Defense of winter-dormant Alaska paper birch against snowshoe hares

Summary Mature growth-phase internodes of Alaska paper birch (Betula resinifera) are preferred by the snowshoe hare (Lepus americanus) over juvenile growth-phase internodes due to the low food value of the latter. While the mature over juvenile preferencec cannot be explained by the levels of inorganic nutrients or gross chemical fractions (resins or phenols), it can be explained by the striking differences in secondary metabolites of the two growth phases. The principle compound which renders the juvenile phase internodes unpalatable is papyriferic acid, a triterpene which is a demonstrated feeding deterrent to snowshoe hares and which is present in juvenile internodes at concentrations 25 times greater than those in mature internodes.     

Structural features are as important as sequence homologies inDrosophila heat shock gene upstream regions

Summary Pelham has shown that theDrosophila hsp 70 gene is not transcribed under heat shock conditions unless a given upstream region is present. Davidson et al. have recently compiled a list of sequences homologous to this region in otherDrosophila heat shock genes. They proposed that a set of unlinked genes, such as the heat shock genes, could be coordinately induced through an interaction in cis with a common regulatory molecule. That this interaction involves structural elements is suggested by the fact that these upstream regions share inverted repeats as well as areas of Z-DNA potential. Furthermore, using the Calladine-Dickerson rules for local helical parameters, we show that these regions share structural homology. This is significant because the presence of regions homologous to a derived consensus sequence does not necessarily imply structural similarity. Therefore, we suggest that these structural features are at least as important as the sequence homologies in enabling the heat shock response.     

Inhibition of in vitro fertilization by mouse anti-mouse sperm sera and preliminary antigen identification

Antisperm antibodies are implicated as one causative factor of infertility, but the target antigens have not been identified. Immune responses to sperm antigens are qualitatively variable even within a single mouse strain. We took advantage of this variability and immunized individual female mice to allogeneic sperm to reflect their natural exposure during mating. We determined the ability of the individual sera to inhibit in vitro fertilization and to bind to sperm antigens separated by electrophoresis. Compared to preimmune sera, four of five immune sera significantly inhibited in vitro fertilization. The serum from individual mice bound variable panels of sperm antigens. By comparing the panels, we identified two polypeptides with molecular weights of 40,000 and 44,000 that were bound by all sera. We propose that these molecules may be good candidates for further investigation of the immunoprophylaxis of pregnancy.     

Host plant resistance for insect control in some important crop plants

Insect pests of cereal crop plants are among the most destructive and devastating factors limiting world food production. Insects often inflict losses of 15 to 50% of the yield of some crops in various parts of the world. Insects also provide infection courts for various pathogens that inflict even greater damage. The nature of these losses is especially tragic for poor farmers in the tropics since the insects consume dry matter already produced using limited resources. Reduction of these losses would enhance the world food supply available to man, even if actual production remains the same, by allotting to man and animals that proportion of production now consumed by insects. Control of insect‐inflicted damage on a world‐wide basis is a very difficult task. Chemical control is effective and readily available in some, but not all, countries. However, chemical control is often unavailable, ineffective, too expensive, and likely to create environmental and safety hazards that make it unsuitable for many parts of the world. Several excellent examples of biological control of insects also attest to the potential usefulness of this method of reducing insect‐inflicted losses, but this method also has been ineffective for certain major insect pests due to lack of effective identification, distribution, and maintenance of biological control agents. On the whole, host plant resistance (HPR) to insects has been the most successful and widely used method of control. HPR has been used successfully in a number of major crop species to help control damage inflicted by major insect pests. However, problems with identifying sources of resistance and transferring it to usable varieties have often been difficult to overcome. Also, once resistance is deployed, changes in insect populations which allow them to overcome the resistance sometimes eliminate the potential advantages of resistant varieties. However, methods to quantify host‐insect interactions have improved significantly over the past few years, and the prospects for developing and maintaining usable levels of resistance to several major insect pests of most major crops are good. Studies of the biochemical and biophysical mechanisms of insect resistance have added a new dimension to HPR work. Knowledge of specific factors that contribute to insect resistance can be extremely useful to plant breeders and entomologists. The ability to identify and select for one specific plant component or group of components can speed the development of resistant varieties. Studies of the effect of such resistance components on insect development and behavior can help determine the likelihood of insects being able to overcome the resistance factors. Studies of the effect of the resistance factors on host plant yield, performance, or quality may help plant breeders overcome the problems often associated with the development of high yielding and high quality resistant varieties. Identification of several different mechanisms of resistance could provide breeders the opportunity to adjust levels of several resistance components in order to arrive at a proper blend of resistance, quality, and yield. Furthermore, development of varieties with multiple mechanisms of resistance should slow the development of new biotypes of insects that could overcome the HPR since the insects would have to simultaneously or sequentially develop the ability to overcome several resistance factors. Therefore, knowledge of mechanisms of insect resistance could facilitate the development of more stable and long‐lasting types of resistance.     

