Showing papers in "American Journal of Botany in 1953"

The association of desert annuals with shrubs

Abstract: IT HAS LONG been noted by both professional and lay observers that many species of annual plants characteristic of desert habitats are more or less strictly confined to sites beneath shrubs. Not all species of desert annuals are thus associated with shrubs. In fact, the herbs of a given area can be classified rather clearly into two groups, one nearly always growing beneath some species of shrubs, the other preponderantly occupying the broad expanses of otherwise bare soil between the widely-spaced shrubs. A few herbaceous species occur more or less indiscriminantly in both kinds of habitats. Furthermore, there are some species of shrubs that do not harbor dependent annual herbs or do so only rarely. The pattern of distribution is thus a very clear one comprising widely-spaced shrubs of several species, annual herbs growing between the shrubs, other annual species more or less confined to the bases of certain shrubs, and other shrub species which seldom or never harbor dependent herbs. This pattern of distribution and association of shrub and herb species was studied by Went (1942) in the Mojave Desert and in the Borego Valley of the Colorado Desert in Southern California. He showed a strong dependence of Malacothrix californica DC., Rafinesquia neomexicana Gray, Phacelia distans Benth., and Emmenanthe penduliflora Benth. upon sites provided by Franseria dumosa Gray, Larrea tridentata CoV., Opuntia echinocarpa Engelm. and Bigel., Hymenocloa salsola Torr. and Gray, and similar woody species. The shrub Encelia farinosa Gray, on the other hand, seldom harbored these annual herbs. He noted also that dead shrubs of any species harbored these herbs in abundance. Where the herbs were found apparently independent of shrubs, investigation invariably revealed a rotting stump of some dead shrub at the site of each. The failure of Encelic fctrinosa to harbor shrubdependent herbs was investigated by Gray and Bonner (1948a). They demonstrated in the leaves of Encelia a growth-inhibiting substance which, in either aqueous or ether extracts, killed tomato seedlings in water culture in 1-3 days. They showed also a marked depression of growth of tomato seedlings in sand culture by the application of Encelia leaves to the top of the sand and irrigation through the Encelia leaf mulch. It is suggested in their paper

Growth and nutrition of water molds in the subgenus euallomyces. ii. optimal composition of the minimal medium

Abstract: THE FOLLOWING PAPER presents the second phase of a series of studies (Machlis, 1953a) designed to increase our knowledge of the nutrition of water molds in the subgenus Euallomyces and, thereby, to permit more effective use of these fungi in the investigation of certain basic biological problems (Emerson, 1941, 1950; Emerson and Wilson, 1949; Wilson, 1952). The first paper in this series (Machlis, 1953a) showed that a number of representative strains of Euallomyces could grow in a medium which was simpler than any previously recommended solutions (Ingraham, 1951; Yaw and Cutter, 1951). This simplified medium was developed by modifying the one described by Ingraham (1951) as follows: (a) the unspecific growth factor requirement, glutamic acid, was omitted; (b) the glucose concentration was increased from 0.3 to 0.5 per cent; (c) MgS04 and (NH4) 2S04 were replaced with MgCl2 and (NH4) 2HP04 with a concomitant decrease in K112P04 so as to maintain the P04 level at its original value; and (d) nominal amounts of trace elements were added. The resulting solution, called Medium A (table 1, column 1) made possible growth, which, with respect to rate, maximum yield, and lag period, equalled or bettered that possible in the unmodified solution. In the continuation of this study of nutrition the answers to two questions were sought. In view of the changes made to obtain growth in the simplified medium, was it possible by still other modifications of Medium A, but not including the addition of new organic compounds, to enhance further the growth of Euallomyces? Secondly, is Medium A a "minimal" medium? METHODS AND MATERIALS.-The methods and the m,aterials are described in detail in the first paper of this series (Machlis, 1953a). The test organism, maintained on yeast-starch agar slants, was Allomyces javanicus var. macrogynus, strain Burma iDa. Liquid cultures were inoculated with mitospores or, occasionally, with zygotes. Medium A and subsequent modifications of it were prepared in at least two steps. The entire medium with the exception of glucose was dispensed into 125 ml. Erlenmeyer flasks and autoclaved. To these sterile flasks, previously autoclaved glucose solution was

