华北棉区第三代棉铃虫对棉花为害损失与经济阈值的研究

通过在华北棉区棉花蕾铃期阶段,连续５ａ的田间蕾铃脱落原因的观察,明确了在第三代棉铃虫的中常发生年份,影响蕾铃期蕾铃脱落的主要因素是棉株本身的自然脱落其脱落率占总脱落的９０％以上,而因第三代棉铃虫为害造成的脱落率在５％以上。根据田间棉铃虫Ｈｅｌｉｃｏｖｅｒｐａ ａｒｍｉｇｅｒａ（ｈｕｂｎｅｒ）３龄幼虫虫量与为害力的关系研究,结合多年第三代棉铃虫田间生命表,文中提出了三代棉铃虫的经济阈值为百株累计卵量     

脱落酸对线粒体Na^＋—K^＋ATPase活性的影响

在提取大豆（Ｇｌｙｃｉｎｅ ｍ ａｘ）黄化子叶的线粒体时,于清洗和悬浮介质中加入ＡＢＡ,发现４０ μｍ ｏｌ／Ｌ（±） ＡＢＡ 对线粒体膜结合Ｎａ＋ －Ｋ＋ ＡＴＰａｓｅ 活性及线粒体吸氧速率有明显的促进作用。ＡＢＡ 可使１６℃与２７℃培养的大豆子叶线粒体膜结合Ｎａ＋ －Ｋ＋ ＡＴＰａｓｅ Ａｒｒｈｅｎｉｕｓ图的折点温度分别下降６．３℃和５．９℃,并将该酶的底物动力学曲线由正协同曲线转变为非协同曲线。表明ＡＢＡ 可降低线粒体的膜相变温度     

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Using dynamic light scattering we have been able to determine precisely the hydrodynamic radius of l-α-dimyristoylphosphatidylcholine (DMPC) vesicles as a function of temperature. We have detected a sharp, thermally reversible change in the vesicle radius at a phase transition temperature 24°C, corresponding to an approximate 11% increase in surface are. In the range 10–20°C, the change in radius is less than 1%.     

The interaction of phenol with lipid bilayers

The depression of the phase-transition temperature of dimyristoyl- and dipalmitoylphosphatidylcholine vesicles induced by phenol has been investigated by fluorescence polarization. This effect is strongly pH and concentration dependent. Only the uncharged phenol molecule influences the fluidity of the bilayer so that the interaction of phenol with the bilayer can be situated in the hydrophobic acyl chain region. Direct measurements of the partitioning of phenol in the phospholipid vesicles confirm these results and show a limited and concentration-dependent solubility. Phase-transition temperature depressions, obtained from thermodynamic analysis of partition coefficient measurement, are in good agreement with the experimental values.     

Population growth and economic development in Chiapas, 1524–1975

In a recent work on the Tzotzil (Maya) of Chiapas, Mexico, George Collier has suggested that indigenous groups frequently employ agricultural practices which are in obvious disequilibrium with their environment. As a result, he claims, such groups bring about the permanent destruction of their lands and forests. In this article, historical and demographic evidence is presented to demonstrate that the development of commencal agriculture outside of native communities, not overpopulation or technological conservatism within them, lies at the heart of such destruction. Finally, it is argued that anthropologists must consider the evolution of social classes in rural areas if they are to understand the difficulties which economic development entails.     

Correlation between temperature range of growth and structural transitions in membranes and lipids of Escherichia coli K12

Purified cytoplasmic and outer membranes isolated from cells of wild-type Escherichia coli grown at different temperatures were labelled with 1,6-diphenyl-1,3,5-hexatriene and anlyzed using fluorescence polarization techniques. Lipids extracted from the membranes were similarly analyzed using fluorescence polarization. The thermotropic structural transition in outer membranes changed as a function of growth temperature. The structural transition in cytoplasmic membranes and lipids extracted from either cytoplasmic or outer membranes did not change with growth temperature. These data suggest that adaptive changes which occur in the outer membrane determine the temperature range of growth of E. coli. These changes apparently require alterations in outer membrane components other than phospholipids.     

Effects of gaseous anaesthetics and inert gases on the phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine

The phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine was studied under high pressures of helium (340 atm), nitrogen (340 atm), nitrous oxide (43 atm), cyclopropane (4.4 atm) and $\text{n-}\text{propane}$ (8.2 atm), using a turbidimetric technique. Helium and nitrogen increased the transition temperature by 0.021 and 0.006°C/atm, respectively, compared with 0.024°C/atm for hydrostatic pressure. Nitrous oxide reduced the transition by 0.58°C/atm. The hydrocarbon gases spread the transition width and lowered the transition temperature with increasing effect at higher doses. Comparisons with other membrane probes are made and the concentration of gases in the bilayer which lower the transition temperature by 1°C are estimated, in mol%: He, 10.2; N₂, 13.2; N₂O, 9.04; $\text{n-}\text{C}{}_3\text{H}{}_8$, 6.3 and cyclopropane, 12.8.