Steady-State Effects of 2,5,2',5'-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum

The steady-state effect of 2,5,2',5'-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 x 10 in steady-state cultures. At a cellular TCBP concentration of 12.2 x 10 ng . cell, growth rate was not affected. However, photosynthetic capacity (P(max)) was significantly enhanced by TCBP (56 x 10 mumol of C . cell . h versus 34 x 10 mumol of C . cell . h in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected.     

Topical chemotherapy of cutaneous Leishmaniasis

Cutaneous leishmaniasis (CL) is one of the most important causes of chronic ulcerative skin lesions. The disease is endemic in many parts of the world, presenting a range of clinical forms - acute, chronic, recurrent and diffuse(1). Several species of Leishmania are involved, including L. major, L. tropica and L. aethiopica in the Old World, and several members of the L. braziliensis and L. mexicana complexes in the New World. Some forms of the disease produce only mild, self-limited lesions, while at the other extreme are the destructive mucocutaneous forms caused by L. braziliensis and L. panamensis(1-7). In all cases, chemotherapy tends to be difficult - often requiring prolonged parenteral administration of toxic drugs such as pentavalent antimonials or amphotericin B. Such drugs are also expensive and relatively inefficient in the sense that much of the active ingredient is excreted by the patient before reaching its target. Consequently, there is renewed interest in the development of active formulations suitable for topical application directly onto the lesions.     

Lipid Saturation Induced Microviscosity Increase Has No Effect on the Reducibility of Flash-Oxidized Cytochrome f in Pea Thylakoids

Homogeneous catalytic hydrogenation was used to modify the level of fatty acid unsaturation of thylakoid membranes in the pea chloroplast. Fluidity alteration has been monitored simultaneously using the spin-label probe, 16-doxyl stearate. Even in the case of 30% hydrogenation, no change in the reduction rate of flash-oxidized cytochrome f was observed, in contrast to the fact that the same decrease in the double-bond content of the thylakoid membrane resulted in a pronounced inhibition in the full-chain electron transport. We conclude that the rate of lateral diffusion of reduced plastoquinone is unaffected by the lowering of the fluidity of the thylakoid lipid matrix.     

Molecular cloning of complementary DNA encoding maize nitrite reductase: molecular analysis and nitrate induction

Complementary DNA has been isolated that codes for maize nitrite reductase (NiR) by using the corresponding spinach gene (E Back et al. 1988 Mol Gen Genet 212:20-26) as a heterologous probe. The sequences of the complementary DNAs from the two species are 66% homologous while the deduced amino acid sequences are 86% similar when analogous amino acids are included. A high percentage of the differences in the DNA sequences is due to the extremely strong bias in the corn gene to have a G/C base in the third codon position with 559/569 codons ending in a G or C. Using a hydroponic system, maize seedlings grown in the absence of an exogenous nitrogen source were induced with nitrate or nitrite. Nitrate stimulated a rapid induction of the NiR mRNA in both roots and leaves. There is also a considerable induction of this gene in roots upon the addition of nitrite, although under the conditions used the final mRNA level was not as high as when nitrate was the inducer. There is a small but detectable level of NiR mRNA in leaves prior to induction, but no constitutive NiR mRNA can be seen in the roots. Analysis of genomic DNA supports the notion that there are at least two NiR genes in maize.     

Evidence for precursor forms of the low isoelectric point alpha-amylase isozymes secreted by barley aleurone cells

Gibberellin-treated barley (Hordeum vulgare L.) aleurone cell protoplasts have been shown previously to contain two α-amylase isozymes which are not secreted (JV Jacobsen, JA Zwar, PM Chandler 1985 Planta 13: 430-438). This report shows that these intracellular forms are immunochemically related to the low isoelectric point but not the high isoelectric point group of α-amylase isozymes and that they arise by new synthesis like the secreted forms. Pulse-chase studies show that the intracellular isozymes are precursors to the secreted isozymes. Conversion of the intra- to the extracellular forms involves decreases in isoelectric points with no change in size detectable by SDS-PAGE. The precursor isozymes were also detected in aleurone layer homogenates but they were unstable. They could be stabilized by various treatments including heating the homogenate to 70°C for 10 minutes indicating that the instability was enzymically mediated. Using purified radioactive precursor isozymes, it was shown that instability did not involve inactivation but the conversion to secreted forms. The nature of the covalent modification associated with conversion was not determined but available data indicate that it does not involve glycosylation.     

Subculture of rabbit articular chondrocytes within a collagen gel: growth and analysis of differentiation

Primary cultures of rabbit articular chondrocytes have been subcultured within three-dimensional (3D) collagen gels. Under these conditions, the cells remained viable and divided, but with a lower proliferation rate than that observed in control monolayer cultures. Flow cytometric analysis of progression of the cells into the cell cycle has confirmed and extended these findings. Also the cellular volume was decreased in 3D-culture, being in the same range as thein vivo size of cartilage cells. Specific staining for proteoglycans and type II collagen immunolocalization on sections of gels showed the expression of differentiated phenotypes and revealed the accumulation of these matrix components in the immediate surroundings of the cells. The use of Ultroser G (a serum substitute) improved the conditions for 3D- culture of rabbit articular chondrocytes.     

保藏菌种的先进方法

目前保藏细菌的常用方法有:①根据不同菌种低温保藏,隔双周或隔月移种传代,②在很低的温度下。使微生物细胞快速冻结且保持完整,然后在真空下使水分升华达到干燥,即冻干保存。前种操作简     

用棉籽饼代替花生饼做幼猪蛋白饲料

导言与花生饼相比,棉子饼的总氮含量略低一些,但其蛋白质中的几种主要的必需氨基酸如赖氨酸、蛋氨酸和胱氨酸含量却很高。对于非反刍动物来说,棉子饼应当是理想的蛋白饲料。然而,由于棉子饼中含有棉酚,这是一种有毒的天然多酚物质,因而妨障了它在猪、家禽和兔子饲料中的随意使用。其中,猪对棉酚的毒性尤为敏感。猪食用棉子饼后会导致厌食、呼吸困难、体虚消瘦等症状。人们一直在寻找根除或减少棉饼用于非反刍动物饲料中所导致的棉酚中毒现象,他们分别用不同量的蛋白质、不同质量的蛋白质、含铁添加剂,以及用含微量棉酚的无腺棉子饼等做饲料进行试验,取得了不同程度的进展。在尼日利亚,尽管棉子饼产量很高,由于缺乏信息,故未对其用于猪饲料予以注意。本研究报告确立了棉子饼与花生饼相比,用于断奶后幼猪饲料中的有关参数。