Influence of A1 cytoplasmic substitution on the downy-mildew incidence of pearl millet

Large-scale cultivation of pearl millet [Pennisetum glaucum (L.) R. Br. F₁ hybrids in India has led to increased incidence of downy-mildew (Sclerospora graminicola). There is concern that the A₁ male-sterile cytoplasm used in all the hybrids released so far is responsible for this increase. The influence of A₁ malesterile cytoplasm on downy-mildew incidence in pearl millet was studied by comparing the disease reaction of 40 pairs of F₁ hybrids, each pair carrying respectively a₁ male-sterile and normal B cytoplasm. Mean downy-mildew incidence was similar in the hybrids carrying either A₁ male-sterile or B cytoplasm. The general combining ability of lines with and without A₁ cytoplasm was found to be similar for downy-mildew incidence. These results indicated that in pearl millet A₁ cytoplasm is not associated with increased downymildew incidence. The possible danger of using only one source of cytoplasm has been briefly discussed.     

Cytological and molecular characterization of a chromosome interchange and addition lines in Cadet involving chromosome 5B of wheat and 6Ag of Lophopyrum ponticum

Efforts to transfer wheat curl mite (Eriophyes tulipae Keifer) resistance from Lophopyrum ponticum 10X (Podb.) Love to bread wheat (Triticum aestivum L.) have resulted in the production of a number of cytogenetic stocks, including an addition line of 6Ag, a ditelo addition line, and a wheat-Lophopyrum translocation line. Characterization of these lines with C-banding, in situ hybridization with a Lophopyrum species-specific repetitive DNA probe (pLeUCD2), and Southern blotting with pLeUCD2 and a 5S ribosomal DNA probe (pScT7) confirmed that the distal portion of the short arm of 6Ag was translocated onto the distal portion of 5BS (5BL. 5BS-6AgS). It was also determined that the ditelo addition was an acrocentric chromosome of 6AgS.     

A medium for enumeration of bacteria in foods containing swarming Bacillus spp.

A new medium containing sodium tripolyphosphate, ethylenediaminetetraacetic acid disodium salt, dihydrate, sodium desoxycholate, supplemented with minerals and nutrient sources was developed, which was very effective in inhibiting swarming of Bacillus spp. This medium polyphosphate-EDTA-desoxycholate agar (PEDA) was compared with tryptone glucose extract agar (Oxoid) for determining the total plate count of various semi-conserved fishery products. While promoting discrete colony formation of Bacillus spp., PEDA provided good bacterial recovery. PEDA is recommended for isolation or enumeration of bacteria in food dominated by swarming Bacillus spp.     

A model for chromatin opening: stimulation of topoisomerase II and restriction enzyme cleavage of chromatin by distamycin.

Histone H1 preferentially and cooperatively binds scaffold-associated regions (SARs) in vitro via specific interactions with the numerous short A + T-rich tracts (A-tracts) contained in these sequences. Selective titration of A-tracts by the oligopeptide distamycin abolishes this interaction and results in a redistribution of H1. Similarly, treatment of intact cells and isolated nuclei with distamycin specifically enhances cleavage of internucleosomal linkers of SARs by topoisomerase II and restriction enzymes. The increased accessibility of these linkers is thought to result from the unfolding (or opening) of the chromatin fiber and to be due to a reduced occupancy by histone H1. Chromatin extraction and H1 assembly experiments support this view. We discuss a model whereby open, H1-depleted chromatin regions may be generated by titration of A-tracts by putative distamycin analogues; this local opening may spread to adjacent regions assuming highly cooperative H1-H1 interactions in chromatin.     

Biochemical analysis of torso and D-raf during Drosophila embryogenesis: implications for terminal signal transduction.

Determination of anterior and posterior terminal structures of Drosophila embryos requires activation of two genes encoding putative protein kinases, torso and D-raf. In this study, we demonstrate that Torso has intrinsic tyrosine kinase activity and show that it is transiently tyrosine phosphorylated (activated) at syncytial blastoderm stages. Torso proteins causing a gain-of-function phenotype are constitutively tyrosine phosphorylated, while Torso proteins causing a loss-of-function phenotype lack tyrosine kinase activity. The D-raf gene product, which is required for Torso function, is identified as a 90-kDa protein with intrinsic serine/threonine kinase activity. D-Raf is expressed throughout embryogenesis; however, the phosphorylation state of the protein changes during development. In wild-type embryos, D-Raf is hyperphosphorylated at 1 to 2 h after egg laying, and thereafter only the most highly phosphorylated form is detected. Embryos lacking Torso activity, however, show significant reductions in D-Raf protein expression rather than major alterations in the protein's phosphorylation state. This report provides the first biochemical analysis of the terminal signal transduction pathway in Drosophila embryos.     

Either alpha-tubulin isogene product is sufficient for microtubule function during all stages of growth and differentiation in Aspergillus nidulans.

