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1.
Agu Laisk  Hardy Pfanz  Ulrich Heber 《Planta》1988,173(2):241-252
A computer model is used to analyze fluxes of SO2 from polluted air into leaves and the intracellular distribution of sulfur species derived from SO2. The analysis considers only effects of acidification and of anion accumulation. (i) The SO2 flux into leaves is practically exclusively controlled by the boundary-layer resistance of leaves to gas diffusion and by stomatal opening. At constant stomatal opening, flux is proportional to the concentration of SO2 in air. (ii) The sink capacity of cellular compartments for SO2 depends on intracellular pH and the intracellular localization of reactions capable of oxidizing or reducing SO2. In the mesophyll of illuminated leaves, the chloroplasts possess the highest trapping potential for SO2. (iii) If intracellular ion transport were insignificant, and if bisulfite and sulfite could not be oxidized or reduced, leaves with opened stomata would rapidly be killed both by the accumulation of sulfites and by acidification of chloroplasts and cytosol even if SO2 levels in air did not exceed concentrations thought to be permissible. Acidification and sulfite accumulation would remain confined largely to the chloroplasts and to the cytosol under these conditions. (iv) Transport of bisulfite and protons produced by hydration of SO2 into the vacuole cannot solve the problem of cytoplasmic accumulation of bisulfite and sulfite and of cytoplasmic acidification, because SO2 generated in the acidic vacuole from the bisulfite anion would diffuse back into the cytoplasm. (v) Oxidation to sulfate which is known to occur mainly in the chloroplasts can solve the problem of cytoplasmic sulfite and bisulfite accumulation, but aggravates the problem of chloroplastic and cytosolic acidification. (vi) A temporary solution to the problem of acidification requires the transfer of H+ and sulfate into the vacuole. This transport needs to be energized. The storage capacity of the vacuole for protons and sulfate defines the extent to which SO2 can be detoxified by oxidation and removal of the resulting protons and sulfate anions from the cytoplasm. Calculations show that even at atmospheric levels of SO2 thought to be tolerable, known vacuolar buffer capacities are insufficient to cope with proton production during oxidation of SO2 to sulfate within a vegetation period. (vii) A permanent solution to the problem of acidification is the removal of protons. Protons are consumed during the reduction of sulfate to sulfide. Proteins and peptides contain sulfur at the level of sulfide. During photosynthesis in the presence of the permissible concentration of 0.05l·l-1 SO2, sulfur may be deposited in plants at a ratio not far from 1/500 in relation to carbon. The content of reduced sulfur to carbon is similar to that ratio only in fast-growing, protein-rich plants. Such plants may experience little difficulty in detoxifying SO2. In contrast, many trees may contain reduced sulfur at a ratio as low as 1/10 000 in relation to carbon. Excess sulfur deposited in such trees during photosynthesis in polluted air gives rise to sulfate and protons. If detoxification of SO2 by reduction is inadequate, and if the storage capacity of the vacuoles for protons and sulfate is exhausted, damage is unavoidable. Calculations indicate that trees with a low ratio of reduced S to C cannot tolerate long-term exposure to concentrations of SO2 as low as 0.02 or 0.03 l·l-1 which so far have been considered to be non-toxic to sensitive plant species.  相似文献   

