Gulf Stream warm core rings: phytoplankton in two fall rings of different ages

Warm core ring (WCR) 82-H was sampled in September–October(1982) as a Gulf Stream meander pinched off and became a ring.It is compared with the 3-month-old WCR 81-D, visited September–October(1981). Although the rings have different histories, their phytoplanktonassemblages share some characteristics. Using cluster analysesbased on quantitative group counts, a station from one ringoccasionally clusters most closely with a station from the otherring, showing a similar balance of organisms. The younger ringat the time of sampling, WCR 82-H, had lower diversity, fewershelf species, and greater consistency between stations, exceptfor a high level of Oscillatoria in the meander before the ringpinched off. Interaction with slope water was seen principallyat the ring margin. WCR 81-D, on the other hand, showed a greatdeal of structure, and immediate dilutions with slope waterand the Gulf Stream were apparent, with higher diversity beforeand a week after such interactions. The upper water column ofwarm core rings, although showing evidence of physical mixing,can exhibit stratification of species, even after a storm.     

Activity of cell wall-associated enzymes in ripening olive fruit

Enzymatically active cell wall isolaled from olive (Olea europaea) fruit was employed Hi investigate some hydrolytic enzymes bound to the cell wall and the changes in these during ripening. Seven glycosidases. β-glucosidase (EC 3.2.1.21) α-galactosidase (EC 3.2.1.22). β-galactosidase (EC 3.2.1.23). α-arabinosidase (EC 3.2.1.55), α-mannosidase (EC 3.2.1,24). β-xylosidase (EC 3.2.1.37) and β-N-acetylglucosamidase (EC 3.2.1.30). as well as Cx-cellulase (EC 3.2.1.4) and endo-polygalacturonase (EC 3.2.1.15). were identified in the cell wall preparation, at four stages of ripeness (mature green. changing colour, black and black-ripe). Activities of all these cell wall-associated enzymes fionicallv and covalently linked) were determined either by cell wall incubation with artificial substrate or after extraction from the cell wall with buffers of high salt concentration (Cx-cellulase). and were compared to those of forms solubilized from acetone powders with 500 nM citrate buffer (cytoplasmic and/or apoplastic plus ionically hound to cell wall) In general, the activities of low ionic strength buffer-soluble enzymes were found to be much higher than those of the bound enzymes. The bound enzymes are present in the fruit at the green colour stage, whereas the activities of the soluble enzymes only increased from the changing colour stage onwards. The tenacity of binding of enzymes to the wall was investigated by treating the walls with high salt and measuring residual activity. The nature of the ionic and covalent binding and the changes during ripening were also established for wall-hound glycosidase During ripening there was a marked change in the percentages of covalently- and tonically linked activities of β-glucosidase and β-galaclosidase: al the changing colour stages about 75–80% of the bound active in was present in high ionic strength buffer while al the black-ripe stage it was only 15–20. A possible role for these cell wall degradative enzymes in olive softening is discussed.     

Structure-function relationships and molecular genetics of the 3β-hydroxysteroid dehydrogenase gene family

The isoenzymes of the 3β-hydroxysteroid dehydrogenase/5-ene-4-ene-isomerase (3β-HSD) gene family catalyse the transformation of all 5-ene-3β-hydroxysteroids into the corresponding 4-ene-3-keto-steroids and are responsible for the interconversion of 3β-hydroxy- and 3-keto-5-androstane steroids. The two human 3β-HSD genes and the three related pseudogenes are located on the chromosome 1p13.1 region, close to the centromeric marker D1Z5. The 3β-HSD isoenzymes prefer NAD⁺ to NADP⁺ as cofactor with the exception of the rat liver type III and mouse kidney type IV, which both prefer NADPH as cofactor for their specific 3-ketosteroid reductase activity due to the presence of Tyr³⁶ in the rat type III and of Phe³⁶ in mouse type IV enzymes instead of Asp³⁶ found in other 3β-HSD isoenzymes. The rat types I and IV, bovine and guinea pig 3β-HSD proteins possess an intrinsic 17β-HSD activity psecific to 5-androstane 17β-ol steroids, thus suggesting that such “secondary” activity is specifically responsible for controlling the bioavailability of the active androgen DHT. To elucidate the molecular basis of classical form of 3β-HSD deficiency, the structures of the types I and II 3β-HSD genes in 12 male pseudohermaphrodite 3β-HSD deficient patients as well as in four female patients were analyzed. The 14 different point mutations characterized were all detected in the type II 3β-HSD gene, which is the gene predominantly expressed in the adrenals and gonads, while no mutation was detected in the type I 3β-HSD gene predominantly expressed in the placenta and peripheral tissues. The mutant type II 3β-HSD enzymes carrying mutations detected in patients affected by the salt-losing form exhibit no detectable activity in intact transfected cells, at the exception of L108W and P186L proteins, which have some residual activity (1%). Mutations found in nonsalt-loser patients have some residual activity ranging from 1 to 10% compared to the wild-type enzyme. Characterization of mutant proteins provides unique information on the structure-function relationships of the 3β-HSD superfamily.     

