Distribution of aquatic yeasts — Effect of incubation temperature and chloramphenicol concentration on isolation

Fresh (river), estuarine, and marine waters in and along the coastline of Connecticut were cultured by the membrane filter technique at 20 and 37°C on a complex medium containing 0–1000 mg/L of chloramphenicol. Using counts on medium with 500 mg/L antibiotic as a base, ratios of total and pink yeast counts were recorded for other chloramphenicol concentrations at both temperatures for the waters sampled. Variable results were obtained; in general, both total and pink yeast counts decreased with increasing antibiotic levels, being most apparent at > 400 mg/L chloramphenicol. Medium without antibiotic and with 100 mg/L always produced baterial overgrowth. A total of 209 white yeasts were isolated from all platings; the genera Torulopsis, particularly T. Candida, and Candida were dominant with lesser numbers of Cryptococcus, Trichosporon, sporogenous genera, and Kloeckera. Most species isolated were found on media at all chloramphenicol levels. Comparisons were made of yeast distributions in these temperate waters with reports from other areas.Contribution No. 101 from the University of Connecticut Marine Research Laboratory.     

Is the ABA concentration in the sap collected by pressurizing leaves relevant for analysing drought effects on stomata? Evidence from ABA-fed leaves of transgenic plants with modified capacities to synthesize ABA.

Most studies on the role of ABA in the stomatal response of the whole plant to drought rely on a good estimate of ABA concentration in xylem sap. In this report, varying volumes of sap (V(sap)) were collected by pressurizing leaves cut from several lines of N. plumbaginifolia with modified capacities to synthesize ABA. Leaves were fed with solutions of known ABA concentration ([ABA](solution) from 0-500 micromol m(-3)) for 2-3 h before sap collection. ABA concentration in extruded sap ([ABA](sap)) was compared with [ABA](solution). In low-volume extracts (less than 0.35 mm(3) cm(-2) leaf area) collected from leaves of well-watered plants, [ABA](sap) was close to [ABA](solution). For all lines, [ABA](sap) decreased with increasing V(sap). The same dilution effect was observed for leaves pressurized just after sampling on droughted plants, suggesting, as for detached leaves fed with ABA, that [ABA](sap) in low-volume extracts approximated well with the concentration of ABA entering leaves still attached on droughted plants. However, ABA-fed leaves sampled from droughted plants yielded higher [ABA](sap) than ABA-fed leaves sampled from well-watered plants. [ABA](sap) was also increased, although very slightly, when leaves were preincubated in highly enriched ABA solution. This indicates that some leaf ABA contributed to the ABA concentration returned in the extruded sap. Consistently, [ABA](sap) in medium-volume extracts (0.35-0.65 mm(3) cm(-2) leaf area) was lower for leaves sampled on under-producing lines than on the wild type. Despite these distortions between [ABA](solution) and [ABA](sap) in medium-volume extracts, stomatal conductance of ABA-fed leaves closely correlated with [ABA](sap) with a similar relationship in all cases, whilst relationships with [ABA](solution) were more scattered.     

Effect of 2,2′-bipyridyl on porphyrin synthesis in etiolated and light-treated barley leaves

The effects of 2,2′-bipyridyl on porphyrin formation differed in illuminated and dark-treated barley leaves. In the dark, bipyridyl treatment increased photoconvertible protochlorophyllide (Pchlide, P650) and decreased the protohaem content. The increase in Pchlide could not be wholly accounted for by a diversion of ‘substrate’ from protohaem synthesis. The rate of Pchlide regeneration was slightly higher in chelator treated leaves which suggests increased δ-aminolaevulinic acid (ALA) synthesis. Only small quantities of Mg-protoporphyrinmonomethylester (Mg-protoME) were detected in etiolated leaves treated with bipyridyl in the dark. Protochlorophyll (P630) synthesis from exogenously supplied ALA was lower in the chelator treatments. The results suggest that only when substantial quantities of ALA are being utilized in dark-grown leaves does a ‘metal’ become limiting in the bipyridyl treated leaves. In the light, bipyridyl inhibited chlorophyll synthesis, again suggesting that when substantial amounts of ALA were being utilized a ‘metal’ becomes rate limiting. Bipyridyl treatment also inhibited ALA production in light-treated leaves. The incorporation of glycine-[¹⁴C] into ALA in the presence of bipyridyl was severely restricted compared to the incorporation of glutamate-[¹⁴C]. The data suggest two pathways for ALA synthesis; the classical ALA-synthetase which utilizes glycine and is operative in dark-grown leaves and a second enzyme system, which uses glutamate, and is of quantitative importance in the light.     

Effect of elevated CO2 on growth and crassulacean-acid-metabolism activity of Kalanchoë pinnata under tropical conditions

 Kalancho? pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO₂ concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO₂ treatments. However, under elevated CO₂, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO₂ was attributable entirely to increased net CO₂ uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO₂ concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO₂ but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO₂. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations. Received: 4 March 1996 / Accepted: 25 May 1996