2.
Leaves of Populus balsamifera grown under full natural sunlight were treated with 0, 1, or 2 l SO2·1-1 air under one of four different photon flux densities (PFD). When the SO2 exposures took place in darkness or at 300 mol photons·m-2·s-1, sulfate accumulated to the levels predicted by measurements of stomatal conductance during SO2 exposure. Under conditions of higher PFD (750 and 1550 mol·m-2·s-1), however, the predicted levels of accumulated sulfate were substantially higher than those obtained from anion chromatography of the leaf extracts. Light-and CO2-saturated capacity as well as the photon yield of photosynthetic O2 evolution were reduced with increasing concentration of SO2. At 2 l SO2·1-1 air, the greatest reductions in both photosynthetic, capacity and photon yield occurred when the leaves were exposed to SO2 in the dark, and increasingly smaller reductions in each occurred with increasing PFD during SO2 exposure. This indicates that the inhibition of photosynthesis resulting from SO2 exposure was reduced when the exposure occurred under conditions of higher light. The ratio F v/F M (variable/maximum fluorescence emission) for photosyntem II (PSII), a measure of the photochemical efficiency of PSII, remained unaffected by exposure of leaves to SO2 in the dark and exhibited only moderate reductions with increasing PFD during the exposure, indicating that PSII was not a primary site of damage by SO2. Pretreatment of leaves with SO2 in the dark, however, increased the susceptibility of PSII to photoinhibition, as such pretreated leaves exhibited much greater reductions inF V/F M when transferred to moderate or high light in air than comparable control leaves.Abbreviations and symbols A1200 photosynthetic capacity (CO2-saturated rate of O2 evolution at 1200 mol photons·m-2·s-1) - Fo instantaneous fluorescence emission - FM maximum fluorescence emission - FV variable fluorescence emission - PFD photon flux density (400–700 nm) - PSII photosystem II  相似文献   

3.
The enzyme catalyzing the reduction of sulfite by reduced benzyl viologen (BVH) was partially purified and characterized from two strains of wine yeasts, a sulfite-producing strain and a non-producing strain.Both enzymes showed corresponding features in pH-optima, optima of buffer and benzyl viologen concentrations.The enzymes did not catalyze the reduction of nitrite by reduced viologen dyes, but the reduction of sulfite was uncompetitively inhibited by nitrite. Compounds of sulfur metabolism such as sulfate, thiosulfate, cysteine, serine and methionine did not influence the activity of either of the enzymes. The main differences between the two enzymes exist in the specific activities in crude extracts, the K m -values for sulfite, substrate inhibition rates, and localization in different fractions during (NH4)2SO4 precipitation. The specific activity in crude extracts of the sulfite-producing strain (0.052 moles S2- x min-1 x mg-1) was about three fold higher than that of the non-producing strain (0.0179 moles S2- x min-1 x mg-1). On the other hand the sulfite-producing strain had a higher K m -value for sulfite (2×10-3 M) and was more strongly inhibited by the substrate than the non-producing strain (6×10-3 M).  相似文献   

4.
Summary Populations of Geranium carolinianum, a winter annual plant common in disturbed habitats, vary in their foliar response to sulfur dioxide, and pollution resistance is characteristic of populations sampled from areas in which SO2 has been a prominent stress. The physiological basis of this ecotypic response was investigated using a whole-plant gaseous exchange system in which leaf resistance to H2O efflux and SO2 influx were concurrently monitored. Individual plants of distinct SO2 susceptibility were exposed to pollutant concentrations of either 0.4, 0.6 or 0.8 l 1-1 in both the dark and light. Total SO2 flux (g cm-2 h-1) to the plant, which is the sum of leaf adsorptive and absorptive loss, varied as an inverse function of leaf resistance (s cm-1), and the relationship was modeled using linear regression techniques. Total SO2 flux was partitioned to leaf surface and internal fractions using estimation procedures with the regression analysis. SO2 flux into the leaf interior, the pollutant fraction responsible for causing foliar injury, was strikingly similar for resistant and sensitive plants at each concentration. Resistant plants must absorb 30% more SO2 than their sensitive counterparts in order to exhibit comparable levels of foliar injury. Therefore, in G. carolinianum the predominant explantation for genetically controlled and quantitatively inherited differences in plant résponse to SO2 is not variable pollutant flux but rather disparate physiological-biochemical processes affecting pollutant toxicity, cellular perturbation and repair. This conclusion is relevant to understanding how populations of G. carolinianum respond over time to elevated levels of SO2 and may explain the inherent susceptibility of this species compared with plants with which it co-exists.  相似文献   

