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991.
The microbial polysaccharides reviewed include xanthan gum, scleroglucan, PS-10, PS-21 and PS-53 gums, polysaccharides from Alcaligenes sp., PS-7 gum, gellan gum, curdlan, bacterial alginate, dextran, pullulan, Baker's Yeast Glycan, 6-deoxy-hexose-containing polysaccharides and bacterial cellulose. Factors limiting the commercial potential of certain microbial polysaccharides such as availability, rheological properties, and polyvalency are outlined. The polysaccharides are classified according to their uses as viscosity-increasing agents and as gelling agents. A third category includes polysaccharides with specific applications such as tailor-made dextran and pullulan and polysaccharides used as substrates for the preparation of rare sugars. The difficulties encountered in development of a polysaccharide at the industrial level are pointed out. 相似文献
992.
Martin Aeschbacher Christoph A. Reinhardt Gerhard Zbinden 《Cell biology and toxicology》1986,2(2):247-255
A reliable and rapid test to detect cytotoxic chemicals which affect cell membranes is described. Fluorescein diacetate freely penetrates intact cells where it is hydrolyzed to its fluorochrome, fluorescein, which is retained in the cell due to its polarity. On the other hand, ethidium bromide is known to be excluded from the intact cell, staining only nucleic acids of membrane-damaged cells. The combination of both fluorochromes results in counter-staining: intact cells fluoresce green (cytoplasm) and membrane-damaged cells fluoresce red (nucleus and RNA). Rat thymocytes freshly isolated without enzyme treatment were incubated simultaneously with test substance and dye solution fluorescein diacetate and ethidium bromide. A two-parameter analysis was performed on a flow cytometer with an on-line computer. Concentration-dependent effects of various detergents and solvents were quantified by measuring the amount of dye retention, i.e., the decrease or increase in fluorescein—fluorescence (peak shift), and the decrease in dye exclusion (increase in ethidium bromide-staining) relative to the untreated control. The assay can be used for rapid monitoring of chemical insults to cell membranes which precede the decrease of the viability measured by pure dye exclusion techniques.Abbreviations DMA
dimethyl sulfate
- DMSO
dimethyl sulfoxide
- EB
ethidium bromide
- F
fluorescein
- FDA
fluorescein diacetate
- FS25
concentration of test substance resulting in a F-peak left-shift of 25% from control
- PBS
phosphate buffered saline
- SCT
forward light scatter
- SDS
sodium dodecyl sulfate 相似文献
993.
994.
The photosynthetic capacity of detached leaves of a non-yellowing mutant of Festuca pratensis Huds. declined during senescence at a similar rate to that in a normal cultivar. Respiratory oxygen uptake in the dark continued at similar rates in both genotypes during several days of senescence. In chloroplasts isolated from leaves at intervals after excision, the rate of photosystem I (PS I)-mediated methyl viologen reduction using reduced N,N,N,N-tetramethyl-p-phenylene diamine as electron donor also declined in both genotypes, possibly due to loss of integrity of the photosynthetic apparatus in the cytochrome f-plastocyanin region. There was a similar fall in PS II electron transport using water as electron donor and measured at the rate of reduction of 2,6-dichlorophenolindophenol. Partial restoration of this activity by the addition of diphenyl carbazide was evidence for lability of the oxygen-evolving complex during senescence. An accentuated difference between mutant and normal material in this case indicated that the mutant retains a greater number of functional PS II centres. Changes in the light-saturation characteristics of the two photosystems have been discussed in relation to the organization of the photosynthetic membranes during senescence.Abbreviations and symbols DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DCPIP
2,6-dichlorophenolindophenol
- DMSO
dimethyl sulphoxide
- DPC
diphenyl carbazide
- MV
methyl viologen
- PS I, PS II
photosystem I, II
- TMPD
N,N,N,N-tetramethyl-p-phenylene diamine 相似文献
995.
We have compared the ability of shadegrown clones of Solamum dulcamara L. from shade and sun habitats to acclimate to bright light, as a function of nitrogen nutrition before and after transfer to bright light. Leaves of S. dulcamara grown in the shade with 0.6 mM NO
3
-
have similar photosynthetic properties as leaves of plants grown with 12.0 mM NO
3
-
. When transferred to bright light for 1–2 d the leaves of these plants show substantial photoinhibition which is characterized by about 50% decrease in apparent quantum yield and a reduction in the rate of photosynthesis in air at light saturation. Photoinhibition of leaf photosynthesis is associated with reduction in the variable component of low-temperature fluorescence emission, and with loss of in-vitro electron transport, especially of photosystem II-dependent processes.We find no evidence for ecotypic differentiation in the potential for photosynthetic acclimation among shade and sun clones of S. dulcamara, or of differentiation with respect to nitrogen requirements for acclimation. Recovery from photoinhibition and subsequent acclimation of photosynthesis to bright light only occurs in leaves of plants provided with 12.0 mM NO
3
-
. In these, apparent quantum yield is fully restored after 14 d, and photosynthetic acclimation is shown by an increase in light-saturated photosynthesis in air, of light-and CO2-saturated photosynthesis, and of the initial slope of the CO2-response curve. The latter changes are highly correlated with changes in ribulose-bisphosphate-carboxylase activity in vitro. Plants supplied with 0.6 mM NO
3
-
show incomplete recovery of apparent quantum yield after 14 d, but CO2-dependent leaf photosynthetic parameters return to control levels.Symbols and abbreviations Fo
initial level of fluorescence at 77 K
- Fm
maximum level of fluorescence at 77 K
- Fv
variable components of fluorescence at 77 K (Fv=Fm-Fo)
- PSI, PSII
photosystem I and II, respectively
- RuBP
ribulose-1,5-bisphosphate
- RuBPCase
ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) 相似文献
996.
