The measurement of enamel and dentine abrasion by tooth whitening products using an in situ model.

OBJECTIVES: To determine the enamel and dentine wear of two whitening toothpastes using an in situ model with ex vivo brushing. METHODS: Human enamel/dentine (approximately 50:50) blocks (approximately 4 x 4mm) were placed in the upper buccal aspects of full or partial dentures of a group of 25 subjects. Subjects brushed the specimens ex vivo with either a calcium carbonate/perlite or silica containing whitening toothpaste under exaggerated conditions as compared to normal for 30 s, twice per day. Specimens were removed after 4, 8 and 12 weeks and the wear to the enamel and dentine was determined. Enamel wear was determined by change in Knoop indent length and dentine wear was determined from the enamel-dentine step height, measured using optical profilometry. RESULTS: The mean wear after 12 weeks was for enamel 0.27 and 0.19 microns, and for dentine 34.3 and 61.1 microns, for the calcium carbonate/perlite and silica toothpastes respectively. There were no significant differences between products after 12 weeks. The rate of wear was found to decrease throughout the duration of the study. CONCLUSION: There were no significant differences between the two whitening toothpastes in terms of enamel and dentine wear after 12 weeks brushing.

Growth, incidence and activities of dissimilatory sulfate-reducing bacteria in the human oral cavity.

Viable counts and activities of sulfate-reducing bacteria were determined in the oral cavities of 12 healthy volunteers. Of these, 10 harboured viable sulfate-reducing bacteria populations. Six separate sites were sampled: the posterior tongue, anterior tongue, mid buccal mucosa, vestibular mucosa, supragingival plaque and subgingival plaque. Sulfate-reducing bacteria occurred in all areas, with the highest incidence in supragingival plaque. Viable counts and sulfate-reducing activities in each of the regions varied from 0 to 10(8) cfu (g wet weight)-1 and from 0 to 50 nmol (g wet weight)-1 h-1, respectively. As sulfate-reducing bacteria can be detected in the oral cavity, they may potentially be involved in terminal oxidative processes carried out by the microflora of the mouth.

Point source inoculation of mesocyclops (Copepoda: Cyclopidae) gives widespread control of Ochlerotatus and Aedes (Diptera: Culicidae) immatures in service manholes and pits in north Queensland, Australia.

This study details the novel application of predacious copepods, genus Mesocyclops, for control of Ochlerotatus tremulus (Theobald) group and Aedes aegypti (L.) mosquito larvae in subterranean habitats in north Queensland, Australia. During June 1997, 50 Mesocyclops sp. 1 were inoculated into one service manhole in South Townsville. Wet season rainfall and flooding in both 1998 and 2000 was responsible for the dispersal of copepods via the underground pipe system to 29 of 35 manholes over an area of 1.33 km2. Significant reductions in Aedes and Ochlerotatus larvae ensued. In these habitats, Mesocyclops and Metacyclops were able to survive dry periods, when substrate moisture content ranged from 13.8 to 79.9%. At the semiarid inland towns of Hughenden and Richmond, cracking clay soil prevents drainage of water from shallow service pits where Oc. tremulus immatures numbered from 292-18,460 per pit. Introduction of Mesocyclops copepods into these sites during May 1999 resulted in 100% control of Oc. tremulus for 18 mo. One uninoculated pit subsequently became positive for Mesocyclops with resultant control of mosquito larvae.

The importance of subterranean mosquito habitat to arbovirus vector control strategies in north Queensland, Australia.

