bluuebunny/crossref_metadata_2025_split huggingface dataset:
Systemin transiently depolarizes the tomato mesophyll cell membrane and antagonizes fusicoccin‐induced extracellular acidification of mesophyll tissue
Authors: MOYEN C. , JOHANNES E. 
Published: April 2006

ABSTRACTThe plant polypeptide signal systemin induces proteinase inhibitor synthesis in tomato leaves. We show here that systemin elicits a transient depolarization of the tomato mesophyll cell membrane. Furthermore it triggers a transient decrease in the external pH of the mesophyll tissue which is followed by a sustained pH increase. In the presence of fusicoccin (which has been shown to antagonize the synthesis of proteinase inhibitors) the depolarization and transient H+ efflux are attenuated whereas the slower phase of the sustained electroneutral H+ influx persists. These results suggest that systemin‐induced changes in ion transport play a role in the early phases of systemin signal transduction.
The utilization of bicarbonate ions by the marine microalga Nannochloropsis oculata (Droop) Hibberd
Authors: MERRETT M. J. , NIMER N. A. , DONG L. F. 
Published: April 2006

ABSTRACTHCO3− utilization by the marine microalga Nannochloropsis oculata was investigated using a pH drift technique in a closed system. Light‐dependent alkalization of the medium resulted in a final pH of 10.5, confirming substantial HCO3− use by this alga. Alkalinity remained constant throughout the pH drift. Measurement of dissolved inorganic carbon (DIC) or the uptake of H14CO3− showed that nearly 50% of the total DIC remained external to the plasma membrane on completion of a pH drift. The rate of light‐driven alkalization was inhibited by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) and thus was dependent on photosynthesis. Light‐driven alkalization was not inhibited by a membrane‐impermeable inhibitor of carbonic anhydrase (CA), dcxtran‐bound sulphonamide (DBS), indicating that external CA was not involved in HCO3− utilization. The anion‐cxchangc inhibitor 4′,4′‐diisothiocyanostilbene‐2,2‐disulphonic acid (DIDS) completely inhibited light‐driven alkalization of the medium and H14CO3− uptake, providing unequivocal support for a direct uptake of H14CO3−. Chloride ions were essential for DIC‐dependent photosynthetic oxygen evolution, suggesting that bicarbonate transport occurs by HCO3−/CI− exchange.
Free Air Temperature Increase (FATI): a new tool to study global warming effects on plants in the field
Authors: NIJS I. , KOCKELBERGH F. , TEUGHELS H. , BLUM H. , HENDREY G. , IMPENS I. 
Published: April 2006

ABSTRACTA new technique, called Free Air Temperature Increase (FATI), was developed to artificially induce increased canopy temperature in field conditions without the use of enclosures. This acronym was chosen in analogy with FACE (Free Air CO2 Enrichment), a technique which produces elevated CO2 concentrations [CO2] in open field conditions. The FATI system simulates global warming in small ecosystems of limited height, using infrared heaters from which all radiation below 800 nm is removed by selective cut‐off filters to avoid undesirable photomorpho‐genetic effects. An electronic control circuit tracks the ambient canopy temperature in an unheated reference plot with thermocouples, and modulates the radiant energy from the lamps to produce a 2.5°C increment in the canopy temperature of an associated heated plot (continuously day and night). This pre‐set target differential is relatively‐constant over time due to the fast response of the lamps and the use of a proportional action controller (the standard deviation of this increment was <1°C in a 3 week field study with 1007 measurements). Furthermore, the increase in leaf temperature does not depend on the vertical position within the canopy or on the height of the stand. Possible applications and alternative designs are discussed.
Effects of parasitism by a mistletoe on the structure and functioning of branches of its host
Authors: TENNAKOON K. U. , PATE J. S. 
Published: April 2006

ABSTRACTInfestation of Acacia acuminata by the xylem‐tapping mistletoe Amyema preissii invariably results in inhibition of growth, defoliation and eventual death of host branch parts distal to the mistletoe. Branch sectional areas proximal (P) and distal (D) to mistletoes are used to classify stages of parasitism, with P:D area ratios of 5–6 invariably associated with distal branch senescence. As monopolization of the branch proceeds, mistletoe leaf area increases in parallel with declining host foliage area, and the specific hydraulic conductivity of distal host wood declines sharply relative to that of proximal wood, mineral composition and concentrations of nitrogenous solutes in xylem sap are at no stage appreciably different from those of proximal wood. After the demise of the distal branch parts, the transectional area of the host branch stump increases linearly with increasing mistletoe leaf area, the branch area supporting a unit of mistletoe leaf area always being about 3 times greater than that supporting a unit of host foliage area on unparasitized branches. This differential, compounded with high transpiration rates and selective uptake of host xylem solutes by the haustorium, fosters substantial mineral enrichment of the mistletoe relative to its host. The study provides a background for future investigation of possible cellular mechanisms continuously driving structural and functional changes in favour of the mistletoe.
Stimulation of root hair elongation in Arabidopsis thaliana by low phosphorus availability
Authors: BATES T. R. , LYNCH J. P. 
Published: April 2006

