ORIGIN OF FRAGARIA POLYPLOIDS. I. CYTOLOGICAL ANALYSIS

The genomic relationships between modern Fragaria diploids (European and American F. vesca and F. viridis—2n = 14) and octoploids (F. virginiana and F. chiloensis—2n = 56) were investigated. This contrasts with previous studies where cultivars have represented the octoploids. Critical information on genomic pairing was obtained by comparing chromosome behavior of pentaploid hybrids with that of hexaploid hybrids (obtained by using a recent colchiploid of European F. vesca). Supporting data were also used from an F. chiloensis × Potentilla glandulosa hybrid (2n = 35). A revision of the AABBBBCC (Federova) genomic formula for the octoploids to AAA'A'BBBB is proposed based upon cytological evidence of homology between the AA and “CC” genomes. The phylogeny of the octoploids is postulated.     

ELECTROPHORETIC EVIDENCE FOR THE ORIGIN OF FERN SPECIES BY UNREDUCED SPORES

Allopolyploid speciation is well documented in the ferns, but data from enzyme electrophoresis have only recently shown that certain sexual and agamosporous taxa are autopolyploids. Autopolyploidy may arise through fertilization involving gametophytes from unreduced spores, a mechanism previously proposed to account for the origin of allopolyploid Asplenium plenum. This report assesses the ability of unreduced spores to function in the origin of polyploid fern species by using enzyme electrophoresis to test their hypothesized role in the origin of A. plenum. Six isozymes of the enzymes PGI, PGM, TPI, 6PGD, and LAP are species-specific for the taxa proposed as parental under two competing hypotheses for the origin of this species. Electrophoretic data reject the more conventional hypothesis involving simple hybridization and agree perfectly with expectations under the more complex hypothesized origin via unreduced spores. The mechanism whereby unreduced spores have functioned in this case is no different from that by which they would function in the origin of autopolyploid taxa and may be more common in the origin of fern species than previously suspected.     

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). II. GAMETES

Transmission electron microscopic examination of Cephaleuros virescens Kunze growing on leaves of Camellia sp. indicates that gametes are similar to those of Trentepohlia aurea. The gametes bear two, smooth isokont “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally. Each basal body is associated with a separate multilayered structure and component microtubular spline. The latter extends posteriorly beneath the plasmalemma. A nucleus, mitochondria, chloroplasts, and cytoplasmic haematochrome droplets are present. Pyrenoids and eyespots are absent. The subcellular components of C. virescens gametes are comparable to those found in gametes of T. aurea; however, the arrangement of basal bodies and multilayered structures differs slightly from that in T. aurea. Comparison of the fine structure of gametes from Cephaleuros, Phycopeltis, and Trentepohlia clearly indicates that the (1) mode of flagellar insertion, (2) morphology, number, and arrangement of multilayered structures, and (3) keeled flagella are common to these three genera and, thus far, unique among the green algae. Although flagellar insertion is apical, it is not bilaterally symmetrical (sensu stricto), nor is it asymmetrical (cf. Chara and Nitella sperms). The arrangement may be termed “reversed bilateral symmetry” and standardization of the terminology is recommended.     

EMBRYOGENY AND HISTOGENESIS IN NERIUM OLEANDER II. ORIGIN AND DEVELOPMENT OF THE NON-ARTICULATED LATICIFER

Mahlberg , P. G. (U. Pittsburgh, Pittsburgh, Pa.) Embryogeny and histogenesis in Nerium oleander. II. Origin and development of the non-articulated Iaticifer. Amer. Jour. Bot. 48(1): 90–99. Illus. 1961.—Laticifer initials, collectively considered as a laticifer system, are differentiated in the globular embryo from meristematic cells which occupy a position within the potential procambial tissue. A total of usually 28 initials, in Nerium oleander, arise as an irregular ring of cells directly below the embryonic shoot apex, during initiation of the cotyledonary primordia. No anastomoses occur between laticifer initials. During subsequent development of the embryo, the laticifer initials grow in a bi-directional manner and penetrate into the root, cotyledons and toward the shoot apex. Upon enlargement the initials bifurcate repeatedly, many branches penetrate into the cotyledons, others grow into the cortex of the hypocotyl or penetrate between cells of the procambium. Repeated nuclear divisions within each initial result in the formation of a multinucleated protoplast in this cell type. The tips of laticifers occupy intercellular spaces during their growth; they do not penetrate into or through adjacent cells. A plexus of laticifer branches is formed within the cotyledonary node of the mature embryo. No new initials are formed during subsequent growth of the plant, rather certain branches from the cotyledonary nodal plexus penetrate into the enlarging shoot system. The nature of their growth habit and branching suggests that the tips of laticifer initials exhibit an intrusive form of growth.     

