Proton-Translocating Inorganic Pyrophosphatase in Red Beet (Beta vulgaris L.) Tonoplast Vesicles

The substrate and ionic requirements of ATP and inorganic pyrophosphate (PPi) hydrolysis by tonoplast vesicles isolated from storage tissue of red beet (Beta vulgaris L.) were compared with the requirements of ATP-and PPi-dependent proton translocation by the same material. Both ATP hydrolysis and ATP-dependent proton translocation are most stimulated by Cl⁻ and inhibited by NO₃⁻. NaCl and KCl support similar rates of ATP hydrolysis and ATP-dependent proton translocation while K₂SO₄ supports lesser rates for both. PPi hydrolysis and PPi-dependent proton translocation are most stimulated by K⁺. KCl and K₂SO₄ support similar rates of PPi hydrolysis and PPi-dependent proton translocation but NaCl has only a small stimulatory effect on both. Since PPi does not inhibit ATP hydrolysis and ATP does not interfere with PPi hydrolysis, it is inferred that the two phosphohydrolase and proton translocation activities are mediated by different tonoplast-associated enzymes. The results indicate the presence of an energy-conserving proton-translocating pyrophosphatase in the tonoplast of red beet.     

Effects of light intensity and oxygen on photosynthesis and translocation in sugar beet

The mass transfer rate of ¹⁴C-sucrose translocation from sugar beet (Beta vulgaris, L.) leaves was measured over a range of net photosynthesis rates from 0 to 60 milligrams of CO₂ decimeters⁻² hour⁻¹ under varying conditions of light intensity, CO₂ concentration, and O₂ concentration. The resulting rate of translocation of labeled photosynthate into total sink tissue was a linear function (slope = 0.18) of the net photosynthesis rate of the source leaf regardless of light intensity (2000, 3700, or 7200 foot-candles), O₂ concentration (21% or 1% O₂), or CO₂ concentration (900 microliters/liter of CO₂ to compensation concentration). These data support the theory that the mass transfer rate of translocation under conditions of sufficient sink demand is limited by the net photosynthesis rate or more specifically by sucrose synthesis and this limitation is independent of light intensity per se. The rate of translocation was not saturated even at net photosynthesis rates four times greater than the rate occurring at 300 microliters/liter of CO₂, 21% O₂, and saturating light intensity.     

Effect of ammonium sulfate on the phytotoxicity, foliar uptake, and translocation of imazamethabenz in wild oat

Experiments were conducted in greenhouse, growth chamber, and laboratory conditions to determine the effect of ammonium sulfate [(NH₄)₂SO₄] on the phytotoxicity, foliar uptake, and translocation of imazamethabenz on wild oat. Rates of (NH₄)₂SO₄ up to 5% (w/v) applied with a greenhouse sprayer did not affect the phytotoxicity of the herbicide when the mix was applied at the one- to two-leaf stage. However, inclusion of 1 and 2% (NH₄)₂SO₄ increased the phytotoxicity of the herbicide when the mix was sprayed at the two- to three-leaf, or the three- to four-leaf stage. At 10%, (NH₄)₂SO₄ decreased the phytotoxicity of the sublethal dosage of the herbicide. When the herbicide was applied as individual drops to the growth chamber-grown plants, inclusion of (NH₄)₂SO₄ at 1% did not affect phytotoxicity as measured by shoot growth. The presence of (NH₄)₂SO₄ did not affect the amount of imazamethabenz retained by wild oat foliage, but it decreased [¹⁴C]imazamethabenz absorption, slightly antagonized acropetal translocation, and increased the basipetal translocation of [¹⁴C]imazamethabenz. It was concluded that application methods greatly modify the effect of (NH₄)₂SO₄ on imazamethabenz phytotoxicity. Herbicide absorption and translocation as determined by one method do not necessarily represent the absorption and translocation patterns when different application methods are used. Absorption and translocation were not the factors that were responsible for the observed effect of (NH₄)₂SO₄ on the herbicide phytotoxicity.Abbreviations SC suspension concentrate     

A G-Protein Subunit Translocation Embedded Network Motif Underlies GPCR Regulation of Calcium Oscillations

