Conditional lethality involving a cytoplasmic mutant and chlorophyll-deficient malate dehydrogenase mutants in soybean

Summary Conditional lethality in soybean, Glycine max (L.) Merr., occurred in F₂ plants when cytoplasmicchlorophyll mutant Genetic Type T275 was the female parent and when either nuclear mutants T253 or T323 plants were the male parents. Mutant T253 [Mdh1-n (Urbana) y20 (Urbana) k2] is missing two of three mitochondrial malate dehydrogenase isozymes [Mdh1-n (Urbana)] and has yellowish-green leaves [y20 (Urbana)] and a tan-saddle pattern seed coat (k2). Mutant T323 [Mdh1-n (Ames 2) y20 (Ames 2)] also is missing two of three mitochondrial malate dehydrogenase isozymes [Mdh1-n (Ames 2)] and has yellowishgreen leaves [y20 (Ames 2)], but has yellow seed coat (K2). Mutants T275, T253, and T323 are viable both in the field and glasshouse. The genotypes cyt-Y2 Mdh1-n (Urbana) y20 (Urbana) k2/Mdh1-n (Urbana) y20 (Urbana) k2 and cyt-Y2 Mdh1-n (Ames 2) y20 (Ames 2)/Mdh1-n (Ames 2) y20 (Ames 2) are conditional lethals. These genotypes are lethal under field conditions, but plants survive in reduced light under shadecloth in the glasshouse. We do not know if their interaction with cyt-Y2 is due to Mdh1-n, y20, or Mdh1-n y20. The reciprocal cross (cyt-Y2 as male parent) gives viable genotypes. These conditional lethal genotypes should be useful for studies on the interaction between organelle and nuclear genomes.This is journal paper no. J-14777 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011-1010. Project 2985     

The public health significance of VTEC O157

ABSTRACT Surveillance of human VTEC O157 has been reported in several countries, based on laboratory evidence. The incidence is generally less than 10 per 100 000 (the highest incidence is in children), with regional variations and a marked seasonality. Laboratory selection criteria and reporting have contributed to, but cannot entirely explain, variations within and between countries. Surveillance data and outbreaks in definable cohorts indicate that the spectrum of illness ranges from diarrhoea through acute bloody diarrhoea, with about 5% of cases developing haemolytic uraemic syndrome; less than 50% of patients report frank blood in their stools. Studies of sporadic cases have associated illness with beef products (particularly if undercooked and eaten outside the home), cooked sliced meat meals and contact with a household member with diarrhoea. Outbreaks have been attributed to contaminated foods (including beefburgers) and water, animal contact and person-to-person spread. Secondary transmission by the primary case in a household is of particular concern, and household transmission has been estimated at 4%, with patients excreting for around 10 days following onset. Recommendations for control have highlighted measures on farms, in slaughterhouses, retail and catering food premises, and in the home.     

Gene expression in Brassica campestris showing a hypersensitive response to the incompatible pathogen Xanthomonas campestris pv. vitians

Xanthomonas campestris pv. vitians, a pathogen of lettuce, elicits a hypersensitive response within 12 hours of inoculation into Brassica leaves, characterized by tissue collapse, loss of membrane integrity, vein blockage and melanin production. In contrast, the compatible pathogen, X. c. pv. campestris, has no visible effects on leaves for 48 hours, after which inoculated areas show chlorosis which eventually spreads, followed by rotting.mRNA was prepared from leaves inoculated with suspensions of both pathovars or with sterile medium up to 24 hours following inoculation. In vitro translation of total and poly A⁺ RNA in rabbit reticulocyte lysate in the presence of ³⁵S methionine followed by separation of the polypeptide products by 2D-PAGE, allowed comparison of the effects of these treatments on plant gene expression. Major changes in gene expression were observed as a consequence of the inoculation technique. In addition, after inoculation with X. c. vitians, up to fifteen additional major polypeptides appeared or greatly increased by four hours. Some of these had disappeared by nine hours and several more had appeared. No major polypeptides disappeared or decreased greatly in intensity following inoculation with X. c. vitians.     

Inhibition by bromoestrogens of the effects of estradiol on apomorphine-induced climbing behavior

The chronic administration of estrogens to mice or rats will result in antidopaminergic effects. Apomorphine-induced climbing behavior in mice, the result of direct stimulation of dopamine receptors in the striatal and mesolimbic regions, is a simple animal model for examining these antidopaminergic effects of estrogens. Bromoestrogens, inhibitors of catechol estrogen formation, have been utilized in order to examine the role of estrogen metabolism in dopaminergic antagonism. Mice were pretreated for 3 days with 2-bromoestradiol, 4-bromoestradiol, or 2,4-dibromoestradiol dibenzoates alone or in combination with estradiol benzoate prior to apomorphine administration. The haloestrogens did not alter the climbing-induced responses elicited by apomorphine, whereas estradiol benzoate clearly attentuated the actions of apomorphine. Furthermore, the bromoestradiol dibenzoates were effective in reversing the effects of estradiol benzoate when the two steroids (estradiol benzoate and a bromoestrogen dibenzoate) were administered simultaneously during pretreatment. Thus, the bromoestrogens are able to inhibit the antidopaminergic effects of estradiol exhibited in the apomorphine-induced mouse climbing model.     