5.
Sulfur cycling in forests   总被引:6,自引:5,他引:1  
Sulfur is essential for the production of certain amino acids in plants. As amino acid sulfur is the major form of sulfur in trees, there is a strong relationship between organic S and organic N in tree tissue. Sulfur deficiencies occur in parts of southeastern Australia and northwestern North America, remote from pollutant inputs. Since bilogical S requirements of forests are modest (< 5 kg · ha–1 yr–1 for net vegetative increment), however, atmospheric S inputs in polluted regions (10–80 kg · ha–1 yr–1 ) often exceed not only the forest ecosystem S requirement but also its ability to biologically accumulate S. There is some increase in the SO2– 4–S content of forest vegetation in response to elevated atmospheric S inputs, but this capacity is apparently easily saturated. Soil SO2–2 4adsorption is often the dominant feature of S cycling in polluted ecosystems and often accounts for net ecosytem S accumulations.Contribution from a symposium on the role of sulfur in ecosystem processes held August 10, 1983, at the annual meeting of the A.I.B.S., Grand Forks, ND; Myron Mitchell, convenor.  相似文献   

6.
Zaroug  M. G.  Munns  D. N. 《Plant and Soil》1979,53(3):319-328
Summary In order to explore interrelations between S nutrition, soluble sugars, leaf area, nodulation and N2 fixation, greenhouse experiments were done with several levels of S added to perlite-sand cultures or to a moderately S-deficient soil. Sulfur had indirect effects on nodulation and N2 fixation, possibly by improving sugars supply and N metabolism.In perlite-sand culture, leaf area increased with concentrations of supplied S up to 50 and 200 M for symbiotic and N-treated plants respectively, then decreased at higher concentrations. Plant yield and total sugars content (mg per plant) for the N-treated plants behaved similar to leaf area in response to added S but in the symbiotic plants maximum values were obtained at 100 M S. In soil, Mo had no effect on growth but interacted significantly with S in affecting total sugars content. High levels of S depressed sugars content at low Mo but raised it at high Mo.Sulfur increased the N content of soil-grown plants. It increased the N content of plants grown in perlite-sand culture except at very high levels of S. There was little effect on concentration of N in the shoots. Nitrogen content correlated significantly with leaf area and sugar content, and highly significantly with S concentration in the shoots.  相似文献   

7.

Key Message

The critical level for SO 2 susceptibility of Populus × canescens is approximately 1.2 μL L ?1 SO 2 . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO 2 detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO2 were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO2 detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO2 (0.65, 0.8, 1.0, 1.2 μL L?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO2 assimilation, SO2 uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO2 that confers injury to the leaves was 1.2 μL L?1 SO2. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO2 uptake of the plant shoot, whereas SO2 uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO2 revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.  相似文献   

8.
Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 L L–1 near the leaf base to below atmospheric (<350 L L–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 mol m–2 s–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by 14CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 L L–1 of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L–1 O2 compared to 20 mL L–1 O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.Abbreviations Ca external CO2 concentration - Ci intercellular CO2 concentration - CO2 compensation concentration - PPFR photosynthetic photon fluence rate  相似文献   