The effects of light on respiration using isotopically enriched oxygen

Abstract: THIS PAPER describes respiratory measurements on illuminated plants using a recording mass spectrometer and employing isotopically enriched oxygen to permit the kinetic separation of oxygen intake from oxygen production This method of measuring respiration, while simple in principle, is somewhat more elaborate than the usual manometric procedures but is necessary to obtain reliable information on the respiratory rate of photosynthesizing plant cells Photosynthesis and respiration involve an exchange of the same gases, oxygen and carbon dioxide By the usual methods of measuring these processes in photo-autotrophic organisms, only net gas exchanges are observable To evaluate correctly the rate of photosynthesis from measurements made in the light, a correction must be applied for respiratory metabolism Some physiologists, recognizing the ambiguity of photosynthetic measurements, attempt no such correction and deal only with rates of "apparent photosynthesis" For certain problems (viz, in ecology) this may be sufficient or even preferable Nevertheless for the solution of other interesting and fundamental problems, reliable evaluations of "true" or "corrected" photosynthetic rates are required For example, a specific problem of considerable interest at present is the determination of the minimal quantum requirement of photosynthesis This determination requires that a suitable respiratory correction be applied to gas exchange measurements made in the light The current lack of consensus among investigators of the problem is due in part to disagreement about the manner in which the respiratory correction can best be evaluated There is an extensive literature concerning the influence of light on respiration of both photosynthetic and nonphotosynthetic organisms Photoeffects on the respiration of non-chlorophyllous plant and animal cells are usually not observed although upon illumination certain photooxidations

Growth and nutrition of water molds in the subgenus euallomyces. i. growth factor requirements

Abstract: THE SUBGENUS Euallomnyces consists of two species of water molds consistently recognized, since Kniep's discovery (1929, 1930) of their sexuality and alternation of generations, as potential tools in the investigation of certain types of biological problems (Kniep, 1929, 1930; Emerson, 1941, 1950; Wilson, 1952; Emerson and Wilson, 1949). The life cycle, which consists of alternating, equal, and independent gametophytic and sporophytic generations, is described in detail in Emerson's monograph of the genus Allomyces (1941) and in Sparrow (1943). This paper, the first of a series of three, reports on the growth factor requirements of the sporophyte. The two succeeding ones will present data on the optimal composition of the minimal medium and the carbon nutrition, respectively. The first significant study of the nutritional requirements of Euallomyces was made by Quantz (1943) with the Bali 1 strain of A. arbuscula ( A. kniepUi, according to Emerson [1941]). He obtained growth in a medium composed of KH2PO4, MgSO4, thiamine, glucose, and glutamic acid, provided the glutamic acid was from a lot containing a substance he was unable to identify. Yaw and Cutter (1951) demonstrated that methionine was the unknown nutrient requirement. In our laboratory, J. L. Ingraham, as part of his doctoral research (1951) 2, independently identified methionine as the unknown factor. The present paper is so intimately based on what Ingraham learned about the nutrition of Allomyces that it is necessary to summarize here, very briefly, certain results which are particularly pertinent. He developed a minimal medium which is described in column 1, table 1 as it appears in his thesis, except for a slightly higher CaCl2 concentration. Although glutamic acid is listed as a component, Ingraham demonstrated that a number of other substances, including certain organic acids, were equally satisfactory. By using organic acids, he was able to show that ammonium nitrogen was a satisfactory source of nitrogen. He also showed that calcium must be included in the medium and that the methionine serves as the source of sulphur. It should also be noted that Yaw and Cutter included asparagine in their minimal medium.

