Hydraulic resistance of two sorghums varying in drought resistance

Genotypes of sorghum [Sorghum bicolor (L.) Moench] vary in drought resistance. Yet it is not known if their hydraulic resistances vary. The objective of this study was to determine if the hydraulic resistance of a drought-resistant sorghum was the same as that of a drought-sensitive sorghum. Leaf water and osmotic potentials were measured daily, during a 14-d period, in leaves of a drought-resistant (‘KS9’) and a drought-sensitive (‘IA25’) sorghum, which had the roots in pots with a commercial potting soil that was either well watered or allowed to dry. Soil water potential, adaxial stomatal resistance, and transpiration rate were determined daily. Hydraulic resistance of the plants was calculated from the slope of the line relating soil water potential minus leaf water potential versus transpiration rate. When the soil was not watered, the drought-sensitive sorghum had a water potential that averaged −0.50 MPa lower and an osmotic potential that averaged −0.57 MPa lower, but a similar adaxial stomatal resistance (1.19 s mm⁻¹), compared with the drought-resistant sorghum. Seven days after the beginning of the experiment, the water potential of the soil with the drought-sensitive sorghum was −0.25 MPa lower than that of the soil with the drought-resistant sorghum. With the water-limited conditions, the drought-sensitive sorghum depleted the soil-water reserve more quickly and died 2 d before the drought-resistant sorghum. Under well watered conditions, the two sorghums had similar water potentials (−1.64 MPa), osmotic potentials (−2.83 MPa), and adaxial stomatal resistances (0.78 s mm⁻¹). The calculated hydraulic resistance of the two sorghums did not differ and averaged 3.4 × 10⁷ MPa s m⁻¹. The results suggested that the variation in susceptibility to drought between the two genotypes was due to differences in rate of soil-water extraction. Contribution No. 86-249-J from the Kansas Agricultural Experiment Station. The paper is dedicated to the memory of Dr Dan M Rodgers.     

The evolution of resistance genes in multi-protein plant resistance systems

The genomic perspective aids in integrating the analysis of single resistance (R-) genes into a higher order model of complex plant resistance systems. The majority of R-genes encode a class of proteins with nucleotide binding (NB) and leucine-rich repeat (LRR) domains. Several R-proteins act in multi-protein R-complexes that mediate interaction with pathogen effectors to induce resistance signaling. The complexity of these systems seems to have resulted from multiple rounds of plant-pathogen co-evolution. R-gene evolution is thought to be facilitated by the formation of R-gene clusters, which permit sequence exchanges via recombinatorial mispairing and generate high haplotypic diversity. This pattern of evolution may also generate diversity at other loci that contribute to the R-complex. The rate of recombination at R-clusters is not necessarily homogeneous or consistent over evolutionary time: recent evidence suggests that recombination at R-clusters is increased following pathogen infection, suggesting a mechanism that induces temporary genome instability in response to extreme stress. DNA methylation and chromatin modifications may allow this instability to be conditionally regulated and targeted to specific genome regions. Knowledge of natural R-gene evolution may contribute to strategies for artificial evolution of novel resistance specificities.     

绿脓杆菌对鲎素耐受性特点及耐受性机制的研究

【目的】为了探讨鲎素作为抗菌药物在临床使用中的安全性问题,通过鲎素连续增高浓度法对绿脓杆菌进行耐受性诱导,并对其耐受性机制进行初步研究,以期为鲎素的广泛应用提供理论依据。【方法】绿脓杆菌ATCC27853为试验菌株,通过连续增高浓度诱导法筛选抗药菌株,并通过抗药稳定性、交叉抗药性、抗药性代偿测定来探究其耐受性特点,通过对其胞外蛋白酶活性、生物膜形成、胞外多糖含量的变化来探讨其抗药性机制。【结果】通过连续增高鲎素浓度法对原始菌株进行30多代诱导后,绿脓杆菌ATCC27853对鲎素的MIC值逐渐增高,80多代时产生了明显抗药性。抗药菌株对丁胺卡那以及pexiganan、鲎素同源肽tachyplesin III、polyphemusin I均能产生不同程度的抗药性。在无药培养基中抗药菌株以更长的延滞期作为抗药性代偿,但在有药培养基中具有更短的延滞期和更大的生长速率。抗药菌株较原始菌株分泌的胞外蛋白酶活性增高,并能降低鲎素的抗菌活性。在同样条件下抗药菌株较原始菌株胞外多糖含量增高,更易形成生物膜。【结论】在长期选择压力下绿脓杆菌ATCC27853对鲎素能产生抗药性,其抗药性机制可能与生物膜形成、胞外蛋白酶失活鲎素有关。关于细菌对鲎素的抗药性机制,有待进一步研究。     