9.
Emission of Hydrogen Sulfide by Leaf Tissue in Response to l-Cysteine   总被引:6,自引:2,他引:4  
Leaf discs and detached leaves exposed to l-cysteine emitted a volatile sulfur compound which was proven by gas chromatography to be H2S. This phenomenon was demonstrated in all nine species tested (Cucumis sativus, Cucurbita pepo, Nicotiana tabacum, Coleus blumei, Beta vulgaris, Phaseolus vulgaris, Medicago sativa, Hordeum vulgare, and Gossypium hirsutum). The emission of volatile sulfur by cucumber leaves occurred in the dark at a similar rate to that in the light. The emission of leaf discs reached the maximal rate, more than 40 picomoles per minute per square centimeter, 2 to 4 hours after starting exposure to l-cysteine; then it decreased. In the case of detached leaves, the maximum occurred 5 to 10 h after starting exposure. The average emission rate of H2S during the first 4 hours from leaf discs of cucurbits in response to 10 millimolar l-cysteine, was usually more than 40 picomoles per minute per square centimeter, i.e. 0.24 micromoles per hour per square decimeter. Leaf discs exposed to 1 millimolar l-cysteine emitted only 2% as much as did the discs exposed to 10 millimolar l-cysteine. The emission from leaf discs and from detached leaves lasted for at least 5 and 15 hours, respectively. However, several hours after the maximal emission, injury of the leaves, manifested as chlorosis, was evident. H2S emission was a specific consequence of exposure to l-cysteine; neither d-cysteine nor l-cystine elicited H2S emission. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate dependent enzymes, inhibited the emission. In a cell free system from cucumber leaves, H2S formation and its release occurred in response to l-cysteine. Feeding experiments with [35S]l-cysteine showed that most of the sulfur in H2S was derived from sulfur in the l-cysteine supplied and that the H2S emitted for 9 hours accounted for 7 to 10% of l-cysteine taken up. 35S-labeled SO32− and SO42− were found in the tissue extract in addition to internal soluble S2−. These findings suggest the existence of a sulfur cycle which converts l-cysteine to SO42− through cysteine desulfhydration.  相似文献   

10.
Summary Stomata of paper birch (Betula papyrifera Marsh.) seedlings were more open at high humidity than at low humidity and responded rapidly to changes in vapor pressure deficit. SO2 at 0.2 or 0.8 l l-1 caused partial stomatal closure. Seedlings fumigated with SO2 at 0.2 or 0.5 l l-1 for 30 h or 0.2 l l-1 for 75 h took up more SO2 at high than at low humidity. Differences in pollutant uptake could be explained by stomatal conductance with no need to invoke changes in mesophyll conductance. Betula seedlings were more sensitive to SO2 when fumigated at high humidity, as manifested in more leaf necrosis, increased leaf abscission, and greater growth inhibition compared to seedlings fumigated at low humidity. Amount of injury to leaves increased with rate of SO2 uptake, and inhibition of root growth increased with total SO2 uptake.Abbreviations RH relative humidity - VPD vapor pressure deficit - RGR mean relative growth rate - PPFD photosynthetic photon flux density (400–700 nm) - LDC leaf diffusive conductance - water potential Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison  相似文献   

11.
Cheng L  Zhou R  Reidel EJ  Sharkey TD  Dandekar AM 《Planta》2005,220(5):767-776
Sorbitol is a primary end-product of photosynthesis in apple (Malus domestica Borkh.) and many other tree fruit species of the Rosaceae family. Sorbitol synthesis shares a common hexose phosphate pool with sucrose synthesis in the cytosol. In this study, Greensleeves apple was transformed with a cDNA encoding aldose 6-phosphate reductase (A6PR, EC 1.1.1.200) in the antisense orientation. Antisense expression of A6PR decreased A6PR activity in mature leaves to approximately 15–30% of the untransformed control. The antisense plants had lower concentrations of sorbitol but higher concentrations of sucrose and starch in mature leaves at both dusk and predawn. 14CO2 pulse-chase labeling at ambient CO2 demonstrated that partitioning of the newly fixed carbon to starch was significantly increased, whereas that to sucrose remained unchanged in the antisense lines with decreased sorbitol synthesis. Total activities of ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), sucrose-phosphate synthase (EC 2.4.1.14), and ADP-glucose pyrophosphorylase (EC 2.7.7.27) were not significantly altered in the antisense lines, whereas both stromal and cytosolic fructose-1,6-bisphosphatase (EC 3.1.3.11) activities were higher in the antisense lines with 15% of the control A6PR activity. Concentrations of glucose 6-phosphate and fructose 6-phosphate (F6P) were higher in the antisense plants than in the control, but the 3-phosphoglycerate concentration was lower in the antisense plants with 15% of the control A6PR activity. Fructose 2, 6-bisphosphate concentration increased in the antisense plants, but not to the extent expected from the increase in F6P, comparing sucrose-synthesizing species. There was no significant difference in CO2 assimilation in response to photon flux density or intercellular CO2 concentration. We concluded that cytosolic FBPase activity in vivo was down-regulated and starch synthesis was up-regulated in response to decreased sorbitol synthesis. As a result, CO2 assimilation in source leaves was sustained at both ambient CO2 and saturating CO2.  相似文献   