G-protein βγ subunits translocate reversibly from the plasma membrane to internal membranes on receptor activation. Translocation rates differ depending on the γ subunit type. There is limited understanding of the role of the differential rates of G_βγ translocation in modulating signaling dynamics in a cell. Bifurcation analysis of the calcium oscillatory network structure predicts that the translocation rate of a signaling protein can regulate the damping of system oscillation. Here, we examined whether the G_βγ translocation rate regulates calcium oscillations induced by G-protein-coupled receptor activation. Oscillations in HeLa cells expressing γ subunit types with different translocation rates were imaged and quantitated. The results show that differential G_βγ translocation rates can underlie the diversity in damping characteristics of calcium oscillations among cells. Mathematical modeling shows that a translocation embedded motif regulates damping of G-protein-mediated calcium oscillations consistent with experimental data. The current study indicates that such a motif may act as a tuning mechanism to design oscillations with varying damping patterns by using intracellular translocation of a signaling component.     

Effects of SO(2) and O(3) on Allocation of C-Labeled Photosynthate in Phaseolus vulgaris

A series of laboratory exposures of two varieties of bush bean (Phaseolus vulgaris L., var 274 and var 290) was conducted to determine the sensitivity of [¹⁴C]photosynthate allocation patterns to alteration by SO₂ and O₃. Experiments with the pollution-resistant 274 variety demonstrated short-term changes in both ¹⁴C and biomass allocation to roots of ¹⁴CO₂-labeled plants but no significant effect on yield by up to 40 hours of exposure to SO₂ at 0.50 microliters per liter or 4 hours of O₃ at 0.40 microliters per liter. Subsequent experiments with the more sensitive 290 variety demonstrated significant alteration of photosynthesis, translocation, and partitioning of photosynthate between plant parts including developing pods. Significant increases in foliar retention of photosynthate (+40%) occurred after 8 hours of exposure to SO₂ at 0.75 microliters per liter (6.0 microliters per liter-hour) and 11 hours of exposure to O₃ at 0.30 microliters per liter-hour (3.3 microliters-hours). Time series sampling of labeled tissues after ¹⁴CO₂ uptake showed that the disruption of translocation patterns was persistent for at least 1 week after exposures ceased. Subsequent longer-term exposures at lower concentrations of both O₃ (0.0, 0.10, 0.15, and 0.20 microliters per liter) and SO₂ (0.0, 0.20, and 0.40 microliters per liter) demonstrated that O₃ more effectively altered allocation than SO₂, that primary leaves were generally more sensitive than trifoliates, and that responses of trifoliate leaves varied with plant growth stage. Altered rates of allocation of photosynthate by leaves were generally associated with alterations of similar magnitude and opposite direction in developing pods. Collectively, these experiments suggest that allocation patterns can provide sensitive indices of incipient growth responses of pollution-stressed vegetation.     

Growth, Respiration, and Polypeptide Patterns of Bradyrhizobium sp. (Arachis) Strain 3G4b20 from Succinate- or Oxygen-Limited Continuous Cultures

Succinate- or oxygen-limited continuous cultures were used to study the influences of different concentrations of dissolved oxygen and ammonia on the growth, respiration, and polypeptide patterns of Bradyrhizobium sp. (Arachis) strain 3G4b20. During succinate-limited growth, molar growth yields on succinate (Y_succ) ranged from 38.9 to 44.4 g (dry weight) of cells mol of succinate⁻¹ and were not greatly influenced by changes in dilution rates or changes in the oxygen concentrations that we tested. Succinate, malate, and fumarate induced the highest rates of oxygen uptake in all of the steady states in which the supply rates of (NH₄)₂SO₄ ranged between 322 and 976 μmol h⁻¹. However, the amino acids aspartate, asparagine, and glutamate could also be used as respiratory substrates, especially when the (NH₄)₂SO₄ supply rate was decreased to 29 μmol h⁻¹. Glutamine-dependent respiration was seen only when the (NH₄)₂SO₄ supply rate was 29 μmol h⁻¹ and thus appears to be under tight ammonia control. Nitrogenase activity was detected only when the culture was switched from a succinate-limited steady state to an oxygen-limited steady state. Comparison of major silver-stained proteins from three steady states by two-dimensional gel electrophoresis revealed that nearly 60% were affected by oxygen and 24% were affected by ammonia. These data are consistent with reports that oxygen has a major regulatory role over developmental processes in Rhizobium sp. and Bradyrhizobium sp.     