In north Queensland, 14 localities were surveyed for mosquito larvae (third and fourth instar) during summer/autumn and winter from 1996 to 1999. Absolute population numbers in subterranean habitats, mainly service manholes and pits (97%) but also some wells, septic tanks, storm drains, and sumps, were expressed as a proportion of total numbers in these sites plus surface sites within a 100-m radius. When correction factors were applied to subterranean samples, the 472,477 larvae mainly of Aedes tremulus (Theobald) group, Aedes notoscriptus (Skuse), and Aedes aegypti (L.) comprised 78% of the total population. In relation to the proportion of the overall immature mosquito population from subterranean habitats (propsub), linear regression coefficients for minimum temperature, relative humidity, and Mesocyclops copepod prevalence were significant for winter data; but for summer, only relative humidity was significant. Linear regression coefficients for Mesocyclops prevalence approached significance (P = 0.061) in summer. When multiple linear regression was used to model propsub, 68% of the variation was accounted for by relative humidity and the prevalence of Mesocyclops. In the drier and cooler towns, increased use of subterranean sites during winter was caused by reduced availability of surface oviposition sites because of the dry season. In the wetter coastal towns, no such restrictions applied and ambient conditions remained more equitable all year round. Mesocyclops were surprisingly common, particularly in these coastal towns. Release of known numbers of Mesocyclops indicated that 3-sweep netting in service manholes was sensitive down to densities of one Mesocyclops per 10 liters, and overall recovery varied from 1 to 4%. In relation to control, service manholes represent a stable habitat for mosquito (7% positive overall) and Mesocyclops populations. If they remained wet, service manholes positive for mosquito immatures or Mesocyclops during summer/autumn had 96% and 85% chance, respectively, of being positive the following winter. Even allowing for the effect of drying, a mosquito-positive manhole had a 79% chance of remaining positive the following winter. In view of the importance of these sites as refuges from adverse ambient conditions, it is proposed that a winter control strategy using Mesocyclops presents a cost-effective control option to reduce the recolonization of surface sites when conditions become more suitable.

The effect of a toothpaste containing 2% zinc citrate/0.3% Triclosan on the glycolysis of plaque bacteria ex vivo after food intake.

OBJECTIVE: To develop an ex vivo plaque pH method to assess the efficacy of a new zinc citrate/Triclosan formulation. METHODS: Study (1) focussed on method development. Study (2) examined the effect of a toothpaste containing 2% zinc citrate/0.3% Triclosan on the pH of plaque after product use and consumption of pizza. Study (3) investigated the effect of the same formulation and a fluoride toothpaste on the pH of plaque without an 'eating occasion'. The pH of plaque samples was measured over 10 minutes in the presence of glucose. RESULTS: The test product significantly reduced the amount of acid produced 30 minutes (p = 0.0035) and 3 hours (p = 0.0018) after brushing (study (2)). In study (3) use of the test product significantly reduced the amount of acid produced 3 hours after brushing (p = 0.0023). No significant benefit was found for the fluoride toothpaste. CONCLUSION: An ex vivo plaque pH method has been developed which can detect changes in acid produced following brushing with different toothpastes. A toothpaste containing 2% zinc citrate/0.3% Triclosan significantly reduced the total acid produced for at least 3 hours after product use. Moreover it has been demonstrated that this effect is detectable even after eating.

Plaque antibacterial levels following controlled food intake and use of a toothpaste containing 2% zinc citrate and 0.3% Triclosan.

OBJECTIVES: To measure the levels of zinc and Triclosan present in plaque 12 hours post-brushing and following two weeks home use of a toothpaste formulation containing 2% zinc citrate and 0.3% Triclosan. To measure the levels of zinc and Triclosan in plaque following two weeks home use of the test toothpaste formulation together with a further morning's brushing and a day of controlled food intake. METHODS: A total of 104 subjects completed the study. Plaque samples were taken before use of the test toothpaste and again after a specified regime of product use and food intake. The samples were analysed for zinc or Triclosan. RESULTS: Levels of zinc and Triclosan in plaque 12 hours after last brushing and following a 2-week home usage of product, were 149.1 microg/g and 8.6 microg/g respectively. Following a morning brushing and a day of controlled food intake zinc and Triclosan levels were 94.7 microg/g and 4.1 microg/g respectively. These levels of agents were found to reduce pH drop in vitro. CONCLUSIONS: Regular use of a toothpaste containing 2% zinc citrate and 0.3% Triclosan can lead to a build-up of antibacterial agents in plaque that continue to work even after controlled food intake.

The effect of a 2% zinc citrate, 0.3% Triclosan dentifrice on plaque acid production following consumption of a snackfood.

