Chalcone synthase catalyzes the initial step of that branch of the phenylpropanoid pathway that leads to flavonoids. A lack of chalcone synthase activity has a pleiotropic effect in maize and petunia mutants: pollen fertility as well as flavonoid synthesis is disrupted. Both maize and petunia mutants are self-sterile due to a failure to produce a functional pollen tube. The finding that the mutant pollen is partially functional on wild-type stigmas led to the isolation and identification of kaempferol as a pollen germination-inducing constituent in wild-ype petunia stigma extracts. We show that adding micromolar quantities of kaempferol to the germination medium or to the stigma at pollination is sufficient to restore normal pollen germination and tube growth in vitro and full seed set in vivo. Further we show that the rescue ability resides in particular structural features of a single class of compounds, the flavonol aglycones. This rmding identifies another constituent of plant reproduction and suggests that addition or removal of the flavonol signal during pollen germination and tube growth provides a feasible way to control plant fertility.
Wine model systems containing equlmolar quantities of malvidindglucoside and d-catechin, with and without acetaldehyde, were stored anaerobically at 22, 32, 42, and 52°C. Malvidind-glucoside and d-catechin disappearance and polymer appearance were monitored by HPLC and calorimetric methods. Reaction rates and activation energies were calculated. The malvidin3glucoside and d-catechin condensation reactions showed pseudo fist order kinetics both with and without the presence of acetaldehyde. However, activation energies were not significantly different.
The antifungal activities of caffeic, p‐coumaric, ferulic, and chloro‐genie acids against Saccharomyces cerevisiae were investigated. Caffeic acid was found to exhibit little inhibition of growth, although the lag period was extended in the presence of 1000 ppm. Chloro‐genie acid had no effect on the organism. In contrast, p‐coumaric acid at 100 ppm increased the lag phase of S. cerevisiae, and above 250 ppm, inhibition after 72 hr growth was proportional to the concentration present. Ferulic acid caused an increase in lag phase at 50 ppm, while as little as 250 ppm resulted in complete inhibition. These results suggest that naturally occurring hydroxycinnamates may interfere with the fermentation of fruits by this yeast.
SUMMARY— Growth rate studies were conducted with Pseudomonas aeruginosa to measure the inhibitory effect of CO2 when such variables as temperature, O2, tension, pH, and ionic strength of the glucose‐salts medium were controlled. Depletion of O2 did not limit growth until more than 75% (v/v) of the air was replaced with nitrogen. Generation time increased with ionic strength of the medium. The influence of pH in the range of 6.0 to 7.4 on the growth rate was negligible. When these variables were controlled, a linear relationship between generation time and CO2 composition of the gas phase was observed. At 70% CO2 (v/v), the generation time was nearly doubled. Thus, CO2 inhibits the metabolism of the organism, and this inhibition is due to gaseous CO2 in the air only when other environmental factors are controlled.
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