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121.
Summary Solution calcium concentrations required for the growth of a range of plant species, including both monocotyledons and dicotyledons,
were determined in two experiments in which plants were grown in flowing solution culture at constantly maintained calcium
concentrations ranging from 0.5 to 3000 μM. Calcium chloride was used as the calcium source in the first experiment, calcium sulphate was used in the second.
At calcium concentrations of 10 μM and below, all species developed calcium deficiency symptoms. The severity of the deficiency was more pronounced in the dicotyledons
than in the monocotyledons. However, cassava was much more tolerant than all other dicotyledons and equally as tolerant as
rice, the most tolerant monocotyledon.
Solution calcium concentrations required for 90% of maximum yield were generally lower for monocotyledons (3 to 20 μM) than for dicotyledons (7 to 720μM) when calcium chloride was used as the calcium source. When calcium sulphate was used, 7 out of 11 species, including 3 monocotyledons,
required external calcium concentrations of 1200 μM and above. The results are discussed in relation to effects of solution composition and the choice of counter-ions on plant
response to calcium and other macronutrient cations. It is concluded that yield depressions due to toxicity of excesses of
chloride, and possibly other counter-ions, can lead to serious underestimation of limiting external cation concentrations
for plant growth. 相似文献
122.
Direct inhibition of epithelial Na+ channels by a pH-dependent interaction with calcium,and by other divalent ions 总被引:4,自引:0,他引:4
Summary Direct inhibitory effects of Ca2+ and other ions on the epithelial Na+ channels were investigated by measuring the amiloride-blockable22Na+ fluxes in toad bladder vesicles containing defined amounts of mono- and divalent ions. In agreement with a previous report (H.S. Chase, Jr., and Q. Al-Awqati,J. Gen. Physiol.
81:643–666, 1983) we found that the presence of micromolar concentrations of Ca2+ in the internal (cytoplasmic) compartment of the vesicles substantially lowered the channel-mediated fluxes. This inhibition, however, was incomplete and at least 30% of the amiloride-sensitive22Na+ uptake could not be blocked by Ca2+ (up to 1mm). Inhibition of channels could also be induced by millimolar concentrations of Ba2+, Sr2+, or VO2+, but not by Mg2+. The Ca2+ inhibition constant was a strong function of pH, and varied from 0.04 m at pH 7.8 to >10 m at pH 7.0 Strong pH effects were also demonstrated by measuring the pH dependence of22Na+ uptake in vesicles that contained 0.5 m Ca2+. This Ca2+ activity produced a maximal inhibition of22Na+ uptake at pH7.4 but had no effect at pH7.0. The tracer fluxes measured in the absence of Ca2+ were pH independent over this range. The data is compatible with the model that Ca2+ blocks channels by binding to a site composed of several deprotonated groups. The protonation of any one of these groups prevents Ca2+ from binding to this site but does not by itself inhibit transport. The fact that the apical Na+ conductance in vesicles, can effectively be modulated by minor variations of the internal pH near the physiological value, raises the possibility that channels are being regulated by pH changes which alter their apparent affinity to cytoplasmic Ca2+, rather than, or in addition to changes in the cytoplasmic level of free Ca2+. 相似文献
123.
Neocallimastix frontalis PN-1 utilized the soluble sugars D-glucose, D-cellobiose, D-fructose, maltose, sucrose, and D-xylose for growth. L-Arabinose, D-galactose, D-mannose, and D-xylitol did not support growth of the fungus. Paired substrate test systems were used to determine whether any two sugars were utilized simultaneously or sequentially. Of the paired monosaccharides tested, glucose was found to be preferentially utilized compared with fructose and xylose. The disaccharides cellobiose and sucrose were preferentially utilized compared with fructose and glucose, respectively, an cellobiose was also the preferred substrate compared with xylose. Xylose was the preferred substrate compared with maltose. In further incubations, the fungus was grown on the substrate utilized last in the two-substrate tests. After moderate growth was attained, the preferred substrate was added to the culture medium. Inhibition of nonpreferred substrate utilization by the addition of the preferred substrate was taken as evidence of catabolite regulation. For the various combinations of substrates tested, fructose and xylose utilization was found to be inhibited in the presence of glucose, indicating that catabolite regulation was involved. No clear-cut inhibition was observed with any of the other substrate combinations tested. The significance of these findings in relation to rumen microbial interactions and competitions is discussed. 相似文献
124.
The oxidation of cytochromeb
561 by ATP was measured in submitochondrial particles inhibited by antimycin. The redox potential of the bulk (M phase) was controlled by the ratio of fumarate:succinate, and the oxidation of cytochromeb was calculated and expressed as a change in redox potential (E
h) measured in millivolts. The oxidation of cytochromeb
561 is an energy-driven reaction affected only by the component of the proton motive force. The oxidation (measured in millivolts) is a function of the phosphate potential, reaching a maximal value of 40 mV at GATP<–12 kcal/mole. The maximal measured value of ATP-dependent was 100 mV. Thus only a fraction of the membrane potential effects the redox state of cytochromeb
561. In contrast to the ATP-induced oxidation of cytochromeb
561, cytochromeb
566 is in redox equilibrium with fumarate succinate either in the presence or in the absence of ATP. The selective oxidation ofb
561 is explained within the term of theQ cycle as a reflection of on the electron electrochemical potential. The positive electric potential of theC phase causes cytochromeb
566 to act as oxidant with respect to cytochromeb
561. In the presence of antimycin cytochromeb
561 cannot equilibrate with the quinone and undergoes oxidation, while cytochromeb
566 reequilibrates with the quinone and thus regains redox equilibrium with the fumarate succinate redox buffer.Abbreviations used: ETPH, phosphorylating submitochondrial particles; TMPD,N
1
N
1
NN-tetramethyl-p-phenylenediamine; FCCP, carbonylcyanidep-trifluoromethoxyphenylhydrazone; Mes, 2-(N-morpholino) ethanesulfonic acid. 相似文献
125.
