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PubMed1998

Reversible male sterility: a novel system for the production of hybrid corn.

Hybrid corn seed is traditionally produced using either mechanical/hand detasseling or cytoplasmic male sterility, or a combination of both. In recent years, the development of transgenic systems to produce hybrid seed in several crops has attracted much attention. Here we describe a transgenic mechanism for production of hybrid corn, reversible male sterility (RMS), in which the action of the cytotoxic gene used to introduce male sterility is suppressed by the application of a chemical to the plant. Reversion of the sterility allows the RMS parent to be self-fertilized, a step which overcomes the need to remove fertile sib plants prior to making the hybrid cross. The key enabling technology in RMS is the use of a plant gene promoter which is specifically induced by chemical application. We have exemplified RMS in transgenic corn plants and believe that it provides specific benefits in the production of hybrid corn seed.

Hybridization, Genetic↗
PubMed2000

Comparative pollen morphology and ultrastructure of the Callitrichaceae.

The Callitrichaceae are an aquatic family of dicots that include the single, geographically cosmopolitan genus Callitriche. Callitriche contains 40-50 terrestrial, amphibious, and obligately submersed species, and it is the only known genus in the plant kingdom with co-occurring aerial and hydrophilous pollination syndromes. Pollen morphology and ultrastructure were described for 13 Callitriche species using scanning electron and transmission electron microscopy. Representative taxa of each growth form were examined; these included three terrestrial species (C. deflexa, C. peploides, and C. nuttallii), nine amphibious species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis hybrid, C. cribrosa, C. hamulata, C. heterophylla var. heterophylla, C. lusitanica, C. marginata, and C. trochlearis), and one obligately submersed species (C. truncata). Of the amphibious taxa, C. heterophylla var. heterophylla and C. trochlearis had internal geitonogamy, a type of internal self-fertilization. Pollen from all taxa was spheroidal, small, intectate, and lacked well-defined apertures. Taxa primarily differed with respect to exine thickness, surface ornamentation, and the presence or absence of aperture-like regions. The pollen of terrestrial species, as well as that of C. marginata, had well-developed exines with thick sculptured and basal layers. In general, amphibious taxa produced pollen with distinct, but thinner, exines than that of terrestrial taxa. Pollen of the amphibious taxa with internal geitonogamy had a thicker basal layer than species without internal geitonogamy, whereas the overall exine was reduced in C. hamulata and absent in C. brutia and C. lusitanica. Pollen of the obligately submersed C. truncata also lacked an exine. These palynological data were correlated with growth habits and related pollination biologies, as well as with phylogenetic interpretations of Callitrichaceae. Exine reduction or loss has evolved at least twice in the family, and it is associated with aneuploid reduction in chromosome number.

Journal Article↗
PubMed2000

[Possibilities of selection with an increase in frequency of meiotic recombination (simulation and experiment)].

Polymorphism of rec genes, modifier genes of recombination frequency (rf), was analyzed. Genetic population analysis was used to estimate the efficiency of some schemes of direct and indirect selection for higher rf in a marked chromosomal region. A new modification of the cyclic selection scheme, based on selection of double recombinant marker genotypes in the offspring of self-fertilized plants, was found to be most effective in many cases. This indirect selection scheme was studied in more detail using deterministic and stochastic computer simulation. Effects of various factors on the efficiency of the modified scheme were analyzed. These factors were different degrees of cross-fertilization, differential adaptation of recombinant and non-recombinant gametes and zygotes, linkage between marker genes and rec genes, and environmental variation of rf. Sample sizes and the number of crosses required for a stable rf increase in experiment were estimated. Statistical properties of two new modified tests for comparison of rf values were studied. An experiment with marker forms of tomato were conducted taking into account the recommendations following from the results of simulation.

Genetic Linkage↗
PubMed2000

Outcrossing rate and inbreeding depression in the perennial yellow bush lupine, Lupinus arboreus (Fabaceae).

