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81.
几种环境因素对玉米叶切块光诱导的影响 总被引:1,自引:1,他引:0
利用液相氧电极研究了暗处理、光强、CO2水平、缺钾和干旱对玉米叶切块光诱导的影响。发现长时间的暗处理、高光强、低CO2浓度、缺钾和干旱均使光合诱导期拉长。影响光合诱导期的外界逆境如低CO2浓度、缺钾和干旱也使玉米叶片的净光合速率下降,并对这些结果产生的原因作了分析。 相似文献
82.
Enhanced ethylene production by primary roots of Zea mays L. in response to sub-ambient partial pressures of oxygen 总被引:1,自引:0,他引:1
R. W. BRAILSFORD L. A. C. J. VOESENEK C. W. P. M. BLOM A. R. SMITH M. A. HALL M. B. JACKSON 《Plant, cell & environment》1993,16(9):1071-1080
Ethylene production by primary roots of 72–h-old intact seedlings of Zea mays L. cv. LG11 was studied under ambient and sub-ambient oxygen partial pressures (pO2) using a gas flow-through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting-up, ethylene production in air was faster during the first 6h than later, in association with a small temporary swelling of the roots. When roots were switched from air (20–8kPa O2) to 3 or 5kPa O2 after 6h, ethylene production increased within 2—3 h. When, the roots were returned to air 16 h later, ethylene production decreased within 2—3 h. The presence of 10kPa CO2 did not interfere with the effect of 3kPa O2. Transferring roots from air to 12–5kPa did not change ethylene production, while a reduction to 1 kPa O2 induced a small increase. The extra ethylene formed in 3 and 5 kPa O2 was associated with plagiotropism, swelling, root hair production, and after 72 h, increased amounts of intercellular space (aerenchyma) in the root cortex. Root extension was also slowed down, but the pattern of response to oxygen shortage did not always match that of ethylene production. On return to air, subsequent growth patterns became normal within a few hours. In the complete absence of oxygen, no ethylene production was detected, even when anaerobic roots were returned to air after 16 h. 相似文献
83.
The kinetic constraints that are imposed on cytochrome oxidase in its dual function as the terminal oxidant in the respiratory process and as a redox-linked proton pump provide a unique opportunity to investigate the molecular details of biological O2 activation. By using flow/flash techniques, it is possible to visualize individual steps in the O2-binding and reduction process, and results from a number of spectroscopic investigations on the oxidation of reduced cytochrome oxidase by O2 are now available. In this article, we use these results to synthesize a reaction mechanism for O2 activation in the enzyme and to simulate time-concentration profiles for a number of intemediates that have been observed experimentally. Kinetic manifestation of the consequences of coupling exergonic electron transfer to endergonic proton translocation emerge from this analysis. Energetic efficiency in this process apparently requires that potentially toxic intermediate oxidation states of dioxygen accumulate to substantial concentration during the reduction reaction. 相似文献
84.
Junichi Mano Kunio Kawamoto G. Charles Dismukes Kozi Asada 《Photosynthesis research》1993,38(3):433-440
A new binding site for anions which inhibit the water oxidizing complex (WOC) of Photosystem II in spinach has been identified. Anions which bind to this site inhibit the flash-induced S2/S0 catalase reaction (2H2O22H2O+O2) of the WOC by displacing hydrogen peroxide. Using a mass spectrometer and gas permeable membrane to detect the 32O2 product, the yield and lifetime of the active state of the flash-induced catalase (to be referred to simply as flash-catalase) reaction were measured after forming the S2 or S0-states by a short flash. The increase in flash-catalase activity with H2O2 concentration exhibits a Km=10–20 mM, and originates from an increase in the lifetime by 20-fold of the active state. The increased lifetime in the presence of peroxide is ascribed to formation of the long-lived S0-state at the expense of the unstable S2-state. The anion inhibition site differs from the chloride site involved in stimulating the photolytic water oxidation reaction (2H2OO2+4e-+4H+). Whereas water oxidation requires Cl- and is inhibited with increasing effectiveness by F-CN-N3
-, the flash-catalase reaction is weakly inhibited by Cl-, and with increasing effectiveness by F-CN-, N3
-. Unlike water oxidation, chloride is unable to suppress or reverse inhibition of the flash-catalase reaction caused by these anions. The inhibitor effectiveness correlates with the pKa of the conjugate acid, suggesting that the protonated species may be the active inhibitor. The reduced activity arises from a shortening of the lifetime of the flash-induced catalase active state by 3–10 fold owing to stronger anion binding in the flash-induced states, S2 and S0, than in the dark S-states, S1 and S-1. To account for the paradoxical result that higher anion concentrations are required to inhibit at lower H2O2 concentrations, where S2 forms initially after the flash, than at higher H2O2 concentrations, where S0 forms initially after the flash, stronger anion binding to the S0-state than to the S2-state is proposed. A kinetic model is given which accounts for these equilibria with anions and H2O2. The rate constant for the formation/release of O2 by reduction of S2 in the WOC is <0.4 s-1.Abbreviations ADRY
acceleration of the deactivation reactions of the water splitting enzyme system Y
- BTP
bis [tris(hydroxymethyl)methylamino]-propane
- CCCP
carbonylcyanide m-chlorophenylhyrazone
- DCBQ
2,5-dichlorobenzoquinone
- DMBQ
2,3-dimethylbenzoquinone
- WOC
water oxidizing complex 相似文献
85.