Sulfur Isotope Fractionation and Kinetic Studies of Sulfite Reduction in Growing Cells of Salmonella heidelberg

A pulsed feeding technique was used during studies of sulfite reduction by Salmonella heidelberg in order to realize large percentages of SO₃⁼ conversion while simultaneously maintaining a reasonably stable cell population. As a consequence, much data for conventional kinetic and sulfur isotope fractionation computations were obtained in any one experiment. Under the conditions of supplying 150 μg glucose per ml of medium every 6 hr, anaerobiosis, and varying the SO₃⁼ concentration, the following observations were made: 1. Below 0.01% w/v Na₂SO₃, the reduction strictly followed first order kinetics with respect to SO₃⁼ concentration. At higher concentrations, the rate of SO₃⁼ reduction fell below that predicted by first order kinetics suggesting that a saturation effect was occurring. 2. At lower concentrations, the ratio of the isotopic rate constants k₁/k₂ was 1.02 whereas at higher SO₃⁼ levels, k₁/k₂ values of 1.04 were found. These latter effects are much higher than those obtained in the equivalent chemical reduction. On the basis of these observations, a model is considered which features two isotopically dependent steps and an intermediate reservoir which forms at higher SO₃⁼ concentrations. Results of an experiment under aerobic conditions and an experiment wherein the reduction rate was thermally altered, are also presented.     

Mechanisms of resistance to sulfur dioxide in the Cucurbitaceae

The relative resistance of four cultivars of the Cucurbitaceae (Cucumis sativus L. cv. National Pickling, and inbred line SC 25; Cucurbita pepo L. cv. Prolific Straightneck Squash, and cv. Small Sugar Pumpkin) to SO₂ was determined. According to plots of the degree of exposure to SO₂ (which depends on the SO₂ concentration and the duration of the exposure), there is an 8-fold difference in resistance to this toxic gas among these cultivars. However, if the degree of injury is plotted as a function of the amount of SO₂ absorbed, all four cultivars appear similarly sensitive to the gas. We conclude that the principal reason for special and varietal differences in resistance among these cultivars is the relative rate of absorption of the gas. The densities of stomata on the upper and lower surfaces of leaves did not differ sufficiently between cultivars to account for the differences in absorption rates. It remains to be determined whether the differences in rate of SO₂ absorption reflect differences in stomatal activity.

Resistance of individual leaves changes with position on the plant axis (age of the leaf). There exists a gradient of decreasing resistance from the apex downward. This resistance gradient cannot be accounted for by differences in rates of SO₂ absorption. We infer the existence of a biochemically based, developmentally controlled resistance mechanism which functions after SO₂ has entered the leaf. Biochemical comparisons of old and young leaves with such differences in resistance should be helpful in determining the biochemistry of SO₂ toxicity.

     

A G-Protein Subunit Translocation Embedded Network Motif Underlies GPCR Regulation of Calcium Oscillations

G-protein βγ subunits translocate reversibly from the plasma membrane to internal membranes on receptor activation. Translocation rates differ depending on the γ subunit type. There is limited understanding of the role of the differential rates of G_βγ translocation in modulating signaling dynamics in a cell. Bifurcation analysis of the calcium oscillatory network structure predicts that the translocation rate of a signaling protein can regulate the damping of system oscillation. Here, we examined whether the G_βγ translocation rate regulates calcium oscillations induced by G-protein-coupled receptor activation. Oscillations in HeLa cells expressing γ subunit types with different translocation rates were imaged and quantitated. The results show that differential G_βγ translocation rates can underlie the diversity in damping characteristics of calcium oscillations among cells. Mathematical modeling shows that a translocation embedded motif regulates damping of G-protein-mediated calcium oscillations consistent with experimental data. The current study indicates that such a motif may act as a tuning mechanism to design oscillations with varying damping patterns by using intracellular translocation of a signaling component.     

Uptake and assimilation of sulphate by sulphur deficient Zea mays cells: The role of O-acetyl-L-serine in the interaction between nitrogen and sulphur assimilatory pathways

