bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fungal saprobes and pathogens as endophytes of rice (Oryza sativaL.)
Authors: FISHER P. J. , PETRINI O. 
Published: April 2006

summaryFungal endophytes have been isolated from inside the leaf blades, leaf sheaths, and roots of six‐week‐old plants as well as from seeds and ten‐day‐old seedlings ofOryza sativa(L.). The fungi isolated can be grouped in two categories; one containing organisms known mainly to be saprotrophic and the other comprising potential pathogens. Of the formerAlternaria alternata(Fr.) Keissler andEpicoccum purpurascensEhrenb. ex. Schlecht preferentially colonize the leaf blades of their host, whereasCladosporium tenuissimumCooke seems more generally distributed between leaf blades and leaf sheaths.Fusarium equiseti(Cords) Sacc.,F. oxysporumSchecht andPhoma sorghina(Sacc. Boerema) are latent in their hosts without causing disease symptoms.A. alternata, E. purpurascens, F, equiseti.andNigraspora oryzaehave also been frequently isolated from seeds and young seedlings and can be considered seed‐borne. Principal components analysis has shown a marked tissue specificity among rice endophytes. Leaf sheaths of the rice varieties grown under dry conditions are colonized by endophyte communities different from those of the wet cultivars.
Utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi (Lohmann) Kamptner
Authors: NIMER N. A. , DIXON G. K. , MERRETT M. J. 
Published: April 2006

summaryInorganic carbon‐dependent photosynthetic oxygen evolution was saturated at a photon flux density of 100 μmol m−2s−1for air‐grown cells of a low calcifying strain of Emittania huxleyi (Lohmann) Kamptner. Measurement of photosynthetic oxygen evolution at constant inorganic carbon concentration but varying pH showed that exogenous bicarbonate was not a major carbon source for photosynthesis. At pH 8.0 the concentration of dissolved inorganic carbon (DIC) required for the half‐maximal rate of photosynthetic O2 evolution (K0.5[DIC]) was 2.86 mm; the rate of non‐enzymic dehydration of HCO3 greatly exceeding the rate of CO2 fixation. Carbon dioxide uptake occurs by diffusive entry as shown by the K0.5 [DIC] of 12.5 μM at pH 5.0.Bicarbonate uptake, measured by the silicone‐oil‐layer centrigual filtering technique, did not show Michaelis‐Menten type kinetics. The electrical membrane potential difference was determined from the distribution of the lipophilic cation tetra[3H]phenylphosphonium (TPP+) between cells and the media. Cells grown at pH 8.0 exhibited a negative membrane potential (inside of cell relative to outside) of about −60 mV.
Growth and carbon economy of a fast‐growing and a slow‐growing grass species as dependent on ontogeny
Authors: POORTER HENDRIK , POTHMANN PETER 
Published: April 2006

summaryIn previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast‐ and slow‐growing plant species. The present experiment was to investigate whether these differences persist when plants become larger. Plants of the inherently fast‐growing Holcus Lanatus L. and the inherently slow‐growing Deschampsia flexuosa (L.) Trin. were grown under standardized conditions and growth, photosynthesis, respiration and carbon and nitrogen content were followed over a period of 4 to 7 weeks. Differences in relative growth rate were mainly due to the higher leaf area ratio (leaf area; plant weight) of the fast‐growing species. Rates of photosynthesis differed substantially when expressed on a leaf weight basis, but only slightly when expressed per unit leaf area. Although most parameters showed some ontogenetic drift, differences found for young seedlings persisted at least until plants reached a dry weight of circa 3 g. Therefore, at least for these two species, the conclusions based on interspecific variation relative growth rate of young seedlings apply to larger plants as well.
Differences in fructan accumulated in induced and field‐grown wheat plants: an elongation‐trimming pathway for their synthesis
Authors: BANCAL P. , CARPITA N. C. , GAUDILLÈRE J. P. 
Published: April 2006

