THE EFFECTS OF CURRENT FLOW ON BIOELECTRIC POTENTIAL : I. VALONIA

The effect of direct current flow upon the potential difference across the protoplasm of impaled Valonia cells was studied. Current density and direction were controlled in a bridge which balanced the ohmic resistances, leaving the changes (increase, decrease, or reversal) of the small, normally negative, bioelectric potential to be recorded continuously, before, during, and after current flow, with a string galvanometer connected into a vacuum tube detector circuit. Two chief states of response were distinguished: State A.—Regular polarization, which begins to build up the instant current starts to flow, the counter E.M.F. increasing most rapidly at that moment, then more and more slowly, and finally reaching a constant value within 1 second or less. The magnitude of counter E.M.F. is proportional to the current density with small currents flowing in either direction across the protoplasm, but falls off at higher density, giving a cusp with recession to lower values; this recession occurs with slightly lower currents outward than inward. Otherwise the curves are much the same for inward and outward currents, for different densities, for charge and discharge, and for successive current flows. There is a slight tendency for the bioelectric potential to become temporarily positive following these current flows. Records in the regular state (State A) show very little effect of increased series resistance on the time constant of counter E.M.F. This seems to indicate that a polarization rather than a static capacity is involved. State B.—Delayed and non-proportional polarization, in which there is no counter E.M.F. developed with small currents in either direction across the protoplasm, nor with very large outward currents. But with inward currents a threshold density is reached at which a counter E.M.F. rather suddenly develops, with a sigmoid curve rising to high positive values (200 mv. or more). There is sometimes a cusp, after which the P.D. remains strongly positive as long as the current flows. It falls off again to negative values on cessation of current flow, more rapidly after short flows, more slowly after longer ones. The curves of charge are usually quite different in shape from those of discharge. Successive current flows of threshold density in rapid succession produce quicker and quicker polarizations, the inflection of the curve often becoming smoothed away. After long interruptions, however, the sigmoid curve reappears. Larger inward currents produce relatively little additional positive P.D.; smaller ones on the other hand, if following soon after, have a greatly increased effectiveness, the threshold for polarization falling considerably. The effect dies away, however, with very small inward currents, even as they continue to flow. Over a medium range of densities, small increments or decrements of continuing inward current produce almost as regular polarizations as in State A. Temporary polarization occurs with outward currents following soon after the threshold inward currents, but the very flow of outward current tends to destroy this, and to decondition the protoplasm, again raising the threshold, for succeeding inward flows. State A is characteristic of a few freshly gathered cells and of most of those which have recovered from injuries of collecting, cleaning, and separating. It persists a short time after such cells are impaled, but usually changes over to State B for a considerable period thereafter. Eventually there is a reappearance of regular polarization; in the transition there is a marked tendency for positive P.D. to be produced after current flow, and during this the polarizations to outward currents may become much larger than those to inward currents. In this it resembles the effects of acidified sea water, and of certain phenolic compounds, e.g. p-cresol, which produce State A in cells previously in State B. Ammonia on the other hand counteracts these effects, producing delayed polarization to an exaggerated extent. Large polarizations persist when the cells are exposed to potassium-rich solutions, showing it is not the motion of potassium ions (e.g. from the sap) which accounts for the loss or restoration of polarization. It is suggested that inward currents restore a protoplasmic surface responsible for polarization by increasing acidity, while outward currents alter it by increasing alkalinity. Possibly this is by esterification or saponification respectively of a fatty film. For comparison, records of delayed polarization in silver-silver chloride electrodes are included.     