Cell suspension cultures of maize (Zea mays) growing on a modified Murashige and Skoog's (MS) medium containing 1/10 of the normal N supply, were subjected to SO₄^2– starvation for 4 d. During the period of the experiment, the batches of cells were growing at similar rates in both +S and –S treatments. S-starved cells (–S) took up SO₄^2– at eight to ten times the rate of S-sufficient (+S) cells. The high uptake rate of –S cells was repressed within 1–2 h after SO₄^2– was re-supplied. The response to S-starvation was strongly diminished in cells which had been deprived of a N-source for 4 d. Cells grown for several culture cycles with homocysteine thiolactone (TL) as sole S-source had greatly increased SO₄^2– uptake rates. This enhanced uptake was repressed at similar rates by provision of SO₄^2– or by the renewal of the TL supply. The latter result was unexpected and cannot be explained at present. ATP-sulphurylase (EC 2.7.7.4) activity was also de-repressed: in –S cells, the measured activity being more than four times that in +S cells. Repression by SO₄^2– was observed although after a longer period than that for the repression of SO₄^2– uptake. In +S cells, SO₄^2– uptake and ATP-sulphurylase activity were increased significantly by the addition of 0.5 mol.m^–3 O-acetyl-L-serine to the culture. Simultaneously, the cysteine pool increased in the same proportion as the former activities. The addition of other amino acids, viz. glutamine or alanine, had either negative effects or no effect on SO₄^2– uptake.     

Effect of salt-stress on translocation of photosynthates in pigeon-pea

Summary An investigation was carried out in order to study the effect of salts namely NaC1 and Na₂SO₄ on the rate of translocation of photosynthates in pigeonpea, at the pod filling stage. At the concentration of 10 EC NaC1 only 17% of the¹⁴C assimilates are translocated from the source leaf to the other parts of the plant. Out of this pods receive about 8%. On the other hand even at a concentration of 15 EC Na₂SO₄ about 30% of the total¹⁴C assimilates get translocated and out of this pods receive about 12%. From this it may be concluded that under salt-stress conditions the rate of translocation of photosynthates is adversely affected and between the two salts, NaC1 was discovered to have a marked inhibitory effect.     

The effect of transpiration on selenium uptake and mobility in durum wheat and spring canola

Aims

The objective of this study was to determine the relative importance of transpirational pull, Se speciation, sulfate and species on Se accumulation by plants, in order to determine which of these factors must be considered in the future development of models to predict Se accumulation by plants.

Methods

Seedlings of durum wheat (Triticum turgidum L. var durum cv ‘Kyle’) and spring canola (Brassica napus L. var Hyola 401) were grown hydroponically and exposed to SeO ₄ ^2- (selenate) with or without SO ₄ ^2- (sulfate), or to HSeO ₃ ^- (biselenite) under different transpiration regimes altered through ‘low’ (~50%) or ‘high’ (~78%) relative humidity (RH). Plants were harvested after 0, 8, 16, or 24?h exposures, digested, and analyzed for Se by GFAAS.

Results

Accumulation and distribution of Se by plants is dependent on plant species, Se speciation in the nutrient solution, SO ₄ ^2- competition, and transpiration regimes. Canola accumulated and translocated more Se than wheat. In wheat and canola, the greatest accumulation and translocation of Se occurred when plants were exposed to SeO ₄ ^2- without SO ₄ ^2- compared to solutions of SeO ₄ ^2- with SO ₄ ^2- or HSeO ₃ ^2- . Wheat plants exposed to SeO ₄ ^2- and SO ₄ ^2- had an increased Se accumulation and translocation under increased transpiration rates than when exposed to SeO ₄ ^2- without SO ₄ ^2- or HSeO ₃ ^2- . On the other hand, increases in transpiration increased the translocation of Se to canola shoots when exposed to HSeO ₃ ^- more than any other treatments.

Conclusions

Overall, our results suggest that plant species is the most important factor influencing Se accumulation and translocation, but that these endpoints can be modified by climate and specific soil Se or S content. Models to predict accumulation of Se by plants must consider all of these factors to accurately calculate the mechanisms of uptake and translocation.     

Reduction of Sulfur Compounds in the Sediments of a Eutrophic Lake Basin

Concentrations of various sulfur compounds (SO₄²⁻, H₂S, S⁰, acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H₂S production was relatively minor. Addition of 1.0 mM Na₂³⁵SO₄ to upper sediments in laboratory experiments resulted in the production of H₂³⁵S with no apparent lag. Kinetic experiments with ³⁵S demonstrated an apparent K_m of 0.068 mmol of SO₄²⁻ reduced per liter of sediment per day, whereas tracer experiments with ³⁵S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m² per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of ³⁵S⁰ occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon.     

