Characterization of diuron-resistant Euglena: Greater tolerance for various phenylurea herbicides and increased sensitivity of thylakoids to ethyl-S-dipropyl thiocarbamate

Adaptation of Fungi to Fungitoxic Compounds

Some fungitoxic chemicals often fail to protect crops because the target fungi develop resistance. Depending on its mechanism of action, the fungicide may lose its effectiveness completely after a limited number of applications, it may show a gradually less satisfactory performance or it may retain its effectiveness unchanged despite extensive use. In all cases investigated, resistance to agricultural fungicides has been shown to result from mutations of chromosomal genes. Biochemical mechanisms of adaptation have been recognized mainly as alterations of the cellular component with which the fungicide interacts, as reduced uptake or increased efflux, and as decreased conversion into a more toxic compound. However, most studies on biochemical genetics have utilized laboratory mutants and it is not always certain that similar mechanisms are responsible for adaptation in nature.

The psbA gene of DCMU-resistant Euglena gracilis has an amino acid substitution at serine codon 265

The psbA gene coding for the herbicide binding QB protein of photosystem II has been sequenced previously (Karabin et al. 1984). A herbicide resistant mutant of Euglena, Euglena gracilis ZR, was studied by sequencing part of the psbA gene and its corresponding mRNA. Sequencing reactions were done by annealing a psbA specific, end-labeled DNA-oligomer to total chloroplast DNA or RNA and extending this primer with reverse transcriptase in the presence of the four dideoxynucleotides. An amino acid substitution from serine to alanine at position 265 was detected. All known herbicide resistant higher plants sequenced to date and the Chlamydomonas mutant DCMU-4 show a change at exactly this same position, but the substitution in higher plants is from serine to glycine.

Spectrophotometric method of controlled pheophytinization for the determination of both chlorophylls and pheophytins in plant extracts

Conventional spectrophotometric methods of chlorophyll (Chl) measurement with double-wavelength readings of absorbances corresponding to the peak values of both Chl a and Chl b are usable only is pheophytins (Pheo) are absent in the pigment extract. We present here a kinetic method of controlled phenophytinization of the Chl present in acetone/water (90/10, v/v) exctracts that allows the measurement of both Chl a and b, as well as of the initial Pheo preexisting in the plant material at the moment of the extraction. This method gives better accuracy in Chl b determination than conventional methods, particularly when Chl a/Chl b ratios are greater than 5. Examples are given illustrating the usefulness of this method.