Potentiation of photosynthetic oxygen evolution in red light by small quantities of monochromatic blue light

Chlorophyll fluorescence kinetics and oxygen evolution in Chlorella vulgaris cells: Blue vs. red light

Oxygen evolution and chlorophyll fluorescence kinetics in cells of the Chlorella vulgaris strain (Europolytest, Russia) were studied under low, moderate and high photosynthetic photon flux densities (PPFD 40, 130 and 350 μmol photons m^-2 s^-1) of the red and blue actinic light. A novel method of a pulse amplitude modulated (PAM) Fourier chlorophyll fluorometry was applied to obtain photoinduction curves simultaneously for the red and blue measuring light for one sample. It was found that the red light did not induce oxygen evolution at low and moderate PPFD, whereas at high PPFD it caused a declining oxygen release. There was only a trace fluorescence kinetics at the low PPFD, but noticeable fluorescence kinetics under the red light was observed at the low and moderate PPFD. Particularly, the moderate red illumination of Chlorella cells excited a high chlorophyll fluorescence kinetics along with the absence of oxygen evolution that suggests anoxygenic photosynthesis. In contrast, the blue light induced a significant oxygen evolution as well as fluorescence kinetics already at low PPFD which were both further increased with the PPFD increasing. In addition, a high value of the chromatic divergence of quantum yield of photosystem II was revealed between the red and blue measuring light under high PPFD of the red actinic light.

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO2 exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA3) at the concentration of 25 μg/1 (GA-plants), and then grown under 17 W/m(2) blue light (B-plants) or 11 W/m(2) red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA3 suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.

Action Spectrum of the Photoinduced Sexual Stage in the Fungus Nectria haematococca Berk. and Br. var cucurbitae (Snyder and Hansen) Dingley

An action spectrum was determined for the photoinduced formation of perithecia in a homothallic strain of Nectria haematococca Berk. and Br. var. cucurbitae (Snyder and Hansen) Dingley. Dose-response curves for perithecial formation were obtained from 340 to 510 nanometers at 10-nanometer intervals. Radiation longer than 510 nanometers was not effective for inducing perithecial formation. The action spectrum indicated peaks of activity near 360, 440, and 480 nanometers with shoulders near 420 and 460 nanometers. Minima occurred near 350 nanometers, 390 to 410 nanometers, and 470 nanometers. The general shape of this action spectrum appears to be similar to those obtained for many different near ultraviolet-blue-sensitive organisms in which a flavoprotein molecule was postulated to be the photoreceptor.

[The influence of red and blue light on the hill activity of Acetabularia mediterranea chloroplasts]

Hill activity (reduction of trichlorophenol indophenol) of chloroplasts isolated after various times from the unicellular alga Acetabularia mediterranea grown under red light conditions decreases with time. After 2 weeks the amount of Hill activity is only about 30-40% of that at the beginning of the red light treatment. On the other hand, Hill activity of chloroplasts from cells grown under blue light does not change remarkably during the course of the experiment. Transfering cells to blue light after 2 weeks in red light results in an increase of Hill activity within 48-72 hours up to the level of Hill activity in cells grown in blue light.It is concluded that the observed changes in the rate of photosynthesis in red and in blue light (Schaeel and Clauss, 1968) are due to an alteration of the photosynthetic apparatus. Apparently processes are affected which are somehow involved in the light reactions.

[Investigations on the effect of blue light on the photosynthetic O2 exchange]

1. In cells of Chlorella fusca darkened for 12 and more hours and preilluminated with red light, irradiation with blue light of low intensity (5×10(-10) einstein cm(-2) sec(-1), 465 nm) for 2 minutes results in a substantial enhancement (up to 80%) of the "gross O2 evolution" (difference between the rate of O2 exchange in dark and light) in a subsequent red light period (5×10(-10) einstein cm(-2) sec(-1), 670 nm). 2. By analysing the kinetics of O2 exchange after the light has been switched on and off it is possible to distinguish between true photosynthetic O2 evolution and a photosynthetic inhibition of respiratory O2 uptake. Only the latter component is strongly enhanced by blue light, whereas O2 evolution is almost unchanged. This is also shown when both components are separated by using various inhibitors. 3. It was shown in different ways that the inhibitory effect of photosynthesis on the respiratory O2 uptake is strongly dependent on the respiratory activity. This inhibition is most pronounced at medium activity, but nearly zero at very low respiratory activity. Therefore it is concluded that blue light works primarily only by enhancing the respiratory activity, which declined to very low values during the preceeding long lasting dark period. 4. This interpretation is strongly supported by the finding that any acceleration of the respiratory dark turnover by uncouplers or by glucose at low concentrations produces quite the same effect on the photosynthetic O2 exchange as blue light does.

