Differential synthesis of peritoxins and precursors by pathogenic strains of the fungus Periconia circinata.

Pathogenic strains of the soilborne fungus Periconia circinata produce peritoxins with host-selective toxicity against susceptible genotypes of sorghum. The peritoxins are low-molecular-weight, hybrid molecules consisting of a peptide and a chlorinated polyketide. Culture fluids from pathogenic, toxin-producing (Tox(+)) and nonpathogenic, non-toxin-producing (Tox(-)) strains were analyzed directly by gradient high-performance liquid chromatography (HPLC) with photodiode array detection and HPLC-mass spectrometry to detect intermediates and final products of the biosynthetic pathway. This approach allowed us to compare the metabolite profiles of Tox(+) and Tox(-) strains. Peritoxins A and B and the biologically inactive intermediates, N-3-(E-pentenyl)-glutaroyl-aspartate, circinatin, and 7-chlorocircinatin, were detected only in culture fluids of the Tox(+) strains. The latter two compounds were produced consistently by Tox(+) strains regardless of the amount of peritoxins produced under various culture conditions. In summary, none of the known peritoxin-related metabolites were detected in Tox(-) strains, which suggests that these strains may lack one or more functional genes required for peritoxin biosynthesis.

Visual information and the control of reaching in children: a comparison between children with and without developmental coordination disorder.

Three experiments were performed on reach and grasp in 9- to 10-year-old children (8 controls and 8 with developmental coordination disorder [DCD]). In normal reaching, children in the DCD group were less responsive to the accuracy demands of the task in controlling the transport component of prehension and spent less time in the deceleration phase of hand transport. When vision was removed as movement began, children in the control group spent more time decelerating and reached peak aperture earlier. Children in the DCD group did not do that, although, like the control group, they did increase grip aperture in the dark. When depth cues were reduced and only the target or only the target and hand were visible, children in the control group used target information to maintain the same grip aperture in all conditions, but DCD children behaved as if the target was not visible. Throughout the studies, the control group of 9- to 10-year-olds did not produce adult-like adaptations to reduced vision, suggesting that they had not yet attained adult-like integration of sensory input. Compared with control children, children with DCD did not exhibit increased dependence on vision but showed less recognition of accuracy demands, less adaptation to the removal of vision, and less use of minimal visual information when it was available.

Development of a transformation system for Mycosphaerella pathogens of banana: a tool for the study of host/pathogen interactions.

A genetic transformation system has been developed for three Mycosphaerella pathogens of banana and plantain (Musa spp.). Mycosphaerella fijiensis and Mycosphaerella musicola, the causal agents of black and yellow Sigatoka, respectively, and Mycosphaerella eumusae, which causes Septoria leaf spot of banana, were transformed with a construct carrying a synthetic gene encoding green fluorescent protein (GFP). Most single-spored transformants that expressed GFP constitutively were mitotically stable in the absence of selection for hygromycin B resistance. Transformants of all three species were pathogenic on the susceptible banana cultivar Grand Nain, and growth in planta was comparable to wild-type strains. GFP expression by transformants allowed us to observe extensive fungal growth within leaf tissue that eventually turned necrotic, at which point the fungi grew saprophytically on the dead tissue. Leaf chlorosis and necrosis were often observed in advance of saprophytic growth of the mycelium on necrotic tissue, which supports previous reports suggesting secretion of a phytotoxin.

On the nature of hereditary cataract in strain 13/N guinea pigs.

PURPOSE: Congenital nuclear cataracts in strain 13/N guinea pigs are caused by a single splice-site mutation in the zeta-crystallin gene. Very little is known of the physical factors involved in lens opacification of this system. The aim of this study is to elucidate the biophysical processes causing the nuclear turbidity. METHODS: Normal, homozygous and heterozygous mutant guinea pig lenses were studied. Polarized light scattering measurements were performed on thin sections of lenses as a function of scattering angle. Scattering intensities were collected in two modes, I- and I+. The total water content of lenses was determined by thermogravimetric analysis. The nonfreezable (bound) water content was obtained by differential scanning calorimetry. The morphology of lenses was investigated by scanning electron microscopy. RESULTS: Normal lenses scatter 5- to 10-fold less light than cataractous lenses at wide angles in both modes. The intensity ratios of the two modes imply that most of the scattering comes from density fluctuations; 10-20% of the turbidity may be contributed by orientation fluctuations. The nucleus of heterozygous cataractous lenses contain less total water than normal lenses, whereas the cortex has the same hydration as the normal lens. The nonfreezable water content of the cataractous nucleus is higher than that of the normal lens. Scanning electron microscopy showed frequent truncation of the fiber cells, cavitations and occasional longitudinal splitting resulting in hollow cylinder formation in the nucleus of the cataractous lens. CONCLUSION: Mutation of zeta-crystallin in guinea pigs causes a congenital cataract. A number of supramolecular events contribute to the turbidity. The mobile water leaves the nuclear fiber cells, causing a collapse of supramolecular structures. Both the size of the aggregates and their refractive index increase by this dehydration process, contributing to the turbidity. The truncation and hollowing of fiber cells causes the orientation fluctuations that also increase turbidity.

