NONSYMBIOTIC AND SYMBIOTIC NITROGEN FIXATION IN A WEAKLY MINEROTROPHIC PEATLAND

The acetylene reduction assay was used to measure nonsymbiotic and symbiotic nitrogen fixation in a weakly minerotrophic peatland throughout the ice-free season. Nonsymbiotic nitrogen fixation was found in surface materials and subsurface peat. In surface materials, nitrogenase activity measured in the field contributed about 0.6 kg N ha^-1 yr^-1, was closely associated with Sphagnum, but was not correlated with temperature between 12 and 27 C. No cyanobacteria were found in association with Sphagnum. In subsurface peat, nitrogenase activity measured in situ contributed no more than 0.4 kg N ha^-1 yr^-1 and was closely correlated with temperature between 7 and 21 C. There were uncertainites in these measurements due to presence of ethylene oxidizing activity and a long time lag. Symbiotic nitrogen fixation was found only in actinomycete-induced root nodules of Myrica gale L. Legumes were absent and the few lichens present lacked nitrogenase activity. Based on acetylene reduction assays, Myrica gale fixed about 35 kg N ha^-1 yr^-1. Nitrogenase activity in Myrica gale showed a strong seasonal pattern which varied little during three consecutive years even though water levels varied substantially. Nitrogen input to the peatland from nonsymbiotic nitrogen fixation was only 15% the amount contributed by bulk precipitation. Symbiotic fixation, in contrast, contributed approximately six times the amount in bulk precipitation.     

Effect of spring flooding on endophyte differentiation,nitrogenase activity,root growth and shoot growth inMyrica gale

Summary Spring flooding was investigated as a possible limiting factor in the development of nitrogenase activity, root growth, and shoot growth inMyrica gale. Dormant, one year oldMyrica gale plants were placed in a greenhouse in early April and given three treatments: control (not flooded), flooded-water (flooded with water to 2.5 cm above the soil level) and flooded-peat (flooded with water-saturated peat to 4.0 cm above the soil level). Nitrogenase activity was absent at budbreak but appeared concurrently with the differentiation of vesicles by theFrankia sp. endophyte. Flooding delayed the onset of nitrogenase activity, substantially reduced the specific nitrogenase activity of the nodules, and also severely limited the production of the new nodule biomass. Consequently by 67 days past budbreak nitrogenase activity was much greater in the control plants (5.55±0.42 mol C₂H₄/plant.h; ± SE; N=9) than in the flooded-water (1.18±0.29) and flooded-peat (0.15±0.05) plants. Production of new secondary roots was substantially reduced in the flooded plants but adventitious roots were rapidly produced along the flooded portion of the stem in the better aerated zone near the surface. New nodules formed on several adventitious roots by 67 days indicating that the plants are able to replace their largely nonfunctional deeply flooded nodules with new nodules in the aerobic zone. Initially shoot growth was unaffected by flooding but by 67 days the flooded plants had substantially less leaf biomass, lower leaf and stem nitrogen concentrations, and less total shoot nitrogen content than the control plants.     

The induction of nitrogenase activity in Rhizobium by non-legume plant cells

Summary Nitrogen fixation was induced in a strain of cowpea rhizobia, 32Hl, when it was grown in association with cell cultures of the non-legume, tobacco (Nicotiana tabacum). Rhizobia grown alone on the various media examined did not show nitrogenase activity, indicating the involvement of particular plant metabolites in nitrogenase induction. Nitrogenase activity, as measured by C₂H₂ reduction, was maximized at an O₂ concentration of 20% and at an assay temperature of 30°C, the conditions under which the plant cell-rhizobia associations developed. Glutamine, as a nitrogen source, could be replaced by other organic nitrogen sources, but NH₄ ⁺ and NO₃ ^- repressed nitrogenase activity. Nitrogenase activity induced in rhizobia when cultured adjacent to, but not in contact with, the plant cells could be stimulated by providing succinate in the medium. At least 12 other strains of rhizobia also reduced C₂H₂ in association with tobacco cells; the highest levels of activity were found among cowpea strains.     

