bluuebunny/crossref_metadata_2025 huggingface dataset:
An ultrastructural comparison of Podosordaria leporina and Poronia oedipus (Ascomycetes)
Authors: Koehn Robert D. , Cole Garry T.
Published: September 2008

Scanning and transmission electron microscopic examinations of the stromata of Podosordaria leporina and Poronia oedipus are reported. Stromal shape, conidiogenesis, and ascospore morphology of these two species are compared. A comparison of the taxonomic concepts of Poronia and Podosordaria is presented. It is suggested that Podosordaria leporina should be transferred back to Poronia.
Tree fern indusia: studies of development and diversity
Authors: Tryon A. F. , Feldman L. J.
Published: September 2008

Early developmental stages of the sorus in Cyathea fulva show that the indusium is initiated from cells of the protoderm on the abaxial leaf surface, closer to the midvein than the margin of the ultimate segment. This contrasts with earlier work on Alsophila tricolor that reported a marginal origin of the indusium and possible phyletic relations with the marginal sorus in the Dicksoniaceae. This new information is considered in an assessment of the numerous forms of the indusia in five genera of the Cyatheaceae. A series of photographs shows the principal forms and the diversity of sori and indusia in Sphaeropteris, Alsophila, Nephelea, Cyathea, and Cnemidaria, including species of both the paleotropics and neotropics. The figures illustrate the inadequacy of the earlier system of classification of these plants in three main genera based upon the type of indusium. The primary role of the indusium is considered to be the retardation of water loss during sporangial development and sporogenesis.
Regulation of seed dormancy m Elaeagnus umbellata by endogenous growth substances
Authors: Hamilton D. F. , Carpenter P. L.
Published: September 2008

The growth-substance content of fruits of Elaeagnus umbellata was examined as part of an investigation of the regulation of seed dormancy of this species. Extracts of dormant seed fractions were separated chromatographically in various solvents and biological activity was determined in a lettuce-seed and a cucumber-seed bioassay. The bioassays showed that a growth-inhibiting substance with an Rf value similar to coumarin was present throughout the dormant seed. Fluorescence also showed that the inhibitor closely resembled coumarin.Activity of the inhibitor did not decrease during 90 days at 5 °C, and evidence indicates it may be physiologically active in preventing germination. On the other hand, germination-promoting substances that may counteract the effect of the inhibitor were found to be produced in the embryo during low-temperature afterripening.
Carrageenans of gametangial and tetrasporangial stages of Iridaea cordata (Gigartinaceae)
Authors: McCandless E. L. , Craigie J. S. , Hansen J. E.
Published: September 2008

Carrageenans from gametangial (male and female) and tetrasporangial plants of the red alga Iridaea cordata were isolated, fractionated, and characterized on the basis of their anhydrogalactose and sulfate content and infrared spectra. As in the case of Chondrus crispas the tetrasporangial plants yielded only λ-carrageenan while the gametangial plants produced carrageenans of the κ-type. The male plants yielded proportionately more KCl-insoluble κ-carrageenan than did the female. The infrared spectra of the various preparations from I. cordata were virtually indistinguishable from those of comparable fractions isolated from C. crispus.
Identification of genomes and chromosomes involved in peroxidase synthesis of wheat seeds
Authors: Kobrehel K. , Feillet P.
Published: September 2008

Polyacrylamide-slab gel electrophoresis of peroxidases of different Triticum and Aegilops species and of nullisomic–tetrasomic lines of Chinese spring wheat showed that T. aestivum chromosomes 7D, 4B, and 7A are the carriers of genes coding the synthesis of peroxidase a, peroxidase c, and peroxidase d, respectively. The indirect effect of modified chromosome systems and a special effect of chromosome 5B on peroxidase synthesis have also been observed. The chromosomal and genomic origin of the three other peroxidases (b, e, and f) detected in common wheat could not be definitively established.
The epidemiology of leaf spot disease in a native prairie. II. Airborne spore populations of Pyrenophora tritici-repentis
Authors: Morrall R. A. A. , Howard R. J.
Published: September 2008

A Burkard 7-day volumetric spore sampler was operated continuously from April 14 to November 23, 1970, and from April 21 to September 29, 1971, at Matador, Saskatchewan, in a native prairie dominated by Agropyron dasystachyum and A. smithii. Both ascospores and conidia of Pyrenophora tritici-repentis were trapped, but the counts of conidia greatly exceeded those of ascospores. The peak catch of ascospores occurred before that of conidia in both years. The total numbers of conidia per month were similar in both years except in June, when six times as many were trapped in 1971 as in 1970. Most conidia and ascospores are believed to have originated on dead infected grasses since P. tritici-repentis was shown not to sporulate on lesions on live Agropyron leaves. There was a marked diurnal periodicity in the trapping of conidia, with the peak usually at about 1200 h. This periodicity probably reflected the effects of light on sporulation and of wind speed on spore dispersal. However, simple meteorological explanations could not be found for the wide fluctuations (0–707) that occurred in the daily total catches of conidia during the midsummer period.
Le gynécée de l’Impatiens Balsamina. Etude morphologique, ontogénique et tératologique
Authors: Simon Liliane
Published: September 2008

