THE REVERSIBLE HEAT ACTIVATION INDUCING GERMINATION AND INCREASED RESPIRATION IN THE ASCOSPORES OF NEUROSPORA TETRASPERMA

The heat activation of Neurospora tetrasperma ascospores is a reversible process, since activated spores may be returned to secondary dormancy by preventing respiration, and these secondarily dormant spores may be induced to germinate by reheating. Activation of the spores brings about a large increase in respiration prior to the germination of the spores. As the spores are reversibly activated or deactivated the rate of respiration is increased or is decreased. By poisoning the cells with iodoacetamide it is possible to prevent all germination without greatly inhibiting this increase in respiration. Precisely with the beginning of germination a secondary rise in respiration occurs. The respiration of the spores is cyanide sensitive. The heat activation has a critical temperature at about 49 to 52°C.; and at a constant temperature within this range, the percentage of the spores activated as plotted against the time, follows an S-shaped population curve.     

CHANGES IN THE HEAT-RESISTANCE OF ASCOSPORES OF NEUROSPORA UPON GERMINATION

Lingappa , Yamuna , and A. S. Sussman . (U. Michigan, Ann Arbor.) Changes in the heat-resistance of ascospores of Neurospora upon germination. Amer. Jour. Bot. 46 (9): 671–678. Illus. 1959.—A rapid loss in heat-resistance accompanies activation of ascospores of Neurospora tetrasperma after incubation at 27°C. When activated spores are given a 5-min. “heat-flash” at 65°C. after only 5 min. at 27°C., fully % fail to germinate. Such treatment, if administered 25 min. after activation, results in the complete destruction of the spores. By contrast, when incubation at 27°C. is not interposed, more than ½ of the spores will germinate, even when they have been exposed to 65°C. for 30 min. Similar results were obtained with “heat-flashes” at 50 and 60°C., although exposures of longer duration were required to affect the spores. Conidia respond very differently to “heat-flashes” in that germination is stimulated if they are provided after an incubation period at 27°C. On the other hand, conidia are killed by short exposures to 60°C., so that they are far more susceptible to such treatment than are ascospores. A study of the cardinal temperatures of germination revealed that the maximum is about 44°C. for both conidia and ascospores. The maximum for the growth of two strains of N. tetrasperma and for one of N. crassa is between 40–45°C.; however, another strain of the latter species grows at 45°C. Dry heat was shown to be less effective than wet in activating ascospores. Removal of the exospore of ascospores results in the loss of considerable heat-resistance. In addition, the requirement for heat-activation is considerably mitigated in such spores, suggesting that the exospore, or an associated layer is the locus of the ascospore's heat-resistance.     

REVERSIBLE INHIBITION OF SPERM-EGG FUSION IN THE HAMSTER BY LOW PH*

To study the effect of pH on sperm-egg fusion, hamster eggs were freed from egg investments (cumulus oophorus and zonal pellucida) and inseminated with acrosome-reacted spermatozoa in media with various pH values. One hundred percent of the eggs were penetrated by spermatozoa in phosphate buffered media with pH value higher than 7.1. The rate of penetration declined sharply below pH 7.0 and was 0 at pH 6.1. At pH 6.0–6.1, acrosome-reacted spermatozoa could bind to the egg plasma membrane, but were unable to fuse with it. Similar results were obtained with media buffered with Hepes and Bes. The block of sperm-egg fusion at low pH appeared to be reversible since the eggs that were not penetrated by spermatozoa at low pH were penetrated when they were returned to more alkaline media.     

THE REVERSIBLE INACTIVATION OF BACTERIOPHAGE BY BICHLORIDE OF MERCURY

1. The complete inactivation of antistaphylococcal phage by HgCl₂ (2.8 per cent for 216 hours) can be reversed by precipitation of Hg⁺⁺ with restoration of the phage to its original titre. 2. This behavior seems more compatible with the known properties of certain enzymes than with those of living protoplasm.     

光还原的硫氧还蛋白对6—磷酸葡萄糖脱氢酶的钝化作用

测定了豌豆(Pisum sativum)幼苗的重组叶绿体中光还原的硫氧还蛋白(Td)对6-磷酸葡萄糖脱氢酶(G6PDH)的钝化作用.结果表明,Td在叶绿体G6PDH的光抑制和暗激活中均起重要的调节作用.在其绿色叶片和黄化组织中,G6PDH都存在着两种同工酶,但二硫苏糖醇(DTT)和Td对黄化幼苗中G6PDH活性的影响与叶绿体的明显不同,DTT对黄化幼苗G6PDH的钝化作用和氧化Td的活化作用均低于对叶绿体中的这两种作用.     

