Effects of self-, chase and mixed self/cross-pollinations on pistil longevity and fruit set in Ceiba species (Bombacaceae) with late-acting self-incompatibility

BACKGROUND AND AIMS: Late-acting self-incompatibility (LSI), in which selfed flowers fail to form fruits despite apparently successful growth of the pollen tubes to the ovules, is a contentious and still poorly understood phenomenon. Some studies have indicated pollen tube-pistil interactions, and major gene control. Others favour an early acting inbreeding depression explanation. METHODS: Experimental pollinations, including selfs (in a subsample of which the style was cut before pollen tubes reached the ovary), chase self/cross-pollinations, crosses, and mixed self/cross-pollinations were used to study floral/pistil longevity and effect on fruit set and seed yield in two Ceiba species known to have LSI. RESULTS: Self-pollinations, including those with a cut style, had extended floral longevity compared with unpollinated flowers. Chase pollinations in which cross-pollen was applied up to 3 h after selfing set fruits, but with reduced seed set compared with crosses. Those with cross-pollen applied at 4 and 8 h after self-pollination all failed to set fruits. Flowers subjected to 1 : 1 and 2 : 1 self/cross-pollinations all produced fruits but again with a significantly lower seed set compared with crosses. CONCLUSIONS: Extended floral longevity initiated with self-pollen tubes growing in the style indicates some kind of pollen tube-pistil interaction. Fruit set only in chase pollinations up to 3 h implies that self-pollen tubes either grow more slowly in the style or penetrate ovules more slowly on arrival at the ovary compared with cross-tubes. This agrees with previous observations indicating that the incidence of penetrated ovules is initially lower in selfed compared with crossed pistils. However, the low seed yield from mixed pollinations indicates that self- and cross-pollen tubes arrive at the ovary and penetrate ovules more or less simultaneously. Possible explanations for these discordant results are discussed.     

Downregulation of nitric oxide formation by cytosolic phospholipase A2-released arachidonic acid

Exposure of PC12 cells to A23187 or thapsigargin caused a concentration-dependent release of arachidonic acid (AA) mediated by cytosolic phospholipase A2 (PLA2). Under the same conditions, however, analysis of nitric oxide (NO) formation revealed that activation of NO synthase (NOS) is best described by a bell-shaped curve. Reduced detection of NO observed at increasing A23187 or thapsigargin concentrations was not due to formation of peroxynitrite or to activation of NO-consuming processes, but rather to AA-dependent inhibition of NOS activity. Furthermore, NO formation observed under optimal conditions for NOS activity was suppressed by AA as well as by the PLA2 activator melittin. Finally, the effects of AA were not the consequence of direct enzyme inhibition, because this lipid messenger failed to inhibit formation of NO by purified neuronal NOS, but were mediated by an AA-dependent signaling and not by downstream products of the cyclooxygenase and lipoxygenase pathways. In conclusion, the present study underscores a novel mechanism whereby endogenous, or exogenous, AA promotes inhibition of NOS activity. Because AA is generated in response to various agonists acting on membrane receptors and extensively released in inflammatory conditions, these findings have important physiopathological implications.     

In vitro exposure of human lymphocytes to 900 MHz CW and GSM modulated radiofrequency: studies of proliferation, apoptosis and mitochondrial membrane potential

The aim of this study was to investigate the nonthermal effects of radiofrequency (RF) fields on human immune cells exposed to a Global System for Mobile Communication (GSM) signal generated by a commercial cellular phone and by a sinusoidal non-modulated signal. To assess whether mobile phone RF-field exposure affects human immune cell functions, peripheral blood mononuclear cells (PBMCs) from healthy donors were exposed in vitro to a 900 MHz GSM or continuous-wave (CW) RF field 1 h/day for 3 days in a transverse electromagnetic mode (TEM) cell system (70-76 mW/kg average specific absorption rate, SAR). The cells were cultured for 48 or 72 h, and the following end points were studied: (1) mitogen-induced proliferation; (2) cell cycle progression; (3) spontaneous and 2-deoxy-D-ribose (dRib)-induced apoptosis; (4) mitochondrial membrane potential modifications during spontaneous and dRib-induced-apoptosis. Data obtained from cells exposed to a GSM-modulated RF field showed a slight decrease in cell proliferation when PBMCs were stimulated with the lowest mitogen concentration and a slight increase in the number of cells with altered distribution of phosphatidylserine across the membrane. On the other hand, cell cycle phases, mitochondrial membrane potential and susceptibility to apoptosis were found to be unaffected by the RF field. When cells were exposed to a CW RF field, no significant modifications were observed in comparison with sham-exposed cells for all the end points investigated.     

