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1.
2.
Effects of tissue position (viz. outer vs inner mesocarp) and heat treatment (48°C, 20 min) on variations in polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activity and ripening of fruits of Carica papaya L. cv. Backcross Solo were investigated. Polygalacturonase activity increased during ripening concomitantly with an increase in tissue softness and soluble polyuronide level. Throughout ripening, inner mesocarp tissue was softer and contained higher polygalacturonase activity than outer mesocarp tissue. Titratable acidity as well as ß-galactosidase (EC 3.2.1.23) activity also increased during ripening; however, unlike polygalacturonase, their level or activity was lower in inner than in outer mesocarp. Ascorbic acid could partially account for the increase in titratable acidity during ripening but contributed very little to the differences in titratable acid levels between outer and inner mesocarp. Heat treatment had no effect on either fruit softness or titratable acidity, but it markedly reduced the increase in ascorbic acid and polygalacturonase activity during ripening. Ripening, as reflected by changes in tissue softness and polygalacturonase activity, progressed outwardly from the interior towards the exterior of the fruit. The effect of heat treatment in suppressing polygalacturonase activity was relatively greater in inner than in outer mesocarp, suggesting that sensitivity of the enzyme to heat treatment may vary with stage of ripeness of the tissue. 相似文献
3.
The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G2/M. The specificity of this response and its relationship to photosynthesis was studied by looking at the effect of DCMU on dark grown wild-type cells, and on two bleached variants of Euglena (W3BUL and W10BSmL) that lack chloroplasts. The drug does block G2/M in these cells, but not entrance into the cell cycle. Our studies show that entrance of cells into the cell cycle from a quiescent state does not require active photosynthesis, and that DCMU has effects on G2/M transit that are independent of the photosynthetic capacity of the cells. 相似文献
4.
Use of a glucocorticoid-inducible promoter for expression of herpes simplex virus type 1 glycoprotein gC1, a cytotoxic protein in mammalian cells. 总被引:3,自引:0,他引:3
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5.
During the past 18 months, 60 tissue expanders were utilized in the reconstruction of 42 children with burn alopecia of the scalp not amenable to a single excision and primary closure at the Shriners Burns Institute in Galveston, Texas. The children were grouped according to the degree of alopecia. All patients with defects of 15 percent or less of the total hair-bearing scalp were able to obtain complete closure of their defects with two operations, i.e., one to place the expander and the second to remove the expander and advance the flaps. Some patients with defects up to 40 percent were closed with serial expansion. Patients with even larger defects had a significant reduction in the percentage of alopecia and benefited from re-creation of anterior hairlines. We have encountered a postoperative complication rate of 10 percent. When compared to previous methods of treating burn alopecia, tissue expansion allows a more rapid closure, fewer operations and coincident anesthetics, and decreased total length of hospitalization. 相似文献
6.
Observation was made on early ontogeny of vascular cambium in the developing root ofGinkgo biloba L. After completion of root elongation, the vascular meristem gradually acquires cambial characteristics. Strips of the periclinal
division of cells in transverse section are observed on the inner side of phloem when the primary xylem and phloem in the
stele have been established. The strips are united into a continuous layer between phloem and xylem. In tangenital section,
the procambium shows a homogeneous structure, which is initially composed of short cells with transverse end walls and subsequently,
of long cells with tapering ends. Then, the procambium is organized into two systems of cells; axial strands of short cells
with transverse end walls resulting from the sporadic transverse divisions of long cells, and long cells with tapering ends.
Still later, the short cells are divided frequently in a trasverse plane exhibiting one or a few cells in width and several
decades of cells in height, while the long cells are elongated. The frequency of transverse divisions of the short cells decreases
in subsequent stages. Eventually, the short cells in axial strands are vertically separated from one another by the elongation
of neighboring long cells and by the decrease in the frequency of transverse divisions of short cells themselves. Cambial
initials occur in two forms; ray initials a few cells in height and one cell in width derived from the short cells, and fusiform
initials with tapering ends derived from the long cells. 相似文献
7.
