Whole Period Of Growth Research Articles

CONTROL OF VALINE AND ISOLEUCINE METABOLISM IN PSEUDOMONAS AERUGINOSA AND ESCHERICHIA COLI.

SUMMARY: Isoleucine increased the quantity of α-acetolactic acid-forming enzyme which takes part in the synthesis of valine and isoleucine in Pseudomonas aeruginosa. Threonine and α-ketobutyric acid, the precursors of isoleucine, had a similar effect. In P. aeruginosa during the initial stage of growth after inoculation, a temporary substantial increase of α-acetolactic acid-forming enzyme can be observed. This increase was not so great when valine was present, and was enhanced by isoleucine, which was effective during the whole period of growth. The repressive effect of valine can be counteracted with isoleucine and the end product inductive effect of isoleucine can be inhibited by valine. In extracts of disrupted organisms the activity of the α,β-dihydroxy acid dehydrase changes parallel with the concentration of the α-acetolactic acid-forming enzyme. In the case of Escherichia coli the repressive effect of valine on the α-acetolactic acid-forming enzyme can be counteracted with isoleucine.

EXPERIMENTS ON THE CONTROL OF BOTRYTIS DISEASE OF LETTUCE

Experiments were made during 1955‐57 on the fungicidal control of Botrytis attack on lettuce, cv. May Queen, matured in frames from November to April, and cv. Trocadero Improved, grown as seedlings in frames from November to March and then matured in the field from March to June. The frame lettuce were treated during their whole period of growth and the field lettuce in the seedling stage only.On both types, 0.33% thiram sprays applied on up to five occasions gave the best control of disease: 5% tecnazene dust was effective on the frame crop, in 2 out of 3 years when applied to the plants and also when incorporated in the top soil at the rate of 15 g. per sq.yd. Tecnazene applications did not give a good control of the disease on the field crop. Sprays with 0.25% captan were almost as effective as the thiram treatments on the field lettuce but not on the frame crop.

Studies on the Influences of Cutting Cotyledons in Soybean Plants

1) The growth of top and root of soybean plant were restricted by cutting-off cotyledons at seedling stage. The effect was observable mot only in the period, directly after cutting but also throughout the whole period of growth. 2) Both the top and the root, were affected. Number of branches, and roots were reduced, and the position of the lowest branching node rose. 3) The percentage of legumes which developed and their yields were decreased in agree with the degree of cutting-trestment: In half cutting plot 73% of legumes developed, producing 66.5% of seeds in weight, compared with thosoe of the control plot and in full plots 55.6% legumes developed, with 51.9% of seeds.

The effect of stage of growth on the copper, zinc, manganese, and molybdenum contents of Algerian oats grown of thirteen soils

Algerian oats were grown on 13 soils in the glass-house. Plants were harvested at intervals throughout the growing period, and when large enough were divided into leaf, stem, and (in later harvests) flowers or fruits. Copper, zinc, manganese, and molybdenum were determined on the separate plant fractions. Characteristic changes in the trace metal contents of the plant with growth were found for each element. These changes were generally similar irrespective of the soil on which the plants were grown. With the exception of manganese, the availability of the element in the soil did not affect the trend of the changes as the plant matured, but only the amount present. The uptake of each of the four elements continued through the whole period of growth. The total amounts of copper and zinc in both the leaf and the stem decreased after flowering as translocation to the grain proceeded. The amount of manganese in the leaf increased throughout the period of growth, although the rate of increase was less after flowering. The amount of molybdenum in the leaf increased until flowering, after which there was little further change. The rate of uptake of manganese was approximately equal to the rate of production of dry matter, whereas that of molybdenum, copper, and zinc was relatively greater in the early stages of growth. There was no observable influence of soil pH on the availability of copper and zinc, but that of manganese decreased with increasing pH. The availability of molybdenum was affected by the combined influences of soil pH and soil iron.

