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1.
Naturally occurring high levels of ethylene can be a problem in spaceflight and controlled environment agriculture (CEA) leading to sterility and irregular plant growth. There are engineering and safety advantages of growing plants under hypobaria (low pressure) for space habitation. The goals of this research were to successfully grow lettuce (Lactuca sativa cv. Buttercrunch) in a long-term study from seed to harvest under hypobaric conditions, and to investigate how endogenously produced ethylene affects gas exchange and plant growth from seed germination to harvest under hypobaric and ambient total pressure conditions. Lettuce was grown under two levels of total gas pressure [hypobaric or ambient (25 or 101 kPa)] in a long-term, 32-day study. Significant levels of endogenous ethylene occurred by day-15 causing reductions in photosynthesis, dark-period respiration, and a subsequent decrease in plant growth. Hypobaria did not mitigate the adverse ethylene effects on plant growth. Seed germination was not adversely affected by hypobaria, but was reduced by hypoxia (6 kPa pO2). Under hypoxia, seed germination was higher under hypobaria than ambient total pressure. This research shows that lettuce can be grown from seed to harvest under hypobaria (≅25% of normal earth ambient total pressure). 相似文献
2.
The objectives of this research were to determine the influence of hypobaria (reduced atmospheric pressure) and reduced partial pressure of oxygen (pO2) [hypoxia] on carbon dioxide (CO2) assimilation (C(A)), dark-period respiration (DPR) and growth of lettuce (Lactuca sativa L. cv. Buttercrunch). Lettuce plants were grown under variable total gas pressures [25 and 101 kPa (ambient)] at 6, 12 or 21 kPa pO2)(approximately the partial pressure in air at normal pressure). Growth of lettuce was comparable between ambient and low total pressure but lower at 6 kPa pO2 (hypoxic) than at 12 or 21 kPa pO2. The specific leaf area of 6 kPa pO2 plants was lower, indicating thicker leaves associated with hypoxia. Roots were most sensitive to hypoxia, with a 50-70% growth reduction. Leaf chlorophyll levels were greater at low than at ambient pressure. Hypobaria and hypoxia did not affect plant water relations. While hypobaria did not adversely affect plant growth or C(A), hypoxia did. There was comparable C(A) and a lower DPR in low than in ambient total pressure plants under non-limiting CO2 levels (100 Pa pCO2, nearly three-fold that in normal air). The C(A)/DPR ratio was higher at low than at ambient total pressure, particularly at 6 kPa pO2- indicating a greater efficiency of C(A)/DPR in low-pressure plants. There was generally no significant interaction between hypoxia and hypobaria. We conclude that lettuce can be grown under subambient pressure ( congruent with25% of normal earth ambient total pressure) without adverse effects on plant growth or gas exchange. Furthermore, hypobaric plants were more resistant to hypoxic conditions that reduced gas exchange and plant growth. 相似文献
3.
Antonella Naldini Fabio Carraro Silvia Silvestri Velio Bocci 《Journal of cellular physiology》1997,173(3):335-342
We have shown that hypoxia (2% O2 ≈ pO2 14 mmHg) as opposed to O2 atmospheric pressure (20.9% O2 ≈ pO2 140 mmHg) can deeply affect the production of cytokines in human peripheral mononuclear cells (PBMC) in the presence or absence of a specific T-cell activator such as phytohemagglutinin (PHA). In hypoxia, interleukin (IL)-2, IL-4, and interferon (IFN)-γ production increased by 110, 70, and 50% over that of controls, respectively, in PHA-stimulated PBMC (P < 0.05). Moreover, in hypoxia, IL-6 production was significantly enhanced in both resting and PHA-stimulated PBMC by 36 and 37%, respectively (P < 0.05). However, in hypoxia, IL-10 production decreased in both resting and stimulated PBMC, being 80 and 67% of controls, respectively (P < 0.05). PBMC proliferation was not significantly affected by hypoxia, although PBMC susceptibility to PHA was about 80% of that of the control (P < 0.05) after 40 hr of treatment, whereas the cycle progression of hypoxic PBMC was delayed. From an evaluation of these results, hypoxia apparently modifies the production of cytokines by PBMC. These results have both theoretical and practical interest because local hypoxia is very common in several conditions, such as inflammation and local ischemia, and is a host-nonspecific defense against infection. Furthermore, these results suggest a differential pattern of cytokine production in vivo in hypoxic tissues. J. Cell. Physiol. 173:335–342, 1997. © 1997 Wiley-Liss, Inc. 相似文献
4.
