Gene Expression in Developing Zea mays Embryos: Regulation by Abscisic Acid of a Highly Phosphorylated 23- to 25-kD Group of Proteins

We have earlier identified a set of proteins of 23 to 25 kilodaltons (kD), covering an isoelectric point (pI) range of 6.2 to 8.2, which accumulate gradually during normal embryogenesis of Zea mays and disappear in early germination. These polypeptides can be induced prematurely in immature embryos by abscisic acid (ABA) treatment. We report here that the more acidic protein forms are due to post-translational phosphorylation of at least two polypeptides of 23 kD, pI 8.2 and 25 kD, pI 8.0. A polyclonal antiserum was obtained which recognizes all forms of both the 23-kD and 25-kD polypeptides. Recovery of cDNA clones corresponding to these proteins was accomplished by hybridization with cDNA made from size-selected mRNA enriched for these sequences. Hybrid selection experiments demonstrate that clone MA12 specifically hybridizes with mRNAs encoding the 23-kD and 25-kD protein set which are recognized by the antiserum. By Northern hybridization analysis, the RNA encoded by clone MA12 is shown to accumulate in mature embryos and to be induced in young embryos upon ABA incubation.     

Regulation of Gene Expression in Developing Zea mays Embryos: Protein Synthesis during Embryogenesis and Early Germination of Maize

Polypeptides synthesized in dissected embryos of Zea mays at different stages of embryogenesis and early germination have been characterized by their migration in two-dimensional gel electrophoresis. This analysis has been carried out with in vivo labeled polypeptides from excised embryos and with proteins synthesized in vitro in the rabbit reticulocyte system directed by poly(A⁺) RNA isolated from the different developmental stages. We have identified three main sets of expressed polypeptides: (a) embryonic set: this group of polypeptides is synthesized in young and mature embryos but not in early germination; (b) maturation set: this group of polypeptides is not present in young embryos and appears during the maturation period. Some of these polypeptides are still present in early germination while others disappear from stored mRNAs in dry embryos. One particular group from this set can be induced prematurely in young embryos by incubation with abscisic acid; and (c) germination set: this group of polypeptides is not expressed in the maturation period and appears after brief imbibition of the dry embryos.     

Fine structure of the spermatozoa of Crassostrea gigas (Mollusca,Bivalvia)

We describe sperm ultrastructure and acrosome differentiation during spermiogenesis in Crassostrea gigas (Mollusca Bivalvia). The sperm cell is a uniflagellated cell of the primitive type. The head region contains a rounded or conical nucleus surmounted by small acrosome. This organelle consists of a membrane-bound acrosomal granule, the contents of which have a homogeneous density, except in the anterior region, which is positive for PTA. The acrosome also surrounds the perforatorium, which includes oriented fibrillar elements: this is the axial body. The middle piece contains four mitochondria encircling two perpendicular centrioles. The distal centriole is provided with a system of mechanical fixation to the plasma membrane, consisting of nine fibers in radial arrangement. The tail flagellum, about 50 m?m long, contains the usual microtubular axoneme. © 1993 Wiley-Liss, Inc.     

EFFECTS OF COMPETITION AND DISTURBANCE ON THE RESPROUTING PERFORMANCE OF THE MEDITERRANEAN SHRUB ERICA MULTIFLORA L. (ERICACEAE)

Two field experiments were designed to evaluate the importance of competition, fire, repeated disturbance, and their interactions on the vegetative and reproductive performance of the Mediterranean shrub Erica multiflora over a 2.5-yr period. In a burn experiment, fire was applied to the ground-level stumps of previously clipped 13-yr-old plants with a propane torch and competition was diminished by removal of neighboring plants. Fire resulted in a reduction of sprout vigor and biomass of flowers; mature neighbors also reduced E. multiflora sprout vigor and flowering. The interaction between fire and competition was nonsignificant. In a stand burned by a wildfire we studied the effects of regenerating neighbors on target plants by removing all neighbors or only Quercus coccifera, the most dominant species in the burned stand. In this stand we also simulated herbivory by repeatedly clipping the sprouts of E. multiflora. Regenerating neighbors did not affect target plant sprout vigor after the wildfire, but did cause a decrease in the biomass of flowers per plant. Survival decreased after repeated clipping but was not affected by neighborhood treatment. The results suggest that the importance of competition on resprouting vigor was temporally variable. Variables related to plant size rather than species determined competitive superiority: resprouting neighbors did not affect resprouting performance of target plants, but mature neighbors did. In nature, fire may directly reduce vegetative and reproductive biomass by the heating effect. But it may have an indirect positive effect on biomass, by reducing competition among plants. Frequent disturbances that removed aboveground biomass of E. multiflora had a detrimental effect on target plant survival independent of neighborhood effect.     

Banding patterns of the chromosomes ofCercopithecus neglectus: Comparison withMiopithecus talapoin andErythrocebus patas

The G, Q, and C bands and the location of the nucleolar organizing regions (NORs) of the chromosomes of two male Cercopithecus neglectusare described. The diploid number of the species is 2n =62. Comparison with the karyotypes of Miopithecus talapoin (2n =54), and Erythrocebus patas (2n =54)showed the presence of total banding homeology for only 10 chromosome pairs.     

Assessment of Real-time PCR Based Methods for Quantification of Pollen-mediated Gene Flow from GM to Conventional Maize in a Field Study

Maize is one of the main crops worldwide and an increasing number of genetically modified (GM) maize varieties are cultivated and commercialized in many countries in parallel to conventional crops. Given the labeling rules established e.g. in the European Union and the necessary coexistence between GM and non-GM crops, it is important to determine the extent of pollen dissemination from transgenic maize to other cultivars under field conditions. The most widely used methods for quantitative detection of GMO are based on real-time PCR, which implies the results are expressed in genome percentages (in contrast to seed or grain percentages). Our objective was to assess the accuracy of real-time PCR based assays to accurately quantify the contents of transgenic grains in non-GM fields in comparison with the real cross-fertilization rate as determined by phenotypical analysis. We performed this study in a region where both GM and conventional maize are normally cultivated and used the predominant transgenic maize Mon810 in combination with a conventional maize variety which displays the characteristic of white grains (therefore allowing cross-pollination quantification as percentage of yellow grains). Our results indicated an excellent correlation between real-time PCR results and number of cross-fertilized grains at Mon810 levels of 0.1–10%. In contrast, Mon810 percentage estimated by weight of grains produced less accurate results. Finally, we present and discuss the pattern of pollen-mediated gene flow from GM to conventional maize in an example case under field conditions.     

The freshwater planarian Dugesia (G.) tigrina contains a great diversity of homeobox genes

To identify potential pattern control and cell determination and/or differentiation genes in the freshwater planarian Dugesial (G.) tigrina, we searched for homeobox genes of different types in the genome of this primitive metazoan. We applied two basic approaches: 1) Screening the cDNA library with degenerate oligonucleotides corresponding to the most conserved amino acid sequence from helix-3 of the homeodomain of each family; and 2) PCR amplification of genomic DNA or cDNA, using two sets of degenerated oligonucleotides corresponding to helices 1 and 3 of the homeodomain or two specific domains of the POU family. Using the first strategy we have identified and characterized two tissue-specific cell determination and/or differentiation NK-type homeobox genes. Using the second strategy we have identified several homeobox genes that belong to the HOM/Hox, paired (prd) or POU families.