Oogenesis of Tilapia mossambica. I. Oogonia and meiotic prophase oocytes

Using light and electron microscopy and autoradiography, the morphology and synthesis of DNA, RNA and proteins in oogonia and early meiotic prophase oocytes in Tilaria mossabique were studied. According to dimensions and morphological features observed it is possible to distinguish between two groups of oogonia: large oogonia corresponding to type A spermatogonia of mammals, and small actively dividing oogonia, located in groups and identical to type B spermatogonia. The morphology of oogonia and of the early meiotic prophase oocytes well compares with the pattern described for other species of bony fishes. In the cytoplasm of these cells dense bodies, nuage-material, free ribosomes, large mitochondria with lamellar cristae and Golgi cisterns are available. In the oocyte nuclei at zygotene and pahytene stages 3H-thymidine incorporation was seen mainly into the nucleolus-associated chromatin. Besides, the formation of a heterochromatin cape and the synaptonemal complex was observed. Incorporation of 3H-uridine and 3H-leucine in the nuclei of these cells was very poor.     

Oogenesis of Tilapia mossambica. III. The cytoplasm of previtellogenic oocytes]

Using methods of light and electron microscopy and of autoradiography, the morphology of cytoplasm in previtellogenic oocytes of tilapia mossambique was studied. Similar to other bony fishes, mitochondria at the early previtellogenic oocytes are mostly located in the perinuclear cytoplasm to be later distributed over the whole volume of growing oocytes. The Golgi complex is poorly developed. In the peripheral regions of the late previtellogenic oocytes, stickform mitochondria, pinocytotic vesicles and microvilli are observed, along with the perioocyte space formation. In the cytoplasm of previtellogenic oocytes polyribosomes appear. No differences in 3H-leucine incorporation intensity was noticed in oocytes of different previtellogenic stages. The characteristic feature of tilapia mossambique previtellogenic oocytes, in comparison with other bony fishes, is the presence of fat droplets in their cytoplasm.     

Hibiscus vitifolius,a new fibre crop

This is a discussion of an investigation conducted on the morphology and anatomy ofHibiscus vitifolius, the physical and chemical properties of its fibre and yarn, and a preliminary study on reaction to dyes. The quality and physical and chemical properties of the fibre closely resemble those of jute. But further agronomic investigations are needed to assess more fully its potentialities as a commercial crop to supplement the growing demand for jute. Because of its short reed length and higher tex values, it may be best utilized, at present, as a mixture with jute.     

Agronomic evaluation of prospective new crop species. VI.Briza humilis—Source of galactolipids

Briza humilis Bieb., a low seed-yielding member of the family Gramineae, showed agronomic promise as a commercial source of galactolipids. The seed lipid contains about 80% galactolipids, compared to little, if any, in other evaluated species ofBriza. An obligate winter annual,B. humilis is a small, noncompetitive grass with good seed retention. Seed (caryopsis) yields ranged from 280 to 1,475 kg/ha. Clean threshing of the light-weight seed (0.5 g/1,000) proved difficult. Because yield and plant size varied, agronomic improvement should be possible.     

Weed-induced crop yield loss: a new paradigm and new challenges

Direct competition for resources is generally considered the primary mechanism for weed-induced yield loss. A re-evaluation of physiological evidence suggests weeds initially impact crop growth and development through resource-independent interference. We suggest weed perception by crops induce a shift in crop development, before resources become limited, which ultimately reduce crop yield, even if weeds are subsequently removed. We present the mechanisms by which crops perceive and respond to weeds and discuss the technologies used to identify these mechanisms. These data lead to a fundamental paradigm shift in our understanding of how weeds reduce crop yield and suggest new research directions and opportunities to manipulate or engineer crops and cropping systems to reduce weed-induced yield losses.     

RNAi technology: a new platform for crop pest control

The insect pests are big threat in meeting the food demands for future generation. The present pest control strategies, including the existing transgenic approaches show certain limitations and are not completely successful in limiting the insect pests. However, the sequence-specific gene silencing via RNA interference (RNAi) holds a great promise for effective management of agricultural pests. RNAi is naturally occurring conserved process responsible for gene regulation and defense against pathogens. The efficacy of RNAi varies among different insect orders and also depends upon various factors, including the target gene selection, method of dsRNAs delivery, expression of dsRNAs and presence of off-target effects. RNAi-mediated silencing of different insect genes involved in various physiological processes was found to be detrimental to insects growth, development and survival. In this article, we have reviewed the potential of RNAi-based strategies for effective management of insect pests. We have also discussed the various parameters, which are to be considered for host-induced RNAi-mediated control of insect pests without producing any effect on non-target organisms and environment.     

