Showing papers by "University of Buenos Aires published in 1995"

Apigenin, a component of Matricaria recutita flowers, is a central benzodiazepine receptors-ligand with anxiolytic effects

Abstract: The dried flower heads of Matricaria recutita L. (Asteraceae) are used in folk medicine to prepare a spasmolytic and sedative tea. Our fractionation of the aqueous extract of this plant led to the detection of several fractions with significant affinity for the central benzodiazepine receptor and to the isolation and identification of 5,7,4'-trihydroxyflavone (apigenin) in one of them. Apigenin competitively inhibited the binding of flunitrazepam with a Ki of 4 microM and had no effect on muscarinic receptors, alpha 1-adrenoceptors, and on the binding of muscimol to GABAA receptors. Apigenin had a clear anxiolytic activity in mice in the elevated plusmaze without evidencing sedation or muscle relaxant effects at doses similar to those used for classical benzodiazepines and no anticonvulsant action was detected. However, a 10-fold increase in dosage produced a mild sedative effect since a 26% reduction in ambulatory locomotor activity and a 35% decrement in hole-board parameters were evident. The results reported in this paper demonstrate that apigenin is a ligand for the central benzodiazepine receptors exerting anxiolytic and slight sedative effects but not being anticonvulsant or myorelaxant.

Colour preferences of flower-naive honeybees

Abstract: Flower-naive honeybees Apis mellifera L. flying in an enclosure were tested for their colour preferences. Bees were rewarded once on an achromatic (grey, aluminium or hardboard), or on a chromatic (ultraviolet) disk. Since naive bees never alighted on colour stimuli alone, a scent was given in combination with colour. Their landings on twelve colour stimuli were recorded. Results after one reward (“first test”) were analysed separately from those obtained after few rewards (“late tests”). 1) After pre-training to achromatic signals, bees preferred, in the first test, bee-uv-blue and bee-green colours. With increasing experience, the original preference pattern persisted but the choice of bee-blue and bee-green colours increased. 2) Neither colour distance of the test stimuli to the background or to the pre-training signal, nor their intensity, nor their green contrast, accounted for the colour choice of bees. Choices reflected innate preferences and were only associated with stimulus hue. 3) Bees learned very quickly the pre-trained chromatic stimulus, the original colour preferences being thus erased. 4) Colour preferences were strongly correlated with flower colour and its associated nectar reward, as measured in 154 flower species. 5) Colour preferences also resemble the wavelength dependence of colour learning demonstrated in experienced bees.

Zinc deficiency causes oxidative damage to proteins, lipids and DNA in rat testes.

Abstract: To investigate the effects of zinc deficiency on oxidative damage to testes proteins, lipids and DNA, weanling male rats were allowed free access to low (0.5 microgram Zn/g) or adequate (25 micrograms Zn/g) zinc diets for 14 d. A third group was restricted intake of the adequate Zn diet to the amount consumed by the low Zn diet-fed group. Compared with ad libitum-fed controls, testes from rats fed the low zinc diet had lower glutamine synthetase activity, lower Fe(2+)-stimulated 2-thiobarbituric acid-reactive substances (TBARS) production, higher protein carbonyl concentrations (P < 0.05), and higher 8-oxo-2'-deoxyguanosine levels (P = 0.06). Glutamine synthetase activity in testes of the food-restricted controls was between the values for the ad libitum controls and zinc-deficient animals. Protein carbonyls were higher in the restricted controls compared with the ad libitum controls, whereas stimulated TBARS production was lower (P < 0.05). Levels of 8-oxo-2'-deoxyguanosine were lower in testes DNA of the restricted controls than in the zinc-deficient group (P < 0.05). Testes iron concentrations were higher in the zinc-deficient and restricted control rats than in ad libitum controls (P < 0.05). The oxidative damage observed may have occurred as a consequence of increased reactive oxygen species generation secondary to tissue iron accumulation and/or reductions in zinc-dependent antioxidant processes.

Control of mitochondrial and cellular respiration by oxygen.