The developmental pattern of Impatiens Balsamina L. gynoecium, established by morphological, anatomical, ontogenical, and teratological studies, leads us to an original conception of its organization. The syncarpous, pentamerous, pentalocular gynoecium is composed of a protecting wall consisting of five congenitally fused sterile carpels and an axial fertile part (placental column), whose vascularization is cauline. These different parts are initiated from distinct organogenic portions of the floral meristem. Carpellary primordia are initiated from lateral, meristematic portions (anneau initial floral) like gamophyllous foliar appendages; the placental column is initiated by dedifferentiation and reactivation of the apical central zone (which was previously inactive) and from cellular proliferation of the subjacent medullary meristem. This placental column represents the ultimate part of the floral axis. Ovarian walls are initiated on the periphery of the apical axial zone like common radiate intercarpellary protuberances.
Carbonic anhydrase levels in blue-green algae
Authors: Ingle R. K. , Colman Brian
Published: September 2008

Carbonic anhydrase (carbonate dehydratase, EC 4.2.1.1) activity was detected in four species of blue-green algae, Anabaena flos-aquae, Anacystis nidulans, Coccochloris peniocystis, and Oscillatoria sp., grown with air, but no significant enzyme activity was detected in these algae when grown with 5% CO2 in air. The enzyme was found not to be membrane-bound, was inhibited by 1 mM Diamox, and had an apparent Km of 15.6 mM. Carbonic anhydrase activity in all four blue-green algae was significantly lower than that reported for unicellular green algae.
Photosynthesis of newly matured leaves during the ontogeny of barley grown at different nutrient levels
Authors: Ma P. , Hunt L. A.
Published: September 2008

Various growth characteristics were measured throughout ontogeny for barley plants (Hordeum vulgare L. cv. Brant) grown in silica sand and irrigated daily with one-eighth (0.125 N), one-fourth (0.25 N), and one-half (0.5 N) dilutions of a modified Hoagland nutrient solution, at day–night temperatures of 25–20 °C, an irradiance of 53 nE cm−2 s−1 (400–700 nm), and a day length of 15.5 h.The net CO2 exchange rate (NCE) of newly matured leaf laminae did not differ between measurements made at the same irradiance before and after noon. By contrast, NCE was greater at all stages except stem elongation for plants supplied with 0.5 N nutrient solution than for those receiving 0.25 N and 0.125 N solutions. The nutrient effect was apparent even for the first leaf produced. A distinct ontogenetic pattern of change in leaf NCE was apparent under all nutrient treatments: NCE increased from leaf 1 to leaf 3, remained constant between leaf 3 and leaf 5, declined between leaf 6 and leaf 9, and then increased markedly from leaf 10 onwards. The changes in leaf NCE appeared to be associated with major events in ontogeny.Rate of leaf appearance was constant through ontogeny and was not affected by nutrient supply. Final leaf number was greater for the 0.5 N nutrient solution. Leaf length, width, area, and specific weight increased throughout the early stages of ontogeny, and decreased later. The decrease in leaf length and area was less for plants supplied with more nutrients.
Phytochrome control of the lag phase of chlorophyll accumulation in Lemna minor
Authors: Frick Hugh
Published: September 2008

The 10- to 12-h lag phase in chlorophyll accumulation preceding the rapid accumulation phase in Lemna minor de-etiolating in the light was eliminated by a red light preillumination given about the length of the lag period before the onset of continuous red light. Neither the rate after the lag nor the extent of cholorophyll accumulation differed between preilluminated and control plants. Both the rate of accumulation in controls and the absolute stimulation by preillumination were shown to depend upon the length of time the etiolated plants had been grown in darkness up to 93 days. Only one photoproduct of preillumination contributed to the elimination of the chlorophyll lag phase, but the effect of red light was only partially (about 60%) nullified by subsequent far-red light.
Etude des protéines des blés résistant, Kharkov, et sensible, Selkirk, au cours de l'endurcissement au froid. I. Protéines solubles
Authors: Rochat E. , Therrien H. P.
Published: September 2008

Electrophoregrams of soluble proteins of winter wheats (Triticum aestivum L.) after incorporation of L-[14C] leucine disclose the synthesis of two particular proteins during the cold hardening processes of the hardier variety, Kharkov, compared with a less-hardy variety, Selkirk. The composition in amino acids of the two proteins has been studied and shown to confer them a higher degree of hydrophily making them capable to bind and retain vital water with enough energy to avoid too much dehydration resulting in denaturation during extracellular ice formation.
Etude des protéines des blés résistant, Kharkov, et sensible, Selkirk, au cours de l'endurcissement au froid. II. Protéines solubles et protéines des chloroplastes et des membranes
Authors: Rochat E. , Therrien H. P.
Published: September 2008

Investigations of quantitative and qualitative changes in protein synthesis in two winter wheat varieties have been made during the early stages of cold hardening. When labelling with 35S is made during the hardening treatment, the incorporation of the tracer into proteins is very low in both varieties. However, if labelling at 22 °C precedes hardening, the hardy variety, Kharkov, shows an increase in the incorporation of 35S into the total soluble proteins, and the rate of synthesis of both chloroplast and membrane proteins is maintained during the hardening process. In the less-hardy Selkirk, a very marked decrease in proteogenesis has been observed.Qualitative studies on the incorporation of 35S have not revealed any changes in specific chloroplast and membrane proteins during early stages of cold hardening of the two varieties of winter wheat.
Revision of the Seuratiaceae. I. Morphology of Seuratia
Authors: Meeker Joseph Andrew
Published: September 2008

