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C S FRENCH

Publications and source records attributed to C S FRENCH.

10 recordsLinked to original sources
PubMed1961

The long wavelength forms of chlorophyll a.

When Euglena gracilis is cultured with light of low intensity (ca. 250 ft-c), an absorption band at 695 mmu is formed in an amount equal to about 20 per cent of the total chlorophyll absorption in this red region. An equally large proportion of C(a)695 is observed in Ochromonas danica, irrespective of light intensity. Other algae tested appear to contain approximately 3 to 5 per cent of their chlorophyll as C(a)695; this proportion does not increase as strikingly with lowering of the light intensity as it does in Euglena. C(a)695 bleaches more readily than the other chlorophyll forms both reversibly, in whole cells, and irreversibly, in homogenates. Cells containing a large proportion of C(a)695 have a fluorescence maximum at 708 mmu, as contrasted to the 687 mmu maximum in other algae. Occasionally, old cultures of Euglena contain cells with an absorption band at approximately 710 mmu. This absorption band is quite stable in aqueous extracts; when the pigment is transferred to ether an equivalent amount of pheophytin a is found to be present. Conditions leading to the formation of the 710 mmu absorption band are not yet known.

Chlorophyll↗
PubMed1961

Computer solutions for photosynthesis rates from a two pigment model.

A kinetic model for a two pigment mechanism of photosynthesis based on observations made on the red alga Porphyridium cruentum is developed. The model supposes that different products are formed by chlorophyll and phycobilin pigments and that these products react to produce oxygen. The product of the chlorophyll reaction is also rapidly utilized for O(2) consumption both in light and in the dark. Rate equations based on the model reactions were derived and put into an analog computer. The effect of varying parameters on the time course curves for oxygen exchange resulting from the model was studied. Appropriate selection of parameters yielded computer curves which resembled fairly closely the oxygen exchange curves obtained using Porphyridium. The model showed the Emerson enhancement effect, chromatic transients, "respiratory stimulation," and other effects observed with live algae.

Chlorophyll↗
PubMed1960

Evidences from action spectra for a specific participation of chlorophyll b in photosynthesis.

Rate of oxygen evolution in photosynthesis was measured as the current from a polarized platinum electrode covered by a thin layer of Chlorella. The arrangement gave a reproducibly measurable rate of photosynthesis proportional to light intensity at the low levels used and gave rapid response to changes in illumination. Two phenomena have been explored. The Emerson effect was observed as an enhancement of photosynthesis in long wavelength red light (700 mmicro) when shorter wavelengths were added. Two light beams of wavelengths 653 and 700 mmicro when presented together gave a photosynthetic rate about 25 per cent higher than the sum of the rates obtained separately. Large and reproducible transients in rate of oxygen evolution were observed accompanying change in illumination between two wavelengths adjusted in intensity to support equal steady rates of photosynthesis. The transients were found not to be specifically related to long wavelength red light. Both enhancement and the transients have identical action spectra which are interpreted as demonstrating a specific photochemical participation of chlorophyll b.

Chlorophyll↗
PubMed1952

The fluorescence spectra of red algae and the transfer of energy from phycoerythrin to phycocyanin and chlorophyll.

1. The fluorescence spectra of the alga Porphyridium have been recorded as energy distribution curves for eleven different incident wave lengths of monochromatic incident light between wave lengths 405 and 546 mmicro. 2. In these spectra chlorophyll fluorescence predominates when the incident light is in the blue part of the spectrum which is strongly absorbed by chlorophyll. 3. For blue-green and green light the spectrum excited in Porphyridium contains in addition to chlorophyll fluorescence, the fluorescence bands characteristic of phycoerythrin and of phycocyanin. 4. From these spectra the approximate curves for the fluorescence of the individual pigments phycoerythrin, phycocyanin, and chlorophyll in the living material have been derived and the relative intensity of each of them has been obtained for each of the eleven incident wave lengths. 5. The effectiveness spectrum for the excitation of the fluorescence of these three pigments in vivo has been plotted. 6. From comparisons of the effectiveness spectrum for the excitation of each of these pigments it appears that both phycocyanin and chlorophyll receive energy from light which is absorbed by phycoerythrin. 7. It is suggested that phycocyanin may be an intermediate in the resonance transfer of energy from phycoerythrin to chlorophyll. 8. Since phycoerythrin and phycocyanin transfer energy to chlorophyll, it appears probable that chlorophyll plays a specific chemical role in photosynthesis in addition to acting as a light absorber.

Chlorophyll↗