Abstract: Control and regulation of mitochondrial and cellular respiration by oxygen is discussed with three aims: (1) A review of intracellular oxygen levels and gradients, particularly in heart, emphasizes the dominance of extracellular oxygen gradients. Intracellular oxygen pressure,\(p_{O_2 } \), is low, typically one to two orders of magnitude below incubation conditions used routinely for the study of respiratory control in isolated mitochondria. The\(p_{O_2 } \) range of respiratory control by oxygen overlaps with cellular oxygen profiles, indicating the significance of\(p_{O_2 } \) in actual metabolic regulation. (2) A methodologically detailed discussion of high-resolution respirometry is necessary for the controversial topic of respiratory control by oxygen, since the risk of methodological artefact is closely connected with far-reaching theoretical implications. Instrumental and analytical errors may mask effects of energetic state and partially explain the divergent views on the regulatory role of intracellular\(p_{O_2 } \). Oxygen pressure for half-maximum respiration,p50, in isolated mitochondria at state 4 was 0.025 kPa (0.2 Torr; 0.3 ΜM O2), whereasp50 in endothelial cells was 0.06–0.08 kPa (0.5 Torr). (3) A model derived from the thermodynamics of irreversible processes was developed which quantitatively accounts for near-hyperbolic flux/\(p_{O_2 } \) relations in isolated mitochondria. The apparentp50 is a function of redox potential and protonmotive force. The protonmotive force collapses after uncoupling and consequently causes a decrease inp50. Whereas it is becoming accepted that flux control is shared by several enzymes, insufficient attention is paid to the notion of complementary kinetic and thermodynamic flux control mechanisms.

Soil organic carbon, microbial biomass and CO2-C production from three tillage systems

Abstract: Organic matter is a major soil component which is influenced by tillage. This paper quantifies the effect of no-till, chisel tillage and plow tillage on the content and depth distribution of organic carbon and microbial biomass after 12 years of each tillage system. The soil was typical of the Argentine Rolling Pampa. The resistance of organic matter to mineralization was evaluated by means of an incubation test. In the no-till and chisel tillage systems, crop debris accumulated within the top 5 cm of soil, especially in the no-till system. Consequently, organic carbon was 42–50% higher (P=0.01) in the no-till soil than in the soil from the plow and chisel tillage systems. Biomass carbon and soil basal respiration (0–10 day period) were noticeably stratified under no-till and chisel tillage, while they were uniform from 0 to 15 cm in the plowed soil. The metabolic quotient of the biomass (basal respiration/biomass) was regulated in all cases by the coarse plant debris content of the soil (r2=0.79, P=0.01). A doubled exponential model was fitted to CO2-C values produced during 160 days of incubation (r2≥0.95). Thisshows that soil carbon dynamics can be described as being composed of two pools: one labile, and one resistant to microbial attack. The proportion of total carbon mineralized and the decomposition of soil-resistant carbon in 160 days in the no-till and chisel tillage soils were high at the soil surface, but decreased with depth. In plowed soil, these parameters were constant from 0 to 20 cm. The organic matter at the soil surface under the no-till and chisel tillage systems was more readily degradable than under plow tillage in the laboratory experiment. Carbon inputs from crops were estimated to be similar between tillage systems. Consequently, in situ accumulation of labile forms of organic matter under a no-till system may be ascribed to a decrease in the mineralization intensity of the soil organic matter. Soil temperature determinations suggested that plowed plots were warmer than no-tilled plots, and this phenomenon could lead to a decrease of microbial respiration in straw-covered soil.

Genetic improvement in wheat yield and associated traits. A re‐examination of previous results and the latest trends

Abstract: Two field experiments were carried out with seven wheat cultivars (three of them, including a commercial hybrid, released during the last 10 years) representing different eras of plant breeding, to evaluate genetic improvement over the last century in grain yield, height, biomass, harvest index and grain yield components. Plots were fertilized and irrigated, and lodging and diseases were prevented. Main culm height was negatively correlated with the year of release of the cultivars, probably as a consequence of selection for increased lodging resistance. There was no significant association between total above-ground biomass and year of release of the cultivars. On the other hand, grain yield increased as newer cultivars were released. Results indicate that during recent years harvest index has been kept as the main attribute responsible for increases in grain yield. In general, number of grains/m2 was associated with increases in grain yield during the century. However, the newest cultivars showed an increased grain weight. In both growing seasons, cultivars released before 1980 showed a trend towards reduced grain weight, but cultivars released after 1987 had a similar number of grains per m2 with a higher grain weight than their predecessors. This was probably because the most modern cultivars have a longer grain-filling duration with a similar length of growth cycle.

