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101.
In the C4 plant, Amaranthus graecizans, increasing [O2] from 2% up to 100% inhibited photosynthesis, quantum yield, and the carboxylation efficiency, and increased the CO2 compensation point () from 2 to about 12 l/l. The O2 inhibition of photosynthesis was fully reversible. When changing from 2.5 to 40% O2 and vice versa, about 1 h was required for full equilibration with an O2 inhibition of 18%; whereas in wheat, a C3 species, inhibition of photosynthesis and its reversal occurs within minutes after changing [O2], resulting in 63% inhibition of photosynthesis by 45% O2. These differences in O2 inhibition between a C4 and C3 species can be explained by high diffusive resistance across bundle-sheath cells of C4 plants and the increased CO2/O2 ratio in bundle-sheath cells which is the consequence of the C4 cycle. In A. graecizans, increased with increasing [O2] but tended to reach a maximum at relatively high O2 levels. The lack of a linear increase in as previously observed for C3 species indicates that a considerable amount of photorespired CO2 may be re-fixed with increasing levels of O2. In comparison to previous reports with other C4 species, photosynthesis of A. graecizans shows greater sensitivity to O2, with a noticeable inhibition occurring with shifts from 2 to 21% O2. A. graecizans has characteristics of other C4 species with respect to Kranz anatomy, localization of PEP carboxylase in mesophyll cells and RuBP carboxylase in bundle-sheath cells, and little fractionation among carbon isotopes during CO2 fixation. The basis for the higher sensitivity of photosynthesis of A. graecizans to O2 may be based upon a lower diffusive resistance of gases across bundle-sheath cells than in some other C4 species.Abbreviations CE
carboxylation efficiency
- RuBP
ribulose-1,5-bisphosphate
-
CO2 compensation point 相似文献
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1. Low-temperature difference spectra of gradient-purified mitochondria of Acanthamoeba castellanii reveal the presence of cytochromes b-555, b-562 and c-549, with a-type cytochromes having a broad asymmetrical maximum at 602 nm; these components were also observed in specta of whole cells. 2. The a-type cytochromes are unusual in that they have split Soret absorption maxima (at 442 and 449 nm) and an uncharacteristic CO difference spectrum. 3. CO difference spectra of whole cells and 'microsomal' membranes show large amounts of cytochrome P-420 compared with cytochrome P-450. 4. Difference spectra in the presence of cyanide indicate the presence of an a-type cytochrome and two cyanide-reacting components, one of which may be cytochrome a3. 5. Whole-cell respiration in a N2/O2 (19:1) atmosphere was decreased by 50%, suggesting the presence of a low-affinity oxidase. This lowered respiration is inhibited by 50% by CO, and the inhibition is partially light-reversible; photochemical action spectra suggest that cytochrome a3 contributes to this release of inhibition. Other CO-reacting oxidases are also present. 6. The results are discussed with the view that cytochrome a3 is present in A. castellanii, but its identification in CO difference spectra is obscured by other component(s). 相似文献
105.
Carbon Dioxide and Ethylene Control of Spore Germination in Onoclea sensibilis L 总被引:1,自引:1,他引:0 下载免费PDF全文
Edwards ME 《Plant physiology》1977,59(4):756-758
Regulation of spore germination in the fern Onoclea sensibilis L. was investigated by applying CO2 alone and in combination with ethylene. Sterile spores were sown aseptically on Knops solution in loosely capped culture tubes, enclosed individually in 2-liter chambers, and grown under continuous white light. When maintained in enclosed containers with the ethylene-absorbent mercuric perchlorate and with atmospheres enriched up to 2% CO2 (v/v), spores germinated without any inhibition. Higher levels of applied CO2 were progressively inhibitory. Inhibition by CO2 was reversible. When CO2 was permitted to escape and spores were exposed subsequently to ambient laboratory air, recovery from inhibition occurred within 48 hours. Also, inhibition by CO2 was specific, since the same degree of inhibition resulted regardless of whether spores were treated with exogenous CO2 for 48, 72, or 96 hours. The effect on germination of 1 μl/l added ethylene depended upon the amount of applied CO2. When containers of KOH were enclosed and ambient CO2 was absorbed, inhibition of germination by 1 μl/l exogenous ethylene was 90%. When CO2 was applied in concentrations from 0.25 to 1.0% (v/v), CO2 increasingly antagonized the inhibitory action of 1 μl/l added ethylene. Thus, photoinduced germination of spores was regulated by competitively interacting levels of CO2 and ethylene. 相似文献
106.
A T Willis I R Ferguson P H Jones K D Phillips P V Tearle R V Fiddian D F Graham D H Harland D F Hughes D Knight W M Mee N Pashby R L Rothwell-Jackson A K Sachdeva I Sutch C Kilbey D Edwards 《BMJ (Clinical research ed.)》1977,1(6061):607-610
A double-blind randomised trial was carried out among 46 patients undergoing elective colonic surgery; 27 patients received prophylactic metronidazole and 19 received placebo. Anaerobic infections did not develop in any of the metronidazole-treated patients, but did develop in 11 (58%) of 19 controls who were subsequently successfully treated with metronidazole. 相似文献
107.
J G Edwards 《BMJ (Clinical research ed.)》1977,2(6079):96-97
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Abstract The respiratory activity of cysts of Azotobacter vinelandii has been compared with that of vegetative cells. Whole cysts had a much reduced respiratory activity which was less sensitive to KCN. Substrate oxidation rates by membrane preparations from cysts were reduced approximately 10-fold and sensitivity to KCN was decreased by a similar factor. Difference spectra of cyst membranes revealed changes in cytochrome content. Cytochrome oxidase d was apparently absent, cytochrome a 1 levels were approximately halved whilst those of cytochrome oxidase o were almost doubled. Cytochromes of the b and c -type were present in similar amounts to those in vegetative cells. 相似文献