Roots Of Higher Plants Research Articles

Influences of Gibberellic Acid on Metabolism of Indoleacetic Acid, Acetate, and Glucose in Roots of Higher Plants

The major effects of the gibberellins (GA) on plants have been reviewed recently (13, 14) but no definite linkage with any metabolic pathway has been established. In their study of photosynthesis in gibberellin treated leaves Haber and Tolbert (8) concluded that gibberellic acid neither enhanced the rate of CO2 fixation per unit of leaf tissue nor altered the general pathways of short time metabolism of the newly fixed C140 in the sugars, organic acids, and amino acid products. In long term experiments, great charnges in carbohydrate constituents of gibberellin treated plants have been reported (4, 9). Inhibition in the level of indoleacetic acid oxidase by gibberellic acid has been reported by Pilet (12). However, Brian and Hemming (5) did not find a similar effect in their system. Recently, Galston and Warburg (7) suggested a possible action of gibberellin through an auxin-sparing mechanism by way of the formation of IAA oxidase inhibitor. It is the purpose of this paper to describe the results of experiments on the influence of GA on plant metabolism. In the method used, plant tissue was first pre-treated with GA and then incubated with a selected isotopically labeled substrate. Samples of the tissue were then harvested after several hours of incubation. The influence of GA on the metabolism of the material was determined bv comparing the extents of the labeled atoms whicl have been metabolized and incorporated into other compouncls between the control and treated tissues.

Biological studies of some tussock-grassland soils

Summary The fungi occurring in three soils, under low-tussock grassland, were examined at various seasons, employing screened immersion plate, soil plate, and rhizosphere and root plating, techniques. Approximately 100 species were isolated. The screened immersion plate method showed that: (a) the three soils were of similar mycelial status; (b) maximum growth was obtained in summer; (c) non-sporing fungi, including Rhizoctonia sp. and Papulaspora sp., accounted for approximately 60 % of all isolations from the three soils; (d) Rhizoctonia sp. dominated all three soils. Soil fungal pattern, based on percentage frequency of occurrence, are shown for the three soils. The broad relationships of the soil fungal floras reflect, generally, the broad relationships between the vegetations and between the soils. Fungal isolations by the soil plate method differed from screened plate isolations, particularly in the absence of Rhizoctonia sp. Rhizosphere platings from tussock plants gave similar results to soil plate isolations. Platings of tussock plant roots were dominated by Trichoderma viride and by members of the Mucorales. It is suggested that the soil fungal populations are greatly influenced by the higher-plant roots.

Germination of Oospores of Pythium mamillatum in Response to Exudates from Living Seedlings

THE exudation of chemical substances from roots of higher plants, and the effect of these substances in increasing general microbial activity in the immediate vicinity of roots growing in soil (that is, the rhizosphere effect), have now been fairly well established. Nevertheless, the possible function of these exudates in the etiology of root disease, bringing about the germination of spores or propagules of root-infecting fungi resting in the soil, has received less attention than it undoubtedly merits. The recent interest shown in this subject1,2 has prompted me to make a preliminary report of some similar studies now in progress with oospores of Pythium mamillatum Meurs.

The Influence of Salts on the Activity of Particulate Cytochrome Oxidase from Roots of Higher Plants.

The Influence of Salts on the Activity of Particulate Cytochrome Oxidase from Roots of Higher Plants.

Spectrophotometrical investigations on enzyme systems in living objects I. The oxidation-reduction systems of baker's yeast

Spectrophotometric records were made from suspensions of living yeast by means of a new automatic recording instrument of special construction. The technique enables a detailed investigation to be made of the steady states of the following enzymes and coenzymes: diphosphopyridine nucleotide and its combination with alcohol dehydrogenase and triosephosphate dehydrogenase, flavoprotein and its combination with cytochromes of b-type, cytochromes c, b, and a (cytochrome oxidase), cytochromes c 1 and b 2, and peroxidase. The author comments on the presence and conditions of oxidation and reduction of the cytochromes c 1 and b 2 in living yeast and the steady states of the DPN compounds. The results are compared with previous investigations on roots of higher plants. The investigation has been aided by a grant from the Swedish Research Council of Science.

