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1.
A family of cloning vectors derived from plasmid pACYC184 and, therefore, compatible with pBR322 and its derivatives (especially the pUC family of vectors), is described. They all contain a multiple cloning site (MCS) and the lacZ alpha reporter gene for easy cloning. They have been grouped in three sets: (i) six of the vectors contain a chloramphenicol-resistance (CmR)-encoding gene and each a different MCS with 16 unique restriction sites overall; (ii) another six vectors contain a kanamycin-resistance (KmR)-encoding gene and the same six MCS; and (iii) two CmR vectors that contain the SP6 and T7 promoters flanking the MCS and lacZ alpha reporter gene of pUC18/19.  相似文献
2.
Cadmium-induced changes in the growth and oxidative metabolism of pea plants   总被引:60,自引:0,他引:60  
The effect of growing pea (Pisum sativum L.) plants with CdCl(2) (0-50 microM) on different plant physiological parameters and antioxidative enzymes of leaves was studied in order to know the possible involvement of this metal in the generation of oxidative stress. In roots and leaves of pea plants Cd produced a significant inhibition of growth as well as a reduction in the transpiration and photosynthesis rate, chlorophyll content of leaves, and an alteration in the nutrient status in both roots and leaves. The ultrastructural analysis of leaves from plants grown with 50 microM CdCl(2), showed cell disturbances characterized by an increase of mesophyll cell size, and a reduction of intercellular spaces, as well as severe disturbances in chloroplast structure. Alterations in the activated oxygen metabolism of pea plants were also detected, as evidenced by an increase in lipid peroxidation and carbonyl-groups content, as well as a decrease in catalase, SOD and, to a lesser extent, guaiacol peroxidase activities. Glutathione reductase activity did not show significant changes as a result of Cd treatment. A strong reduction of chloroplastic and cytosolic Cu,Zn-SODs by Cd was found, and to a lesser extent of Fe-SOD, while Mn-SOD was only affected by the highest Cd concentrations. Catalase isoenzymes responded differentially, the most acidic isoforms being the most sensitive to Cd treatment. Results obtained suggest that growth of pea plants with CdCl(2) can induce a concentration-dependent oxidative stress situation in leaves, characterized by an accumulation of lipid peroxides and oxidized proteins as a result of the inhibition of the antioxidant systems. These results, together with the ultrastructural data, point to a possible induction of leaf senescence by cadmium.  相似文献
3.
A new series of vectors, pSU2716, pSU2717, pSU2718, and pSU2719, has been constructed. The plasmids contain (i) the P15A replicon, (ii) the chloramphenicol acetyl transferase (CAT)-coding gene from Tn9, and (iii) the HaeII fragment which carries the multiple cloning site and the lacZ alpha reporter gene of pUC8, pUC9, pUC18 and pUC19, respectively. These vectors allow rapid and simple transfer of inserts from pUC plasmids, have an intermediate copy number (which allows regulated expression from the lac promoter), and are compatible with ColE1-derived vectors (and, therefore, can be used in studies requiring the joint expression of two genes, for example, in genetic complementation analysis). Furthermore, the accumulation of CAT instead of beta-lactamase, allows an easy visualization in sodium dodecyl sulfate-polyacrylamide-gel electrophoresis of proteins of 28-35 kDa, which can otherwise be obscured by the beta-lactamase.  相似文献
4.
Ridente Y  Aubard J  Bolard J 《FEBS letters》1999,445(2-3):283-286
A protein band of approximately 166 kDa was detected in the soluble fraction of root tips and young leaves of maize seedlings, based on Western blot analysis using antibodies raised against mouse macrophage nitric oxide synthase (NOS) and rabbit brain NOS. NOS activity was present in these soluble fractions, as determined by L-[U-14C]citrulline synthesis from L[U-14]arginine. Immunofluorescence showed that the maize NOS protein is present in the cytosol of cells in the division zone and is translocated into the nucleus in cells in the elongation zone of maize root tips. These results indicate the existence of a NOS enzyme in maize tissues, with the localization of this protein depending on the phase of cell growth.  相似文献
5.
A global analysis of root distributions for terrestrial biomes   总被引:44,自引:0,他引:44  
Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biomes, and fitted the depth coefficient to the data for each biome (Gale and Grigal 1987). is a simple numerical index of rooting distribution based on the asymptotic equation Y=1-d, where d = depth and Y = the proportion of roots from the surface to depth d. High values of correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles (=0.913, 0.943, and 0.943, respectively), with 80–90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles (=0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m-2. Tropical evergreen forests had the highest root biomass (5 kg m-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m-2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil. (=0.952), while shrubs had only 21% in the same depth increment (=0.978). The rooting distribution of all temperate and tropical trees was =0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was =0.966 (r 2=0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.  相似文献
6.
A novel P-type ATPase from yeast involved in sodium transport.   总被引:43,自引:0,他引:43  
The gene ENA1 was cloned by its ability to complement the Li+ sensitivity of a low Li(+)-efflux strain. The nucleotide sequence of the cloned DNA fragment showed that there are two almost identical genes in tandem, and predicts that they encode P-ATPases. Disruption of both genes originated a strain defective in Na+ and Li+ effluxes, and sensitive to Na+, to Li+ and to alkaline pH. By transformation with ENA1 the defective effluxes and tolerances were repaired.  相似文献
7.
8.