OBJECTIVES: A) To assess plaque lactate production following consumption of three foods (cake, chocolate/caramel bar, sweetened coffee), and B) To measure the effect of a fluoride dentifrice containing 2% zinc citrate and 0.3% Triclosan on plaque lactate and pH drop following consumption of cake. METHODS: A) 10 subjects completed the first study. Plaque samples taken before and at 8,15 and 30 minutes after eating. Samples were analysed for lactate via Capillary Electrophoresis. B) 30 subjects completed the second study. Plaque samples were taken before and after cake and use of test dentifrice or no treatment control. Plaque pH and lactate content were assessed. RESULTS: A) Plaque lactate levels increased after all three foods; peak lactate levels occurred 8 minutes after eating. B) Plaque lactate concentrations after eating cake were 39.2mM for the control treatment and a significantly lower value, 23.6mM, for the test 2% zinc citrate, 0.3% Triclosan dentifrice. After food challenge, pH values were 5.53 for the no treatment group and a significantly higher value of 5.79 for the test dentifrice group. CONCLUSIONS: A toothpaste containing 2% zinc citrate, 0.3% Triclosan can significantly reduce plaque lactate generation and pH drop induced by cake, compared to no treatment control.

Comparison of Triazine-Resistant and -Susceptible Biotypes of Senecio vulgaris and Their F(1) Hybrids.

The relationship of triazine resistance to decreased plant productivity was investigated in Senecio vulgaris L. F(1) reciprocal hybrids were developed from pure-breeding susceptible (S) and resistant (R) lines. The four biotypes (S, S x R, R, R x S) were compared in terms of atrazine response, electron transport, carbon fixation, and biomass production. Atrazine response, carbon fixation rate, and PSII and whole-chain electron transport rates of hybrids were nearly identical to those of their respective maternal parents. Significant differences occurred between the two susceptible (S, S x R) and two resistant (R, R x S) biotypes in atrazine response (I(50)), carbon fixation rate, and PSII and whole-chain electron transport rates; PSI rates were identical in all four biotypes. Coupled and uncoupled, whole-chain electron transport rates of thylakoids of the two susceptible biotypes were approximately 50% greater than those of the two resistant biotypes at photon flux densities greater than 215 micromoles per square meter per second. Carbon exchange rates of the two susceptible biotypes were 23% greater than those of the two resistant biotypes. Hybrid biotypes (S x R, R x S) were not identical to their maternal parents in biomass production. The S, S x R, and R x S plants all achieved greater biomass than R plants. These results suggest that while the resistance mutation influences thylakoid performance, reduced productivity of triazine-resistant plants cannot be ascribed solely to decreases in electron transport or carbon assimilation rates brought about by the altered binding protein. Since the F(1) hybrids differed from their maternal parents only in nuclear genes, it appears that the detrimental effects of the triazine resistance mutation on plant growth may be attenuated by interactions of the plastid and nuclear genomes.

Altered Leaf Structure and Function in Triazine-Resistant Common Groundsel (Senecio vulgaris).

Anatomical and physiological characteristics of leaves of triazinesusceptible and -resistant biotypes of common groundsel (Senecio vulgaris L.) were studied in order to explain the differences in light-saturated photosynthetic rates previously reported. Leaves were of uniform leaf plastochron index from greenhouse-grown plants. Susceptible plants had greater leaf fresh and dry weights and leaf areas, while resistant plants had greater specific leaf mass (mg fresh weight/cm(2)). Susceptible plants had greater amounts of total chlorophyll per unit leaf weight and a higher chlorophyll a/b ratio. Soluble protein in leaves was higher in susceptible chloroplasts on a weight and area basis, but similar to resistant chloroplasts on a unit chlorophyll basis. Activity of ribulose 1,5-bisphosphate carboxylase was higher in resistant plants on a fresh weight, leaf area, and milligram chlorophyll basis. Stomatal frequency, length, and arrangement were similar between biotypes, as were transpiration and conductance. Resistant leaves had less air space (v/v), more cells in palisade and spongy mesophyll, and a greater volume of palisade tissue than spongy, when compared to susceptible leaves. Differences in leaf structure and function between biotypes are probably due to a complex of developmental adaptations which may be only indirectly related to modified photosystem II in resistant plants. These results indicate that the consistently lower rates of net photosynthesis and yield in resistant plants cannot be explained solely on the basis of these leaf characteristics. Several possible mechanisms to account for reduced productivity are suggested.

