Inhibition of protein synthesis by D-threo-chloramphenicol in the laboratory and nodule forms of Rhizobium lupini.
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Protein synthesis by both laboratory-grown bacteria and isolated nodule bacteroids of Rhizobium lupini (strain WU8) is inhibited by D-threo-chloramphenicol, the bacteroid form being the more sensitive to the antibiotic. A comparison between the two forms of the uptake of [14C]chloramphenicol showed that the bacteria always attained a lower intracellular chloramphenicol concentration. It is proposed that the sensitivity difference is due to a difference in membrane permeability between the two forms. (+info)
A large population of small chloroplasts in tobacco leaf cells allows more effective chloroplast movement than a few enlarged chloroplasts.
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We generated transgenic tobacco (Nicotiana tabacum cv Xanthi) plants that contained only one to three enlarged chloroplasts per leaf mesophyll cell by introducing NtFtsZ1-2, a cDNA for plastid division. These plants were used to investigate the advantages of having a large population of small chloroplasts rather than a few enlarged chloroplasts in a leaf mesophyll cell. Despite the similarities in photosynthetic components and ultrastructure of photosynthetic machinery between wild-type and transgenic plants, the overall growth of transgenic plants under low- and high-light conditions was retarded. In wild-type plants, the chloroplasts moved toward the face position under low light and toward the profile position under high-light conditions. However, chloroplast rearrangement in transgenic plants in response to light conditions was not evident. In addition, transgenic plant leaves showed greatly diminished changes in leaf transmittance values under both light conditions, indicating that chloroplast rearrangement was severely retarded. Therefore, under low-light conditions the incomplete face position of the enlarged chloroplasts results in decreased absorbance of light energy. This, in turn, reduces plant growth. Under high-light conditions, the amount of absorbed light exceeds the photosynthetic utilization capacity due to the incomplete profile position of the enlarged chloroplasts, resulting in photodamage to the photosynthetic machinery, and decreased growth. The presence of a large number of small and/or rapidly moving chloroplasts in the cells of higher land plants permits more effective chloroplast phototaxis and, hence, allows more efficient utilization of low-incident photon flux densities. The photosynthetic apparatus is, consequently, protected from damage under high-incident photon flux densities. (+info)
Photoinhibition in mutants of Arabidopsis deficient in thylakoid unsaturation.
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Thylakoid lipid composition in higher plants is characterized by a high level of fatty acid unsaturation. We have screened four mutants of Arabidopsis that have reduced levels of fatty acid unsaturation. Three of the mutant lines tested, fad5, fad6, and the fad3-2 fad7-2 fad8 triple mutant, were more susceptible to photoinhibition than wild-type Arabidopsis, whereas one mutant, fab1, was indistinguishable from wild type. The fad3-2 fad7-2 fad8 triple mutant, which contains no trienoic fatty acids in its thylakoid membranes, was most susceptible to photoinhibition. Detailed investigation of photoinhibition in the triple mutant revealed that the rate of photoinactivation of PSII was the same in wild-type and mutant plants. However, the recovery of photoinactivated PSII was slower in fad3-2 fad7-2 fad8, relative to wild type, at all temperatures below 27 degrees C. These results indicate that trienoic fatty acids of thylakoid membrane lipids are required for low-temperature recovery from photoinhibition in Arabidopsis. (+info)
Excess copper predisposes photosystem II to photoinhibition in vivo by outcompeting iron and causing decrease in leaf chlorophyll.