Changes in Nitrogen Metabolism of Vigna Radiata in Response to Elevated CO2

With the aim to determine the effects of CO₂ on nitrogen metabolism mungbean (Vigna radiata) plants were grown from seedling emergence to maturity inside open top chambers under ambient CO₂ (CA, 350 ± 25 µmol mol^–1) and elevated CO₂ (CE, 600 ± 50 µmol mol^–1) concentrations at the Indian Agricultural Research Institute, New Delhi. Leaflet blades of the same physiological age were sampled at 20, 35 and 50 d after germination. Total nitrogen concentration in dry mass was consistently lower under CE than in CA. Non-protein nitrogen and protein nitrogen were also decreased under CE Total soluble protein content also decreased up to 35 d after germination under CE. However, a 27 % increase in protein content at 50 d after germination due to CE was observed. A significant decrease in total free amino acid under CE at 20 d after germination was observed. CE also brought about a remarkable decrease in the activity of nitrate reductase in leaves at 20 d after germination but increase at 35 d and 50 d after germination. Nitrogenase activity increased at all growth stages due to CE. Although total harvested leaves of CE plants accumulated more nitrogen, the relative amount of nitrogen on a percentage basis was low, probably due to a comparatively greater accumulation of sugars in the leaves of CE plants.     

The effects of elevated temperature and humidity on rectal temperature and respiration rate in the New Zealand white rabbit

In 2 replicated factorial experiments, 7-h climate chamber exposures were used to study the responses of adult NZW rabbits to a range of elevated temperatures and humidities. At 18 mm Hg water vapour pressure, 23.8° C was well tolerated, rectal temperature (RT) and respiration rate (RR) averaging 38.6±0.3° C and 82.9±15.5 breaths/min, respectively. Both parameters were elevated (P<0.001) at 32.2°, 37.8° and 43.3° C. RT and RR reached plateau levels of 39.5–40.1° C and 410–460/min at 32.2° C, which was tolerated for the full 7-h test period. Test temperatures of 37.8° and 43.3° C, on the other hand, could be tolerated for only 80 and 40 min respectively, before RT reached the safe upper limit of 41.7° C. Final RR values at 37.8° and 43.3° C were 701.6±42.7 and 812±55.1/min, respectively. In a 34.5° C atmosphere a humidity of 21 mm Hg water vapour pressure was classified as dry, and was tolerated for 323±123 min. RT and RR increased by 0.6° C and 316/min during the first 20 min of exposure (P<0.05). Thereafter both parameters increased progressively, but with no significant differences between successive recording periods, until RR reached 550.3±88.8/min at 41.7° C RT. Humidities of 25, 29 and 33 mm Hg water vapour pressure were, on the other hand, classified as wet and were tolerated for only 92±22, 81±16 and 119±50 min, respectively. RR at the times that RT reached 41.7° C at these 3 humidities was 732±26, 789±30 and 764±23/min, respectively. The results point to the likelihood that thermal stress will adversely affect the productivity and welfare of NZW rabbits in the tropics unless adequate housing environments are provided. Significant between-individual phenotypic differences in heat tolerance suggest the need for genetic studies of the possibility of selecting for improved heat tolerance.     

Denitrification and dinitrogen fixation in two quaking fens in the Vechtplassen area,The Netherlands

This paper reports laboratory experiments on dinitrogen fixation and denitrification for two small quaking fens (discharge fen and recharge fen) using the acetylene reduction assay and the acetylene inhibition technique, respectively.Nitrogenase activity was detected in peat muck and associated with Alnus glutinosa saplings throughout the study period (May–October 1987), whereas no activity was observed with Sphagnum species. The annual amount of dinitrogen fixed was estimated at 2.1 and 12.7 kg N/ha/y for the recharge fen and the discharge fen, respectively.Denitrification at ambient nitrate levels (0.1 ppm NO₃) was absent in the discharge fen and very low in the recharge fen (0.1 g N/g/d, or 0.3 kg N/ha/y). In nitrate-amended soil samples denitrification rates were 2 to 3 orders of magnitude higher. It is argued that in situ denitrification rates in the fens studied will depend almost entirely on the nitrate supply by precipitation. Denitrification rates associated with precipitation are estimated at 1.1 kg N/ha/y for both fens.     