Activity and structure-sensitivity of the water-gas shift reaction over CuZnAl mixed oxide catalysts

Abstract: The activity and structure-sensitivity of the water-gas shift (WGS) reaction over Cu Zn Al mixed oxide catalysts were studied. Three sets of samples with different Cu/Zn and (Cu+Zn)/Al atomic ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary hydroxycarbonate precursors contained hydrotalcite, aurichalcite and/or rosasite phases. The decomposed precursors contained CuO, ZnO, ZnAl 2 O 4 , and Al 2 O 3 . The relative proportion of these phases depended on both the chemical composition of the sample and the calcination temperature employed for decomposing the precursor. After activation with hydrogen, samples were tested for the WGS reaction at 503 K. The turnover frequency of the eighteen samples tested was essentially the same (0.2–0.3 s −1 ) irrespective of changing the copper metal surface area between 3 and 35 m 2 /g Cu and the metallic copper dispersion between 0.5 and 5.0%. This indicated that the WGS reaction is a structure-insensitive reaction, as the specific reaction rate r 0 (mol CO/h/g Cu) is always proportional to the copper metal surface area. Preparation of mixed oxides with a high copper dispersion is therefore required for obtaining more active catalysts. It was found that the value of the metallic copper dispersion is related to the amount of hydrotalcite contained in the hydroxycarbonate precursor: the higher the hydrotalcite content in the precursor, the higher the copper metal dispersion in the resulting catalyst and, as a consequence, the higher the catalyst activity. Ternary Cu/ZnO/Al 2 O 3 catalysts exhibited a substantially faster WGS activity than binary Cu/ZnO catalysts. The addition of aluminium, although inactive for the WGS reaction, is required for improving the catalyst performance.

Oxidative stress and antioxidant content in Chlorella vulgaris after exposure to ultraviolet‐B radiation

Abstract: Growth of Chlorella vulgaris was measured in cultures irradiated with 0, 0.8, 2.0 and 4.4 kJ m -2 UV-B. Growth expressed as chlorophyll content, declined significantly with increased UV-B dose. Ultraviolet-B irradiated cultures in log phase of growth showed a 284% increase in oxygen radical generation and a 145% increase in lipid peroxidation compared with unirradiated cultures, whereas cultures in the stationary growth phase showed no significant changes in these parameters. The activities of superoxide dismutase and catalase increased by 40 and 500%, respectively, after exposure to a UV-B dose of 4.4 kJ m -2 . Contents of the lipophilic antioxidants α-tocopherol and β-carotene increased by 180 and 63 amol cell -1 respectively, between log and stationary phases in unirradiated cultures ; but in UV-B-irradiated cultures these increases were significantly depressed. Photoreducing capacities of chloroplasts were decreased following UV-B irradiation of both isolated chloroplasts and those isolated from irradiated algae. Cells exposed to UV-B exhibited increased size and starch accumulation. These results suggest that oxidative stress conditions related to UV-B exposure trigger an antioxidant response that includes an increase in the activity of the antioxidant enzymes (superoxide dismutase and catalase).

Molecular basis of antigen mimicry by an anti-idiotope

Abstract: IDIOTOPES are antigenic determinants, unique to an antibody or group of antibodies, defined by the reaction of anti-idiotopic antibodies with the antibodies bearing the idiotopes. The ensemble of idiotopes of an antibody constitutes its idiotype. Idiotypes are useful as markers to follow specific antibodies and clones of cells in immune responses and the inheritance of immunoglobulin genes. As external antigens and anti-idiotypic antibodies can competitively bind the combining site of specific antibodies, some anti-idiotypic antibodies may resemble the external antigen, thus mimicking its structure. It has been proposed1–5 that an anti-idiotypic antibody, anti-anti-X, may resemble the external antigen X and thus carry its 'internal image', but this idea is not unequivocally supported by the three-dimensional structures of anti-idiotopic antibodies6–9, either because the structures of the external antigen8 or of the anti-idiotopic antibody7 were unknown, or because the anti-idiotopic antibodies showed no resemblance to the external antigens6,9 (reviewed in ref. 10). Functional mimicry of ligands of biological receptors by anti-idiotypic antibodies has been described in several systems (reviewed in ref. 11). But how closely can antibodies mimic antigens at the molecular level? Here we present the crystal structure of an idiotope-anti-idiotope complex between the Fv fragments of the anti-lysozyme antibody D1.3 and the anti-D1.3 antibody E5.2. D1.3 contacts the antigen, lysozyme and the anti-idiotopic E5.2 through essentially the same combining-site residues. In addition, E5.2 interacts with D1.3, making contacts similar to those between lysozyme and D1.3. Thus, the anti-idiotopic antibody E5.2 mimics lysozyme in its binding interactions with D1.3. Validating these observations, E5.2, used as an immu-nogen, induces an anti-lysozyme response.

