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  • Title: [Effects of pyridazinones and cerulenin on the biosynthesis and functional state of photosystem 2 in barley leaves].
    Author: Rakhimberdieva MG, Lekhotski E, Karapetian NV, Krasnovskiĭ AA.
    Journal: Biokhimiia; 1982 Apr; 47(4):637-46. PubMed ID: 7044428.
    Abstract:
    The effects of pyridazinones and cerulenin on the formation of photosystem 2 in etiolated barley leaves and its functional state in green leaves were studied. It was shown that the reaction centers of photosystem 2 in greening leaves are formed after 2.5--3.0 hrs of illumination independently of herbicide treatment. In the leaves greening in the presence of pyridazinones and cerulenin and in green leaves treated by these substances a change in the chlorophyll state takes place, which is detected by a shortwave shift of the low temperature fluorescence maximum at 740 nm. Long-term treatment of greening and green leaves by pyridazinones increases variable fluorescence at 20 degrees. The inhibition of carotene synthesis by pyridazinones SAN 6706 and SAN 9789 during the greening is accompanied by a decrease of variable fluorescence at - 196 degrees and of its reversible part, as well as by an appearance of a light-induced dip of the fluorescence yield at 20 degrees slowly reversible in the dark. It is suggested that pyridazinones produce a 3-fold effect on the photosynthetic apparatus: 1) they block electron transport in the acceptor part of photosystem 2 and affect directly the reaction centers of this photosystem; 20 SAN 6706 and SAN 9789 inhibit carotene biosynthesis during greening of leaves, resulting in a formation of a photounstable pigment apparatus with a low amount of the reaction centers of photosystem 2; 3) pyridazinones which damage the membrane structure and probably the lipid composition of chloroplasts cause significant changes of the chlorophyll state; this effect is similar to that exerted by cerulenin.
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