Reduction of acetylene by nodules of Trifolium subterraneum as affected by root temperature,Rhizobium strain and host cultivar

Summary The nitrogenase activity (measured by reduction of C₂H₂ to C₂H₄) of nodules of Trifolium subterraneum grown at root temperatures from 7°C–19°C was broadly correlated with nitrogen fixation. Root temperature did not affect enzyme activity per se but did affect the amount of enzyme formed. Exposure of nodules to 7°C for 24 h did not decrease activity cf. 19°C. Activity was greatest when nodules were about 4 days old, before swollen bacteroid forms were produced, and then declined. The effectiveness of a bacterial strain at a given temperature was related to the amount of enzyme produced and to its persistence. Nitrogenase activity should be measured throughout the plant growth cycle for valid comparisons of strain effectiveness.     

Calmodulin selectively modulates the guanylate cyclase activity by repressing the lipid phase separation temperature in the inner half of the bilayer of rat brain synaptosomal plasma membranes

The association of [¹²⁵I-]calmodulin with rat brain synaptosomal plasma membranes, when incubated for 1 h at 25° in the presence or in absence of 20 M Ca²⁺, follows a sigmoid path with a Hill coefficient h=1.79±0.12 and h=1.72±0.11, respectively. The total association of calmodulin with the membrane increased approx. 60%–80% at all the range of calmodulin concentrations used in the presence of 20 M Ca²⁺. A three fold increase of guanylate cyclase activity was shown in the presence of low concentrations of calmodulin (up to 10 mM); higher concentrations (up to 40 mM) however, led to a progressive inhibition of the enzyme activity with respect to maximal stimulation. Calmodulin increased the lipid fluidity of synaptosomal plasma membranes labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH), as indicated by the steady-state fluorescence anisotropy [(r_o/r)-1]^–1. Arrhenius-type plots of [(r_o/r)-1]^–1 indicated that the lipid separation of the membrane at 22.7±1.2° was perturbed by calmodulin such that the temperature was reduced to 16.3±0.9° and 15.5±0.8° in the absence or in the presence of 20 M Ca²⁺. Arrhenius plots of guanylate cyclase and acetylcholinesterase activities exhibited brak points at 25.7±1.4° and 22.3±1.0° in control synaptosomal plasma membranes, respectively. The break point for the guanylate cyclase was reduced to 16.3±0.9° in calmodulin treated synaptosomal plasma membranes whereas that of acetylcholinesterase remained unaffected (21.1±0.9°). The allosteric properties of guanylate cyclase by Mn-GTP (as reflected by changes in the Hill coefficient) were modulated by calmodulin while those of acetylcholinesterase by fluoride (F^–) were not altered. We propose that calmodulin achieves these effects through asymmetric perturbations of the membrane lipid structure and that increase in membrane fluidity of the inner leaflet of the membrane induced by calmodulin may be an early key event to the process of neurotransmitter release.     

Influence of photoperiod,temperature and host plant on the production of diapause eggs inPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) diapauses in the egg stage. Adult females lay either diapause or nondiapause eggs. On the University of Thessaloniki campus (41°N), the mite was found to develop on leaves ofOxalis corniculata L. throughout the year, while no mites were found on leaves ofOxalis articulata Savigny growing in the same area. In the laboratory the mite could be maintained equally well on detached leaves of both plant species, kept on wet cotton-wool.Forty to 90% females laying diapause eggs (dlf) were produced when the mites developed under LD 1212 and 19±1 °C, or LD 168 and 19±1 °C or 25±1 °C on leaves ofO. articulata detached from plants grown in the open in various seasons. Under the same conditions, a very low to zero percentage ofdlf was produced onO. corniculata. By rearing certain feeding stages on one of these twoOxalis hosts, and the other feeding stages on the other host, various percentages ofdlf were obtained. These percentages were the net effect of the antagonistic action of the twoOxalis species.By rearing the mites at LD 8.515.5, LD 1212 or LD 168 and a temperature of 19±1 °C onO. articulata leaves renewed every 3 days, or every 16–18 days, or not at all, it could be shown that diapause induction or aversion is caused by the direct effect of photoperiod on the mites, and not by an effect through the host leaves.When wholeO. articulata plants were grown under LD 168 and 19±1 °C in the laboratory, or developed in the open during April and May, flowers were produced, while under LD 1212 no flowering occurred. In the laboratory under diapause-inducing conditions, higher percentages ofdlf were produced on leaves detached from flowering plants than on leaves detached from plants not flowering.OnO. articulata leaves at 20 °C, photoperiods with photophases equal to or longer than 12 h induced from 70 to 80%dlf, while photoperiods with photophases equal to or shorter than 10.9 h induced very low to zero percentages. By transferring different chrysalis stages from a diapause-inducing (LD 1212) to a diapause-averting (LD 8.515.5) photoperiod, and vice versa, it was found that the nymphochrysalis through deutonymph stages were sensitive to photoperiod, the deutochrysalis and deutonymph being the most sensitive.Under an LD 1212 photoperiod, a temperature of 20 °C induced diapause, whereas 25 °C, 30 °C, or a daynight thermoperiod of 25 °C18 °C suppressed it.     