Studies on abscission: the inhibiting effect of auxin

Abstract: THE FIRST INDICATION that abscission of leaves is controlled by auxin was given by the work of Laibach (1933). He showed that pollinia of orchids, applied to the distal cut end of a petiole, inhibited abscission of the petiole. Orchid pollinia were known to contain auxin, and a few years later La Rue (1936) reported an experiment showing that synthetic auxin in the form of indoleacetic acid (IAA) was also very effective in delaying abscission, if it were applied in the dark or in shade. The first thorough investigation as to whether auxin was the factor which typically in nature controlled petiolar abscission was the work of Myers (1940a). Using Coleus as his experimental miaterial, he showed that those leaves which normally stayed longest on the plant were also those which gave the greatest amount of diffusible auxin; that removing the leaf blade greatly accelerated petiolar abscission; and that the presence of IAA on the debladed petiole inhibited abscission as well as did the presence of the leaf blade. The experiments cited above give a picture of abscission in which the speed with which any given petiole abscises is directly controlled by the amount of diffusible auxin coming down from the leaf blade. That is, so far as abscission is concerned, each leaf seems to act as a physiological entity. The experiments to be described below confirm and extend these earlier experiments, while the experiments in the second paper of this series (Rossetter and Jacobs, 1953) show that we must discard as being too simple the view that "with respect to abscission, each leaf is a physiological entity." METHODS. A clonal stock of Coleus blumei Benth. was grown in the greenhouse. The variety was the same as that used by Jacobs (1952), Rossetter and Jacobs (1953), and Jacobs and Bullwinkel (1953). Supplementary lighting was used during winter months to obtain faster growth. The plants were trained to a two-branched form by excising the main stem and allowing only two of the axillary branches to develop. All other axillary branches were removed. The terminology used in referring to parts of each shoot is the same as that used in Jacobs (1952) and is shown diagrammatically in fig. 1. A "spiral" pattern of deblading was used: that is, the leaf blade of one member of each leaf pair below the apical bud was excised, and the debladed petioles were arranged in a spiral on the stem (see fig. 1 of Rossetter and Jacobs, 1953). The intact leaf of each pair is listed as the control; the debladed petiole as the treated petiole. IAA and naphthaleneacetic acid (NAA) were applied at 1 per cent concentrations in lanolin; 8

The influence of light on the rate of respiration of the blue‐green alga anabaena

Abstract: THE INTERRELATIONS of photosynthesis and respiration are of perennial interest. In the past a variety of methods have been employed for investigating the effects of light on the respiratory activities of photosynthetic cells and tissues. Until recently it had been necessary to seek such effects indirectly because traditional methods of measurement were unable to distinguish between an influence of light on the rate of respiration or an effect on the rate of photosynthesis. Respiration is here defined operationally as the cellular consumption of molecular oxygen. Thus, by definition, it is not germane whether or not the consumption is balanced partly or entirely by oxygen production. Experimentally, however, the distinction is important if the measuring techniques at one's disposal can detect only net oxygen changes. To measure respiration rate in the light independently of concurrent photosynthesis becomes possible, at least in principle, with the use of isotopes of the metabolic gases, oxygen or carbon dioxide. Thus, in a closed system containing green plant tissue or whole organisms, the source of either respiratory or photosynthetic oxygen may be labelled isotopicallye.g., tracer oxygen may be introduced into the molecular oxygen of the gas phase or into the combined oxygen of the water. Alternatively the respiratory or photosynthetic carbon dioxide may be labelled with isotopic carbon. The latter device was employed by Weigl et al. (1951) in the first application of the isotopic method to this kind of kinetic problem. This principle of effecting a kinetic separation of respiration and photosynthesis by tagging the gas consumed but not the gas produced has been employed in a number of different studies in the authors' laboratory using isotopically labelled oxygen and carbon dioxide and employing a recording mass spectrometer to follow the metabolic gas exchanges (Brown et al., 1952; Mehler and Brown, 1952; Van Norman and Brown, 1952; Brown, 1953). In general it has been found with a variety of algae and higher plants that light does not exert a marked effect on the respiratory rate of photosynthetically active cells or tissues. Never-

2,4-dinitrophenol and plant respiration

Abstract: NEWCOMB (1950) has briefly reviewed the pertinent literature in his report on the respiration of tobacco callus and its response to 2,4-dinitrophenol (DNP). It is now established that in a wide variety of tissues and organisms (including fungi, bacteria, animals, and higher plants) DNP and allied substances have profound effects on metabolism. In low concentrations, of the order of 10-5 M at pH 5.0, they may prevent growth and other energy requiring events while respiration rate, as judged by 02 uptake, is unaffected or even strongly stimulated. In more recent papers on higher plant tissues, effects on glucose uptake (Stenlid, 1949) and salt uptake (Robertson et al., 1952) and associated respiratory responses to DNP have been described. The experimental part of the present paper is concerned with respiratory responses. 02 uptake, C02 output, and fermentation products liave been measured to obtain quantitative relationships between respiratory reactants and end products over a wide series of finely graded dilutions of DNP, and to construct a general picture of its effects on several plant tissues.

