THE INFLUENCE OF CULTURAL CONDITIONS ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Apogamous sporophytes formed on Pteridium gametophytes in response to concentrations of certain sugars which supported gametophytic growth. High osmotic concentration of the medium inhibited apogamy, while variations in the basic medium were not stimulatory. Agar, autoclaving, the ammonium ion, and dry media were not required for apogamy. Renewing the medium during an experiment enhanced the apogamous response. Changing the medium at set intervals facilitated the separation of apogamous plant development into gametophytic, initiative, and developmental phases, thus enabling testing of various factors at each of these stages. Apogamy was light-initiated, while the actual development of apogamous sporophytes was caused by light, succinic acid or sugar.     

THE EFFECT OF DIFFERENT LIGHT CONDITIONS AND SUCROSE ON THE GROWTH AND DEVELOPMENT OF THE GAMETOPHYTE OF THE FERN,ONOCLEA SENSIBILIS

Miller , J. H. (Yale U., New Haven, Conn.), and P. M. Miller . The effect of different light conditions and sucrose on the growth and development of the gametophyte of the fern, Onoclea sensibilis. Amer. Jour. Bot. 48(2): 154–159. Illus. 1961.—Gametophytes grow rapidly under the highest intensity white fluorescent light used, 400 ft.-c. Growth is correspondingly less at 220 and 28 ft.-c., and at the lowest light intensity the gametophytes are markedly longer than wide. One percent sucrose added to the medium reverses the growth limitation imposed by low light intensity and produces a morphology comparable to that found under higher intensities. Sucrose does not sustain heterotrophic growth in total darkness, but permits growth if the gametophytes are given low dosages of red light. The effect of red light is reversible by far-red illumination.     

INTERPOPULATIONAL VARIATION IN THE GAMETOPHYTES OF PELLAEA ANDROMEDAEFOLIA

The development and mature morphology of the gametophytes from both sexual and apogamous populations of the fern Pellaea andromedaefolia were investigated. While most sexual examples were indistinguishable, some differences were noted. An insular collection was distinctive in its variability and irregularity of form. Although the latter was a representative of var. pubescens, other collections of the variety could not be distinguished from var. andromedaefolia on the basis of gametophytic characteristics. The apogamous gametophytes were decidedly more variable in development and often very different from sexual thalli. The mature asexual thalli tended to be more irregular in form and usually sharply divergent from the typical cordate type characteristic of the sexual populations. Each of the five apogamous samples was unique with respect to gametophyte development. The differences among the gametophytes of the various populations do not correlate with the sporophytic characteristics which differentiate the two varieties of the species.     

The effect of thiouracil on the viability of eggs and embryogeny in Pteridium aquilinum

Summary Gametophytes of Pteridium aquilinum fed for six days with 50 and 75 p.p.m. thiouracil ceased to produce archegonia, but archegonia already initiated completed their development. Eggs produced in the presence of 50 p.p.m. thiouracil were viable, but embryogenesis was retarded. Gametophytes fed with 75 p.p.m. thiouracil mostly remained barren after insemination, the eggs being inviable, but others produced outgrowths from the archegoniate region which were either gametophytic, or sporophytic with a tendency to revert morphologically and functionally to gametophytic tissue.Thiouracil administered after fertilization either prevented embryogenesis, or retarded it, the sporophytes then being deformed and often showing a tendency to produce gametophytic tissue. The embryo became less sensitive to short periods of thiouracil as it developed, possibly because of the appearance of relatively quiescent regions, serving as reservoirs of unaffected cells.The results are held to support the view that the genes responsible for sporophytic growth become activated during oogenesis, and that the cytoplasm of the mature egg already contains the information leading to this kind of growth.     