Physiology of nitrogen fixation in Azospirillum lipoferum Br 17 (ATCC 29 709)

Changes of cellular activities during batch cultures with Azospirillum lipoferum strain Br 17 (ATCC 29 709) were observed within the growth cycle, at optimal pO₂ (0.002–0.003 atm). The relative growth rate for cells growing with N₂ as sole nitrogen source during log phase was =0.13 h^-1 and the doubling time was 5.3 h. Nitrogenase activity was not accompanied by hydrogen evolution at any growth stage, and a very active uptake hydrogenase was demonstrated. The hydrogenase activity increased towards the end of the growth period when glucose became limiting and N₂ fixation reached its maximal specific activity. Oxygen consumption and oxygen tolerance at the various growth stages, increased simultaneously with the uptake hydrogenase activity indicating a possible role of this enzyme in an oxygen protection mechanism of A. lipoferum nitrogenase. The efficiency of nitrogen fixation expressed as mg total nitrogen fixed in cells and supernatant per g glucose consumed, was 20 at the early log phase and increased to 48 at the late log phase. About 25% of the total fixed nitrogen was recovered in the culture supernatant.Abbreviations DOT Dissolved oxygen tension - PHB Poly--hydroxybutyric acid - O.D. Optical density (560 nm) - A.T.C.C. American type culture collection - NTA Nitrilotriacetic acid Graduate student of the Universidade Federal Rural do Rio de Janeiro, Brazil     

Solid-state fermentation of carob pods for ethanol production

The production of ethanol from carob pods by Saccharomyces cerevisiae in solid-state fermentation was investigated. The maximal ethanol concentration (160±3 g/kg dry pods), ethanol productivity (6.7 ± 0.2 g/kg per hour), ethanol yield (40 ± 1.8%), biomass concentration (7.5 ± 0.4 x 10⁸ cells/g carob pulp) and fermentation efficiency (80 ± 2%) were obtained at an inoculum amount of 3%, a particle size of 0.5 mm, a moisture level of 70%, a pH of 4.5 and a temperature of 30°C. Under the same fermentation conditions both sterilized and non-sterilized carob pods pulp gave the same maximum ethanol concentration.     

Prediction of evapotranspiration and grain yield of rice (Oryza sativa L. cv Thriveni) in a humid tropical climate

Summary In a humid tropical climate at Pattambi (10° 48 N, 76° 12 E), the evapotranspiration (ET) rates of rice (Oryza sativa L. cv. Thriveni) were 2.8–5.7 mm/day during the first crop season (May–September) and 6.2–9.1 mm/day during the second crop season (September–January). The crop was grown at the Station in the irrigated lowlands on sandy soils with average yields of 3025 and 2925 kg/ha in the first and second cropping seasons, respectively. The seasonal ET, water requirements, water use efficiency and field water use efficiency of the crop were 400 mm, 1150 mm, 7.56 and 2.63 kg/ha per mm in the first crop season and 650 mm, 1500 mm, 4.50 and 1.95 kg/ha per millimetre in the second crop season. Using the reference crop ET computed by Blaney-Criddle, Radiation, and Penman methods and measured evaporation from class A pan, Colorado and GGI 3000 pans, the crop coefficients were worked out. Correlations between weather parameters and the biomass of rice were obtained. The grain yield (Y, in kg/ha) of the crop was predicted using the equationY=1.71Y ₀–56S+85F–2430 (N=8,r=0.920), whereY ₀ is the sample of biomass of the rice at flowering in kg/ha,S andF are the duration of sunshine hours and maximum air temperatures (°C) between the 46th day of transplanting and maturity.     