Comparative structure and possible trends of specialization of the phloem

Abstract: INFORMATION ON evolutionary changes in the phloem is meager and fragmentary. In contrast, data on the phylogenetic. trends in the xylem are extensive and well correlated (cf. Tippo, 1946). There are several reasons for this difference in our knowledge of the two vascular tissues. The xylem cells generally have rigid persisting walls, whereas the phloem contains a large proportion of soft-walled cells that readily collapse or become distorted in material not specifically treated for the preservation of its original structure. This characteristic of the phloem is in part responsible for the commonly poor preservation of this tissue in fossils (cf. Hofmann, 1934) and limits the value of material preserved in dehydrated state (e.g., herbarium inaterial) for the study of phloem. With increasing age the conducting elements and certain parenchyma cells in the phloem become much modified before the tissue as a whole ceases to be concerned with vital activities. Therefore, the most characteristic cells of the phloem, the sieve elements, generally must be studied in an active, conducting tissue, especially if physiologic considerations are included. Such tissue is available onlv during a part of the season. The xylem, on the other hand, shows relatively minor morphologic changes with increasing age, and, when properly manipulated, it continues to reveal the original structure even after it has been dead for many years. Much can be learned about the xylem without a consideration of the cytologic characteristics of this tissue. The understanding of the phloem tissue, on the other hand, would be incomplete without a study of the cytophysiology of the living components of the tissue, particularly of the sieve elements. Such a study involves a consideration of developmental changes and requires specialized and exacting techniques. The foregoing comparison of xylem and phloem, with regard to their structural peculiarities, emphasizes the fact that availability of living material and the treatment of such material with due recognition of the cytological and physical instability of the phloem tissue are basic requirements for successful research on phloem. Extensive comparative studies on the phloem of living species can be expected to compensate for the lack of an adequate fossil record on the primitive structure of this tistue. Judging by the angiosperms (Bailey, 1949),

The effect of certain metabolic inhibitors on vascular tissue differentiation in isolated pea roots

Abstract: THE SEQUENCE of events occurring during cellular differentiation may be described and, to some degree, understood in terms of manifest structural changes which the individual cell undergoes during its ontogeny. Yet little is known concerning the biochemical processes in plant tissues which are fundamentally related to these ontogenetic changes. Isolated pea root tips, cultured in the dark in a sterile synthetic nutrient medium, grow in a reproducible manner, showing usual patterns of tissue differentiation. Inhibition of elongation in cultured roots may be produced by a variety of metabolic inhibitors which act through their effect on biochemical processes essential for normal root growth. This paper describes the effects of three inhibitors, indole-3-acetic acid, iodoacetic acid, and 2,4-dinitrophenol on primary vascular tissue differentiation in isolated pea roots which have been subjected in each case to reagent concentrations causing approximately 90 per cent inhibition of root elongation. The purpose of such a study is to attempt to relate biochemical processes to the known anatomical stages in primary vascular tissue differentiation. Attempts to relate root elongation and cellular differentiation have been made in several studies of inhibited root elongation. As early as 1893 Pfeffer reported apparent acceleration of acropetal differentiation of vascular tissue elements in the roots of a number of plants when root elongation was inhibited mechanically by plaster of Paris encasement of the root. Using Vicia faba roots grown in solid gypsum, Pfeffer found acropetal differentiation of pitted vessel elements to within 1 mm. from the tip at the end of 15 days, as compared to 25-35 mm. in uninhibited roots. Pfeffer's finding has been substantiated by numerous subsequent workers (Nathansohn, 1898) . More recently Kojima (1931, 1933), also using the technique of Pfeffer, reported that such mechanical pressure inhibits cell division in the root tip as early as 16 -hr. after beginning treatment. In inhibited roots, xylem elements were apparent at an average distance of 1.4 mm. from the root apex at the end of one week, while in control roots, xylem was apparent first at 13.7 mm. Kojima (1931) pointed out that in terms of position, the inhibited roots appeared to show accelerated differentiation of xylem cells, but in terms of age of cells, cellular differentiation in the inhibited roots was actually hindered. He concluded