THE VARIATION OF ELECTRICAL RESISTANCE WITH APPLIED POTENTIAL : III. IMPALED VALONIA VENTRICOSA

Electrical resistance and polarization were measured during the passage of direct current across a single layer of protoplasm in the cells of Valonia ventricosa impaled upon capillaries. These were correlated with five stages of the P.D. existing naturally across the protoplasm, as follows: 1. A stage of shock after impalement, when the P.D. drops from 5 mv. to zero and then slowly recovers. There is very little effective resistance in the protoplasm, and polarization is slight. 2. The stage of recovery and normal P.D., with values from 8 to 25 mv. (inside positive). The average is 15 mv. At first there is little or no polarization when small potentials are applied in either direction across the protoplasm, nor when very large currents pass outward (from sap to sea water). But when the positive current passes inward there is a sudden response at a critical applied potential ranging from 0.5 to 2.0 volts. The resistance then apparently rises as much as 10,000 ohms in some cases, and the rise occurs more quickly in succeeding applications after the first. When the potential is removed there is a back E.M.F. displayed. Later there is also an effect of such inward currents which persists into the first succeeding outward flow, causing a brief polarization at the first application of the reverse potential. Still later this polarization occurs at every exposure, and at increasingly lower values of applied potentials. Finally there is a "constant" state reached in which the polarization occurs with currents of either direction, and the apparent resistance is nearly uniform over a considerable range of applied potential. 3. A state of increased P.D.; to 100 mv. (inside positive) in artificial sap; and to 35 or 40 mv. in dilute sea water or 0.6 M MgSO₄. The polarization response and apparent resistance are at first about as in sea water, but later decrease. 4. A reversed P.D., to 50 mv. (outside positive) produced by a variety of causes, especially by dilute sea water, and also by large flows of current in either direction. This stage is temporary and the cells promptly recover from it. While it persists the polarization appears to be much greater to outward currents than to inward. This can largely be ascribed to the reduction of the reversed P.D. 5. Disappearance of P.D. caused by death, and various toxic agents. The resistance and polarization of the protoplasm are negligible. The back E.M.F. of polarization is shown to account largely for the apparent resistance of the protoplasm. Its calculation from the observed resistance rises gives values up to 150 mv. in the early stages of recovery, and later values of 50 to 75 mv. in the "constant" state. These are compared with the back E.M.F. similarly calculated from the apparent resistance of intact cells. The electrical capacitance of the protoplasm is shown by the time curves to be of the order of 1 microfarad per cm.² of surface.     

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.     

THE ACCUMULATION OF ELECTROLYTES : X. ACCUMULATION OF IODINE BY HALICYSTIS AND VALONIA

Analyses of the sap of Halicystis Osterhoutii and of Valonia macrophysa for iodide indicate accumulations of the order of 1000 to 10,000-fold in the first case, and 40 to 250-fold in the second case. The chemical potential of KI, NaI, HI, and CaI₂ is greater inside than outside.     

Intercellular Transport in Plants: I. THE RATE OF TRANSPORT OF CHLORIDE AND THE ELECTRIC RESISTANCE

A quantitative study has been made of the intercellular movementof chloride in Chara corallina, using pairs of joined internodalcells. One cell of the pair (cell 1) was exposed to a solutioncontaining ³⁶Cl; the distribution of this tracer between thecells was determined at the end of the uptake period. Of thechloride taken up, 0.29 was transported out of cell 1 for alluptake times from 1.8 to 22 ks and 0.57 was transported to thevacuole of cell 1, in experimental series I. In series II, thefraction transported out of cell 1 was 0.43 at 22 and 43 ks,but 0.17 at 600 s. These results represent a rate of transport of 4 to 60 pmols^–1, across an intercellular wall of area 1.5 x 10^–6m²; the wall has 0.03 to 0.04 of its area occupied by plasmodesmata.The estimate of transport rate is based on an attempt to determinethe specific activity of the cytoplasm of cell 1. The electricresistance of the node was found to be 47 m m². The observed transport rate can be explained by diffusion inthe plasmodesmata, without the need to postulate active processes.Diffusion in the plasmodesmata is slower than in free solutionby an ‘impediment factor’ of 7 to 700, dependingon the assumed chloride concentration of the ground-plasm. Ifthe plasmodesmata offer the major conducting path for electriccurrent, the electric impediment factor is 390. Chloride entersthe plasmodesmata from the same small kinetic compartment whichsupplies the flux to the vacuole, or from a smallintermediatecompartment.     