summaryMature blades of wheat seedlings were induced to form fructan by excision and continuous illumination, and their sugars were analyzed either 24 or 60 h after induction by both gel permeation and high performance liquid chromatography. The earliest accumulated fructan consisted mainly of 1‐kestose, nystose, bifurcose, and short oligomers rich in (2→1)‐linkages and branch point residues. After several days, fructan included more than fifty compounds, among which one‐half of the total were heptamers or larger. Oligomers accumulated during long‐term incubation contained a higher proportion of (2→6)‐linkages than those accumulated early after induction. Stems of field‐grown wheat contained about the same amount of fructan as blades of induced seedlings, but with larger proportions of phlein oligomers initiating with 6‐kestose, phlein‐like oligomers initiating with bifurcose, and other branched oligomers enriched in (2→6)‐linkages. An ‘elongation‐trimming’ pathway is proposed in which a (2→1)‐specific fructan fructosyl transferase and O‐6 branching activity produce branched oligomers rich in (2→1)‐linkages, and in which a fructan exo‐hydrolase cleaves 1‐linked terminal‐fructosyl units selectively to have phlein‐like oligomers resistant to further hydrolysis.
In situ studies of crassulacean acid metabolism in Kalanchoë beharensis Drake Del Castillo, a plant of the semi‐arid southern region of Madagascar
Authors: KLUGE MANFRED , RAZANOELISOA BAKOARSINA , RAVELOMANANA DIDIER , BRULFERT JEANNE 
Published: April 2006

summaryThe first comprehensive field study has been conducted of crassulacean acid metabolism in a Kalanchoë species, namely K. beharensis Drake Del Castillo, a plant of the flora of the semi‐arid southern part of Madagascar. The study includes measurements of diel patterns of CO2 exchange and transpiration, and of fluctuations in organic acid levels, PEP carboxylase properties and water relations.In contrast to the other Kalanchoë species studied so far, the CAM behaviour of K. beharensis is very uniform. Regardless of whether the plants were naturally droughted for several months or had received 6 wk of daily watering, CO2 uptake was quantitatively the same and occurred entirely during the night. Watering also had no effect on the amplitude of the diel fluctuation of titratable acidity. The fluctuating citrate level was somewhat higher in the droughted plants. The data on PEP carboxylase indicate a diel change between an active night‐form and a less active day‐form of the enzyme known already from other CAM plants studied in the laboratory.Experiments with leaves kept in situ artificially darkened during the day revealed that the onset of deacidification was under the control of an external stimulus, presumably of temperature. In the CAM performing leaves, neither water status nor seasons were associated with significant differences in leaf water potential, osmotic pressure and turgor pressure. The lower amplitude of titratable acidity found during the dry season is presumably more due to suboptimal night temperatures during this time than to plant water relations.Altogether, the study shows that K. beharensis is capable of maintaining the full CAM performance throughout the entire arid seasons, and thus avoids CAM idling. It is assumed that this advantageous behaviour is based on the capability to maintain appropriate water status in the photosyntheticaily active leaves even during long‐lasting drought. This capability is due, on the one hand, to minimization of transpiration by the extreme CAM mode, accompanied by very low cuticular transpiration, and on the other hand due to water transfer from the older leaves which then wilt and are shed.
Tolerance of wheat (Triticum aestivum cvs Gamenya and Kite) and triticale (Triticosecale cv. Muir) to waterlogging
Authors: THOMSON C. J. , COLMER T. D. , WATKIN E. L. J. , GREENWAY H. 
Published: April 2006

summaryResponses of two genotypes of wheat (Triticum aestivum cvs. Gamenya and Kite) and one genotype of triticale (Triticosecale cv. Muir) were evaluated in stagnant solution culture and in waterlogged soil, using 23‐ to 36‐d‐old plants. Stagnant nutrient solutions decreased shoot fresh weight of Gamenya by 21% compared with aerated plants, while shoot fresh weight of Muir was unaffected. Reductions in nodal root fresh weight under stagnant conditions were also less for Muir than Gamenya.Aerenchyma in nodal roots of stagnantly grown plants accounted for 6.7 and 12.7% of the root cross sectional area for Gamenya and Muir, respectively. Oxygen supplied via this aerenchyma was substantially greater for Muir than Gamenya, and greatest for nodal roots of Kite. Elongation rates of stagnantly grown nodal roots in an Oa‐free medium reflected the amount of O2 supplied via the aerenchyma, and were 0.11, 0.17 and 0.27 mm h−1 for Gamenya, Muir and Kite, respectively.Waterlogging in soil decreased the redox potential from +600 to − 200 mV after 35 d. Waterlogging decreased shoot fresh weight of Gamenya, Kite and Muir by 63–82% compared with drained plants, with similar reductions in growth of seminal roots. Nodal root growth was little affected by waterlogging in soil, although Muir had a 1.6‐2.4‐fold greater nodal root mass than Gamenya and Kite. Furthermore, after two cycles of 7 d waterlogging and 7 d drainage the seminal roots of Muir were at least double the length of Gamenya and Kite.Under the same waterlogged conditions, the shoot growth of rice (Oryza sativa cv, Calrose) was much greater than for wheat and triticale, and this reflected differences in morphology and anatomy of the root systems. Nodal root/shoot ratios indicated the major factor limiting shoot growth of wheat was the small mass of nodal roots per plant. However, a possible additional factor is the poor function of nodal roots of wheat and triticale in waterlogged soil.
Ontogeny of synthesized Picea abies (L.) Karst.–Hebeloma crustuliniforme (Bull. ex St Amans) Quél. ectomycorrhizas
Authors: BRUNNER I. , SCHEIDEGGER C. 
Published: April 2006

