ON THE RELATION BETWEEN GROWTH AND RESPIRATION IN THE AVENA COLEOPTILE

1. The growth of Avena coleoptile sections in sucrose and auxin solutions is inhibited by various substances which are known to act as dehydrogenase inhibitors. 2. Iodoacetate, which is particularly active in this connection, inhibits all growth at a concentration of 5 x 10^–5 M, but produces only a slight inhibition of oxygen uptake. 3. The growth inhibition by iodoacetate is completely removed by malate and fumarate, and to a lesser extent by succinate and pyruvate. 4. These acids themselves increase the effect of auxin on growth and also increase the respiration of the coleoptile sections, but only if auxin is present. 5. When sections have been soaked in malate or fumarate, the addition of auxin considerably increases the total respiration. Further, the concentration range over which this increase takes place parallels that active in promoting growth. 6. The four-carbon acids provide a respiratory system which is part of the chain of growth processes, and which is in some way catalyzed by auxin. It represents a small but variable fraction of the total respiration.     

THE EFFECTS OF SULFATHIAZOLE AND OF PROPYL CARBAMATE ON THE RATE OF OXYGEN CONSUMPTION AND GROWTH IN ESCHERICHIA COLI

1. The rates of growth and of oxygen consumption by cells of E. coli have been measured under identical conditions, and the effects of sulfathiazole (ST) and of n-propyl carbamate (PC) on these two processes have been compared. 2. The rate of growth was measured by (a) the increase in the viable cell count, (b) the increase in the optical density of the culture, (c) the increase in the rate of oxygen consumption, and (d) the decrease in the ammonia of the medium. The results as indicated by these several measures were identical under the conditions of these experiments. 3. Concentrations of ST or of PC which are just sufficient to stop growth completely, lower the rate of oxygen consumption per unit of bacterial protoplasm to a value approximately 50 per cent of that seen in the absence of the inhibitor. 4. It is shown that the rate of oxygen consumption in cells from old cultures is less affected by ST than is the rate of oxygen consumption by cells from young cultures. It is probable that the rate of oxygen consumption by "old" cells is lower than that of "young" cells. 5. The effects of ST and PC on both the rate of oxygen consumption and the rate of growth are very similar, indicating in a general way, that the mechanism of the actions of these two inhibitors is similar. Furthermore, since both of them produce appreciable inhibition of the rate of oxygen consumption while they are inhibiting growth, the possibility that the effect on oxygen consumption is the immediate cause of the effect on growth must be entertained.     

EFFECT OF AUXIN AND OXALIC ACID ON THE CELL WALL PROPERTY OF AVENA COLEOPTILE

In accelerating the elongation of excised Avena coleoptile cylinders,the effect of oxalic acid was found to be additive to that ofindole-3-acetic acid. Elastic and plastic extensions of the coleoptile cylinder weremeasured by using the plasmolytic method. Both indole-3-aceticacid and oxalic acid increased the elastic extension quickly,while their effect in increasing the plastic extension appeared2 hours after their application. The mechanism of auxin action is discussed in connection withthe effect of removal of calcium from the pectic substance ofthe primary cell wall. (Received November 15, 1960; )     

THE OXYGEN CONSUMPTION ASSOCIATED WITH GROWTH IN ESCHERICHIA COLI AND THE EFFECT OF SULFATHIAZOLE AND OF n-PROPYL CARBAMATE ON IT

1. The rate of oxygen consumption by E. coli has been observed both in the presence and absence of ammonia which substance is used by this organism in these experiments as the sole source of nitrogen for growth. 2. After the ammonia has been completely taken up in a culture of E. coli, the rate of oxygen consumption by the culture is observed to fall rapidly. It becomes relatively constant again at a rate approximately 45 per cent of that existing immediately prior to the exhaustion of the nitrogen source. It appears that the fixation of ammonia, that is, growth, requires approximately 55 per cent of the oxygen consumed by the growing cell. 3. Inhibition of the oxygen consumption which is associated with ammonia fixation, by both sulfathiazole (ST) and n-propyl carbamate (PC) closely parallels the inhibition of growth by these compounds (as measured by viable cell counts, etc.). 4. The concentrations of ST and PC which inhibit growth exert little or no inhibitory effect on the rate of oxygen consumption by cells after the rate has fallen to the resting value. 5. It is pointed out that the above observations would be adequately accounted for if growth depended on a discrete fraction of the total oxygen consumption of the growing cell. 6. It is noted that PC, but not ST, has a significant accelerating effect on the oxygen consumption of the resting cell; and that for a given inhibition of growth, PC produces less inhibition of the total oxygen consumption of the cells, than does ST. The latter of these two observations would follow from the former if the resting oxygen consumption were a discrete entity.     