Response of the Endophytic Diazotroph Gluconacetobacter diazotrophicus on Solid Media to Changes in Atmospheric Partial O2 Pressure 总被引:2,自引:0,他引:2
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Gluconacetobacter diazotrophicus is an N2-fixing endophyte isolated from sugarcane. G. diazotrophicus was grown on solid medium at atmospheric partial O2 pressures (pO2) of 10, 20, and 30 kPa for 5 to 6 days. Using a flowthrough gas exchange system, nitrogenase activity and respiration rate were then measured at a range of atmospheric pO2 (5 to 60 kPa). Nitrogenase activity was measured by H2 evolution in N2-O2 and in Ar-O2, and respiration rate was measured by CO2 evolution in N2-O2. To validate the use of H2 production as an assay for nitrogenase activity, a non-N2-fixing (Nif−) mutant of G. diazotrophicus was tested and found to have a low rate of uptake hydrogenase (Hup+) activity (0.016± 0.009 μmol of H2 1010 cells−1 h−1) when incubated in an atmosphere enriched in H2. However, Hup+ activity was not detectable under the normal assay conditions used in our experiments. G. diazotrophicus fixed nitrogen at all atmospheric pO2 tested. However, when the assay atmospheric pO2 was below the level at which the colonies had been grown, nitrogenase activity was decreased. Optimal atmospheric pO2 for nitrogenase activity was 0 to 20 kPa above the pO2 at which the bacteria had been grown. As atmospheric pO2 was increased in 10-kPa steps to the highest levels (40 to 60 kPa), nitrogenase activity decreased in a stepwise manner. Despite the decrease in nitrogenase activity as atmospheric pO2 was increased, respiration rate increased marginally. A large single-step increase in atmospheric pO2 from 20 to 60 kPa caused a rapid 84% decrease in nitrogenase activity. However, upon returning to 20 kPa of O2, 80% of nitrogenase activity was recovered within 10 min, indicating a “switch-off/switch-on” O2 protection mechanism of nitrogenase activity. Our study demonstrates that colonies of G. diazotrophicus can fix N2 at a wide range of atmospheric pO2 and can adapt to maintain nitrogenase activity in response to both long-term and short-term changes in atmospheric pO2. 相似文献
5.
As a step in developing an understanding of plant adaptation to low atmospheric pressures, we have identified genes central to the initial response of Arabidopsis to hypobaria. Exposure of plants to an atmosphere of 10 kPa compared with the sea-level pressure of 101 kPa resulted in the significant differential expression of more than 200 genes between the two treatments. Less than one-half of the genes induced by hypobaria are similarly affected by hypoxia, suggesting that response to hypobaria is unique and is more complex than an adaptation to the reduced partial pressure of oxygen inherent to hypobaric environments. In addition, the suites of genes induced by hypobaria confirm that water movement is a paramount issue at low atmospheric pressures, because many of gene products intersect abscisic acid-related, drought-induced pathways. A motivational constituent of these experiments is the need to address the National Aeronautics and Space Administration's plans to include plants as integral components of advanced life support systems. The design of bioregenerative life support systems seeks to maximize productivity within structures engineered to minimize mass and resource consumption. Currently, there are severe limitations to producing Earth-orbital, lunar, or Martian plant growth facilities that contain Earth-normal atmospheric pressures within light, transparent structures. However, some engineering limitations can be offset by growing plants in reduced atmospheric pressures. Characterization of the hypobaric response can therefore provide data to guide systems engineering development for bioregenerative life support, as well as lead to fundamental insights into aspects of desiccation metabolism and the means by which plants monitor water relations. 相似文献
6.