The type genus of the family Seuratiaceae is described as consisting of four highly variable species. The origin and location of the conidiogenous areas (sporodochia), pycnidia, and pseudothecia are demonstrated to be related to the size and shape of the colonies, which are in turn dependent upon ecological factors of substratum and duration of wet season. The microstructure of the intercellular matrix varies from amyloid through pseudoamyloid to inamyloid. Each of these characteristics completely intergrades between the extremes. The pattern is considered to reflect nutritional differences rather than climatic factors. Asexual reproduction is by multicellular, holoblastic thallospores originating from superficial layers of the colonies. The variation of the thallospores (conidia) arises from indeterminate but ecologically limited growth. Asci arise from superficial croziers which proliferate indefinitely before aborting. The zone of ascogenous tissue is therefore a pseudothecium. Pseudoparaphyses are lacking but an indefinite epithecium is sometimes found. Interthecial tissue arises from budding croziers or by their abortion and from persistent sterile tissue. With the production of mature asci, colonies cease to grow and soon drop from the leaves.
Saprophytic survival of Bipolaris sorokiniana on detached laminae of Poa pratensis
Authors: Hodges Clinton F.
Published: September 2008

Saprophytic growth of Bipolaris sorokiniana (Sacc. in Sorok.) Shoem. was evaluated on the four youngest, visible, detached laminae of Poa pratensis L. Non-infected laminae and laminae infected with B. sorokiniana before detachment were used in all studies. Mycelial growth and sporulation from lesions on infected laminae and on non-infected laminae infested with B. sorokiniana was influenced by whether lamina tissue was killed, method of killing, and degree of sterilization. Mycelial growth generally was rapid on both non-infected laminae and infected laminae of all ages. Sporulation was rapid on non-infected laminae of all ages, but progressively slower on each older lamina of laminae infected preceding detachment. Total sporulation was greatest on both non-infected and infected laminae that were most extensively sterilized; less extensive sterilization resulted in fewer conidia being produced on all laminae. In all instances, however, total sporulation was greater on non-infected laminae than on infected laminae. The results suggest that the transition from parasitic to sarophytic development of B. sorokiniana on P. pratensis laminae is not passive. There is an interaction between B. sorokiniana and the host tissue during the parasitic stage of the organism that results in conditions detrimental to sporulation and the number of conidia produced. Mycelial growth generally was prolific on all laminae, and it is suggested that mycelial growth on lamina tissues may constitute an important source of inoculum for primary infections in P. pratensis monocultures.
Surface-active spore slimes
Authors: Bandoni R. J.
Published: September 2008

Twenty-four species of fungi with slimy spore masses were examined for surface activity of the slime. The species fell into four categories: (1) slime highly surface-active and spores dispersed primarily at the air-water interface; (2) slime rapidly spreading in the bulk phase and the spores spread throughout; (3) slime weakly spreading or insoluble in water; (4) slime insoluble in water, but showing some activity in oil or lactophenol solution. The significance of this activity with respect to spore dispersal is discussed.
Secondary dormancy in light-sensitive lettuce seeds incubated anaerobically or at elevated temperature
Authors: Vidaver William , Hsiao A. I.
Published: September 2008

Light-sensitive lettuce seeds become secondarily dormant within 8–10 days if initial germination is suppressed by far-red light or incubation at elevated temperature (≥30 °C). When germination is suppressed by temperature, induction of dormancy occurs in both red and far-red irradiated seeds and the process is, therefore, independent of the phytochrome system. Dormancy induction requires oxygen, but reversion of phytochrome from the far-red- to the red-absorbing form appears to take place anaerobically.
Observations on the genus Exobasidiellum
Authors: Bandoni R. J. , Johri B. N.
Published: September 2008

The type specimens of Exobasidiellum graminicola (Bres.) Donk and E. culmigenum Webster & Reid were examined. The basidia of E. graminicola are elongate and taper basally as in other Exobasidiaceae; as in some species of Exobasidium, the basidiospores become transversely septate and produce small conidia during germination. The basidia of Exobasidiellum culmigenum develop in two distinct phases: (1) a probasidium is formed and within this karyogamy occurs; (2) a metabasidium develops from the probasidium and the diploid nucleus migrates into the apex of this structure before undergoing meiosis. The basidiospores of E. culmigenum germinate by germ tube. On the basis of these and other features, E. culmigenum is transferred to Galzinia as G. cubnigena (Webster & Reid) Johri & Bandoni comb. nov.
Callus cultures from potato tissues and the exclusion of potato virus X from plants regenerated from stem tips
Authors: Wang P.-J. , Huang L.-C.
Published: September 2008

Callus cultures were established from shoot and root tips and from stem, leaf, and tuber tissue of potato infected with potato virus X. Roots developed in callus from all sources, but shoots developed only in callus from shoot and stem sections. Of 37 plants which originated from shoot tips 0.5 mm long, 17 were free of the virus.
The epidemiology of common root rot in Manitou wheat. III. Development of lesions on subcrown internodes and the effect of added phosphate
Authors: Verma P. R. , Morrall R. A. A. , Randell R. L. , Tinline R. D.
Published: September 2008