Little is known about the breeding systems of perennial Lupinus species. We provide information about the breeding system of the perennial yellow bush lupine, Lupinus arboreus, specifically determining self-compatibility, outcrossing rate, and level of inbreeding depression. Flowers are self-compatible, but autonomous self-fertilization rarely occurs; thus selfed seed are a product of facilitated selfing. Based on four isozyme loci from 34 maternal progeny arrays of seeds we estimated an outcrossing rate of 0.78. However, when we accounted for differential maturation of selfed seeds, the outcrossing rate at fertilization was lower, ∼0.64. Fitness and inbreeding depression of 11 selfed and outcrossed families were measured at four stages: seed maturation, seedling emergence, seedling survivorship, and growth at 12 wk. Cumulative inbreeding depression across all four life stages averaged 0.59, although variation existed between families for the magnitude of inbreeding depression. Inbreeding depression was not manifest uniformly across all four life stages. Outcrossed flowers produced twice as many seeds as selfed flowers, but the mean performance of selfed and outcrossed progeny was not different for emergence, seedling survivorship, and size at 12 wk. Counter to assumptions about this species, L. arboreus is both self-compatible and outcrosses ∼78% of the time.

Journal Article↗
PubMed2000

Cleistogamous capitulum in Centaurea melitensis (Asteraceae): heterochronic origin.

Cleistogamous capitula formed by Centaurea melitensis display a number of morphological and functional changes with respect to chasmogamous capitula that ensure self-fertilization. Because no studies have hitherto addressed the evolution of cleistogamy in Asteraceae, it was considered useful to ascertain whether these changes are attributable to one or more of the heterochronic processes reported in the literature. Bivariate allometric analyses were performed, and changes were represented graphically using Gould's clock models for size, shape, and age of several capitulum and floret structures. Results suggest that the partially paedomorphic appearance of cleistogamous with respect to chasmogamous capitula is attributable to three processes: (1) early onset of floral development (predisplacement), (2) decreased growth rate of the whorls studied (except gynoecium width) and (3) early offset time (progenesis). The latter appears to play the most significant role in the origin of the cleistogamous capitulum.

Journal Article↗
PubMed1999

Transposon dynamics and the breeding system.

The selfish DNA hypothesis predicts that natural selection is responsible for preventing the unregulated build up of transposable elements in organismal genomes. Accordingly, between-species differences in the strength and effectiveness of selection against transposons should be important in driving the evolution of transposon activity and abundance. We used a modeling approach to investigate how the rate of self-fertilization influences the population dynamics of transposable elements. Contrasting effects of the breeding system were observed under selection based on transposon disruption of gene function versus selection based on element-mediated ectopic exchange. This suggests that the comparison of TE copy number in organisms with different breeding systems may provide a test of the relative importance of these forces in regulating transposon multiplication. The effects of breeding system also interacted with population size, particularly when there was no element excision. The strength and effectiveness of selection against transposons was reflected not only in their equilibrium abundance, but also in the per-site element frequency of individual insertions and the coefficient of variation in copy number. These results are discussed in relation to evidence on transposon abundance available from the literature, and suggestions for future data collection.

Breeding↗
PubMed2000

Experimental analysis of protogyny in Aquilegia canadensis (Ranunculaceae).

Dichogamy is very common in flowering plants and is widely thought to reduce pollen-pistil interference, especially self-pollination. Yet, the functional significance of dichogamy has rarely been studied. We investigated the nature and functioning of dichogamy in eastern Ontario populations of Aquilegia canadensis, a highly selfing columbine previously described as protogynous. We then manipulated flowers to determine whether increased protogyny would reduce self-fertilization. Contrary to previous reports, A. canadensis is not dichogamous. Controlled pollinations in a greenhouse showed that pollen tubes generally begin to develop after anther dehiscence. Although stigmas can collect pollen early in floral development, naturally pollinated flowers collected from four populations had few pollen grains on stigmas and almost no pollen tubes in styles until after anther dehiscence. Limited pollen deposition before anther dehiscence was also associated with low nectar availability and limited sepal expansion. Because inbreeding depression is strong in this species, selection may favor increased protogyny if it reduces selfing. We tested this hypothesis by comparing the level of selfing in flowers rendered protogynous by the removal of the first 19 (of 39) anthers to develop, with nonprotogynous control flowers. Contrary to expectations, protogyny did not reduce selfing. Our results emphasize the importance of detailed field observations and manipulative experiments in understanding the nature and functional significance of dichogamy.

