Paraquat resistance of weeds--the case of Conyza canadensis (L.) Cronq.

The paper gives an overview of literature on paraquat resistance of weeds and the proposed mechanism of resistance. New results we achieved on horseweed (Conyza canadensis /L./, Cronq.) are discussed in detail. It was demonstrated that there is no significant constitutive difference related to the paraquat resistance between untreated susceptible and paraquat-resistant horseweed plants. The lower sensitivity of flowering resistant plants may be due to the fact that paraquat content in treated leaves of flowering resistant plants was only 25% as compared to those measured at rosette stage. Our results confirm that paraquat resistance is not based on elevated level and activity of antioxidant enzyme system. The hypothesized role of polyamines in the resistance mechanisms can be excluded. The higher putrescine and total polyamine content of paraquat treated resistant leaves can rather be regarded as a general stress response, than as a symptom of paraquat resistance. A paraquat-inducible protein is supposed to play a role in the resistance, which presumably functions by binding paraquat to an inactivating site and/or by carrying paraquat to metabolically inactive cell compartment (vacuole, cell wall). From model experiments it is concluded that paraquat and diquat preferentially form hydrophylic interactions with proteins containing a higher amount of lysine and glutamic acid. Consequently, the reason for paraquat resistance in horseweed is probably a hydrophylic interaction of paraquat with a protein, leading to inactivation of paraquat through forming a conjugate and/or sequestration into the vacuole or the cell wall.

Intraspecific invariability of the internal transcribed spacer region of rDNA of the truffle Terfezia terfezioides in Europe.

ITS regions (internal transcribed spacers--ITS1 and ITS2--with the 5.8S gene of the nuclear rDNA) of 25 fruit body samples of Terfezia terfezioides, originating from Hungary and Italy, were compared. The amplification and sequencing of the ITS region was successful with both the ITS1-ITS4 and ITS1F-ITS4 primer pairs. No differences of the restriction fragment length polymorphism profiles were detected among 19 samples collected in one place at the same time. The sequences of the ITS region of 9 samples collected in different localities were highly invariable, differing in only two bases. Thus the intraspecific homogeneity of the ITS region seems to be an important species-specific characteristic of T. terfezioides in contrast to other Terfezia species. As the samples of the species were collected from different and distant localities of Europe, the ITS sequence of T. terfezioides can be considered a very conservative, reliable molecular marker of the fungus.

Some characteristics and partial purification of the Ganoderma lucidum cellulase system.

The extracellular cellulase system of the white-rotting basidiomycete Ganoderma lucidum was characterised while growing in cellulose-containing shaken liquid culture. The protein content of the culture filtrate reached its maximum after 36 days and cellulase activity at about 60 days. Different cellulase activities (endoglucanase, cellobiohydrolase and beta-glucosidase) were determined in a range of pH extending from 6 to 2. All of the three enzyme activities have at least three peaks between pH 6 and 2, although optimum points of the different enzymes are slightly different, showing that the enzyme complex consists of a number of enzymes and isozymes. Partial purification of the enzyme complex was carried out by DEAE-cellulose column chromatography. Using 0-3 M linear urea gradient, protein was eluted in one sharp peak corresponding mainly to beta-glucosidase activity. Comparing crude extracellular protein with that of purified by the column using PAGE indicated that this method was suitable for the separation and partial purification of one type of Ganoderma cellulases.

Characterization of carbohydrate metabolism and demonstration of glycosomes in a Phytomonas sp. isolated from Euphorbia characias.