Cold-hardening results in increased activity of enzymes involved in carbon metabolism in leaves of winter rye (Secale cereale L.)

Light- and CO₂-saturated photosynthesis of nonhardened rye (Secale cereale L. cv. Musketeer) was reduced from 18.10 to 7.17 mol O₂·m^–2·s^–1 when leaves were transferred from 20 to 5°C for 30 min. Following cold-hardening at 5°C for ten weeks, photosynthesis recovered to 15.05 mol O₂·m^–2·s^–1,comparable to the nonhardened rate at 20°C. Recovery of photosynthesis was associated with increases in the total activity and activation of enzymes of the photosynthetic carbon-reduction cycle and of sucrose synthesis. The total hexose-phosphate pool increase by 30% and 120% for nonhardened and cold-hardened leaves respectively when measured at 5°C. The large increase in esterified phosphate in coldhardened leaves occurred without a limitation in inorganic phosphate supply. In contrast, the much smaller increase in esterified phosphate in nonhardened leaves was associated with an inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase and sucrose-phosphate synthase activation. It is suggested that the large increases in hexose phosphates in cold-hardened leaves compensates for the higher substrate threshold concentrations needed for enzyme activation at low temperatures. High substrate concentrations could also compensate for the kinetic limitations imposed by product inhibition from the accumulation of sucrose at 5°C. Nonhardened leaves appear to be unable to compensate in this fashion due to an inadequate supply of inorganic phosphate.Abbreviations DHAP dihydroxyacetone phosphate - Fru6P fructose-6-phosphate - Fru 1,6BP fructose-1,6-bisphosphate - Fru1,6BPase fructose-1,6-bisphosphatase - Glc6P glucose-6-phosphate - PGA 3-phosphoglycerate - PPFD photosynthetic photon flux density - CH cold-hardened rye grown at 5°C - NH nonhardened rye grown at 24°C - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - SPS sucrose-phosphate synthase - UDPGlc uridine 5-diphosphoglucose This work was supported by operating grants from the Swedish Natural Sciences Research Council to G.Ö. and P.G.     

Properties of microsomal acyl-CoA: lysophosphatidylcholine acyltransferase from liver of thermally-acclimated rainbow trout,Salmo gairdneri

Summary Acyl-CoA: lysophosphatidylcholine acyltransferase (LPCAT) (EC 2.3.1.23) activity was assayed in liver microsomes from rainbow trout,Salmo gairdneri, acclimated to 5°C and 20°C to assess its contribution to the temperature-induced restructuring of phospholipid acyl chain composition. The synthesis of phosphatidylcholine (PC) (from lyso-PC) was threefold the synthesis of phosphatidylethanolamine (PE) (from lyso-PE) under similar assay conditions. LPCAT activity (i) displayed an absolute requirement for lysophosphatidylcholine (LPC) and was enhanced by the presence of ATP, MgCl₂ and CoA (which reduced the impact of endogenous acyl-CoA hydrolase activity by regenerating the acyl-CoA substrate) in the assay medium; (ii) remained linear with time up to 30 min; and (iii) increased linearly with microsomal protein concentration up to 0.2 mg/ml for the 20°C assay and 0.4 mg/ml for the 5°C assay. There was no difference in K_m or V_max values due to the acclimation history of the fish, but there were obvious differences due to assay temperature. The apparent K_m values for LPC were 58.54±7.24 M and 12.26±2.14 M when assayed at 5°C and 20°C respectively; values for oleoyl-CoA were 9.11±0.78 M and 1.23±0.25 M under the same assay conditions. Activity was 1.99±0.31 nmol min^–1 mg protein^–1 when assayed at 5°C, and 3.8±0.45 nmol min^–1 mg protein^–1 when assayed at 20°C. These findings indicate that adjustments in the activity of LPCAT play no significant role in the temperature-induced restructuring of PC molecular species composition. However, the marked temperature dependence of the K_m values for LPC and oleoyl CoA suggest that patterns of fatty acid incorporation (i.e. substrate preference) may vary with assay temperature, and in this way LPCAT could contribute to the restructuring response.Abbreviations PC phosphatidylcholine - PE phosphatidylethanolamine - LPCAT acyl-CoA: lysophosphatidylcholine acyltransferase - LPEAT acyl-CoA: lysophosphatidylethanolamine acyltransferase - LPC 1-palmitoyl,2-lysophosphatidylcholine     

