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The role of cytoplasmic pH in guard cell signal transduction was investigated in epidermal strips of Commelina communis. The cytoplasmic pH of guard cells was measured by dual excitation ratio confocal laser scanning microscopy. Large transient alkalinisations occurred for up to 20 minutes both during closure, in response to ABA and calcium, and opening in response to IAA and fusicoccin. Therefore the direction of the pH change does not determine the direction stomatal movement in Commelina communis in contrast to previous reports in Paphiopedilum tonsum. Furthermore, CO₂ caused a slow acidification during stomatal closure, indicating that pore movements are not always associated with a transient cytoplasmic alkalinisation. The internal pH of guard cells was buffered by low concentrations of isobutyrate. Small reductions in stomatal closure in response to ABA and calcium were observed, however, responses to CO₂, IAA and fusicoccin were unaltered. High levels of isobutyrate stimulated wide stomatal opening for all stimuli. Therefore manipulation of cytoplasmic pH only give limited support in the case of ABA and calcium that cytoplasmic pH changes are either necessary for or modulate stomatal movements. The observed pH changes may therefore be a consequence of the mechanism underlying pore movement rather than genuine cytoplasmic signals per se, A model is described based on strong ion and weak acid chemistry which predicts that the observed pH transients result from changes in the concentrations of chloride and malate which charge balance the potassium fluxes during stomatal movements. No suitable fluorescent indicator was found to measure pH in either the apoplast or vacuole. However the volume of the guard cell lumen, vacuole, nucleus and chloroplast were directly measured during stomatal movements and the cytoplasmic volume was calculated. These volumes were used to re-calculate compartmental pH and ion concentrations from previous reports.

Abstract The carbonic anhydrases (CAs) participate in the maintenance of pH homeostasis in various tissues of the human body by catalyzing the reversible reaction CO2 + H2O ⇔ HCO3- + H+. Carbonic anhydrase isoenzyme VI (CA VI) is secreted into the human saliva by the serous acinar cells of the parotid and submandibular glands. The present work was undertaken in order to gain an understanding of the physiological role of CA VI in the oral cavity. CA VI concentrations were compared with other salivary characteristics and with the clinical dental status of the subjects. Saliva samples were collected under strictly controlled conditions from 209 young, healthy men and their CA VI concentrations determined by means of a specific time-resolved immunofluorometric assay. Salivary secretion rate, pH, buffering capacity, α-amylase activity level and counts of lactobacilli and mutans streptococci were also determined. Salivary CA VI concentrations showed positive correlations with salivary secretion rate (r = 0.20, p = 0.003) and amylase activity level (r = 0.46, p < 0.001), but not with pH, buffering capacity, or counts of mutans streptococci or lactobacilli. Salivary CA VI concentration, pH and buffering capacity correlated negatively with the number of decayed, missing or filled teeth (DMFT index). The correlation between salivary CA VI concentration and DMFT index was closest in the subjects with poor oral hygiene. No correlation was found between salivary secretion rate or amylase activity and the DMFT index. The location of CA VI in the enamel pellicle, a thin layer of proteins on dental surfaces providing a protective interface between the tooth surface and the external environment, was demonstrated in samples of extracted teeth using immunostaining with anti-CA VI antibody. Immunostaining for salivary α-amylase, which was used as a positive control, produced virtually the same staining patterns. The presence of CA VI in the natural enamel pellicle was confirmed by Western blotting of pellicle proteins. Histochemical staining of enamel pellicle formed in vitro showed that the bound enzyme retains its CA activity. To determine whether CA VI is transferred into the circulation, blood and saliva samples were collected from four healthy male volunteers at 3-h intervals throughout a 24-h period and assayed for CA VI concentration. CA VI was present in all the serum samples, although its concentration was about 22 times lower than in the saliva. The presence of CA VI in serum was confirmed using a sensitive Western blotting method. Western blotting also showed that serum CA VI is associated with IgG, which may protect the enzyme from proteolytic degradation or target it to sites that do not contain CA VI. The present results suggest that salivary CA VI is not involved in regulation of the actual pH or buffering capacity of the saliva, but it does seem to have a specific role in the oral cavity. High salivary concentrations of CA VI appear to be associated with low caries experience. Since active CA VI is located in the enamel pellicle, it may function locally in the microenvironment of the dental surfaces and accelerate the neutralization of the acid metabolic products of bacterial plaque.

