Sand burial effects on seed germination, seedling emergence and establishment of Panicum virgatum

Studies in the field and in a greenhouse were conducted to examine the effects of sand burial on seed germination, seedling emergence and establishment of Panicum virgatum L. on the foredunes of Lake Erie. Under natural conditions, the seedlings emerged from sand burial depths ranging from 0 to 11 cm, with a mean ± SD of 4.73 ± 1.82 cm. The frequency distribution of the depth of emergence of seedlings in the field was significantly skewed to the right and platykurtic. In the greenhouse, some seedlings emerged from a burial depth of as much as 16 cm. Although percent germination of seeds was not affected by sand burial, the percent emergence and the rate of emergence of seedlings were significantly reduced by excessive sand burial. Seedling mortality was found only among seedlings that emerged from sand burial depths of 10 cm or more. In the field, all the seedlings established in one growing season had originally emerged from sand burial depths of less than 12 cm. Within this burial range, seedlings from shallower burial depths had lower chances of establishment than expected, whereas those from deeper burial depths had higher probabilities of establishment than expected.     

Role of oxidatively modified LDL in atherosclerosis

Oxidative modification of LDL is accompanied by a number of compositional and structural changes, including increased electrophoretic mobility, increased density, fragmentation of apolipoprotein B, hydrolysis of phosphatidylcholine, derivatization of lysine amino groups, and generation of fluorescent adducts due to covalent binding of lipid oxidation products to apo B. In addition, oxidation of LDL has been shown to result in numerous changes in its biologic properties that could have pathogenetic importance, including accelerated uptake in macrophages, cytotoxicity, and chemotactic activity for monocytes. The present article summarizes very recent developments related to the mechanism of oxidation of LDL by cells, receptor-mediated uptake of oxidized LDL in macrophages, the mechanism of phosphatidylcholine hydrolysis during LDL oxidation, and other biologic actions of oxidized LDL including cytotoxicity, altered eicosanoid metabolism, and effects on the secretion of growth factors and chemotactic factors. In addition, this review will examine the evidence for the presence of oxidized LDL in vivo and the evidence that oxidized LDL plays a pathogenetic role in atherosclerosis.     

β-lactamase as a probe of membrane protein assembly and protein export

The enzyme TEM beta-lactamase constitutes a versatile gene-fusion marker for studies on membrane proteins and protein export in bacteria. The mature form of this normally periplasmic enzyme displays readily detectable and distinctly different phenotypes when localized to the bacterial cytoplasm versus the periplasm, and thus provides a useful alternative to alkaline phosphatase for probing the topology of cytoplasmic membrane proteins. Cells producing translocated forms of beta-lactamase can be directly selected as ampicillin-resistant colonies, and consequently a beta-lactamase fusion approach can be used for positive selection for export signals, and for rapid assessment of whether any protein expressed in Escherichia coli inserts into the bacterial cytoplasmic membrane. The level of ampicillin resistance conferred on a cell by an extracytoplasmic beta-lactamase derivative depends on its level of expression, and therefore a beta-lactamase fusion approach can be used to directly select for increased yields of any periplasmic or membrane-bound gene products expressed in E. coli.     

Molecular characterization of immune inhibitor A, a secreted virulence protease from Bacillus thuringiensis

The gene for the secreted neutral metalloprotease, immune inhibitor A (InA), from Bacillus thuringiensis var. alesti has been cloned and sequenced. The deduced amino acid sequence has been confirmed by partial amino acid sequencing. The central part of the amino acid sequence showed similarity to the active site in thermolysin. Southern and Western blots show that InA-related sequences are common among other B. thuringiensis subspecies. In Western blots, 17 out of 25 tested species gave a positive signal. Culture filtrates from subspecies expressing InA were toxic when injected in Trichoplusia ni larvae, whereas filtrate from a strain negative in Western blot had no effect when injected. The LD50 dose of purified InA protein injected in T. ni larvae was 12.5 +/- 2.5 ng per mg of larval body weight.     