The relationship between absorption of sulfur dioxide (SO2) and inhibition of photosynthesis in several plants

Photosynthetic rate, transpiration rate and SO₂ absorption rate were simultaneously measured under exposure to SO₂ (0.1–1.0 μl l ^?1) for 5 or 8 hr in six species belonging to C₄ or C₃ plants (Zea mays, Sorghum vulgare, Amaranthus tricolor, Oryza sativa, Avena sativa andHelianthus annuus). Distinct interspecific differences were found as to the extent of inhibition of photosynthetic rate. Calculation of diffusive resistance to H₂O(r) and SO₂(r′) showed that the ratio of r′/r was 1.9 irrespective of species and coincided well with the theoretical value based on molecular diffusion. Thus it was made clear that the absorption of SO₂ was dependent upon the gas exchange capacity of leaf blade. Using the ratio of r′/r the rate of SO₂ absorption could be calculated from transpiration rate and was compared with the inhibition rate of photosynthesis. In three C₄ species, the inhibition of photosynthesis increased linearly with the amount of SO₂ absorbed during a 5-hour period. The pattern of inhibition of photosynthesis inA. sativa andH. annuus among C₃ species was similar to that of C₄ species until the amount of SO₂ absorbed reached 60 mg-SO₂ m^?2 above which the inhibition abruptly increased. The inhibition of photosynthesis inO. sativa was exceptionally severe even with only a small amount of SO₂ absorbed.     

Light-dependent incorporation of selenite and sulphite into selenocysteine and cysteine by isolated pea chloroplasts

Illuminated intact pea chloroplasts in the presence of O-acetylserine (OAS) catalysed incorporation of SeO₃^2- and SO₃^2- into selenocysteine and cysteine at rates of ca 0.36 and 6 μmol/mg Chl per hr respectively. Sonicated chloroplasts catalysed SeO₃^2- and SO₃^2- incorporation at ca 3.9 and 32% respectively of the rates of intact chloroplasts. Addition of GSH and NADPH increased the rates to ca 91 and 98% of the intact rates, but SeO₃^2- incorporation under these conditions was essentially light-independent. In the absence of OAS, intact chloroplasts catalysed reduction of SO₃^2- to S^2- at rates of ca 5.8 μmol/mg Chl per hr. In the presence of OAS, S^2- did not accumulate. Glutathione (GSH) reductase was purified from peas and was inhibited by ZnCl₂. This enzyme, in the presence of purified clover cysteine synthase, OAS, GSH and NADPH, catalysed incorporation of SeO₃^2- into selenocysteine (but not SO₃^2- into cysteine). The reaction was inhibited by ZnCl₂. Incorporation of SeO₃^2- into selenocysteine by illuminated intact chloroplasts and sonicated chloroplasts (with NADPH and GSH) was also inhibited by ZnCl₂ but not by KCN. Conversely, incorporation of SO₃^2- into cysteine was inhibited by KCN but not by ZnCl₂. It was concluded that SeO₃^2- and SO₃^2- are reduced in chloroplasts by independent light-requiring mechanisms. It is proposed that SeO₃^2- is reduced by light-coupled GSH reductase and that the Se^2- produced is incorporated into selenocysteine by cysteine synthase.     

Development and Application of Different Methods for the Detection of Toxoplasma gondii in Water

Two methods, centrifugation and flocculation, were evaluated to determine their efficiencies of recovery of Toxoplasma gondii oocysts from contaminated water samples. Demineralized and tap water replicates were inoculated with high numbers of sporulated or unsporulated T. gondii oocysts (1 × 10⁵ and 1 × 10⁴ oocysts). The strain, age, and concentration of the seeded oocysts were recorded. Oocysts were recovered either by centrifugation of the contaminated samples at various g values or by flocculation with two coagulants, Fe₂(SO₄)₃ and Al₂(SO₄)₃. The recovery rates were determined with the final pellets by phase-contrast microscopy. Sporulated oocysts were recovered more effectively by flocculation with Al₂(SO₄)₃ (96.5% ± 21.7%) than by flocculation with Fe₂(SO₄)₃ (93.1% ± 8.1%) or by centrifugation at 2,073 × g (82.5% ± 6.8%). For the unsporulated oocysts, flocculation with Fe₂(SO₄)₃ was more successful (100.3% ± 26.9%) than flocculation with Al₂(SO₄)₃ (90.4% ± 19.1%) or centrifugation at 2,565 × g (97.2% ± 12.5%). The infectivity of the sporulated oocysts recovered by centrifugation was confirmed by seroconversion of all inoculated mice 77 days postinfection. These data suggest that sporulated Toxoplasma oocysts purified by methods commonly used for waterborne pathogens retain their infectivity after mechanical treatment and are able to induce infections in mammals. This is the first step in developing a systematic approach for the detection of Toxoplasma oocysts in water.     