Nodulation,accumulation and redistribution of nitrogen in soybean (Glycine max (L.) Merrill) as influenced by seed inoculation and scheduling of irrigation

Summary A field experiment was conducted on soybean (Glycine max (L.) Merrill) with a view to find out the effect of seed inoculation and scheduling of irrigation on nodulation, accumulation and re-distribution of nitrogen in plant tops and soil. The eight treatment combinations consists of two seed inoculations,viz. uninoculated and inoculated with rhizobium culture, and four irrigation schedules,viz. irrigation water to the cumulative pan evaporation (IW/CPE) ratio of 0.5, 0.7, 0.9 and a control (rainfed). Seed inoculation by, rhizobium culture increased the number, dry-weight and N content of nodules per plant. Inoculation of seeds also increased the N accumulation rate in plant top and it was 2.48 kg/ha/day during the flower-initiation to the pod-initiation stage (30–60 days interval). At harvest, 32.2, 47.8 and 26.2 kg N/ha was re-distributed from the stems, leaves and pods-wall of inoculated plants to the grains, respectively. A total of 186.5 kg N/ha was harvested and 64.7 kg N/ha, was accumulated in soil under the inoculated condition.Scheduling of irrigation at 0.7 IW/CPE proved better, than other irrigation schedules and helped in increasing the nodulation, nitrogen accumulation and grain yield. As compared to control, 8.4, 17.8 and 18.4 kg more of N/ha was redistributed from the stems, leaves and pods-wall respectively when the irrigations were scheduled at 0.7 IW/CPE ratio. Under this irrigation schedule the total N harvest was 200.1 kg/ha while the total N increased by 55.9 kg over that present in soil at the time of sowing.     

Stable sulfur isotopic biogeochemistry of the Hubbard Brook Experimental Forest, New Hampshire

In natural ecosystems, differences often exist in the relative abundanceof stable S isotopes (°³⁴S) that can provide clues as tothe source, nature, and cycling of S. Values of °³⁴S inprecipitation, throughfall, soils, soil solution, and stream waters weremeasured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire.Values of °³⁴S in precipitation and throughfall weresimilar to each other but differed seasonally. Precipitation°³⁴S values were higher in the dormant season[°³⁴S = 5.9±0.6 (17)][Mean + SE(N)]than in the growing season [°³⁴S = 5.0±0.6(40)] but throughfall growing-season values were higher[°³⁴S = 5.6±0.6(68)] than for the dormantseason [°³⁴S = 4.9±0.7 (9)]. Different treespecies did not affect throughfall °³⁴S values. In soilsolution, °³⁴S values were higher in the growing season(°³⁴S = 8.9±2.8; 8.8±1.7;and 4.0±0.6 for Oa, Bh, and Bs horizons, respectively) thanin the dormant season (°³⁴S = 5.6±1.5;3.7±2.4; and 3.4±1.2 for Oa, Bh, and Bshorizons, respectively). These seasonal differences in°³⁴S were probably caused by biological isotopicfractionation. The °³⁴S values in streams were generally2 lower and more variable than those in precipitation andthroughfall, suggesting fractionation and/or different isotopic sources inthe soil.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.     