The development of common root rot lesions on subcrown internodes of Manitou wheat was followed in growth-chamber tests. Visible lesions caused by Cochliobolus sativus appeared 3 to 5 days after inoculation. The vertical spread of subcrown internode lesions was much faster than the lateral spread; normally, lateral spread did not start until maximum vertical extension had occurred. Considerable variation in rate of development of lesions was evident between individual plants. The overall mean daily rate of vertical extension of subcrown internode lesions was in the range of 0.3 to 0.5 mm. The rate was faster immediately after infection and declined with time. Lesion development on plants generally was more rapid in low-phosphate soil than in high-phosphate soil. This finding was exemplified by higher percentages of severely diseased plants at the end of the experiments; higher probabilities of transfer of plants from less to more severe categories in the intervals between observations; higher disease ratings; and higher mean daily rates of linear extension of lesions in low- than high-phosphate soil. The possible application of some techniques in developing a model for forecasting severity of disease is discussed.
The ultrastructure of M1-a-mediated resistance to powdery mildew infection in barley
Authors: Edwards H. H.
Published: September 2008

M1-a-mediated resistance in barley to invasion by the CR3 race of Erysiphe graminis f. sp. hordei does not occur in every host cell with the same speed and severity. In some cells ultrastructural changes within the host cell as a result of resistance will occur within 24 h after inoculation, whereas in other cells these changes may take up to 72 h. In some cells the ultrastructural changes are so drastic that they give the appearance of a hypersensitive death of the host cell, whereas in other cells the changes are very slight. In any case, at the end of these changes the fungus ceases growth. The ultrastructural changes occur in penetrated host epidermal cells as well as non-infected adjacent epidermal and mesophyll cells.The following ultrastructural changes have been observed: (1) an electron-dense material which occurs either free in the vacuole or adhering to the tonoplast (the material is granular or in large clumps); (2) an increased electron density of the host cytoplasm and nucleus; (3) a breakdown of the tonoplast so that the cytoplasmic constituents become dispersed throughout the cell lumen; and (4) the deposition of papillar-like material in areas other than the penetration site. The first three changes take place within the host cell protoplasts and are directly attributable to the gene M1-a. These changes are typical of stress or incompatibility responses and thus M1-a appears to trigger a generalized incompatibility response in the presence of race CR3. The papillar-like material occurs outside the host cell protoplast in the same manner as the papilla and probably is not directly attributable to M1-a.
Studies on lichen-dominated systems. XIII. Seasonal and geographical variation of net CO2 exchange of Alectoria ochroleuca
Authors: Larson D. W. , Kershaw K. A.
Published: September 2008

By using a new gas-exchange method, the seasonal changes in net photosynthetic rates of Alectoria ochroleuca were examined in relation to thallus moisture content, thallus temperature, and light intensity. These experiments were run using samples collected from both the top and bottom positions of a raised-beach ridge and showed very little intraspecific variation. Collections made from other geographical locations, however, showed that considerable intraspecific variation was possible within this species.At the Pen Island site, A. ochroleuca shows patterns of net photosynthesis adapted to the xeric ridge-top environments on which it is most abundant.Rapid seasonal acclimation to temperature and changes in the response to light intensity were found for both ridge-top and ridge-bottom collections of A. ochroleuca. The ecological significance of these findings is discussed.
Changes in phenolic compounds of sunflowers infected by Plasmopara halstedii
Authors: Cohen Yigal , Ibrahim R. K.
Published: September 2008

Fluorescent materials were found to accumulate in sunflower plants infected by Plasmopara halstedii. The main site of accumulation was the upper part of the stem. Chromatographic studies indicated that the major fluorescent compound is scopoletin (6-methoxy-7-hydroxycoumarin). In stem tissues, there was a 23-fold increase in the amount of scopoletin-like fluorescent materials in the 4th week after bud inoculation, and this continued to rise until the 10th week, while it declined in other parts of the infected plant. ‘Chlorogenic acid value’ increased in leaf lesions during the first 2 weeks of pathogenesis and declined by 50% and 80% in infected stems and leaves, respectively, by the 4th week after inoculation. The severe stunting of sunflowers induced by P. halstedii may be connected to the alterations in the phenolic compounds of the host.
Changes in proteins and free and total amino acids of peanuts (Arachis hypogaea) infected with Aspergillus parasiticus
Authors: Cherry John P. , Young Clyde T. , Beuchat Larry R.
Published: September 2008

Protein and amino acid composition of peanuts (Arachis hypogaea L.) inoculated with Aspergillus parasiticus Speare were compared with those of non-infected seeds during an 18-day test period to determine metabolic changes within this interrelationship. The levels of buffer-soluble proteins of infected peanuts decreased rapidly to quantities much lower than those of non-infected seeds shortly after inoculation. Simultaneously, the levels of insoluble proteins increased to quantities greater than those contained in soluble fractions. Gel electrophoresis of soluble extracts from inoculated peanuts showed that proteins were hydrolyzed to many small-molecular-weight components, which eventually disappeared as fungal growth progressed. A corresponding increase in quantity of most free amino acids was observed shortly after inoculation of the peanuts. Major changes in free amino acid content coincided with substantial alterations of proteins in both soluble and insoluble fractions. These data suggested that inoculation of peanuts with A. parasiticus initiated a sequence of events whereby proteins were hydrolyzed first to small polypeptides and (or) insoluble components, then to free amino acids. After extended periods of infection, levels of free amino acids varied from day to day, suggesting that differential utilization of these components by the fungus was occurring. Quantities of total amino acids in whole seeds and soluble and insoluble fractions were different for non-inoculated and inoculated peanuts. Distinct differences were especially notable among samples of these three fractions of inoculated seeds. Differences in total amino acid contents apparently reflect qualitative and quantitative changes in proteins and (or) polypeptides present in various fractions examined during the infection period.
Effects of gibberellic acid on DNA synthesis and histology in the shoot apex of Helianthus annum during the transition to flowering
Authors: Langenauer Haviva D. , Atsmon Dan , Arzee Tova
Published: September 2008