Phytochrome A, phytochrome B and HY4 are involved in hypocotyl growth responses to natural radiation in Arabidopsis: weak de‐etiolation of the phyA mutant under dense canopies

Abstract: The roles of phytochrome A (phyA), phytochrome B (phyB) and a putative blue-light (BL) photoreceptor (HY4) in the control of hypocotyl growth by natural radiation were investigated using phyA, phyB and hy4 mutants of Arabidopsis thaliana. Full sunlight inhibited hypocotyl growth to a larger extent in wild-type (WT) than in phyA, phyB and, particularly, hy4 seedlings. In WT seedlings, hypocotyl growth was promoted by selectively lowering BL irradiance, lowering red-light (R) plus far-red-light (FR) irradiance or lowering the R/FR ratio (which was achieved either by increasing FR or by reducing R). The effects of lowering BL were reduced in hy4 and exaggerated in phyA seedlings. The effects of lowering R+FR were reduced in phyA and exaggerated in hy4 seedlings. Neither phyB nor hy4 mutants responded to low R/FR ratios. Neighbouring plants reflecting FR without shading caused subtle reductions of the R/FR ratio. This signal promoted hypocotyl growth in WT but not in phyA, phyB or hy4 seedlings. Intermediate canopy shade produced similar effects in all genotypes. Under deep shade, de-etiolation was severely impaired in phyA seedlings, which died prematurely. Thus, the FR ‘high-irradiance reaction’ mediated by phyA could be important for seedling survival under dense canopies.

Role of nitric oxide in control of prolactin release by the adenohypophysis.

Abstract: Nitric oxide synthase-containing cells were visualized in the anterior pituitary gland by immunocytochemistry. Consequently, we began an evaluation of the possible role of NO in the control of anterior pituitary function. Prolactin is normally under inhibitory hypothalamic control, and in vitro the gland secretes large quantities of the hormone. When hemipituitaries were incubated for 30 min in the presence of sodium nitroprusside, a releaser of NO, prolactin release was inhibited. This suppression was completely blocked by the scavenger of NO, hemoglobin. Analogs of arginine, such as NG-monomethyl-L-arginine (NMMA, where NG is the terminal guanidino nitrogen) and nitroarginine methyl ester, inhibit NO synthase. Incubation of hemipituitaries with either of these compounds significantly increased prolactin release. Since in other tissues most of the actions of NO are mediated by activation of soluble guanylate cyclase with the formation of cyclic GMP, we evaluated the effects of cyclic GMP on prolactin release. Cyclic GMP (10 mM) produced an approximately 40% reduction in prolactin release. Prolactin release in vivo and in vitro can be stimulated by several peptides, which include vasoactive intestinal polypeptide and substance P. Consequently, we evaluated the possible role of NO in these stimulations by incubating the glands in the presence of either of these peptides alone or in combination with NMMA. In the case of vasoactive intestinal polypeptide, the significant stimulation of prolactin release was augmented by NMMA to give an additive effect. In the case of substance P, there was a smaller but significant release of prolactin that was not significantly augmented by NMMA. We conclude that NO has little effect on the stimulatory action of these two peptides on prolactin release. Dopamine (0.1 microM), an inhibitor of prolactin release, reduced prolactin release, and this inhibitory action was significantly blocked by either hemoglobin (20 micrograms/ml) or NMMA and was completely blocked by 1 mM nitroarginine methyl ester. Atrial natriuretic factor at 1 microM also reduced prolactin release, and its action was completely blocked by NMMA. In contrast to these results with prolactin, luteinizing hormone (LH) was measured in the same medium in which the effect of nitroprusside was tested on prolactin release, there was no effect of nitroprusside, hemoglobin, or the combination of nitroprusside and hemoglobin on luteinizing hormone release. Therefore, in contrast to its inhibitory action on prolactin release NO had no effect on luteinizing hormone release. Immunocytochemical studies by others have shown that NO synthase is present in the folliculostellate cells and also the gonadotrophs of the pituitary gland. We conclude that NO produced by either of these cell types may diffuse to the lactotropes, where it can inhibit prolactin release. NO appears to play little role in the prolactin-releasing action of vasoactive intestinal polypeptide and substance P, but mediates the prolactin-inhibiting activity of dopamine and atrial natriuretic factor.