Renal vascular resistance in glomerular diseases--correlation of resistance index with biopsy findings

Duplex Doppler sonography has been recognized as a noninvasive method to evaluate hemodynamic features of renal blood in renal and intrarenal arteries in patients with various renal diseases. The significance of duplex Doppler sonography in the evaluation of renal vascular resistance in glomerular diseases has not yet been clearly determined. The aim of the present study was to evaluate renal vascular resistance in patients with glomerular diseases by measuring intrarenal arterial resistance (RI) and to correlate RI with renal functional tests and other clinical and laboratory data. The Doppler parameters were also correlated with histopathological findings in the kidney which underwent the percutaneous biopsy. Duplex Doppler sonography was used to measure RIs in intrarenal arteries in 50 patients with glomerular diseases and 60 age-matched control subjects. The renal vascular resistance index (RI) was determined by the use of Doppler sonography. The mean RI in 50 patients with glomerular diseases was 0.68 +/- 0.09, which was statistically significantly higher than in 60 control subjects (the mean RI was 0.596 +/- 0.035). In a group of patients with membranoproliferative glomerulonephritis the mean RI was 0.817 +/- 0.624 which was statistically significantly higher than in other groups of glomerulonephritis. The renal vascular (resistance) RI significantly correlated with serum creatinine, creatinine clearance and beta2 microglobulin. Qualitative duplex sonography measure of renal arterial resistance-resistive index does not appear to be reliable in distinguishing different types of glomerulonephritis.     

Imazaquin and chlorsulfuron resistance and cross resistance in mutants of Chlamydomonas reinhardtii

Summary Chlorsulfuron and/or imazaquin resistant mutants of Chlamydomonas reinhardtii strain CW15 have been obtained and shown to have actolactate synthase (ALS) with altered sensitivity to one or both of these herbicides. Herbicide resistance in the three mutants described is allelic, and resistance appears to result from a dominant or semidominant mutation in a single, nuclear gene. Imazaquin and chlorsulfuron resistant ALS from imazaquin and chlorsulfuron resistant mutants, together with single-gene Mendelian inheritance of these phenotypes, suggests that ALS is the sole site of action of the two herbicides in Chlamydomonas. A high degree of cross resistance between the two herbicides was found in only one mutant. This mutant (IM-13) was selected for resistance to imazaquin and has a high level of in vitro resistance to both imazaquin (270-fold increased I₅₀) and chlorsulfuron (900-fold increased I₅₀). In another mutant selected for resistance to imazaquin (IMR-2), hyper-sensitivity to chlorsulfuron was found. A mutant selected for resistance to chlorsulfuron (CSR-5), had a substantial degree of resistance of chlorsulfuron (80-fold increased I₅₀), but not to imazaquin (7-fold increased I₅₀).     

Suppression of fluorophenylalanine resistance by mutation to streptomycin resistance in Pseudomonas aeruginosa

Waltho, Judith A. (University of Melbourne, Victoria, Australia), and B. W. Holloway. Suppression of fluorophenylalanine resistance by mutation to streptomycin resistance in Pseudomonas aeruginosa. J. Bacteriol. 92:35-42. 1966.-Fluorophenylalanine-resistant mutants (fpa-r) of Pseudomonas aeruginosa have been isolated. By cotransduction analysis, the mutations were shown to have at least two chromosomal locations. One locus (fpaA) showed linkage to three other markers, str, try-3bi, and arg-3, and the order of these four linked markers was found to be try-3bi, arg-3, fpaA, str. The linkage relationships of the other fpa loci are not yet known. The phenotypic expression of resistance at the fpaA locus can be suppressed by mutation of the str locus from str-s to str-r, whereas that at an unlinked fpa locus cannot.     