Stagnant immigrant social networks and cycles of exploitation

Based on over four years of ethnographic research among street vendors in Los Angeles and on interviews with family members of vendors and former vendors living in Mexico, this article examines the influence of a sending community and its social networks on migrant outcomes in the USA. These social networks affect migration patterns, ease entry into the fruit-vending business but also facilitate exploitation. Furthermore, these social networks do not always function as effective conduits of information because its members, due to feelings of shame or embarrassment, often fail to add to the existing body of knowledge. As a result, international migration patterns, job placement and exploitative practices do not change or improve for subsequent migrants. This creates a cycle in which social networks become stagnant and successively fail to function as effective conduits of information and resources in ways that might help network members equally and in the aggregate.     

The Archaeal Diversity and Population in a Drained Alkaline Saline Soil of the Former Lake Texcoco (Mexico)

Draining soil of the former Lake Texcoco, Mexico with pH > 10.0 and electrolytic conductivity (EC) > 100 dS m^?1 for 17 years has reduced pH to 7.8 and EC to 0.68 dS m^?1. Metagenomic DNA from the archaeal community was extracted directly from this soil and used as template to amplify the 16S ribosomal genes by PCR to construct gene libraries. Most of the cloned Archaea were related to mesophilic crenarchaeota and were not-yet-cultured. Sequence and phylogenetic analyses of these clones identified a group of Archaea with close affiliation to the ammonia-oxidizing Archaea. The cloned sequences from the drained soil diverged clearly from Haloarchaea found in the undrained soil from the lake.     

Isolation and Characterization of Mercury Resistant Bacillus sp. from Soils with an Extensive History as Substrates for Mercury Extraction in Mexico

Metal phytoextraction assisted by bacteria plays an important role in bioremediation systems. In this work, mercury-resistant bacterial strains were isolated from soils with high levels of mercury (San Joaquin, Queretaro State, Mexico) and identified as Bacillus sp. based on the 16S rDNA gene sequence analysis. The bacterial strains were found to exhibit different multiple mercury-resistance and carbon source utilization characteristics. The mercury reduction ability was tested through a volatilization assay. The bacterial isolates were also evaluated for their ability to promote growth and mercury uptake in tomato plants. In a roll towel assay, the maximum vigor index of tomato plants was obtained with the inoculation of Bacillus sp. A2, A12, B11, B15 and C1, while in a pot assay, the maximum vigor index was obtained with the inoculation of Bacillus sp. A6, A7 and B20, compared with un-inoculated controls in the presence of HgCl₂. Maximum Hg accumulation in the roots and shoots of tomato plants was obtained only with Bacillus sp. A7 in the roll towel assay, whereas in the pot assay, maximum accumulation was obtained with Bacillus sp. A12 compared with un-inoculated controls. Our results show that mercury accumulation in tissue is enhanced by these plant growth promoting bacterial strains, which recommends their possible use as microbe-assisted phytoremediation systems in mercury-polluted soils.     

cGMP-independent inhibition of integrin alphaIIbbeta3-mediated platelet adhesion and outside-in signalling by nitric oxide

We examined the influence of S-nitrosoglutathione (GSNO) on alpha(IIb)beta(3) integrin-mediated platelet adhesion to immobilised fibrinogen. GSNO induced a time- and concentration-dependent inhibition of platelet adhesion. Inhibition was cGMP-independent and associated with both reduced platelet spreading and protein tyrosine phosphorylation. To investigate the cGMP-independent effects of NO we evaluated integrin beta(3) phosphorylation. Adhesion to fibrinogen induced rapid phosphorylation of beta(3) on tyrosines 773 and 785, which was reduced by GSNO in a cGMP independent manner. Similar results were observed in suspended platelets indicating that NO-induced effects were independent of spreading-induced signalling. This is the first demonstration that NO directly regulates integrin beta(3) phosphorylation.     