Triazine Resistance in Senecio vulgaris Parental and Nearly Isonuclear Backcrossed Biotypes Is Correlated with Reduced Productivity.

Isonuclear triazine-susceptible and triazine-resistant Senecio vulgaris L. biotypes were developed by making reciprocal crosses between susceptible and resistant biotypes to obtain F(1) hybrids and backcrossing the hybrids to the appropriate pollen parent. The electrophoretic isozyme patterns of the enzyme aconitase obtained from leaf extracts of triazine-susceptible parental (S) and backcrossed (SxR(BC6)) biotypes, and triazine-resistant parental (R) and backcrossed (RxS(BC6)) biotypes verified that the biotypes had the expected nuclear genomes. Atrazine inhibition of chloroplast whole chain electron transport from water to methyl viologen was measured to verify susceptibility or resistance to triazine herbicides. The photosynthetic rate and biomass accumulation of greenhouse grown susceptible and resistant S. vulgaris biotypes were measured 28, 35, 42, 50, 57, and 64 days after planting to determine the effect of altered chloroplast function. S and SxR(BC6) biotypes had CO(2) assimilation rates of 16.2 and 16.6 micromoles CO(2) per square meter per second, respectively, and I(50) values (herbicide concentration producing 50% inhibition) of about 0.49 micromolar atrazine. The corresponding values for the R and RxS(BC6) biotypes were 14.7 and 14.6 micromoles CO(2) per square meter per second with I(50) values of 65.0 micromolar atrazine. The S biotype was larger and more productive than the R biotype at all harvests. At the harvest 57 days after planting, mean shoot dry weight was 33.2 and 8.7 grams for the S and R biotypes, respectively. The growth effect associated with chloroplast differences was shown in comparisons of the S biotype with the RxS(BC6) biotype and of the SxR(BC6) biotype with the R biotype. The RxS(BC6) biotype had 72% of the shoot dry weight of the S biotype while the R biotype had 55% of the shoot dry weight of the SxR(BC6) biotype. The RxS(BC6) and R biotypes produced about 73 and 62% of the leaf area of the S and SxR(BC6) biotypes, respectively. Relative growth rate was similar in biotypes with the same nuclear genome; however, instantaneous unit leaf rate was higher in the S compared to the RxS(BC6) biotype and in the SxR(BC6) compared to the R biotype. At 57 days after planting, the cumulative leaf area duration (i.e. photosynthetic opportunity) of the RxS(BC6) and R biotypes was 86 and 66% of that of the S and SxR(BC6) biotypes, respectively. Our data indicate that impaired chloroplast function in triazine resistant S. vulgaris biotypes limits growth and productivity at the whole plant level.

Isolation of sealed plasma membrane vesicles from Phytophthora megasperma f. sp. glycinea: II. Partial characterization of Ca2+ transport and glyceollin effects.

Calcium uptake was examined in sealed plasma membrane vesicles isolated from the plant pathogenic fungus, Phytophthora megasperma f. sp. glycinea. Calcium uptake was ATP-dependent and by the addition of various ionophores in the presence of ATP, it was shown that Ca2+ transport was mediated by a nH+/Ca2+ antiport. Further evidence for this antiport mechanism included Ca2+ uptake driven by an imposed pH gradient and the observation that calcium could dissipate a steady-state pH gradient across the vesicle membrane. Transport mediated by the nH+/Ca2+ antiport was optimal at pH 7.0, and demonstrated saturation kinetics for Ca2+ with a Km of about 7 microM. Glyceollin, a soybean phytoalexin, was found to inhibit Ca2+ transport consistent with its ability to increase H+ conductance. In the presence of glyceollin, calcium leakage from Phytophthora membrane vesicles also increased. This study provides basic information about calcium transport in a plant pathogenic fungus as well as demonstrating a possible mode of action of a phytoalexin.