THE RELATIONS OF TEMPERATURE TO THE POTASSIUM EFFECT AND THE BIOELECTRIC POTENTIAL OF VALONIA

The effect of temperature upon the bioelectric potential across the protoplasm of impaled Valonia cells is described. Over the ordinary tolerated range, the P.D. is lowest around 25°C., rising both toward 15° and 35°. The time curves are characteristic also. The magnitude of the temperature effect can be controlled by changing the KCl content of the sea water (normally 0.012 M): the magnitude is greatly reduced at 0.006 M KCl, enhanced at 0.024 M, and greatly exaggerated at 0.1 M KCl. Conversely, temperature controls the magnitude of the potassium effect, which is smallest at 25°, with a cusped time course. It is increased, with a smoothly rising course, at 15°, and considerably enhanced, with only a small cusp, at 35°. A temporary "alteration" of the protoplasmic surface by the potassium is suggested to account for the time courses. This alteration does not occur at 15°; the protoplasm recovers only slowly and incompletely at 25°, but rapidly at 35°, in such fashion as to make the P.D. more negative than at 15°. This would account for the temperature effects observed in ordinary sea water.     

THE ACCUMULATION OF ELECTROLYTES : XII. ACCUMULATION OF HALIDE AND NITRATE BY VALONIA IN HYPERTONIC SOLUTIONS

When cells of Valonia macrophysa were placed in hypertonic sea water, the concentration of halide and of nitrate increased, and the sum of halide + nitrate became 0.05 M greater inside than outside, which is about the same difference as is found in cells in normal sea water. In ordinary sea water the ratio of halide to nitrate is 80,000 to 1. When this was changed by substituting nitrate for halide so that the concentration of halide was 1.75 times that of nitrate the rate of entrance of halide was 1.68 times that of nitrate in 276 hours and the ratio of halide to nitrate in the sap decreased from 38 to 18.5. No halide came out in exchange for entering nitrate. The retention of chloride may well be due to the fact that even when the halide concentration of the sea water is reduced as low as 0.4 M, there is still an inwardly directed activity gradient of sodium chloride.     

THE ACCUMULATION OF ELECTROLYTES : III. BEHAVIOR OF SODIUM,POTASSIUM, AND AMMONIUM IN VALONIA

When 0.001 M NH₄Cl is added to sea water containing Valonia macrophysa there seems to be a rapid penetration of undissociated NH₃ (or NH₄OH) which raises the pH value of the sap so that the thermodynamic potential of KOH becomes greater inside than outside and in consequence K leaves the cell: NaOH continues to go in because its thermodynamic potential is greater outside than inside. NH₄Cl accumulates, reaching a much higher concentration inside than outside. This might be explained on the ground that NH₃, after entering, combines with a weak organic acid produced in the cell whose anion is exchanged for the Cl^- of the sea water, or (more probably) the organic acid is exchanged for HCl.     

