金粉蕨配子体发育及其无配子生殖的研究

采用光学显微镜和半薄切片技术对金粉蕨(Onychium siliculosum(Desv.)C.Chr.)的配子体发育及其无配子生殖进行了研究。金粉蕨孢子黄褐色,具三裂缝,孢子萌发时先产生假根,然后长出原叶体细胞,萌发类型为书带蕨型。原叶体细胞经丝状体、片状体发育为原叶体,发育类型为水蕨型。金粉蕨配子体分枝发达,成熟配子体呈丛状。多次培养表明金粉蕨只能产生精子器,不能产生颈卵器,为专性无配子生殖。半薄切片观察表明配子体生长点下方的细胞经分裂产生一群小型细胞,由它们发育为无配子生殖胚。小型细胞先分化出无性胚芽,再分化出胚根。胚芽与胚根,胚与配子体之间由分化出的导管连接。     

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.     

Exogenous and endogenous growth regulators on apogamy in Dryopteris affinis (Lowe) Fraser-Jenkins sp. affinis

This work showed for the first time the relationship between the effect of exogenous auxins and gibberellins on apogamy in Dryopteris affinis (Lowe) Fraser-Jenkins sp. affinis and its endogenous contents during early apogamic events. The addition of NAA (0.53 and 5.37 μM) or GA₃ 2.8 μM to an MS solid medium significantly increased apogamous sporophyte formation. BA induced brown callus that regenerated sporophytes in a hormone-free medium. The endogenous contents of GA₁, GA₃, GA₄, GA₇, GA₉ and IAA were determined by GC–MS in gametophytes cultured on MS solid medium, before and during early stages of apogamous embryo development. The accumulation of both GA₉ and IAA before embryo development was evident as high levels of GA₄ in the earliest analysed stage of embryo development and high levels of GA₃ in elongating shoots were found. The role of gibberellins on apogamy was also supported by data showing a decrease in the percentage of gametophytes developing embryos because of the addition of flurprimidol to the culture medium.     

Development of the intercalary meristem in Chorda filum (Laminariales, Phaeophyceae) and other primitive Laminariales

Development of the intercalary meristem in the terete laminarialean species Chorda filum (L.) Stackhouse was studied in culture using light and transmission electron microscopy as well as by tracing elongation and cell divisions in various parts of the sporophyte. Growth of C. filum sporophytes could be classified into three developmental stages: (i) diffuse growth; (ii) basal meristematic growth; and (iii) intercalary meristematic growth. In the diffuse growth stage, elongation and cell division frequency were almost the same in each cell. In the basal meristematic growth stage, elongation and division of cells became localized in the tissues derived from the meristematic initial cell. Cells of the basal meristematic region contained smaller chloroplasts and many small opaque vesicles. In the intercalary meristematic growth stage, there was further elongation and differentiation of cells originating from the meristematic region, and this became more active in adjacent regions below the meristem than in regions above the meristem, causing the relative position of the intercalary meristem to shift towards the tip of the sporophyte. Meristematic cells of C. filum contained well-developed Golgi vesicles around the nucleus (perinuclear Golgi), many secretion vesicles and many small disk-shaped chloroplasts whose thylakoids were not well developed. Sporophytes of three other terete members of Laminariales, Chorda tomentosa Lyngbye, Pseudochorda nagaii (Tokida) Kawai et Kurogi, and Pseudochorda gracilis Kawai et Nabata, show diffuse growth and basal meristematic growth, but no intercalary meristematic growth. This suggests that the common ancestor of the Pseudochordaceae and Chordaceae had basal meristematic growth, and intercalary meristematic growth evolved more recently in C. filum.     

Gametophyte development and reproduction of <Emphasis Type="Italic">Argyrochosma nivea</Emphasis> (Pteridaceae)

The gametophyte of Argyroschosma nivea was studied, mainly focusing in its morphological development, and in the apogamous production of sporophytes. Some observations on the spores were also made. As far as it is known, this is the second species of the genus whose gametophytes are studied. The germination pattern followed the Vittaria type. The subsequent developmental processes followed the Ceratopteris type. Some of the gametophytes reached an adult stage with a cordate, symmetric shape, but most of them developed as irregular, lobed prothalli. The sporophyte emerged from the anterior part of the prothallus, without formation of gametangia. First, a cell became active and originated a proliferating area of small cells. From this area, long glandular hairs were formed followed by a projected conical cluster of cells. The cluster elongated into a sporophytic structure and its apex became progressively spatulate and finally trilobulate, with marginal, glandular hairs, stomata and tracheids continuously produced. This sporophyte secreted granules of white farina from its beginnings. The production of farina in the sporophyte but not in the gametophyte could help to support the idea of the segregation of this species from its traditional location in Notholaena to Argyrochosma, as farinose gametophytes seem to be a synapomorphy of the notholenoids, group that includes Notholaena but not Argyroschoma.     

