Robert R. Schmidt

Effect of different photosystem II inhibitors on chloroplasts isolated from species either susceptible or resistant toward s-triazine herbicides

Abstract In chloroplasts isolated from susceptible and atrazine-resistant Amaranthus retroflexus, the inhibition of photosynthetic electron transport by various classes of herbicides has been investigated. Resistance of mutant Amaranthus is not restricted to s-triazines but also extends to uracils, 1,2,4-triazine-5-ones, and ureas. For 1,2,4-triazin-5-ones and chloroplasts of both biotypes, a correlation between inhibition of photosynthetic electron transport and the partition coefficient could be established. In the case of phenolic herbicides only modestly decreased or even higher sensitivity of chloroplasts from the resistant biotype as compared to the susceptible one could be observed. These results are confirmed by binding of radioactively labeled herbicides to chloroplasts of both plants. Specific binding of atrazine or metribuzin to resistant chloroplasts is completely abolished, and that of diuron or phenisopham diminished as compared to susceptible chloroplasts. In contrast, binding of phenolic herbicides generally is enhanced in resistant chloroplasts. Photoaffinity labeling of thylakoids from both biotypes by 2-azido-4-nitro-6-[2′,3′-3H]isobutylphenol yields almost identical labeling patterns. These results are consistent with a recently proposed model (W. Oettmeier, K. Masson, and U. Johanningmeier, Biochim. Biophys. Acta 679, 376 (1982) of two different herbicide binding proteins at the reducing side of photosystem II: a 32- to 34-kdalton protein responsible for binding of triazines, triazinones, ureas, and related herbicides and a photosystem II reaction center protein for binding of phenolic herbicides.

BEHAVIOUR OF METRIBUZIN IN TOLERANT AND SUSCEPTIBLE SOYBEAN VARIETIES

Abstract Two tolerant (Bragg, Tracy M) and two susceptible (Tracy, Coker 156) soybean varieties were compared. In the tolerant plants metribuzin (4-amino-6- tertbutyl 3-(methylthic)- as -triazin-5 (4 H )-one) was more rapidly deaminated in vivo and in vitro. The stem exhibited high rates of metabolic conversion, also leading to less metribuzin arriving in the leaves of the tolerant plants.

Naramycin B, an Antibiotic from Streptomyces griseus Strain 587 with Herbicidal Properties-Fermentation, Isolation, and Identification

Abstract From the culture filtrate of Streptomyces griseus strain 587 a herbicidal active fraction was isolated by adsorption on Lewapol® , methanolic desorption, and chromatography on Sephadex® LH-20. Further purification was achieved by HPLC. The pure product was characterized by TLC and different colour reactions. By MS, 1H-NM R, IR and ORD spectroscopy the herbicidal compound could be identified as naramycin B. Naramycin B is an optical isomer of cycloheximide (naramycin A, Actidione®, Acti-Aid®). This communication reports on the fermentative production of naramycin B with strain 587, its isolation, identification, and herbicidal activity.

Characterization of the Metamitron Deaminating Enzyme Activity from Sugar Beet ( Beta vulgaris L.) Leaves

Abstract The enzymatic activity from sugar beet leaves which is responsible for the detoxification of the herbicide metamitron (4-amino-4,5-dihydro-3-methyl-6-phenyl-1, 2, 4-triazin-5-one, trade name Goltix®) has been characterized in vitro. The detoxification occurs by rapid deamination in vivo as well as in vitro. However, the deamination in vitro is only maximal under reducing conditions, i. e. with an electron donor and in a nitrogen atmosphere. The electron donor may be cystein, glutathione, dithionite or ascorbate. The enzymatic deamination further requires the addition of cytochrome c and a “supernatant factor”, which may be replaced by FMN, FAD or DCPIP. However, in the presence of FMN or DCPIP cytochrome c is not essential but only stimulatory. The particulate as well as the soluble metamitron deaminating enzyme preparations obtained take up oxygen when supplied with cysteine and FMN. The particulate enzyme appears in the peroxysome-fraction. It is therefore suggested, that the enzymatic deamination of metamitron in sugar beet leaves is mediated by a proxisomal membrane bound electron transport system which alternatively may reduce oxygen or metamitron (deaminating).