Jonathan H. A. Nugent Dugald J. Maclachlan Stephen E. J. Rigby Michael C. W. Evans 《Photosynthesis research》1993,38(3):341-346
Our recent EPR and EXAFS experiments investigating the structure of the oxygen-evolving complex of PS II are discussed. PS II treatments which affect the cofactors calcium and chloride have been used to poise samples in modified forms of the S-states, S1, S2 and S3. X-ray absorption studies indicate a similar overall structure for the manganese complex between treated and native samples although the influence of the treatments and cofactors is observed. Manganese oxidation (or oxidation of a ligand to the manganese cluster) is indicated to occur on each of the transitions S1 S2 and S2 S3 in these modified samples. The cluster appears to contain at least two inequivalent Mn-Mn pairs. In the native samples the Mn-Mn distance is 2.7 Å, but in samples where the calcium site is affected, one of the pairs has a 3.0 Å Mn-Mn distance. The intensity of the 3.3/3.6 Å interaction is reduced on sodium chloride treatment (calcium depletion) perhaps indicating calcium binding close to the manganese cluster. From EPR data we also propose that treatments which affect calcium and chloride binding cause a modification of the native S2 state, slow the reduction of Yz
and allow an S3 EPR signal to be observed following illumination. The origin of the S3 EPR signal, a modified S3 or S2 X where X is an organic radical of unknown charge, is discussed in relation to the results from the EXAFS studies.Abbreviations EPR
electron paramagnetic resonance spectroscopy
- EXAFS
extended X-ray absorption fine structure
- HTG
n-heptyl -d-thioglucoside
- MES
2(N-morpholino)ethanesulfonic acid
- OEC
oxygen evolving complex
- PPBQ
phenyl-1,4-benzoquinone
- PS II
Photosystem II
- Yz
redox active tyrosine 相似文献
86.
Selective solubilization of Photosystem II membranes with the non-ionic detergent octyl thioglucopyranoside has allowed the isolation of a PS II system which has been depleted of the 22 and 10 kDa polypeptides but retains all three extrinsic proteins (33, 23 and 17 kDa). The PS II membranes which have been depleted of the 22 and 10 kDa species show high rates of oxygen evolution activity, external calcium is not required for activity and the manganese complex is not destroyed by exogenous reductants. When we compared this system to control PS II membranes, we observed a minor modification of the reducing side, and a conversion of the high-potential to the low-potential form of cytochrome b
559.Abbreviations Chl-
chlorophyll
- DCBQ-
2,5-dichloro-p-benzoquinone
- DCMU-
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- ESR-
electron spin resonance
- MES-
2-(N-morpholino)ethanesulfonic acid
- OTG-
octyl--d-thioglucopyranoside
- PS II-
Photosystem II
- PEG-
polyethylene glycol, Mr=6000
- Tris-
2-amino-2-hydroxyethylpropane-1,3-diol 相似文献
87.
研究发现,分离原生质体的酶解脱壁处理可以诱导苜蓿细胞产生活性氧。培养基中添加抗氧化剂,有助于提高培养原生质体的分裂频率,缓解褐化现象的出现。经紫外照射处理的培养基不利于苜蓿原生质体的生长和分裂,添加抗氧化剂后,紫外辐射所引起的不良效应则被抵消。因而,通过抗氧化剂对活性氧的清除,有助于早期原生质体的培养。 相似文献
88.
Benzene is strongly suspected of being an animal and human carcinogen, but the mechanisms by which it induces tumors of lymphoid and hematopoietic organs are unknown. Production of active oxygen species from benzene metabolites [hydroquinone (HQ), catechol and 1,2,4-benzenetriol (1,2,4-BT) and related polyphenols (resorcinol, pyrogallol and phloroglucinol) are investigated. Pyrogallol and 1,2,4-BT can produce H2O2, O
2
–
and·OH simultaneously, and have powerful mutagenic potential. Resorcinol and phloroglucinol cannot produce all of the active oxygen species, and show no mutagenic effects. Catechol can produce H2O2, but cannot produce O
2
–
and·OH, and has no mutagenic activity. These data strongly support the hypothesis that benzene metabolites can cause mutagenicity via the generation of oxygen radicals. Although HQ produces H2O2 only, and less than produced by pyrogallol and 1,2,4-BT, the mutagenicity of HQ is higher. The results indicate that HQ may act via another mechanism to cause mutagenicity. In the presence of trace metal ions, the reactivity of polyphenols is increased. The biological significance of these phenomena are investigated and discussed. 相似文献
89.
安徽宿县夹沟寒武-奥陶系界线附近生物群演变及地球化学特征 总被引:2,自引:0,他引:2
对宿县夹沟地区跨寒武系与奥陶系的三山子组的碳、氧同位素和微量元素地球化学的研究表明,寒武-奥陶系界线附近有δ^13C和δ^18O的负异常,亲铁元素、亲铜元素的正异常。这些异常与生物群面貌的变化在时间上是同步的。据此认为研究区在寒武纪末可能存在灾变事件。同时,考虑到寒武纪末和奥陶纪初生物群面貌的重大差异,综合国内,外有关研究,认为寒武纪末期可能存在全球性的重大地质事件。 相似文献
90.
The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m–2 a–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount. 相似文献