Effect of Selected Herbicides on Bacterial Growth Rates

Specific growth rate constants were used to evaluate the effects of selected herbicides on Erwinia carotovora, Pseudomonas fluorescens, and Bacillus sp. Comparison of growth rate constants permitted the identification of either stimulatory or inhibitory effects of these substances. E. carotovora was inhibited by 6,7-dihydrodipyrido(1,2-a:2'-c)pyrazinediium (diquat) and 4-hydroxy-3,5-diiodobenzonitrile (ioxynil) at 25 mug/ml; 1,1'-dimethyl-4,4'-bipyridinium (paraquat) at 50 mug/ml; and pentachlorophenol (PCP) at 10 mug/ml. P. fluorescens was inhibited by paraquat and PCP at 25 mug/ml and by 4-amino-3,5,6-trichloropicolinic acid (picloram) at 50 mug/ml. Stimulation of P. fluorescens was observed with 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) at 25 mug/ml. The Bacillus species was inhibited by diquat (25 mug/ml), ioxynil (10 mug/ml), and paraquat and PCP (5 mug/ml). No significant effect of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), or 1,1-dimethyl-3-(alpha,alpha,alpha-trifluoro-m-tolyl)urea (fluometuron) on growth rates of the bacteria was observed at 25 and 50 mug/ml.     

Host tree resistance against the polyphagous wood-boring beetle Anoplophora glabripennis

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiini) is an invasive wood‐boring beetle with an unusually broad host range and a proven ability to increase its host range as it colonizes new areas and encounters new tree species. The beetle is native to eastern Asia and has become an invasive pest in North America and Europe, stimulating interest in delineating host and non‐host tree species more clearly. When offered a choice among four species of living trees in a greenhouse, adult A. glabripennis fed more on golden‐rain tree (Koelreuteria paniculata Laxmann) and river birch (Betula nigra L.) than on London planetree (Platanus × acerifolia (Aiton) Willdenow) or callery pear (Pyrus calleryana Decaisne). Oviposition rate was highest in golden‐rain tree, but larval mortality was also high and larval growth was slowest in this tree species. Oviposition rate was lowest in callery pear, and larvae failed to survive in this tree species, whether they eclosed from eggs laid in the trees or were manually inserted into the trees. Adult beetles feeding on callery pear had a reduced longevity and females feeding only on callery pear failed to develop any eggs. The resistance of golden‐rain tree against the larvae appears to operate primarily through the physical mechanism of abundant sap flow. The resistance of callery pear against both larvae and adults appears to operate through the chemical composition of the tree, which may include compounds that are toxic or which otherwise interfere with normal growth and development of the beetle. Unlike river birch or London planetree, both golden‐rain tree and callery pear are present in the native range of A. glabripennis and may therefore have developed resistance to the beetle by virtue of exposure to attack during their evolutionary history.     

Simplified spectrophotometric assay for microsomal 3-hydroxy-3-methylglutaryl CoA reductase by measurement of coenzyme A

A new assay for 3-hydroxy-3-methylglutaryl CoA reductase (mevalonate:NADP oxidoreductase [acylating CoA], EC 1.1.1.34) is based upon the measurement of released coenzyme A (SH) during the reduction of 3-hydroxy-3-methylglutaryl CoA to mevalonate. Coenzyme A was measured in the presence of dithiothreitol, required for activity, by reaction with 5,5'-dithiobis(2-nitrobenzoic acid). Sodium arsenite forms a complex with the dithiol, but not with monothiols. Thus, reduced coenzyme A reacts instantaneously with the reagent and dithiothreitol reacts slowly. The absorbance due to the coenzyme A-5,5'-dithiobis(2-nitrobenzoic acid) reaction is determined by extrapolating the linear (dithiol) absorbance-time curve to the time of addition of the reagent. After subtraction of control absorbance (deletion of NADPH), the concentration of CoA-SH is calculated from epsilon(max) = 1.36 x 10(4) at 412 nm. The method of protein removal and reduction of sulfhydryl groups on the enzyme are critical. This method provides an immediate assay. Recovery of reduced coenzyme A was 98.7%. The assay is applicable for microsomes or purified enzyme and has an effective range of 0.5-50 nmoles of coenzyme A. It was applied to kinetic measurement of the pigeon liver microsomal enzyme reaction. The apparent K(m) value for 3-hydroxy-3-methylglutaryl CoA was 1.75 x 10(-5) M, and for NADPH the value was 6.81 x 10(-4) M. This method was compared with the dual-label method at high and low levels of activity. The data were not statistically different.