Sowing Date Effects on Grain Yield Components for Different Maize Genotypes

Abstract: Shoot dry weight of maize (Zea mays L.) depends on the amount of photosynthetically active radiation intercepted by the crop (IPAR). The present work was conducted to analyze the variation in shoot dry weight production and its partitioning to reproductive sinks when seasonal changes of temperature and solar radiation occur during the growing cycle of the crop. Four commercial hybrids were grown at 8 plants m -2 on four sowing dates (20 Aug., 20 Sept., 20 Oct., and 20 Nov.) at Rojas (34 o 08'S, 60 o 59'W), Argentina, on a silty clay loam soil (Typic Argiudoll) during 1990-1991 and 1991-1992, with no water or nutrient restrictions. Shoot dry weight at physiological maturity was associated with the amount of IPAR, with radiation use efficiency before silking (4.14 g MJ -1 ) higher than after silking (2.45 g MJ -1 ). Grain yield was correlated with shoot dry weight at physiological maturity, resulting in a stable (0.46±0.02) harvest index. Shoot dry weight at silking showed a significant relationship with final grain number (r 2 =0.52, n=32) as well as with grain yield (r 2 =0.55, n=32). Ear dry weight at silking was associated with grain yield particularly for prolific hybrids (r 2 =0.64, n=16). Provided postsilking conditions do not limit assimilate supply to the grains, shoot dry weight at silking could be considered a good grain yield predictor. In temperate regions, maize potential productivity seems to be more limited by the amount of solar radiation available around silking (determinant of grain set) than during grain filling (determinant of grain weight). Early and intermediate sowings tend to best utilize solar radiation for grain production

Yield, biomass and yield components in dwarf, semi-dwarf and tall isogenic lines of spring wheat under recommended and late sowing dates

Abstract: Grain yield and some of its physiological determinants were analysed in a field study conducted over two growing seasons with standard-height (SH), semi-dwarf(SD) and dwarf (DD) isogenic lines ofa spring wheat sown at recommended and delayed dates. The objective was to test whether the action of Rht1 and Rht2 alleles in improving grain yield depended upon sowing date. As expected, the dwarfing genes significantly reduced plant height in both sowings and growing seasons. There was a tendency for the SD line to produce more biomass than the SH and DD lines, although the differences were mostly not significant. Harvest index was linearly and negatively related to plant height. Consequently, the SD and SH line showed the highest and lowest grain yields in all environments. The optimum height for grain yield was estimated to be c. 70 cm, and this value was not affected by sowing date. Lines carrying Rhtl and/or Rht2 alleles always showed more grains/m 2 (owing to an increased number of grains per spike and spikes/m 2 ) than the SH line. Conversely, average grain weight was negatively associated with the number of grains/m 2 . Because the slope of this negative relationship was smaller (less negative) than that representing complete compensation, the relationship between grain yield and number of grains/m 2 was hyperbolic. Although these relationships are frequently regarded as a reflection of increased competition among grains when the number of grains/m 2 is increased owing to the use of semi-dwarf genes, two alternative hypotheses are analysed and discussed.

An L ∞ bound for solutions of the Cahn-Hilliard equation

Abstract: In this paper we consider the equation $$\partial _t u^\varepsilon = \Delta u^\varepsilon + \sum\limits_{i,j = 1}^n {\partial _{ij} f_{ij} (} u^\varepsilon ,x) - \varepsilon ^2 \Delta ^2 u^\varepsilon $$ with fij constant when u e is large, and we obtain L∞ bounds independent of ɛ > 0.

Mycoflora of Argentinian corn harvested in the main production area in 1990.

Abstract: Corn (Zea mays) is the main cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the corn kernels. This paper reports on the identification of internal and external mycoflora of corn kernels harvested in the main production area in Argentina in 1990. A mycological survey was carried out on 178 corn samples, from five locations in that area and the isolation frequency and relative density of the prevalent fungal genera compared. GenusFusarium was the most prevalent component of the internal seedborne mycoflora in the five locations.Penicillium was prevalent in all locations, taking into account the frequency. However, this genus was predominant only in two locations, when the relative density was considered. The predominantFusarium wasF. moniliforme and the most frequently isolated species ofAlternaria, Aspergillus andPenicillium wereA. alternata, A. flavus andP. decumbens, respectively.Diplodia species were not isolated from any of the samples.