British Food Journal Volume 49 Issue 5 1947

British Food Journal Volume 49 Issue 5 1947

Studies in the physiology of the onion plant

This paper completes the survey of the effects of five factors on flowering behaviour, bulbing, and ripening of onions grown from sets (Heath, 1943) and deals with the factors day length and temperature in the second season. The results from both papers are discussed and the main conclusions are as follows: Flowering is greatly reduced or completely inhibited by submitting the plants to high temperature whether (1) during the whole period of growth from seed to set, (2) during the first part or whole of the storage period (Oct.‐Mar.), or (3) throughout the second season of growth from set to mature onion bulb. Unless very high temperature (35d̀; C.) is reached, heat storage restricted to the last part of the dormant period may only delay but not reduce flowering. Cold storage (od̀; C.) throughout or for the first part of the storage period reduces flowering; when restricted to the last part it tends to increase bolting, but at any other period in the life history of the onion plant bolting is apparently favoured by medium temperature (10–15d̀ C). Long days (16 hr.) throughout the second season inhibit inflorescence emergence irrespective of temperature within the range investigated. Conditions of day length and temperature in the second season favourable to bulbing are inimical to flowering: thus both long days and high temperature tend to encourage bulbing and prevent bolting, while short days inhibit bulbing but allow of bolting if the temperature is not too high. Late planting of sets in the field therefore reduces bolting. Leaf emergence ceases abruptly when bulbing begins at high temperature, and even at low temperature few if any more leaves expand. The relation of this fact to optimal time of planting and the use of American varieties capable of bulbing in short photoperiods is discussed. Seedlings apparently need a longer photoperiod for bulbing than plants grown from sets. A day length just adequate for bulbing at high temperature will not allow of bulbing at low temperature, with the result that seedlings sown very late produce good bulbs at high temperature but may fail to bulb at low temperatures. High‐temperature storage, especially during the last part of dormancy, tends to the production of distorted leaves, especially when followed by growth of the sets at high temperature. Such plants show a high mortality. Heat storage also delays and restricts bulbing, which is reflected in the increased number of expanded leaves. Ripening is similarly delayed; this effect is not directly due to water loss during storage.

The Relation Between the Number of Bacteria and Acid Production in the Fermentation of Xylose

The study of the rate of growth of bacteria and the extent of the changes in the composition of the nutrient medium which accompany growth has engaged the attention of bacteriologists for many years. The most important contributions to this problem may be divided along two lines: first, the relation between the number of bacteria and the amount of the end products at different times; second, involved mathematical equations and formulae to explain the rate of multiplication of bacteria in nutrient solutions. The usual method of investigation is to seed a small number of bacteria into a suitable medium under known conditions, and after given intervals of time to estimate the number by the plate method. The rate of development can be obtained for many kinds of bacteria by measuring their products, i. e.,* the extent of fermentation is assumed to be proportional to the number of bacteria that have developed. This article is primarily concerned with the rate at which byproducts are formed and their relation to the number of bacteria. In order to study the mechanism of fermentation reactions, the rate of development of the micro-organism is of importance. At present, observations are not available which cover the whole period of growth from commencement of seeding to the period when growth ceases altogether, and by-products are no longer formed. It is true that there are ample observations available on the reproduction of bacteria and yeasts in the early stages of growth.

The Teaching of Science in Secondary Schools

THE following notes on the subject of science teaching in grant-earning secondary schools in England are based on the reports and observations of certain of the Board's inspectors, who were instructed to pay special attention to this matter during the past year. While an attempt will be made to note the principal changes that have occurred in recent years, to point out certain directions in which improvements have taken place, and to direct attention to some existing defects, the time has not yet come when a detailed and systematic survey of the state of scientific instruction in English secondary schools could profitably be undertaken. Since 1902, when the schools of science or “organised science schools” of the Science and Art Directory became the Division A Schools of the Regulations of that year, the number of secondary schools recognised for grant has risen from 348 to its present figure, 841. The earlier portion of this period was one which saw a gradual transformation from curricula which were predominantly scientific and mathematical to curricula in which a more even balance of studies was (secured; and the whole period of growth and transition has been characterised (quite apart from the effect of alterations in the Board's Regulations) by notable changes in the methods, and to some extent also in the aims, of science teaching.