AN ULTRASTRUCTURAL STUDY OF GAMETES AND FERTILIZATION IN PATELLA VULGATA L.

Gametes of Patella vulgata L. have been studied using electronmicroscopy and their ultrastructure described. Changes in ultrastructureoccurring during and after fertilization have been characterized,especially those occurring in the cortical region. These changesinclude appearance of Golgi bodies, mitochondria and agglomerationsof microtubular material. Cortical granules disappear and glycogengranules begin to be degraded. (Received 13 February 1984;     

ATTACHMENT AND FUSION OF GAMETES DURING FERTILIZATION OF PALMARIA SP. (RHODOPHYTA)1

Fertilization of cultured microscopic female gametophytes by spermatia from field-collected male gametophytes of Palmaria sp. was observed by light and transmission electron microscopy. Liberated spermatia had a prophase-arrested nucleus with a pair of polar rings. The protoplast of spermatia was covered with ca. a 3-μm-thick hyaline covering. After spermatium inoculation, the spermatial covering was attached specifically to the coat surrounding the cell wall of the trichogyne. The spermatial covering was eliminated only at the site of gamete attachment, resulting in direct attachment of the spermatial plasma membrane to the trichogyne within 5 min after spermatium inoculation. This direct attachment was followed by completion of spermatial nuclear division and cell wall formation. The polar rings disappeared before prometaphase. The cytoplasm of the binucleate spermatium invaded the trichogyne cell wall and subsequently fused with the trichogyne cytoplasm. The trichogyne could fuse with many spermatia, and many male nuclei (the derivative nuclei of spermatial nuclear division) could enter the trichogyne cytoplasm.     

PRODUCTION OF MALE GAMETES AND AUXOSPORES IN THE CENTRIC DIATOMS CYCLOTELLA MENEGHINIANA AND C. CRYPTICA12

Vegetative cells of Cyclotella meneghiniana Kützing form male gametes and anxospores following transfer from a synthetic freshwater medium to a modified artificial seawater. Both spermatogenesis and auxospore formation are correlated with an increase in the Na⁺ concentration in the medium. Spermatogenesis can also be induced in C. cryptica Reimann, Lewin, and Guillard in artificial seawater with an adjusted sodium level.     

RECURRENT FORMATION AND POLYPHYLY OF NORDIC POLYPLOIDS IN DRABA (BRASSICACEAE)

Draba (Brassicaceae) is well known for its taxonomic complexity in arctic and alpine floras, and the polyploids in particular present vexing taxonomic problems. It has been suggested that polyploids in Draba may have formed recurrently from different populations of the parental species (polytopy), and it is also possible that a given taxonomic species may actually comprise several polyploid races, each originating from different progenitor species (polyphyly). To unravel the taxonomic complexity of polyploid Draba in the Nordic area, we investigated three of the most morphologically variable species and their possible progenitors using enzyme electrophoresis and restriction site analysis of chloroplast DNA (cpDNA) and nuclear ribosomal RNA genes (rDNA): D. norvegica (6x), D. lactea (6x), and D. corymbosa (16x). Electrophoretic analyses of progeny showed high levels of fixed heterozygosity in all three polyploids, demonstrating that all are genetic alloploids. Electrophoretic and rDNA data indicate that polytopic and/or polyphyletic origins have contributed to the complexity of these polyploids. However, a lack of cpDNA variation among the species limited the usefulness of this molecule for analysis of polyploid origins. The considerable electrophoretic variation observed in D. norvegica necessitates a minimum of three and probably 13 independent origins. Electrophoretic and rDNA data suggest that D. lactea and D. corymbosa are polyphyletic polyploids. Crossing data also support that D. corymbosa is polyphyletic. Given the widespread geographic distributions of these species and their possible progenitors, and that the populations analyzed represent only a small fraction of their geographic distributions, it is likely that these species have formed numerous times in different areas. As more molecular analyses of polyploids are completed, the data continue to suggest that multiple origins of polyploids are the rule rather than the exception.