The filamentous fungus Aspergillus nidulans has two genes encoding alpha-tubulin, tubA and tubB, which are differentially required at distinct stages during the life cycle. The tubA gene is required during vegetative growth for mitosis and nuclear migration (B. R. Oakley, C. E. Oakley, and J. E. Rinehart, Mol. Gen. Genet. 208:135-144, 1987; P. Doshi, C. A. Bossie, J. H. Doonan, G. S. May, and N. R. Morris, Mol. Gen. Genet. 225:129-141, 1991). The tubB gene is not required for any detectable aspect of vegetative growth or asexual reproduction but is essential during sexual development prior to the first meiotic division (K. E. Kirk and N. R. Morris, Genes Dev. 5:2014-2023, 1991). In this study, we determined whether the role of each alpha-tubulin gene is to provide a specific isotype necessary for a particular microtubule function or whether either alpha-tubulin isotype, if present in sufficient quantities, can participate effectively in all types of microtubule. Strains carrying a deletion allele of tubB (tubB delta) produce no ascospores from a cross. When one copy of a plasmid containing the region upstream of the tubB gene fused to the tubA coding region was integrated into a tubB delta strain, ascosporogenesis proceeded beyond the tubB delta block and resulted in the formation of sexual spores. However, irregular numbers of spores formed in some asci during development, and the ascospores had greatly diminished viability and aberrant morphologies. These defects were nearly corrected when two additional copies of the tubA coding region were integrated into the tubB delta strain. These results indicate that the tubA alpha-tubulin isotype can form functional microtubules during sexual development in the absence of tubB protein. In a reciprocal set of experiments, we examined whether upregulation of tubB can complement the tubA4 mutation, which causes supersensitivity to benomyl during vegetative growth. When tubA4 strains integrated a plasmid containing an alcohol-inducible promoter joined to the tubB coding region and subsequently overexpressed the tubB isotype, the benomyl supersensitivity normally caused by the tubA4 allele was relieved. These results indicate that when enough tubB alpha-tubulin is supplied, strains lacking functional tubA isotype can still form microtubules which effectively carry out mitosis and nuclear migration.     

Video microscopic analysis of ionophore induced acrosome reactions of lobster (Homarus americanus) sperm

Sperm from the American lobster (Homarus americanus) are normally nonmotile. However, during fertilization, the sperm undergo a calcium-dependent acrosome reaction that propels them forward about 18 μMm. The reaction occurs in two phases, eversion and ejection, which take place too quickly to permit analysis by direct observation. The purposes of this study were to examine the structural changes occurring in sperm during the normal acrosome reaction and to determine the rate of the reaction using video microscopy. The reaction was induced in vitro by ionophore A23187 and recorded using a video system attached to a Nikon Nomarski interference microscope. Videotapes were played back frame by frame (30 frames/sec), and images of reactions from 10 sperm were analyzed. The acrosome reaction, including the eversion of the acrosomal vesicle and ejection of the subacrosomal material and nucleus, can be divided into 4 steps: (1) expansion of the apical cap followed by expansion of the remainder of the acrosomal cylinder; expansion of the cylinder begins at its apical end and proceeds toward its base, (2) eversion of the apical half of the acrosomal vesicle and initial contraction of the apical cap, (3) eversion of the basal half of the acrosomal vesicle, continued contraction of the apical cap, and ejection of the subacrosomal material and nucleus, and (4) final contraction of the apical cap and ejection of the acrosomal filament. During steps 2, 3, and 4, the mean forward movement of sperm is 12.7, 3.9, and 1.1 μMm, respectively. Although the time required to complete the reaction ranged from 0.66 to 5.16 s, most sperm reacted in less than 3. s, and these sperm were considered to have typical rates. For sperm that reacted in less than 3 s, both step 1 and step 4 take about 0.2 s and show little variation among sperm. the time required to complete steps 2 and 3 averaged 0.63 and 0.37 s, respectively. Forward movement of the sperm during the acrosome reaction is caused by eversion of the inner and outer acrosomal material and contraction of the apical cap. The protein(s) responsible for this contraction is not yet known. © 1993 Wiley-Liss, Inc.     

Cellular Concentrations and Uniformity of Cell-Type Accumulation of Two Lea Proteins in Cotton Embryos

The levels and cell-type distribution of late embryogenesis abundant (Lea) proteins D-7 and D-113 have been determined in mature cotton embryos by immunochemical methods. The two proteins were expressed in and purified from Escherichia coli and utilized for antibody production in rabbits. The antiserum to each protein was found to interact with all members of each protein family in cotton extracts by protein gel blotting. Using these antibodies in quantitative "rocket" immunoelectrophoreses, D-7 proteins were found to accumulate to ~8 x 1015 molecules per embryo, which is equivalent to ~109 molecules per "average cell." D-113 proteins accumulate to ~1016 molecules per embryo, which equates to ~1.3 x 109 molecules per average cell. These values calculate to concentrations of about 226 and 283 [mu]M, respectively, in the cell aqueous phase immediately prior to seed desiccation. In immunocytochemical studies using the fluorophor rhodamine linked to the secondary antibody, both proteins appeared to be evenly present in the cytosol of all cell types present in the embryo, including both cotyledon and axis epidermal cells. Thus, their function does not appear related to unique functions of specific cell or tissue types. The very high molar concentrations of the two proteins, coupled with their unusual predicted structure and their cytosol location, would seem to reduce the number of their conceivable functions.