Carcass glycogen repletion on carbohydrate re-feeding after starvation.

In mice, the response of carcass glycogen to glucose re-feeding after starvation is biphasic. The initial repletive phase is followed by partial (greater than 50%) glycogen mobilization. This turnover of carcass glycogen in response to carbohydrate re-feeding may play an important role in the provision of C3 precursors for hepatic glycogen synthesis.     

Heme spin states and peroxide-induced radical species in prostaglandin H synthase

We have examined the optical, magnetic circular dichroism, and electron paramagnetic resonance (EPR) spectra of pure ovine prostaglandin H synthase in its resting (ferric) and ferrous states and after addition of hydrogen peroxide or 15-hydroperoxyeicosatetraenoic acid. In resting synthase, the distribution of heme between high- and low-spin forms was temperature-dependent: 20% of the heme was low-spin at room temperature whereas 50% was low-spin at 12 K. Two histidine residues were coordinated to the heme iron in the low-spin species. Anaerobic reduction of the synthase with dithionite produced a high-spin ferrous species that had no EPR signals. Upon reaction with the resting synthase, both hydroperoxides quickly generated intense (20-40% of the synthase heme) and complex EPR signals around g = 2 that were accompanied by corresponding decreases in the intensity of the signals from ferric heme at g = 3 and g = 6. The signal generated by HOOH had a doublet at g = 2.003, split by 22 G, superimposed on a broad component with a peak at g = 2.085 and a trough at g = 1.95. The lipid hydroperoxide generated a singlet at g = 2.003, with a linewidth of 25 G, superimposed on a broad background with a peak at g = 2.095 and a trough around g = 1.9. These EPR signals induced by hydroperoxide may reflect synthase heme in the ferryl state complexed with a free radical derived from hydroperoxide or fragments of hydroperoxide.     

Functional effects of heme orientational disorder in sperm whale myoglobin

The optical absorption and ligand binding properties of newly reconstituted sperm whale myoglobin were examined systematically at pH 8, 20 degrees C. The conventional absorbance and magnetic circular dichroism spectra of freshly reconstituted samples were identical to those of the native protein. In contrast, reconstituted azide or CO myoglobin initially exhibited less circular dichroism in the Soret wavelength region than native myoglobin. These data support the theory proposed by La Mar and co-workers (La Mar, G. N., Davis, N. L., Parish, D. W., and Smith, R. M. (1983) J. Mol. Biol. 168, 887-896) that protoheme inserts into apomyoglobin in two distinct orientations. The equilibrium and kinetic parameters for O2 and CO binding to newly reconstituted myoglobin were observed to be identical to those of the native protein. Thus, the orientation of the heme group has no effect on the physiological properties of myoglobin. This result is in disagreement with the preliminary report of Livingston et al. (Livingston, D. J., Davis, N. L., La Mar, G. N., and Brown, W. D. (1984) J. Am. Chem. Soc. 106, 3025-3026) which suggested that the abnormal heme conformation exhibited a 10-fold greater affinity and association rate constant for O2 binding. Significant kinetic heterogeneity was observed only for long-chain isonitrile binding to newly reconstituted myoglobin, and even in these cases, the rate constants for the abnormal and normal heme conformations differed by less than a factor of 4.     

Ion selectivity of epithelial Na channels

Epithelial Na channels are apparently pore-forming membrane proteins which conduct Na much better than any other biologically abundant ion. The conductance to Na can be 100 to 1000 times higher than that to K. The only other ions that can readily get through this channel are protons and Li. Small organic cations cannot pass through the channel, and water may also be impermeant. The selectivity properties of epithelial Na channels appear to be determined by at least three factors: A high field-strength anionic site, most likely a carboxyl residue of glutamic or aspartic acid residues on the channel protein, probably accounts for the high conductance through these channels of Na and Li and to the low conductance of K, Rb and Cs. A restriction in the size of the pore at its narrowest point probably accounts for the low conductance of organic cations as well as the possible exclusion of water molecules. The outer mouth of the channel appears to be negatively charged and may control access to the region of highest selectivity and may serve as a preliminary selectivity filter, attracting cations over anions. These conclusions are illustrated by the cartoon of the channel in Fig. 3. This picture is obviously both fanciful and simplified, but its general points will hopefully be testable. It leaves open a number of important questions, including: does amiloride block the channel by binding within the outer mouth? what does the inner mouth of the channel look like, and does this part of the channel contribute to selectivity? and what, if any, are the interactions between the features of the channel that impart selectivity and those that control the regulation of the channel by hormonal and other factors?