PROBLEMS IN THE IDENTITY AND ORIGIN OF THE APPALACHIAN VITTARIA GAMETOPHYTE,A SPOROPHYTELESS FERN OF THE EASTERN UNITED STATES

Populations of a fern gametophyte presumed to be of the genus Vittaria occur commonly in the uplands of the southeastern United States. The gametophytes occur on non-calcareous rock outcrops of various composition in areas which provide continuous moisture and protection from temperature extremes. Gametophytes in these habitats are robust and long lived, frequently forming the dominant vegetation in areas covering several square feet. Reproduction is exclusively vegetative by production of gemmae. Although sex organs are present in most populations, viable sporophytes are never produced. The gametophytes have previously been considered most likely to be V. lineata, which occurs in Florida, but morphological and physiological comparisons do not support that conclusion. Significant differences between Appalachian and Florida gametophytes occur in growth form, growth rate, cold hardiness, sporophyte production, and patterns of gemma production. The distribution of the Appalachian gametophytes correlates with old, unglaciated land masses suggesting antiquity rather than recent introduction. Present evidence favors the interpretation that the Appalachian Vittaria gametophytes either belong to a tropical American species from which they have long been separated, or that they represent a distinct species of which the sporophyte no longer exists.     

Biological and nutritional aspects involved in fern multiplication

Gametophytes of several species of ferns were mechanically triturated and the resulting homogenates cultured in vitro for propagation purposes. Differences in the time period from spore culture to sporophyte development were perceivable between species. For those species with a fast life cycle and high sporophyte production such as Woodwardia virginica and Dryopteris affinis sp. affinis, homogenization of gametophytes can be considered to be excellent method for propagation, yielding hundreds of sporophytes in a short period of time. Sporophyte formation was inhibited in O. regalis by the succesive application of homogenization to gametophytes regenerated by this technique. The effect of the culture medium composition on fern production was also studied in O. regalis and P. ensiformis gametophytes. In these species, sporophyte formation increased when the gametophytes were cultured in a medium containing water+0.7% agar. Addition of sucrose inhibited gametophyte development and induced their necrosis. The 1/2 dilution of Murashige and Skoog basal medium, without sucrose, favoured leaf expansion in P. ensiformis sporophytes. This revised version was published online in June 2006 with corrections to the Cover Date.     

OBLIGATE OUTCROSSING IN A HOMOSPOROUS FERN: FIELD CONFIRMATION OF A LABORATORY PREDICTION

While homosporous ferns are potentially capable of producing totally homozygous sporophytes in one generation via selfing of their bisexual gametophytes, laboratory analyses indicate that a variety of mechanisms promote gametophytic outcrossing. The operation of these mechanisms in natural sporophyte populations, however, has not been previously demonstrated. Laboratory analyses of gametophyte ontogeny show that Bommeria hispida is obligately outcrossing. Electrophoretic data presented here indicate that individuals from natural sporophyte populations of this species are highly heterozygous. Electrophoretic data, therefore, corroborate evidence from the in vitro analysis of gametophyte development and demonstrate that sporophytes of B. hispida in nature typically are products of outcrossing between genetically different gametophytes. Extrapolations from the literature, together with our findings, indicate that outcrossing mechanisms may operate frequently in ferns, thereby maintaining genetic variability between individuals within populations. This evidence questions whether most ferns are highly inbred and therefore predominantly homozygous.     

The effect of sucrose on the differentiation of excised fern leaf tissue into either gametophytes of sporophytes

Excised juvenile leaves of Microgramma vacciniifolia (Polypodiaceae) develop sporophytic regenerants when grown on mineral agar with sucrose. The ratio of sporophytes to gametophytes produced from the leaf tissue increases with higher percentages of sucrose such that at 4% sucrose, the induction of aposporous gametophytes is a rare occurrence. Experiments varying the osmotic potential with sorbitol and those holding the osmotic potential of the culture medium constant while varying the sucrose level indicate that the effect of sucrose on the differentiation of fern leaf tissue into either gametophyte or sporophyte is nutritional rather than osmotic. A significant effect of sucrose in altering the differentiation of fern leaf tissue is the increased rate of senescence promoted by high sucrose concentrations.     