G Bakkeren B Gibbard A Yee E Froeliger S Leong J Kronstad 《Molecular plant-microbe interactions : MPMI》1992,5(4):347-355
The smut fungi are obligately parasitic during the sexual phase of their life cycle, and the mating-type genes of these fungi play key roles in both sexual development and pathogenicity. Among species of smut fungi it is common to find a bipolar mating system in which one locus with two alternate alleles is believed to control cell fusion and establishment of the infectious cell type. Alternatively, several species have a tetrapolar mating system in which two different genetic loci, one of which has multiple alleles, control fusion and subsequent development of the infection hyphae. Cloned sequences from the a and b mating-type loci of the tetrapolar smut fungus Ustilago maydis were used as hybridization probes to DNAs from 23 different fungal strains, including smut fungi with both tetrapolar and bipolar mating systems. In general, all of the smut fungi hybridized with the mating-type genes from U. maydis, suggesting conservation of the sequences involved in mating interactions. A selection of DNAs from other ascomycete and basidiomycete fungi failed to hybridize with the U. maydis mating-type sequences. Exceptions to this finding include hybridization of DNA from the a1 idiomorph of U. maydis to DNA from one strain of U. violacea and hybridization of both a idiomorphs to DNA from Saccharomyces cerevisiae. 相似文献
8.
Cognitive schema were used to explain health and illness behaviors among Chinese students. University students in Hong Kong were asked to attribute causes and suggest solutions to five health/mental health problems: Weakness/Fatigue, Tension/ Anxiety, Sleep Difficulty, Hollow/Emptiness, and Headache. The patterns of endorsement on the causal and solution categories used for the five problems were compared using a new asymptotic chi-squared test. The response patterns were found to be significantly different across the five problems. Each problem was attributed to multiple causes including psychological, social, situational, somatic, and existential factors. The intended solutions were often related to the nature of the causal attributions especially when the problems were mild. In lay help-seeking, the Hong Kong students would attempt a variety of self-help measures. However, for professional consultation, the medical doctor would be the primary care professional the students would turn to for most of the problems except in the case of Hollow/Emptiness. 相似文献
9.
Mutagenesis of the Tra1 core region of RK2 by using Tn5: identification of plasmid-specific transfer genes. 总被引:5,自引:5,他引:0
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D G Guiney C Deiss V Simnad L Yee W Pansegrau E Lanka 《Journal of bacteriology》1989,171(7):4100-4103
The conjugation system of the IncP alpha plasmid RK2/RP4 is encoded by transfer regions designated Tra1, Tra2, and Tra3. The Tra1 core region, cloned on plasmid pDG4 delta 22, consists of the origin of transfer (oriT) and 2.6 kilobases of flanking DNA providing IncP alpha plasmid-specific functions that allow pDG4 delta 22 to be mobilized by the heterologous IncP beta plasmid R751. Tn5 insertions in pDG4 delta 22 define a minimal 2.2-kilobase region required for plasmid-specific transfer of oriT. The Tra1 core contains the traJ and traK genes as well as an 18-kilodalton open reading frame downstream of traJ. The traJ and traK genes were shown to be required for transfer by complementation of inserts within these genes. Genetic evidence for the role of the 18-kilodalton open reading frame in transfer was obtained, although this protein has not been detected in cell lysates. These studies indicate that at least three transfer proteins are involved in plasmid-specific interactions at oriT. 相似文献
10.
Daniel K. Yee Anna Pastuszko David Nelson David F. Wilson 《Journal of neurochemistry》1989,52(1):54-60
Incubation of synaptosomes from rat brain with DL-2-amino-5-phosphonovalerate (APV) stimulated an increased release of dopamine, and this effect was strictly dependent on the extrasynaptosomal calcium level. APV increased biosynthesis of dopamine from tyrosine by 30%, whereas monoamine oxidase activity was inhibited by 30%. When synaptosomes were incubated with radioactive dopamine, APV caused a large decrease in incorporation of label into 3,4-dihydroxyphenylacetic acid but greatly increased incorporation into norepinephrine and its N-methyl derivatives. Quantification of dopamine and its metabolites in synaptosomes, using electrochemical detection, indicated that the presence of APV resulted in changes in the absolute levels of the aforementioned dopamine metabolites similar to the changes in radiolabel incorporation. Omission of Ca2+ from the extrasynaptosomal medium greatly diminished the APV-induced changes in catecholamine metabolism. The metabolic changes appear to largely result from an increased intrasynaptosomal Ca2+ level due to the APV-induced increase in calcium permeability of the plasma membrane. 相似文献