7.
Elevated levels of ethylene occur in enclosed crop production systems and in spaceflight environments, leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa) and wheat (Triticum aestivum). Plants were grown under variable total gas pressures [from 30 to 101 kPa (ambient)]. In one study, lettuce and wheat were direct seeded, germinated and grown in the same chambers for 28 d at 50 or 101 kPa. Hypobaria increased plant growth and did not alter germination rate. During a 10-day study, 28-day-old lettuce and 40-day-old wheat seedlings were transplanted together in the same low and ambient pressure chambers; ethylene accumulated in the chambers, but the rate of production by both lettuce and wheat was reduced more than 65% under 30 kPa compared with ambient pressure (101 kPa). Low O2 concentrations [partial pressure of O2 (pO2) = 6.2 kPa] inhibited ethylene production by lettuce under both low (30 kPa) and ambient pressure, whereas ethylene production by wheat was inhibited at low pressure but not low O2 concentration. There was a negative linear correlation between increasing ethylene concentration and decreasing chlorophyll content of lettuce and wheat. Lettuce had higher production of ethylene and showed greater sensitivity to ethylene than wheat. The hypobaric effect on reduced ethylene production was greater than that of just hypoxia (low oxygen). 相似文献
8.
Plant growth-promoting rhizobacteria (PGPR) may provide a biological alternative to fix atmospheric N2 and delay N remobilisation in maize plant to increase crop yield, based on an understanding that plant-N remobilisation is directly correlated to its plant senescence. Thus, four PGPR strains were selected from a series of bacterial strains isolated from maize roots at two locations in Malaysia. The PGPR strains were screened in vitro for their biochemical plant growth-promoting (PGP) abilities and plant growth promotion assays. These strains were identified as Klebsiella sp. Br1, Klebsiella pneumoniae Fr1, Bacillus pumilus S1r1 and Acinetobacter sp. S3r2 and a reference strain used was Bacillus subtilis UPMB10. All the PGPR strains were tested positive for N2 fixation, phosphate solubilisation and auxin production by in vitro tests. In a greenhouse experiment with reduced fertiliser-N input (a third of recommended fertiliser-N rate), the N2 fixation abilities of PGPR in association with maize were determined by 15N isotope dilution technique at two harvests, namely, prior to anthesis (D50) and ear harvest (D65). The results indicated that dry biomass of top, root and ear, total N content and bacterial colonisations in non-rhizosphere, rhizosphere and endosphere of maize roots were influenced by PGPR inoculation. In particular, the plants inoculated with B. pumilus S1r1 generally outperformed those with the other treatments. They produced the highest N2 fixing capacity of 30.5% (262 mg N2 fixed plant−1) and 25.5% (304 mg N2 fixed plant−1) of the total N requirement of maize top at D50 and D65, respectively. N remobilisation and plant senescence in maize were delayed by PGPR inoculation, which is an indicative of greater grain production. This is indicated by significant interactions between PGPR strains and time of harvests for parameters on N uptake and at. % 15Ne of tassel. The phenomenon is also supported by the lower N content in tassels of maize treated with PGPR, namely, B. pumilus S1r1, K. pneumoniae Fr1, B. subtilis UPMB10 and Acinetobacter sp. S3r2 at D65 harvest. This study provides evidence that PGPR inoculation, namely, B. pumilus S1r1 can biologically fix atmospheric N2 and provide an alternative technique, besides plant breeding, to delay N remobilisation in maize plant for higher ear yield (up to 30.9%) with reduced fertiliser-N input. 相似文献
9.