Variable resistance versus constant resistance strength training in adult males

Changes in strength, body composition and anthropometric measures for groups training with constant resistance and variable resistance training procedures was compared. Thirty-six male volunteers were randomly assigned to one of three groups: Constant Resistance (CR), Variable Resistance (VR) and Control (C). Strength training was conducted 3 days per week, 45 min per day, for 10 weeks. The results demonstrated that both the CR and the VR groups increased muscular strength. The CR group demonstrated significant increases in strength over the VR group when strength was assessed by CR procedures. Conversely, the VR group demonstrated significant increases in strength over the CR group when strength was assessed by VR procedures. Neither group exhibited superiority over the other relative to changes in body composition and anthropometric measures. The significance of these results is discussed.     

Mupirocin resistance in staphylococci: development and transfer of isoleucyl-tRNA synthetase-mediated resistance in vitro

Mupirocin resistance could be transferred from highly resistant clinical isolates of Staphylococcus aureus to highly sensitive recipients of Staph. aureus, Staph. epidermidis and Staph. haemolyticus. Transconjugants of the latter two organisms could transfer this resistance into mupirocin-sensitive Staph. aureus. Moderately resistant strains did not transfer this resistance to sensitive recipients, nor did strains with high-level mupirocin resistance developed by serial transfer or habituation. The inhibitory effects of mupirocin on crude isoleucyl-tRNA synthetases (IRS) isolated from mupirocin-sensitive and -resistant strains of Staph. aureus have been determined. Drug concentrations needed to produce 50% inhibition, I50 values, were very low against IRS from a highly sensitive strain, somewhat higher against IRS from moderately resistant strains, much higher against enzyme from strains trained in vitro to high-level resistance, and considerably higher still against IRS extracted from clinical isolates possessing high-level mupirocin resistance and from the transconjugates of such strains resulting from crosses with mupirocin-sensitive strains. It is concluded that high-level resistance in clinical isolates is plasmid-mediated involving a second, mupirocin-resistant IRS whereas in moderately resistant strains, and in strains trained in vitro to high-level resistance, chromosomal mutations are likely to be responsible for decreasing IRS sensitivity.     

抗生素抗性基因在环境中的传播扩散及抗性研究方法

抗生素在医药、畜牧和水产养殖业的大量使用造成了环境中抗性耐药菌和抗性基因日益增加,抗生素抗性基因作为一种新型环境污染物引起人们的广泛关注.本文综述了近年来国内外有关抗生素抗性基因的研究进展,其在水、土壤、空气等环境介质中和动,植物体内的传播扩散,以及开展环境中抗生素抗性基因研究的必要性,重点介绍了有关抗生素抗性（包括抗性细菌和抗性基因）的研究方法,指出抗性基因研究中存在的问题,并对未来的相关研究进行了展望.     

Drug resistance in schistosomes

Drug resistance in schistosomes is confined essentially to compounds of the hyconthone/oxamniquine family, since no documented case of resistance has so far been reported for the widely used drug praziquantel. The availability of strains of Schistosoma mansoni that are resistant to hyconthone and oxomniquine has permitted a detailed genetic and biochemical study of the mechanism of action of these compounds. Drugs must be activated by enzymatic esterification and this ultimately results in the production of an electrophilic moiety capable of alkylating DNA and other parasite macromolecules. As reviewed here by Donato Cioli, Livia Pica-Mattoccia and Sydney Archer, resistance is due to the loss of a drug-activating enzyme that is present in sensitive schistosomes and absent in resistant worms and in the mammalian hosts. Further study of this enzyme may yield valuable clues for drug design and for a basic understanding of parasite metabolism.