Identification of a Ca(2+)-pectate binding site on an apoplastic peroxidase

An apoplastic isoperoxidase from zucchini (APRX) was shown to bind strongly to polygalacturonic acid in their Ca(2)+-induced conformation. By homology modeling, we were able to identify a motif of four clustered arginines (positions 117, 262, 268, and 271) that could be responsible for this binding. To verify the role of these arginine residues in the binding process, we prepared three mutants of APRX (M1, R117S; M2, R262Q/R268S; and M3, R262Q/R268S/R271Q). APRX and the three mutants were expressed as recombinant glycoproteins by the baculovirus-insect cell system. This procedure yielded four active enzymes with similar molecular masses that were tested for their ability to bind Ca(2)+-pectate. Recombinant wild-type APRX exhibited an affinity for the pectic structure comparable to that of the native plant isoperoxidase. The mutations impaired binding depending on the number of arginine residues that were replaced. M1 and M2 showed intermediate affinities, whereas M3 did not bind at all. This was demonstrated using an in vitro binding test and on cell walls of hypocotyl cross-sections. It can be concluded that APRX bears a Ca(2)+-pectate binding site formed by four clustered arginines. This site could ensure that APRX is properly positioned in cell walls, using unesterified domains of pectins as a scaffold.     

How Bacillus thuringiensis has evolved specific toxins to colonize the insect world

Bacillus thuringiensis is a bacterium of great agronomic and scientific interest. Together the subspecies of this bacterium colonize and kill a large variety of host insects and even nematodes, but each strain does so with a high degree of specificity. This is mainly determined by the arsenal of crystal proteins that the bacterium produces during sporulation. Here we describe the properties of these toxin proteins and the current knowledge of the basis for their specificity. Assessment of phylogenetic relationships of the three domains of the active toxin and experimental results indicate how sequence divergence in combination with domain swapping by homologous recombination might have caused this extensive range of specificities.     

Neuronal and mixed neuronal glial tumors associated to epilepsy. A heterogeneous and related group of tumours

The group of brain tumors with mature components encompasses several pathological entities including: the ganglioneuroma; the gangliocytoma; the ganglioglioma; the desmoplastic ganglioglioma; the neurocitoma and a group of glioneuronal hamartomatous tumorous lesions, such as meningoangiomatosis. The dysembryoplastic neuroepithelial tumor is characterized by the presence of multiple cortical nodules made up of small, oligo-like cells and a myxoid pattern rich in mucopolysaccharides. Mature neuronal cells are frequently detected throughout the tumor. Most of them are associated with microhamartias in the adjacent brain and pharmacoresistant epilepsy. The excellent prognosis of the majority of these tumors and the potential for malignant transformation of the glial component in the ganglioglioma are the two most remarkable findings. Histological signs of anaplasia and greater mitotic and proliferative activities are associated with local recurrences. Atypical neurocytomas occur only exceptionally. Treatment choices are surgical resectioning and, in those cases presenting greater proliferative activity and cytological atypia, postoperative radiotherapy may be recommended. This paper reviews this heterogeneous group of neoplasms and hamartomatous lesions, pointing out presumable transitions among the different types of mixed neuronal and glial brain tumors. A single term of "mixed neuronal-glial tumors" is defended, distinguishing different subgroups of tumors, depending on the predominant cellular component.     

ATP-dependent calcium accumulation in brain microsomes. Enhancement by phosphate and oxalate.

1. ATP-dependent calcium uptake by a rabbit brain vesicular fraction (microsomes) was studied in the presence of phosphate or oxalate. These anions, which are known to form insoluble calcium salts, increased the rate of calcium uptake and the capacity of the vesicles for calcium accumulation. 2. The degree of activation depended on the concentration of phosphate or oxalate. Under optimal conditions, phosphate promoted a 5-fold increase in the amount of calcium stored at steady state. This level was 200-250 nmol Ca-2+/mg protein. 3. Initial rate of calcium uptake followed Michaelis-Menten kinetics with an apparent Km for calcium of 6.7-10-minus 5 M and a V of 44 nmol/min per mg protein. Optimal pH was 7.0. With 2 mM ATP, optimal Mg-2+ concentration was 2 mM. 4. Dintrophenol and NaN3 inhibited calcium uptake in a mitochondria-enriched fraction but not in the microsomal fraction. 5. Calcium uptake activity was compared in the six subfractions prepared from the whole microsomal fraction by means of a sucrose density gradient fractionation. 6. The Mg-2+-dependent ATPase activity of brain microsomes was activated by calcium. Maximal activation was attained with 100 muM CaCl2. Greater calcium concentrations caused a progressive inhibition. 7. The data suggest that the ATP-dependent calcium uptake in brain microsomes, as in muscle microsomes, is brought about by an active transport process, calcium being accumulated as a free ion inside the vesicles.     

