bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaf anatomy of ocotillo (Fouquieria splendens; Fouquieriaceae), especially vein endings and associated veinlet elements
Authors: Lersten Nels R. , Carvey Kathryn A.
Published: September 2008

Leaves of ocotillo, a shrub of southwestern North America, lack xeromorphic features. After rain, a few leaves at each node expand and function for a short period, then abscise. This cycle may be repeated several times each year. Palisade layers occur interior to both epidermal surfaces, and the spongy mesophyll is reduced. Venation is camptodromous, with many vein endings. In the distal lamina half, sclerified bundle sheath cells ("veinlet elements") become increasingly common in minor veins and vein endings. Near the leaf tip, adjacent mesophyll cells also become sclerified, to such an extent that some areoles appear filled with these cells ("accessory veinlet elements"). Phloem is conspicuous because it stains intensely and occupies more volume than xylem in most bundles. In minor veins and vein endings, sieve tube members become increasingly more slender than associated phloem cells, and xylem frequently changes its position, becoming parallel with, or even abaxial to, the phloem. Phloem mostly ends before, less commonly with, the xylem.
A freeze-etch study of plant cell walls for ectodesmata
Authors: Lyon N. C. , Mueller W. C.
Published: September 2008

Leaf tissue of Phaseolus vulgaris L. and Plantago major L. was prepared by the freeze-etch technique and examined in the electron microscope for the presence of ectodesmata. No structures analagous to ectodesmata observed with light microscopy could be found in freeze-etched preparations of chemically unfixed material or in material fixed only in glutaraldehyde. Objects appearing as broad, shallow, granular areas in the epidermal cell wall beneath the cuticle were observed in leaf replicas after fixation in complete sublimate fixative, the acid components of the sublimate fixative, or mercuric chloride alone. Because of their distribution and location, these objects can be considered analagous to ectodesmata observed by light microscopists. Because these areas occur only in chemically fixed walls and are localized within the walls in discrete areas, their presence supports the contention that ectodesmata are sites in the outer cell wall with defined physicochemical characteristics.
Nuclear proteins of quiescent and mitotically active cells in shoot meristems of Tradescantia paludosa
Authors: Tobin R. S. , Yun Kyu-Byung , Naylor J. M.
Published: September 2008

In inhibited lateral buds of Tradescantia paludosa, interphase nuclei in the apical zone of inhibition contain higher levels of arginine per unit DNA than those of mitotically active cells in interphase or prophase. Supplementary dye-binding experiments suggest that this reflects a corresponding difference between the composition of the histone complement of chromatin in the two cells populations. The possible implications of this phenomenon are discussed.
Translocation of mycoplasma-like bodies through sieve pores in plant tissue cultures infected with aster yellows
Authors: Jacoli G. G.
Published: September 2008

Ultrathin sections of carrot root explants infected with aster yellows showed extensive invasion of the phloem area by mycoplasma-like bodies (MLB's). MLB's were equally distributed on both sides of the sieve plates. The sieve pores in infected tissue cultures appeared mostly to be open and the apparent plugging sometimes seen was due to fixation artifacts as well as to MLB's. As pleomorphic structures, MLB's translocated with or without distorting their shape, according to their size and the degree of plugging of the sieve pores. Small particles, up to 200 nm diam, appeared to move with little or no distortion, but particles larger than 200 nm diam changed their shape to pass through the sieve pore. Three phases were postulated to explain the translocation of large MLB's.
The hexosamine content of leaves
Authors: Racusen David , Foote Murray
Published: September 2008

Leaves of 20 species contained both polymer-bound and 80%-acetone-soluble forms of hexosamine. Similar amounts of polymer-bound hexosamine (about 1.9 μg/mg protein) were found in all the leaves, suggesting that it may be an essential element of membrane structure.
Soluble carbohydrates in soybean
Authors: Phillips D. V. , Smith A. E.
Published: September 2008

Gas–liquid chromatographic analysis of the trimethylsilyl ethers of the ethanol (90%)-extracted carbohydrates (soluble carbohydrates) from soybean (Glycine max) plants demonstrated the presence of major quantities of O-methylinositol, glucose, fructose, and sucrose, minor quantities of myo-inositol, and two unidentified components. In leaf blades and petioles of 6-vveek-old plants, O-methylinositol accounted for more than 50% of the total soluble carbohydrates present.
Subbaromyces splendens: development and infrastructure
Authors: Cole Garry T. , Hardcastle Ronald V. , Szaniszlo Paul J.
Published: September 2008

Perithecial formation, the mechanism of ascospore release, and conidiogenesis in Subbaromyces splendens Hesseltine are described from light microscopic and scanning electron microscopic investigations. Growth of the neck of the perithecium, which apparently involves elongation of hyphal cells, is pointed out as an unusual developmental feature in this fungus. The potential of using S. splendens as an experimental organism in studies of fungal morphogenesis is discussed.
Investigations of growth-promoting factors in conditioned soybean root cells and in the liquid medium in which they grow: cytokinin-like compounds
Authors: Sargent P. A. , King J.
Published: September 2008