Relative Rates of Nitric Oxide and Nitrous Oxide Production by Nitrifiers, Denitrifiers, and Nitrate Respirers 总被引:10,自引:7,他引:10
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Biogenic emissions of nitric and nitrous oxides have important impacts on the photochemistry and chemistry of the atmosphere. Although biogenic production appears to be the overwhelming source of N2O, the magnitude of the biogenic emission of NO is very uncertain. In soils, possible sources of NO and N2O include nitrification by autotrophic and heterotrophic nitrifiers, denitrification by nitrifiers and denitrifiers, nitrate respiration by fermenters, and chemodenitrification. The availability of oxygen determines to a large extent the relative activities of these various groups of organisms. To better understand this influence, we investigated the effect of the partial pressure of oxygen (pO2) on the production of NO and N2O by a wide variety of common soil nitrifying, denitrifying, and nitrate-respiring bacteria under laboratory conditions. The production of NO per cell was highest by autotrophic nitrifiers and was independent of pO2 in the range tested (0.5 to 10%), whereas N2O production was inversely proportional to pO2. Nitrous oxide production was highest in the denitrifier Pseudomonas fluorescens, but only under anaerobic conditions. The molar ratio of NO/N2O produced was usually greater than unity for nitrifiers and much less than unity for denitrifiers. Chemodenitrification was the major source of both the NO and N2O produced by the nitrate respirer Serratia marcescens. Chemodenitrification was also a possible source of NO and N2O in nitrifier cultures but only when high concentrations of nitrite had accumulated or were added to the medium. Although most of the denitrifiers produced NO and N2O only under anaerobic conditions, chemostat cultures of Alcaligenes faecalis continued to emit these gases even when the cultures were sparged with air. Based upon these results, we predict that aerobic soils are primary sources of NO and that N2O is produced only when there is sufficient soil moisture to provide the anaerobic microsites necessary for denitrification by either denitrifiers or nitrifiers. 相似文献
10.
Adaptation of Nitrogen Fixation by Intact Soybean Nodules to Altered Rhizosphere pO(2) 总被引:4,自引:4,他引:0
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The N2-fixing legume nodule requires O2 for ATP production; however, the O2 sensitivity of nitrogenase dictates a requirement for a low pO2 inside the nodule. The effects of long term exposures to various pO2s on N2[C2H2] fixation were evaluated with intact soybean (Glycine max [L.] Merr., var. Wye) plants. Continuous exposure of their rhizosphere to a pO2 of 0.06 atmospheres initially reduced nitrogenase activity by 37 to 45% with restoration of original activity in 4 to 24 hours and with no further change in tests up to 95 hours; continuous exposure to 0.02 atmosphere of O2 initially reduced nitrogenase activity 72%, with only partial recovery by 95 hours. Similar exposures to a pO2 of 0.32 atmospheres had little effect on N2[C2H2] fixation; a pO2 of 0.89 atmospheres initially reduced nitrogenase activity by 98% with restoration to only 14 to 24% of that of the ambient O2 controls by 95 hours. Re-exposure to ambient pO2 of plants adapted to nonambient pO2s reduced N2[C2H2] fixation to similar magnitudes as the reductions which occurred upon initial exposure to variant pO2 conditions, and a time period was required to readapt to ambient O2. It is concluded that the N2[C2H2]-fixing system of intact soybean plants is able to adapt to a wide range of external pO2s as probably occur in soil. We postulate that this occurs through an undefined mechanism which enables the nodule to maintain an internal pO2 optimal for nitrogenase activity. 相似文献
11.
