Flower change in Oenothera drummondii Hooker as a response to pollinators' visits

Flower change in Oenothera drummondii Hooker as a response to pollinators' visits. The colour and shape of flowers of Oenothera drummondii change owing to senescence, pollination and/or nectar withdrawal. This phenomenon is interpreted as a signal emitted by the plant to 'inform' the potential pollinator of its new status as a rewardless flower. This method of signalling might be important for the pollinators in order to save energy in seeking the correct flowers and for the plant to ensure visits to those flowers that have not yet been visited.     

Reproductive success,spontaneous embryo abortion,and genetic load in flowering plants

Summary Reproductive success is divided into two phases: preemergent (the number of viable seeds that enter the ambient environment) and postemergent (the percentage of progeny that survive to reproduce). We studied preemergent reproductive success (PERS) in flowering plants by measuring the fruit/flower (Fr/Fl) ratio and the seed/ovule (S/O) ratio in a number of species of outcrossing and inbreeding plants, where PERS=the product of (Fr/Fl) and (S/O). In order to determine the influence of the ambient environment (including resource availability) we studied pairs of outcrossing and inbreeding species occurring in the same habitat. Among outcrossing species PERS averaged about 22%, whereas in inbreeding species the average was approximately 90%. The progeny/zygote (P/Z) ratio was studied in hand-pollinated populations in Epilobium angustifolium (a strongly outcrossing species) from populations in Oregon and Utah, by direct observation of embryogenesis at twoday intervals throughout the course of seed development. The P/Z ratio in both populations averaged near 30%, and the developing embryos showed a surprising array of abnormalities that resulted in embryo death. During early development >95% of the ovules had normally developing globular embryos, but beginning with differentiation (cotyledon formation) about 70% of the original globular embryos aborted during the course of embryogenesis and seed development. The clustering of developmental lethals during peroids of major differentiation events parallels the animal model of development. We found little evidence that PERS was limited by the ambient environment (including resource availability), pollination, or factors associated with the inbreeding habit. Instead, PERS was found to be inextricably linked to outcrossing plants, whose breeding systems promote genetic variability. The high incidence of developmental lethals in E. angustifolium and the resulting low P/Z ratio (ca. 30%) is attributed to genetic load (any lethal mutation or allelic combination) possibly working in combination with developmental selection (interovarian competition among genetically diverse embryos). Examples of maternally controlled, fixed patterns of ovule abortion with respect to position or number are discussed. However, we found no need to employ female choice as a hypothesis to explain our results for the extensive, seemingly random patterns of embryo abortion in E. angustifolium and other outcrossing species. A more parsimonious, mechanistic explanation based on genetic load-developmental selection is sufficient to account for the differential survivorship of embryos. Likewise, the traditional concept of a positive growth regulator feedback system based on the number of surviving ovules in an ovary can account for subsequent fruit survivorship.     

A new infrageneric classification and phylogenetic trends in the genusRhododendron (Ericaceae)

Recent studies have improved the infrageneric classification ofRhododendron, including my own investigations on flavonoids and anthocyanins as chemosystematic markers. From a synoptical comparison of morphological, anatomical and phytochemical characters a new system for the genus is proposed. Phylogenetic character progressions and relationships among subgenera, sections and subsections are discussed and illustrated. Key positions for subg.Candidastrum between chori subgenerumRhododendron andNomazalea, and for subg.Choniastrum between chori subgenerumHymenanthes andNomazalea are suggested.     

Restriction fragment length polymorphisms in dairy and beef cattle at the growth hormone and prolactin loci

Two bovine populations, a Holstein-Friesian dairy stock and a synthetic (Baladi X Hereford X Simmental X Charolais) beef stock, were screened for restriction fragment length polymorphisms (RFLPs) at the growth hormone and prolactin genes. Most RFLPs at the growth hormone gene are apparently the consequence of an insertion/deletion event which was localized to a region downstream of the structural gene. The restriction map for the genomic region including the growth hormone gene was extended. Two HindIII RFLPs at the growth hormone locus, as well as several RFLPs at the prolactin gene, seemed to be the consequence of a series of point mutations. The results are discussed in terms of the possibility that minor genomic variability underlies quantitative genetic variation.     

An unusual wheat insertion sequence (WIS1) lies upstream of an alpha-amylase gene in hexaploid wheat, and carries a "minisatellite" array

Summary Comparison of the 5′ flanking regions of three α-amylase genes from chromosome 6B of hexaploid wheat by heteroduplex and sequence analysis revealed the presence of a 1.6 kb stem-loop insertion sequence (WIS1) in one of them. Polymorphism among hexaploid wheat varieties suggests the relatively recent insertion/excision of this sequence from its present position. The complete sequence of the stem-loop insertion shows that it has many of the features found in transposable elements, including target site duplication and terminal inverted repeats. One unusual feature is a tandem array of direct repeats comprising a wheat “minisatellite” sequence. Both the insertion sequence and the minisatellite are found at multiple locations in the wheat genome, but the functional significance of their association in WIS1 is unknown. The minisatellite arrays share a common core structure, and long arrays are polymorphic between different hexaploid varieties.     

