Fern (Onoclea sensibilis L.) gametophytes exposed to blue light are induced to undergo a morphological transition from a tip-growing filament to a planar prothallus. Extracellular measurements of electric currents and localized ion activities around the apical cell of 8 to 10 day-old gametophytes were made with a vibrating probe and ion selective electrodes. In darkness, we observed exit current densities of an average of 75 nanoamperes per square centimeter near the tip and 2 to 15 nanoamperes per square centimeter along the lateral walls of this cell. Measurements with ion selective electrodes for H+, K+, and Ca2+ showed that this cell was bounded by a thin layer of medium that was depleted in K+ and Ca2+ and exhibited a lower pH than the bulk solution. Both the K+ and Ca2+ depletion zones and the zone of higher acidity were particularly pronounced at the tip end of the cell; the pH at 2 micrometers from the tip was nearly 0.5 units more acid than the bulk medium at pH 6. Disruption of steady state, external gradients with media that contained lower concentrations of H+, K+, Ca2+, or Cl− produced certain differences in the rates of restoration of particular ion zones, raising the possibility that some of the ion migrations are interdependent. Within 15 minutes after irradiation with blue light, current leaving the tip declined to levels which were indistinguishable from those leaving the lateral walls and there was a rapid lowering in the rates of tip acidification and K+ depletion near the tip. The rapid dissipation of both the longitudinally aligned electrical field and the tip-localized asymmetries in external cation distribution in blue light suggest that loss of electrical polarity in this tip growing cell may be an initial step in the chain of events which govern changes in cell shape. 相似文献
The fungus Cochliobolus victoriae causes victoria blight of oats and produces the host-specific toxin victorin. The reaction of oats to the fungus and its toxin is controlled by a single dominant gene whose product has been hypothesized to function as the site of action (receptor) of the toxin in susceptible oat genotypes. Previously, using a biologically active 125I derivative of the toxin, we identified a 100 kilodalton victorin-binding protein (VBP) which binds victorin in a ligand-specific manner and binds in vivo only in susceptible oat genotypes. However, a VBP in both the susceptible and resistant oat genotypes was identified by in vitro binding experiments. One interpretation of the lack of genotype-specific binding in vitro is that the 100 kilodalton protein detected in vitro is not the same 100 kilodalton protein detected in vivo. To clarify the relationship between the 100 kilodalton protein(s) labeled in vivo and in vitro, we developed antisera to the in vitro-labeled VBP from the susceptible genotype and demonstrated that these preparations react with the in vivo-labeled VBP from the susceptible genotype. This finding coupled with previous observations strongly suggest that the VBP observed in vivo is the same protein detected in vitro. Furthermore, the results support our previous observations which suggest that the VBPs labeled in vitro in susceptible and resistant genotypes are closely related or identical. 相似文献
It was shown previously that when peas (Pisum sativum L.) are grown with suboptimal sulfur supply the level of legumin (the more S-rich of the two major seed storage proteins) in the mature seed is selectively reduced (Randall, Thomson, Schroeder, 1979 Aust J Plant Physiol 6: 11-24). This paper reports a study of the cellular mechanisms involved in regulating legumin synthesis under these conditions. Pulse and pulse-chase labeling experiments were carried out with excised, immature cotyledons from normal and S-deficient plants. Legumin was isolated from cotyledon extracts by immunochromatography, and the proportion of legumin synthesis relative to total protein synthesis was determined. Results showed that reduced legumin accumulation could largely be accounted for by a greatly reduced level of legumin synthesis (80-88% reduction) rather than by a major increase in legumin breakdown.
Legumin mRNA levels were assayed by two methods. In vitro translation of polysomal RNA from cotyledons of normal and S-deficient plants indicated a reduction of 60 to 70% in synthesis of legumin-related products by preparations from S-deficient plants. A legumin cDNA clone was constructed, characterized, and used to measure the levels of legumin mRNA in polysomal and total RNA preparations from developing cotyledons. Legumin mRNA levels were reduced by 90% in preparations from S-deficient plants.
When restored to an adequate S supply, S-deficient plants (or pods taken from such plants) recovered normal levels of legumin synthesis (in vivo and in vitro) and of legumin mRNA. These results indicate that reduced legumin accumulation under conditions of S deficiency is primarily a consequence of reduced levels of legumin mRNA.
Serum levels of ticarcillin disodium, a semi-synthetic penicillin (Beecham Laboratories, Bristol, Tennessee, 37620), were measured at various time intervals up to and including 24 h after intrauterine and intramuscular administration in adult female horses. Three separate studies were conducted in Part I: in the first and second studies, serum levels were measured after intrauterine administration of 1 and 3 g of ticarcillin, respectively, and in the third study, levels were measured after intramuscular administration of 6 g of ticarcillin. In Part II, serum levels of ticarcillin were measured after intramuscular administration of ticarcillin at dosages based on body weight: 10 mg/lb (22 mg/kg) of body weight, 15 mg/lb (33 mg/kg) of body weight and 20 mg/lb (44 mg/kg) of body weight. Results showed little if any absorption of the antibiotics into the systemic circulation after intrauterine administration. All serum levels measured after administration of both intrauterine dosages of 1 and 3 g were less than 4.0 ug/ml. Peak serum concentrations, after intramuscular administration of 6 g of ticarcillin, occurred between 20 and 45 min after administration and averaged 15.97 +/- 5.0 ug/ml. Average peak serum concentrations, after intramuscular administration of 10 mg/lb (22 mg/kg) of body weight, 15 mg/lb (33 mg/kg) of body weight, 15 mg/lb (33 mg/kg) and 20 mg/lb (44 mg/kg) of body weight, were 16.12 ug/ml, 25.75 ug/ml and 50.25 ug/ml, respectively. After intramuscular administration of 6 g of ticaracilin, average serum half-life was determined to be 2.9 h. 相似文献
Spherosomes of cotyledons of germinating peanuts (Arachis hypogea L.) were examined by electron microscopy and found to be particles about 1.0 to 2.0 μ in diameter bounded by a limiting membrane. Isolated spherosomes appear similar to spherosomes in situ. The isolated spherosomes are composed of 98.1% total lipids, 0.77% phospholipid and 1.27% protein by dry weight. The amounts of protein and phospholipid associated with the isolated spherosomes are sufficient to account for limiting membranes. Spherosomes amply account for the lipid in a peanut cotyledon. The activity of lipase and fatty acyl-Coenzyme A synthetase is not associated with the isolated spherosomes. This suggests that peanut spherosomes are principal sites of lipid storage but not of lipid degradation. 相似文献