HYPOGEOUS FUNGI

SUMMARY Hypogeous fungi are those soil fungi which produce macroscopic fruit‐bodies partially or completely embedded in soil or humus. While showing a superficial similarity correlated with habitat, they include members of the Basidiomycetes, Ascomycetes and Phycomycetes. The edible truffles have been known from very early times, and speculations as to their nature are found in Greek and Roman literature. Other groups, which are not edible, were described later. The monographs of Vittadini (1831, 1842) and L. R. & C. Tulasne (1851) are the starting‐point for all modern work on these fungi. The true truffles and various related forms are included in the Tuberales and show obvious relationship with the Pezizales. Young fruit‐bodies of the more complex species, such as Tuber, resemble mature ones of the simpler forms, such as Gyrocratera, or of the Pezizales. The group is best divided into four subfamilies (Knapp, 1950‐2): Pseudotuberaceae, Geneaceae, Eutuberaceae and Terfeziaceae. The hart's truffle, Elaphomyces granulatus, has long been known and was valued as an aphrodisiac. Together with other species of the genus Elaphomyces, the related Ascoscleroderma and the Australian Mesophelia, it is included by Dodge (1929) in the family Elaphomycetaceae of the Plectascales. The hypogeous Basidiomycetes, which were formerly grouped in the family Hypogeous fungi Hymenogastrales (or Hymenogastraceae of some authors), have not yet been satisfactorily classified owing to lack of detailed knowledge of fruit‐body development for all except a few species. It is clear, however, that they do not form a single homogeneous group. They may be provisionally divided into the groups Proto‐gastraceae, Hysterangiaceae, Rhizopogonaceae (or Melanogastraceae), Hymenogastraceae and Hydnangiaceae. The epigeous Secotiaceae probably provides a link with the Agaricaceae, and relationships have been traced between the Hydnangiaceae and the Russula‐Lactarius group of agarics and between the Hysterangiaceae and the epigeous gasteromycetous group of the Phallales. The genus Endogone formerly included species producing zygospores, chlamydospores or sporangia in definite fruit‐bodies. The method of zygospore production is such that there is no doubt that the zygosporic species are best classified as a separate family, the Endogonaceae, within the Mucorales. The chlamydosporic species are of similar general structure and are probably related to the zygosporic forms, since Thaxter (1922) demonstrated the presence of both types of spore within the same fruit‐bodies of E.fasciculata. Cultural studies by Kanouse (1936) showed that a zygosporic species (E. sphagnophila) produced sporangia resembling those of Mucor. Kanouse suggested that the forms producing sporangia aggregated in loose hyphal wefts, formerly attributed to Endogone, are in fact more closely allied to Mortierella and should be transferred to the new genus Modicella and excluded from the Endogonaceae. Some other little‐known genera producing chlamydospores aggregated in definite fruit‐bodies are included in Endogonaceae by Thaxter. Most hypogeous fungi are found only in woodlands. Fruit‐body formation is, in general, favoured by a light, well‐drained soil, with a slightly alkaline hydrogen‐ion concentration, although a few species occur in acid soils. Growth is inhibited or checked by extreme cold or by drought. Considerable circumstantial evidence exists for a mycorrhizal association between many, but not all, species of hypogeous fungi and trees or other plants. In a few examples there is definite proof. Other species are probably true parasites on roots of higher plants. Very few species have been isolated in artificial culture and very little is known of their nutritional requirements. Those which have been investigated resemble other mycorrhizal species in requiring organic nitrogen and vitamin B1. Attempts have been made, particularly in France, to stimulate the development of edible truffles in known truffle‐grounds and to establish them in new places. Some success has been claimed by inoculation of the soil of young tree plantations both with soil from known truffle grounds and with pieces of mature fruit‐bodies. No attempts to produce mycelium by germinating spores of hypogeous fungi have so far been successful. Various authors have depicted what they claim to be early stages of germination, some of which have been shown to be in error.