By using the soybean cotyledon callus bioassay for cytokinin-like compounds and two methods of extraction of cytokinins from plant tissues, the presence of growth-active compounds of a purine nature has been detected in soybean (Glycine max. L. cv. Mandarin) root cell suspension cultures growing in a medium containing NH4+. These compounds can be added to residual NH4+, glutamine, and an adequate supply of amino acids as conditioning substances in these cultures.
Quantitative comparison of foliage display in two plots of corn
Authors: Kyle W. J. , Davies J. A.
Published: September 2008

A quantitative comparison of foliage display in two plots of corn, seeded differently, revealed that the plants in both have essentially the same architecture despite differences in planting procedure. No significant azimuth preferences were found. Investigations of leaf inclinations indicated that leaf distribution functions are very close to the theoretical spherical distribution, with the result that radiation interception calculations are independent of solar altitude. This greatly facilitates the incorporation of canopy structure variables into theoretical models of canopy radiation interception.
Postinfectional inhibitors from plants. XIII. Fungitoxicity of the phytoalexin, capsidiol, and related sesquiterpenes
Authors: Ward E. W. B. , Unwin C. H. , Stoessl A.
Published: September 2008

Capsidiol, the phytoalexin from peppers, rishitin, the phytoalexin from potatoes, and 20 other derivatives or model compounds related to capsidiol were compared for fungitoxicity against a range of pathogenic and non-pathogenic fungi, using spore germination and growth assay procedures. Capsidiol was the most active compound tested (mean effective dose (ED50) vs. Phytophthora infestons, 1 × 10−5 M) and all derivatives examined had decreased activity. No correlations were found between sensitivity to capsidiol or rishitin and pathogenicity for peppers or potatoes, nor were there any clear correlations between structure and activity. Activity was greatly influenced by minor structural changes and such changes frequently had differential effects on different fungi. The results suggest that phytoalexins such as capsidiol, even if not primary determinants of disease resistance, could influence the progress of disease and the sequence of subsequent colonization.
Production and bioassay of gene-specific RNA determining resistance of wheat to stem rust
Authors: Howes N. K. , Samborski D. J. , Rohringer R.
Published: September 2008

Gene-specific RNA directly involved in resistance of wheat (Triticum aestivum L.) to stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. and E. Henn.) was produced only in interactions involving an avirulent race of stem rust. The genotype of the host did not affect the production of this RNA, suggesting that the RNA involved in the expression of resistance is a product of the gene for avirulence.Several parameters affecting the bioassay used for the detection of this active RNA were investigated. These included temperature, infection density, the time interval between infection and injection of extract, and the time interval between injection and harvest.A comparison between the number of necrotic sites produced after injection of active RNA into leaves of the resistant line and the number produced in the incompatible interaction showed that 2–7% of the potentially reactive sites respond in the bioassay by becoming necrotic.The active RNÀ isolated from a stem rust – wheat interaction involving a given gene for avirulence produced a response in bioassay plants only when both the corresponding gene for resistance and stem-rust haustoria were present.
Changes in leucyl, seryl, and tyrosyl tRNAs in aging soybean cotyledons
Authors: Pillay D. T. N. , Cherry Joe H.
Published: September 2008

Application of different concentrations of the naturally occurring cytokinin zeatin 6(4-hydroxy-3-methyl trans-2-butenylamino)purine caused changes in one or more species of tRNAs. With the depletion of storage products from senescing cotyledons quantitative changes in tRNAleu1, 5, 6, tRNAser1–3, and tRNAtyr1–4 were observed. Higher concentrations of zeatin applied as a single spray did not produce significant changes either in the cotyledon or the hypocotyl. The relationship of cytokinin activity to senescing soybean cotyledons is discussed.
Montane zone vegetation of the Alsek River region, southwestern Yukon
Authors: Douglas George W.
Published: September 2008

A rapid reconnaissance technique was used to sample montane vegetation in the Alsek River region, southwest Yukon. Twenty-one major community types are described from 223 sample stands. The forest vegetation of the region is interspersed with numerous shrub and herb vegetation types. This vegetation diversity is extraordinarily rich for a forest region and is due primarily to the variable climate (both local and regional) and the frequency of disturbance by fire and geomorphological processes.Ten communities, within four forest types, are distinguished in the region. The most widespread forest type is dominated by Picea glauea. The remaining three are dominated by Populus tremuloides, P. balsamifera, and Salix scouleriana. Shrub communities recognized include the Betula glandulosa – Festuca altaica, Salix glauca, Juniperus communis – Arctostaphylos uva-ursi, Artemisia frigida – Poa glauca, Artemisia alaskana, and Salix setchelliana – Oxytropis campestris types. Herb communities distinguished include the Carex sabulosa, Hedysarum boreale – Agropyron yukonense, Calamagrostis, and Agropyron yukonense types.Examination of diversity and its components during succession in the Alsek River region indicates that, in general, richness and general diversity increase and dominance decreases until the later stages of succession, when these trends are subsequently reversed. Evenness, while somewhat more variable, showed trends similar to that of the dominance component. Deviations from these trends occurred when the habitat was either extremely homogeneous or extremely heterogeneous.The flora of the region is relatively rich and derived from many North Temperate elements. The largest segment (64%) is derived from the more northern (Circumarctic-alpine, Circumboreal-montane, Amphi-beringian, Amphi-atlantic) elements.
Analysis of sugars in dwarf mistletoe nectar
Authors: Brewer J. W. , Collyard K. J. , Lott Jr. C. E.
Published: September 2008