REACTIONS OF VALONIA AND OF HALICYSTIS TO COLLOIDS

From the results of these tests it is clear that both Halicystis and Valonia have a high degree of tolerance for animal peptone, and a very high degree of tolerance for animal proteose and for egg albumen. The products of bacterial growths fostered by these proteins have a deleterious effect upon both species of algae; but, if it were possible to prevent bacterial growth entirely and at the same time supply proper food, it is probable that Halicystis and Valonia would show normal growth indefinitely in the presence of these three colloids. This is not true where exposure is made to yeast nucleic acid dissolved in sea water containing 0.00093 gm. per cc. of NaOH. Valonia is markedly less tolerant of this medium (perhaps of NaOH rather than the colloid used) than Halicystis. Such differential effects, however, reach a high point in the case of the solutions of diphtheria toxin and of edestin. Halicystis has a very high tolerance for diphtheria toxin, and Valonia a very low tolerance. In the case of edestin, the relationship is reversed. Here Halicystis has a very low tolerance, and Valonia a very high tolerance. In fact, it may be said that diphtheria toxin has no appreciable effect upon Halicystis, and edestin a very slight effect upon Valonia; while diphtheria toxin is extremely toxic to Valonia, and edestin is extremely toxic to Halicystis. We can offer no suggestions, at present, as to the way in which these effects are produced. It is probable that the very thin protoplasmic layer of these species, which is certainly no thicker than 8µ, is sufficient to obstruct the passage of proteins having large molecules, like egg albumen, with a degree of efficiency that is extraordinary. In the tests we have reported, areas of from 20 sq. cm. to 40 sq. cm. have been submitted to the action of a relatively high concentration of egg albumen for several days without permitting the passage of sufficient amounts to give definable tests either with Spiegler''s or with Tanret''s method,— presumably less than 1 part in 250,000. In the tests of the proteins having much smaller molecules (though the size may not be the explanation), there is some probability that the membranes exhibit a little permeability. The peptone and the proteose of animal origin, or biuret-positive substances derived from them, apparently pass the protoplasmic membranes occasionally in quantities sufficient to give biuret tests. The most probable case of protein passage, however, was that of the proteose of the scarlet runner bean, where specific detection of less than 1 part per 80,000 was possible. In this instance the proteose appeared to pass membranes that were healthy and were functioning normally. But since the cells of the algae had to be destroyed in making the tests, one cannot maintain this point. All one can say is that protein passage was indicated in carefully examined cells of both species, where no breaks in the protoplasmic membrane were discernible, and where samples of the treated cells behaved normally after treatment.     

甲氰菊酯与阿维菌素单用、轮用和混用对朱砂叶螨抗性进化的影响

应用数量遗传学的方法分析朱砂叶螨(Tetranychus cinnabarinus)实验种群对甲氰菊酯、阿维菌素及其混剂甲氰—阿维(甲氰菊酯:阿维菌素=8.9:0.1,m/m)的抗性现实遗传力,并测定了甲氰菊酯、阿维菌素分别连续单用、轮换使用、混合使用对朱砂叶螨抗性进化的影响。结果表明,筛选16代后,朱砂叶螨对甲氰菊酯、阿维菌素和甲氰—阿维的抗性现实遗传力分别为0.2853、0.1695和0.0804,朱砂叶螨对混剂的抗性现实遗传力低于对2个单剂的遗传力的一半,混用延缓抗性的效果将好于轮用。药剂连续单用、轮换使用和混合使用16代,朱砂叶螨对甲氰菊酯的抗性分别为28.52、28.03和10.81倍,对阿维菌素的抗性分别为3.24、2.82和1.41倍。朱砂叶螨对2种杀螨剂抗性进化速率为单用>轮用>混用,抗性测定结果表明甲氰菊酯与阿维菌素混用能有效延缓朱砂叶螨对2种药剂抗性的发展速率。     

示波极谱滴定法测定植物中钾含量的研究

示波极谱滴定法测定植物中的钾未见报道,本文用示波极谱滴定法对植物中钾的测定,做了多方面的研究。实验表明以ＨＡｃ－ＮａＡｃ为底液ｐＨ＝５．０的缓冲溶液中,加入过量的标准四苯研究钠（Ｎａ－ＴＰＢ）溶液,然后用标准ＡｆＮＯ３溶液滴定过量的四苯硼钠,利用四苯硼钠示波极谱曲线（ｄＥ／ｄｔ＝ｆ（Ｅ））上有切口,并和Ａｇ＋能定量反应,使切口消失为终点。测定结果满意。该法直观、简便、快速、灵敏、准确、不用加指示剂。溶液混浊、沉淀及有色,均不干扰测定,适用于植物中钾的测定。     

DISSIMILARITY OF INNER AND OUTER PROTOPLASMIC SURFACES IN VALONIA. III

Evidence that the inner and outer protoplasmic surfaces in Valonia are unlike is found in the high P.D. across the protoplasm when the external solution has the same composition as the vacuolar sap. Earlier experiments with artificial sap have been repeated, using natural as well as artificial sap. Good agreement between the data with the natural and the artificial solution was found both in the magnitude of the P.D.''s observed and in the shape of the P.D.-time curves. The P.D.''s, however, were considerably higher than the values formerly reported as usual, while the cells proved much less liable to alteration produced by exposure to sap. It is suggested that the cells used in the recent experiments were in a more vigorous condition, perhaps as a result of exposure to stronger illumination. The interpretation of the shape of the P.D.-time curves, proposed in an earlier report, and based on the theory of protoplasmic layers, is further discussed. It is assumed that the fluctuations in P.D. are due to an increase in the concentration of K in the main body of the protoplasm.     