Summary Artificial bileaflet membranes were formed from extracts of chloroplasts. Gradients of a redox potential were created across the membranes by adding various concentrations of ceric-cerous ions, ferric-ferrous ions, and ascorbic acid to the aqueous solutions on either side of the membrane. When a membrane interposed between solutions of different redox potential was irradiated with light, a potential difference of up to 50 mV was recorded. Analysis of the photoresponse allowed its separation into two components: a photoelectromotive driving force dependent upon the redox potential gradient, and a photoconductive pathway dependent upon the amount of light absorbed by the membranes. There appeared to be a limit to the photocurrent that could be drawn from a membrane at a particular intensity of irradiation; i.e., it did not increase indefinitely with increase of the redox potential gradient. Conductance of the photoconductive pathway was independent of temperature. Phycocyanin added to the aqueous solution participated in the photoresponse in a unidirectional manner that suggested facilitation of electron transport from membrane to acceptors in the aqueous solution. 相似文献
126.
Frequency-Dependent Capacitance of Hydrophobic Membranes Containing Fixed Negative Charges 总被引:1,自引:1,他引:0
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Asher Ilani 《Biophysical journal》1968,8(5):556-574
Filters containing fixed negative charges were saturated with hydrophobic solvent and interposed between aqueous solutions. The capacitance of such membranes was measured in the frequency range of 0.05-30 kc. The capacitance increased with decrease in frequency. The frequency dependence of the capacitance was sensitive to nature of the cation present and to salt concentration in the aqueous solution. It is suggested that variation of membrane resistivity in the space charge region of the membrane is responsible for this phenomenon. Possible effects of the potential and counterion concentration profiles at the membrane-water interface are discussed. 相似文献
127.
Leon Asher 《Reviews of Physiology, Biochemistry and Pharmacology》1932,34(1):1-17
Ohne Zusammenfassung 相似文献
128.
Selenium nutrition of green plants. Effect of selenite supply on growth and selenium content of alfalfa and subterranean clover 总被引:2,自引:1,他引:1
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Alfalfa and subterranean clover plants were grown in highly purified nutrient solutions to which selenite selenium had been added at 0, 0.025, 0.25, 2.5 or 25.0 μg-atoms/liter. In both species, yields of tops and roots were significantly less at 25.0 μg-atoms/liter than at lower selenium concentrations (p < 0.01). The results indicated that growth was adversely affected when the concentration of selenium in mature leaf tissue reached 0.2 to 0.8 μg-atom/g dry weight. 相似文献
129.
Effects of culture duration and time of gonadotropin addition on in vitro maturation and fertilization of red deer (Cervus elaphus) oocytes 总被引:1,自引:0,他引:1
Immature red deer (Cervus elaphus ) oocytes (n = 1208) were collected from 1 to 4 - mm diameter follicles on ovaries and then cultured for 16, 20, 24 or 28 h (Groups I to IV) in TCM 199 supplemented with 10% FCS, 1 x 10(6) granulosa cells/ml and 1 mug/ml estradiol at 39 degrees C under 5% CO(2) in air. Gonadotropins (10 mug/ml, FSH and LH) were added to the culture medium at the start of culture (0 h) or after 6 h. Approximately one-third of the oocytes were examined for maturation, and the remainder were fertilized in vitro with frozen-thawed semen collected from a stag by electroejaculation. In vitro fertilized oocytes (n = 309) from four of the maturation treatment (Groups II and III in both gonadotropin treatments) were cultured for 7 d and examined for cleavage. Oocytes cultured for 16 h (Group I) had lower (P < 0.001) maturation rates (4.7%) than those in the longer culture durations (Groups II to IV: 68.9%). Culture for 20 (Group II) and 24 h (Group III) resulted in higher (P <0.001) fertilization rates than culture for 16 (Group I) and 28 h (Group IV) (18.3, 20.5, 7.1, 7.8%, respectively). The time of gonadotropin addition did not affect maturation or fertilization rates, but its addition at 6 h increased (P < 0.05) the percentage of oocytes cleaving (5.7 vs 12.5%). Oocytes cultured for 20 h (Group II) and with the delayed addition of gonadotropins cleaved most readily (18.2%). No embryos developed beyond eight-cell stage. 相似文献
130.
In cell extracts of Methanosarcina barkeri, the methylcoenzyme M methylreductase system with H2 as the electron donor was inhibited by NAD+ and NADP+, but NADH and NADPH had no effect on enzyme activity. NAD+ (4 and 8 mM) shifted the saturation curve for methylcoenzyme M from hyperbolic (Hill coefficient [nH] = 1.0; concentration of substrate giving half maximal velocity [Km] = 0.21 mM) to sigmoidal (nH = 1.5 and 2.0), increased Km (Km = 0.25 and 0.34 mM), and slightly decreased Vmax. Similarly NADP+ at 4m and 8 mM increased nH to 1.6 and 1.85 respectively, but the Km values (0.3 and 0.56 mM) indicated that NADP+ was a more efficient inhibitor than NAD+. 相似文献