Biomedical subjects

W G Hagar

Publications and source records attributed to W G Hagar.

5 recordsLinked to original sources

PubMed2000

Comparing and assessing acid rain-sensitive ponds.

Changes in pH and temperature were monitored in two freshwater ponds in Southeastern Massachusetts from 1990 to 1993 using a remote-sensing system that collected data on a continuous basis. The sensing system included a combination electrode, pH meter and portable computer powered by a marine battery. Temperature and pH information from the pH meter were acquired every 10 min and stored in the computer. The two ponds, located within 2 km of one another, have a different average pH and sensitivity to acid precipitation. Maquan Pond has an average pH of 6.0 and an alkalinity of 7.4 mg/l, while Furnace Pond has an average pH of 6.9 and alkalinity of 14.9 mg/l. The pH of both ponds varied seasonally and showed diel changes due to the photosynthetic and respiratory activity of aquatic organisms. Precipitation events did not change the pH of Furnace Pond. Maquan Pond on the other hand, did exhibit changes in surface water pH due to specific acidic precipitation events. During certain rainstorms, the pH of Maquan surface waters dropped to values as low as pH 4. In addition to the transient changes in pH, the acid-sensitive pond also exhibited differences in planktonic distribution patterns.

Acid Rain↗

PubMed1986

Manganese toxicity to chlorophyll synthesis in tobacco callus.

Tobacco (Nicotiana tabacum) pith explants were grown on manganese containing medium. At moderate concentration (10 millimolar), manganese selectively inhibited chlorophyll synthesis, resulting initially in growth of white callus. Several weeks later the white callus turned brown due to the accumulation of a pigment identified as protoporphyrin IX by its elution profile using high performance liquid chromatography, by its absorption spectrum, and by its fluorescence properties. At a concentration of 100 millimolar manganese the pigment accumulated without growth of the explant.

Journal Article↗

PubMed1980

Photosynthetic Rates of Sporophytes and Gametophytes of the Fern, Todea barbara.

The photosynthetic rates of intact sporophytes or gametophytes of the fern Todea barbara grown in sterile culture were measured using an infrared gas analyzer. Sporophytes consisted of single whole plants with roots and leaves grown in tubes of agar. Gametophytes were grown as several plants covering the surface of the agar. Sporophytes had photosynthetic rates at light saturation of 8.50 microliters CO(2) per hour per milligram dry weight and 1,300 microliters CO(2) per hour per milligram chlorophyll, whereas rates for gametophytes were lower, 2.36 microliters CO(2) per hour per milligram dry weight and 236 microliters CO(2) per hour per milligram chlorophyll.O(2) inhibited the photosynthetic rates of both plants to a degree typical of C-3 plants. The light-saturated photosynthetic rates of sporophytes increased 42% and gametophytes increased 27% when the O(2) concentration was changed from 21 to 1%.

Journal Article↗

PubMed1979

Characterization of the Light-induced Transient States of the Chlorophyll Proteins 668 and 743 from Atriplex rosea.

The light-induced transient states of chlorophyll-protein 668 (Cp668) and its photoconverted from Cp743 were investigated using flash photolysis. Short lived transient species induced by a short flash were detected in both Cp668 and Cp743. The Cp668 transient had a half decay time of 2.0 milliseconds and showed a broad absorption band at 460 nanometers. The Cp743 transient had a half decay time of only 0.6 millisecond and had a major absorption peak at 410 nanometers in addition, to a broad absorption band around 530 nanometers. Both transient signals were quenched by oxygen. Cp668 had a temperature-dependent delayed fluorescence at room temperature with a half-life of 2.0 milliseconds, the same as the life-time of the absorption transient. This suggests that the transient species observed was a triplet state of chlorophyll.The light-induced transients of both Cp668 and Cp743 were formed with high efficiency. A very low quantum efficiency was found for the photoconversion of Cp668 to Cp743 suggesting another intermediate in the conversion sequence. The photoconversion reaction requires oxygen suggesting that an intermediate in the reaction sequence might be superoxide or singlet oxygen.

Journal Article↗

PubMed1973

Probit transformation: improved method for defining synchrony of cell cultures.

Cell numbers can be converted to probits that are used to compare the degree and timing of synchronized cell cultures. Data from synchronous cultures of Chlorella pyrenoidosa have been analyzed by this method by means of a readily available computer program. The method can be used with any biological system that generates normal sigmoidal data.

Cell Division↗