summaryEctomycorrhizas were synthesized between Picea abies (L.) Karst. and Hebeloma crustuliniforme (Bull. ex St Amans) Quél. in growth pouches containing activated charcoal filter paper. Immediately emanating hyphae from inoculated plugs contacted root hairs and root surfaces, hyphal morphology was altered. They became short‐celled with few clamp connections, highly branched, and lacked cell wall ornamentation. Then, hyphae on root surfaces formed an inner synenchymatous mantle and loose hyphae formed an outer prosenchymatous mantle. Simultaneously, root cap cells became invaded by fungal hyphae and their remnants were incorporated into the inner mantle. Further root elongation took place but root hair production was suppressed. Thirdly, a Hartig net began to form in basal portions of developing ectomycorrhizas and the fungal mantle became denser and thicker. Fourthly, growth of the root was reduced and the hyphae of the Hartig net penetrated between cortical cells moving toward the apex. Fifthly, metacutis occasionally surrounded the meristem. At this stage the formation of the ectomycorrhiza can be considered to be complete and the rootlet itself is temporarily in a dormant state.
Effects of low‐concentration sulphur dioxide fumigation and vesicular–arbuscular mycorrhizas on 14C‐partitioning in Phleum pratense L.
Authors: CLAPPERTON M. JILL , REID DAVID M. 
Published: April 2006

summaryThe effect of long‐term low‐concentration (0.04–0.065 μl l−1) exposure to sulphur dioxide (SO2) on assimilate partitioning in Phleum pratense colonized by vesicular‐arbuscular (VA) mycorrhizal fungi from field soil was examined by supplying leaves with 14CO2. Seedlings were grown and exposed to SO2 for six weeks and then pulsed with 4CO2 for 15 min. The distribution of the 14C was analysed after a 12 h chase. SO2 fumigation had little effect on plant dry matter production, however, it had significant effects on the assimilation of 14CO2.Plants colonized by VA mycorrhizal fungi, both fumigated and controls, had a greater percentage of the total incorporated 14C in the roots, a significantly lower percentage of the total as 14C‐labelled soluble carbohydrates in the shoots, and a greater percentage of the total as 14C‐labelled amino‐ and organic acids in the shoots and roots than non‐mycorrhizal plants. SO2 exposure reduced root length, root length colonized by VA mycorrhizal fungi, and the length of root infected with arbuscules. It appeared that colonization by VA mycorrhizal fungi in field soil had an overriding effect on carbon assimilation, use, and translocation in the host, and these probably affect host sensitivity to SO2 exposure.
Timing of ozone stress and resulting status of ribulose bisphosphate carboxylase/oxygenase and associated net photosynthesis
Authors: PELL E. J. , ECKARDT N. , ENYEDI A. J. 
Published: April 2006

summaryExperiments were conducted to determine how the timing of an exposure to ozone influenced the impact of the gas on ribulose‐ 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) throughout the life span of a designated leaf. Saplings of Populus maximowizii×trichocarpa NE 388 received 5‐d exposures to O3 in growth chambers during and at the termination of presumed synthesis of Rubisco in a designated leaf. Ozone had no detectable impact on Rubisco activity or quantity when the exposure occurred during the time of increasing concentration of the protein in the leaf. When the concentration of Rubisco was near its peak, O3 induced a reduction in quantity and activity of Rubisco, but after cessation of the O3 stress, levels converged with those of the untreated tissue. When O3exposure occurred after full leaf expansion, minimal effects of the gas could be detected. When plants of hybrid popular or Raphanus sativus L. cv. Cherry Belle received chronic O3 treatment throughout the lifespan of the leaf, Rubisco activity and quantity declined more rapidly and never converged with values of untreated tissue.Studies of gas exchange revealed that changes in Rubisco were associated with a decline in net photosynthesis (A) and that these effects preceded the observed reduction in foliar conductance. CO2 response curves were measured periodically, and the initial slope (linear portion) of the curve, reflecting carboxylation capacity, declined more rapidly with leaf age in O3‐treated than in untreated poplars. There was no effect of O3 on stomatal limitation to CO2, assimilation except for a slight increase during the last 2 wk of the 9‐wk experiment. This supported the hypothesis that O3 effects on A were associated with CO2‐fixing capability of the leaf.
Plastid development in distinctively coloured juvenile leaves
Authors: WHATLEY JEAN M. 
Published: April 2006