Electrophoretic evidence for homoeologous chromosome pairing in the apogamous fern species<Emphasis Type="Italic"> Dryopteris nipponensis</Emphasis> (Dryopteridaceae)

Segregation of genotypes through homoeologous chromosome pairing in the apogamous species Dryopteris nipponensis was tested by electrophoretic analysis. Of 284 progeny examined (250 gametophytes and 34 sporophytes), from the parental sporophyte with the Pgi-2 genotype abc, five showed different genotypes from that of the parent (three aac, one bbc and one bcc). This is the first evidence for genetic segregation in the progeny of apogamous fern species. Electronic Publication     

The role of ethylene in the induction of apogamous buds in Pteridium gametophytes

Summary The level of induced apogamy in gametophytic colonies of Pteridium aquilinum (L.) Kuhn is altered by varying the number of colonies per culture vessel or by including a constant number of colonies in culture vessels of different volumes. In either case, placing vials of mercuric perchlorate, an absorber of ethylene, within the closed culture vessels reduced the apogamous response to a very low level. Production of ethylene by the gametophytes was demonstrated by gas chromatography. Ethylene supplied in a continuous-flow system promoted the apogamous response above that of an air control.     

Phenology of Paralemanea mexicana (Batrachospermales,Rhodophyta) in a high‐altitude stream in central Mexico

The morphology and phenology of Paralemanea mexicana (Kützing) Vis et Sheath was evaluated seasonally in a fifth order high‐altitude stream in central Mexico. The gametophytes grew during oligotrophic and eutrophic conditions, and during particular microhabitat conditions: high current velocity (40–240 cm s^?1), low to medium irradiance (5–973 μmol photons m^?2 s^?1), and shallow depth (1–30 cm). The abundance of gametophytes was positively correlated with low temperature, high current velocity and concentrations of soluble reactive phosphorus. Interestingly, monoecious gametophytes formed two types of branches, true branches with sympodial pattern originating from meristematic cells in variable number, and abundant false branches produced during the development of the ‘Chantransia’ stage in the surface of the gametophyte or by uniseriate filaments arising within the thallus lumen. These filaments generally produce gametophytes and suggest that they could support the germination of carpospores. The frequently whorled branches are the result of a false branching pattern and are exclusive to P. mexicana. These morphological and reproductive characteristics appear to be biomechanical adaptations to avoid detachment and increase reproductive success. Efficient reproductive strategies of P. mexicana observed in this study can be interpreted as adaptations to successfully colonize streams; however, these features may not have been common in the study region due to restricted microhabitat conditions and geographic isolation.     

Ultrastructural characterization of apospory in Panicum maximum

The nucellar ultrastructure of apomictic Panicum maximum was analyzed during the meiocytic stage and during aposporous embryo sac formation. At pachytene the megameiocyte shows a random cell organelle distribution and sometimes only an incomplete micropylar callose wall. The chalazal nucellar cells are meristematic until the tetrad stage. They can turn into initial cells of aposporous embryo sacs. The aposporous initials can be recognized by their increased cell size, large nucleus, and the presence of many vesicles. The cell wall is thin with few plasmodesmata. If only a sexual embryo sac is formed, the nucellar cells retain their meristematic character. The aposporous initial cell is somewhat comparable to a vacuolated functional megaspore. It shows large vacuoles around the central nucleus and is surrounded by a thick cell wall without plasmodesmata. In the mature aposporous embryo sac the structure of the cells of the egg apparatus is similar to each other. In the chalazal part of the egg apparatus the cell walls are thin and do not hamper the transfer of sperm cells. Structural and functional aspects of nucellar cell differentiation and aposporous and sexual embryo sac development are discussed.     

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.     

Regulation of a Sub-sexual Life Cycle in a Moss: Evidence for the Occurrence of a Factor for Apogamy in Physcomitrium

As demonstrated in our earlier studies, the differentiationof apogamous sporophytes on the secondary protonema of the mossPhyscomitrium pyriforme Brid. requires an exogenous supply ofsucrose in the medium. In the present work, similar differentiationwas observed in the leaf cells of aged gametophytes. The experimentsindicate an accumulation in the leaves of a sporophytic factorwhich initiates a de novo differentiation of sporophytes fromleaf cells without the intervention of sexual reproduction.In the absence of sucrose, the factor for apogamy was not present.Highlight intensity (5000–6000 lx) also inhibited itsproduction. There was no evidence that its presence interferedwith or inhibited production of gameto-phores. Growth regulatorssuch as IAA and kinetin altered only the effectiveness of thissporophytic factor, demonstrating that it was endogenous. Sporogenesisin the apogamous sporophytes took place without orthodox meiosis. Results obtained by using different exogenous environments forthe in vitro differentiation of callus into gametophytes orsporophytes are also reported. These support our contentionthat there is an accumulation of a sporophytic factor in thegametophytic callus cells, which is diluted during the processof differentiation. The morpho-regulatory influence of lightin the differentiation of apical cells with three cutting facesfrom unorganized callus is also considered.     