Nectar produced by pistillate flowers of the dwarf mistletoe Arceuthobium abietinum Engelm. was analyzed by thin-layer and gas–liquid chromatography. The inconspicuous (0.5–1.5 mm) flowers produce relatively large (0.24 μliter) droplets of highly concentrated nectar (58–92% total solids, expressed as sugars). The major components were glucose (48%), fructose (39%), and sucrose (11%). Traces of other sugars were also present. It is suggested that nectar of this high sugar content is probably a strong insect pollinator attractant, and this, in turn, may be a major factor in the successful spread of the parasitic dwarf mistletoes.
Seasonal changes in photosynthate transport within elongating shoots of Populus grandidentata
Authors: Donnelly John R.
Published: September 2008

Individual leaves on 5-year-old suckers of bigtooth aspen (Populus grandidentata Michx.) were exposed to 14CO2 to detect seasonal changes in photosynthate transport. As new leaves developed at the base of currently elongating shoots, they initially acted as translocation sinks and utilized stored carbohydrates. Basal (first-formed) leaves began to translocate around the first of June. Initially, these leaves transported mainly acropetally to the shoot tip, but within 2 weeks they were transporting photosynthate basipetally toward the main stem. Translocation patterns from leaves midway on the shoot were similar, but these leaves continued to export mainly to the stem tip until early July. Tip (last-formed) leaves did not begin to translocate significant quantities of photosynthates until late July.Basal, middle, and tip leaves transported photosynthates into axillary buds; base leaves mainly in June, middle leaves mainly in July, and tip leaves mainly in August. The terminal bud imported photosynthates from all leaves on the shoot and accumulated several times more 14C label than did axillary buds at the base of the shoot.
Differences in the uptake of glucose and glycerol by Tieghemiomyces parasiticus in axenic culture
Authors: Binder Frank L.
Published: September 2008

Tieghemiomyces parasiticus, a biotrophic haustorial mycoparasite, makes excellent axenic growth on a glycerol – casein hydrolysate medium, while growth on a glucose – casein hydrolysate medium is equivalent to that of a control medium containing only the nitrogen source. A comparison of 14C-glucose and 14C-glycerol uptake indicates these substrates enter this mycoparasite at significantly different rates. Incorporation of 14C-glucose is extremely slow and limited, while 14C-glycerol incorporation is very rapid. Excellent axenic growth of this mycoparasite occurs when a glucose – casein hydrolysate medium is supplemented with the surface-active agent Tween 80. These findings suggest that the inability of glucose to support growth results from the inability of this substrate to readily enter the vegetative hyphae of this mycoparasite when cultured axenically.
Fine structure of the septum in Wallemia sebi
Authors: Terracina Fred C.
Published: September 2008

The septa of the deuteromycete Wallemia sebi (Fr.) v. Arx have expanded pore margins surrounding a central pore and lack parenthesomes. At each end of the pore there is an electron-dense region with a distinct five-banded pattern (three electron-dense bands separated by two less-electron-dense bands) oriented parallel to the septum. These septa are compared with similar septa in phycomycetes, the dolipore septa reported in the ascomycetous yeast genus Ambrosiozyma and the dolipore–parenthesome septa of the basidiomycetes. It is proposed that the term dolipore be applied to any septum having expanded pore margins.
Effects of pretreatment with low ozone concentrations on ozone injury to bean and mint
Authors: Runeckles V. C. , Rosen P. M.
Published: September 2008

Acute ozone injury to bean (an ozone-sensitive species) is reduced more than 50% by pretreatment with a low level of ozone (0.02 μl/liter), as compared with pretreatment in ozone-free air. In contrast, mint (an ozone-tolerant species) demonstrates a synergism of low and injurious doses. The reduction in susceptibility of bean is accompanied by a long-term effect of low ozone levels on stomatal conductance.
In vitro studies on the induction of sporogenous tissue on leaves of cinnamon fern. III. The role of reduced nitrogen
Authors: Harvey William H. , Caponetti James D.
Published: September 2008

Excised set III leaf primordia of cinnamon fern cultured on either Knop's or Knudson's medium containing ammonium sulfate produced fertile leaves provided that the media included the appropriate concentration of sugar and the cultures were exposed to the optimal environmental factors. The highest percentage of fertility (about 80%) was obtained on leaves cultured on media containing 6% sucrose and the usual concentration (250 mg/liter) of ammonium sulfate, and placed in continuous darkness at 26 °C. However, leaf primordia cultured under the same conditions without ammonium sulfate or this substance included at concentrations 3 × or higher than the usual amount produced sterile leaves only.From other experimental evidence, a possible mechanism by which sugar supply and ammonium ions influence development is postulated and discussed for the induction of sporangia on cultured cinnamon fern leaves. However, further research is necessary to uncover the biochemical role of reduced nitrogen and carbohydrate in leaf fertility.
Electron microscopy studies on infection of resistant (Sr6 gene) and susceptible near-isogenic wheat lines by Puccinia graminis f. sp. tritici
Authors: Skipp R. A. , Harder D. E. , Samborski D. J.
Published: September 2008