Yan Zhao Bin Guo Kehong Liang Donghua Wang Shuming Yang 《In vitro cellular & developmental biology. Plant》2017,53(2):113-121
The effects of hypobaric conditions on stable isotope and mineral element concentrations during the germination of mungbean [Vigna radiata (Linn.) Wilczek] were evaluated. Mungbean seeds were cultured in lower atmospheric pressure (60 kPa) and normal air pressure (101 kPa) conditions, respectively. Oxygen and carbon dioxide partial pressures were maintained at 21 and 0.04 kPa, respectively. At 60 kPa, the fresh weight (FW) and dry weight (DW) of plants significantly increased by 5.41 and 9.62%, respectively, compared to those at 101 kPa after culturing for 7 d. Twelve mineral elements were compared among three organs (leaf, stem, and root) from seedlings grown under hypobaric and normal atmospheric conditions. This showed that lower air pressure generally improved element accumulation in the plant. A significantly lower value of δ 13C was observed at 60 kPa compared to that at 101 kPa. In addition, a significant increase in δ 15N value was detected in three different organs of plants grown under 60 kPa. Our survey provides a foundation for future field and laboratory studies on the influence of air pressure on plants, particularly in terms of stable isotope and mineral elements. 相似文献
12.
The effects of increasing rhizosphere pO2on nitrogenase activity and nodule resistance to O2diffusion were investigated in soybean plants [Glycine max (L.) Merr. cv. Harosoy 63] in which nitrogenase (EC 1.7.99.2) activities were inhibited by (a) removal of the phloem tissue at the base of the stem (stem girdling), (b) exposure of roots to 10 mM NO3over 5 days (NO3-treated), or (c) partial inactivation of nitrogenase activity by an exposure of nodulated roots to 100 kPa O2(O2-inhibitcd). In control plants and in plants which had been treated with 100 kPa O2, increasing rhizosphere O2concentrations in 10 kPa increments from 20 to 70 kPa did not alter the steady-state nitrogenase activity. In contrast, in plants in which nitrogenase activities were depressed by stem girdling or by exposure to NO3, increasing rhizosphere pO2resulted in a recovery of 57 or 67%, respectively, of the initial, depressed rates of nitrogenase activity. This suggests that the nitrogenase activity of stem-girdled and NO3-treated soybeans was O2-limited. For each treatment, theoretical resistance values for O2diffusion into nodules were estimated from measured rates of CO2exchange, assuming a respiratory quotient of 1.1 and 0 kPa of O2in the infected cells. At an external partial pressure of 20 kPa O2, the stem-girdled and NO3--treated plants displayed resistance values which were 4 to 8.6 times higher than those in the nodules of the control plants. In control and O2-inhibited plants, increases in pO2from 20 to 70 kPa in 10 kPa increments resulted in a 2.5- to 3.9-fold increase in diffusion resistance to O2, and had little effect on either respiration or nitrogenase activity. In contrast, in stem-girdled and NO3--treated plants, increases in external pO2had little effect on diffusion resistance to O2, but resulted in a 2.3- to 3.2-fold increase in nodule respiration and nitrogenase activity. These results are consistent with stem-girdling and NO3--inhibition treatments limiting phloem supply to nodules causing an increase in diffusion resistance to O2at 20 kPa and an apparent insensitivity of diffusion resistance to increases in external pO2. 相似文献
13.
Gas films on hydrophobic surfaces of leaves of some wetland plants can improve O2 and CO2 exchange when completely submerged during floods. Here we investigated the in situ aeration of rhizomes of cordgrass (Spartina anglica) during natural tidal submergence, with focus on the role of leaf gas films on underwater gas exchange. Underwater net photosynthesis was also studied in controlled laboratory experiments. In field experiments, O2 microelectrodes were inserted into rhizomes and pO2 measured throughout two tidal submergence events; one during daylight and one during night‐time. Plants had leaf gas films intact or removed. Rhizome pO2 dropped significantly during complete submergence and most severely during night. Leaf gas films: (1) enhanced underwater photosynthesis and pO2 in rhizomes remained above 10 kPa during submergence in light; and (2) facilitated O2 entry from the water into leaves so that rhizome pO2 was about 5 kPa during darkness. This study is the first in situ demonstration of the beneficial effects of leaf gas films on internal aeration in a submerged wetland plant. Leaf gas films likely contribute to submergence tolerance of S. anglica and this feature is expected to also benefit other wetland plant species when submerged. 相似文献
14.