Transition to flowering is described in gibberellic acid (GA) - treated and control plants of Helianthus annuus. Hormonal treatment accelerates reproductive development without reducing the number of leaves developed before flowering. Studies of [3H]thymidine incorporation in the apex show that a non-synthesizing summital group of cells, the central zone, is present in the vegetative as well as the transitional apex. During transition to the floral apex the size of the central zone is gradually diminished, as its peripheral and basal cells undergo synthetic activity and the apex develops a domed shape. In GA-treated shoots the order is changed so that development of a dome precedes activity in the central zone. Cells of the second tunica layer of the central zone are the last to incorporate thymidine. They are conspicuously enlarged and distinct before development of the inflorescence. It is suggested that this layer has a specialized role in flowering.
Light-induced inhibition of sporangial formation of Phytophthora infestans on potato leaves
Authors: Cohen Yigal , Eyal Helena , Sadon Tova
Published: September 2008

Phytophthora infestans failed to produce sporangia on infected potato leaves under continuous light conditions. Blue light (λmax = 450 nm) was most inhibitory, while red light (λmax = 650 nm) was ineffective in inhibiting sporangial formation. Low intensity of blue light (3.7 μEinstein m−2 s−1) induced about 85% inhibition. The inhibitory effect of blue light upon sporulation was temperature dependent: it increased with rise in the temperature from 10 °C to 25 °C. 3,3,4-Dichlorophenyl-1,1-dimethyl urea (DCMU), which blocks the Hill reaction of photosynthesis, did not enable the fungus to sporulate on leaves under light conditions. Preceding dark treatments did not remove the inhibitory effect of blue light; this suggested that sporulation of the fungus is not a 'dark induction phenomenon.'
Microfibrils in primary and secondary wall growth develop trellis configurations
Authors: Boyd J. D. , Foster R. C.
Published: September 2008

In primary growth, protoplasmic pressure expands the cell wall as its cellulosic framework is being built up and strengthened. Numerous micrographs provide evidence that as each lamella of the wall is differentiated, randomly spaced bonds tend to develop between its adjacent microfibrils. Apparently the number of bonds so developed, and the number retained unbroken subsequently, are related to the rate of cell wall extension.Between unbroken bonds, tensions associated with growth cause adjacent transverse microfibrils to bend successively to each side of their original general orientation. Thus, within a lamella they form lenticular, trellis-like configurations. Large extensions cause large local variations in direction; some microfibrils remain adjacent within groups, but the groups may be widely separated. Such microfibril configurations are generally incompatible with the multinet theory. Apparently also, the very large extensions of the lamellae formed soon after cell division can cause breaking of bonds, wide dispersion, and even breaking of microfibrils.In secondary growth, similar bonding between microfibrils occurs within lamellae and also between lamellae of the cell wall. Again, there is associated development of trellis configurations, but in this case it is due to swelling within the wall during lignification. Resulting changes in microfibrillar directions between bonded positions are much less extreme than in primary walls, but they are highly significant physiologically.
Ultrastructure of wilt syndrome caused by Verticillium dahliae. II. In sunflower leaves
Authors: Robb Jane , Busch Lloyd , Brisson Jean D. , Lu B. C.
Published: September 2008

Ultrastructural changes occurred in sunflower leaves that were infected by Verticillium dahliae Kleb. during the appearance of foliar symptoms. Early in symptom development major degenerative changes took place in the leaf mesophyll tissue particularly in the vicinity of the xylem of the major veins. During these early stages vessel wall breakdown occurred in the vicinity of the fungus, but this degradation was not accompanied by swelling. Occlusion of the vessel elements by fungus, fibrillar material, or electron-dense plugs was not significant until late in disease development. Comparison of these observations with those that were made in a previous parallel study of Verticillium-infected chrysanthemum suggested that the ultrastructural changes induced by the fungus in the two hosts are similar but that the timing is different. In chrysanthemum, degenerative changes in the mesophyll are not extensive until after chlorosis, but vessel blockage is advanced before wilting is noticeable. The significance of this difference in the development of foliar symptoms is discussed in relation to the plugging and toxin theories of wilt induction in fungus-caused vascular diseases.
Variability of host and pathogen in Hypoxylon canker of aspen
Authors: French J. R. , Manion P. D.
Published: September 2008