Intracellular hyphae, haustoria, and infected host cells in young stem rust infections of a wheat line containing resistance gene Sr6 were compared by electron microscopy with those of a near-isogenic susceptible line. Mesophyll cells of the resistant line which had undergone a rapid necrotic response to haustorial invasion were collapsed and lacked the thin layer of cytoplasm that typically bounded the vacuole of infected cells of the susceptible line. Instead, the lumen was filled with an electron-dense ground material of mixed cytoplasmic and vacuolar constituents containing organelles at various stages of disorganization. Haustoria within these cells were necrotic, as were their mother cells. Apart from a dense staining of mitochondrial membranes there was little evidence of damage to the infection hypha proximal to the septum of the haustorium mother cell. The cytoplasm of host cells adjacent to those showing necrosis was often diffuse and vesiculated. A deposit of electron-dense granular material was found between the wall of a necrotic cell and its plasmalemma, and a similar deposit was present inside the adjoining wall of a contiguous non-necrotic cell.These findings are discussed in relation to the inhibition of fungal growth that accompanies host cell necrosis in the resistant wheat line.
Effect of high temperature on the growth, sporulation, and pigment production of Botryodiplodia theobromae
Authors: Uduebo Agnes E.
Published: September 2008

The effect of a high temperature on the growth, sporulation, and pigment production of Botryodiplodia theobromae Pat. was investigated. At 35 °C vegetative growth was diminished, there was no sporulation, and a pink pigment was produced. The pigment was released into the culture medium. The inhibitory effect of the high temperature on sporulation was considered to be partially owing to the reduced vegetative growth. Other possibilities are discussed. The pink pigment was preferentially produced in acid media. It inhibited neither growth nor sporulation under the usual conditions.
Chromosome numbers from pollen in some North American Impatiens (Balsaminaceae)
Authors: Chinnappa C. C. , Gill L. S.
Published: September 2008

Chromosome counts for eight species of Impatiens from North American populations have been determined from herbarium specimens. The chromosome number n = 10 for I. ecalcarata Blank, is a new report. It is apparent from the present survey that there are at least three basic numbers (n = 7, 10, and 13) represented in North America as opposed to the one (n = 10) suggested by the earlier workers.
The occurrence of functional non-chlorophyllous guard cells in Paphiopedilum spp.
Authors: Nelson Sherman D. , Mayo James M.
Published: September 2008

Hypostomatous lady slipper orchids, Paphiopedilum spp., were found to have non-chlorophyllous epidermal cells, including guard cells. The lack of chlorophyll within the guard cells was demonstrated by fluorescence microscopy. A "normal" chlorophyllous mesophyll was present. The leaf resistances of intact leaves were about 5–10 s cm−1 in the light and were greater than 100 s cm−1 in the dark, indicating light opening and dark closure of the stomata. A CO2-dependent stomatal response (i.e., a tendency to close at elevated CO2 levels) was demonstrated, as was a CO2-independent light response (i.e., greater opening in blue light than in red). This provides direct evidence to support the idea that guard cell chlorophyll is not necessary for stomatal functioning.
Rhymokalon, a new plant with cladoxylalean anatomy from the Upper Devonian of New York State
Authors: Scheckler Stephen E.
Published: September 2008

Rhymokalon trichium, gen. et sp. nov., is a new plant with cladoxylalean anatomy from Upper Devonian rocks (Oneonta Formation) of New York. The new plant consists of three orders of helically arranged branches. Compressed axes have numerous longitudinal ridges, which are interpreted as resulting from the collapse of external tissues onto the dissected xylem during compaction of the sediment. Distal branchings bear small numbers of fine hairs. Petrified basal branches contain a multiribbed stele, from which are produced numerous xylem strands which enter the branches. Lateral branches have many xylem strands, which divide and anastomose freely. This type of anatomy relates Rhymokalon best with Cladoxylales, a group of Devonian and Carboniferous plants with dissected xylem.
Ascospore germination, growth in culture, and imperfect spore formation in Cookeina sulcipes and Phillipsia crispata
Authors: Paden J. W.
Published: September 2008

Ascospores of Cookeina sulcipes germinate by one of two modes: (1) by the production of blastoconidia on sympodially proliferating conidiogenous cells which may arise from any point on the spore surface, and (2) by a thick polar germ tube. No ascospores were seen to germinate both ways. The conidiogenous cells are occasionally modified into narrow hyphae. The blastoconidia germinate readily but are evidently very short-lived. Ascospores of Phillipsia crispata germinate by two polar germ tubes; there is no formation of blastoconidia. In both species the inner ascospore wall separated from an outer wall layer during germination. In culture both C. sulcipes and P. crispata form arthroconidia. The arthroconidia are uninucleate; they germinate readily and reproduce the species when transferred to fresh plates.
Thielavia australiensis sp. nov., a new thermophilic fungus from incubator-bird (mallee fowl) nesting material
Authors: Tansey Michael R. , Jack Michele A.
Published: September 2008

A new thermophilic species of Thielavia Zopf, T. australiensis, isolated from nesting material of an incubator bird (mallee fowl, Leipoa ocellata Gould), is described and illustrated.
Effect of naphthalene and aqueous crude oil extracts on the green flagellate Chlamydomonas angulosa. II. Photosynthesis and the uptake and release of naphthalene
Authors: Soto C. , Hellebust J. A. , Hutchinson T. C.
Published: September 2008