Effect of Altered pO(2) in the Aerial Part of Soybean on Symbiotic N(2) Fixation 总被引:6,自引:6,他引:0
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Dry matter accumulation, nitrogen content and N2 fixation rates of soybean (Glycine max [L.] Merr. cv. Wye) plants grown in chambers in which the aerial portion was exposed to a pO2 of 5, 10, 21, or 30% and a pCO2 of 300 μl CO2/l or a pO2 of 21% and a pCO2 of 1200 μl CO2/l during the complete growth cycle were measured. Total N2[C2H2] fixed was increased by CO2/O2 ratios greater than those in air and was decreased by ratios smaller than those in air; the effects on N2 fixation of decreased pO2 or elevated pCO2 were quantitatively similar during the period of vegetative growth. Decreased pO2 produced a smaller increase then elevated pCO2 during the reproductive period, presumably because of the decreased sink activity of the arrested reproductive growth under subambient pO2. At a pO2 of 5% and a pCO2 of 300 μl CO2/l total N2 fixed was increased 125% and per cent nitrogen content in the vegetative parts was increased relative to air while that in the seed was decreased. Dry matter production was increased and reproductive growth was arrested as previously reported for plants receiving only fertilizer nitrogen. At a pO2 of 30% and a pCO2 of 300 μl CO2/l total N2 fixed was decreased 50% and per cent nitrogen content in the vegetative part was increased relative to air while that in the reproductive structures was unaffected. Dry matter production was similarly decreased in both vegetative and reproductive structures. These effects of altered pO2 in the aerial part on N2 fixation are consistent with the hypothesis that the amount of photosynthate available to the nodule may be the most significant primary factor limiting N2 fixation while sink activity of the reproductive structures may be a secondary factor. 相似文献
15.
Effect of pO(2) on Growth and Nodule Functioning of Symbiotic Cowpea (Vigna unguiculata L. Walp.)
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Nodulated cowpea (Vigna unguiculata L. Walp. cv Vita 3:Bradyrhizobium CB 756) plants were cultured with their whole root system or crown root nodulation zone maintained for periods from 5 to 69 days after planting in atmospheres containing a range of pO2 (1-80%, v/v) while the rest of the plant grew in normal air. Growth (dry matter yield) and N2 fixation were largely unaffected by pO2 from 10 to 40%. Decrease in fixation at pO2 below 5% was due to lower nodulation and nodule mass and, at pO2 above 60%, to a fall in specific N2-fixing activity of nodules. Root:shoot ratios were significantly lower at pO2 below 2.5%. The effect of pO2 on nitrogenase activity (acetylene reduction), both of whole nodulated root systems and crown root nodulation zones, varied with plant age but was generally lower at supra- and subambient extremes of O2. H2 evolution showed a sharp optimum at 20% O2 but was at most 4% of total nitrogenase activity. The ratio of CO2 evolved to substrate (C2H2+H+) reduced by crown root nodulation zones was constant (6 moles CO2 per mole substrate reduced) from 2.5 to 60% O2 but at levels below 2.5 and above 80% O2 reached values between 20 and 30 moles CO2 per mole substrate reduced. Effects of long-term growth with nonambient pO2 on adaptation and efficiency of functioning of nodules are discussed. 相似文献
16.