Sapling-sized quaking aspen (Populits tremuloides) in five natural clones were inoculated with mass and single ascospore cultures of Hypoxylon mammatum. Fungus isolates varied in ability to produce cankers. 'Conidial-type' isolates generally produced few cankers, while 'mycelial-type' isolates produced cankers on 87.7% of inoculated branches. Isolates from a given ascus inoculated into a clone generally produced cankers of similar length after 2 months. However, some significant differences in canker length did occur. Clones varied in susceptibility to canker enlargement. No single isolate produced the largest cankers on all clones.
Ontogeny of phloem transfer cells in Hieracium floribundum
Authors: Peterson R. L. , Yeung E. C.
Published: September 2008

The primary phloem system in the rhizome of Hieracium floribundum has transfer cells that have developed from companion cells and parenchyma cells, which are adjacent to sieve elements. In both cell types changes occur in the cytoplasmic organelles at the time of wall ingrowth formation. Dicytosomes and polyribosomes become more numerous and 'boundary formations' and other multivesiculated structures appear. Few microtubules were found in the cytoplasm at this time. After the wall ingrowths become obvious, the transfer cells develop numerous mitochondria and an enlarged nucleus. The phloem transfer cells become vacuolated with age and the wall ingrowths become less numerous. This may be associated with a change in the translocation pattern in the phloem after the inception of vascular cambium activity. Parenchyma cells in the secondary phloem usually become rather vacuolated and develop few wall ingrowths.
Effect of cultural conditions on apothecial morphogenesis in Pyronema domesticum
Authors: Moore-Landecker Elizabeth
Published: September 2008

Pyronema domesticum (Sow. ex Gray) Saccardo was cultured at temperatures ranging from 5 to 10 °C; relative humidities (RH) from 100% to near 0%; on an inorganic salts medium supplemented with 0.5–1.0 g dextrose, 0.5–3.5 g Casamino acids, 10 g charcoal, or 20 g inulin per litre; and on potato dextrose agar. The effects of these different cultural conditions on apothecial morphogenesis were evaluated. Fully expanded, globose ascogonia predominated in the control, at 20–25 °C, 93–100% RH, 0.5 g dextrose, or 0.5 g Casamino acids/litre. Undifferentiated (without a trichogyne) or poorly differentiated ascogonia predominated at extremely unfavorable conditions (5–10 and 30 °C; about 0–20% RH; 3.5 g/litre Casamino acids, 5–6.5 × normal concentration of inorganic salts). These latter conditions sometimes prevented fusion and (or) plasmogamy. Under all remaining conditions, the ascogonia were predominately clavate to obovate with a delimited trichogyne, and the normal sexuality was unaffected. Morphological abnormalities were common among the poorly differentiated gametangia but less common among those that were better differentiated. Ascogenous hyphae were produced by all types of ascogonia. There was generally some reduction in ascus production, and asci with mature ascospores were not formed at 5 or 30 °C, near 0% RH, on 3.5 g Casamino acids/litre, or on 3.5–6.5 × inorganic salts. There was some reduction in the sterile system under the most extreme conditions, and a palisade of paraphyses was not formed at 5–10 °C, and 4.5–6.5 × inorganic salts. Sclerotia were formed only on potato dextrose agar.
Megasporogenesis and microsporogenesis in Vicia faba
Authors: Mitchell John P.
Published: September 2008

A multicellular archesporium develops beneath two layers of cells in the young ovules of Vicia faba L. The megaspore mother cell differentiates from the apical cell of this archesporial group. A linear array of megaspores results from a normal meiosis. The inner integument is initiated by periclinal divisions in a ring of two ovule epidermal cells while the outer integument arises as a bump at the base of the ovule. Integument development starts while the megaspore mother cell is in early prophase I. The megaspore second from the chalazal end is the functional megaspore. In the anthers, meiosis in the microsporocytes is initiated before meiosis in the megaspore mother cells and follows the classic pattern. The tapetum becomes progressively more distinct during early prophase I. The nuclei complete several DNA replications without dividing. The tapetum finally disintegrates after the uninucleate microspore goes through mitosis. Endothecium development is apparent accompanying the elongation of the newly formed isodiametric microspores, as is the formation of the complex spore wall architecture.
Sugar composition of ergot honeydews
Authors: Mower R. L. , Hancock J. G.
Published: September 2008

Honeydews of several Claviceps spp., Sphacelia spp., and Sphacelia-like fungi were analyzed for differences in their sugar composition. Sugars were separated for comparative and preparative purposes by gel filtration and paper chromatography. The structures of pure sugars were determined with the use of periodate, enzymes, deuterium labeling, nuclear magnetic resonance spectroscopy, and methylation analysis by combined gas–liquid chromatography (glc) and mass spectrometry. Three sugars, 6 kestose, O-β-D-Fruf-(2 → 1)-O-β-D-Fruf-(2 → 6)-O-α-D-Glcp-(1 → 2)-β-D-Fruf, and O-β-D-Fruf-(2 → 6)-O-β-D-Fruf-(2 → 1)-O-α-D-Glcp-(6 → 2)-β-D-Fruf, not previously detected in ergot are reported.Sugar analysis of honeydews from infected hosts indicates that synthesis of the major sugars is controlled by the parasite and that sugar composition is distinct for each fungus. There were a number of taxonomic subgroupings that could be formed on the basis of honeydew constituents.
Mechanism of honeydew formation by Claviceps species
Authors: Mower R. L. , Hancock J. G.
Published: September 2008