Comparisons have been made of the effects of crude oil extracts and naphthalene on the photosynthesis of the alga Chlamydomonas angulosa. The addition of the hydrocarbon naphthalene to C. angulosa cultures causes an immediate and almost complete loss of photosynthetic capacity. When cells that have been incubated in closed systems containing naphthalene-saturated media are transferred to open systems which allow loss by volatilization of naphthalene, the rate of recovery of photosynthesis is inversely proportional to the length of incubation in the closed system with naphthalene. Incubation of cells in open systems with media containing aqueous crude oil extracts has no significant effect on their photosynthetic capacity as compared with that of cells incubated in control media. However, the photosynthetic capacity is decreased when cells are incubated in closed systems with media containing aqueous crude oil extracts. This is followed by a gradual recovery with time of incubation after treatment in the closed systems.Experiments using labelled naphthalene indicate that C. angulosa cells accumulate naphthalene from the medium in closed systems for up to 7 days. When such cells are transferred to fresh media not containing naphthalene, there is an almost immediate loss of the aromatic hydrocarbon from the cells. However, when cells are retained in their original medium after opening the culture system to allow naphthalene to escape, the decrease in naphthalene content per cell appears dependent upon resumption of cell division and occurs in a stepwise manner, which suggests cell retention rather than an actual loss of naphthalene to the medium.
On the physiology of a fungus symbiotic with orchids
Authors: Harvais Gaëtan , Raitsakas Ain
Published: September 2008

A fungus (Rs10) symbiotic with orchids was grown in axenic liquid-still culture on mineral–sugar media. Dextrose was limiting at 1% and 2%, with mycelium dry weights directly proportional to the amount of sugar in the medium, but not at 3%. Sucrose gave similar results and was converted into reducing sugars, in the medium, in excess of utilization. With 3% sugar growth was not much better than with 2%, and daily dry weight values were more variable after the active growth phase. With 1% and 2% dextrose in the media, and 10, 20, and 30 ml/flask, dry weight was not affected by the different aeration conditions. Inocula failed to grow on media with pH 3.0, but growth seemed normal with pH 4.5. Ninhydrin-positive substances were not released in the culture media but were found in ethanol extracts of the mycelium. They were more abundant during the active growth phase and on media with 1% vs. 2% dextrose; with less sugar, high levels were maintained for longer periods. They consisted mainly of glutamic acid, glutamine, and aspartic acid, with some fluctuations in concentration related to growth phase. Metabolism seemed different on media with ammonium + nitrate vs. nitrate alone as nitrogen source. The hyphal wall contained chitin.Protocorms of Dactylorhiza purpurella (an orchid with which Rs10 is symbiotic) were grown on eight nutrient media with one amino acid in each, until only the latter were depleted. The best results were with glutamic acid, ornithine, and arginine, followed by aspartic acid and glycine. Alanine, serine, and lysine were toxic. N-acetyl-D-glucosamine derived from chitin was drip-fed to other cultures. It was ineffective at low and toxic at high concentrations.Implications of the results relating to mycorrhizal associations are briefly discussed.
Vitamin production by a fungus symbiotic with orchids
Authors: Harvais Gaëtan , Pekkala David
Published: September 2008

The results of earlier axenic and dual cultures of Dactylorhiza purpurella and its symbiont indicated that the fungus may provide the orchid with some, if not all, of the vitamins in yeast extract. Here, the fungus was studied for such production in axenic liquid still cultures on mineral–sugar media, using bioassays and chemical methods. The latter proved too insensitive. Bioassays were considerably more sensitive and, after various modifications of the techniques, gave consistent results. They showed that about 33 parts per billion (ppb) nicotinic acid and (or) nicotinamide ('niacin'), 1.5 ppb thiamine, but no pantothenic acid, were readily secreted in the culture medium by the fungus. These were, respectively, at about 10% and 50% of their concentrations in the medium used for axenic orchid cultures. 'Niacin' production was studied further. There was no real correlation with dry weights. Production was greatest with 1% dextrose (vs. 2%), during the active growth phase, and on a medium containing ammonium and nitrate vs. nitrate alone as nitrogen source. On that medium, greatest yield was under restricted aeration, and conversely for the nitrate medium. Ten micrograms 'niacin' per gram dry mycelium was released into the filtrate, and 14 μg, i.e. 40% more, was retained in the mycelium. Ammonium seems more important in the synthesis of 'niacin' than of amino acids. These findings may be of great significance in relation to symbiotic associations in dual cultures and in nature. They indicate that orchids would derive more benefit from active endophytic fungi than upon their digestion.
Morphology and zoospore discharge in single-pored, epibiotic Chytridiales
Authors: Barr D. J. S.
Published: September 2008

Five eucarpic, epibiotic chytrids with single discharge pores were examined in culture, and morphological variation on different substrates was reported. Species studied include Rhizophydium constantineani Saccardo; Rhizophydium sphaerocarpum (Zopf) Fischer var. sphaerocarpum; Rhizoclosmatium globosum H. E. Petersen; Chytridium lagenaria Schenk, and Chytridium confervae (Wille) Minden. These chytrids could be classified according to four methods of zoospore discharge: (I) inoperculate and non-vesicular; (II) inoperculate and vesicular; (III) operculate and non-vesicular; and (IV) operculate and vesicular. Presence of a membraneless vesicle during discharge was shown to be of as much taxonomic significance as the presence of an operculum. Taxonomic criteria and phylogeny are discussed.
Organization of the nucleus, nucleolus, and protein-synthesizing apparatus in relation to cell development in roots of Pisum sativum
Authors: Chaly Nathalie M. , Setterfield George
Published: September 2008