Light scattering and morphology of cataract formation in transgenic mice containing the HIV-1 protease linked to the lens alpha A-crystallin promoter.

Two constructs of transgenic mice, TG61 and TG72, containing the HIV-1 protease linked to the lens alpha A-crystallin promoter develop cataract. The TG61 construct develop cataract in utero, while the TG72 construct exhibit frank opacities on the 24th day (homozygotes) and 26th day (hemizygotes) post natum. Polarized light scattering measurements were performed on cortical and nuclear sections of TG72 lenses from day 19 to day 26 as a function of scattering angle. The parallel components of the scattered light intensity increase gradually during opacification, the perpendicular components show very low values from day 19 to day 22 after which they increase exponentially. Analysis of the scattered light intensities yielded parameters describing the size of the protein aggregates, the size of the domains exhibiting optical anisotropy/birefringence, the difference in refractive index between (a) the protein aggregates and their surroundings and (b) the birefringent units and their surroundings. The last parameter accounts for the major portion of the increase in lens turbidity. The TG72 construct shows normal lens development on day 16. By day 21 the posterior cortex shows some disintegration, while the lens is still clear. By day 26 the lens nucleus migrates toward the posterior pole and there is a major alteration in the cortical fibers. Scanning electron microscopic studies reveal normal fiber cell organizations in control animals. In the TG72 construct the fiber cells are well organized at 16 days after birth but already develop some slight separation in the posterior cortical part of the lens. By post-natal day 21, the nucleus and the anterior cortex still exhibit well aligned fiber cell organization, but the posterior cortex shows disalignment. By day 26 in the TG72 construct, all areas of the lens show complete disintegration of the fiber cells and amorphous masses are present throughout. The light scattering parameters describing changes on the nanometer scale can be correlated with the changes in lens morphology during cataractogenesis that occur on the micrometer scale. In comparison, the light and scanning electron microscopic examinations of the postnatal TG61 construct show that the lens is severely disrupted and contains completely disintegrated fiber cell remnants at an early age.

Hypovirulence-associated traits induced by a mycovirus of Cryphonectria parasitica are mimicked by targeted inactivation of a host gene.

Expression of the Vir2 gene of Cryphonectria parasitica is down-regulated in strains of the fungus containing a double-stranded RNA genetic element that reduces fungal virulence (W. A. Powell and N. K. Van Alfen, Mol. Cell. Biol. 7:3688-3693, 1987). We have sequenced the Vir2 gene and characterized its structure; the mRNA contains a short open reading frame whose product has structural similarities to several fungal pheromones. A null mutant was constructed by homologous recombination to determine the function of the Vir2 gene and whether its disruption resulted in any of the altered phenotypes exhibited by many hypovirulent strains, such as reductions in virulence, pigmentation, and sporulation. The Vir2 null mutant (18dm) exhibited a wild-type phenotype with respect to gross colony morphology, growth rate, pigmentation, asexual spore viability, and virulence in apple fruit and chestnut trees. However, numbers of asexual fruiting bodies (pycnidia) and conidia were reduced significantly in comparison with the wild-type strain EP155/2. In sexual crosses of 18dm with a wild-type strain of the opposite mating type, perithecia (sexual fruiting bodies) developed but were barren. Deletion of the Vir2 gene results in a phenotype that mimics that of many double-stranded-RNA-containing hypovirulent strains; i.e., the null mutant exhibits significant reductions in asexual sporulation and pycinidum production as well as impaired sexual crossing ability. To our knowledge, this is the first report of the partial reproduction of a virus-induced phenotype by deletion of a virus-perturbed host gene.

Measurement of the severity of amphetamine dependence.

A Severity of Amphetamine Dependence Questionnaire (SAmDQ) was administered to 101 subjects attending an Australian drug dependency treatment centre. The SAmDQ was adapted from the Severity of Opiate and Alcohol Dependence Questionnaires (SODQ & SADQ). The structural characteristics of the SAmDQ were examined and compared with previous findings reported on samples of opiate addicts with the SODQ. A high degree of consistency was found between the results obtained with the SAmDQ and previous findings with the SODQ. The relationship between the SAmDQ and the Severity of Dependence Scale (SDS) was also examined. The findings suggest that further development of amphetamine dependence measurement is required.