THE ACCUMULATION OF ELECTROLYTES : XI. ACCUMULATION OF NITRATE BY VALONIA AND HALICYSTIS

The nitrate concentration in the sap of Valonia macrophysa, Kütz., is at least 2000 times that of the sea water, and in Halicystis Osterhoutii, Blinks and Blinks, at least 500 times that of the sea water.     

DIFFERING RATES OF DEATH AT INNER AND OUTER SURFACES OF THE PROTOPLASM : II. NEGATIVE POTENTIAL IN NITELLA CAUSED BY FORMALDEHYDE

A previous paper showed that when the inner protoplasmic surface has lost its potential under the influence of formaldehyde the outer surface can still respond to changes in the concentration of electrolytes. The present paper indicates that after the inner surface has lost its potential there may be a sudden development of negative potential at the outer surface due to substances coming out of the sap and combining with formaldehyde.     

DIFFERING RATES OF DEATH AT INNER AND OUTER SURFACES OF THE PROTOPLASM : I. EFFECTS OF FORMALDEHYDE ON NITELLA

When protoplasm dies it becomes completely and irreversibly permeable and this may be used as a criterion of death. On this basis we may say that when 0.2 M formaldehyde plus 0.001 M NaCl is applied to Nitella death arrives sooner at the inner protoplasmic surface than at the outer. If, however, we apply 0.17 M formaldehyde plus 0.01 M KCl death arrives sooner at the outer protoplasmic surface. The difference appears to be due largely to the conditions at the two surfaces. With 0.2 M formaldehyde plus 0.001 M NaCl the inner surface is subject to a greater electrical pressure than the outer and is in contact with a higher concentration of KCl. In the other case these conditions are more nearly equal so that the layer first reached by the reagent is the first to become permeable. The outer protoplasmic surface has the ability to distinguish electrically between K⁺ and Na⁺ (potassium effect). Under the influence of formaldehyde this ability is lost. This is chiefly due to a falling off in the partition coefficient of KCl in the outer protoplasmic surface. At about the same time the inner protoplasmic surface becomes completely permeable. But the outer protoplasmic surface retains its ability to distinguish electrically between different concentrations of the same salt, showing that it has not become completely permeable. After the potential has disappeared the turgidity (hydrostatic pressure inside the cell) persists for some time, probably because the outer protoplasmic surface has not become completely permeable.     

pH dependence of folding of iso-2-cytochrome c

Starting from a standard unfolded state (3.0 M guanidine hydrochloride, pH 7.2), the kinetics of refolding of iso-2-cytochrome c have been investigated as a function of final pH between pH 3 and pH 10. Absorbance in the ultraviolet and visible spectral regions and tryptophan fluorescence are used to monitor folding. Over most of the pH range, fast and slow folding phases are detected by both fluorescence and absorbance probes. Near neutral pH, the rate of fast folding appears to be the same when monitored by absorbance and fluorescence probes. At higher and lower pH, there are two fast folding reactions, with absorbance-detected fast folding occurring in a slightly faster time range than fluorescence-detected fast folding. The rates of both fast folding reactions pass through broad minima near neutral pH, indicating involvement of ionizable groups in rate-limiting steps. The rates of slow folding also depend on the final pH. At acid pH, there appears to be a single slow folding phase for both fluorescence and absorbance probes. At neutral pH, the absorbance-detected and fluorescence-detected slow folding phases separate into distinct kinetic processes which differ in rate and relative amplitude. At high pH, absorbance-detected slow folding is no longer observed, while fluorescence-detected slow folding is decreased in amplitude. In contrast, the equilibrium and kinetic properties of proline imide bond isomerization, believed to be involved in the slow folding reactions, are largely independent of pH. The results suggest that the pH dependence of slow folding involves coupling of pH-sensitive structure to proline imide bond isomerization.(ABSTRACT TRUNCATED AT 250 WORDS)     

WATER RELATIONS IN THE CELL : I. THE CHLOROPLASTS OF NITELLA AND OF SPIROGYRA

Chloroplasts may contract under natural conditions and give up water to the rest of the cell, thus indicating changes in metabolism or constitution. Such contractions may be produced experimentally. In Nitella the chloroplasts are ellipsoid bodies which, under natural conditions, may contract to spheres with a loss of volume. This may be brought about by lead acetate, ferric chloride, and digitonin: the contraction may occur while the cell is alive. The contraction in lead acetate is reversible (in lead nitrate little or no contraction occurs). In Spirogyra the chloroplast is a long, spirally coiled ribbon which may contract under natural conditions to a short nearly straight rod with a loss of volume. This can be brought about by inorganic salts and in other ways while the cell is still alive.     

东亚飞蝗hunchback基因在卵子形成和胚胎发育过程中的原位表达

hb（hunchback）基因是昆虫胚胎前后轴模式形成的关键基因．对东亚飞蝗（Locusta migratoria manilensis,Meyen）hb基因的功能已有报道,但其表达模式还不清楚．为了研究胁基因在东亚飞蝗卵子形成和胚胎发育过程中的时空表达情况,本研究采用免疫组化方法在蛋白质水平上检测了hb基因的时空表达模式．在卵子形成过程中,hb基因局限在卵细胞核区中表达,随着卵子的发育逐渐移至卵细胞的后端;卵受精后,核区里的Hb蛋白向外扩散,在卵后端形成浓度梯度;胚盘期,hb基因在胚盘中央呈带状表达;胚盘分化为原头和原躯干后,表达条带变宽,并呈现出梯度表达,该表达区域将形成颌、胸部的部分体节;随着腹节开始形成,hb基因在颌胸部的表达逐渐减弱,而在腹部后端的“生长区”表达,并呈现出不连续性．经比较,hb易基因在昆虫颌胸部的表达较为保守,而在卵子形成过程中和腹部的表达具有较大的变异性．与黑腹果蝇等长胚带昆虫相比,东亚飞蝗hb基因在体节形成的基因级联调控中具有更重要、更直接的调控作用．     

心脏特异表达LMNA^E82K转基因小鼠的建立

目的建立心脏特异表达LMNAE82K转基因小鼠,为研究LMNAE82K与心肌病发病机制的关系提供工具动物。方法把LMNAE82K基因插入α-MHC启动子下游,构建转基因表达载体,显微注射法建立C57BL/6JLMNAE82K转基因小鼠,PCR鉴定转基因小鼠的基因型,采用Western Blot鉴定LMNAE82K在心脏组织中的表达,H＆E染色和超声检测转基因小鼠心脏的病理改变。结果建立了2个心脏组织特异表达LMNAE82K的转基因小鼠品系。超声检查显示转基因小鼠心室壁变薄,收缩期容积和舒张期容积增加,射血分数及短轴缩短率降低。结论LMNAE82K转基因小鼠具有LMNAE82K引起的家族性扩心病有类似的病理变化,为研究LMNAE82K与心肌病发病机制的关系的研究提供了有价值的疾病动物模型。