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991.
The cell wall of Cobaea scandens seed hairs developed in a characteristic sequence, with the deposition of a cellulose thread onto a pectic swelling layer was the final event. The cellulose thread was intracellularly accompanied by a band of 10–18 microtubules. During the formation of the swelling layer the microtubules were homogeneously distributed; they ran circumferentially normal to the cell axis. When cellulose-thread formation started, the microtubules became arranged in a helical band. The density of the microtubules varied during the different phases of development. The highest density was observed before cellulosethread formation and ranged from 6–15 m·m-2. The length of the microtubules, 20–30 m, was determined by direct measurements, as well as estimated from the total microtubular length in a given area and the counted free ends. With the indirect immunofluorescence technique the microtubules of the band stained inhomogeneously. Those which were located at the edges of the band fluoresced more intensely than those of the central part. Attempts to visualize actin filaments in the hair cells with rhodaminyl-conjugated phalloidin resulted in a homogeneous staining of the area of the microtubular band, indicating that actin filaments may be present in this region. Though, in thin sections and dry-cleaved cells, filamentous structures were observed between the microtubules, caution is expressed that the observed fluorescence was, indeed, due to actin filaments. The role of the filamentous structures is discussed with respect to formation and maintenance of the microtubular band. Microtubules apparently did not cross coated pits which were visualized in the plasma membrane through the dry-cleaving technique.Abbreviations IFT
indirect immunofluorescence technique
- RP
rhodaminyl-conjugated phalloidin
- SEM
scanning electron microscopy 相似文献
992.
Specific protein inhibitors of microbial serine proteinases were isolated from wheat (Triticum aestivum L.), rye (Secale cereale L.) and triticale using affinity chromatography on subtilisin-Sepharose 4B. The wheat inhibitor had an isoelectric point (pI) at pH 7.2, while the rye inhibitor consisted of two forms with pI values of 6.8 and 7.1. In triticale, two components were present with pIs 7.2 and 6.8. All the inhibitors had M
r values of approx. 20 000. The isolated proteins were effective inhibitors of subtilisins Carlsberg and BPN, and of fungal proteinases (EC 3.4.21.14) from the genus Aspergillus, but they were completely inactive against trypsin (EC 3.4.21.4) chymotrypsin (EC 3.4.21.1) and pancreatic elastase (EC 3.4.21.36). The inhibitors formed complexes with subtilisin in a molar ratio of 1:1. The results of chemical modifications seem to indicate that the isolated inhibitors have methionine residues in their reactive sites.Abbreviation pI
isoelectric point 相似文献
993.
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
994.
K. Manning 《Planta》1986,168(1):61-66
The relationship between ethylene production and the CN--assimilating enzyme -cyanoalanine synthase (CAS; EC 4.4.1.9) was examined in the carnation (Dianthus caryophyllus L.) flower. In petals from cut flowers aged naturally or treated with ethylene to accelerate senescence the several hundred-fold increase in ethylene production which occurred during irreversible wilting was accompanied by a one- to twofold increase in CAS activity. The basal parts of the petal, which produced the most ethylene, had the highest CAS activity. Studies of flower parts (styles, ovaries, receptacles, petals) showed that the styles had a high level of CAS together with the ethylene-forming enzyme (EFE) system for converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The close association between CAS and EFE found in styles could also be observed in detached petals after induction by ACC or ethylene. Treatment of the cut flowers with cycloheximide reduced synthesis of CAS and EFE. The data indicate that CAS and ethylene production are associated, and are discussed in relation to the hypothesis that CN- is formed during the conversion of ACC to ethylene.Abbreviations ACC
1-aminocyclopropane-1-carboxylic acid
- AVG
aminoethoxyvinylglyoine
- CAS
-cyanoalanine synthase
- CHI
cycloheximide
- EFE
ethylene-forming enzyme 相似文献
995.
996.
We have investigated fluid phase cleavage of C3b by peritoneal polymorphonuclear leukocytes of guinea pigs and found that polymorphonuclear leukocytes expressed an iC3b forming enzyme as well as C3b receptor with maturation in peritoneal cavity. The iC3b forming enzyme was found to be distinct from C3bINA, a physiological iC3b forming enzyme in plasma, since the activity was inhibited by monoiodoacetic acid and did not require a cofactor plasma protein, beta 1H, for the cleavage of C3b into iC3b. The iC3b forming enzyme is gradually released upon incubation of PMN at 37 degrees C. The molecular weight of the iC3b forming enzyme was estimated to be 48,000 from gel filtration on Sephadex G-200. 相似文献
997.