The biochemical and biophysical relationships of sugar movement were studied in ergot-infected grasses. The results indicate a mechanism for honeydew formation by various Claviceps species. Significant increases in the rates of translocation and transpiration were noted in culms of grasses infected with ergot and appear to be due in part to a 10- to 50-fold difference in water potential between the host and the parasite. The conversion of host sucrose to fungal honeydew sugars was demonstrated by radioactive labeling techniques. The creation of a 'sucrose sink' is probably the major driving force behind increased translocation in the direction of the parasite.
Immunochemistry of carrageenans from gametophytes and sporophytes of certain red algae
Authors: Hosford S. P. C. , McCandless E. L.
Published: September 2008

Quantitative and qualitative precipitin tests using antibodies prepared against specific carrageenans from Chondrus crispus were performed on carrageenans that were extracted from plants of known stages in the life cycle of various other species of red algae. Species from three genera in the family Gigartinaceae were studied and it was determined that specific anti-κ-carrageenan serum was precipitated by carrageenans that were extracted from gametophytic plants but not by carrageenans from tetrasporic plants. Carrageenans and related polysaccharides from several species outside of the family did not show this difference.KCl-soluble carrageenan from female plants precipitated less antibody than KCl-insoluble carrageenan, but the soluble fraction that was treated with alkaline borohydride precipitated as much antibody as the insoluble fraction. Alkaline-borohydride-treated λ-carrageenan also precipitated the anti-κ-carrageenan serum. Other polysaccharides that precipitated anti-κ-carrageenan serum include iota carrageenan and furcellaran.Evidence presented from the above precipitin reactions indicates that 3,6-anhydrogalactose is involved in the determinant site of the antigen.
Cell enlargement and tissue differentiation during leaf expansion in beech, Fagus grandifolia
Authors: Dengler Nancy G. , Mackay Lynette B. , Gregory Linda M.
Published: September 2008

Cell enlargement and differentiation of leaf tissues have been studied from the stage of bud expansion to leaf maturation in beech. Fagus grandifolia Ehrh. Leaf tissue was collected at weekly intervals and observations were made on plastic-embedded, 2-μm serial sections; all measurements were made using a microprojector. At the earliest stages examined, six cell layers are present, and with the exception of a slightly elongated palisade layer, cells of the protoderm and ground meristem are similar in size, shape, and staining characteristics. The following observations have been made during maturation: (1) cell division occurs in the upper palisade layer for at least 1 week longer than in other cell layers: (2) the highest relative rates of leaf expansion are due to increase in cell number rather than to cell enlargement; (3) relative rates of cell enlargement in all cell layers peak during the same time period, but are highest and of longer duration in the upper and lower epidermis; (4) relative rates of increase in cell height are highest and of longest duration in the palisade. These and other observations demonstrate the important role that is played by duration and rates of enlargement as well as direction of expansion in the differentiation of mature leaf tissues.
Penetration of Zea mays by Helminthosporium carbonum
Authors: Murray Gordon M. , Maxwell Douglas P.
Published: September 2008

Light microscopy showed that on corn leaves, 81–93% of appressoria of Helminthosporium carbonum races I and II are formed over junctions of epidermal cells. During the early stages of penetration of corn plants resistant and susceptible to race I, 63–83% of appressoria have an epidermal cell nucleus within 10 μm. Transmission electron microscopy of race II on inbred W187R showed that appressoria are attached to the cuticle by fibrillar material. Vesicles are present in the appressorium at the site of cuticle penetration and initial cuticle penetration appears to be enzymic; subsequent rupture may be mechanical as the penetration peg widens. A septum forms between the appressorium and the subcuticular hyphae. Epidermal cell cytoplasm is thicker beneath penetration sites than elsewhere under the epidermal wall. Changes in epidermal cytoplasm were observed 8 h after inoculation; by 18 h epidermal cells beneath subcuticular hyphae have electron-opaque contents. Hyphae are mainly subcuticular up to 48 h after inoculation, and underlying epidermal and mesophyll cells are frequently collapsed. Results indicate that H. carbonum races I and II have similar initial reactions on susceptible and resistant genotypes and that penetration occurs by degradation of the cuticle and host cell walls.
Studies on lichen-dominated systems. XVI. Comparative patterns of net CO2 exchange in Cetraria nivalis and Alectoria ochroleuca collected from a raised-beach ridge
Authors: Larson D. W. , Kershaw K. A.
Published: September 2008

Seasonal patterns of net photosynthesis in Cetraria nivalis that was collected from the top and bottom positions of a raised-beach ridge were examined in relation to those for Alectoria ochroleuca from the same site. While seasonal acclimation is pronounced in C. nivalis to an extent equal to that found in A. ochroleuca, C. nivalis showed significant intraspecific difference in these patterns. Cetraria nivalis that was collected from the bottom position of the beach ridge is more active metabolically than the ridge-top collections. Cetraria nivalis is most abundant on the lower slopes of these ridges. A comparison of the physiological data matrices for both ridge-top and ridge-bottom collections of A. ochroleuca and C. nivalis partly explains the patterns of species distribution that are observed in the field.
Proline accumulation in flooded and wilted sunflower and the effects of benzyladenine and abscisic acid
Authors: Wample Robert L. , Bewley J. Derek
Published: September 2008