Pulsed field gel electrophoresis and physical mapping of large DNA fragments in the Tm-2a region of chromosome 9 in tomato

Summary A method has been developed which allows the isolation of very high molecular weight DNA (>2 million bp) from leaf protoplasts of tomato (Lycopersicon esculentum). The DNA isolated in this manner was digested in agarose with rare-cutting restriction enzymes and separated by pulsed field gel electrophoresis. The size range of the reslting fragments was determined by hybridization to a number of single copy clones and the suitability of these enzymes for the mapping of large DNA fragments was evaluated. Furthermore, five genetically tightly linked single copy clones have been used to begin the construction of a physical map in a region of the genome containing the Tm-2a gene which confers resistance to tobacco mosaic virus. Two of the five clones were found to be on the same 560 kb SalI fragment and therefore are no further apart than that distance. The remaining three markers are distributed over at least 3 million bp, so that the total minimum physical distance of that cluster is at least 4 million bp. The results are discussed with respect to correlations between recombination frequencies and physical distance as well as physical mapping large regions of a complex plant genome like tomato.     

Restriction fragment length polymorphisms distinguish ectomycorrhizal fungi

Basidiomycetous fungi, two saprophytes and three mycorrhizal, were used to assess the specificity of DNA hybridization for distinguishing genera from one another. Interspecific comparisons were done with several isolates of mycorrhizal fungi,Laccaria bicolor andL. laccata, collected from diverse geographical sites. The DNAs were digested with four restriction nucleases and separated by gel electrophoresis into patterns of DNA fragments called restriction fragment length polymorphisms (RFLPs). The RFLPs were hybridized with a radioactively-labeled DNA probe encoding Basidiomycetous ribosomal RNA genes. The five genera were discernable using both unprobed and probed RFLPs. Hybridization of probe DNA with RFLPs was isolate-specific for all nine Laccaria isolates examined. The reclassification of aL. bicolor isolate is supported, demonstrating that hybridization of RFLPs offers an additional tool for taxonomy of ectomycorrhizal fungi. The method may have field application for distinguishing known isolates if their DNA fingerprints are previously ascertained and are distinct from RFLPs of indigenous organisms.     

DNA polymorphism in Allium cepa cytoplasms and its implications concerning the origin of onions

Summary Mitochondrial and chloroplast DNA was isolated from fertile and cytoplasmic male sterile cultivars of cultivated onions. Restriction fragment length polymorphism led to the distinction between cytoplasms S and M. Mitochondrial DNA patterns from S cytoplasms appeared dentical and characterized mostly male sterile lines. An open-pollinated variety was found to bear this cytoplasm and thought to be the origin of S types. Mitochondrial DNA patterns from M cytoplasms were subdivided into four types, M₁ and M₂ corresponding to normal N cytoplasm, M₃ and M₄ probably corresponding to T cytoplasms. S and M cytoplasms were also distinguished by chloroplast DNA restriction patterns. Our results confirm previous genetic distinction between S, N and T cytoplasms.     

A comparison of anther and microspore culture as a breeding tool in Brassica napus

Summary A direct comparison of microspore culture and anther culture was made in Brassica napus using F₁ crosses of Regent (canola) by Golden (rapeseed), and their reciprocals, as well as a hybrid between Reston and a highly embryogenic, canola-quality breeding line (G231) as donor plants. The study confirmed that microspore culture can be ten times more efficient than anther culture for embryo production. Embryo yields from cultures initiated from the Reston x G231 were four-fold greater than those initiated from the Regent x Golden crosses, and significant differences were also detected among cultures initiated from the different Regent x Golden crosses. These results illustrate the influence that donor plant genotype has on embryo production. However, superior embryogenic potential among donor material was not always coincident with superior plant production. The average haploid-todiploid ratio in microspore-derived regenerates was 21 for the population obtained from the Regent x Golden crosses but 11 for the Reston x G231 cross. For both types of material, the frequency of diploids increased upon repeated cycles of explanting. A field study showed that there were no differences between the populations of anther-derived and microspore-derived spontaneous diploid and doubled haploid lines, with respect to the days required for them to flower or to mature. The information is valuable for canola breeding programs considering the use of haploidy.     

Genomic organization of the ribosomal DNA of sorghum and its close relatives

Summary The structure and organization of the ribosomal DNA (rDNA) of sorghum (Sorghum bicolor) and several closely related grasses were determined by gel blot hybridization to cloned maize rDNA. Monocots of the genus Sorghum (sorghum, shattercane, Sudangrass, and Johnsongrass) and the genus Saccharum (sugarcane species) were observed to organize their rDNA as direct tandem repeats of several thousand rDNA monomer units. For the eight restriction enzymes and 14 cleavage sites examined, no variations were seen within all of the S. bicolor races and other Sorghum species investigated. Sorghum, maize, and sugarcane were observed to have very similar rDNA monomer sizes and restriction maps, befitting their close common ancestry. The restriction site variability seen between these three genera demonstrated that sorghum and sugarcane are more closely related to each other than either is to maize. Variation in rDNA monomer lengths were observed frequently within the Sorghum genus. These size variations were localized to the intergenic spacer region of the rDNA monomer. Unlike many maize inbreds, all inbred Sorghum diploids were found to contain only one rDNA monomer size in an individual plant. These results are discussed in light of the comparative timing, rates, and modes of evolutionary events in Sorghum and other grasses. Spacer size variation was found to provide a highly sensitive assay for the genetic contribution of different S. bicolor races and other Sorghum species to a Sorghum population.