Cytoplasmic inheritance and reciprocal amphiploidy in tragopogon

Abstract: DISCOVERY OF EXTENSIVE NATURAL HYBRIDIZATION and two newly-formed amphiploid species in the genus Tragopogon (Ownbey, 1950) has led to an ambitious program of cytogenetic investigation of species relationships in this Old World genus of the Compositae. Although Tragopogon has furnished some classic examples of interspecific hybridization over a period of nearly two centuries, only a single comprehensive cytogenetic study, that of Winge (1938), has been made. The species of this genus, however, are uniquely suited to such studies. Not only are interspecific hybrids easily obtained, but the clear-cut morphological character-. istics and distinctive karyotypes of the various species (Ownbey and McCollum, in press) make cytogenetic analyses unusually instructive. In an attempt to resynthesize the two tetraploid species, Tragopogon mirus (amphiploid T. dubius X plorrifolius) and T. miscellus (amphiploid T. dubius X pratensis), and the naturally occurring hybrids of the diploid species mentioned, reciprocal cross pollinations were made. Five of the six possible combinations were successful (only the cross T. dubius 9 X pratensis 8 failed), and a selfed F2 population was grown from each of the five. In addition, reciprocal cross pollinations were made between one race of T. mirus and two morphologially different races of T. miscellus and a number of tetraploid interspecific hybrids obtained. Striking reciprocal differences appeared in the F1 hybrids involving T. pratensis and apparently the same phenomenon occurs on the tetraploid level. The present paper will consider these possible additional examples of cytoplasmic inheritance. MATERIALS AND METHODS.-The diploid plants used in most of these studies were transplanted into the garden from populations growing without cultivation at Pullman, Washington (T. dubius and T. p!orrifolius), and Moscow, Idaho (T. pratensis). The plants of T. dutbius and T. pratensis were very uniform, but those of T. porrifolius included both paleand dark-liguled individuals. Only plants of this species with dark violet ligules were used for crossing, but it is not improbable that some were heterozygous in this respect. The tetraploid plants used were grown from open-pollinated seeds from "wild" plants collected in Pullman (T. mirus) and Moscow (T. miscellus). Two races of the latter were used, a short-liguled form from one of the original colonies and a long-liguled form from a distinct population about 1/4 mi. distant. The two

Chromosome studies on ferns

Abstract: THESE STUDIES were undertaken to add to our knowledge of the chromosome numbers of the ferns of eastern North America. Since many of the species are also native to the British Isles it was felt that the findings of Manton (1950) could be checked for technical accuracy. Also, it could be seen if the chromosome numbers of species collected in Britain were identical with the chromosome numbers of the same species collected in Ontario, Canada, or whether geographical races are common in the Filicales.

Identification of crystalline inclusion bodies extracted intact from plant cells infected with tobacco mosaic virus