STUDIES ON THE LACTASE OF ESCHERICHIA COLI

A "lactase solution" was prepared from Escherichia coli. The mechanism of its action has been studied and changes in the rate of hydrolysis under various conditions investigated. The hydrolysis of lactose by the enzyme approximates the course of reaction of the integrated Michaelis-Menten equation. One molecule of enzyme combines with one molecule of substrate. E. coli lactase is readily inactivated at pH 5.0, and its optimal activity at 36°C. is reached between pH 7.0 and pH 7.5. The optimal temperature for its action was found to be 46°C. when determinations were carried out after an incubation period of 30 minutes. Its inactivation by heat follows the course of a first order reaction, and the critical thermal increment between the temperatures of 45°C. and 53°C. was calculated to be 56,400 calories per mol. The enzyme is activated by potassium cyanide, sodium sulfide, and cysteine, and irreversibly inactivated by mercuric chloride, silver nitrate, and iodine. After inactivation with copper sulfate partial reactivation is possible, while the slight inhibition brought about by hydrogen peroxide is completely reversible. The possible structure of the active groups of E. coli lactase as compared with other enzymes has been discussed.     

乙酸对重组大肠杆菌生长及个源基因表达的影响

在重组基因工程菌ＤＨ５α（ＰＧ－ＦＧＦ）的高密度培养过程中,发现培养液中有大量代谢副产物－乙酸的产生和积累,乙酸的存在抑制了工程菌的生长及外源的表达。研究民乙酸在Ｍ９培养基中对工程菌ＤＨ５α（ＰＧ－ＦＧＦ）及生长外源基因表达的影响。结果表明,乙酸的存在不仅导致重组菌生长速率的降低及延迟期的增长,而且对外源基因产物的表达具有强烈的抑制作用,这为该工程菌的高密度培养及外源基因产物的高表达打下了基础。     

EFFECT OF YEAST SEXUAL HORMONES ON ELONGATION OF AVENA COLEOPTILE

Effect of yeast (Saccharomyces cerevisiae) sexual hormones on the elongation of etiolated Avena coleoptile segments was studied. The elongation was promoted by a hormone excreted by cells of mating type a, but not by α hormone excreted by cells of α type. The effect of the former was as great as that of 5 mg/1 indole-3-acetic acid in the first hour of application. The optimal concentration of a hormone was 10 units/ml. Its growth promoting effect was greatly inhibited by an antiauxin, 2,4,6-trichlorophenoxyacetic acid. a Hormone increased cell wall extensibility just as auxin does. Testosterone, β-estradiol, progesterone and ergosterol showed very little effect on the elongation of coleoptile segments.     

HISTOLOGICAL STUDIES ON THE COLEOPTILE. II. COMPARATIVE VASCULAR ANATOMY OF COLEOPTILES OF AVENA AND TRITICUM

The vascular bundles in the uppermost 1-4 mm of the coleoptiles of 9 varieties of Avena sativa, and also of Avena fatua L., all terminate essentially vertically with a small “cap” of tracheary elements. In Triticum vulgare Vill., by contrast, they terminate with a horizontal or downward-pointing section. This brings the two bundles more or less together and may result in their complete fusion, usually with a short vascular extension. In both genera the bundles contain one or more series of apparently active, undifferentiated cells. In the mature embryos the bundles are entirely procambial in nature, but xylem differentiation begins rapidly upon germination and proceeds towards the tip, which is reached by the time the coleoptile is 1.5 mm long; thereafter it proceeds basipetally and it may continue at the base after elongation has ceased there. The differentiation of stomata also appears to proceed basipetally. It may be deduced that the coleoptile cannot form lignin while in the embryo but begins to do so upon germination. Parallels are brought out between auxin production first by the endosperm and then by the tip, on the one hand, and lignification in the xylem and in the stomata, on the other.