cerulenin and norflurazone

Astaxanthin accumulation by green microalgae is a natural phenomenon known as red snows and blood rains. The fact that astaxanthin synthesis requires oxygen, NADPH and Fe(2+) led Cunningham and Gantt [Annu. Rev. Plant Physiol. Plant Mol. Biol. 49 (1998) 557-583] to propose that a cytochrome P450-dependent enzyme might be involved in the transformation of beta-carotene to astaxanthin. In Haematococcus only esterified astaxanthin molecules accumulate, but it is not determined whether a fatty acid synthesis should occur simultaneously to allow pigment accumulation. The aim of this contribution was to answer these two questions using specific inhibitors of beta-carotene (norflurazon) and fatty acid (cerulenin) synthesis, and of cytochrome P450 enzyme activity (ellipticine).

Topics: beta Carotene; Cerulenin; Chlorophyta; Cytochrome P-450 Enzyme System; Ellipticines; Enzyme Inhibitors; Fatty Acids; Light; Mixed Function Oxygenases; Pyridazines; Xanthophylls; Zeaxanthins

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.

Topics: Antifungal Agents; Cerulenin; Darkness; Electron Transport; Herbicides; Hordeum; Light; Light-Harvesting Protein Complexes; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Plant Proteins; Plants; Pyridazines