ABSTRACTLow phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 mmol m−3) or low (1 mmol m−3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low‐phosphorus plants developed root hairs averaging 0.9 mm in length while high‐phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low‐phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild‐type high‐phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low‐phosphorus plants. These results indicate that auxin may be involved in the low‐phosphorus response in root hairs.
Proteolytic analysis of polymerized maize tubulin: regulation of microtubule stability to low temperature and Ca2+ by the carboxyl terminus of β‐tubulin
Authors: BOKROS C. L. , HUGDAHL J. D. , BLUMENTHAL S. S. D. , MOREJOHN L. C. 
Published: April 2006

ABSTRACTTo obtain information on plant microtubule stability to low temperature and Ca2+, the regulatory domain of polymerized tubulin from maize (Zea mays ev. Black Mexican Sweet) was dissected by limited proteolysis with subtilisin. Tubulin in taxol‐stabilized microtubules was cleaved in a subtilisin concentration‐ and time‐dependent manner. Immunoblotting of microtubules with antibodies having mapped epitopes on α‐ and β‐tubulins revealed that cleavage initially removed ≤15 residues from the β‐tubulin carboxyl terminus to produce αβs‐microtubules. Subsequent cleavage occurred at an extreme site and an internal site within the α‐tubulin carboxyl terminus. Electron microscopy revealed that αβs‐microtubules were ultra structurally indistinguishable from uncleaved control αβ‐micro‐tubules. Quantitative polymer sedimentation showed that low temperature treatment (0°C) caused significant depolymerization of αβ‐microtubules, but little depolymerization of αβs‐microtubules. Ca2+ enhanced the cold‐induced depolymerization of both αβ‐ and αβs‐microtubules. However, αβs‐microtubules were significantly more stable to depolymerization by cold and Ca2+ than were αβ‐micro‐tubules. The results showed that maize microtubules containing shortened β‐tubulin carboxyl termini are relatively resistant to the combined depolymerizing effects of cold and Ca2+. Thus, the extreme carboxyl terminus of β‐tubulin is a crucial element of the plant tubulin regulatory domain and may be involved in the modulation of microtubule stability during the chilling response in plants.
The response of isoprene emission rate and photosynthetic rate to photon flux and nitrogen supply in aspen and white oak trees
Authors: Litvak M. E. , Loreto F. , Harley P. C. , Sharkey T. D. , Monson R. K. 
Published: April 2006

ABSTRACTIsoprene is the primary biogenic hydrocarbon emitted from temperate deciduous forest ecosystems. The effects of varying photon flux density (PFD) and nitrogen growth regimes on rates of isoprene emission and net photosynthesis in potted aspen and white oak trees are reported. In both aspen and oak trees, whether rates were expressed on a leaf area or dry mass basis, (1) growth at higher PFD resulted in significantly higher rates of isoprene emission, than growth at lower PFD, (2) there is a significant positive relationship between isoprene emission rate and leaf nitrogen concentration in both sun and shade trees, and (3) there is a significant positive correlation between isoprene emission rate and photosynthetic rate in both sun and shade trees. The greater capacity for isoprene emission in sun leaves was due to both higher leaf mass per unit area and differences in the biochemical and/or physiological properties that influence isoprene emission. Positive correlations between isoprene emission rate and leaf nitrogen concentration support the existence of mechanisms that link leaf nitrogen status to isoprene synthase activity. Positive correlations between isoprene emission rate and photosynthesis rate support previous hypotheses that isoprene emission plays a role in protecting photosynthetic mechanisms during stress.
Growth and maintenance respiration in leaves of northern red oak seedlings and mature trees after 3 years of ozone exposure
Authors: WULLSCHLEGER S. D. , HANSON P. J. , EDWARDS G. S. 
Published: April 2006