Inhibition of hypocotyl elongation by ultraviolet‐B radiation in de‐etiolating tomato seedlings. I. The photoreceptor

Abstract: Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by 620 μmol m −2 s −1 between 320 and 800 nm), and was similar in wild-type and phytochrome-I-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m −2 s −1 of monochromatic UV radiation against a white light background (63 μmol m −2 s −1 ) showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN 3 and phenylacetic acid) largely abolished the inhibitory effect of broad-band UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10 −4 M, which have been shown in vitro to be effective in quenching the triplet excited states of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation exerted by UV-B. KI applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system involved in UV-B perception by tomato seedlings during de-etiolation may be a flavin

Cardiovascular tests of autonomic function and sympathetic skin responses in patients with major depression.

Abstract: To assess the function of the autonomic nervous system in major depression, a series of cardiovascular tests, together with the recording of sympathetic skin response, were performed in 18 depressed patients (melancholic type, DSM-III-R criteria) and in 18 healthy control subjects. Depressed patients showed significantly poorer performance in Valsalva's, deep breathing, and lying to standing manoeuvres than controls, indicating an impairment of parasympathetic function. Depressed patients developed a significantly larger sympathetic skin response than controls during the lying to standing and hand grip manoeuvres, whereas cardiovascular sympathetic performance (as assessed by the responses to hand grip, cold, mental arithmetic, explosive sound, or hyperventilation) was similar in both groups. The results are compatible with the view that a diminished parasympathetic reactivity, and presumably an increased sympathetic reactivity, occur in patients with major depression.

Time-frequency analysis of electroencephalogram series.

Abstract: In this paper we propose a method, based on the Gabor transform, to quantify and visualize the time evolution of the traditional frequency bands defined in the analysis of electroencephalogram (EEG) series. The information obtained in this way can be used for the information transfer analyses of the epileptic seizure as well as for their characterization. We found an optimal correlation between EEG visual inspection and the proposed method in the characterization of paroxism, spikes, and other transient alterations of background activity. The dynamical changes during an epileptic seizure are shown through the phase portrait. The method proposed was examplified with EEG series obtained with depth electrodes in refractory epileptic patients.

Oxidative damage to proteins and lipids of CNS myelin produced by in vitro generated reactive oxygen species

Abstract: Purified myelin isolated from 70-day-old rats was submitted to nonenzymatic peroxidative systems containing 100 μM FeC13.6H2O,100 μM ascorbic acid, and 100 μM CuSO4.6H2O 10 mM H2O2 in order to investigate the extent of damage produced by reactive oxygen species (ROS). Iron and copper catalyzing systems were selected because of the known importance of these metals in producing free radical chain reactions in biological membranes (Halliwell and Gutteridge: “Free Radicals in Biology and Medicine,” Oxford: Clarendon Press, 1989). Our findings, show that (1) although after 1 hour of peroxidation, an important level of thiobarbituric acid-reactive substances (TBARS) was detected, polyunsaturated fatty acids (20:2; 20:4; 22:4 and 22:6) were markedly affected only after 14 hours of incubation; (2) protein thiol groups were very sensitive to the attack of ROS generated by copper but resistant to iron-generated ROS; (3) aggregation of myelin proteins produced by peroxidation could be prevented by sulfhydryl (SH)-reducing agents, and (4) as a consequence of these modifications, compact myelin suffered disruption of its intraperiodic line. In conclusion, our results demonstrate that this unique membrane of the central nervous system (CNS) is highly vulnerable to oxidative stress and that this susceptibility to oxidative damage could be prevented, at least partially, by the use of SH-protective molecules. © 1995 Wiley-Liss, Inc.

Using phenology prediction in weed management: a review

Abstract: Summary The success of weed management based on ecological principles and weed biology will depend on a better understanding of the effect of environment on lift history strategies, growth, and competition of weeds; and crops, and particularly upon the ability to predict weed and crop phenology, This paper reviews the importance of phenotypic plasticity to weed and crop competition and other biological interactions We also discuss the utility of phenological predictions in weed management and review current weed phenology models that are based on thermal time By understanding the variables that drive plant phenotypic responses, new approaches and more long-term solutions for weed problems can be developed