Isolation of iron-containing superoxide dismutase from Bacteroides fragilis: reconstitution as a Mn-containing enzyme

Superoxide dismutase from the anaerobe Bacteroides fragilis has been purified to apparent homogeneity. The protein, Mr 42,000, is a dimer of equally sized subunits joined by noncovalent interactions. Metal analysis of the native enzyme revealed 1.8-1.9 g-atoms Fe, 0.2 g-atoms Zn, and less than 0.05 g-atoms Mn per mole dimer in a preparation whose specific activity was 1200 U/mg. Exposure of the enzyme to guanidinium chloride plus 8-hydroxyquinoline (T. Kirby, J. Blum, I. Kahane, and I. Fridovich, 1980, Arch. Biochem. Biophys. 201, 551-555) resulted in complete loss of enzymatic activity. Activity could be restored by dialysis of the denatured apoprotein against Tris buffer containing either ferrous ammonium sulfate or manganous chloride. The Fe-reconstituted enzyme was inhibited by 1 mM azide and inactivated by H2O2 in a manner similar to the native enzyme. Mn-reconstituted enzyme was inhibited by azide but resisted inactivation by H2O2 comparable to other purified manganese-containing superoxide dismutases. The manganese reconstituted protein contained approximately 1 gm-atom Mn/mol dimer. Zn ion potently inhibited reconstitution of the denatured apoprotein by either Mn or Fe and bound to the protein with a stoichiometry of 2-3 g-atoms/mol dimer.     

Effect of heme on Bacteroides distasonis catalase and aerotolerance

Parallel increases in intracellular catalase activity and resistance to extracellular H2O2 and to hyperbaric O2 toxicity were observed when Bacteroides distasonis VPI 4243 (ATCC 8503, type strain) was grown in either complex or defined medium containing graded amounts of hemin. Virtually all of the cells with high catalase activity (greater than 200 U/mg) remained viable upon exposure at 37 degrees C to 100-lb/in2 O2 on agar surfaces for 1 h, whereas low-catalase cells (less than 10 U/mg) lost 1.2 log units of viable cells during that treatment. Upon exposure to 500 microM H2O2, high-catalase cells lost 0.4 log units of the initial viable colonies during the same period in which low-catalase cells lost 3 log units of viable cells. The superoxide dismutase activity was the same in each test culture. These data support the role of intracellular catalase in protecting B. distasonis from oxidative damage resulting from hyperbaric oxygenation or H2O2 exposure. Catalase activity elicited by adding hemin to cells grown previously in medium lacking hemin was inhibited only 40% by prior incubation of the cells with chloramphenicol (30 micrograms/ml) and only 22% with rifampin (5 micrograms/ml). A model which is consistent with these data involves the production of an apocatalase in cells grown in low-hemin medium. Addition of hemin to the cells would result in a rapid chloramphenicolor rifampin-insensitive stimulation of catalase activity followed by further de novo biosynthesis of catalase.     

