Alterations in the antioxidative system of suspension-cultured soybean cells (Glycine max) induced by oxidative stress. -Physiol. Plant. 97: 388-396.The objectives of this study were the changes of antioxidative key enzyme activities under stress conditions induced by a peroxidizing herbicide using photoheterotrophically grown, suspension-cultured soybean celts (Glycine max L.). Within two days, 50 to 500 ruW oxyfluorfen, a p-nitrodiphenyl ether herbicide, caused up to 100% inhibition of growth, while simultaneously, the chlorophyll was 25% to completely bleached. The major cellular antioxidants aseorbate and glutathione showed different responses. Under stress conditions with more than 250 nM oxyfluorfen, the eellular ascorbale concentration was halved, whereas dehydroascorbate remained roughly constant. The glutathione content (approximately one-fifth of that of aseorbate in untreated control cells) increased nearly 3-fold in the presence of 250 TM oxyfluorfen. Under this condition, oxidized glutathione was 5 times above the control level. The specific activities of selected enzymes participating in cellular defence, namely aseorbate peroxidase, glutathione reduetase, monodehydroascorbate reduetase. peroxidase and catalase increased by 40 to 70% with oxyfluorfen concentrations between 50 and 500 nM, while dehydroascorbate reduetase showed a significant decrease. Glutathione transferase activity even increased 6-fold under oxyfluorfen stress.

No abstract

The phytotoxic effect of Cu via the photosynthetic electron transport system was studied with isolated spinach chloroplasts. Cu(II) ions Induce a Ught-iven peroxidation of membrane lpids leading to ethylene formadon, the latter dominating over a concurrent ethane production. Seemingly, the hydroxyl radical originating from superoxide anion is the starting reactive 02 species. Cu ions inhibit photosynthetic electron transport and apparently catabze the formation of hydroxyl radical and Fenton-type reactions that result in destruction of unsaturated membrane fatty acids. 2Abbreviations: MV (methylviologen), 1,1'-dimethyl-4,4'-dipyridylium dichloride; DAD (diaminodurene), 2,3,5,6-tetramethyl-p-phenylenediamine; DCIP, 2,6-dichlorophenolindophenol; DCMU, 3-(3,4-dichlorophenyl)l,I-dimethylurea; SOD, superoxide dismutase DABCO, 1,4-diazobicyclo-2,2,2-octane. MATERIALS AND METHODSChloroplasts from fresh spinach leaves (Spinacia oleracea, strain Atlanta) grown in the open during fall were prepared according to reference 4 and suspended in 50 mm phosphate buffer (pH 7.5), including 5 mm MgCl2. To obtain chloroplasts with high endogenous O2 uptake (as in Table V), the harvested leaves were stored at room temperature for 8 h prior to chloroplast preparation.Chloroplast incubation for the determination of either the lightinduced formation of C2H6, and C2H4 or O2 was carried out in a Warburg apparatus (Braun, Melsungen) using 150 w/m2 light, provided by simple tungsten light bulbs. The reaction mixture to measure O2 generation included, in a 2-ml reaction volume: 50 mim phosphate buffer (pH 7.5), 5 miM MgCl2, 5 mm NH4Cl, 0.5 mM hydroxylamine, and chloroplast material equivalent to 100 ,ug Chl. The time of incubation was 10 min. Then, the nitrite formation from the added hydroxylamine due to the presence of superoxide was measured as described (9).The medium for production of C2H6 and C2H4 contained 10 mm phosphate buffer (pH 7.5), 5 mM MgCl2, 5 mm NH4Cl, and chloroplasts equivalent to 200 jig Chl in a 2-ml final reaction volume. Incubation was over a period of 1 h in 10-ml vessels sealed with gas-tight rubber caps. The separation of both gases was performed with a 2-m column of activated alumina using a temperature program from 60 to 140 C and a gas chromatograph (model F22, Perkin-Elmer) equipped with an automatic headspace sampler (20).Photosynthetic NADP+ and DCIP reduction was performed and measured continuously in 50 mm phosphate buffer (pH 7.5), including 5 mM MgCl2 and 5 mm NH4Cl, using a split-beam spectrophotometer (Hitachi, model 124) equipped with a 40-w tungsten lamp for actinic cross-illumination. In addition, the H20 --NADP+ reaction mixture contained 0.4 mi NADP+ and 2 uM Bumilleriopsis ferredoxin; with DAD as electron donor, this assay included additionally 1 mm sodium ascorbate, 100 tLM DAD, and 100 /M DCMU. The DCIP concentration was 50 tiM when using the H20 --DCIP system. 02 uptake of isolated chloroplasts was measured with a Clarktype 02 electrode with red light (140 w/m2) using an RG 610 Schott c...

The response of the terrestrial blue-green algae Nostoc flagelliforme, Nostoc commune, and Nostoc spec. to water uptake has been investigated after a drought period of approximately 2 years. Rapid half-times of rewetting (0.6, 3.3, and 15.5 min, respectively) are found. The surfaceto-mass ratio of the three species is inversely correlated to the speed of water uptake and loss. The ecological relevance of these different time courses is discussed.Respiration starts immediately after a 30-min rewetting period, whereas photosynthetic oxygen evolution reaches its maximum activity after 6 and 8 h with N. commune and N. flagelliforme, respectively. In the dark, recovery of oxygen uptake by N. commune is somewhat impaired, while slightly stimulated with N. flagelliforme. With both species, recovery of photosynthesis is inhibited by darkness.Using colonies kept dry for two years, nitrogenase activity of N. commune attains its maximum 120 to 150 h after rewetting, while only 50 h were needed with algal mats kept dry for two days.Thus, after a 2-year drought period, the physiological sequence of reactivation is respiration-photosynthesis-nitrogen fixation. Respiration and photosynthesis precede growth and are exhibited by existing vegetative cells, whereas recovery of nitrogen fixation is dependent on newly differentiated heterocysts.

Quantitative Taq nuclease assays (TNAs) (TaqMan PCR), nested PCR in combination with denaturing gradient gel electrophoresis (DGGE), and epifluorescence microscopy were used to analyze the autotrophic picoplankton (APP) of Lake Constance. Microscopic analysis revealed dominance of phycoerythrin (PE)-rich Synechococcus spp. in the pelagic zone of this lake. Cells passing a 3-m-pore-size filter were collected during the growth period of the years 1999 and 2000. The diversity of PE-rich Synechococcus spp. was examined using DGGE to analyze GC-clamped amplicons of a noncoding section of the 16S-23S intergenic spacer in the ribosomal operon. In both years, genotypes represented by three closely related PE-rich Synechococcus strains of our culture collection dominated the population, while other isolates were traced sporadically or were not detected in their original habitat by this method. For TNAs, primer-probe combinations for two taxonomic levels were used, one to quantify genomes of all known Synechococcus-type cyanobacteria in the APP of Lake Constance and one to enumerate genomes of a single ecotype represented by the PE-rich isolate Synechococcus sp. strain BO 8807. During the growth period, genome numbers of known Synechococcus spp. varied by 2 orders of magnitude (2.9 ؋ 10 3 to 3.1 ؋ 10 5 genomes per ml). The ecotype Synechococcus sp. strain BO 8807 was detected in every sample at concentrations between 1.6 ؋ 10 1 and 1.3 ؋ 10 4 genomes per ml, contributing 0.02 to 5.7% of the quantified cyanobacterial picoplankton. Although the quantitative approach taken in this study has disclosed several shortcomings in the sampling and detection methods, this study demonstrated for the first time the extensive internal dynamics that lie beneath the seemingly arbitrary variations of a population of microbial photoautotrophs in the pelagic habitat.