PROTAMINE PURIFICATION OF STREPTOKINASE AND EFFECT OF pH AND TEMPERATURE ON REVERSIBLE INACTIVATION

1. Treatment of crude concentrates of streptokinase with protamine results in removal of about 90 per cent of the nitrogenous material, including nucleic acid and protease inhibitor, with little or no loss of activity. 2. Streptokinase solutions undergo reversible inactivation with changes in pH. The rate and extent of inactivation are dependent on pH, being greatest over a very narrow range about pH 5. The rate and extent of inactivation are also a function of temperature, both increasing with the temperature of incubation. The rate of reactivation is a function of pH and temperature, increasing as either is raised. However, as the temperature is raised above about 23°C., or the pH above about 9, a secondary, irreversible inactivation of streptokinase occurs.     

低温辐射聚合用于酵母细胞固定化的高分子载体的研究

本文报导了一种新的用于酵母细胞固定化的高分子载体,该载体是用亲水／疏水性单体在－７８℃辐射聚合而成,讨论交联剂,乳化剂,增韧剂和致孔剂的加入对载体的制备以及载体固定化细胞的雪酵醇量的影响,同时对固定化细胞的重复反应性做了研究。     

THE REVERSIBLE INACTIVATION OF TOBACCO MOSAIC VIRUS BY CRYSTALLINE RIBONUCLEASE

The reversible inactivation of tobacco mosaic virus by crystalline ribonuclease is reported. Studies on the effect of time of standing on the amount of inactivation, and on the effect of dilution and repeated high speed centrifugation on the recovery of virus activity, and the preparation of an insoluble virus-enzyme complex show that the inactivation is brought about at least in part by a combination between virus and enzyme. The significance of the fact that ribonuclease has no detectable effect on the virus nucleic acid when the latter is in combination with protein in the form of virus is discussed with respect to the structure of the virus.     

低温处理对糖槭（Acer saccharum）种子萌芽效应的研究

槭属某些种的种子具有休眠生物学特性,如糖槭(Acer saccharum)和茶条槭(Acer ginnala)。本试验采用低温处理糖槭种子,打破它的休眠,获得高达95%的种子萌芽率,并用这种已萌芽的种子播种,出苗速度快,缩短了播种管理时间。试验还表明,主要存在于糖槭种子子叶、种皮中抑制种子萌芽的调节物质,在0—8℃低温、相对湿度90—100%(遮光)的条件下,能够被逐渐转化、消失,使种子得以萌芽出苗。不经低温处理的种子则不能萌芽,而且低温处理只有伴随高湿的条件才会发生良好的效应。     

野油菜黄单胞菌低温分泌黄原胶微细结构特征和化学特性

首次发现２８℃培养至对数期且未分泌黄原胶的野油菜黄单胞菌（Ｘａｎｔｈｏｍｏｎａｓ ｃａｍｐｅｓｔｒｉｓ）移 至４℃低温培养仍合成分泌黄原胶。黄原胶低温分泌最微细的结构单位是微丝,多根微丝进一步组成 纤维、类似双螺旋或纤维束等级结构形式。低温分泌的黄原胶与２８℃常温分泌的黄原胶相比有相同 的化学组成与结构,但分子量、丙酮酸含量低。     

南极衣藻谷胱甘肽-S-转移酶基因的表达及其对大肠杆菌低温耐受性的增强作用

谷胱甘肽-S-转移酶(Glutathione-S-transferase, GST, EC2.5.1.18)是生物体内一种重要的抗氧化酶, 为阐明GST在南极衣藻(Chlamydomonas sp. ICE-L)中的具体地位, 采用实时荧光定量PCR对不同温度下南极衣藻的GST基因的表达进行了分析; 并构建了原核表达载体pET28a(+)-GST, 转化至大肠杆菌BL21(DE3)中进行诱导表达, 通过平板培养法探讨了重组菌E. coli BL21(pET28a(+)-GST)对低温胁迫的耐受性。结果显示, GST在0℃时表达量最高, 最高可达对照组的两倍多; pET28a(+)-GST重组表达载体在E. coli BL21中实现了高效表达, 且主要以包涵体形式存在, 经HisTrap HP柱分离纯化获得高纯度的GST融合蛋白, 并通过SDS-PAGE及Western blot分析得以验证; 对低温胁迫实验发现南极衣藻GST蛋白的表达可以提高重组菌E. coli BL21对低温的耐受性, 说明GST基因对南极衣藻适应南极低温环境具有重要作用。