Expression of the hygromycin B phosphotransferase gene confers tolerance to the herbicide glyphosate

Escherichia coli cells and tobacco (cv. Xanthi) plants transformed with the hygromycin B phosphotransferase gene were able to grow in culture medium containing glyphosate at 2.0 mM. The growth of tobacco calli in media containing increasing glyphosate concentrations was measured. The ID₅₀ for glyphosate was 1.70±0.03 mM for hygromycin-B resistant plants, and 0.45±0.02 mM for control plants. Regenerated plants and progeny selected for resistance to hygromycin B were tested for glyphosate tolerance by spraying them with Faena herbicide (formulated glyphosate with surfactant) at a dose equal to 0.24 kg/ha. This was two times the dose required to kill 100 percent of the control plants. Phosphotransferase activity was measured in the extracts of the transformed leaves by the incorporation of ³²P from [^–32P]ATP and it was observed that hygromycin B phosphotransferase was able to recognize the molecule of glyphosate as substrate.Abbreviations (Hyg) Hygromycin - (Km) Kanamycin - (Glp) Glyphosate - (Sarc) Sarcosine - (AMPA) Aminomethylphosphonic acid     

Effects of constitutive expression of nitrate reductase in transgenic Nicotiana plumbaginifolia L. in response to varying nitrogen supply

Transformed Nicotiana plumbaginifolia plants with constitutive expression of nitrate reductase (NR) activity were grown at different levels of nitrogen nutrition. The gradients in foliar NO ₃ ^– content and maximum extractable NR activity observed with leaf order on the shoot, from base to apex, were much decreased as a result of N-deficiency in both the transformed plants and wild type controls grown under identical conditions. Constitutive expression of NR did not influence the foliar protein and chlorophyll contents under any circumstances. A reciprocal relationship between the observed maximal extractable NR activity of the leaves and their NO ₃ ^– content was observed in plants grown in nitrogen replete conditions at low irradiance (170 mol photons·m^–2 ·s^–1). This relationship disappeared at higher irradiance (450 mol photons·m^–2·S^–1) because the maximal extractable NR activity in the leaves of the wild type plants in these conditions increased to a level that was similar to, or greater than that found in constitutive NR-expressors. Much more NO ₃ ^– accumulated in the leaves of plants grown at 450 mol photons·m^–2·s^–1 than in those grown at 170 mol photons·m^–2·s^–1 in N-replete conditions. The foliar NO ₃ ^– level and maximal NR activity decreased with the imposition of N-deficiency in all plant types such that after prolonged exposure to nitrogen depletion very little NO ₃ ^– was found in the leaves and NR activity had decreased to almost zero. The activity of NR decreased under conditions of nitrogen deficiency. This regulation is multifactoral since there is no regulation of NR gene expression by NO ₃ ^– in the constitutive NR-expressors. We conclude that the NR protein is specifically targetted for destruction under nitrogen deficiency. Consequently, constitutive expression of NR activity does not benefit the plant in terms of increased biomass production in conditions of limiting nitrogen.Abbreviations Chl chlorophyll - N nitrogen - NR NADH-nitrate reductase - WT wild type     

Myocardial content of selected elements in experimental anthracycline-induced cardiomyopathy in rabbits

Cardiotoxicity represents the main drawback of clinical usefulness of anthracycline antineoplastic drugs. In this study, a content of selected elements (Ca, Mg, K, Se, Fe) in the post-mortem removed samples of the myocardial tissue was studied in three groups of rabbits: 1) control group (i.v. saline; n = 10); 2) daunorubicin-receiving animals (DAU; 3 mg/kg, i.v; n=11); 3) animals receiving cardioprotective iron-chelating agent dexrazoxane (DEX; 60 mg/kg, i.p.; n=5) prior to DAU. Drugs were administered once weekly for 10 weeks. 5–7 days after the last administration, cardiac left ventricular contractility (dP/dt_max) was significantly decreased in DAU-treated animals (745 ± 69 versus 1245 ± 86 kPa/s in the control group; P < 0.05), while in the DEX+DAU group it was insignificantly increased (1411 ± 77 kPa/s). Of the myocardial elements content studied, a significant increase in total Ca against control (16.2 ± 2.4 versus 10.6 ± 0.9 g/g of dry tissue; P < 0.05) was determined in the DAU-group, which was accompanied with significant decreases in Mg and K. In the heart tissue of DEX-pretreated animals, no significant changes of elements content were found as compared to controls, while the Ca content was in these animals significantly lower than in the DAU group (9.1 ± 0.4 versus 16.2 ± 2.4 g/g; P < 0.05). Hence, in this study we show that systolic heart failure induced by chronic DAU administration is primarily accompanied by persistent calcium overload of cardiac tissue and the protective action of DEX is associated with the restoration of normal myocardial Ca content.Published online: March 2005