ABSTRACT
It was found that chlorophyll fluorescence spectra and spectra of fluorescence excitation of pigment-protein complexes of photosystem II are affected by treatment with DNase. Pigment-protein complexes were isolated from pea thylakoid membranes. Spectra were measured at room temperature. It was shown that the treatment with DNase leads to a 30% increase in fluorescence yield at excitation in chlorophyll absorption bands in the fraction containing CP47, CP43, and CP29, and also in the fraction containing reaction center complexes with minor contaminations of light-harvesting complexes. Upon excitation at 260-300 nm and in the region of 500 nm, a diminishing of fluorescence yield takes place. These results suggest that pigments and/or pigment-protein complexes are bound to nucleic acids. This association, by influencing the pigment properties, can participate in the photoregulation of biochemical reactions through changes in the thermal dissipation of excited chlorophyll molecules.
Subject(s)
Deoxyribonucleases/chemistry , Photosystem II Protein Complex/chemistry , Pigments, Biological/chemistry , Plant Proteins/chemistry , Spectrometry, FluorescenceABSTRACT
Fluorescence yield dependence on external magnetic field (0-600 G) was measured for chlorophyll-protein complexes enriched with Photosystem I. Maximal relative changes of fluorescence yield at room temperature (1.0-2.5%) were dependent on the chlorphyll a:P-700 ratio. Magnetic field-induced changes were observed only in the presence of dithionite. At low temperatures (down to -160 degrees C) the magnetic field-induced effect decreased. The effect is obviously connected with the functions of reaction centers in Photosystem I. An explanation of the effect is proposed based on the hypothesis of radical pairs recombination within the reaction center. For the radical pair (P-700+. A-.), an intermediate acceptor, A-., with a g-value approximately equal to that of P-700+. is proposed.