12.
The effect of sulfur limitation on sulfate transport and metabolism was studied in four bradyrhizobia strains using sulfur-limited and sulfur-excess chemostat cultures. Characteristics of bradyrhizobia associated with sulfurlimitation were determined and these parameters used to bioassay the sulfur status of bacteroids in nodules on sulfur adequate or sulfur deficient soybean and peanut plants. Sulfur-limited cells took up sulfate 16- to 100-fold faster than sulfur-rich cells. The sulfate-uptake system appeared similar in all strains with apparent K m values ranging from 3.1 M to 20 M sulfate with maximum activities between 1.6 and 10 nmol·min-1·mg-1 protein of cells. Sulfate-limited cells of all strains derepressed the enzyme alkaline sulfatase in parallel with the derepression of the sulfate transport system. Similarly, the initial enzyme of sulfate assimilation (ATP sulfurylase) was fully derepressed in sulfur-limited cultures. Bacteroids isolated from sulfur adequate and sulfur deficient soybean and peanut possessed very limited sulfate uptake activity and low levels of activity of ATP sulfurylase as well as lacking alkaline sulfatase activity. These results indicate bacteriods have access to adequate sulfur to meet their requirements even when the host plant is sulfur-deficient.Abbreviations CCCP Carbonyl cyanide m-chlorophenylhydrazone - DCCD N,N-dicyclohexyl carbodiimide  相似文献   

13.
Summary Two deciduous tree species (yellow poplar and red maple) on Walker Branch Watershed (WBW), near Oak Ridge, Tennessee, were radiolabeled with 35S (87 day halflife) to study internal cycling, storage, and biogenic emission of sulfur (S). One tree of each species was girdled before radiolabeling to prevent phloem translocation to the roots, and the aboveground biomass was harvested prior to autumn leaf fall. Aboveground biomass, leaf fall, throughfall, and stemflow were sampled over a 13 to 24 week period. Sulfur-35 concentrations in tree leaves reached nearly asymptotic levels within 1 to 2 weeks after radiolabeling. Foliar leaching of 35S and leaf fall represented relatively unimportant return pathways to the forest soil. The final distribution of 35S in the nongirdled trees indicated little aboveground storage of S in biomass and appreciable (>60%) capacity to cycle S either to the belowground system by means of translocation or to the atmosphere by means of biogenic S emissions. Losses of volatile 35S were estimated from the amount of isotope missing (33%) in final inventories of the girdled trees. Estimated 35S emission rates from the girdled trees were 10-6 to 10-7 Ci cm-2 leaf d-1, and corresponded to an estimated gaseous S emission of approximately 0.1 to 1 g S cm-2 leaf d-1. Translocation to roots was a significant sink for 35S in the red maple tree (40% of the injected amount). Research on forest biogeochemical S cycles should further explore biogenic S emissions from trees as a potential process of S flux from forest ecosystems.  相似文献   