GROWTH AND DEVELOPMENT OF THE MALE GAMETOPHYTE OF GINKGO BILOBA WITHIN THE OVULE (IN VIVO)

The mature male gametophyte of Ginkgo biloba can be divided into two regions: a large saccate structure that is suspended within the fertilization chamber above the archegonia, and a pervasive, highly branched haustorial system that ramifies through the intercellular air spaces of the apex of the nucellus. This morphology appears to differ in many ways from the simpler more typical male gametophytes of most other groups of seed plants. Growth and development of the male gametophyte of Ginkgo biloba were studied using computer reconstruction techniques to generate images of the gametophyte from data derived from serial sections through the ovule. These investigations reveal that morphological development of the male gametophyte of Ginkgo biloba is divided into three distinct phases: 1) Germination, characterized by an initial brief period of diffuse growth. This phenomenon has not been described for any other seed plant male gametophyte; 2) Initiation of tip growth and the formation of a tubular body, as typifies all seed plant male gametophytes. In Ginkgo, this is accompanied by a high degree of branching, giving rise to an extensively branched haustorial system; 3) Late swelling of the proximal unbranched portion of the gametophyte resulting in formation of the saccate structure that is characteristic of the mature gametophyte. This process appears to be very similar to late development in cycad male gametophytes. Thus, despite the seemingly anomalous morphology of the mature male gametophyte of Ginkgo biloba, specific patterns of growth and development are in many ways similar to growth processes expressed by the male gametophytes of some or all major groups of seed plants.     

WILD GAMETOPHYTES OF PHANEROSORUS MAJOR (MATONIACEAE)

The gametophytes of Phanerosorus major collected from wild populations in Seram Island are described. Young gametophytes are slender, ribbon-like and uniformly one cell thick. They develop to old gametophytes with a broad thick cushion and coarsely ruffled wings. The gametophytes are monoecious and protandrous, although archegonia-bearing thalli occasionally become antheridia-bearing. Massive antheridia form on the ventral surface of young and old gametophytes while archegonia are borne on the cushion of old ones. Both young and old gametophytes reproduce vegetatively. The gametophytic characters are compared with those of Matonia. The life cycle of P. major is discussed with reference to its ecology.     

Growth and reproductive characteristics in artificially formed clonal gametophytes ofDryopteris filix-mas (Dryopteridaceae)

Artificially formed clonal gametophytes ofDryopteris filix-mas (L.)Schott were able to grow and reproduce, although growth rates, proportions of hermaphrodites and reproductive efforts were low. Variable density and nutrient levels appeared to affect gametophytic life histories and they continued to influence the viability of the developing sporophyte generation. Differences between populations and sporophytes were discovered in life histories. Hermaphroditic gametophytes were considerably larger and possessed higher viability than did males. Clear differences between clones in the level of phenotypic plasticity in gametophyte size were observed. No neighbor effect on gametophyte sex expression was detected with the densities and nutrient levels used.     

THE DEVELOPMENT OF THE FEMALE GAMETOPHYTE OF EPIPACTIS (ORCHIDACEAE) AND ITS INFERENCE FOR REPRODUCTIVE ECOLOGY

The development of the female gametophytes of Epipactis atrorubens, E. helleborine, and E. palustris have been investigated using confocal scanning laser microscopy. These species have T-tetrads and eight-nucleate female gametophytes in common. The development of the female gametophyte is monosporic in accordance with the Polygonum type. Furthermore, the outer integument grows slowly and reaches to the middle of the inner integument, when the female gametophyte is mature. In the first two species, T-tetrads develop prior to anthesis, which may be correlated with autogamy. The development of the female gametophyte of E. palustris appears to be similar in plants from different localities.     

