Where water is oxidized to dioxygen: structure of the photosynthetic Mn4Ca cluster

The oxidation of water to dioxygen is catalyzed within photosystem II (PSII) by a Mn(4)Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn(4)Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 angstrom-resolution x-ray structures or other previously proposed models.     

Thyroid Dysplasia in Wistar Hannover GALAS Rats

Thyroid dysplasia was recognized in WistarHan GALAS rats and confirmed as a heritable congenital disorder. The gene or genes involved were not identified, but homozygous animals with thyroid dysplasia also exhibited stunted growth, had reduced pituitary gland growth hormone (GH) and were hypothyroid. Heterozygous animals exhibited thyroid dysplasia with normal thyroid hormonal homeostasis and no difference in the incidence of preneoplastic or neoplastic lesions in oncogenicity studies.     

Participation of Xanthomonas axonopodis pv. citri hrp cluster in citrus canker and nonhost plant responses

The participation of the Xanthomonas axonopodis pv. citri hypersensitive response and pathogenicity ( hrp ) cluster in interactions with host and nonhost plants was characterized in pathogenicity and avirulence models. The hrp cluster encodes the type III secretion system indispensable for trafficking of proteins to the plant cell. Mutations in operons hrpB and hrpD and the hrpF gene failed to produce canker in citrus plants or hypersensitive response in cotton plants. The interaction of the phytopathogen with various nonhost plants has been characterized . The results showed that the hypersensitive response is activated in leaves of cotton, bean, tobacco, tomato, pepper and Nicotiana benthamiana , and that genes present in operons hrpB and hrpD and the hrpF gene are required for pathogenicity in hosts and induction of the hypersensitive response in nonhost plants.     

Isomers of sterol synthesis inhibitors: Fungicidal effects and plant growth regulator activities

The chemical diversity of fungicides and antimycotics interfering with the C-14 demethylation of fungal sterols indicates a rather high structural flexibility of the sterol binding site at the specific cytochrome P-450 mixed-function oxygenase. The structural flexibility, however, is opposed by a remarkable stereochemical selectivity. A similar, though not identical, stereochemical discrimination is observed with a group of plant growth regulators chemically related to the fungicidal demethylation inhibitors. The relationship between chemical structure and stereochemical requirements is discussed for both biological activities.     

Insertional mutagenesis of <Emphasis Type="Italic">Magnaporthe grisea</Emphasis> toward decreased responsiveness of alternative respiration to inhibition by azoxystrobin

 Inhibitors of respiration with high affinity to the Qo site of cytochrome b constitute a major class of modern agricultural fungicides. Many fungal organisms, including plant pathogens, can circumvent this inhibition site by expressing alternative respiration, a pathway dependent on alternative oxidase and other unidentified gene products. The restriction enzyme-mediated insertion (REMI) technique was employed in this study to disrupt genes involved in the expression of fully functional alternative respiration of Magnaporthe grisea. In one of the REMI mutants obtained, the rescue response mediated by alternative respiration was completely abolished. In two other mutants, the response was diminished but not entirely silenced. For all three mutants, phenotype changes were not explained by an altered structure of the alternative oxidase gene AOXMg or by a decreased level of gene expression in response to the Qo inhibitor azoxystrobin. The gene potentially affected in one of the REMI mutants was a homolog of the ABC1 family of genes encoding chaperone-like proteins with roles in the optimal assembly of mitochondrial membrane complexes. Received: May 28, 2002 / Accepted: October 16, 2002 Acknowledgments The research was funded, in part, by financial support to C. Avila-Adame provided by the Fulbright-Garcia Robles Foundation, the Institute of International Education, CONACYT-Mexico, and the Colegio de Postgraduados-Mexico.     

Suppression of cytokine-inducible nitric oxide synthesis during intraperitoneal meth a tumor growth

Nitric oxide (NO*) synthesis is induced within many tumors. The timecourse of NO* synthesis was evaluated during intraperitoneal Meth A fibrosarcoma progression. While increasing macrophage recruitment into ascites was noted, inducible nitric oxide synthase (iNOS) antigen and function peaked between days 3-6 after tumor implantation. The capacity of cells to respond to LPS and IFNgamma stimulation was markedly depressed on day 9 and 11. Cellular proliferation correlated in an inverse fashion with levels of NO* synthesis. Electron paramagnetic resonance spectroscopy and nitrotyrosine immunostaining failed to show accumulation of characteristic target cell lesions induced by NO*. These findings lead us to conclude that NO* production was increasingly suppressed during Meth A tumor progression. Depression of NO* production did not correlate with levels of the inhibitory cytokines TGFbeta and IL-10, but could be partially overcome by addition of sepiapterin (a tetrahydrobiopterin prodrug). Thus, depletion of essential co-factors necessary for iNOS function may contribute to depressed NO* responses during cancer progression.     

Different methods for the evaluation of species of the genus Mesaphorura (Collembola, Tullbergiinae)

Field studies and laboratory investigations based upon cultures, isoenzyme electrophoresis and RAPD-PCR were carried out to get a better understanding of the value of morphospecies within the genus Mesaphorura.Culturing of seven Mesaphorura species under constant as well as variable conditions provided a basis for evaluation of morphological characters, but did not yield any statistically supportable evidence that intraspecific variability reached interspecific delimitations.In enzyme tests, esterases gave the best results. The search for species-specific band patterns is, however, time and material consuming. DNA investigations using RAPD-PCR resulted in band patterns that appeared to be species specific. Nevertheless, these require further investigations.None of the studies carried out gave any conclusive evidence for invalidation of the morphologically defined species of the genus Mesaphorura.