−6m 2iP were totally ineffective in inducing embryo growth after culture for 28 days. However, lower concentrations of these compounds (4.4 × 10−8m BAP, 4.6 × 10−8m KIN, 4.5 × 10−8m ZEA, or 4.9 × 10−8m 2iP) promoted embryo growth. TDZ at 9.9 × 10−9m, 9.9 × 10−8m, or 9.9 × 10−7m induced embryo growth at similar rates. The maximum percentage of embryos converted to seedlings was achieved when the medium was supplemented with 4.5 × 10−7m ZEA.

Morphological Development of Pawpaw [Asimina triloba (L.) Dunal] during Seed Germination and Seedling Emergence

Little scientific information is available describing morphological development of pawpaw during seed germination. To provide this information, a study was designed to outline important developmental stages and describe seedling characteristics within each stage. Stratified pawpaw seeds were sown in vermiculite and germinated at 25°C in a growth chamber. Ten seedlings were randomly chosen and destructively harvested at 5-day intervals starting at radicle protrusion. Length (mm), fresh and dry weight, and percentage of total dry weight were determined for seedling components. Pawpaw seeds have a small rudimentary embryo with all food reserves stored in a ruminate endosperm. Dry weight measurements showed a dramatic reallocation of reserves from the storage tissue to developing seedling parts. Initial embryo length was less than 3 mm, but within 70 days seedlings exceeded 350 mm. Twelve days after planting, simultaneous radicle and cotyledon growth occurred (3.4 and 3.0 mm, respectively), but neither hypocotyl nor epicotyl was visible. Radicle protrusion was observed at 15 days with radicle, cotyledon and hypocotyl lengths increasing to 4.4, 4.0, and 3.2 mm, respectively. Endosperm comprised 99.1% of total dry weight at this stage. The hypocotyl hook emerged after 30 days and endosperm comprised 76.1% of total dry weight. Cotyledons reached maximum length (29.0 mm) at day 40 and the epicotyl was discernible. At 55 days, the seed coat containing cotyledons and residual endosperm abscised and the average radicle, hypocotyl and epicotyl lengths were 182.0, 61.1, and 7.3 mm, respectively. It is suggested that the cotyledons primary function is absorption of food reserves from the endosperm for transfer to the developing seedling.

Light-mediated Inhibition of in Vitro Late Embryogeny of Ilex

Abstract An inhibitory effect of light on in vitro late embyogeny of I. aquifolium and I. opaca cv. Farage was observed. A negative log-linear correlation between the final embryo size and hours of continuous light during preincubation, at an intensity of 64 W·m−2, was established with I. aquifolium. It took ≈ 15 hr of pre-incubation light to result in 50% growth inhibition. Negative log-linear correlations between the final embryo lengths and light intensities were also observed for I. aquifolium and I. opaca. The rudimentary embryos of I. opaca were more sensitive to light inhibition than those of I. aquifolium. During incubation for 11 and 14 days with a 16-hr photoperiod, light intensities for 50% growth inhibition were ≈ 5 and 11 W·m−2 for I. opaca and I. aquifolium, respectively. Since growth inhibition by light could not be reversed by the presence of GA3 concentrations up to 1000 μm, some factor(s) other than the accumulation of abscisic acid or related compounds is probably responsible for such a phenomenon.

Germination Ecophysiology of an Eastern Deciduous Forest Herb Stylophorum diphyllum

Stylophorum diphyllum (Michx.) Nutt. is an herbaceous polycarpic perennial that grows in mesic deciduous forest from western Pennsylvania and southern Ontario to Wisconsin S to southwestern Virginia, northern Alabama, northern Arkansas and Missouri. Seeds are dormant at dispersal in late May and early June. Dormancy is due to a rudimentary (i.e., underdeveloped) embryo which requires incubation at low moist temperatures (stratification) for growth. In the habitat, embryo elongation occurs during the cold season and seeds germinate in early spring. A warm pretreatment is not required for subsequent embryo growth and germination. Embryos in freshly matured seeds averaged 0.41 mm long but after 10 weeks of chilling at 5 C they averaged 1.41 mm. Germination of seeds incubated continuously at 5 C began after 11 weeks and after 19 weeks 80 %O had germinated. Seeds stratified for 6 weeks and then transferred to (12/12 hr) daily thermoperiods of 15/6 and 20/10 C germinated to 75 and 65 %O, respectively, whereas 12 weeks of stratification were required before a comparable percentage of seeds would germinate at 25/15 C. Seeds of S. diphyllum fit Nikolaeva's definition of morphophysiological complex dormancy.