Agronomic evaluation of prospective new crop species

Preliminary field evaluations for 162 species are reported. This work represents a portion of a team-oriented effort to develop new crops for American agriculture. These species are potential new oilseed sources of epoxy, crepenynic, erucic, and other fatty acids, and sources of seed gum, steroids, and pulp. Euphorbia lagascae andCephalaria setosa show the most promise for crop development as epoxy acid sources, but both require substantial improvement through breeding.Crepis alpina, a small-seeded species with excellent seed retention, is the best prospect for providing an oil rich in crepenynic acid. A selection and breeding program is under way. None of the species tested as erucic acid sources equalled the crop potential of crambe and selected Brassicas.Briza spicata, a small, moderately productive grass, is the richest known source of glycolipids.B. spicata has been grown successfully as a winter annual at several locations. Earlier maturity and better seedling vigor is needed inSatureja hortensis, a source of oil similar to linseed oil.Xeranthemum annuum, an attractive, winter annual and everlasting, is very good agronomically, but the use of the oil with its mixture of several fatty acids is not economically favorable.Solanum khasianum shows agronomic promise as a source of the steroid, solasodine.Cassia occidentalis, C. bonariensis, Crotalaria leioloba, andC. stipularia are productive potential seed gum sources. These species, especiallyCassia occidentalis, seem to be sufficiently good agronomically to justify intensive breeding. Of the various sources of pulp, emphasis is on kenaf because highyielding, well-adapted varieties are available.Crotalaria juncea merits breeding effort, and other species show sufficient promise for further evaluation.     

The 1H nuclear-magnetic-resonance spectra of Neurotoxin I and cardiotoxin Vii4 from Naja mossambica mossambica.

Two toxins from the venom of Naja mossambica mossambica, neurotoxin I and cardiotoxin VII4, were investigated in aqueous solution by high-resolution 1H nuclear magnetic resonance (NMR) techniques at 360 MHz. The spectral characterization of the proteins included determination of the number of slowly exchanging amide protons which can be observed in 2H2O solution, measurement of the amide proton chemical shifts and exchange rates, characterization of the aromatic spin systems and the internal mobilities of aromatic rings, and studies of the pH dependence of the NMR spectra. For numerous resonances of labile and non-labile protons quite outstanding pH titration shifts were observed. It is suggested that these NMR parameters provide a useful basis for comparative structural studies of different proteins in the large group of homologous snake toxins. As a first application the NMR data presently available in the literature on neurotoxin II from Naja naja oxiana, toxin alpha from Naja nigricollis and erabutoxin a and b from Laticauda semifasciata have been used to compare these three proteins with neurotoxin I from Naja mossambica mossambica. This preliminary comparative study provides evidence that the same type of spatial structure prevails for these four homologous neurotoxins and that the folding of the backbone corresponds quite closely to that observed in the crystal structure of erabutoxin b. A second application is the comparison of cardiotoxin VII4 from Naja mossambica mossambica with the neurotoxins. The experimental data indicate that the folding of the polypeptide backbone is closely similar, but that the cardiotoxin molecule is markedly more flexible than the neurotoxins.     

Genomics reveals new landscapes for crop improvement

The sequencing of large and complex genomes of crop species, facilitated by new sequencing technologies and bioinformatic approaches, has provided new opportunities for crop improvement. Current challenges include understanding how genetic variation translates into phenotypic performance in the field.     