summaryThe juvenile leaves of many tropical and a few temperate plants are translucent and apparently colourless or are white, red or brown in colour rather than green. It is already known that the distinctive colours of the young leaves can result from a delayed increase in chlorophyll content and/or from the masking effects and changing levels of other pigments. The present study deals with the patterns of chloroplast development during leaf growth in Coffea arabica L., Durio zibethinus Murray, Mangifera indica L., Photinia×Fraseri Dress. Red Robin and Theobroma cacao L. Even in very young leaves the mesophyll cells contain chloroplasts, but these are small and few in number. Although conspicuous greening usually takes place only after the leaves are fully expanded, chloroplast development proceeds without interruption throughout leaf growth. The late increase in chlorophyll content is associated with a noticeable increase in the long axes of the chloroplasts and/or their numbers within each cell section. The way in which the overall increase in chloroplast volume per cell is achieved varies between species.
Visualization of the cytoskeleton in red algae using fluorescent labelling
Authors: GARBARY DAVID J. , McDONALD A. ROSA , DUCKETT JEFFREY G. 
Published: April 2006

summaryCytoskeletal components have been visualized for the first time in red algae using fluorescent labelling. Rhodamine‐phalloidin was used to stain actin in a variety of filamentous species: Griffithsia pacifica, Tiffaniella snyderae, Ceramium strictum, Antithamnion kylinii (Ceramiales) and Audouinella dasyae (Acrochaetiales). Immunofluorescent labelling of microtubules was obtained only in Griffithsia pacifica. In both procedures, successful labelling was achieved only after wall digestion with glucuronidase and protocols using cellulase resulted in no labelling. Both microfilaments and microtubules formed extensive arrays in the peripheral cytoplasm of Griffithsia. Microtubules were associated with nuclei in these highly multinucleate cells, suggesting that they maintain the extremely regular nuclear arrangement. Dense labelling of microfilaments occurred at rhizoid apices, however, this was not observed in apical cells, suggesting that two distinct mechanisms of tip growth may be present. Of the algae studied, only Griffithsia formed extensive peripheral arrays of microfilaments in all cells; the remaining genera showed actin labelling in a variety of different structures including, long and short ‘ropes’ of varying thicknesses, basket‐like structures and ‘spikes’. In Griffithsia extensive actin staining was often associated with the pit plugs between adjoining cells. Cytoskeletal components often showed a polar distribution with denser labelling towards the bases or apices of cells. In dividing apical cells of Griffithsia, a band of microfilaments was observed prior to deposition of the new cross wall. These preliminary results suggest that cytoskeletal studies will provide important insights into understanding development and cell function in red algae.
Ammonia and ammonium fluxes between photolithotrophs and the environment in relation to the global nitrogen cycle
Authors: RAVEN JOHN A. , LINDA BERND WOLLENWEBER , HANDLEY L. 
Published: April 2006