Associations between microorganisms and higher plants (mycorrhiza).

The work done in recent years upon the association between roots of higher plants and microorganisms has proved to be of fundamental impor­ tance in various bra!1ches of botanical study: in the study of plant pathology, of soil activity, and of mycorrhiza. In particular there has been a tendency to emphasise the differences between those populations of microorganisms to be found in the root regions of plants and those in the soil. There are nu­ merous reviews already published, such as that of Katznelson and his col­ leagues (1), covering the subject in general. The emphasis on living root sur­ faces is understandable since these are of interest to all those engaged in the study of the growth and health of plants in natural conditions or in cultiva­ tion. Nevertheless the root regions of living plants are by no means the only series of sites bearing populations strikingly different from the remainder of the soil either in types or numbers of organisms. This point has been made by Smith (2), Harley (3), and Garrett (4) who have approached the sub­ ject from different angles, and its importance will become more apparent in the course of this article. Garrett (5) has stated that soil can be considered to show stages of loss of competitive saprophytic ability and can be grouped accordingly. His group of root-infecting fungi includes specialised parasites and mycor­ rhizal fungi. These he believes to be inhabitants of root surfaces and tissues owing to their inability to compete with saprophytic soil organisms for es­ sential nutrients.

EXPERIMENTS ON THE CARBOXYLASE OF PEA ROOTS

It is known that vitamin B1 is a growth factor for numerous bacteria and fungi including the yeasts (see the summary in Koser and Saunders (1938)). It has also been demonstrated that vitamin B1 is essential for the growth of the isolated roots of higher plants (Bonner, 1937; Robbins and Bartley, 1937). Because of this general vitamin B1 requirement of living organisms, it would seem a priori probable that the vitamin plays a role in some basic cellular process. That this is indeed the case was shown conclusively by the work of Peters and coworkers (see Peters and O’Brien (1938)) and of Lohmann and Schuster (1937). The latter workers found that the prosthetic group of yeast carboxylase is vitamin B1 pyrophosphate. In the case of yeast, vitamin B1 is, then, a constituent of a respiratory enzyme and vitamin B1 pyrophosphate is hence commonly referred to as “cocarboxylase,” a terminology used throughout this paper. Although considerable information is available concerning the role of vitamin B1 as a growth factor for roots, there is little known about the carboxylase of such roots. The present work was undertaken with the hope of elucidating possible relationships between vitamin B1 and the carboxylase of pea roots.

Excretion of Thiamin and Biotin by the Roots of Higher Plants

THE fact that soil in the immediate vicinity of plant roots supports a much higher microbial population than that existing outside the plant's zone of influence has been recognized for many years. Although it has been suggested that ‘root excretions’ account for this effect, these hypothetical exudates have never been identified, nor has their mode of action been satisfactorily explained. In studying the relation of plants to soil-borne diseases, it was considered desirable, therefore to examine the possibility that excretion of minute amounts of bacterial growth factors by the growing plant might be a fundamental factor in determining the character of the rhizosphere microflora.

Migration of Salts and Water into Xylem of the Roots of Higher Plants

Migration of Salts and Water into Xylem of the Roots of Higher Plants

Importance of Carbohydrate Supply in Legume Symbiosis

EXPERIMENTAL evidence, which has been accumulating for a number of years, but especially more recently, emphasises the importance of carbohydrate in nodule development and nitrogen fixation in leguminous plants inoculated with effective bacterial strains. There are, however, certain facts well known to plant physiologists which deserve greater emphasis in this connexion: (a) An abundant supply of nitrogen is conducive to top growth while a wide carbohydrate-nitrogen ratio favours root growth. The carbohydrate-nitrogen relations may be altered by changing the conditions for photosynthesis, by varying the nitrogen additions to the culture medium, and by supplying sugars to the roots. (b) During active photosynthesis a sugar concentration gradient1, decreasing downward, commonly exists between the leaves and roots of higher plants. These synthesised sugars usually2 do not remain long in this form; a considerable portion, 20 per cent or more, is required for respiration, while the remainder is either used for growth or is stored largely as starch.