Die Wirkung von Blaulicht auf den photosynthetischen Elektronentransport bei gelbgrünen Mutanten von Chlorella fusca: The Effect of Blue Light on the Photosynthetic Electron Transport in Chlorophyll-Deficient Mutants of Chlorella fusca

Abstract

Summary Chlorophyll-deficient mutants of Chlorella fusca show photosynthetic rates based on the chlorophyll content which are 4-5 times higher than that of the normal form. The mutants show light saturation of photosynthesis at much higher light intensities too. Hill-reaction activities are found to have the same differences when measured with whole algal cells with benzoquinone, 2,6-dichlorophenolindophenol (DPIP) and methylviologen as electron acceptors. DPIP and methylviologen Hill-reactions measured with intact algal cells had only be possible after a treatment of the cells with benzoquinone or glutardialdehyde. These reagents produce an increase in the permeability of the membranes. The higher capacity of CO, fixation and electron transport reactions are due to the formation of smaller photosynthetic units. Thus the reduced chlorophyll synthesis is not correlated with an attendant reduction of the number of electron transfer chains. It is assumed that the deficiences of antenna chlorophyll, especially of chlorophyll b, is caused by a lack of the light-harvesting chlorophyll a/b-protein complex. Blue light of high intensity, especially of 452 nm wavelength, strongly inhibits CO, fixation in the mutants compared to red light. The photosynthetic rate of normal strains of Chlorella is not or only slightly affected by blue light of high intensities. Anerobic conditions and a-HPMS, an inhibitor of light respiration, do not influence the extent of the blue light depression. The Hill-reaction of whole cells, measured with p-benzoquinone as electron acceptor for photosystem II, also shows a blue light depression comparable to that of photosynthesis. After treatment of the cells with glutardialdehyde the blue light effect on DPIP reduction disappears totally. The studies of the 520 nm absorbance change show clear differences between the mutants and the normal green strain.