Cultivation in the laboratory is essential for understanding the phenotypic characteristics and environmental preferences of bacteria. However, basic phenotypic information is not readily accessible. Here, we compiled phenotypic and environmental tolerance information for > 5,000 bacterial strains described in the International Journal of Systematic and Evolutionary Microbiology (IJSEM) with all information made publicly available in an updatable database. Although the data span 23 different bacterial phyla, most entries described aerobic, mesophilic, neutrophilic strains from Proteobacteria (mainly Alpha-and Gammaproteobacteria), Actinobacteria, Firmicutes, and Bacteroidetes isolated from soils, marine habitats, and plants. Most of the routinely measured traits tended to show a significant phylogenetic signal, although this signal was weak for environmental preferences. We demonstrated how this database could be used to link genomic attributes to differences in pH and salinity optima. We found that adaptations to high salinity or high-pH conditions are related to cell surface transporter genes, along with previously uncharacterized genes that might play a role in regulating environmental tolerances. Together, this work highlights the utility of this database for associating bacterial taxonomy, phylogeny, or specific genes to measured phenotypic traits and emphasizes the need for more comprehensive and consistent measurements of traits across a broader diversity of bacteria. IMPORTANCE Cultivation in the laboratory is key for understanding the phenotypic characteristics, growth requirements, metabolism, and environmental preferences of bacteria. However, oftentimes, phenotypic information is not easily accessible. Here, we compiled phenotypic and environmental tolerance information for > 5,000 bacterial strains described in the International Journal of Systematic and Evolutionary Microbiology (IJSEM). We demonstrate how this database can be used to link bacterial taxonomy, phylogeny, or specific genes to measured phenotypic traits and environmental preferences. The phenotypic database can be freely accessed (https://doi.org/10.6084/m9.figshare.472392), and we have included instructions for researchers interested in adding new entries or curating existing ones.

Magister Scientiae Dentium - MSc(Dent) / Introduction: Saliva is a significant biological fluid involved in the maintenance of good oral health. Cigarette smoking exerts detrimental effects on oral health and has been shown to affect saliva, but with no consensus regarding its effect on the quantity (flow rate) and quality (pH) of the saliva. Aim: To assess the effect of cigarette smoking on the flow rate and pH of whole stimulated saliva. Method: A case control study was conducted using patients who presented at the UWC Oral Health Centre patient sifting/waiting area. The patients who agreed to participate were assessed for inclusion into the study until the sample size was (n=60), stratified by smoking (n=30) and non-smoking (n=30). Stimulated saliva samples were collected in specimen jars by asking patients to chew a sterilized rubber band for 5 minutes and spit the contents into the specimen jar provided at 1 minute intervals. The specimens were transported to the laboratory within 30 minutes to measure the salivary quantity and pH. Results: No statistically significant difference in the salivary flow rates was found between smokers and non smokers (p=0.5273). Smokers showed a statistically significant decrease in their pH compared to non smokers (p=0.028). Conclusion: Cigarette smoking reduces the salivary pH, thereby producing an acidic environment.