Abstract: THE INTRACELLULAR amorphous and crystalline inclusion bodies found particularly in the epidermal cells of plants infected with tobacco mosaic virus (TMV) have been the object of considerable investigation following the first description of them by Iwanowski (1903). There has been much speculation as to the nature and composition of both types of inclusions. The amorphous inclusions were called X-bodies by Goldstein (1924, 1926), who postulated that they were the infectious agent, and who also advanced the notion that the crystalline inclusions ("striated bodies") were "reaction products" of the cell. The most critical observations of crystalline inclusion bodies have been made by Beale (1937), who described and illustrated the transformation of crystalline plates into needle crystals upon the addition of dilute acid or salt to the water in which epidermal strips had been mounted under the microscope. Beale considered these needle crystals to be identical with those obtained by Stanley, and concluded that the crystalline inclusions were the source of Stanley's purified TMV protein. The amorphous inclusions (X-bodies) found in cells of plants infected with aucuba mosaic virus have been isolated by Sheffield (1939), who was able to show that they contain active virus. She was unable to isolate any crystalline inclusions, however, and consequently could not make an unequivocal identification of their contents. Interest has recently been revived concerning the nature of the hexagonal crystalline inclusion bodies by the publication of a paper by Wilkins et al. (1950), who have investigated particularly, some of the optical properties of the crystals. They report that, in the great majority of the crystals, the previously observed (Bawden and Sheffield, 1939) striations are seen only between crossed Nicols and when the crystal is observed on edge with its principal axis near the extinction position. (The "principal axis" is a direction perpendicular to the hexagonal faces of the crystal.) They conclude that the crystals are built,up of thin, flat layers lying parallel to the hexagonal face of the crystal, and that within each layer the individual TMV rods are aligned parallel to each other, but with an orientation not quite parallel to that of the TMV rods in the adjacent layers. The principal axes of adjacent layers would consequently be non-parallel by a few degrees. This conclusion is largely based upon their reported observation that the light and dark bands (the striations) appear to interchange

Cytogenetic studies of deficient‐duplicate chromosomes derived from inversion heterozygotes in maize

Abstract: THE PRESENT INVESTIGATION was the outgrowth of studies of the chromosome homology of maize from Central and South America. Strains of maize from Latin America exhibit an extraordinarily wide range of phenotypic appearance owing to genic differences. Since many of these strains presumably have been isolated for centuries, it was thought possible that the genic diversity had been accompanied by changes in chromosomal structure. Cooper and Brink (1937) found no evidence of reciprocal translocations in their study of chromosome homology in 55 strains of maize from Latin America but their method of analysis would not permit the detection of inversions. Inasmuch as inversions in Drosophila populations are of frequent occurrence (Patterson and Stone, 1952) while reciprocal translocations are rarely encountered, it seemed desirable to test exotic races of maize for the presence of inverted segments. F1 seed from crosses of two genetic testers with 90 different races of Latin American origin was obtained through the courtesy of Dr. P. C. Mangelsdorf. Eighty-five of these hybrid combinations involved a Pr-tester and five, a Tu stock. Microsporocytes for cytological examination were collected from a number of plants of each F1 family. Pollen samples were obtained for all of the F1 individuals. Plants heterozygous for a single reciprocal translocation usually have 50 per cent of aborted pollen and ovules while plants heterozygous for inversions produce varying amounts of aborted grains depending on the frequency of crossing over within the inverted segment. The absence of any considerable amount of aborted pollen indicated that all of the 85 progenies involving the Pr-tester possessed chromosomes with no major structural differences. In two of the five families where the Tu line was used, all of the plants had approximately 20 per cent aborted pollen while in two other families one half of the plants had a comparable degree of pollen abortion and the other half had all normal grains. The fifth family consisted only of plants with all normal pollen. When the cytological material from the four families with aborted pollen was examined it was found that all plants with aborted grains were heterozygous for a paracentric inversion in chromosome 3. There was no evidence of reciprocal translocation in any of the 90 exotic races nor was there any indication of inversions. The inversion found was obviously one which came from the Tu stock where it was segregating since some plants were homozygous normal, others homozygous for the inversion and some were heterozygous. It should be recognized

Photoreversal of ultraviolet effects in soybean leaves

Abstract: effects of ultraviolet radiation on plant growth, noted that injury was found only when the radiation was used to interrupt a dark period. Results of a more detailed study on the effect of ultraviolet radiation on a higher plant are reported here. These results point to a similarity in the nature of photoreactivation in higher plants and in lower plants and animals. METHODS.-Preliminary experiments indicated that soybean leaves (Glycine max, var. Wabash) irradiated with ultraviolet lost chlorophyll when kept in darkness for about 3 days, while leaves exposed to visible light for about 10 min. following ultraviolet irradiation remained green during the same dark period. The loss of chlorophyll in ultraviolet-irradiated leaves has been used as a measure of radiation damage and has been found to be