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Photoinhibition of photosystem II was studied in vivo with bean (Phaseolus vulgaris) plants grown in the presence of 0.3 (control), 4, or 15 microM Cu(2+). Although photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu(2+)-treated plants than in control leaves, thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition. Direct effects of excess Cu(2+) on chloroplast metabolism are actually unlikely, because the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves. Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection. Thus, these hypothetical effects can be eliminated as causes for Cu-enhanced photoinhibition in intact leaves. However, Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network. The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium. The addition of Fe lowered the Cu(2+) concentration of the leaves, suggesting that Cu outcompetes Fe in Fe uptake. We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu(2+)-treated plants. A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species. Plant species adapted to high-light habitats apparently benefit from thick leaves because the rate of photoinhibition is directly proportional to light intensity, but photosynthesis becomes saturated by moderate light. (+info)
Therapeutic effect of topical application of linoleic acid and lincomycin in combination with betamethasone valerate in melasma patients.
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Melasma is an acquired symmetric hypermelanosis characterized by irregular light-to gray-brown macules and patches on sun-exposed areas. Many therapeutic agents are available but are unsatisfactory. Recently, it has been demonstrated that lincomycin (LM) and linoleic acid (LA) can inhibit melanogenesis in vitro. Our purpose was to investigate the clinical efficacy of topical application of LM and LA in combination with betamethasone valerate (BV) in melasma patients. Forty-seven Korean female adults with clinically diagnosed melasma were enrolled in a 6-week, double-blind, randomized clinical trial. Patients were treated with one application of the vehicle (group A), 2% LM mixed with 0.05% BV (group B), or 2% LM mixed with 0.05% BV and 2% LA (group C) on the face every night. Determination of efficacy was based on the Melasma Area and Severity Index (MASI) score and objective assessment (no effect, mild, moderate, or excellent) at intervals of 2 weeks until the end of the study at 6 weeks. After 6 weeks, in comparison with the pre-treatment MASI score, the average MASI score of group C decreased to 68.9%, compared with 98% in group A (p<0.05) and 85.4% in group B. There was no statistically significant difference between group A and group B. Seven patients (43.7%) in group C revealed more than moderate improvement in objective assessment, compared with none in group A and two patients (12.5%) in group B. There were no significant side effects. Topical application of linoleic acid is considered to be effective in the treatment of melasma patients. (+info)
Determination of sensitivity of Mycoplasma hyosynoviae to tylosin and selected antibacterial drugs by a microtiter technique.
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A microtiter technique was used for determination of the sensitivity of Mycoplasma hyosynoviae to antibiotics and other drugs. Use of a biphasic agar-broth medium in microtiter plates allowed direct visualization of growth. Results were more reproducible with this system than when broth alone was used and evaluation based on color change was required. Attempts to adapt the test for use with Mycoplasma hyorhinis were not successful. Minimal inhibitory concentrations of 12 drugs and drug combinations for 12 strains of M. hyosynoviae are presented. Drugs with the lowest minimal inhibitory concentrations were tylosin (0.37 mcg/ml)and lincomycin (0.88 mcg/ml), both of which have been used for treatment and control of M. hyosynoviae arthritis. Comparison of the minimal inhibitory concentrations of tylosin for 43 isolates of M. hyosynoviae obtained in 1959 and 1960 and from 1966 through 1971 indicated the possibilty of decreasing sensitivity to the drug although differences between recent isolates and earlier ones were not statistically significant. (+info)
Studies on the control of Mycoplasma gallisepticum in hatching eggs.
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Lincomycin-spectinomycin, while effective in eliminating Mycoplasma gallisepticum from hatching eggs when administered via the yolk sac, had a marked deleterious effect on hatch-ability when given by this route. On the other hand when lincomycin-spectinomycin was injected into the air cell there was a reduction in the level of experimental infection with an acceptable effect on hatchability. (+info)
Lincomycin resistance mutations in two regions immediately downstream of the -10 region of lmr promoter cause overexpression of a putative multidrug efflux pump in Bacillus subtilis mutants.
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We isolated 19 lincomycin-resistant Bacillus subtilis mutants by expressing lmrB encoding a putative multidrug efflux protein. Eighteen of the mutants altered at two regions (-3 to -1 and +15) immediately downstream of the -10 region of the lmr promoter increased lmr transcription in vivo and in vitro. (+info)