Journal Article↗
PubMed2000

Evolution of the self-pollinating flower in Clarkia xantiana (Onagraceae). I. Size and development of floral organs.

Clarkia xantiana has two subspecies that differ in breeding system: ssp. xantiana, which is outcrossing, and ssp. parviflora, which is self-fertilizing. Outcrossing is the ancestral breeding system for the genus Clarkia. Flowers of ssp. parviflora have characteristics commonly associated with selfing taxa: they are smaller and have little temporal and spatial separation between mature anthers and stigma (dichogamy and herkogamy, respectively). Flower morphology and development were studied in four populations of each subspecies to establish the developmental changes that occurred in the evolution of selfing. In particular, we sought to evaluate the hypothesis that the selfing flower may have arisen as a byproduct of selection for rapid maturation in the arid environment occupied by ssp. parviflora. This hypothesis predicts that development time should be reduced in spp. parviflora relative to ssp. xantiana. We also sought to compare the pattern of covariation of flower morphology and development between subspecies to that within subspecies. Similar within vs. between patterns of covariation could be indicative of developmental or functional constraints on the independent evolution of floral parts. In spite of significant variation among populations within subspecies, the subspecies clearly differ in flower morphology and development. All floral organs, except ovaries, are smaller in ssp. parviflora than in ssp. xantiana. The flower plastochron, the duration of flower development from bud initiation to anthesis, and the duration of protandry are all shorter in ssp. parviflora than in ssp. xantiana. Maximum relative growth rates are higher for all organs in ssp. parviflora than in ssp. xantiana. Thus, progenesis (i.e., via a reduction in development time) is combined with growth acceleration in the evolution of the selfing flower. Since reduced development time and growth acceleration both allow selfing flowers to mature earlier than outcrossing ones, selection for early maturation may have contributed to the evolution of the selfing flower form. The pattern of trait covariation differs within spp. parviflora relative to the patterns within spp. xantiana and between the two subspecies, suggesting that floral parts can and have evolved independently of one another.

Journal Article↗
PubMed2000

The molecular basis of the high linoleic acid content in Petunia seed oil: analysis of a seed-specific linoleic acid mutant.

From a random transposon mutagenesis experiment, using Petunia line W138, a seed-specific linoleic acid mutant was isolated. The tagged gene was cloned and identified as a microsomal Delta(12) desaturase. Expression of the gene, however, was constitutive and not, as might have been expected, seed-specific. Moreover, self-fertilized homozygous mutants still contain 40% 18:2 in the seed lipid fraction. This suggests that at least two (seed-specific) Delta(12) desaturase genes are responsible for the high linoleic acid content in Petunia seed oil. Five members of the microsomal Delta(12) desaturase gene family have been identified and isolated. Data are presented on the molecular characterization and tissue-specific expression of these genes, which suggest that, in Petunia, the flux through the prokaryotic and eukaryotic pathways of lipid synthesis might be different from the situation found in Arabidopsis.

Cloning, Molecular↗
PubMed2001

[Genetic analysis of T1 progeny of transgenic tobacco with metallothionein gene and metallothionein domain mutant alpha alpha gene].

The chimeric gene containing a cloned mouse metallothionein processed gene or a cloned mouse metallothionein domain mutant alpha alpha gene was respectively introduced into tobacco (Nicotiana tobacum L. cv. NC89) on a disarmed Ti-plasmid of Agrobacterium tumefaciens. T1 seeds from self-fertilized transgenic tobacco were germinated on media containing cadmium or herbicide PPT. The PPT tolerance trait followed Mendelian inheritance and co-segregated with heavy metal tolerance. Meanwhile Southern blot and Western blot verified the existence of the MT gene and alpha alpha mutant gene in the T1 generation plants which keep tolerance to heavy metal. All the results demonstrated the stable integration and inheritance of exotic genes. In addition, assay of the root length and fresh weight of T1 seedlings indicate that transgenic tobacco plants with alpha alpha mutant gene still have a little higher tolerance than that with matural MT gene.

Animals↗
PubMed2001

Brachypodium distachyon. A new model system for functional genomics in grasses.

