The Differentiation of Infection Structures as a Result of Recognition Events between some Biotrophic Parasites and their Hosts

Most uredospores of rust fungi develop infection structures in a typical pattern so that they can infect the host plant. The function of these infection structures is divided into the following three phases:

• 1 In the recognition phase, the germ tube recognizes the cuticle and the stoma. This process may occur independently from the host plant since copies of the cuticle induce similar reactions of the fungus. During fungal growth on the epidermis, unspecific stress responses of the plant are triggered.
• 2 In the signal phase, the fungal substomatal vesicle and infection hypha(e) contact the host cells within the leaf parenchyma. A signal from the host induces further development of the fungus. Haustorium mother cell differentiation is effected and haustorium formation is initiated. At the same time, the fungus suppresses the synthesis of stress metabolites by the plant.
• 3 In the parasitic phase, the fungus penetrates the host cell and complex interactions between host and parasite begin. A highly specialized interface around the haustorium develops presumably in order to allow a more efficient nutrient transfer from host to parasite. Eventual defence reactions of the plant, generally on the race-cultivar level, fail to be evoked or are suppressed in compatible combinations.

     

Screening of yeasts for production of xylitol fromd-xylose and some factors which affect xylitol yield inCandida guilliermondii

Summary The ability to convertd-xylose to xylitol was screened in 44 yeasts from five genera. All but two of the strains produced some xylitol with varying rates and yields. The best xylitol producers were localized largely in the speciesCandida guilliermondii andC. tropicalis. Factors affecting xylitol production by a selectedC. guilliermondii strain, FTI-20037, were investigated. The results showed that xylitol yield by this strain was affected by the nitrogen source. Yield was highest at 30–35°C, and could be increased with decreasing aeration rate. Using high cell density and a defined medium under aerobic conditions, xylitol yield byC. guilliermondii FTI-20037 from 104 g/ld-xylose was found to be 77.2 g/l. This represented a yield of 81% of the theoretical value, which was computed to be 0.9 mol xylitol per mold-xylose.Issued as NRCC publication No. 28798.     

3-Mercaptopropionic acid administration increases the affinity of [H]Quinuclidinyl benzilate binding to membranes of the striatum and cerebellum

It is known that quinuclidinyl benzilate (QNB) binds specifically and with high affinity to the cholinergic muscarinic receptor and that behaves as a potent antagonist of this receptor.

We have analysed -[³H]QNB binding to rat CNS membranes after the administration of the convulsant 3-mercaptopropionic acid (MP) (150 mg·kg⁻¹, i.p.). The studies were done in rats killed at two stages: during and after seizures. No changes in [³H]QNB binding to hippocampus and cerebral cortex membranes were found. [³H]QNB binding increased about 40 and 80% in striatum and cerebellum membranes, respectively. The changes were observed both in seizure and postseizures states. The study was extended to the assay of [³H]QNB binding kinetic constants in the anatomical areas modified by the convulsant. The analysis of the saturation curves indicated an increase in the binding affinity but no change in the number of binding sites. Hill number values were near the unit suggesting a non-cooperative interaction between the ligand and the receptor, and the labelling of a homogeneous population of receptor sites.

The results suggest the participation of some cholinergic pathways in the development and maintenance of MP-induced seizures.     

Singlet oxygen induced mutation spectrum in mammalian cells.

In order to characterize the molecular nature of singlet oxygen (1O2) induced mutations in mammalian cells, a SV40-based shuttle vector (pi SVPC13) was treated with singlet oxygen arising from the thermal decomposition of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). After the passage of damaged plasmid through monkey COS7 cells, the vector was shuffled into E. coli cells, allowing the screening of supF mutants. The mutation spectrum analysis shows that single and multiple base substitutions arose in 82.5% of the mutants, the others being rearrangements. The distribution of mutations within the supF gene is not random and some hotspots are evident. Most of the point mutations (98.4%) involve G:C base pairs and G:C to T:A transversion was the most frequent mutation (50.8%), followed by G:C to C:G transversion (32.8%). These results indicate that mutagenesis in mammalian cells, mediated by 1O2-induced DNA damage, is targeted selectively at guanine residues.     

