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61.
In order to study the influence of Arbuscular Mycorrhiza (AM) on the development of root rot infection, tomato plants were raised with or withoutGlomus mosseae and/orPhytophthora nicotianae var.parasitica in a sand culture system. All plants were fed with a nutrient solution containing one of two phosphorus (P) levels, 32µM (I P) or 96µM (II P), to test the consequence of enhanced P nutrition by the AM fungus on disease dynamics. Mycorrhizal plants had a similar development to that of control plants. Treatment withPhytophthora nicotianae var.parasitica resulted in a visible reduction in plant weight and in a widespread root necrosis in plants without mycorrhiza. The presence of the AM fungus decreased both weight reduction and root necrosis. The percentage reduction of adventitious root necrosis and of necrotic root apices ranged between 63 and 89% The enhancement of P nutrition increased plant development, but did not appreciably decrease disease spread. In our system, mycorrhiza increased plant resistance toP. nicotianae var.parasitica infection. Although a contribution of P nutrition by mycorrhiza cannot be excluded, other mechanisms appear to play a crucial role. 相似文献
62.
Angelo De Milito Marinunzia Catucci Francesco Iannelli Laura Romano Maurizio Zazzi Pier Egisto Valensin 《Molecular biotechnology》1995,3(2):166-169
A reliable selective PCR procedure that combines the use of additionally mutated primers with the specificity-enhancing properties
of a commercial preparation (Perfect Match, Stratagene) is described. The human immunodeficiency virus type 1pol gene point mutations known to confer in vitro resistance to azidothymidine were examined as a model for optimization of the
assay. The usual strategy of deliberately introducing an additional mismatch 1 residue from the 3′ end in the wild-type and
mutant primers did not allow reproducible discrimination between wild-type and mutant target sequences. Addition of minimal
amounts of Perfect Match to the same PCR mixtures resulted in a significantly enlarged range of selective annealing temperatures,
providing a valuable and cost-effective means for reliable detection of known mutations by selectivePCR. 相似文献
63.
Ellen C. Breen Ronald A. Ignotz Laura McCabe Janet L. Stein Gary S. Stein Jane B. Lian 《Journal of cellular physiology》1994,160(2):323-335
This study examines the mechanism by which TGF-β1, an important mediator of cell growth and differentiation, blocks the differentiation of normal rat diploid fetal osteoblasts in vitro. We have established that the inability for pre-osteoblasts to differentiate is associated with changes in the expression of cell growth, matrix forming, and bone related genes. These include histone, jun B, c-fos, collagen, fibronectin, osteocalcin, alkaline phosphatase, and osteopontin. Morphologically, the TGF-β1-treated osteoblasts exhibit an elongated, spread shape as opposed to the characteristic cuboidal appearance during the early stages of growth. This is followed by a decrease in the number of bone nodules formed and the amount of calcium deposition. These effects on differentiation can occur without dramatic changes in cell growth if TGF-β1 is given for a short time early in the proliferative phase. However, continuous exposure to TGF-β1 leads to a bifunctional growth response from a negative effect during the proliferative phase to a positive growth effect during the later matrix maturation and mineralization phases of the osteoblast developmental sequence. Extracellular matrix genes, fibronectin, osteopontin and α1(I) collagen, are altered in their expression pattern which may provide an aberrant matrix environment for mineralization and osteoblast maturation and potentiate the TGF-β1 response throughout the course of osteoblast differentiation. The initiation of a TGF-β1 effect on cell growth and differentiation is restricted to the proliferative phase of the culture before the cells express the mature osteoblastic phenotype. Second passage cells that are accelerated to differentiate by the addition of dexamethasone or by seeding cultures at a high density are refractory to TGF-β1. These in vitro results indicate that TGF-β1 exerts irreversible effects at a specific stage of osteoblast phenotype development resulting in a potent inhibition of osteoblast differentiation at concentrations from 0.1 ng/ml. © 1994 Wiley-Liss, Inc. 相似文献
64.
65.
