[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.