Studie über einen Trichophyton - quinckeanum -Stamm mit ausgeprägter Fluoreszenz des Scutulums em Tierversuch

A vesicular skin lesion which existed since 1 week in the lower part of the leg of a 45-year-old woman appeared to be caused by fungus which was identified as Trichophyton quinckeanum (Zopf) MacLeod & Muende. The patient could not state to have had contact with animals. Peroral administration of griseofulvin and local application of 2% salicyl--5% sulfur--vaseline alternate with tonoftal cream healed the lesion completely. The fast growing fungus produced white, convoluted colonies with a brown, lat er wine-red reverse. Globose and club-shaped, one- and two-celled microconidia were formed especially 'en thrse'. The majority of the thin-walled macroconidia had rounded apices but a fusiform type of spore was also seen. Germination of the macroconidia was frequently observed. Experimental infection into the dorsal skin of white laboratory mouse produced a scutulum with a bright yellow later green fluorescence in Wood's light. The taxonomy of Trichophyton quinckeanum is briefly discussed.     

Tree size and flowering intensity as affected by nitrogen fertilization in non-bearing orange trees grown under Mediterranean conditions

A field experiment was conducted in the South of Portugal with young (0-3 years old) non-bearing ‘Lane Late’ orange trees. Five nitrogen (N) rates were used in a randomised block design with three replicates. The 180 g N tree⁻¹ over three years led to the greatest canopy width (176 cm) and volume (2,697 dm³). The greatest rate applied (720 g N tree⁻¹ in the three years) led to the largest flower yield. Nitrogen concentration in the flowers significantly increased with fertilizer N, and also with the flowering period up to the 23^rd day, declining thereafter. Flower yield was strongly correlated (r = 0.99, p < 0.001) with flower N concentration. Nutrient composition of flowers and of mature leaves from the spring flush was compared. Significant correlations were found for N (r = 0.47, p <0.01), P (r = -0.49, p <0.01), K (r = 0.44, p <0.05) and Ca (r = 0.87, p <0.001), suggesting that flowers can be used as a tool to diagnose the nutritional status of trees. Canonical analysis (with N treatment as dummy-variables) showed strong relationships between canopy width and N, which were greater at the larger rates of fertilizer application, and strong and inverse relationships between K and Mg, also with the greatest N rates.     

<Emphasis Type="Italic">ZWILLE</Emphasis> buffers meristem stability in<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

The shoot apical meristem of higher plants consists of a population of stem cells at the tip of the plant body that continuously gives rise to organs such as leaves and flowers. Cells that leave the meristem differentiate and must be replaced to maintain the integrity of the meristem. The balance between differentiation and maintenance is governed both by the environment and the developmental status of the plant. In order to respond to these different stimuli, the meristem has to be plastic thus ensuring the stereotypic shape of the plant body. Meristem plasticity requires the ZWILLE (ZLL) gene. In zll mutant embryos, the apical cells are misspecified causing a variability of the meristems size and function. Using specific antibodies against ZLL, we show that the zll phenotype is due to the complete absence of the ZLL protein. In immunohistochemical experiments we confirm the observation that ZLL is solely localized in vascular tissue. For a better understanding of the role of ZLL in meristem stability, we analysed the genetic interactions of ZLL with WUSCHEL (WUS) and the CLAVATA1, 2 and 3 (CLV) genes that are involved in size regulation of the meristem. In a zll loss-of-function background wus has a negative effect whereas clv mutations have a positive effect on meristem size. We propose that ZLL buffers meristem stability non-cell-autonomously by ensuring the critical number of apical cells required for proper meristem function.Edited by G. JürgensAn erratum to this article can be found at     

Anti-oxidant defences and peroxidation in liver and brain of aged rats.

Old rats (28 months), when compared with young adults (9 months), did not show differences in activities of superoxide dismutase (SOD) or selenium-dependent and -independent glutathione peroxidases (GPx), or in levels of GSH, GSSG, GSSG/GSH and endogenous peroxidation in liver and brain. Rates of stimulated peroxidation in vitro were decreased in the livers of old rats. Old animals showed decreased levels of hepatic catalase and glutathione reductase. Nevertheless, when enzyme activities were referred to cytochrome oxidase activity these decreases disappeared, and GPx and SOD (brain) were even increased in old rats.