M Solti P Dévay I Kiss J Londesborough P Friedrich 《Biochemical and biophysical research communications》1983,111(2):652-658
Like adult heads and whole flies, larval brains of wild type Drosophila melanogaster contain two major soluble cyclic nucleotide phosphodiesterases, forms I and II. Larval brains of the learning-defective mutant strain, dunceM11, contain only the form I enzyme. In both wild type and dunce strains the form I enzyme is activated by Ca2+/calmodulin. A time-dependent loss of this Ca2+ activation was observed. 相似文献
998.
In intact, uncoupled type B chloroplasts from spinach, added ATP causes a slow light-induced decline () of chlorophyll a fluorescence at room temperature. Fluorescence spectra were recorded after fast cooling to 77 K and normalized with fluorescein as an internal standard. Related to the fluorescence quenching at room temperature, an increase in Photosystem (PS) I fluorescence (F735) and a decrease in PS II fluorescence (F695) were observed in the low-temperature spectra. The change in the ratio was abolished by the presence of methyl viologen. Fluorescence induction at 77 K of chloroplasts frozen in the quenched state showed lowered variable (Fv) and initial (F0) fluorescence at 690 nm and an increase in F0 at 735 nm. The results are interpreted as indicating an ATP-dependent change of the initial distribution of excitation energy in favor of PS I, which is controlled by the redox state of the electron-transport chain and, according to current theories, is caused by phosphorylation of the light-harvesting complex. 相似文献
999.
Chlorotetracycline inhibits the uncoupled oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L.) mitochondria extensively (over 80%) and rapidly (inhibition complete in 10 s) in the presence of added Ca2+. Half-maximal inhibition is observed at 15 μM chlorotetracycline in the presence of 2 mM Ca2+. The oxidation of succinate is only affected marginally by chlorotetracycline plus Ca2+. The inhibition of NADH oxidation and the fluorescence of CTC are well correlated. Mn2+ is the only other cation which shows an (increased) inhibition in the presence of chlorotetracycline. The inhibition by Ca2+ and chlorotetracycline disappears at acid pH, and the pH optimum in their presence is 6.4. The inhibition caused by other lipid-soluble Ca2+-chelators is not reversible or is enhanced by the addition of excess Ca2+. In contrast, inhibition caused by relatively water-soluble chelators is completely reversed by added Ca2+. It is suggested that a neutral 1:2 complex is formed between Ca2+ and chlorotetracycline which can substitute for Ca2+ bound at sites in the lipophilic phase of the inner mitochondrial membrane, which are essential for the activity of the external NADH dehydrogenase. 相似文献
1000.
The electron-transport chain catalyzing fumarate reduction by formate has recently been reconstituted from the formate dehydrogenase complex and the fumarate reductase complex from Vibro succinogenes, in a liposomal preparation containing vitamin K-1 (Unden, G. and Kröger, A. (1982) Biochim. Biophys. Acta 682, 258–263). We have now investigated the structural properties of this preparation. The preparation was found to consist of a homogeneous population of unilamellar proteoliposomes with an average diameter of about 100 nm and an internal volume of 2–4 ml / g phospholipid. The buoyant density (1.07 g / ml) was consistent with the protein / phospholipid ratio (0.2 g / g) of the preparation. Leakage of glucose from the internal spaces of the proteoliposomes was negligibly slow. Proteoliposomes prepared with either of the enzyme complexes showed peripheral projections mainly on the outer surface, when examined by electron microscopy after negative staining. The size, orientation and surface density of the projections were consistent with those of the enzymes. Most of the substrate and dye-reactive sites (70–90%) of the enzymes in the proteoliposomes were accessible to external non-permeant substrates. The proteoliposomes catalyzing electron transport were formed by freeze-thawing a mixture of liposomes and protein-phospholipid complexes which did not perform electron transport from formate to fumarate. Nearly the entire amount of the enzymes supplied (0.2 g protein / g phospholipid) was incorporated into the liposomes by this procedure. The transformation of liposomes into proteoliposomes was accompanied by exchange of the internal solutes with the external medium. 相似文献