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1.
R. L. LUCAS 《The Annals of applied biology》1955,43(1):134-143
The competitive saprophytic ability of Ophiobolus graminis has been compared with that of Fusarium cultnorum. Test pieces of wheat straw were buried in maize-meal-sand inoculum mixed in various proportions with unsterilized soil, according to the technique already described by Butler (1953). Some possible sources of variation in the results obtained by this technique have been investigated. Saprophytic colonization of the straw tissues by Ophiobolus graminis appeared to decline as invasion progressed from the outer to the inner tissues, presumably owing to continued competition with other saprophytes. An experiment using as inoculum the stubble of plants naturally infected by O. graminis suggests that saprophytic colonization of wheat straw by the take-all fungus can occur only to a negligible extent in the field. 相似文献
2.
Abstract. In some parasitoid species, the serosa membrane breaks apart at hatching and produces teratocyte cells that assume various functions (immunossupression, secretion and nutrition) mediating host–parasitoid relationships. Teratocyte growth pattern may thus reflect the host suitability for a parasitoid. The teratocyte growth pattern (increase in size and number of teratocytes as a function of time) is studied and used as an indirect measure of fitness to compare the development of the endoparasitoid Dinocampus coccinellae in a marginal host, the coccinellid Harmonia axyridis , and in a suitable host, Coleomegilla maculata . Indirect measures of fitness recorded in both host species confirm that C. maculata is a suitable host for D. coccinellae contrary to the marginal host H. axyridis. According to regression analysis, teratocyte numbers decrease linearly whereas teratocyte size increases linearly with time in the suitable host C. maculata (larvae or adults). In the marginal host, parasitism occurs only in the larval stage where a delay in the parasitoid larval development is observed. Increase in teratocyte size is also highly variable. The teratocyte growth pattern of the parasitoid in the marginal host does not follow the linear model found in the suitable host. Teratocyte growth pattern may be a useful criterion to evaluate host-suitability and host range of parasitoids. 相似文献
3.
Kinetic studies were performed on fresh-cut and aged leaf discsof Spinacia oleracea L. in order to investigate the regulatoryprocesses involved in sugar transport across the mesophyll plasmamembrane. A comparison of the kinetic profiles for fructose,glucose, sucrose and arginine obtained on freshly-cut and ageddiscs revealed that during wound-recovery, uptake is enhanced,but that this enhancement varies considerably for the differentsubstrates tested. Variation in the saturable and first-orderkinetic components of uptake was also observed. The involvementof a phosphoinositide-signalling mechanism in the wounding processwas examined by pretreating spinach leaves with lithium. Lithiuminhibited the enhancement of uptake and this effect was reversedby the addition of miro-inositol. However, in some experimentsthe tissue appeared to be insensitive to Li+. Gas chromatographicanalyses performed on cut discs indicated that ethylene wasproduced in response to wounding and that the addition of cobaltto the ageing media inhibited this ethylene production. Comparativekinetic studies of control and cobalt-treated discs indicatedthat ethylene was essential for the enhancement of transportacross the plasma membrane. However, addition of ethylene touncut tissue caused only a partial increase in the uptake offructose, which indicates that some additional wound-signallingcomponent is involved. Addition of cycloheximide to the recoverymedia completely inhibited this enhancement phenomenon. Thecycloheximide-response was not due to an inhibition of ACC synthasesynthesis nor to a reduction of ATP levels. We concluded thatthe effect of cycloheximide was on protein synthesis. Our resultsare discussed in terms of possible cellular and molecular mechanismsregulating sugar transport. Key words: Sugar transport, wounding, ethylene production, spinach leaves 相似文献
4.
Payant V; Abukashawa S; Sasseville M; Benkel BF; Hickey DA; David J 《Molecular biology and evolution》1988,5(5):560-567
Nuclear DNA was extracted from each of the eight species comprising the
Drosophila melanogaster species subgroup. Southern hybridization of this
DNA by using a molecular probe specific for the alpha-amylase coding region
showed that the duplicated structure of the amylase locus, first found in
D. melanogaster, is conserved among all species of the melanogaster
subgroup. Evidence is also presented for the concerted evolution of the
duplicated genes within each species. In addition, it is shown that the
glucose repression of amylase gene expression, which has been extensively
studied in D. melanogaster, is not confined to this species but occurs in
all eight members of the species subgroup. Thus, both the duplicated gene
structure and the glucose repression of Drosophila amylase gene activity
are stable over extended periods of evolutionary time.