summaryAmmonium (used here to signify NH4+ plus NH3) is the immediate inorganic precursor of organic nitrogen in photolithotrophs. In marine habitats ammonium is also the major exogenous nitrogen source, and the same is probably true of terrestrial habitats. In addition to this major role of ammonium as exogenous nitrogen source, it is also quantitatively very important as an endogenous nitrogen source with nitrate or N2 as exogenous nitrogen source, and as a recycled nitrogen compound in photorespiration and in phenylpropanoid synthesis. The shoots of terrestrial plants have higher NH3 compensation partial pressures than most natural soils, and especially higher than that of the sea. However, long‐distance transport of gaseous NH3 (e.g. from continents to oceans) is a negligible component of the ‘natural’ global nitrogen cycle. Current concepts of evolution of the atmosphere and biosphere do not involve high partial pressure of NH3 in the atmosphere: any ammonium produced in inorganic or biological processes is removed from the atmosphere by rain‐out, or, over larger time‐scales, by the action of ultraviolet radiation (especially before the ozone screen came into being) and of hydroxyl radicals (especially after oxygenation of the atmosphere). In addition to posing problems for the origin of life and arguing for an early rather than a late evolution of diazotrophy, a low NH3 partial pressure renders implausible arguments that phenylpropanoid synthesis was restricted early in evolution by the effect of high ammonia in reversing phenylalanine ammonia‐lyase.
A comparison of ammonium and nitrate as nitrogen sources for photolithotrophs
Authors: RAVEN JOHN A. , WOLLENWEBER BERND , HANDLEY LINDA L. 
Published: April 2006

summaryPotential advantages of ammonium relative to nitrate assimilation (assuming equal nitrogen supply in the two forms), deduced from known biochemical pathways and the site of nitrate assimilation in vascular land plants, include (i) a greater maximum specific growth rate, (ii) lower costs of photons and (in transpiring plants) water per unit carbon assimilated, and (iii) lower costs of iron, manganese and molybdenum per unit carbon assimilated per unit time. Actual measurements show that the growth rate and photon cost predictions are often, but not invariably, borne out; while data on the water cost of growth almost invariably contradict the prediction by showing a lower water cost from nitrate‐supplied than ammonium‐supplied plants. Few data seem to be available that test the predictions as to metal costs of growth; some of the predictions are borne out. These possible or realised advantages to the photolithotroph of using ammonium must be considered in the context of the relative availability of the two sources of combined nitrogen. In the oceans nitrification of ammonium produced in mineralization does not compete well with photolithotrophic assimilation of ammonium in the euphotic zone, so ammonium is the major combined nitrogen source for ‘recycled’ primary production, while ‘new’ production largely uses nitrate produced in deep, dark water. When both nitrogen sources are available to phytoplankton organisms ammonium is almost invariably preferred, with complete suppression of nitrate use with as little as 1–2 mmol m−3ammonium. In terrestrial habitats the nitrification of ammonium produced in mineralization is not photoinhibited (as can occur in the surface water of the ocean) but is subject to inhibition by anoxia, low pH and (possibly) plant‐produced defence compounds. However, the lower diffusion coefficient for ammonium than for nitrate in soils means that nitrogen‐limited plant growth as a given rate needs a higher mean dissolved ammonium concentration in the soil than is the case for nitrate when the soil contains only one of these nitrogen sources and root distribution and morphology are unaffected by the nitrogen source. With equal mean ammonium and nitrate concentrations, a nitrogen‐limited plant supplied solely with ammonium would need a more extensive root/root hair/mycorrhiza system to attain the same nitrogen uptake rate on a per plant basis as would a nitrate‐supplied plant, with consequences for resource allocation by, and growth rate of, the ammonium‐grown plant. In addition to the larger mean area‐based ammonium assimilation rate by photolithotrophs in the oceans, consideration of the interactions among ammonium diffusion coefficient, ammonium diffusion distance, organism surface area per unit biomass and the organism maximum specific growth rate in the ocean relative to soils can plausibly account for the lower mean ammonium concentrations in the ocean than in soils.
Oxygen controls the development of Frankia vesicles in continuous culture
Authors: HARRIS S. L. , SILVESTER W. B. 
Published: April 2006

summaryDaily addition of sterile media at a dilution rate of 0.100–0.125 d−1 allowed Frankia to be maintained in continuous, derepressed (N2‐fixing) culture for periods of more than 30 d. Continuous cultures yielded Frankia populations with stable levels of growth and nitrogenase activity as well as constant vesicle morphology. These were then used to investigate the influence of oxygen on vesicle development.Timing of vesicle induction is independent of po2 although thickening of the vesicle envelope and stalk, a ‘normal’ developmental process, is specifically controlled by oxygen. At higher po2 levels vesicles are thicker‐walled and therefore offer greater resistance to oxygen diffusion. Oxygen also influences induction of nitrogenase. Greater delay in the onset of acetylene reduction activity at highpo2 is apparently due to the time taken for vesicles to reach a critical minimum wall thickness. Recovery of nitrogenase underwent a similar time lag when Frankia cultures were exposed to a sudden increase in po2.