Allelochemical Stress Can Trigger Oxidative Damage in Receptor Plants: Mode of Action of Phytotoxicity

Plants can interact with other plants through the release of chemical compounds or allelochemicals. These compounds released by donor plants influence germination, growth, development, and establishment of receptor plants; having an important role on the pattern of vegetation, i.e as invasive strategy, and on crop productivity. This phytotoxic or negative effect of the released allelochemicals (allelochemical stress) is caused by modifying or altering diverse metabolic processes, having many molecular targets in the receptor plants. Recently, using an aggressive and allelopathic plant Sicyos deppei as the donor plant, and Lycopersicon esculentum as the receptor plant, we showed that the allelochemicals released by S. deppei caused oxidative damage through an increase in reactive oxygen species (ROS) and activation or modification of antioxidant enzymes. Based on this study, we proposed that oxidative stress is one of the mechanisms, among others, by which an allelopathic plant causes phytotoxicity to other plants.Key Words: allelochemical stress, Sicyos deppei, Lycopersicon esculentum, plant allelochemicals, phytotoxicity, ROS, lipid peroxidationIt is well known that plants interact with many organisms, including co-habitation with other plants. Among these relations are the ones referred to as allelochemical interactions. Allelopathy can be defined as a mechanism of interference in plant growth and development mediated by the addition of plant-produced secondary products (allelochemicals) to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation.^1–3 These released allelochemicals become stressful only when they are toxic or when they affect the growth and development of surrounding plants (phytotoxicity). Studies on allelochemical stress have been expanding; recently the phenomenon has taken on increased importance, since it can help explain plant growth inhibition in interspecies interactions and in structuring the plant community. It appears to be one mechanism or strategy used by invasive plants to become successful and replace other native ones.^4–6On the other hand, the chemical diversity of the organic compounds that mediate these allelochemical interactions is as diverse as their modes of action. Many studies have shown that allelochemicals interfere with several physiological processes in the receptor organism.^3,7,8 The physiological effects on receptor plants or other organisms are useful in determining the role of the allelochemicals in the system. Recently, it has been proposed that allelochemicals can cause oxidative stress in target plants and therefore activate the antioxidant mechanism.^3,8–12 In particular; our studies have been focused on knowing the physiological targets of the phytotoxic compounds released by a noxious and endemic weed Sicyos deppei G. Don (Cucurbitaceae). We have taken as the model the receptor or damaged plant Lycopersicon esculentum Mill (Solanaceae), since in Mexican crop-fields, it is common to find both plants. We have observed the strong allelopathic potential of S. deppei and are exploring the potential metabolic target that could be involved in the strong phytotoxic effect of this weed.^13–16 We recently documented the oxidative damage that an aqueous leachate of S. deppei caused in the target plant L. esculentum.¹⁶ In this work we explored in seeds and in primary roots the antioxidant mechanism of tomato to determine whether or not the inhibitory effect of S. deppei was due to oxidative damage. We analyzed the activity and expression of some antioxidant enzymes involved in the detoxification of ROS, and found an imbalance in its activity as well as an increase in the levels of H₂O₂ at 24 h of treatment. Additional studies on the levels of ROS, including hydrogen peroxide, were monitored in primary roots from germinating seeds under allelochemical stress by imaging the ROS-sensitive fluorescent dye dichlorofluorescein (_H2DCFDA, carboxy-2′, 7′-diclhlorofluorescein diacetate) in a confocal microscope (BIORAD 1024, 488 nm dichroic and 510–560 nm emission). DCFDA fluorescence increases as the dye is oxidized by ROS to dichlorofluorescein (DCF). Figure 1 shows a marked increase in fluorescence at 48 h and 72 h of treatment (Fig. 1A–C) compared with the same treatment at 24 h, and with the corresponding control. This fluorescence was more evident at the root cap and at the zone of root hairs in treated seeds.Open in a separate windowFigure 1Allelochemical stress caused by S. deppei elicits ROS generation in tomato germinating seeds. Panels show control (left) and treatment (right) at 24 h (A), 48 h (B), and 72 h (C). Lower panels show higher magnification (40X) of the corresponding time. Seedlings with primary roots were stained for 10–15 minutes with 25 µM DCFDA in distilled water.Clearly, allelochemical stress caused by S. deppei is producing an oxidative imbalance as evidenced by generation of ROS and alteration of activity of antioxidant enzymes. Another result that supports this observation is the high level of lipid peroxidation that we observed at 48 and 72 h, which correlates with the inhibition of two membrane-associated enzymes, H⁺-ATPase¹⁵ and NADPH oxidase.¹⁶ We believe, however, that the oxidative damage we observed is not solely responsible for the phytotoxic effect of S. deppei on tomato growth. In other words, we suggest that its inhibitory effect represents the sum of many metabolic processes affected at different times. Currently we are studying the dynamics of carbohydrate mobilization, cell wall loosing of the endosperm to allow the protrusion of the radicle, and ABA content. Preliminary results have shown that there is a delay in expression of some enzyme activities and a high content of ABA.