Adaptation of Nodulated Soybean (Glycine max L. Merr.) to Growth in Rhizospheres Containing Nonambient pO(2) 总被引:3,自引:3,他引:0
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Nodulated soybean (Glycine max L. Merr. cv White Eye inoculated with Bradyrhizobium japonicum strain CB 1809) plants were cultured in the absence of combined N from 8 to 28 days with their root systems maintained continuously in 1, 2.5, 5, 10, 20, 40, 60, or 80% O2 (volume/volume) in N2. Plant dry matter yield was unaffected by partial pressure of oxygen (pO2) and N2 fixation showed a broad plateau of maximum activity from 2.5 to 40 or 60% O2. Slight inhibition of nitrogenase activity occurred at 1% O2 and as much as 50% inhibition occurred at 80% O2. Low pO2 (less than 10%) decreased nodule mass on plants, but this was compensated for by those nodules having higher specific nitrogenase activities. Synthesis and export of ureides in xylem was maintained at a high level (70-95% of total soluble N in exudate) over the range of pO2 used. Measurements of nitrogenase (EC 1.7.99.2) activity by acetylene reduction indicated that adaptation of nodules to low pO2 was largely due to changes in ventilation characteristics and involved increased permeability to gases in those grown in subambient pO2 and decreased permeability in those from plants cultured with their roots in pO2 greater than ambient. A range of structural alterations in nodules resulting from low pO2 were identified. These included increased frequency of lenticels, decreased nodule size, increased volume of cortex relative to the infected central tissue of the nodule, as well as changes in the size and frequency of extracellular voids in all tissues. In nodules grown in air, the inner cortex differentiated a layer of four or five cells which formed a band, 40 to 50 micrometers thick, lacking extracellular voids. This was reduced in nodules grown in low pO2 comprising one or two cell layers and being 10 to 20 micrometers thick in those from 1% O2. Long-term adaptation to different external pO2 involved changes which modify diffusive resistance and are additional to adjustments in the variable diffusion barrier. 相似文献
17.
Limitations on photosynthesis, characterized by leaf CO2 exchange, chlorophyll fluorescence, and thylakoid structure, were studied under environmental conditions simulating culturein vitro. These were simulated by growingPhaseolus vulgaris plants in nutrient solution under high relative humidity of air (>90%), and CO2 concentrations (ca) that decreased with the development of photosynthetic activities during plant ontogeny (1200 to 300 mg m?3). The ontogeny of such model plants was more rapid, primary leaves reached photosynthetic maturity 2 to 3 d earlier and their life span was 7 to 14 d shorter than in control plants. Their photosynthetic activityin situ was limited, after reaching “photosynthetic maturity”, similarly to plants grownin vitro. When measured under optimal conditions, however, 50 to 70% higher net photosynthetic rates (PN) were found in leaves of different ages as compared with plants grown under ca of 700 mg m?3 and a lower air humidity (30–35%). This increase in PN was associated with a high conductance for CO2 transfer by adaxial and abaxial epidermes. In model plants, the dark respiration rate (RD) was almost twice that in the control, while the photorespiration rates were similar to controls; CO2 compensation concentration was about 50% of that in controls. The ratios PN/RD were similar in control and in model plants. Chlorophylla+b content in leaves of the model plants was lower than that in the control plants. Grana extent increased with plant age in the model plants while it decreased in the control ones. In both the stromal and granal membranes of the chloroplasts in model plants, a marked accumulation of carotenoids occurred independent of age. The ratio of variable to maximal fluorescence, Fv/Fm, did not differ in the model and the control plants. In the control plants, photochemical quenching (qP) slightly increased with plant age and was not affected by CO2 concentration present during measurement. In the model plants, qP increased with elevated CO2 concentration in young plants and decreased in saturating CO2 concentrations in older plants. Nonphotochemical quenching (qNP) was lower in the model plants and increased under CO2 saturating conditions. Vitality index, Rfd, was markedly lower in the model plants than in the control ones and a decline was found in saturating CO2 concentration. 相似文献
18.
Effects of altered gaseous environments (parabarosis) on interferon production in mice were studied, with Newcastle disease virus (NDV) as the inducer. Increased levels of interferon in lung tissue were observed when mice were exposed to 11% O2 in N2 for 3 days before and after, or only after, injection of NDV. However, serum interferon levels remained unchanged. Exposure of mice to 77% O2 for up to 7 days did not affect the response to interferon induction as assayed in lungs or sera. Interferon levels were significantly depressed in mice exposed to a simulated depth of 213 ft in seawater [with normal partial pressure of O2 (pO2) in N2] for 2 or 4 weeks. Whereas definite depression of interferon was also observed in mice maintained at a simulated altitude of 37,000 ft (with normal pO2) for 2 weeks, those maintained at the same condition for 4 weeks showed a normal level of interferon. The results obtained with hypoxia are compatible with other reports on the influence of O2 tension on viral infection. The factors responsible for alterations observed in interferon level in mice kept in normal pO2, but under altered pressure, have not yet been identified. 相似文献
19.