Michael A. Kron Laura Gately Janardan P. Pandey Miguel H. Jurado Jose Rumbea Guzman 《Human genetics》1994,93(5):517-519
Indigenous Indian groups comprise approximately 20% of Ecuador's population, the third largest percentage in all of Central or South America, yet immunogenetic data on these groups are lacking in the literature. In the course of population migration studies, sera collected from 65 Ecuadorians living in the northern province of Esmeraldas were typed for six GM and two KM markers. The study population consisted of 47 Cayapa Indians and 18 blacks of African origin, descendants of slaves imported into the area during the seventeenth century. The Cayapa demonstrated three GM phenotypes, two of which are common to other South American Indian tribes. The frequency of KM1 positive Cayapa Indians (63%) is similar to other South American Indian tribes, but is significantly greater than the Huaorani of eastern Ecuador (2%), the only other Ecuadorian Indian group for whom limited immunoglobulin allotype data are available (
2=35.8, P<0.0001). 相似文献
66.
67.
68.
Carles Campmajó Jordi Joan Cairó Anna Sanfeliu Esteve Martínez Salvador Alegret Francesc Gòdia 《Cytotechnology》1994,14(3):177-182
A flow injection anlytical system based on a gas diffusion membrane module for ammonia and an ammonium flow-through potentiometric detector has been set up for measurement of L-glutamine and ammonium ions in hybridoma cell cultures. The main feature of the system is that the same basic analytical concept and equipment is used in both measurements, the only difference being for the determination of L-glutamine, in which the sample flows through an immobilized glutaminase cartridge. The conditions to enable the performance of both analysis consecutively, avoiding potential interferences by unwanted deamination of other compounds in the samples, have been determined. Finally, the proposed system has been compared with reference analytical methods for batch hybridoma cell culture experiments. 相似文献
69.
Even Amler Nelvio Cester Eleonora Salvolini Roberto Staffolani Martin Burkhard Laura Mazzanti Arnot Kotyk Carlo Romanini 《Cell biology international》1994,18(7):723-727
Placentas of women suffering from pregnancy-induced hypertension (PIH) were found to contain a greater amount of Na,K-ATPase molecules, estimated from anthroyl ouabain binding, than normotensive individuals. Both the microsomal fraction of placental cells and purified Na,K-ATPase showed an increased affinity for the specific inhibitor ouabain which, in the case of the microsomes, bound with a dissociation constant of 0.9 nM as compared with 3.4 nM in the controls. Likewise, the dissociation constant of the ouabain complex with purified Na,K-ATPase was about 3.5 times lower in the hypertensive patients. The differences are apparently caused by a different microenvironment of the ouabain-binding site, as reflected in the quantum yield of bound anthroyl ouabain. If an endogenous digitalis-like factor is present in the body fluids to regulate Na,K-ATPase activity, the present results render its role quite plausible. 相似文献
70.
Jeffrey C. Geesin Laura J. Brown Joel S. Gordon Richard A. Berg 《Experimental cell research》1993,206(2)
Ascorbic acid has been shown to stimulate collagen synthesis in monolayer cultures of human dermal fibroblasts. In the present studies, we examined whether the presence of a collagen matrix influences this response of dermal fibroblasts to ascorbic acid. Fibroblasts and collagen were mixed and allowed to gel and contract for 6 days to form a matrix prior to determining the concentration and time dependence for ascorbic acid to affect collagen synthesis by fibroblasts within the matrix. Collagen synthesis was stimulated at levels at or above 10 μM ascorbic acid and was maximal after 2 days of treatment. This concentration and time dependence is similar to that of cells grown in monolayer cultures. The effects of transforming growth factor-β (TGF-β) and fibroblast growth factor (FGF) were also examined in this model. TGF-β increased and FGF inhibited collagen synthesis in the gels, as has been shown for cells in monolayer cultures. The effects of potential inhibitors of lipid peroxidation induced by ascorbic acid were also examined in these matrices and compared to previous results obtained in monolayer cultures. Propyl gallate, cobalt chloride, α,α-dipyridyl, and α-tocopherol inhibited the ascorbic acid-mediated stimulation of collagen synthesis while mannitol had no effect. Natural retinoids inhibited total protein synthesis without the specific effect on collagen synthesis that was seen in monolayer cultures. These results indicate that ascorbic acid stimulates collagen synthesis in fibroblasts grown in a collagen matrix in a manner similar to that found in monolayer cultures. In contracting collagen gels, however, the magnitude of the effect is less and retinoids do not specifically inhibit collagen synthesis. 相似文献