Practical methodology for gametophyte proliferation and sporophyte production in green penny fern (Lemmaphyllum microphyllum C. Presl) using mechanical fragmentation

Propagation of gametophytes and sporophytes using mechanical fragmentation has been considered a suitable method for mass production of ferns. This study aimed to develop a practical propagation method for Lemmaphyllum microphyllum C. Presl, which is a fern of significant ornamental and medicinal value. Gametophytes were obtained through in vitro spore germination and used for propagation experiments. The gametophyte was mechanically fragmented using a scalpel into small fragments, which were then used to investigate gametophyte proliferation. In addition, the gametophyte was fragmented using a blender and then used to study sporophyte formation. Optimal proliferation conditions of the gametophyte were determined using Murashige and Skoog (MS) basal medium (double-, full-, half-, quarter-strength), Knop medium, and medium components (sucrose, nitrogen sources, activated charcoal), at various concentrations. The fresh weight of the gametophyte was 14-fold higher than that of gametophytes (300 mg) used as culture material, when cultured on double-strength MS. Moreover, 1 g of the gametophyte fragmented in 25 mL of distilled water formed more than 430 sporophytes in a soil mixture in an area of 7.5 cm². The sporophytes were successfully cultivated in the greenhouse after acclimation. A large-scale production method for L. microphyllum that can be easily implemented in a fern production farm is outlined.

     

CHELATED IRON AND GAMETOGENESIS IN MACROCYSTIS

Stekoll, M. S. Juneau Center for Fisheries and Ocean Sciences, University of Alaska, Juneau, AK 99801 USA Gametophytes of Macrocystis can be vegetatively propagated indefinitely in the laboratory in media that lacked chelated iron. When clones of vegetatively propagated female gametophytes of Macrocystis pyrifera (L.) C. Ag. were exposed to varying levels of chelated iron in both enriched natural and artificial seawater, low levels of chelated iron (1-5 micromoles/liter) stimulated the onset of gametogenesis as measured by egg production. In contrast higher iron concentrations strongly inhibited egg production. Gametophyte growth as measured by the increase in cell number was not affected by iron concentration in the medium. At all iron concentrations there was a tendency for the larger gametophytic fragments to become fertile earlier. The results suggest that iron may play a critical role in the development of Macrocystis gametophytes.     

GROWTH INHIBITION IN GAMETOPHYTES AND OAT COLEOPTILES BY THELYPTERIN A AND B RELEASED FROM ROOTS OF THE FERN THELYPTERIS NORMALIS

Gametophytes, when grown in the immediate vicinity of a Thelypteris normalis sporophyte—in soil or in sterile culture on agar—showed a reduced number of cells and an altered gross morphology. This is attributed to the action of the thelypterins, which are inhibitors released from T. normalis sporophytes. Growth inhibition of the gametophytes was greatest when thelypterins were added during early stages of gametophyte development. Removal of thelypterin A permitted resumption of growth. Thelypterin A noncompetitively inhibited auxin-enhanced elongation of A vena coleoptiles. The growth of T. normalis root segments was not affected by thelypterins. The growth of young sporophytes of T. normalis was inhibited by mature sporophytes.     

Somatic embryogenesis and organogenesis induced on the immature zygotic embryo of sunflower (Helianthus annum L.) cultivated in vitro: role of the sugar

Summary Immature zygotic embryos of sunflower constitute an experimental system where the change of a single key factor (sucrose concentration) conditions the in vitro morphogenesis to either organogenesis (87 mM sucrose) or somatic embryogenesis (350 mM sucrose). Experiments with a variety of culture media differing in the sugar type and concentration, as well as osmotic pressure, indicate that a minimal threshold level of both, sugar supply and osmotic pressure, are required for somatic embryogenesis, but not organogenesis, to occur. The nature of the sugar used, though, was less important.Abbreviations IZE immature zygotic embryo     