ULTRASTRUCTURE OF THE CORALLINACEAE (RHODOPHYTA) II. VEGETATIVE CELLS OF LITHOTHRIX ASPERGILLUM1

The ultrastructure of the calcareous red coralline alga Lithothrix aspergillum Gray and the development of the various tissue types has been studied. The sub-apical meristematic tissue alternately produces genicular or intergenicular cells. The genicular cells rapidly elongate and their cell walls thicken and become denser as more fibrillar wall material is laid down within the cell wall. These cells contain little cytoplasm and few organelles. The inter genicular cells which elongate only slightly during development have a small vacuole and many free starch grains in the cytoplasm. The peripheral cells in each inter genicular layer remain meristematic and form a cortical cell layer over the genicular cells. These cortical cells and the apical meristematic cells are covered by small epidermal cells which have extensive cell wall ingrowths between the chloroplasts. The inter genicular cells are calcified. Although the CaCO₃ is laid down within the cell walls, there is always a thin layer of CaCO₃-free organic cell wall material between the plasmalemma and the CaCO₃ impregnated wall. Only the distal tips of the genicular cells are calcified. In old genicular tissues of Lithothrix, secondary deposits of CaCO₃ of unknown crystallography are also found in the spaces between the cell walls. Thus there appear to be at least two mechanisms of calcification in this alga.     

Chloroplastenausbildung und Morphogenese der Gametophyten von Dryopteris filix-mas (L.) Schott nach Applikation von Chloramphenicol und Actidion (Cycloheximid)

Summary Morphogenesis and differentiation of the young gametophytes (=sporelings) of Dryopteris filix-mas are controlled by light. Blue light leads to the formation of normal two-dimensional prothallia; under red light, however, the gametophytes grow as cellular filaments. Morphogenesis in blue light is connected with an increase in protein synthesis; in red light the protein content of the sporelings is markedly lower. The size of the chloroplasts is correlated with the protein content of the sporelings.In the present paper the diverse effect of chloramphenicol (CAP) and actidione (cycloheximide, ACT) was studied in connection with the formation of chloroplasts. ACT blocks the growth of the gametophytes, while the chloroplasts remain functional. On the other hand, CAP does not influence morphogenesis of the gametophytes. In particular the activity of the dividing apical cells remains untouched. Even when the light quality is changed during the development the corresponding specific effect of the light quality on morphogenesis is normal. The chloroplasts, however, become smaller, probably by inhibition of synthesis of structural proteins. But their synthetic activity is not completely suppressed. The specific blue or red light dependent morphogenesis is not changed, when protein synthesis in the chloroplasts is inhibited.     

Optimization of in vitro multiple shoot clump induction and plantlet regeneration of Kentucky bluegrass (Poa pratensis)

An efficient protocol for Kentucky bluegrass (Poa pratensis L.) in vitro culture was established using shoot apices of seedlings as explants. The optimal procedure of this protocol for majority of the genotypes was that meristematic cell clumps and small calluses were firstly induced from the bases of explants on initial culture medium supplemented with 0.9 μM 2,4-d and 8.9 μM 6-BA for 20 d, then were separated and transferred to shoot clumps induction medium containing 8.9 μM 6-BA for the formation of multiple shoot clumps. The percentage of multiple shoot clumps and numbers of shoots per clump were deeply related with the combinations of different plant growth regulators, duration of initial culture, the intensity of illumination and genotypes. Histological observation of the induced explants revealed that the meristematic cell clumps were produced from repeated division of the cortical cells and original meristematic primodium cells of explants, and the multiple shoots were formed via organogenesis pathway in the meristematic cell regions of cultures on shoot clumps induction medium. In this study, plantlets were efficiently regenerated on large scale from seven cultivars of Kentucky bluegrass. Hence the meristematic cell clumps and small calluses in this protocol could be considered good targets for genetic transformation of Kentucky bluegrass.     