14.
A. Melzer  G. Gebauer  H. Rehder 《Oecologia》1984,63(3):380-385
Summary The aim of this work was to investigate the effect of nitrogen starvation and subsequent fentilization with nitrate or ammonium on nitrate content and nitrate reductase activity of Rumex obtusifolius L. under natural conditions.When plants were transplanted to nitrate-poor media, endogenous nitrate was reduced within a few days. In parallel, nitrage reductase activities dropped to about 25% of the initial values. As a consequence of nitrate fertilization (1; 10 or 100 mmol KNO3/l substrate), endogenous nitrate content of the plant abruptly increased within one day. In extreme cases, nitrate concentrations of up to 10% of plant dry weight could be observed without being lethal. High external nitrate concentrations caused an inhibition of nitrate reductase within the leaves, while low external concentrations provoked an increase in the enzyme activity of about 450% within one day. Ammonium fertilization (5 mmol (NH4)2SO4/l substrate) also caused an increase in nitrate reductase activity and nitrate content within leaf blades. This observation indicates a rapid nitrification of ammonium in the substrate. When plants were fertilized with ammonium plus nitrate (2.5 mmol (NH4)2SO4+ 5 mmol KNO3/l substrate), an extremely high and long term increase in nitrate reduction could be observed. Due to an intensive enzymatic nitrate turnover, the nitrate content of leaf blades then remained relatively low. Our observations do not point to an inhibition of nitrate reductase activity in leaves of Rumex obtusifolius by ammonium. Despite temporarily high endogenous nitrate concentrations, Rumex obtusifolius may not be termed as a nitrate storage plant, since the accumulation of nitrate is a short term process only.  相似文献   

15.
Stable sulfur isotope analysis of SO2 pollution impact on vegetation   总被引:1,自引:0,他引:1  
Summary The 34S value of SO2 emitted by natural gas refineries is about +25, which is higher than that for non-industrial sulfur sources in our study areas. Terrestrial mosses absorb SO2 from the atmosphere and have a 34S value which is directly related to the degree of SO2 stress to which they are subjected. The 34S values for conifer needles are lower than for mosses at the same collection site, which indicates that trees obtain sulfur from both atmospheric and soil sources.Potted conifers were transferred to sites differing in their degree of SO2 stress. This difference is reflected by the change of 34S values of their needles. SO2 absorbant pot covers, such as charcoal and moss, reduce the amount of airborne sulfur which is available to tress. Moss also may reduce SO2 absorbed by soils in forest stands. We have used analysis of 34S values to (1) help define SO2 dispersion patterns; (2) reveal the rates at which plants accumulate this pollutant; and (3) associate suspected SO2 injury more closely to an emission source.  相似文献   

16.
The leaves and nodules from the shrub and tree legumes, particularly, Aeschynomene spp., Sesbania spp., Mimosa spp. and Leucaena spp., and Casuarina spp. and the leaves from neighbouring non-fixing plants were analyzed for their natural abundances of 15N ( 15N).The 15N in the leaves of non-fixing plants was +5.9% on average, whereas those from shrub legumes and Casuarina spp. were lower and close to the values of atmospheric N2, suggesting the large contribution of N2 fixation as the N source in these plants. The 15N values of the leaves from tree legumes except for Leucaena spp. were between the shrub legumes and non-fixing plants, which suggests that the fractional contribution of fixed N2 in tree legumes may be smaller than that in the shrub legumes. Casuarina spp. was highly dependent on N2 fixation. The 15N values of the nodules from most of the shrub legumes investigated were higher than those of the leaves.  相似文献   

17.
SO2 and NO2 effects on microbial activity in an acid forest soil   总被引:1,自引:0,他引:1  
The rate of glucose decomposition and the pH fell in a forest soil (initial pH 4.06) exposed to 1.0 ppm SO2. No such effect was noted if the soil was exposed to 1.0 ppm nitrogen dioxide (NO2). Nitrite but not bisulfite (5g N or S/g of soil) inhibited O2 consumption and CO2 evolution in the glucose-amended forest soil, and nitrite and bisulfite acted synergistically in inhibiting these processes. Iron and manganese were solubilized when the soil was exposed to 10 ppm SO2, but NO2 caused no such change.  相似文献   

