The broad‐spectrum fungicide CGA 219417 inhibits mycelial growth of Botrytis cinerea Pers ex Fr. Pseudocercosporella herpotrichoides (Fron.) Deighton and Helminthosporium oryzae B. de Haan on defined media lacking amino acids. The growth inhibition of B. cinerea is reversed by the addition of a mixture of 19 amino acids at a concentration of 100 μM each or by the addition of methionine or homocysteine in concentrations of 100 μM or 1 mM, respectively. In the case of B. cinerea, the reversal of growth inhibition by methionine could also be shown for pyrimethanil and mepanipyrim. These findings suggest that the pyrimidinamine fungicides inhibit the biosynthesis of methionine in phytopathogenic fungi.
Photosystem I reaction center was isolated from the cyanobacterium Mastigocladus laminosus. It contained four different subunits with molecular masses (as determined by sodium dodecyl-sulfate gels) of about 70,000 (subunit I), 16,000 (subunit II), 11,000 (subunit Ill), and 10,000 (subunit IV) daltons. The purified reaction center contained about 100 chlorophyll a moleoules per P700; however, they could be readily depleted down to about 50 chlorophyll a per P700 without loss in the photochemical activities. The reaction center was active in cytochrome c photooxidation, but the photooxidation of an acidic cytochrome, like the Euglena cytochrome 552, required the presence of cations. The purified reaction center was found to be similar in several respects to the photosystem I reaction centers from higher plants and, especially, to the one isolated from green algae. Subunit I appeared -on sodium dodecyl sulfate gels in the same position and possessed the same shape of an apparent double band as the corresponding subunits I of green plants and of algae. Subunits I and II of photosystem I reaction centers from Mastigocladus, higher plants, and green algae showed immunological crossreactivity. This observation might serve as biochemical evidence for the common evolution of the photosystem I reaction centers. In higher plants and green algae subunit II is a product of cytoplasmic ribosomes and therefore, a high degree of homology should have been preserved upon transfer of its gene from the prokaryote to the nucleus of the eukaryotes.
The thermophilic cyanobacterium Mastigocladus laminosus was grown in a steady state continuous culture. Regulation and data sampling of the turbidostat was done with a microcomputer. Growth performance was measured as a function of temperature and pH from 30 to 62°C and between pH 4 and 10. The temperature optimum was between 45 and 55°C. Under optimal conditions the filaments contained predominantly 8 cells with a high phycocyanin content but at the temperature extremes and at high pH, 2-and 4-cell filaments containing little phycocyanin were more abundant.
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