IAA-induced apogamy in Platycerium coronarium (Koenig) Desv. gametophytes cultured in vitro

Apogamous sporophytes were produced on Platycerium coronarium gametophytes cultured in the presence of indole-3-acetic acid (IAA). The percentage of apogamy as well as the total number of apogamous sporophytes produced per gametophyte clump were highest in the presence of 40 M IAA. When ethylene was allowed to accumulate in the culture vessel in the presence of an optimum level of IAA, the percentage and total number of apogamous sporophyte production decreased significantly. Using light microscope and confocal laser scanning microscope we have shown that nuclear size can be used as a quick parameter to estimate the ploidy level of P. coronarium.Abbreviations CLSM confocal laser scanning microscope - IAA Indole-3-acetic acid - MS Murashige and Skoog     

Sexuality and apogamy in the Cuban Asplenium auritum–monodon complex (Aspleniaceae)

Asplenium auritum Sw. is a sexual fern that produces 64 spores per sporangium, while A. monodon Liebm. is an apogamous species that produces 32 spores. The hybrid between them, A. × lellingerianum Sánchez & Regalado, also shows an apogamous life cycle, with mainly abortive spores. The scope of this work was to study the sexual and apogamous behavior in these taxa. We studied spore germination and gametophyte development of the three species, a process that followed the Adiantum type. Afterward, we observed morphological apogamous characters in A. monodon and A. × lellingerianum. Apogamous sporophytes arose from apical and basal regions of gametophytes, lacking feet and roots in the first instance, but developing other normal sporophytic structures, such as tracheids, stomata, glandular hairs, and scales. Finally, we studied the gametangia production in all three taxa, finding that the scarce production of antheridia in A. monodon is indicative of the Braithwaite apogamous life cycle scheme, and this scheme has probably been inherited by A. × lellingerianum.     

Life History,Reproductive Morphology and Development of the Antarctic Brown Alga Desmarestia menziesii J. Agardh*

The life history, reproduction and development of Desmarestia menziesii J. Agardh from Antarctica is described. Unilocular sporangia occur singly or in small groups in the outermost cortical layer of the sporophyte. They are formed by periclinal division of cortex cells into a stalk cell and the sporangium initial. Meiospores germinate into dioecious microscopic filamentous gametophytes. As in other perennial Antarctic species of the Desmarestiales, gametangia are formed in culture under short-day conditions or in darkness. In nature, juvenile sporophytes should therefore be formed in winter. They develop only attached to the oogonium. At first they are uniseriate and elongate by means of an intercalary meristem located in their middle part. Laterals are formed predominantly in this region, and they subsequently give rise to secondary laterals. The branching pattern is opposite to alternate in both young and adult plants. Cortication of the main axis is initiated by filaments growing out from the lowermost cells of the primary laterals. In sporophytes of this developmental stage the meristem of the main axis is confined to a small region where cortication starts and above. Lateral branches elongate and become corticated in the same way as the main axis. In mature plants, cells of the inner cortex can become meristematic again and form a meristoderm which contributes to axis thickness by periclinal and anticlinal divisions. The observations are discussed in relation to possible evolutionary relationships in the genus Desmarestia and in the order Desmarestiales.     

MORPHOLOGY AND REPRODUCTION OF THE RED ALGA ACROCHAETIUM PECTINATUM IN CULTURE12

The life history of the marine red alga Acrochaetium pectinatum (Kylin) Hamel was studied in unialgal culture using supplemented natural seawater media. The tetrasporophytes are larger than the gametophytes, have a compact filamentous basal system, and produce monosporangia and tetrasporangia. Mono-spores give rise to tetrasporophytes. Tetraspores develop into small gametophytes with unicellular bases. The gametophytes are heterothallic when small (usually less than 500 μ) but as some females become larger (2-3 mm) they produce spermatangia as well as carpogonia. Gametophytes may bear mono-sporangia in addition to carpogonia or spermatangia. These monospores give rise to gametophytes. Fertilization of the carpogonia has not been observed. The tetrasporophytes produce only monosporangia in day-lengths of 12-16 hr, but both tetrasporangia and monosporangia are formed in daylengths of 6–10 hr. Tetrasporangial production is reduced at 15 C compared with 10 C. Light intensity in the range of 5-200 ft-c (cool white fluorescent lighting) has no apparent influence on induction of tetrasporangia. Induction of tetrasporangia is not a photoperiodic response because their development is not inhibited by a brief light break in the middle of the dark period in short daylengths. Plastid morphology, origin, and frequency of sporangia and vegetative branching are variable during the ontogeny, and consequently are somewhat unreliable as taxonomic criteria. Differences in basal systems between gametophytes and tetrasporophytes also indicate that this feature, which is used to distinguish major subgeneric groupings in Acrochaetium, may not be as useful as previously thought.