A simple and efficient method for the oligodeoxyribonucleotide-directed mutagenesis of double-stranded plasmid DNA.

A method for the oligodeoxyribonucleotide-directed mutagenesis of double-stranded DNA without the necessity for phenotypic selection is described. Plasmids denatured with alkali and purified by adsorption to and elution from nitrocellulose have single-stranded regions where primers can hybridize and serve as templates for a T7 DNA polymerase-catalyzed synthesis of complementary mutant DNA strands. When this procedure was carried out such that the original nonmutant strand contained uracil [method of Kunkel, Proc. Natl. Acad. Sci. USA 82(1985)488-492], mutation frequencies of between 30% and 40% were obtained. The technique has been used to generate mutant genes in plasmids of a wide variety of sizes. The largest plasmid manipulated and successfully mutagenized was 22 kb. The method is rapid and efficient and is not dependent upon either f1 phage vectors or the presence of restriction sites in the vicinity of the sequence targeted for mutation.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

Somatic embryogenesis in leaves and leaf-derived protoplasts of Actinidia deliciosa var. deliciosa cv. Hayward (kiwifruit)

Summary The obtention of embryogenic competence in Actinidia deliciosa var. deliciosa cv. Hayward is reported. Axillary buds from shoots submitted to cold (4°C) and starvation for 1.5 months, developed leaves with embryogenic competence. These leaves, cultured in darkness for 1.5 months on a medium containing zeatin as a sole growth regulator, originated compact structures from which embryos developed. The plating orientation and sectioning of leaves strongly affected the expression of the embryogenic potential. A selected fraction of the protoplasts isolated from these leaves was able to develop in an embryogenic way. The germination of the embryos is still only occasional.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 2-iP 6-dimethylallyl aminopurine - IAA indole-3-acetic acid - NOA naphthoxyacetic acid - SEM Scanning Electron Microscopy     

Theory of molecular machines. II. Energy dissipation from molecular machines

Single molecules perform a variety of tasks in cells, from replicating, controlling and translating the genetic material to sensing the outside environment. These operations all require that specific actions take place. In a sense, each molecule must make tiny decisions. To make a decision, each "molecular machine" must dissipate an energy Py in the presence of thermal noise Ny. The number of binary decisions that can be made by a machine which has dspace independently moving parts is the "machine capacity" Cy = dspace log2 [(Py + Ny)/Ny]. This formula is closely related to Shannon's channel capacity for communications systems, C = W log2 [(P + N)/N]. This paper shows that the minimum amount of energy that a molecular machine must dissipate in order to gain one bit of information is epsilon min = kB T ln (2) joules/bit. This equation is derived in two distinct ways. The first derivation begins with the Second Law of Thermodynamics, which shows that the statement that there is a minimum energy dissipation is a restatement of the Second Law of Thermodynamics. The second derivation begins with the machine capacity formula, which shows that the machine capacity is also related to the Second Law of Thermodynamics. One of Shannon's theorems for communications channels is that as long as the channel capacity is not exceeded, the error rate may be made as small as desired by a sufficiently involved coding. This result also applies to the dissipation formula for molecular machines. So there is a precise upper bound on the number of choices a molecular machine can make for a given amount of energy loss. This result will be important for the design and construction of molecular computers.     

Hemobilia--evolution of current diagnosis and treatment.

"Hemobilia," upper gastrointestinal tract bleeding that originates from within the biliary tract, has become widely recognized due to an increased clinical awareness of the disorder and to improvements in diagnostic techniques. In addition, the growing use of percutaneous liver puncture for the diagnosis of and therapy for hepatobiliary diseases and the increased incidence of both blunt and penetrating hepatic trauma have contributed to a rising incidence of hemobilia. We review the history, pathophysiology, and current approaches to the diagnosis and treatment of this disease.