相似文献
5.
Lucas, W. J. and Ogata, K. 1985. Hydroxyl and bicarbonateassociatedtransport processes in Chara corallintr. Studies on the lightdarkregulation mechanism.J. exp. Bot. 36: 19471958.Experiments were undertaken on the fresh water alga Chara corallinato investigate the nature of the coupling between the chloroplastsand the lightdependent OH and -associated plasmalemma transport systems. Electrophysiologicalexperiments, in which DCMU was employed, revealed that thischemical could elicit a hyperpolarization of the membrane potentialthat was identical to that normally obtained by turning offthe light. This DCMUinduced hyperpolarization was obtainedunder control () and phosphatedecoupled conditions (). Measurements of the extracellular electric potentialswhich are associated with the acidic () and alkaline (OH) regions, indicated that, in the presenceof control ()or phosphatedecoupled conditions, normal profiles were established under air, oxygenor nitrogen environments. These results indicate that the generationof the control signal(s) is related to events associated withchloroplast electron transport, rather than to changes in theflow or levels of carbon intermediates within the reductivepentose phosphate or photorespiratory cycles. Although the levelof oxygen was found to have no effect on the lightinducedactivation of the OH regions, we found that in pure oxygen thedarkinduced inactivation of the OH efflux systemwas delayed, and that partial transport function could be maintainedin the dark. The possible involvement of changes in either theratio of oxidized to reduced ferridoxin or NADP? to NADPH, aspart of this lightmediated control signal, is discussed. Key words: Chara corallina, Plasma membrance transport, OH and , regulation 相似文献
6.
JOÃO BATISTA TAVARES DA SILVA ISAAC ROITMAN 《The Journal of eukaryotic microbiology》1990,37(6):521-523
ABSTRACT. Three strains of Phytomonas serpens two from tomatoes, Lycopersicon esculentum one from the insect Phtia picta (Hemiptera, Coreidae), were cultivated in a chemically defined medium developed from a defined medium for cultivating insect flagellates. Besides organic growth factors required by other insect trypanosomatids this flagellate requires, serine and inositol. Glutamine stimulates growth, and, surprisingly, does not require heme. 相似文献
7.
MARC J. FAZIO ALBA C. DA SILVA THOM K. ROSIERE G. BENJAMIN BOUCK 《The Journal of eukaryotic microbiology》1995,42(5):570-580
ABSTRACT. Proteins of the membrane skeleton of Euglena gracilis were extensively phosphorylated in vivo and in vitro after incubation with [32 P]-orthophosphate or γ-[32 P] ATP. Endogenous protein threonine/serine activity phosphorylated the major membrane skeletal proteins (articulins) and the putative integral membrane protein (IP39) anchor for articulins. The latter was also the major target for endogenous protein tyrosine kinase activity. A cytoplasmic domain of IP39 was specifically phosphorylated, and removal of this domain with papain eliminated the radiolabeled phosphoamino acids and eliminated or radically shifted the PI of the multiple isoforms of IP39. In gel kinase assays IP39 autophosphorylated and a 25 kDa protein which does not autophosphorylate was identified as a threonine/serine (casein) kinase. Plasma membranes from the membrane skeletal protein complex contained threonine/serine (casein) kinase activity, and cross-linking experiments suggested that IP39 was the likely source for this membrane activity. pH optima, cation requirements and heparin sensitivity of the detergent solubilized membrane activity were determined. Together these results suggest that protein kinases may be important modulators of protein assembly and function of the membrane skeleton of these protistan cells. 相似文献
8.
9.
Borrelia burgdorferi is a spirochete pathogen transmitted among warm-
blooded hosts by ixodid ticks. Frequency-dependent selection for variant
outer-surface proteins might be expected to arise in this species, since
rare variants are more likely to avoid immune surveillance in previously
infected hosts. We sequenced the OspA and OspB genes of nine North American
strains and compared them with nine strains previously described. For each
gene, the mean number of synonymous substitutions per synonymous site and
the mean number of nonsynonymous substitutions per nonsynonymous site show
only a twofold excess of silent mutations. Synonymous rates vary widely
along the OspB protein. Some regions show a significant excess of silent
substitutions, while divergence in other regions is constrained by biased
base composition or selection. The presence, in antigenically important
regions of the protein, of significant variation among strains, as well as
evidence for recombination among strains, should be considered in attempts
to develop vaccines against this disease.
相似文献
10.