A new model for grass functional genomics is described based on Brachypodium distachyon, which in the evolution of the Pooideae diverged just prior to the clade of "core pooid" genera that contain the majority of important temperate cereals and forage grasses. Diploid ecotypes of B. distachyon (2n = 10) have five easily distinguishable chromosomes that display high levels of chiasma formation at meiosis. The B. distachyon nuclear genome was indistinguishable in size from that of Arabidopsis, making it the simplest genome described in grasses to date. B. distachyon is a self-fertile, inbreeding annual with a life cycle of less than 4 months. These features, coupled with its small size (approximately 20 cm at maturity), lack of seed-head shatter, and undemanding growth requirements should make it amenable to high-throughput genetics and mutant screens. Immature embryos exhibited a high capacity for plant regeneration via somatic embryogenesis. Regenerated plants display very low levels of albinism and have normal fertility. A simple transformation system has been developed based on microprojectile bombardment of embryogenic callus and hygromycin selection. Selected B. distachyon ecotypes were resistant to all tested cereal-adapted Blumeria graminis species and cereal brown rusts (Puccinia reconditia). In contrast, different ecotypes displayed resistance or disease symptoms following challenge with the rice blast pathogen (Magnaporthe grisea) and wheat/barley yellow stripe rusts (Puccinia striformis). Despite its small stature, B. distachyon has large seeds that should prove useful for studies on grain filling. Such biological characteristics represent important traits for study in temperate cereals.

Anti-Bacterial Agents↗
PubMed2002

[Biological characteristics of different forest soils in Nanjing-Zhenjiang mountan area].

Studies on the biological characteristics, including soil microbe, soil enzyme activity, soil nutritient content, and litter decomposition of different forest soils in Nanjing-Zhenjiang mountain area showed that the amounts of microbes and the activities of six enzymes in forest soils changed regularly in different forests during different months. The contents of nutritional elements varied regularly with forest growth bio-cycles, and were inerrelated prominently with the amounts of soil microbes and the activities of soil enzymes. There existed temporal-spatial differences in the decomposition rate of litters and the reverted velocity of nutrients among different forests. The comparisons of various biological characteristics among secondary Quercus variabilis forest, Phllostachys pubescens forest, and Cunninghamia lanceolata forest indicated that secondary Quercus variabilis forest had the most abundant nutrients in soil, and possessed the strongest ability of self-fertilization. Therefore, to construct coniferous forests with broadleaf trees in this area could avoid or abate the decline of soil fertility.

Biomass↗
PubMed1992

Mating behavior in the pulmonate small melampus: can regeneration restore function?

Previous anatomical observations have established that the penial complex of adult Melampus bidentatus is specifically reinnervated and that the penial complex itself can regenerate. This review describes experiments to determine whether a reinnervated penial complex and a regenerated penial complex can function in mating. The snails are not self-fertile, so the ability to transfer sperm, evaluated by production of fertile eggs, was the test of successful regeneration. Snails with nerve transections produced fertile eggs within the time-span expected for axonal regeneration to the target organ. Penial complex ablation interfered with sperm transfer for two egg-laying cycles but fertile eggs were laid within a time-span consistent with regeneration of a penial complex.

Animals↗
PubMed1990

Sexuality and hermaphroditism in fishes. I. Synchronous functional hermaphroditism in the serranid fish Serranus scriba L.

Anatomical and histological examination of Serranus scriba L. showed the existence of primary females (67%), hermaphrodites (31%) and primary males (2%). Synchronous functional hermaphroditism is described on the basis of an anatomical and histological study of the gonads. Although they function simultaneously, the testicular and ovarian parts of hermaphrodite gonads have completely separate ducts. Females and hermaphrodites have the same annual reproduction cycle. In hermaphrodites, the testicular part matures one month sooner than the ovarian part. Cross fertilization between primary females and hermaphrodite individuals and between two different hermaphrodites probably occurs, while self-fertilization is less likely. The testicular tissues of primary males are of the acinar type and those of hermaphrodites are of the radial type. It is possible that primary males do not take part in reproduction. Serranus scriba in Egyptian Mediterranean waters is a longperiod spawner, which spawns from June to the end of October, i.e. it is a summer-autumn spawner.

