Search for Drosophila genes encoding a conserved domain present in the achaete-scute complex and myc proteins

Summary Several genes of the achaete-scute complex (ASC) of Drosophila melanogaster encode a 60 amino acids long conserved domain which shares a significant homology with a region of the vertebrate myc proteins. Based on these results, the existence of a family of Drosophila genes that would share both this conserved domain and the neurogenic function of the AS-C has been postulated. To test this proposal, we have searched a D. melanogaster genomic library with a probe that encodes the conserved domain. Only under very low stringency hybridization conditions, clones not belonging to the AS-C cross-hybridized with the probe. Those that gave the strongest signals were characterized. Sequencing of the cross-hybridizing regions showed that they had no significant homology with the conserved domain, the sequence similarity extending at the most for 37 nucleotides. Although our results do not conclusively disprove the existence of a family of AS-C-like genes, they indicate that the conservation of the domain would be lower than that found for shared motifs in other families of Drosophila developmental genes.     

Development of the preprophase band from random cytoplasmic microtubules in guard mother cells of Allium cepa L.

The organization of microtubule (MT) arrays in the guard mother cells (GMCs) of A. cepa was examined, focussing on the stage at which a longitudinal preprophase band (PPB) is established perpendicular to all other division planes in the epidermis. In the majority of young GMCs, including those seen just after asymmetric division, MTs are distributed randomly throughout the cortex and inner regions of the cytoplasm. Few MTs are associated with the nuclear surface. As the GMCs continue to develop, MTs cluster around the nucleus and a PPB appears as a wide longitudinal band. Microtubules also become prominent between the nucleus and the periclinal and transverse walls, while they decrease in number along the radial longitudinal walls. The PPB progressively narrows by early prophase, and a transversely oriented spindle gradually ensheaths the nucleus. These observations indicate that the initial, broad PPB is organized by a rearrangement of the random cytoplasmic array of MTs. Additional reorganization is responsible for MTs linking the nucleus and the cortex in the future plane of the cell plate, and for narrowing of the PPB.Abbreviations GMC guard mother cell - MT microtubule - PPB preprophase band     

A planar microtubule-organizing zone in guard cells of Allium: experimental depolymerization and reassembly of microtubules

The generation of the unique radial array of microtubules (MTs) in stomatal guard cells raises questions about the location and activities of relevant MT-organizing centers. By using tubulin immunofluorescence microscopy, we studied the pattern of depolymerization and reassembly of MTs in guard cells of Allium cepa L. Chilling at 0°C reduces the MTs to small remnants that surround the nuclear surface of cells in the early postcytokinetic stage, or form a dense layer along the central portion of the ventral wall in older guard cells. A rapid reassembly on rewarming restores either MTs extending from the nuclear surface randomly throughout the cytoplasm in very young cells, or an array of MTs radiating from the dense layer at the ventral wall later in development. A similar pattern of depolymerization and reassembly is achieved by incubation with 100 M colchicine followed by a brief irradiation with ultraviolet (UV) light. Incubation with 200 M colchicine leads to a complete depolymerization that leaves only a uniform, diffuse cytoplasmic fluorescence. Nonetheless, UV irradiation of developing guard cells induces the regeneration of a dense layer of MTs at the ventral wall. The layer is again positioned centrally along the wall, even if the nucleus has been displaced by centrifugation in the presence of cytochalasin D. Neither the regenerated layer nor the perinuclear MTs seen earlier are related to the staining pattern of serum 5051, which reportedly binds to centrosomal material in animal and plant cells. The results support the view that, soon after cytokinesis, a planar MT-organizing zone is established in the cortex along the central portion of the ventral wall, which then generates the radial MT array.Abbreviations GC guard cell - MT microtubule - MTOC microtubule-organizing center - UV ultraviolet To whom correspondence should be addressed.     

Binding and precipitating activities ofErythrina lectins with complex type carbohydrates and synthetic cluster glycosides. A comparative study of the lectins fromE. corallodendron,E. cristagalli,E. flabelliformis,andE. indica

Erythrina lectins possess similar structural and carbohydrate binding properties. Recently, tri- and tetra-antennary complex type carbohydrates with non-reducing terminal galactose residues have been shown to be precipitated as tri- and tetravalent ligands, respectively, with certainErythrina lectins [Bhattacharyya L, Haraldsson M, Brewer CF (1988) Biochemistry 271034-41]. The present work describes a comparative study of the binding and precipitating activities of fourErythrina lectins,viz. E. corallodendron, E. cristagalli, E. flabelliformis, andE. indica, with multi-antennary complex type carbohydrates and synthetic cluster glycosides. The results show that though their binding affinities are very similar, theErythrina lectins show large differences in their precipitating activities with the carbohydrates. The results also indicate significant dependence of the precipitating activities of the lectins on the core structure of the carbohydrates. These findings provide a new dimension to the structure-activity relationship of the lectins and their interactions with asparagine-linked carbohydrates.Abbreviations EAL, ECorL, ECL, EFL, and EIL represent the lectins from the seeds ofErythrina arborescens, - E. corallodendron, E. cristagalli, E. flabelliformis, andE. indica respectively - AFOS thetri-antennary complex type oligosaccharide from asialofetuin - AFGP the tri-antennary glycopeptide from asialofetuin - MeGal methyl -d-galactopyranoside Unless stated otherwise all sugars are in thed-configuration.     