The influence of sublethal concentrations of sulfur dioxide on morphology,growth and product yield of the duckweed Lemna minor L.

Summary There was no disturbance in the growth of Lemna minor L. with a SO₂ concentration of up to 0.3 ppm in air. A SO₂ concentration of 0.6 ppm caused an initial depression of the growth rate of about 25%, but in the course of adaptation, the rate rose to the values of the control. The average dry weight per frond was not influenced by the SO₂ fumigation. The initial sporadic appearance of chloroses by fumigation with 0.6 ppm SO₂ was considered a sign of the proximate toxicity limit for Lemna minor L. With 0.15 ppm SO₂ in air, the size of the fronds was reduced. The average surface of the fronds was diminished by 0.3 ppm SO₂ for about 16% as compared with the control plants.The protein remained quantitatively uneffected up to a SO₂ concentration of 0.6 ppm. As a qualitative influence of SO₂, the nitrogen content of the proteins remained constant, but the sulfur content of the proteins increased.Under 0.3 and 0.6 ppm SO₂, the starch content decreased immediately by 20–30%, under 0.15 ppm SO₂ the decrease reached the same level after a longer time than in the case of the higher concentrations.The SO₂ concentrations up to 0.6 ppm had no effect on chlorophyll concentration.The contents of C, N, H, P, K, Na, Ca, Mg, Mn, and Fe were not effected by SO₂ fumigation.Conclusion: SO₂ may have some effects on product yield, even under low concentrations, without provoking acute damage; the plant is able to adapt by regulation of its metabolism, and enters a new steady state.The study was supported by a grant of the Swiss National Science Foundation (project number 3.866.71)     

Effect of sulphur dioxide exposure on human chromosomes

The genotoxic effects of an average concentration of 41.7 mg/m³ of SO₂ exposure on 42 workers of a fertilizer factory were investigated. Mitotic index (MI), chromosomal aberrations (CAs), sister-chromatid exchanges (SCEs) and satellite associations (SA) were observed. In SO₂-exposed workers, a higher mitotic index (7.09) was recorded in comparison to controls (4.34). The MI, however, declined with duration of exposure. Satellite associations showed a two-fold increase (17.1) as compared to controls (8.11). Among chromosomes, D-G group associations were the highest (7.43%), while 3D type associations were the lowest (0.4%). There was a significant difference (p < 0.05) in the mean frequency of CAs per cell in the exposed workers (3.262%) and the controls (0.833%). The mean frequency of SCEs per cell increased from 3.32 ± 0.1 in controls to 7.72 ± 0.19 in the exposed group. The difference was significant (p < 0.05). In smokers, alcoholics and smoker-alcoholics, the frequency of CAs and SCEs per cell was significantly higher than the non-smokers and non-alcoholics, both in the controls and the SO₂-exposed workers and showed a correlation with the duration of exposure. SO₂ is therefore a clastogenic and genotoxic agent for which necessary precautions must be taken.     

盐胁迫对藜麦种子萌发的影响研究

再生水资源可浇灌农田,但水中含有的阴离子可使土壤产生盐胁迫。为研究盐胁迫对藜麦(Chenopodium quinoa)种子萌发特性及胚根、胚芽生长的影响,该研究以6个藜麦品种(红藜麦、国红藜麦、台红藜麦、台紫红藜麦、黄藜麦、台黄红藜麦)为材料,分别以NaCl、Na₂SO₄、NaHCO₃和对照(CK)处理6个藜麦品种种子,测定其发芽率、胚根、胚芽抑制率等指标,运用均方差决策法对不同藜麦品种耐盐性进行综合评价,初步筛选出不同盐胁迫下耐盐性较强的品种。结果表明：(1)三种盐胁迫中,Na₂SO₄对种子萌发指标抑制作用最明显,6个藜麦品种的发芽率均相对较低,一直保持在5%以下,除黄藜麦、台黄红藜麦,其余4个品种的活力指数和生长速率均为0,除黄藜麦外,Na₂SO₄ 对其余5个藜麦品种的胚根、胚芽抑制率均达到100%;NaCl对种子萌发和生长的抑制作用较小,甚至可促进胚根和胚芽生长,国红藜麦和台黄红藜麦的生长速率在NaCl处理下始终高于对照,在9 ...