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91.
92.
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
93.
Tissue culture selection techniques were used to isolate a maize (Zea mays L.) variant D33, in which the aspartate family pathway was less sensitive to feedback inhibition by lysine. D33 was recovered by successively subculturing cultures originally derived from immature embryos on MS medium containing growth-inhibitory levels of lysine+threonine. The ability of D33 to grow vigorously on lysine+ threonine medium was retained after growth for 12 months on nonselection medium. New cultures initiated from shoot tissues of plants regenerated from D33 also were resistant to lysine+threonine inhibition. The Ki of aspartokinase for its feedback inhibitor, lysine, was about 9-fold higher in D33 than for the enzyme from unselected cultures. The free pools of lysine, threonine, isoleucine and methionine were increased 2–9-fold in D33 cultures. This was consistent with the observed change in feedback regulation of aspartokinase, the first enzyme common to the biosynthesis of these amino acids in the aspartate pathway. The accumulated evidence including the stability of resistance in the cultures, the resistance of cultures initiated from regenerated plants, the altered feedback regulation, and the increased free amino acids, indicates a mutational origin for these traits in line D33.Abbreviation LT
lysine+threonine in equimolar concentration
Paper No. 10880, Scientific Journal Series, Minnesota Agricultural Expertment Station 相似文献
94.
Summary Differentiating cells ofMicrasterias denticulata have been treated with aqueous solutions of the antibiotic gougerotin. Strong and characteristic cytomorphogenetic aberrations, resembling those of the anuclear type of development could be observed. It has been speculated that the aberrant growth of the growing half cell is the result of inhibition of protein synthesis by gougerotin.In addition to the morphogenetic influence, nuclear migration has been strongly inhibited by the drug. Therefore, it might be suggested that gougerotin is an active anti-microtubule agent. 相似文献
95.
Isoelectric focusing following by electrophoresis of proteins for visualizing their titration curves by zymogram and immunofixation 总被引:1,自引:0,他引:1
After isoelectric focusing followed by electrophoresis at right angles in the same gel slab, it is possible to visualize the titration curve of proteins by zymograms or immunofixation even of an unpurified sample. This information can be very useful for the selection of the proper purification strategy by charge-dependent methods, e.g. ion-exchange chromatography, zone and disc electrophoresis and isotachophoresis. The titration curve also gives information on the stability of the protein as a function of the prevailing pH of the medium, in the pH 3-10 range. A region of instability is found for most proteins in acidic conditions, below pH 4.5, while most proteins are stable in the alkaline pH region, at least up to pH 10. The best method for developing zymograms and immunoprints appears to pH 10. The best method for developing zymograms and immunoprints appears to be the 'sandwich technique', by which a thin agarose slab, cast on an hydrophilic polyester sheet, and impregnated with appropriate reagents, is left in contact with a polyacrylamide gel thin layer used to generate the titration curves. 相似文献
96.
The effect of the addition of different concentratons of cystine and cysteine on sporulation and parasporal crystal formation
inBacillus thuringiensis var.thuringiensis was studied. The effect was well pronounced when the cystine/cysteine additions were made after the stationary phase. Heat
stable spores and crystals were formed when the culture was provided with a low concentration of cystine/cysteine (0.05 per
cent w/v). At a moderate concentration of cystine or cysteine (0.15%), only heat labile spores were formed without the production
of the crystal. When the cystine/cysteine concentration was high (0.25%), spore and crystal formation were completely inhibited.
Partial reversal of inhibition of sporulation was brought about by sodium sulphate or Zinc sulphate and lead, copper, cadmium
or cobalt acetate at 0.2 mM or at 0.2% of sodium or potassium pyruvate, citrate, cisaconitate, oxalosuccinate, ∞ -keto-glutarate,
succinate, fumarate, malate, or oxalacetate. Glutamate (0.2%) overcame the inhibitory effect of cystine/cysteine completely.
The structural changes observed using phase contrast microscopy were dependent upon the concentration of cystine/cysteine. 相似文献
97.
This report demonstrates that the commonly used anesthetic agent, pentobarbital sodium, in concentrations of 1 · 10?4 to 2 · 10?3 M inhibits calcium (Ca2+) uptake in both rat aortic and portal venous smooth muscle. The data indicate that total exchangeable Ca2+ in portal vein is reduced by about 15% in 1 · 10?4 M pentobarbital sodium, while the intracellular exchangeable Ca2+ is reduced by 24%. On the other hand, in aortic smooth muscle, while 5–20 · 10?4 M pentobarbital sodium reduces total exchangeable Ca2+ by about 15%, intracellular Ca2+ is reduced by 22% in 5 · 10?4 M pentobarbital sodium and by 38% in 2 · 10?3 M pentobarbital sodium. The present studies thus reveal that concentrations of pentobarbital sodium known to be present during induction of surgical anesthesia can exert significant inhibitory effects on exchangeability and transmembrane movement of Ca2+ in at least two different types of blood vessels. 相似文献
98.
- 1. (1) VO3− combines with high affinity to the Ca2+-ATPase and fully inhibits Ca2+-ATPase and Ca2+-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca2+-dependent phosphoenzyme.
- 2. (2) VO3− blocks hydrolysis of ATP at the catalytic site. The sites for VO3− also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca2+-ATPase.
- 3. (3) The sites for VO3− show positive interactions in affinity with sites for Mg2+ and K+. This accounts for the dependence on Mg2+ and K+ of the inhibition by VO3−. Although, with less effectiveness, Na+ substitutes for K+ whereas Li+ does not. The apparent affinities for Mg2+ and K+ for inhibition by VO3− seem to be less than those for activation of the Ca2+-ATPase.
- 4. (4) Inhibition by VO3− is independent of Ca2+ at concentrations up to 50 μM. Higher concentrations of Ca2+ lead to a progressive release of the inhibitory effect of VO3−.
Keywords: Ca2+-ATPase; Vanadate inhibition; K+; Li+; (Red cell membrane) 相似文献
99.
100.
Summary The effects of anthraquinones and some other quinonoid and phenolic compounds on mineralization of urea N in soils were studied by estimating the influence on urease activity and nitrification. Anthraquinones did not affect the mineralization of urea N but 1,4-naphthoquinone; 2-methyl-1,4-naphthoquinone; 2–3-dichlorohydroquinone; 4,6-di-tert.butyl-o-benzoquinone; 4-tert.butylpyrocatechol and 4,6-di-tert.butylpyrocatechol inhibited urease activity and nitrification. The hydrolysis of urea (100 ppm) was not prevented by partial reduction in urease activity. The effective substances also inhibited dehydrogenase activity. 相似文献