For analysis, roots were divided into 10 1-mm segments starting at the tip. Root marking and cell-length measurements revealed three main developmental zones in the cortex: segment 1, cell division with compensating cell growth; segments 3–5, rapid cell elongation; segments 7–10, cell maturation without growth. Nuclear volume increased steadily to segment 5 and remained high. Chromatin was moderately condensed in segment 1, became quite decondensed in many nuclei of segment 3, and showed strongly condensed regions in about half of the maturing cells. Karyosomes, chromatin 'puffs,' and perichromatin granules were present in segments 1 and 3 but became much reduced as development proceeded. The nucleolus was large in segments 1 and 3 but was markedly smaller in segment 5 and beyond. As nucleolar size decreased the granular zone was reduced and chromatin within lacunae was withdrawn. Nucleoli of maturing cells were small compact fibrillar bodies. Nucleolar vacuoles were present in segment 1 but varied in size and frequency from root to root. The cytoplasm of segment 1 was packed with ribosomes and contained only isolated elements of endoplasmic reticulum (ER). By segment 3 extensive rough ER (RER) was present; this persisted through to segment 9, although becoming reduced in extent. Segments 3–7 showed the highest density of ribosomes on the ER. Ribosome number was decreased in the fully elongated cells. Incorporation of 3H-cytidine into ribosomal RNA was highest in segment 1 and declined steadily with development. The functional role of the described chromatin organizations is unresolved; the nucleolar and ribosomal changes seem characteristic of plant cell development and their significance is discussed.
Relationship between S-ethyl dipropylthiocarbamate injury and peroxidase activity in corn seedlings
Authors: Harvey B. M. R. , Chang F. Y. , Fletcher R. A.
Published: September 2008

The herbicide EPTC (S-ethyl dipropylthiocarbamate) stimulated peroxidase activity in corn seedlings and enhanced lignin deposition during the first few days after treatment. A time study showed that the increase in peroxidase was concomitant with the inhibition in growth. The effects of EPTC on growth and peroxidase activity were annulled by the herbicide antidote (N,N-diallyl-2,2dichloroacetamide) but not by indoleacetic acid or gibberellic acid. The mechanism of action of EPTC and the antidote are discussed.
Bud, root, and growth-regulator activity in Acer saccharum during the dormant season
Authors: Taylor J. S. , Dumbroff E. B.
Published: September 2008

Exposure of dormant sugar maple seedlings to over 2000 h of winter temperatures of 5 °C and below was required for rapid and normal growth when seedlings were transferred to a warm greenhouse and extended photoperiods. Although chilling requirements were not fully satisfied until mid-March, a resurgence of metabolic activity occurred in early February. There was a marked shift in the potential for budbreak from the axillary to the terminal buds, and a surge in root growth occurred after a period of inactivity when the ground was frozen from late December to mid-January. The water content of the buds followed a pattern similar to that of the roots. It fell to a plateau in late fall well before the soil froze but began a steady increase with the resumption of active root growth in February. Inhibitory substances present in the buds did not exhibit significant changes during the overwintering period. However, cytokinin activity was observed beginning in February at the same time that root growth and bud succulence showed upward inflections. By the beginning of April there were two distinct peaks of activity which persisted through budbreak in early May.Seedlings that were brought into the greenhouse in the fall and never exposed to chilling temperatures did not break dormancy or show significant cytokinin activity or exhibit the physiological changes that occur under normal winter conditions.
Observations on Thraustochytrium sp.: development and behavior in culture
Authors: Kazama Frederick Y. , Zachary Arthur L. , Schornstein Kathleen L.
Published: September 2008

Taxonomic characters such as sporangium size, sporangium wall behavior at the time of spore discharge, presence or absence of basal rudiments, and cleavage patterns of an isolate of Thraustochytrium (isolate 70–2) were found to vary. Variations occurred between individuals under presumably the same environmental conditions. Variations also occurred when the organism was grown under different conditions and compared. Repeated emergence and motility of cells with and without visible ectoplasmic nets were observed. Amoeboid and amoeboflagellate cells were produced in cultures contaminated with bacteria.
The involvement of ethylene and sucrose in the inductive and developmental phases of apogamous bud formation in Pteridium gametophytes
Authors: Elmore H. W. , Whittier D. P.
Published: September 2008

The appearance of apogamous buds was studied in Pteridium gametophytes grown on medium containing sucrose and supplied with ethylene continuously or for brief periods followed by transfer to a flowing-air system without exogenous ethylene for the duration of the experimental period. Apogamy was induced in response to ethylene during a minimal 8-day induction period. Differentiation and growth of the apogamous sporophytes to observable buds occurred during the remaining 28 days of the experimental period. Ethylene was required for the induction period but was active only if supplied in conjunction with sucrose. Development of the buds, once induction was complete, was independent of ethylene but dependent on exogenous carbohydrate.
Net carbon dioxide exchange of wheat, sorghum, and soybean
Authors: Kanemasu E. T. , Hiebsch C. K.
Published: September 2008