[Enhancement of respiration by light in photosynthesizing chlorella and its dependence on the wavelength of light]

During 20 min of photosynthesis in red light (λ 680 nm) the rate of O2-production of Chlorella remains constant; in blue light (λ 455 nm), however, it decreases within 5-10 min from the initially high rate to a stable lower rate (Fig. 1a and b). Two action spectra (measured at non-compensating intensity) of photosynthetic O2-production, one determined for the beginning (0.-5. min="early"), the other for the end (15.-20. min="late") of this light period are, therefore, congruent in the red and divergent in the blue part of the visible spectrum (Fig. 6a). The difference between both spectra-expressed in terms of the ratio of "late" to "early" O2-production (l/e×100; or S/F×100 in Fig. 6a)-is most pronounced around λ 460nm, smaller in near ultraviolet and green light and nonexistent in orange, red, and far red (Fig. 6b). This spectral dependence of the decline in O2-liberation during photosynthesis with different wavelengths resembles the action spectrum for an enhancement of endogenous respiration by light of an achlorophyllous, yellow Chlorella mutant (KOWALLIK, 1967) (Fig. 9 upper), a fact which led us to examine the following dark respiration. The latter is enhanced after exposure to all wavelengths tested; after red light it is enhanced for only a few minutes, probably because of rapid decomposition of intermediates of photosynthesis. After blue light, however, the initial enhancement decreases only slowly, a fact which indicates an additional long lasting, specific effect of blue light (Fig. 3). An approximative action spectrum for this long lasting enhancement of respiration after photosynthesis-determined with the O2-consumption following λx as per cent of that after λ680 nm - also shows one high peak around λ 460 nm, rather steep slopes to the short and the long wave sides and no effect of red light (Fig. 5; compare Fig. 9, lower).-Calculation of "late" photosynthetic O2-production using the following instead of the preceding dark-O2-uptake yields an action spectrum which does not deviate any more from the one of "early" O2-production, calculated with the preceding dark-O2-uptake (Fig. 7).In DCMU-poisoned Chlorella the O2-uptake is strongly enhanced in blue but not in red light (Fig. 2). Glucose-fed algae in which respiration can no longer be light-stimulated (KOWALLIK, 1966) do not show any decrease in the rate of O2-production in blue light (Fig. 8). The course of CO2-exchange in blue and red light resembles that of O2-exchange.We feel that these results indicate a wavelength dependent enhancement of respiration in photosynthesizing Chlorella.

[Specific role of carotenoid-absorption in photosynthetic oxygen evolution]

The photosynthetic oxygen evolution rate of the unicellular green algae Ankistrodesmus braunii slowly decreased in the course of time when the algae were illuminated only by interrupted or continuous red light. Illumination with blue-green light (493 nm and 2 min duration) instead of one red light exposure induced oxygen uptake and produced a higher efficiency of oxygen evolution in the following illuminations with red light.This effect has been observed with red light absorbed by chlorophyll a1 (wave-length longer than 680 nm) as well as with light of 647 nm which is mainly absorbed by chlorophyll b. For this reason and because of the long-lasting enhancement of the O2-evolution after a short blue-green illumination and the absence of the effect under anaerobic conditions, it is not possible to interpret this phenomenon as an Emerson-enhancement-effect.

[The influence of red light and blue light on the photosynthetic activity of Acetabularia mediterranea]

In blue light (350-500 nm) the rate of photosynthesis (oxygen evolution) of Acetabularia is almost constant after a short period of transition (Fig. 1). In red light (600-700 nm), however, it decreases within 2-3 weeks almost to zero (compensation point). The photosynthetic apparatus is not damaged irreversibly by red light, because transfering the cell from continuous red light (2 weeks) to continous blue light results in an increase of the rate of photosynthesis within 3 days up to the level in blue light (Fig. 5). Photosynthesis can also be stimulated if continuous red light is interrupted daily by short breaks of blue light. The rate of photosynthesis at the end of the induction period depends upon the amount of blue light per day (Fig. 5 and 6) and is probably proportional to the logarithm of this amount.Cell growth (Figs. 2, 7, 8) and formation of dry matter (Figs. 3, 9) in continuous red light, in blue light and in continuous red light supplemented by blue light is controlled by the rate of photosynthesis under these light condition.

The action spectrum for blue-light-stimulated oxygen uptake in Chlorella

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