Enhanced polarizing microscopy as a new tool in aneuploidy research in oocytes

Chromosomal non-disjunction in female meiosis gives rise to reduced fertility and trisomy in humans. Human oocytes, especially from aged women, appear especially susceptible to non-disjunction. The oocyte spindle is crucial for high fidelity of chromosome segregation at meiotic divisions, and alterations in spindle morphology are therefore indicators of adverse conditions during oocyte development that may result in meiotic aneuploidy. In the past, oocytes had to be fixed for spindle analysis, precluding direct non-invasive identification of aneugens and adverse maturation conditions that affect spindle integrity and chromosome behaviour. Aneuploidy research for detection of spindle aberrations was therefore mainly focused on in vivo or in vitro exposed, fixed animal oocytes or cytogenetic analysis of spread oocytes. Orientation independent enhanced polarizing microscopy with nearly circularly polarized light and electronically controlled liquid crystal compensator optics is a new tool to study spindle morphology non-invasively in vivo for qualitative as well as quantitative analysis. Image generation by polarization microscopy depends on the intrinsic optical properties of the spindle with its paracrystalline microtubule lattice. When polarized light passes through such a lattice it induces a splitting of the beam and shift in the plane of vibration and retardation of light (termed birefringence and retardance). Studies of animal oocytes and follicle-cell denuded human oocytes fertilized by intracytoplasmic sperm injection for assisted conception have demonstrated the safety and efficacy of enhanced polarization microscopy. The method can be employed in aneuploidy research for non-invasive dose-response studies to detect spindle aberrations, for instance, in combination with cytogenetic analysis. Due to the non-invasive nature of the technique it may be employed in routine analysis of human oocytes to assess risks by lifestyle factors, and occupational and adverse environmental exposures.     

Plant species evaluated for new crop potential

About 500 plant species from various regions of the United States have been screened previously at the USDA Northern Regional Research Center for their multipurpose, energy-producing potential. Most collections have been from the rich flora of central Illinois. For this report, 92 additional species were collected from southern Illinois and evaluated by criteria previously established at this Center. Plant samples were analyzed for “oil,” “polyphenol,” “hydrocarbon,” and protein. Oil fractions of selected species were analyzed for classes of lipid constituents and were saponified to determine yields of unsaponifiable matter and fatty acids. Hydrocarbon fractions of selected species were analyzed for rubber, gutta, and waxes. Average molecular weight and molecular weight distribution of rubber and gutta were determined. of the 92 species, complete analytical data are presented for 16 selected species. Substantial quantities of oil were obtained fromPhiladelphias coronarius (5.0%; dry, ash-free sample basis),Cacalia muhlenbergii (4.1%),Lindera benzoin (4.1 %), andKoelreuteria paniculata (4.0%). High yields of polyphenol were obtained fromAcer ginnala (33.1%),Cornus obliqua (20.8%), andSalix caprea (20.0%). Maximum yields of hydrocarbon and protein were fromElymus virginicus (0.6%) andLindera benzoin (11.1%), respectively. Data are discussed with respect to species previously analyzed at this Center.     

The crop milk: a potential new route for carotenoid-mediated parental effects

Allocation of carotenoid pigments, either through nutritional provisioning or from endogenous reserves, makes up a form of non-genetic parental investment to progeny that may contribute to fitness. To date, carotenoids derived from endogenous reserves have been acknowledged as important vectors in translating only avian female phenotype and environmental conditions experienced prior to laying. Here, we show that in columbidae, crop milk delivered by both parents may provide chicks with a large amount of endogenous carotenoids at the postzygotic stage. Major carotenoids were xanthophylls and beta-carotene, but their concentrations showed large variation among individuals. Interestingly, a large amount of this variation was explained by brood identity, suggesting either environmental influences and/or phenotypic influences on a parent's ability to transfer these biomolecules. Our study therefore illuminates a potential new route for endogenous carotenoid-mediated parental effects.     

Selecting karyophilic DNA cis elements in Xenopus laevis oocytes; a new approach

The intracellular localisation and mobility of exogenous DNA introduced into Xenopus laevis oocytes is largely unknown. In this paper, we report a new technique to investigate the cytoplasmic/nuclear transport of a random pool of linear, double-stranded, oligomeric DNA of 147 bp in length. We chose a combinatorial approach which made use of repetitive rounds of selection and amplification to search for new cis elements mediating nuclear import or retention. A new PCR-based methodology was established to reliably detect exogenous DNA in subcellular and total extracts prepared from Xenopus laevis oocytes. Studies in vivo and with cellular extracts indicate the presence of a highly efficient nuclease activity in the nuclear compartment. The described combinatorial approach constitutes a promising tool for the isolation of novel DNA cis elements which may play an important role in the nuclear internalisation and retention of exogenous DNA in Xenopus laevis oocytes.