Endosperm and pericarp involvement in the supercooling of imbibed lettuce seeds

Fully hydrated lettuce (Lactuca sativa L.) seeds showed dual freezing exotherms (−9 and −18°C), even after 10 hours imbibition. Only the −9°C exotherm was observed in seeds imbibed for 20 hours, but without external nucleation, all water in the embryo supercooled. Results indicate that the endosperm acts as a barrier to ice propagation. Other experiments suggest that the pericarp may also protect the embryo under certain freezing conditions.     

High specific activity ribulose 1,5-bisphosphate carboxylase-oxygenase from Nicotiana tabacum

Ribulose 1,5-bisphosphate carboxylase (EC.4.1.1.39) has been obtained from Nicotiana tabacum leaf homogenates with specific activites from 0.5 to 0.8 µmol CO₂ fixed (mg protein min)^-1. These activities are reconciled with much lower, previously reported activities. The results suggest that if the tobacco enzyme is assayed under optimum conditions there is little difference in the intrinsic specific activities of tobacco and spinach ribulose 1,5-bisphosphate carboxylase. Several factors affecting activity measurements were examined.     

Derivation of a physical map of chloroplast DNA from Nicotiana tabacum by two-dimensional gel and computer-aided restriction analysis

A combined approach was used to derive a detailed physical map of Nicotiana tabacum chloroplast DNA for the restriction enzymes SalI, SmaI, KpnI, and BamHI. Complete maps for the restriction enzymes SalI, SmaI, and KpnI were derived by using two-dimensional agarose gel analysis of fragments obtained by reciprocal double digestion of chloroplast DNA. We have characterized a complete cloned library of N. tabacum chloroplast DNA which contains overlapping restriction fragments resulting from partial digestion by BamHI. With these clones and existing data, we used a novel computer-aided analysis to derive a detailed map for the enzyme BamHI. A comparison and compilation of all published N. tabacum chloroplast DNA restriction maps is presented. Differences between ours and a previously published SmaI and BamHI restriction map are discussed.     

Mapping of rRNA genes in an inverted repeat in Nicotiana tabacum chloroplast DNA.

Nicotiana tabacum chloroplast DNA contains two copies each of 16S and 23S rRNA genes. These genes are located in an inverted order as determined from restriction fragment mapping and Southern hybridization to restriction fragments. The position of these genes on the N. tabacum chloroplast DNA molecule has been established relative to a complete map of SalI and SMaI restriction enzyme cleavage sites.     

Functional changes in human leukemic cell line HL-60. A model for myeloid differentiation

Polar solvents induce terminal differentiation in the human promyelocytic leukemia cell line HL-60. The present studies describe the functional changes that accompany the morphologic progression from promyelocytes to bands and poly-morphonuclear leukocytes (PMN) over 9 d of culture in 1.3 percent dimethylsulfoxide (DMSO). As the HL-60 cells mature, the rate of O(2-) production increase 18-fold, with a progressive shortening of the lag time required for activation. Hexosemonophosphate shunt activity rises concomitantly. Ingestin of paraffin oil droplets opsonized with complement or Ig increases 10-fold over 9 d in DMSO. Latex ingestion per cell by each morphologic type does not change significantly, but total latex ingestion by groups of cells increases with the rise in the proportion of mature cells with greater ingestion capacities. Degranulation, as measured by release of β-glucuronidase, lysozyme, and peroxidase, reaches maximum after 3-6 d in DMSO, then declines. HL-60 cells contain no detectable lactoferrin, suggesting that their secondary granules are absent or defective. However, they kill staphylococci by day 6 in DMSO. Morphologically immature cells (days 1-3 in DMSO) are capable of O(2-) generation, hexosemonophosphate shunt activity, ingestion, degranulation, and bacterial killing. Maximal performance of each function by cells incubated in DMSO for longer periods of time is 50-100 percent that of normal PMN. DMSO- induced differentiation of HL-60 cells is a promising model for myeloid development.     