Roles of nitric oxide in brain hypoxia-ischemia.   总被引:37,自引:0,他引:37  
A large body of evidence has appeared over the last 6 years suggesting that nitric oxide biosynthesis is a key factor in the pathophysiological response of the brain to hypoxia-ischemia. Whilst studies on the influence of nitric oxide in this phenomenon initially offered conflicting conclusions, the use of better biochemical tools, such as selective inhibition of nitric oxide synthase (NOS) isoforms or transgenic animals, is progressively clarifying the precise role of nitric oxide in brain ischemia. Brain ischemia triggers a cascade of events, possibly mediated by excitatory amino acids, yielding the activation of the Ca2+-dependent NOS isoforms, i.e. neuronal NOS (nNOS) and endothelial NOS (eNOS). However, whereas the selective inhibition of nNOS is neuroprotective, selective inhibition of eNOS is neurotoxic. Furthermore, mainly in glial cells, delayed ischemia or reperfusion after an ischemic episode induces the expression of Ca2+-independent inducible NOS (iNOS), and its selective inhibition is neuroprotective. In conclusion, it appears that activation of nNOS or induction of iNOS mediates ischemic brain damage, possibly by mitochondrial dysfunction and energy depletion. However, there is a simultaneous compensatory response through eNOS activation within the endothelium of blood vessels, which mediates vasodilation and hence increases blood flow to the damaged brain area.  相似文献
9.
The classical approach of limnologists has been to consider the interactions between lake ecosystem components as an unidirectional flow of influence from nutrients to the phytoplankton, to the zooplankton, and finally to the fish, through successive controls by physical, chemical, and biological processes (Strakraba, 1967). The effect of planktivorous fishes on zooplankton and phytoplankton communities was not recognized until the studies of Hrbáek et al. (1961), Hrbáek (1962), Brooks & Dodson (1965) and Strakraba (1965). They showed that (1) in ponds and lakes in the presence of planktivorous fishes the zooplankton communities were composed of smaller bodied species than in those lacking planktivores, and (2) the resulting small-bodied zooplankton communities affected the phytoplankton communities. Although the variability of the phytoplankton response to fish predation showed the importance of other factors (such as nutrient limitation and interspecific competition of algae), these studies emphasized that zooplankton and phytoplankton communities can be affected by the feeding selectivity of planktivorous fishes. During the last two decades, many limnological studies have focused on this dramatic impact of fish on plankton communities. The direct response of zooplankton communities to visual fish predation (i.e. particulate feeding) has been of major interest, whereas the multilevel effects of filter-feeding fish (predation on zooplankton plus grazing on phytoplankton) have been neglected. The objectives of this review are to document fish-plankton interrelationships in order to (1) provide insights into the impact of fish on plankton communities, and (2) outline mechanistic models of planktivory according to the feeding repertory and the selectivity of the fish, the adaptive responses of the plankton, and the environmental conditions.The approach adopted here is based on field and laboratory experimental results derived from the literature on tropical and temperate freshwater (occasionally marine) systems. Four types of planktivorous fish are distinguished: the gape-limited larvae and small fish species, the particulate feeders, the pump filter feeders, and the tow-net filter feeders. For each type of planktivore, the mechanisms of prey selection are analyzed from the point of view of both the predator and the prey. To investigate the main determinants of the predator feeding selectivity, and to discuss its potential effects on prey communities, the predation-act is divided into a sequence of successive events (Holling, 1966): detection, pursuit, capture, retention, and digestion for particulate feeders; and capture, retention, and digestion for filter feeders. The strengths and weaknesses of various measures of selectivity (i.e. electivity indices), as well as their appropriate usages are considered. Available prey selection models and optimal foraging theories are analyzed for the different planktivore feeding modes. Mechanistic models based on Holling's (loc. cit.) approach are proposed for each feeding mode to determine differential prey vulnerabilities and optimal diet breadth.This review has application to several fields, including general ecology, limnology, fisheries management (for example, utilization of planktonic resources, stocking, introduction, or maintenance of natural fish populations), and biological control of the eutrophication processes (biomanipulation approaches). It emphasizes the real need for more knowledge of the feeding selectivity and food utilization of planktivores. It concludes that predator and prey are mutually adapted. Thus, in most cases, study of plankton dynamics and water quality should include the assessment of fish predation and grazing pressures.  相似文献
10.
The small average cell size of in situ bacterioplankton, relative to cultured cells, has been suggested to be at least partly a result of selection of larger-sized cells by bacterivorous protozoa. In this study, we determined the relative rates of uptake of fluorescence-labeled bacteria (FLB), of various cell sizes and cell types, by natural assemblages of flagellates and ciliates in estuarine water. Calculated clearance rates of bacterivorous flagellates had a highly significant, positive relationship with size of FLB, over a range of average biovolume of FLB of 0.03 to 0.08 microns3. Bacterial cell type or cell shape per se did not appear to affect flagellate clearance rates. The dominant size classes of flagellates which ingested all types of FLB were 3- to 4-microns cells. Ciliates also showed a general preference for larger-sized bacteria. However, ciliates ingested a gram-positive enteric bacterium and a marine bacterial isolate at higher rates than they did a similarly sized, gram-negative enteric bacterium or natural bacterioplankton, respectively. From the results of an experiment designed to test whether the addition of a preferentially grazed bacterial strain stimulated clearance rates of natural bacterioplankton FLB by the ciliates, we hypothesized that measured differences in rates of FLB uptake were due instead to differences in effective retention of bacteria by the ciliates. In general, clearance rates for different FLB varied by a factor of 2 to 4. Selective grazing by protozoa of larger bacterioplankton cells, which are generally the cells actively growing or dividing, may in part explain the small average cell size, low frequency of dividing cells, and low growth rates generally observed for assemblages of suspended bacteria.  相似文献
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