Isolation of sealed plasma membrane vesicles from Phytophthora megasperma f. sp. glycinea. I. Characterization of proton pumping and ATPase activity.

Sealed vesicles were isolated from a plant pathogenic fungus Phytophthora megasperma f. sp. glycinea using a modification of a method previously developed for plant plasma membrane vesicle isolation. Vanadate-sensitive, proton pumping microsomal membrane vesicles were resolved on a linear sucrose density gradient and found to comigrate with a vanadate-sensitive ATPase. Both the proton pumping and ATPase activity of these vesicles had a pH optimum of 6.5 and demonstrated similar properties with respect to substrate specificity and inhibitor sensitivity. These properties were in agreement with previously published data on the Phytophthora plasma membrane ATPase. In contrast with previous reports there was no K+ stimulation of the plasma membrane ATPase and the Km for Mg:ATP (1:1 concentration ratio) was higher (2.5 mM). A comparison of anion (potassium salts) effects upon delta pH and delta psi formation in sealed Phytophthora plasma membrane vesicles revealed a correspondence between the relative ability of anions to stimulate proton transport and to reduce delta psi. The relative order for this effect was KCl greater than KBr much greater than KMes, KNO3, KClO3, K2SO4. This study presents a method for the isolation of sealed vesicles from Phytophthora hyphae. It also provides basic information on the plasma membrane H+-ATPase and its associated proton pumping activity.

Estimation of base temperatures for nine weed species.

Experiments were conducted to test several methods for estimating low temperature thresholds for seed germination. Temperature responses of nine weeds common in annual agroecosystems were assessed in temperature gradient experiments. Species included summer annuals (Amaranthus albus, A. palmeri, Digitaria sanguinalis, Echinochloa crus-galli, Portulaca oleracea, and Setaria glauca), winter annuals (Hirschfeldia incana and Sonchus oleraceus), and Conyza canadensis, which is classified as a summer or winter annual. The temperature below which development ceases (Tbase) was estimated as the x-intercept of four conventional germination rate indices regressed on temperature, by repeated probit analysis, and by a mathematical approach. An overall Tbase estimate for each species was the average across indices weighted by the reciprocal of the variance associated with the estimate. Germination rates increased linearly with temperature between 15 degrees C and 30 degrees C for all species. Consistent estimates of Tbase were obtained for most species using several indices. The most statistically robust and biologically relevant method was the reciprocal time to median germination, which can also be used to estimate other biologically meaningful parameters. The mean Tbase for summer annuals (13.8 degrees C) was higher than that for winter annuals (8.3 degrees C). The two germination response characteristics, Tbase and slope (rate), influence a species' germination behaviour in the field since the germination inhibiting effects of a high Tbase may be offset by the germination promoting effects of a rapid germination response to temperature. Estimates of Tbase may be incorporated into predictive thermal time models to assist weed control practitioners in making management decisions.

Differential Light Responses of Photosynthesis by Triazine-resistant and Triazine-susceptible Senecio vulgaris Biotypes.

Studies were conducted to determine a physiological basis for competitive differences between Senecio vulgaris L. biotypes which are either resistant or susceptible to triazine herbicides. Net carbon fixation of intact leaves of mature plants was higher at all light intensities in the susceptible biotype than in the resistant biotype. Quantum yields measured under identical conditions for each biotype were 20% lower in the resistant than in the susceptible biotype. Oxygen evolution in continuous light measured in stroma-free chloroplasts was also higher at all light intensities in the susceptible biotype than in the resistant biotype. Oxygen evolution in response to flashing light was measured in stroma-free chloroplasts of both biotypes. The steady-state yield per flash of resistant chloroplasts was less than 20% that of susceptible chloroplasts. Susceptible chloroplasts displayed oscillations in oxygen yield per flash typically observed in normal chloroplasts, whereas the pattern of oscillations in resistant chloroplasts was noticeably damped. It is suggested that modification of the herbicide binding site which confers s-triazine resistance may also affect the oxidizing side of photosystem II, making photochemical electron transport much less efficient. This alteration has resulted in a lowered capacity for net carbon fixation and lower quantum yields in whole plants of the resistant type.