Biology of the first generation of a laboratory colony of Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) (Diptera: Psychodidae)

The phlebotomine sand flies Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) are very close and may be involved in the transmission of Leishmania spp. Ross, 1903 in Brazil. The biology of the first laboratory-reared generations of these species, descended from insects captured in Além Paraíba (N. intermedia) and Corinto (N. neivai) in the Brazilian state of Minas Gerais, is described here. The captured females were fed on hamsters and maintained individually in rearing pots. Laboratory temperature and relative humidity were maintained at 25-26 masculineC and 80% respectively. The productivity of the first generation of N. intermedia was greater than that of N. neivai, and its development time clearly shorter, particularly for the second and third larval instars.     

Mercuric chloride-induced alterations in stress protein distribution in rat kidney

Mercuric chloride (HgCl2) induces acute renal failure associated to tubular impairment in experimental animals and humans. Stress proteins are a superfamily of proteins, comprising heat- shock proteins (HSP) and glucose-regulated proteins (GRP), enhanced or induced in the kidney in response to stress. They act as molecular chaperones that protect organelles and repair essential proteins which have been denatured during adverse conditions. The involvement of stress proteins in mercury-nephrotoxicity has not yet been well clarified. This study was undertaken to detect the tubular distribution of four stress proteins (HSP25, HSP60, GRP75, HSP72) in the rat kidney injected with HgCl2 and to quantify lysosomal and mitochondrial changes in straight proximal tubules, the main mercury target. Sprague-Dawley rats were administered i.p. with progressive sublethal doses of HgCl2 (0.25 mg/kg, 0.5 mg/kg, 1 mg/kg and 3.5 mg/kg) or saline (as controls) and sacrificed after 24 h. In dosages over 0.50 mg/kg, stress proteins increased and changed localization in a dose-dependent manner. HSP25 was focally expressed in altered proximal tubules at 1 mg/kg but in the macula densa it was at 3.5 mg/kg. HSP60 and GRP75 were intense in the nucleus and cytoplasm of proximal tubules but moderate in distal tubules. HSP72 was induced in distal tubules after low exposures but in proximal tubules it happened at the highest dose. Moreover, a significant increase in lysosomal and total mitochondria (normal and with broken cristae) area and density were progressively found after HgCl2 treatments. Stress proteins could represent sensitive biomarkers that strongly correlate with the degree of oxidative injury induced by HgCl2 in the rat proximal tubules.     

HMGB1 is an endogenous immune adjuvant released by necrotic cells

Immune responses against pathogens require that microbial components promote the activation of antigen-presenting cells (APCs). Autoimmune diseases and graft rejections occur in the absence of pathogens; in these conditions, endogenous molecules, the so-called 'innate adjuvants', activate APCs. Necrotic cells contain and release innate adjuvants; necrotic cells also release high-mobility group B1 protein (HMGB1), an abundant and conserved constituent of vertebrate nuclei. Here, we show that necrotic HMGB1(-/-) cells have a reduced ability to activate APCs, and HMGB1 blockade reduces the activation induced by necrotic wild-type cell supernatants. In vivo, HMGB1 enhances the primary antibody responses to soluble antigens and transforms poorly immunogenic apoptotic lymphoma cells into efficient vaccines.     

Karyotype evolution in South American subterranean rodents Ctenomys magellanicus (Rodentia: Octodontidae): chromosome rearrangements and (TTAGGG)n telomeric sequence localization in 2n=34 and 2n=36 chromosomal forms

Ctenomys is the most numerous genus of South American subterranean rodents and one of the most karyotypically diverse clades of mammals known. Ctenomys magellanicus is the southernmost species of the group and the only one living in Isla Grande de Tierra del Fuego (Argentina). This species presents two chromosomal forms, i.e. 2n=34, and 2n=36 (FN=68). Recent studies suggest that genetic divergence between both karyotypic forms resulted from a chromosomal speciation process. In order to identify the chromosomal rearrangement involved in the process of karyotype evolution in this species, we used chromosome banding techniques and fluorescence in situ hybridization with a telomeric probe to metaphase chromosomes of the two chromosomal forms of Ctenomys magellanicus. Chromosome analysis of Giemsa-stained and G-banding preparations showed that Cm34 and Cm36 karyotypes differ in one rearrangement involving chromosomes A9 from Cm34 and B12 and B17 from Cm36. In addition FISH analysis showed that all of the chromosomes from both chromosomal forms exhibit a telomeric-only distribution pattern of the (TTAGGG)n sequence, indicating that none of the chromosomal forms of Ctenomys magellanicus has true telocentric chromosomes. Our results suggest that a chromosome fission event would have occurred during the process of karyotype evolution in this species.