Ultrastructure of carotenoid deprivation in photoreceptors of Manduca sexta: myeloid bodies and intracellular microvilli

Summary The ultrastructural effects of carotenoid (vitamin A) deprivation were studied in the adult photoreceptors of the tobacco hornworm moth Manduca sexta. Moths were reared on a deprived diet, which lacked the carotenoid sources of the photopigment chromophore, 3-hydroxy retinal, or on a control, fortified diet, containing ample carotenoid. The latter supported normal levels of visual function, whereas visual pigment and sensitivity were reduced by at least 3 log units in moths reared on the deprived diet. Myeloid bodies, massed cisternae of hypertrophied smooth endomembrane, filled the cytoplasm in the receptors of deprived animals. The myeloid bodies assumed various configurations that included lamellate stacks of parallel cisternae, and tubular networks in a paracrystalline form. Freeze-fracture preparations of myeloid membranes revealed a high density of P-face particles. Vacuoles containing microvilli similar to those of the rhabdomere were also present in deprived photoreceptors. We suggest that the elaboration of smooth endoplasmic reticulum as myeloid bodies in chromophore-deprived photoreceptors may stem from the hypertrophy of a biochemical system for processing the chromophore or the interruption of the intracellular pathway that normally carries visual pigment to the rhabdomere.     

Citric acid excretion and precipitation of calcium citrate in the rhizosphere of white lupin (Lupinus albus L.)

Abstract. White lupin ( Lupinus albus L.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO₃, pH(H₂O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X-ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13-week-old plants was about 1 g plant⁻¹, representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO₃ and precipitation of calcium citrate in the zone of proteoid roots.     

Effect of nutritional copper deficiency on carrageenin edema in the rat

The effects of nutritional copper deficiency on carrageenin edema in the rat were investigated with emphasis on studying the correlation between the degree of copper deficiency and the degree of edema. Carrageenin paw edema in both copper-sufficient and copper-deficient groups of rats was compared after either 20, 40, or 60 d on respective diets. The degree of copper deficiency was quantitated by analyzing total copper concentrations in a number of tissues. Other copper dependent parameters were also determined. Results indicated that: (1) although copper sufficient rats showed relatively little change in the degree of edema, copper-deficient rats showed a steady and significant increase in edema from d 20 to 40 to 60; (2) paw edema in copper-deficient animals was highly and negatively correlated to the concentrations of copper in the liver; the correlation with liver Cu,Zn-superoxide dismutase activity, however, was inconsistent; (3) paw edema was not correlated either to copper concentration in tissues other than liver or to plasma ceruloplasmin activity; and (4) aggravation of carrageenin edema in copper-deficient animals seemed to be mediated via an as yet unknown secondary effect of copper deficiency.     

Regulation of the distribution of excitation energy in Ochromonas danica,an organism containing a chlorophyll-A/C/carotenoid light harvesting antenna

A chlorophyll a, c-fucoxanthin pigment-protein complex8 functions as the major light harvesting antenna in the Chrysophyte Ochromonas danica. The regulated distribution of excitation energy between the two photosystems was investigated in these organisms and was shown to be strongly wavelength dependent. A light state transition was induced by pre-illumination of cells using light 2 (640 nm) and light 1 (700 nm) of equal absorbed intensity, and detected by reversible changes in the 77 K chlorophyll fluorescence emission spectra. Peaks at 690 nm and 720 nm in the low temperature spectra are most likely associated with PS2 and PS1 respectively. A room temperature fluorescence emission at 680 nm induced by modulated light 2 (500 nm) was strongly quenched in the presence of background light 1 (720 nm). Removal of light 1 led to an increase in fluorescence followed by a slow quenching. The room temperature fluorescence changes were directly correlated with changes in the 77 K emission spectra that indicated a change in the distribution of excitation energy between the two photosystems. It was established that DCMU (1 mol) prevented the state 2. The conversion to state 1 followed a simple photochemical dose dependence and had a half-time of 20 s-1.5 min at 6 W m^-2. In contrast, the conversion to state 2 was independent of light intensity. These data indicate that O. danica undergoes a light state transition in response to the preferential excitation of PS2 or PS1.Abbreviations PS2 photosystem 2 - PS1 photosystem 1 - LHC light harvesting chlorophyll a/b protein - fx fucoxanthin - PQ plastoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea     

Kinetic measurement of bacterial adherence to eukaryotic cells

We developed a kinetic assay using a monolayer of differentiated respiratory epithelium in culture to assess bacterial adherence. Mean residence time of bacteria in the tissue culture chamber was estimated from a model-independent (moment) analysis of the rate of bacterial washout from perfused Rose chambers. Results with this method compared favorably with visual assessment of adherence and double radiolabel method with H. influenzae. Adherence was assessed with low inoculae of H. influenzae, P. cepacia and P. aeruginosa avoiding cytotoxic effects seen when large inoculae are added to eukaryotic cells. This method will provide a means of assessing adherence of pathogenic respiratory bacteria to their cellular target at low inoculae.     

Farnesylacetone, a sesquiterpenic hormone of Crustacea, inhibits electron transport in isolated rat liver mitochondria

Farnesylacetone (C18 H30 0) is a male hormone extracted from the androgenic gland of crab, Carcinus maenas. Appropriate enzymatic assays, as well as spectrophotometric studies, indicate that micromolar concentrations of farnesylacetone interact with the electron transport pathway of rat liver mitochondria. By the use of artificial electron donors and electron acceptors, it is shown that farnesylacetone immediately inhibits the electron transfer within complex I (NADH ubiquinone reductase activity) and complex II (succinate ubiquinone reductase activity). It is proposed that farneylacetone could interact with these two complexes of the respiratory chain at the level of the iron-sulfur centers implicated in the dehydrogenase activities. These observations are compared with the results obtained with terpenic molecules which interact with mitochondrial respiration.