Mutant strains of the fern Ceratopteris richardii Brongn. were selected in vitro for tolerance to culture medium containing Al2(SO4)3-Na2EDTA at pH 4.4. Three strains, HαAT3, HαAT7, and HαAT29 showed enhanced growth relative to the wild type on selection medium. Because of the complex nature of the selection conditions, the mutants were tested for tolerance to low pH and other individual components of the selection medium. All three mutant strains were notably more tolerant to acidic conditions and slightly more tolerant to Na2EDTA, relative to the wild type. No consistent differences in response to Na2SO4 were evident. Genetic characterization indicated a single nuclear gene basis of inheritance for strain HαAT3. Strains HαAT7 and HαAT29 showed a nuclear basis of tolerance, but responses of gametophytes from F1 hybrids suggested segregation at two or more loci.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Polyhalite is a natural mineral that could be fed as an acidogenic product to induce a metabolic acidosis and prevent clinical hypocalcemia in dairy cows after calving. The overall objective of this study was to determine if the use of polyhalite mineral in the diets of pre-partum non-lactating dairy cows was effective as an acidogenic product. We measured the urine pH, dry matter intake, milk yield, and calcium and magnesium concentration of urine and serum in pre-partum and non-lactating dairy cows consuming diets containing a low dose of polyhalite (200 g/cow/day), a high dose of polyhalite (400 g/cow/day), calcium chloride (250 g/cow/day), or no acidogenic product. We hypothesized that including polyhalite mineral as an acidogenic product in the diets of pre-partum and non-lactating dairy cows will reduce urine pH and stimulate calcium metabolism mechanisms. We found that polyhalite effectively reduced urine pH and did not affect dry matter intake, and the stimulation of calcium metabolism was observed through an increase of calcium output in urine. In conclusion, feeding polyhalite mineral is an effective means for inducing metabolic acidosis without reducing dry matter intake. Based on these results, polyhalite should be fed at a dose of 400 g or more per cow per day to reduce urine pH. / Master of Science in Life Sciences / Low blood calcium concentration, also known as hypocalcemia, is one of the common metabolic disorders that affect dairy cows transitioning from the pre-partum to post-partum period. Reducing the dietary cation anion difference (DCAD) in cows during the close-up period is known to effectively reduce the probability of cows developing hypocalcemia after calving. Polyhalite is a natural mineral that could be fed as an acidogenic product to induce a metabolic acidosis and prevent hypocalcemia in dairy cows after calving. The overall objective of this study was to determine if the use of polyhalite mineral in the diets of pre-partum and non-lactating dairy cows was effective as an acidogenic product. We evaluated the urine pH, dry matter intake, milk yield, and calcium and magnesium concentration of urine and serum in pre-partum and non-lactating dairy cows consuming diets containing a low dose of polyhalite (200 g/cow/day) , a high dose of polyhalite (400 g/cow/day), calcium chloride (250 g/cow/day), or no acidogenic product. We hypothesized that including polyhalite mineral as an acidogenic product in the diets of pre-partum and non-lactating dairy cows will reduce urine pH and stimulate calcium metabolism mechanisms. We found that polyhalite effectively reduced urine pH and did not affect dry matter intake, and the stimulation of calcium metabolism was observed through an increase of calcium output in urine. In conclusion, feeding polyhalite mineral is an effective means for inducing metabolic acidosis without reducing dry matter intake. Based on these results, polyhalite should be fed at a dose of 400 g or more per cow per day to reduce urine pH.

Current feeding strategies for dairy cows focus on meeting the energy requirements for high levels of milk production. However a major concern is the effect that these feeding regimes might have on rumen pH, which can have harmful effects on the cow and rumen microbial population. Several interventions have been used to counteract the effects of low rumen pH such as the use of probiotics e.g. yeast (Saccharomyces cerevisiae). However benefits have been inconclusive due to large individual animal variation in responses to treatment observed. The use of novel monitoring technologies can help assess the effect that different dietary interventions have on performance, rumen pH and rumen health. Data from three on-farm dairy cow trials (Trial 1 standard diet plus yeast; Trial 2 standard diet plus acidotic challenge plus yeast; Trial 3 cows grazing grass plus yeast) was used to evaluate the use of rumination collars (RC), rumen pH boluses, a whole cow dynamic mechanistic simulation model (SM) and the effect that different feeding strategies have on performance rumen pH dynamics and rumination time. No statistically significant differences between Control (no yeast) and Treatment (addition of yeast) diets were observed on any of the parameters measured. The lack of animal response to yeast supplementation observed in the three feeding Trials could be attributed to the stage of lactation, as the cows were passed peak lactation. Comparison of rumination time obtained with the RC and visual observations (obtained directly and from video recordings) suggest that the RC can be used to determine rumination time in housed cows. However its poor performance in grazing environments makes its use not advisable in cows outside at grass. The rumen pH boluses provided detailed and accurate data on circadian rumen pH. Highly varied individual responses to the feeding strategies were observed. This resulted in a diverse degree of risk of individual cows which experienced sub-acute rumen acidosis. The SM was able to accurately predict circadian pH, compared against the data obtained from Trials 1 and 2. The model provided pH values that were in agreement with those obtained with the rumen boluses. The use of new technologies to monitor cows individually could aid in whole-herd management, for example by setting thresholds for rumen pH and rumination time related to individual cow status, and then trigger appropriate interventions.