Phytomonas sp. isolated from Euphorbia characias was adapted to SDM-79 medium. Cells isolated in the early stationary phase of growth were analyzed for their capacity to utilize plant carbohydrates for their energy requirements. The cellulose-degrading enzymes amylase, amylomaltase, invertase, carboxymethylcellulase, and the pectin-degrading enzymes polygalacturonase and oligo-D-galactosiduronate lyase were present in Phytomonas sp. and were all, except for amylomaltase, excreted into the external medium. Glucose, fructose and mannose served as the major energy substrates. Catabolism of carbohydrates occurred mainly via aerobic glycolysis according to the Embden-Meyerhof pathway, of which all the enzymes were detected. Likewise, the end-products of glycolysis, acetate and pyruvate, glycerol, succinate and ethanol were detected in the culture medium, as were the enzymes responsible for their production. Mitochondria were incapable of oxidizing succinate, 2-oxoglutarate, pyruvate, malate and proline, but had a high capacity to oxidize glycerol 3-phosphate. This oxidation was completely inhibited by salicylhydroxamic acid. No cytochromes could be detected either in intact mitochondria or in sub-mitochondrial particles. Mitochondrial respiration was not inhibited by antimycin, azide or cyanide. The glycolytic enzymes, from hexokinase to phosphoglycerate kinase, and the enzymes glycerol kinase, glycerol-3-phosphate dehydrogenase, phosphoenolpyruvate carboxykinase, malate dehydrogenase and adenylate kinase, were all associated with glycosomes that had a buoyant density of about 1.24 g cm-1 in sucrose. Cytochemical staining revealed the presence of catalase in these organelles. The cytosolic enzyme pyruvate kinase was activated by fructose 2,6-bisphosphate, typical of all other pyruvate kinases from Kinetoplastida. The energy metabolism of the plant parasite Phytomonas sp. isolated from E. characias resembled that of the bloodstream form of the mammalian parasite Trypanosoma brucei.

The effect of ethanol in the separation of wheat gliadins by CM- and DEAE-cellulose chromatography.

The effect of ethanol on the fractionation of gliadin by cellulose-based ion exchange column chromatography was studied. Ten peaks have been separated on DEAE- and 12 peaks on CM-cellulose column using a complex elution technique. By SDS-polyacrylamide gel electrophoresis of the separated fractions, it was observed that ethanol incorporated into the eluent improved the resolution of some fractions. Some of the peaks gave only 2 or 3 protein bands in electrophoregrams. Since ethanol does not affect the reproducibility in the two types of chromatographic medium, the method seems to be suitable for purification of gliadin fractions in large quantities.

Effect of a new fungicide (PNDP) on the minor nucleotide content of Fusarium oxysporum.

The minor nucleotide constituents of rRNA from the plant pathogenic fungus Fusarium oxysporum were investigated. When the fungus was grown for 8 days in aerated liquid culture the following minor nucleotides were identified from 18S and 25S rRNA: m6A, m2A , m2(6)A, m1G, m2G , m2(2)G, m3C , Cm, m5C, m3U , Um, cm5U , rT and psi. PNDP (+/- threo-1-phenyl-2-nitro-1,3 diacetoxy-propane), a new fungicide of unknown biochemical mode of action, caused a great decrease in the minor nucleotide content of the fungus. Only seven minor nucleotides were present in the rRNA of the fungus grown in PNDP -containing medium. A hypermodified nucleotide, mcm5S2U , was found in treated but not in untreated fusarium. On comparing the effect of PNDP with that of known protein synthesis inhibitors such as cycloheximide and chloramphenicol, it was concluded that PNDP acted similarly to cycloheximide, a cytoplasmic protein synthesis inhibitor. It is suggested that the mode of action of PNDP may be the inhibition of the synthesis of RNA modifying enzymes of F. oxysporum.

Changes in the content of modified nucleotides of total transfer RNA of wheat seedlings during greening.

The contents in minor nucleotides of total transfer RNA (tRNA) of etiolated and light-grown wheat (Triticum aestivum L.) seedlings and of seedlings illuminated for 24 or 48 h were examined. The total tRNA of seedlings illuminated 24 h contained more, and that from seedlings illuminated 48 h still more modified nucleotides than that from etiolated ones. Thus, the appearance of the characteristic minor nucleotides of tRNA of light-grown wheat seedlings needs a rather long greening period, of at least 48 h.