THE REGULATION OF ALTERNATION OF GENERATION IN FLOWERING PLANTS

The developmental changes involved in the alternation of generation represent the major gene-switching events in the life history of plants. While a large number of genes are common to both sporophyte and gametophyte, many thousand sequences are specifically expressed in each generation; indeed, certain key constituents (e.g. tubulin) are encoded by different genes in each generation, indicating that sporophyte and gametophyte are responding to different evolutionary pressures. Evidence is accumulating that major gene-switching events in plants, such as flowering, are regulated by complex control systems which ensures that development occurs only in the correct groups of cells at the appropriate time. A similar, or more sophisticated system might thus be expected to regulate alternation of generation. It is not possible to manipulate alternation of generation in a similar fashion to flowering, but study of apparent aberrations of development occurring in nature and in vitro suggests that alternation only occurs in cells which have become competent to receive particular developmental stimuli. Further, in certain cases, competent cells may be switched either into sporophytic or gametophytic developmental pathways depending upon the nature of the stimulus. Acquisition of competence seems to involve isolation of cells from the symplast, some cytoplasmic dedifferentiation, and perhaps cell cycle arrest or transition. The stimuli in vivo appear metabolic in nature, although embryogenesis may be activated by specific classes of glycoproteins. Interestingly, examination of agamospermic systems suggests that fertilization of the egg per se is not the signal which activates sporophytic development. Once competent cells have received the stimulus they start to develop, with no delay in a ‘determined’ state. Sporophytic and gametophytic development in vivo and in vitro both start with an asymmetric division, except for the female gametophyte which may arise via a range of developmental pathways, depending on the species.     

Control of in vitro somatic embryogenesis of the spindle tree (Euonymus europaeus L.) by the sugar type and the osmotic potential of the culture medium

 In vitro somatic embryogenesis was achieved from zygotic embryo explants of a woody angiosperm species, the spindle tree, cultivated on various culture media differing in their sugar type and concentration, or in the applied osmotic potential. The highest frequency of somatic embryogenesis was obtained with a 350 mM sucrose, or a 89 mM glucose concentration in the culture medium. Experiments with culture media differing only in osmotic potential indicated that a minimal threshold osmotic potential is required to stimulate the emergence of somatic embryos. Elevated concentrations of glucose have an inhibitory effect, independent of their osmotic effect, while elevated concentrations of sucrose mainly act osmotically, stimulating the emergence of numerous somatic embryos. Received: 15 July 1997 / Revision received: 27 October 1997 / Accepted: 24 March 1998     

依兰(番荔枝科)雌配子体发育研究

荔枝科是被子植物的基部类群之一,依兰属是番荔枝科较为原始的类群,其有性生殖过程,特别是胚胎发生与发育的研究结果,可以补充被子植物胚胎学原始特征的相关基础资料。该研究利用常规石蜡切片技术,对依兰胚珠、大孢子和雌配子体的发生发育过程进行了观察。结果表明:依兰的胚珠为倒生胚珠、厚珠心、三层珠被,第三层珠被(中间珠被)发生在大孢子母细胞时期,于外珠被与内珠被之间、胚珠合点端两侧发生并隆起;雌配子体为蓼型。此外,依兰的个别胚珠中存在双雌配子体现象,且两个雌配子体均由大孢子母细胞发育而来,大小、形状相近,呈线形排列。该研究结果对于揭示原始被子植物胚胎发育特征具有重要意义。     

THE INITIATION OF SPOROPHYTES BY OBLIGATE APOGAMY IN CHEILANTHES CASTANEA

The initiation of apogamous sporophytes in Cheilanthes castanea was recorded by daily photography of individual gametophytes. Whereas an ordinary embryo arises from a zygote, apogamous embryos of C. castanea originate from one to three initial cells which occur just behind the apical region of the prothallus. The initial (or initials) produce cells with small chloroplasts behind the sinus of the gametophyte. The appearance of cells with smaller chloroplasts than those normally found in gametophytes is the first indication that apogamy is occurring. The cells with small plastids produce a group of densely-cytoplasmic meristematic cells. The size of the meristematic mass increases until shoot and root apices of the apogamous embryo are organized.