Animals↗
PubMed1986

Diethylnitrosamine-induced pancreatic neoplasms in the fish Rivulus ocellatus marmoratus.

Diethylnitrosamine [(DEN) CAS: 55-18-5] caused neoplasms of the exocrine pancreas in rivulus, Rivulus ocellatus marmoratus, a self-fertilizing hermaphroditic fish, after a single exposure to 810, 270, or 130 mg DEN/liter or after a continuous exposure to 50, 17, or 9 mg DEN/liter. Rivulus developed pancreatic adenomas after a single exposure. After continuous exposure, pancreatic adenomas, cystadenomas, and adenocarcinomas developed. Adenocarcinoma developed in fish first exposed as larvae but not in those first exposed as juveniles. Adenocarcinoma of pancreatic or biliary origin invaded the intestinal muscularis layer and mucosa. Dedifferentiation of acinar cells preceded the formation of adenomas, and atypical acinar cells formed parts of some of the ductlike structures in the pancreatic neoplasms.

Adenocarcinoma↗
PubMedDate not supplied

Population genetics of Biomphalaria straminea in Hong Kong. A neotropical schistosome-transmitting snail recently introduced into China.

Since its introduction in the early 1970s Biomphalaria straminea (Gastropoda: Planorbidae) has spread rapidly and is locally the most abundant fresh water snail in Hong Kong. Studies of 19 electrophoretically detected loci in four populations show that the colonists retain high levels of variability (P = 0.26, H = 0.056 - 0.097), comparable with those found in autochthonous samples of related species. Genotype frequencies at the five polymorphic loci, and a comparison of maternal and progeny genotypes of individual field-collected snails, revealed no evidence for self-fertilization in these functional hermaphrodites. F statistics indicated minimal genetic structuring, presumably because of outcrossing and recency of origin of the populations. Geographic distribution of various alleles and their frequencies suggest that two southern populations were derived from the original colonists by dispersal but that a northern population represents a second introduction in about 1982. This interpretation (based on genetics) is consistent with the known history of the various populations. The Asian populations of this South American snail are interpreted as being in the "flush" phase of the colonization process. Finally, the probability of the secondary spread of this snail from Hong Kong, and the probability of its parasite, the human blood fluke Schistosoma mansoni, being introduced to Asia are discussed.

Alleles↗
PubMed1984

Covariances of relatives stemming from a population undergoing mixed self and random mating.

We consider covariances of all parent and first-generation relatives from outcrossing or self-fertilization in a parent population that is in equilibrium with respect to these processes. The results, which are for any number of alleles and loci with additive and dominance effects, are phrased in terms of six quadratic genetic components whose coefficients are given by descent measures for equilibrium populations. Because of the variation in the inbreeding coefficients for this system of mating, the expressions include joint contributions of loci to the variances and covariances of relatives. By inclusion of the full complement of relatives, all quadratic components can be estimated. The findings of Ghai (1982, Biometrics 38, 87-92) for compound functions of the covariances with two alleles at a single locus are analyzed in terms of the more general model.

Alleles↗
PubMed1984

Usefulness of the hermaphroditic marine fish, Rivulus marmoratus, in carcinogenicity testing.

Hepatocellular carcinoma and other pathological changes were induced in the self-fertilizing hermaphroditic fish Rivulus marmoratus by aqueous exposure to 15, 30, and 45 ppm diethylnitrosamine (DENA). Fish exposed as larvae for 12 weeks and adults exposed for 5 weeks showed rates of hepatocellular carcinoma as high as 76.5 and 31.3%, respectively, when examined 1 year later. Fish exposed as embryos in various stages of development for 1 week to 10, 32, 100, 320, and 1,000 ppm DENA were without neoplasms when examined 1 year later. Other pathological changes of rivulus livers were cholangioma, adenofibrosis, and granuloma with incidences as high as 38.9, 88.9, and 61.1%, respectively. Simple rearing methods were developed and relevant biological data pertaining to reproduction, embryonic development, and subsequent growth of R. marmoratus are discussed. Advantages and disadvantages of the use of R. marmoratus as a carcinogenicity test animal are assessed.

Animals↗