Sunflower accumulates proline in its aerial and subterranean parts when subjected to water stress. Decreases in the proline pool on recovery are slow. Plants that wilted in darkness do not accumulate proline, and plants that are subjected to a 16-h photoperiod and are sprayed with benzyladenine also show reduced accumulation. Flooded plants show increases in their endogenous free-proline pool, which can be reduced by aeration of the roots or by foliar application of benzyladenine. Abscisic acid does not induce free-proline accumulation in unstressed plants.
Moisture stress and its effect on photosynthesis in Dicranum polysetum
Authors: Peterson Wilbur L. , Mayo James M.
Published: September 2008

The effect of water stress on the moss Dicranum polysetum Sw. was studied in the growth chamber, and water potential (ψ) was found to vary as much as 15 atm between the tip of the plant and areas 2 to 4 cm within the cushion, which suggests that very little water is transported from the base of the stem to its tip. With an infrared gas analyzer it was determined that photosynthesis ceases at −21 to −23 atm and the moss remains dormant until it is rewetted. Upon rewetting, there is a sharp burst of respiration that doubles the normal CO2 output. This burst reached its maximum level of 4 mg CO2 g−1 h−1 within 15 min and was of short duration. Full photosynthetic rate was restored in 8 h.
Ultrastructure of chlamydospores of Phytophthora cinnamomi during development and germination
Authors: Hemmes Don E. , Wong Lester D. S.
Published: September 2008

Thin sections of developing, fully expanded, and germinating chlamydospores of Phytophthora cinnamomi were studied by electron microscopy. Expanding chlamydospores had thin walls and contained nuclei, mitochondria, dictyosomes, rough endoplasmic reticulum, lipid-like bodies, peripheral vesicles, and small vacuoles with dense, spherical inclusions. Small vesicles, about 200 nm in diameter, were occasionally observed underlying the plasmalemma.In fully expanded chlamydospores, structures that are necessary for zoosporogenesis, i.e. exit pores, flagella, and cleavage vesicles, were not present. The vacuoles with dense, spherical inclusions constituted a large proportion of fully expanded chlamydospores and had usually fused to form a large central vacuole. The walls of two-week-old chlamydospores were similar in density to sporangial walls and were non-layered.Chlamydospore germination was direct, i.e. by the production of germ tubes with numerous vesicles at the tips which ruptured through the chlamydospore wall. A germination wall was formed de novo beneath the chlamydospore wall and extended with the germ tube to form the germ tube wall.The distinguishing ultrastructural characteristics between chlamydospores and sporangia, aged sporangia, oogonia, and oospores of Phytophthora are discussed.
A study of the mature megagametophyte of Stipa elmeri
Authors: Maze Jack , Lin Shu-Chang
Published: September 2008

In Stipa elmeri Piper & Brodie ex Scribn., the pollen tube enters at the filiform apparatus of the degenerated synergid. The degenerated synergid has electron-dense cytoplasm in which organelles are not discernible. All other cells of the mature megagametophyte have nuclei, endoplasmic reticulum, plastids, mitochondria, dictyosomes, and vacuoles. Starch is found in the persistent synergid (in minute quantities), egg, and central cell. Lipids occur in the persistent synergid, central cell, and antipodals. The filiform apparatuses of the two synergids are hypothesized to perform different functions. In the degenerated synergid, the filiform apparatus serves to increase the surface area of the plasma membrane and thereby to offer a large area for pollen-tube-growth-directing compounds to diffuse out of the synergid. In the persistent synergid, the filiform apparatus is part of a suite of features which indicate that the persistent synergid is involved in the transference of materials into the megagametophyte. Another possible function of the persistent synergid is to aid in establishing the polarity of the egg. The pollen grain and tube have distinctive polysaccharide spheres that serve to delimit the pollen tube cytoplasm after discharge into the degenerated synergid. Associated with the degenerated synergid are bodies of dense materials as seen under electron microscopy, and bodies of RNA and protein as determined histochemically. These are probably the same thing and come from the degenerating synergid. The antipodals are the most cytologically active cells of the megagametophyte. They have some features which are characteristic of transfer cells and possibly function in the transference of materials into the megagametophyte. Other studies (Brink and Cooper 1944) have indicated that grass antipodals are involved in the control of endosperm development. The active cytoplasm of the antipodals may reflect the synthesis or transference of growth-controlling substances.
Inhibition of cambial activity in Abies balsamea by internal water stress: role of abscisic acid
Authors: Little C. H. A.
Published: September 2008

In experiments with attached and detached shoots of balsam fir, Abies balsamea L., synthetic (±)abscisic acid (ABA) (1) reduced photosynthesis and transpiration by inducing stomatal closure, (2) inhibited indoleacetic acid (IAA) - induced cambial activity in photosynthesizing and non-photosynthesizing shoots, and (3) inhibited the basipetal movement of [14C]IAA. Neither gibberellic acid nor kinetin counteracted the inhibitory effect of (±)ABA on IAA-induced cambial activity. In addition it was demonstrated that increasing the internal water stress increased the level of endogenous ABA in the phloem–cambial region of bark peelings and decreased the basipetal movement of [14C]IAA through branch sections. On the basis of these findings it is proposed that internal water stress inhibits cambial activity, partly through increasing the level of ABA; the ABA acts to decrease the provision of carbohydrates and auxin that are required for cambial growth.