THE INJECTION OF SULFATES INTO VALONIA

Potassium chloride and sulfate were injected into the vacuole of Valonia. The surviving cells tolerated the presence of these solutions. Sulfate, although ordinarily absent from the sap, is not rapidly eliminated when introduced. Hence the sulfate occasionally found in cells of normal appearance may have entered due to temporary injury followed by recovery.     

CHANGES OF APPARENT IONIC MOBILITIES IN PROTOPLASM : I. EFFECTS OF GUAIACOL ON VALONIA

In normal cells of Valonia the order of the apparent mobilities of the ions in the non-aqueous protoplasmic surface is K > Cl > Na. After treatment with 0.01 M guaiacol (which does not injure the cell) the order becomes Na > Cl > K. As it does not seem probable that such a reversal could occur with simple ions we may assume provisionally that in the protoplasmic surface we have to do with charged complexes of the type (KX _I)⁺, (KX _II)⁺, where X _I and X _II are elements or radicals, or with chemical compounds formed in the protoplasm. When 0.01 M guaiacol is added to sea water or to 0.6 M NaCl (both at pH 6.4, where the concentration of the guaiacol ion is negligible) the P.D. of the cell changes (after a short latent period) from about 10 mv. negative to about 28 mv. positive and then slowly returns approximately to its original value (Fig. 1, p. 14). This appears to depend chiefly on changes in the apparent mobilities of organic ions in the protoplasm. The protoplasmic surface is capable of so much change that it does not seem probable that it is a monomolecular layer. It does not behave like a collodion nor a protein film since the apparent mobility of Na⁺ can increase while that of K⁺ is decreasing under the influence of guaiacol.     

昆虫对生物农药的抗性机制及对策

本文综述了昆虫对B.t等生物杀虫剂的抗性机制及延缓昆虫抗性发展所应采取的措施.昆虫通过下列不同机制产生抗生:1)昆虫的血淋巴对B.t等生物杀虫剂的营养细胞的抑制作用.2)各种来源的蛋白酶对毒素蛋白的过度降解作用.3)昆虫中肠沉淀蛋白对毒素蛋白的沉淀作用.4)中肠上皮修复能力增强.5)中肠的吸附位点对毒素蛋白的亲和力下降.通过加强对B.t菌株的选育,合理科学的用药方式及采用不同的模式进行植物基因操作以提高杀虫蛋白的表达和活性等综合措施,减缓和降低昆虫抗性的发展.     

颅容积的测量与推算的改进

颅容积对鉴别颅骨的性别具有一定的意义。国内外至今仍沿用传统的测量方法,即堵塞孔缝、灌注介质(菜子或砂等),再间接用量具测出其容积。此法烦琐费时,如不严格统一标准重复误差一般达几十毫升。1964年Uspenskii改用颅内放一橡皮球,球内注水加压法,大大地提高了测量速度,并使重复误差降低到7ml,缺点是必须有加压设备,另外橡皮球易破裂。本测量法采用厚度适中的乳胶囊放入颅腔,囊内灌注汞,取其净重和测时室温,用计算机换算成颅容积。经不同时间对112个颅骨测量两次,结果相差平均为2.27±0.17(0—7.9)ml。乳胶囊使用寿命一般可达20次。本法主要优点是:精确度高和测量速度快;不够理想之处:由于汞重,在密闭箱内操作不便,尽管汞蒸气远低于允许浓度,仍需注意其安全防护问题。此外,求出用颅周长、颅顶正中弧、耳上颅高、颅高等项推算颅容积的回归方程式和关系图,便于实际应用。