Enhancement and phototransduction in the ventral eye of limulus

Limulus ventral photoreceptors were voltage clamped to the resting (dark) potential and stimulated by a 20-ms test flash and a 1-s conditioning flash. At a constant level of adaptation, we measured the response to the test flash given in the dark (control) and the incremental response produced when the test flash occurred within the duration of the conditioning flash. The incremental response is defined as the response to the conditioning and test flashes minus the response to the conditioning flash given alone. When the test flash was presented within 100 ms after the onset of the conditioning flash we observed that: (a) for dim conditioning flashes the incremental response equaled the control response; (b) for intermediate intensity conditioning flashes the incremental response was greater than the control response (we refer to this as enhancement); (c) for high intensity conditioning flashes the incremental response nearly equaled the control response. Using 10-μm diam spots of illumnination, we stimulated two spatially separate regions of one photoreceptor. When the test flash and the conditioning flash were presented to the same region, enhancement was present; but when the flashes were applied to separate regions, enhancement was nearly absent. This result indicates that enhancement is localized to the region of illumination. We discuss mechanisms that may account for enhancement.     

Angiostrongylus vasorum infection in a coyote (Canis latrans) from Newfoundland and Labrador, Canada

Tissue samples and feces were collected from a dead, adult female coyote (Canis latrans) found at the side of the road in late March 2003 in the Avalon Peninsula region of Newfoundland, Canada. The coyote apparently died of vehicular-related trauma. Samples of lung, brain, heart, liver, and kidney were fixed in formalin and submitted for histologic examination. The entire remaining lung and heart also were submitted for examination. The coyote was diagnosed with moderate, multifocal, granulomatous interstitial pneumonia with eosinophilic vasculitis and many intralesional nematode eggs, larvae, and occasional intravascular adult worms. Adult nematodes recovered from the pulmonary arteries were identified as Angiostrongylus vasorum. Small foci of granulomatous inflammation, often containing nematode eggs and larvae, were scattered in the brain and kidney. To our knowledge, this is the first report of A. vasorum infection in a coyote from the only endemic area of infection in North America.     

Proteinaceous and oligosaccharidic elicitors induce different calcium signatures in the nucleus of tobacco cells

We previously reported elevated cytosolic calcium levels in tobacco cells in response to elicitors [D. Lecourieux, C. Mazars, N. Pauly, R. Ranjeva, A. Pugin, Analysis and effects of cytosolic free calcium elevations in response to elicitors in Nicotiana plumbaginifolia cells, Plant Cell 14 (2002) 2627-2641]. These data suggested that in response to elicitors, Ca2+, as a second messenger, was involved in both systemic acquired resistance (RSA) and/or hypersensitive response (HR) depending on calcium signature. Here, we used transformed tobacco cells with apoaequorin expressed in the nucleus to monitor changes in free nuclear calcium concentrations ([Ca2+](nuc)) in response to elicitors. Two types of elicitors are compared: proteins leading to necrosis including four elicitins and harpin, and non-necrotic elicitors including flagellin (flg22) and two oligosaccharidic elicitors, namely the oligogalacturonides (OGs) and the beta-1,3-glucan laminarin. Our data indicate that the proteinaceous elicitors induced a pronounced and sustainable [Ca2+](nuc) elevation, relative to the small effects of oligosaccharidic elicitors. This [Ca2+](nuc) elevation, which seems insufficient to induce cell death, is unlikely to result directly from the diffusion of calcium from the cytosol. The [Ca2+](nuc) rise depends on free cytosolic calcium, IP3, and active oxygen species (AOS) but is independent of nitric oxide.     

The source of heme for vascular heme oxygenase I: heme uptake in rat aorta

During the last decade, heme oxygenase (HO) and carbon monoxide (CO) have garnered substantial research interest in terms of cell and organ regulation, especially as they bear on the central nervous system, organ transplantation, and the cardiovascular system. While the enzymatic mechanism, substrates, and products of HO are well known, it is not clear whether the cardiovascular system derives its supply of the heme substrate through de novo synthesis or uptake from the extracellular milieu. The objective of the present study was to test the latter possibility in rat aorta and to determine the influence of plasma proteins that bind heme in vivo, viz. hemopexin and albumin. Aortic tissue was exposed to [14C]heme in vitro, and the concentration and time dependence of heme uptake was assessed. The presence of hemopexin or albumin in the incubation medium dramatically decreased heme uptake by the aorta. Heme uptake by aortic tissue was not altered after induction of HO-1, which would be expected to increase tissue heme demand. In summary, the rat, isolated aorta was capable of obtaining heme from its external milieu, but this was obtunded in the presence of the plasma proteins hemopexin or albumin. For normal physiological situations, heme uptake may not be a usual source of substrate for vascular HO and hemoenzymes such as nitric oxide synthase, soluble guanylyl cyclase, and cyclooxygenase.