Nitrogenase Activity (Acetylene Reduction) of Root-Associated, Cold-Climate Azospirillum, Enterobacter, Klebsiella, and Pseudomonas Species During Growth on Various Carbon Sources and at Various Partial Pressures of Oxygen 总被引:3,自引:2,他引:1
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A comprehensive view of the diazotrophic bacterial flora of plants requires that attention be paid to the appropriate carbon and oxygen requirements during isolation of the bacteria. Twenty compounds (monosaccharides, disaccharides, polyols, and organic acids) were therefore examined as carbon and energy sources for nitrogenase activity in semisolid stab cultures at pO2 values of 0.21, 0.02, and ≤0.002 with 12 strains of diazotrophic root-associated bacteria. With the facultatively anaerobic bacteria of the genera Klebsiella and Enterobacter, the best substrate was sucrose, followed by fructose and mannitol, whereas among the organic acids, only malic and fumaric acids supported any activity. With the obligately aerobic bacteria of the genera Azospirillum and Pseudomonas, disaccharides were not utilized for nitrogen fixation, but several organic acids were accepted in addition to monosaccharides and polyols; malate and glucose were the best substrates. The patterns of the carbon sources utilized for nitrogen fixation were coherent within the species, with the exception of one Klebsiella pneumoniae and one Enterobacter agglomerans strain, both isolated from the same individual grass plant, which were unable to utilize lactose. Anaerobic conditions (pO2 value of ≤0.002) were required for maximum nitrogenase activity with the facultatively anaerobic bacteria, with the exception of one strain of E. agglomerans, which required atmospheric oxygen (pO2 value of 0.21). Also, the obligately aerobic diazotrophs required atmospheric oxygen for maximum nitrogenase activity. The maximum specific nitrogenase activities (expressed as micromoles of C2H4 · milligram of bacterial protein−1 · hour−1) noted during the exponential growth phase of the bacteria were the following: 2.68 with Azospirillum lipoferum on malate, 2.41 with K. pneumoniae and 1.58 with E. agglomerans on sucrose, and 0.95 with Pseudomonas sp. on malate. 相似文献
20.
Transient responses of nitrogenase to acetylene and oxygen in actinorhizal nodules and cultured frankia 总被引:6,自引:4,他引:2
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Nitrogenase activity in root nodules of four species of actinorhizal plants showed varying declines in response to exposure to acetylene (10% v/v). Gymnostoma papuanum (S. Moore) L. Johnson. and Casuarina equisetifolia L. nodules showed a small decline (5-15%) with little or no recovery over 15 minutes. Myrica gale L. nodules showed a sharp decline followed by a rapid return to peak activity. Alnus incana ssp. rugosa (Du Roi) Clausen. nodules usually showed varying degrees of decline followed by a slower return to peak or near-peak activity. We call these effects acetylene-induced transients. Rapid increases in oxygen tension also caused dramatic transient decreases in nitrogenase activity in all species. The magnitude of the transient decrease was related to the size of the O2 partial pressure (pO2) rise, to the proximity of the starting and ending oxygen tensions to the pO2 optimum, and to the time for which the plant was exposed to the lower pO2. Oxygen-induced transients, induced both by step jumps in pO2 and by O2 pulses, were also observed in cultures of Frankia. The effects seen in nodules are purely a response by the bacterium and not a nodule effect per se. Oxygen-induced nitrogenase transients in actinorhizal nodules from the plant genera tested here do not appear to be a result of changes in nodule diffusion resistance. 相似文献