In vitro formation and development of floral buds on tobacco stem explants: effects of kinetin and other factors

Stem segments were excised from plants of Wisconsin 38 tobacco (Nicotiana tabacum L.) in three regions differing in their distance below the inflorescence. They were cultured in vitro in 8- or 16-hr days. After 8 weeks, floral and vegetative buds were counted, and extent of floral development was assessed. Kinetin at 10(-5)m inhibited formation and development of floral buds regardless of indoleacetic acid concentration. Supplied at this concentration with adequate auxin, kinetin stimulated vegetative bud formation and may have caused floral bud abortion. Indoleacetic acid (>/= 10(-6)m) inhibited vegetative and floral bud formation when supplied with low kinetin concentration (/= 10(-6)m), it inhibited floral bud formation and stimulated vegetative bud formation. More floral buds were formed in 16-hr days than in 8-hr days. Few formed on explants other than those derived from the region nearest the inflorescence regardless of other treatment.     

Methods for Determining the Uncertainty of Population Estimates Derived from Satellite Imagery and Limited Survey Data: A Case Study of Bo City,Sierra Leone

This study demonstrates the use of bootstrap methods to estimate the total population of urban and periurban areas using satellite imagery and limited survey data. We conducted complete household surveys in 20 neighborhoods in the city of Bo, Sierra Leone, which collectively were home to 25,954 persons living in 1,979 residential structures. For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images. We used bootstrap statistical methods to estimate the total population of the pooled sections, including the associated uncertainty intervals, as a function of sample size. Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size. We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs.     

Dimeric structure of the six-domain VibF subunit of vibriobactin synthetase: mutant domain activity regain and ultracentrifugation studies

Nonribosomal peptide synthetases (NRPS), fatty acid synthases (FAS), and polyketide sythases (PKS) are multimodular enzymatic assembly lines utilized in natural product biosynthesis. Previous data on FAS and PKS subunits have indicated that they are homodimers and that some of their catalytic functions can work in trans. When NRPS assembly lines have been probed for comparable formation of stable oligomers, no evidence had been forthcoming that species other than monomer forms were active. In this work we focus on the six-domain (Cy1-Cy2-A-C1-PCP-C2) enzyme VibF from the vibriobactin synthetase assembly line, which contains three other proteins, VibB, VibE, and VibH, that--when purified and mixed with VibF and the substrates ATP, threonine, 2,3-dihydroxybenzoate (DHB), and norspermidine--produce the iron chelator vibriobactin. Using a deletion of the Cy1 domain and separate inactivating mutations in the Cy2, A, PCP, and C2 domains of VibF, we report regain of catalytic activity upon mutant protein mixing that argues for heterodimer formation, stable for hundreds to thousands of catalytic cycles, with acyl chain processing and transfer around blocked domains. Ultracentrifugation data likewise confirm a dimeric structure for VibF and establish that domains within NRPS dimeric modules can act on acyl chains in trans. The results described here are the first indication for an NRPS subunit that homodimerization can occur and that there is a continuum of functional oligomerization states between monomers and dimers in nonribosomal peptide synthetases.     

SBOL Visual: A Graphical Language for Genetic Designs

Synthetic Biology Open Language (SBOL) Visual is a graphical standard for genetic engineering. It consists of symbols representing DNA subsequences, including regulatory elements and DNA assembly features. These symbols can be used to draw illustrations for communication and instruction, and as image assets for computer-aided design. SBOL Visual is a community standard, freely available for personal, academic, and commercial use (Creative Commons CC0 license). We provide prototypical symbol images that have been used in scientific publications and software tools. We encourage users to use and modify them freely, and to join the SBOL Visual community: http://www.sbolstandard.org/visual.     

Protocol of a prospective study on the diagnostic value of transcranial duplex scanning of the substantia nigra in patients with parkinsonian symptoms

Background  

Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD.     

Catalytically inactive condensation domain C1 is responsible for the dimerization of the VibF subunit of vibriobactin synthetase

Nonribosomal peptide synthetases (NRPS), fatty acid synthases (FAS), and polyketide synthases (PKS) are multimodular enzymatic assembly lines utilized in natural product biosynthesis. The oligomeric structure of these assembly line enzymes has been a topic of interest because higher order oligomeric quaternary structural arrangements allow for alternate paths of acyl intermediate elongation and present unique challenges for the chimeric engineering of hybrid assembly lines. Unlike other NRPS systems that in general appear to be monomeric, the six domain (Cy1-Cy2-A-C1-PCP-C2) VibF subunit of vibriobactin synthetase has previously been shown to be dimeric, the same oligomeric state as that observed for FAS and PKS assembly lines. It has been demonstrated that the C1 domain within VibF is catalytically inactive and is not required for vibriobactin production. Utilizing sedimentation equilibrium analytical ultracentrifugation experiments to determine the oligomeric states of several VibF subfragments, we report that the C1 domain is largely responsible for VibF dimerization. Comparative rates of vibriobactin production, coupled with dissociation constants for VibF subfragment pair heterocomplexes, suggest that the mere presence of C1 does not detectably enhance the catalytic rates of neighboring domains, but it may properly orient Cy1-Cy2-A relative to PCP-C2.     

Relationship of enamel hypoplasia to the pattern of tooth crown growth: A discussion

The defects of enamel hypoplasia can be related to the layered structure of enamel which represents the sequence of development in tooth crowns. From such studies, it is possible to see that furrow-type enamel defects (the most common form of hypoplasia seen with the naked eye) are just the most prominent expression of a continuum which extends ever smaller, down to a microscopic disturbance to a single layer in the crown formation sequence. Furthermore, the progressive decrease in spacing between development layers which occurs down the crown sides, from occlusal to cervical, affects both the prominence and apparent width of the defects. This makes it difficult to use measurements as a means of estimating the duration of the disturbance causing a particular defect. The difficulty is even greater for the less common pitted or exposed-plane-type defects, for which the apparent width bears very little relationship with the duration of the growth disturbance. The defects of enamel hypoplasia can therefore be understood clearly only when examined under the microscope in relation to the structures which mark the development sequence of the tooth crown. Am J Phys Anthropol 104:89–103, 1997. © 1997 Wiley-Liss, Inc.