Specific binding and uptake of apolipoprotein E-free high density lipoproteins by cultured liver parenchymal cells of copper-deficient rats

The influence of copper deficiency on the binding and uptake of apolipoprotein E-free high density lipoprotein (apo E-free HDL) in cultured rat hepatic parenchymal cells was examined in this study. Male weanling Sprague-Dawley rats were randomly divided into two treatments, a Cu-adequate (7.33 mg Cu/kg diet) or a Cu-deficient (1.04 mg Cu/kg diet) group. After 7 weeks, plasma apo E-free HDL were isolated by a combination of ultracentrifugation, gel filtration, and heparin-Sepharose affinity chromatography. Parenchymal cells were isolated from collagenase perfused liver of Cu-deficient and adequate rats and cultured for 16 hours at 37 degrees C prior to incubation with iodinated apo E-free HDL from the same treatment group. Cells were incubated with 5 microg/ml(125) I-apo E-free HDL for 2, 6, or 12 hours in the presence or absence of 200 microg/ml (40-fold) excess unlabeled apo E-free HDL. Increases in specific binding at 4 degrees C and specific cell-associated uptake at 37 degrees C as a function of time were observed with cells and HDL from Cu-deficient rats. Cells were also incubated for 6 hours with 8 concentrations of (125)I-apo E-free HDL in the presence or absence of excess unlabeled HDL. Although no significant increase in specific binding was detected at 4 degrees C as a function of ligand concentration, the response tended to be higher at 5 to 15 microg HDL/ml for the Cu-deficient treatment. However, at 37 degrees C the specific cell-associated uptake was increased markedly with cells and HDL from Cu-deficient rats. The observed increases in HDL binding and uptake indicate that these processes may be enhanced in Cu-deficient rats. These data are also consistent with recent in vivo results which indicate that plasma clearance and tissue uptake of HDL are increased in Cu-deficient rats.     

生长期-定时一年生植物群体光合产物的最优分配策略的理论分析

本工作建立了一个一年生植物群体的生长模型,利用以梯度法为基础的离散系统最优控制的计算方法,计算并分析了一年生植物群体光合产物的营养器官间分配的最优策略,以及这一策略对植物群体最大生长速率和消光系数的依赖关系。用Pontryagin最小值原理和奇异最优控制的条件证明了光合产物的最优分配方法是:在营养和生殖生长并行阶段,群体叶片的死亡量恰好等于新形成量,植物干重随时间线性增加。     

昆都仑鱼(Kuntulunia)的新材料及其系统位置的讨论

本文根据对宁夏六盘山群马东山组的长鳍昆都仑鱼(Kuntulunia longipterus, Liu, Ma et Liu 1982)的新材料的研究,对其形态特征做了一些补充和订正。在此基础上,笔者支持刘宪亭等人将昆都仑鱼归入华夏鱼科(Huashiidae)及华夏鱼科归入骨舌鱼类的观点。并且认为华夏鱼类代表了一新的亚目——华夏鱼亚目(Huashioidei subordo. nov.)。     

中国3个地区汉族人群补体C6的遗传多态性研究

运用聚丙烯酰胺凝胶等电聚焦(PAGIF)和免疫吸引技术,研究了3个地区汉族人群的C6多态性。得到的基因频率如下:漳州市——C6*A:0.4634、C6*B:0.5000、C6*R:0.0366(C6*B2:0.0317);成都市——C6*A:0.4975,C6*B:0.4484,C6*R:0.0545(C6*B2:0.0395);哈尔滨市——C6*A:0.4708,C6*B:0.5219,C6*R:0.0073(C6*B2:0.0073)。蒙古人种的C6*A频率一般都低于0.5,高加索人种的C6*A频率一般都高于0.6。黑人则介于两者之间。蒙古人种与高加索人种的另一个区别在于前者的C6*B2频率在0.03到0.07之间,而后者几乎没有C6*B2。     

玉米8个栽培亚种（类型）的核型和C—带带型的比较研究

本文首次报道了玉米8个亚种、2个亚型和2个杂交品种的核型和Giemsa C-带带型。所有材料的根尖细胞染色体数目均为2n=20。主要由中部和亚中部着丝点染色体组成。第6染色体短臂均具随体,但大小不同。所有材料均显示有亚端带和端带,在第6染色体的短臂上显示有NOR或/和随体带。C-带的分布、总数目和总长度各不相同。其总带数变异于6至18之间,C-带总长度为5.65—11.40％之间。在核型中,具中部着丝点的染色体数目及C-带总数,罕见栽培或原始的类型通常多于广泛栽培的类型。此外,有关核型和C-帝的变异和进化也进行了简略的讨论。