18.
Plant growth depends on the coordinated acquisition and allocation of carbon, water, and nutrient resources to the major plant organs (root, stem, leaf, flower, and fruit) and to the major classes of metabolic function (vegetative growth, maintenance, defense, and reproduction). Air pollutants like SO2, NO2, and O3 can directly damage plant tissues and disrupt normal patterns of resource acquisition and allocation. These disruptions in turn potentially will influence the plant’s ability to defend itself against pests and pathogens. This review summarizes the quantitative and qualitative changes that have been observed when plants are exposed to low levels of SO2, NO2, and O3; the following generalizations emerge:
  1. Root biomass is reduced more than shoot biomass in plants exposed to SO2 or O3, but NO2 does not appear to induce the differential suppression of above-versus below-ground organs.
  2. Quantitative allocation to leaves increases and to stem decreases under SO2 pollution regimes; too few data are available to generalize about O3 or NO2 effects on leaf: stem ratio.
  3. Root carbohydrate concentrations sometimes increase and sometimes decrease after SO2 or O3 fumigations. Leaf nitrogen concentrations tend to decrease after exposure to air pollutants, and leaf carbohydrate concentrations can increase or decrease. Too few data on leaf concentrations of lipids and secondary chemicals are available to justify any generalizations on pollutant responses.
  4. Reproduction is suppressed by O3, SO2, and NO2, with O3 appearing to have the most marked effects. Seed lipid and protein composition can be altered by exposure to pollutants. While both quantitative and qualitative changes in plant resource allocation after exposure to pollutants are common, the importance of these diverse changes for plant-pest and plant-pathogen interaction requires more comprehensive study. Ideally, the time course of plant growth and of metabolite pools critical to particular pests or pathogens should be followed in plants exposed to realistic pollutant regimes and related to pest or pathogen performance on the treated plants.
  相似文献   

19.
Two iso-osmotic concentrations of NaCl and Na2SO4 were used for discriminating between the effects of specific ion toxicities of salt stress on pepper plants (Capsicum annuum L.) grown in hydroponic conditions, in a controlled-environment greenhouse. The two salts were applied to plants at different electrical conductivities, and leaf water relations, osmotic adjustment and root hydraulic conductance were measured. Leaf water potential (w), leaf osmotic potential (o) and leaf turgor potential (p) decreased significantly when EC increased, but the decrease was less for NaCl- than for Na2SO4-treated plants. The reduction in stomatal conductance was higher for NaCl-treated plants. There were no differences in the effect of both treatments on the osmotic adjustment, and a reduction in root hydraulic conductance and the flux of solutes into the xylem was observed, except for the saline ions (Na+, Cl and SO4 2–). Therefore, pepper growth decreased with increasing salinity because the plants were unable to adjust osmotically or because of the toxic effects of Cl, SO4 2– and/or Na+. However, turgor of NaCl-treated plants was maintained at low EC (3 and 4 dS m–1) probably due to the maintenance of water transport into the plant (decrease of stomatal conductance), which, together with the lower concentration of Na+ in the plant tissues compared with the Na2SO4 treatment, could be the cause of the smaller decrease in growth.  相似文献   

20.
In Cucurbitaceae young leaves are resistant to injury from acute exposure to SO2, whereas mature leaves are sensitive. After exposure of cucumber (Cucumis sativus L.) plants to SO2 at injurious concentrations, illuminated leaves emit volatile sulfur, which is solely H2S. Young leaves emit H2S many times more rapidly than do mature leaves. Young leaves convert approximately 10% of absorbed [35S]SO2 to emitted [35S]H2S, but mature leaves convert less than 2%. These results suggest that a high capability for the reduction of SO2 to H2S and emission of the H2S is a part of the biochemical basis of the resistance of young leaves to SO2.  相似文献   

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