Isolation of intact polysomes from mechanically dehulled developing grain

A rapid method for obtaining large quantities of developing groats suitable for the isolation of highly intact polysomes has been developed. Developing spikelets were harvested directly from oat panicles into liquid nitrogen and then quickly passed through a dehuller. Chaff was removed by air aspiration and the resultant groats were collected directly back into liquid nitrogen. Approximately 250 g of groats could be isolated each man-hour by the above method. In comparison, only 10 g of endosperm could be collected by squeezing it out of spikelets using an endosperm mangle. Membrane-bound polysomes extracted from the immature groats were compared to those extracted from endosperm. The largest polysomes discernable as unique peaks on sucrose gradients were ten-mers and nine-mers for groats and endosperm, respectively. Polysomes isolated from both starting materials stimulated similar incorporations of [³⁵S]methionine into trichloroacetic acid-insoluble products during in vitro translations in wheat germ extract. Both polysome preparations directed the synthesis of similar high-molecular-weight proteins. Based on these criteria, polysomes from both preparations were found to be of similar intactness, although the groat starting material was much more readily obtained. The polysome classes having the maximum absorbance peak for endosperm and groat polysomes were six-mers and eight-mers, respectively.     

Some Properties of Thiosulfate-Oxidizing Enzyme from Marine Heterotroph 16B

Thiosulfate-oxidizing enzyme has been demonstrated in cell-free extracts of the marine, thiosulfate-oxidizing pseudomonad strain 16B. The enzyme, partially purified by ion-exchange chromatography and calcium phosphate gel treatment, catalyzed the oxidation of thiosulfate to tetrathionate with the concomitant reduction of ferricyanide. Native but not mammalian cytochrome c was also reduced by the enzyme in the presence of thiosulfate. The enzyme was located exclusively in the supernatant of ultracentrifuged cell extracts. The most purified enzyme preparation, like intact cells, exhibited a temperature optimum of 30 to 31°C. However, it exhibited no definite pH optimum. At pH 6.1 to 6.3 and 30°C, the K_m for thiosulfate was 1.57 mM. At lower temperatures, the apparent K_m for thiosulfate increased, but the apparent maximum velocity remained virtually unchanged. Thiosulfate oxidation in intact cells exhibited an increase in the pH optimum at lower temperatures. The thiosulfate-oxidizing enzyme of marine heterotroph 16B is compared with thiosulfate-oxidizing enzymes from other bacteria, and the effect of temperature on the relationship between pH and thiosulfate oxidation is discussed with reference to the natural habitat of the bacterium.     

Effect of dietary fiber on absorption of B-6 vitamers in a rat jejunal perfusion study

Previous research has indicated that dietary fiber may affect the absorption and utilization of certain nutrients. To determine the effect of certain fiber materials on the absorption of B-6 vitamers, jejunal segments from young male adult rats were perfused in situ with a control solution containing 0.02 mM pyridoxine (PN), 0.02 mM pyridoxal (PL), and 0.02 mM pyridoxamine (PM), followed by a test solution containing the same vitamin B-6 mixture and one of five fiber-rich test materials (cellulose, pectin, lignin, homogenized fresh carrot, or carrot homogenized after 10 min boiling) added at a concentration of 1-3%. The mean absorption rates of PL, PN, and PM from the control solution were, respectively, 3.66 +/- 0.23, 2.06 +/- 0.23, and 1.74 +/- 0.37 nmole/min/20 cm jejunal segment. There were no significant differences between the absorption rates of B-6 vitamers from control and test solutions containing cellulose, pectin, and lignin. The absorption rates of PM and PL were significantly depressed (P less than 0.05 and P less than 0.01, respectively) by the presence of fresh or cooked carrot. The absorption rate of PN in presence of cooked carrot was also decreased relative to the control value but the difference was only marginally significant (P less than 0.10). When the concentration of fresh carrot in the test solution was increased to 10% by weight and the perfusion rate was decreased from 1.91 to 0.49 ml/min in a second perfusion experiment, there was a significant increase in variability and the differences between absorption rates of the B-6 vitamers in control and test solutions were not statistically significant. The limited evidence of adverse effect of carrot on absorption of vitamin B-6 suggested the need for further clarification of the influence of dietary fiber in an unrefined state on the bioavailability of vitamin B-6.