Canopy net carbon dioxide exchange (NCE) rates are needed to understand the effect of light on crop growth and development. NCE rates of sorghum, soybean, and wheat canopies were determined using field chambers and an infrared gas analyzer throughout a growing season. Whereas sorghum attained peak NCE rates early in season, soybean and wheat did not reach maximum rates until the late reproductive growth stage. Frequently during the season, NCE rates of sorghum were nearly four times those of soybeans and wheat. Solar radiation had a much greater affect on the NCE of sorghum than on that of soybeans. Apparent light saturation was observed in both soybeans and wheat. An expression for dry matter production of sorghum was derived using chamber data. The expression simulated the total dry matter production for sorghum in 1973, 1972, and 1970 within 20%.
The correlative inhibition of bud and shoot growth in flax (Linum usitatissimum). Some factors affecting the pattern and degree of inhibition
Authors: McIntyre Gordon I.
Published: September 2008

When flax (Linum usitatissimum L.) seedlings were grown in sand culture under controlled conditions, growth of the lateral buds and their release from apical dominance showed a positive correlation with the N supply. The response of the buds was related to their position on the shoot and a well-defined gradient of bud growth potential was apparent at all N levels. Removal of the basal buds, which have the highest growth potential, induced the outgrowth of buds at higher nodes and increased the growth of the main shoot apex. Similar effects were produced by increasing the N supply to the intact plant.Providing N only as nitrate inhibited apical growth and caused severe leaf necrosis. These effects were due to zinc deficiency and could be prevented or significantly reduced not only by increasing the zinc supply but also by reducing the N level, providing some NH4-N, reducing the light intensity, or increasing the depth of planting. They could also be prevented by removal of the lateral buds at the basal nodes, thus indicating that the shoot apex and lateral buds may compete for the limited zinc supply. The obviously complex relationship between zinc and nitrogen nutrition in this species requires further investigation.
Ultrastructure of somatic mitosis in a diploid strain of the plant pathogenic fungus Cochliobolus sativus
Authors: Huang H. C. , Tinline R. D. , Fowke L. C.
Published: September 2008

An ultrastructural study of mitosis in a diploid strain of Cochliobolus sativus showed the event to be intranuclear. Two nucleoli occasionally were present in interphase nuclei. During division the spindle pole body peripheral to the nuclear envelope divided; spindle microtubules radiated into the nucleoplasm from the amorphous granular region abutting the nuclear envelope beneath the bodies; chromosomes condensed at prophase, approached the equatorial plane at metaphase, and moved asynchronously at anaphase; single microtubules appeared attached to kinetochore-like structures. At telophase, nuclei exhibited maximal elongation; fissures of the nuclear envelope appeared in the interzonal region; the nucleolus dispersed. The polar nuclear areas became new daughter nuclei with nucleoli.
Comparative accumulation of manganese in leaves and stems of woody plants native to acidic and non-acidic substrates
Authors: Small Ernest
Published: September 2008

Nine woody plant species typically found in non-acidic substrates, and 12 woody plant species typically found in acidic substrates, were cultivated at three levels of manganese availability. Considered collectively, the group of plants from the acidic habitats accumulated less manganese in the foliage compared with the group of plants from non-acidic habitats, suggesting adaptation by means of exclusion to the potentially toxic levels of manganese of acid soils. No significant differences were found for the two groups with respect to manganese accumulation in the stems.
Natural occurrence of barley stripe mosaic virus in wild oats (Avena fatua)
Authors: Chiko Arthur W.
Published: September 2008

Wild oats (Avena fatua), naturally infected with barley stripe mosaic virus, were detected in Manitoba in 1973 and 1974. The identity of the virus was confirmed on the basis of particle morphology, infectivity, and serological assays. Infected wild oats were rare and were found only in fields of barley in which a high proportion of the latter plants were also infected. The virus was transmitted through 22% of the seeds collected from naturally infected wild oats. Pale green spindle-shaped stripes were the most prominent symptom in leaves of naturally infected wild oats, whereas in leaves of seedlings infected by seed only mosaic symptoms developed.
The use of an ionizing unit for improved ultrathin sectioning
Authors: Haskins R. H. , Nesbitt L. R.
Published: September 2008

A readily available polonium ionizing unit placed near the ultramicrotome knife greatly facilitated ultrathin sectioning and subsequent handling of the sections.
Effects of Helminthosporium maydis race T toxin on protoplasts of resistant and susceptible corn (Zea mays)
Authors: Pelcher L. E. , Kao K. N. , Gamborg O. L. , Yoder O. C. , Gracen V. E.
Published: September 2008

Leaf protoplasts from resistant (N, C, and S cytoplasm) and susceptible (T cytoplasm) corn inbred W182B (Zea mays L.) exhibited a differential response after exposure to Helminthosporium maydis race T toxin. The volume of untreated protoplasts increased twofold during the first 24 h after isolation and by 48–72 h, most protoplasts exhibited an extensive network of cytoplasmic strands and the chloroplasts were distributed throughout the cytoplasm by cyclosis. However, susceptible protoplasts exposed to ≥2 μg toxin/ml failed to increase in volume and cytoplasmic streaming was rarely observed. By 72 h there was extensive degradation and collapse of susceptible protoplasts exposed to toxin. Resistant protoplasts exposed to up to 100 μg toxin/ml exhibited a twofold volume increase and were indistinguishable from untreated protoplasts. Susceptible protoplasts exposed to 0.1 μg toxin/ml also appeared unaffected, but at 1.0 μg toxin/ml an intermediate response was observed. The differential response to H. maydis race T toxin of protoplasts from resistant and susceptible corn correlates well with those effects observed in intact plant tissues and may serve to explain further the mode of action of the toxin on susceptible corn cells.
Fine structure during ontogeny of xylem transfer cells in the rhizome of Hieracium floribundum
Authors: Yeung Edward C. , Peterson R. L.
Published: September 2008