Selective expression of a probable amylase/protease inhibitor in barley aleurone cells: Comparison to the barley amylase/subtilisin inhibitor 总被引:5,自引:0,他引:5
We have cloned and sequenced a 650-nucleotide cDNA from barley (Hordeum vulgare L.) aleurone layers encoding a protein that is closely related to a known -amylase inhibitor from Indian finger millet (Eleusine coracana Gaertn.), and that has homologies to certain plant trypsin inhibitors. mRNA for this probable amylase/protease inhibitor (PAPI) is expressed primarily in aleurone tissue during late development of the grain, as compared to that for the amylase/subtilisin inhibitor, which is expressed in endosperm during the peak of storage-protein synthesis. PAPI mRNA is present at high levels in aleurone tissue of desiccated, mature grain, and in incubated aleurone layers prepared from rehydrated mature seeds. Its expression in those layers is not affected by either abscisic acid or gibberellic acid, hormones that, respectively, increase and decrease the abundance of mRNA for the amylase/subtilisin inhibitor. PAPI mRNA is almost as abundant in gibberellic acid-treated aleurone layers as that for -amylase, and PAPI protein is synthesized in that tissue at levels that are comparable to -amylase. PAPI protein is secreted from aleurone layers into the incubation medium.Abbreviations ABA
abscisic acid
- ASI
barley amylase/subtilisin inhibitor
- bp
nucleotide base pairs
- Da
dalton
- dpa
days post anthesis
- GA3
gibberellic acid
- PAPI
probable amylase/protease inhibitor
- poly(A)RNA
polyadenylated RNA
- SDS-PAGE
sodium dodecyl sulfate-polyacrylamide gel electrophoresis 相似文献
997.
The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.Abbreviations ABA
abscisic acid
- TMV
tobacco mosaic virus 相似文献
998.
Phyllodia of the Crassulacean acid metabolism (CAM) plant Kalanchoë tubiflora were allowed to fix 13CO2 in light and darkness during phase IV of the diurnal CAM cycle, and during prolongation of the regular light period. After 13CO2 fixation in darkness, only singly labelled [13C]malate molecules were found. Fixation of 13CO2 under illumination, however, produced singly labelled malate as well as malate molecules which carried label in two, three or four carbon atoms. When the irradiance during 13CO2 fixation was increased, the proportion of singly labelled malate decreased in favour of plurally labelled malate. The irradiance, however, did not change either the ratio of labelled to unlabelled malate molecules found in the tissue after the 13CO2 application, or the magnitude of malate accumulation during the treatment with label. The ability of the tissue to store malate and the labelling pattern changed throughout the duration of the prolonged light period. The results indicate that malate synthesis by CAM plants in light can proceed via a pathway containing two carboxylation steps, namely ribulose-1,5-bisphosphate-carboxylase/oxygenase (EC 4.1.1.39) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) which operate in series and share common intermediates. It can be concluded that, in light, phosphoenolpyruvate carboxylase can also synthesize malate independently of the proceeding carboxylation step by ribulose-1,5-bisphosphate carboxylase/oxygenase.Abbreviations CAM
Crassulacean acid metabolism
- PEP
phosphoenolpyruvate
- PEPCase
phosphoenolpyruvate carboxylase (EC 4.1.1.31)
- RuBPCase
ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39)
- TMS
trimethylsilyl 相似文献
999.
Vacuoles isolated from the storage roots of red beet (Beta vulgaris L.) accumulate sucrose via two different mechanisms. One mechanism transports sucrose directly, and its rate is increased by the addition of MgATP. The other mechanism utilizes uridine diphosphate glucose (UDP-glucose) to synthesize and simultaneously transport sucrose phosphate and sucrose into the vacuole. This group translocation mechanism has also been found in sugarcane vacuoles. As in sugarcane, the beet group translocator does not require fructose 6-phosphate, nor is the latter substance transported into the vacuole. The uptake of UDP[14C]glucose in inhibited by high concentrations of osmoticum.Abbreviations EDTA
ethylenediaminetetraacetic acid
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- UDP
uridine 5-diphosphate 相似文献
1000.
The effect of phosphate feeding on the influence of low (2%) oxygen on photosynthetic carbon assimilation has been investigated in leaf discs of spinach (Spinacia oleracea L.) at 12°C. The following observations were made. First, after the transition from 20% O2 to 2% O2, the rate of CO2 uptake was inhibited at CO2 concentrations between about 250 and about 800 l CO2·l-1. Second, phosphate feeding stimulated the rate of CO2 uptake in 20% O2 at higher concentrations of CO2 (500–900 l·l-1). Third, phosphate feeding stimulated the rate of CO2 uptake in 2% O2 at all but the highest (900 l·l-1) and lowest 74 (l·l-1) concentrations of CO2 employed. Phosphate thereby restored the stimulation of photosynthesis by 2% O2 and it did so over a wide range of lower temperatures. Fourth, oscillatory behaviour, however generated, was dampened by phosphate feeding, even at very low concentrations of CO2. Contents of leaf metabolites were measured during the transition to 2% O2 in control and phosphate-fed leaf discs. During this period the ratio glycerate-3-phosphate/triose phosphate rose steeply, but fell again only in the phosphate-treated leaf discs. These data, taken together with measured ATP/ADP ratios, showed that assimilatory power, the ratio [ATP]·[NAD(P)H]/[ADP]·[Pi]·[NAD(P)], decreased when leaves were exposed to 2% O2, but that this decrease was minimised by previous feeding of phosphate. The mechanism of phosphate limitation is discussed in the light of the results.Abbreviations Ci
intercellular concentration of CO2
- RuBP
ribulose-1,5-bisphosphate 相似文献