Enhancement effect, Emerson

Why is the Emerson enhancement effect (i.e., light at 650 nm plus 680 nm gives a higher rate of photosynthesis than either one alone) not observed with photosynthetic bacteria ... 

To explain the Emerson enhancement effect, Govindjee and Rahinowitch ° obtained evidence from the action spectra of the enhancement effect the presence of two distinct forms of Chl-a in vivo presumably present in two different pigment systems. Soon, new experimental evidence in support of the two-photo-system concept was reported independently by Govindjee etal and by Kautsky eta/. from evidence obtained from fluorescence and by Kok and Hoch Duysens " and Witt based on measurements of absorbance changes. We present here two results based on absorbance changes associated with changes in the redox state of electron carriers in the chloroplast. 

What is the Emerson enhancement effect How was it used to demonstrate the existence of two different photosystems (Hint Refer to Biochemical Methods 13.1.)... 

The enhancement effect" (Emerson s 2nd effect), i. e. the increase of photosynthesis quantum yield in the far-red spectral region at simultaneous illumination of chlorophyll-containing cells with shorter-wave light, has been drawing attention of researchers for almost 30 years. 

CO2, as well as O2 assimilation and evolution should should be simultaneously enhanced, which actually takes place in the investigation of Emerson s effect has been shown in the Table. On the other hand, the enhancement effect of photosynthesis by CO2 and O2 quantitatively differs from one another. The reactions of water photolysis are compartmentalized in the membrane of tilakoids in close proximity from ETC, while reactional centres of carboxyliration are in the strom of the chloroplasts and, thus, should be at greater distance from ETC. 

This effect is pH dependent (Emerson, 1975) and is most important at low wind speeds and high water temperatures (e.g., equatorial regions). Modeling studies have indicated that chemical enhancement may increase fe o by up to 8% in these regions (Boutin andEtcheto, 1995). 

This effect on B12 synthesis possibly explains the activity of riboflavin and certain substituted benzimidazoles in stimulating growth of rats and chicks on Bi2-deficient diets (Emerson et al., 1951 Cooperman ei al., 1952 Hartman et al., 1951). It seems likely that their inclusion in the diet would enhance the gut synthesis of forms of vitamin B12 active for higher animals. 

On illumination of Chlorella, a green alga, at wavelengths above 680 nm at which only chlorophyll a may absorb light, Emerson and coworkers in 1943 observed a progressive decline in photosynthesis as measured by oxygen evolution. This phenomenon was termed the red drop effect. By the simultaneous use of additional wavelengths below 680 nm, photosynthesis was enhanced by over 30% beyond the sum of the rates obtained by separate monochromatic illumination. This observation,... 

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