A number of cytological changes occur in rhizome transfer cells with age, the most striking being the appearance of microbodies each with a crystalline nucleoid and the presence of unusual plastids. Plastids in older transfer cells develop one or more electron-translucent regions and lack a defined thylakoid system. The number and size of vacuoles increases until ultimately one large vacuole is formed in old transfer cells. Accompanying these cytological changes in the cytoplasm the wall ingrowths change from being highly involuted and reaching a considerable distance into the cytoplasm of the cell to becoming thicker and less numerous, and finally form a rather uniformly thickened wall layer. The orientation of microfibrils in the thickened cell wall, resulting from the joining of the original wall projections adjacent to the tracheary elements, is random, while the wall thickenings away from the tracheary elements have more orderly arrangements of cellulose microfibrils.
Zoospore formation in Cylindrocapsa
Authors: Hoffman Larry R. , Hofmann Cecilia S.
Published: September 2008

Quadriflagellate zoospores and conditions for their induction are described for an algal isolate tentatively identified as Cylindrocapsa geminella Wolle. Previous to this report, only biflagellate zoospores were known for Cylindrocapsa while quadriflagellate zoospores were thought to characterize the closely related Cylindrocapsopsis; this distinction is no longer valid. In our isolate, a vegetative cell may differentiate directly into a single zoospore or, more commonly, zoosporogenesis is preceded by division of a vegetative cell into two, four, or eight daughter cells, each of which becomes a zoospore. Variation in zoospore arrangement depends on the number and nature of the division sequences. Ultimately, zoospores are released from the more-or-less dissociated parental cell wall in one or more vesicles. Each primary vesicle contains one, two, four, or occasionally eight zoospores; zoospore release follows the gradual distention and dissolution of the enclosing vesicle. Light microscopic observations suggest that the zoospore-containing vesicles arise from altered cell wall material. Zoospore germlings and variations in the appearance of vegetative filaments are aiso described and attention is called to the nature of the cell wall, which is quite unlike that of most other filamentous green algae.
Inhibition of gas exchange in bean leaves by NO2
Authors: Srivastava H. S. , Jolliffe P. A. , Runeckles V. C.
Published: September 2008

An open gas-flow system was used to examine the effects of the air pollutant NO2 on gas exchange by primary leaves of bean (Phaseolus vulgaris L.). Apparent photosynthesis and dark respiration were both inhibited by NO2 concentrations between 1.0 and 7.0 ppm. The degree of inhibition was increased by increasing NO2 concentration and increasing exposure time. Leaf susceptibility to NO2 varied during leaf growth. NO2 was most inhibitory at the ages when maximum rates of apparent photosynthesis or respiration were observed in the NO2-free controls (11 or 12, or 8 days after sowing, respectively). The rate of absorption of NO2 by leaves increased in direct proportion with the NO2 concentration and declined with increasing exposure time. The NO2 uptake rate in the dark was about half of its rate during illumination because of greater stomatal resistance to NO2 absorption in the dark. Transpiration rate was less affected by NO2 than was photosynthesis or respiration. Accordingly, it is suggested that the principal effects of NO2 on leaf gas exchange are exerted in the leaf mesophyll and are not on the stomata.
The effects of environmental conditions on the inhibition of leaf gas exchange by NO2
Authors: Srivastava H. S. , Jolliffe P. A. , Runeckles V. C.
Published: September 2008

An open flow system was used to examine the uptake and effects of NO2 on gas exchange by primary leaves of bean (Phaseolus vulgaris L.) under a variety of conditions of irradiance, temperature, humidity, and atmospheric CO2 and O2 concentrations. At 3.0 ppm, NO2 inhibited apparent photosynthesis and dark respiration in all the conditions tested. Both 3.0 ppm and 7.0 ppm NO2 inhibited the evolution of CO2 into CO2-free air. The absolute magnitude of photosynthetic inhibition by NO2 was greatest at high irradiance, at the optimum temperature for apparent photosynthesis, and at high humidities. Changes in CO2 concentration from 100 to 600 ppm and in O2 concentration from 0 to 21% did not affect the percentage inhibition of apparent photosynthesis by NO2. High temperatures increased the inhibitory effects of NO2 on dark respiration.The effects of NO2 on apparent photosynthesis, dark respiration, and CO2 evolution into CO2-free air were based on inhibitory effects exerted within the leaves and not on CO2 diffusion into the leaf. Transpiration rate and stomatal diffusion resistance were only slightly affected by NO2. The uptake of NO2 was enhanced by high temperature, low CO2 concentration, and high humidity. The results of these studies support the view that NO2 uptake is subject to internal limitations ("mesophyll resistance") under many environmental conditions.The range and prevalence of NO2 effects suggest that NO2 may cause general detrimental changes in the physiology of leaf cells. Furthermore, the circumstances under which NO2 effects were found to occur indicate that such effects may be significant in natural ecosystems.