ABSTRACTA two‐component model of growth and maintenance respiration is used to study the response of northern red oak (Quercus rubra L.) seedlings and 32‐year‐old trees to sub‐ambient (10 μmol h; cumulative dose based on 7 h daily mean), ambient (43 μmol h), and twice‐ambient (85 μmolh) ozone. The relative growth rates (RGR) of leaves sampled from seedlings and trees were similar across treatments, as were specific leaf respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25‐3 mol CO2 kg−1 leaf dry mass produced for seedlings and 21‐5 mol kg−1 for trees. Maintenance coefficients ranged from 0‐89 to 1‐07 mol CO2 kg−1 leaf dry mass d−1 for seedlings and from 0‐64 to 0‐84 mol kg‐1 d−1 for trees. Neither coefficient was affected by ozone. Leaves sampled throughout the growing season also showed little response of respiration to ozone. This occurred despite a 30% reduction in net photosynthesis for trees grown at twice‐ambient ozone. These results suggest that growth and maintenance respiration in young northern red oak leaves are not affected by ozone and that in older leaves injury can occur without a parallel increase in so‐called ‘maintenance’ respiration.
Growth, CO2 uptake, and responses of the carboxylating enzymes to inorganic carbon in two highly productive CAM species at current and doubled CO2 concentrations
Authors: NOBEL P. S. , Israel A. A. , Wang N. 
Published: April 2006

ABSTRACTIn Agave salmiana Otto ex Salm. var. salmiana grown for 4½ months in open‐top chambers, 55% more leaves unfolded and 52% more fresh mass was produced at 730 than at 370μmol CO2 mol−1. A doubling of the CO2 concentration also stimulated growth in another highly productive CAM species, Opuntia ficus‐indica (L.) Miller, leading to earlier initial ion and 37% more daughter cladodes. Substantial net CO2 uptake occurred earlier in the afternoon and lasted longer through the night for A. salmiana at 730 than at 370μmol CO2 mol−1, resulting in 59% more total daily net CO2 uptake. The Michaelis constant (HCO3−) for PEPCasc was 15% lower for A. salmiana and 44% lower for O. ficus‐indica when the CO2 concentration was doubled; the percentage of Rubisco in the activated state in vivo was on average 64% higher at the doubled CO2 concentration. Thus the substantial increases in net CO2 uptake and biomass production that occurred in these two CAM species when the ambient CO2 concentration was doubled resulted mainly from higher inorganic carbon levels for their carboxylating enzymes, a greater substrate affinity for PEPCase, and a greater percentage of Rubisco in the activated state.
A flavonoid mutant of barley (Hordeum vulgare L.) exhibits increased sensitivity to UV‐B radiation in the primary leaf
Authors: REUBER S. , BORNMAN J. F. , WEISSENBÖCK G. 
Published: April 2006

ABSTRACTThe aim of the present investigation was to define the role of soluble flavonoids as UV‐B protectants in the primary leaf of barley (Hordeum vulgare L.). For this purpose we used a mutant line (Ant 287) from the Carlsberg collection of proanthocyanidin‐free barley containing only 7% of total extractable flavonoids in the primary leaf as compared to the mother variety (Hiege 550/75). Seven‐day‐old leaves from plants grown under high visible light with or without supplementary UV‐B radiation were used for the determination of UV‐B sensitivity. UV‐B‐induced changes were assessed from parameters of chlorophyll fluorescence of photosystem II, including initial and maximum fluorescence, apparent quantum yield, and photochemical and non‐photochemical quenching. A quartz fibre‐optic microprobe was used to evaluate the amount of potentially harmful UV‐B (310 nm radiation) penetrating into the leaf as a direct consequence of flavonoid deficiency. Our data indicate an essential role of flavonoids in UV‐B protection of barley primary leaves. In leaves of the mutant line grown under supplementary UV‐B, an increase in 310nm radiation in the mesophyll and a strong decrease in the quantum yield of photosynthesis were observed as compared to the corresponding mother variety. Primary leaves of liege responded to supplementary UV‐B radiation with a 30% increase in the major flavonoid saponarin and a 500% increase in the minor compound lutonarin. This is assumed to be an efficient protective response since no changes in variable chlorophyll fluorescence were apparent. In addition, a further reduction in UV‐B penetration into the mesophyll was recorded in these leaves.
Effects of red light on the fluence–response relationship for pulse‐induced phototropism of maize coleoptiles
Authors: LIU Y.J. , LINO M. 
Published: April 2006

ABSTRACTDark‐adapted coleoptiles of maize (Zea mays L.) were treated with red light (3min at 10.5 μmol m−2S−1) and were Stimulated, after a dark interval, with a pulse of unilateral blue light to induce phototropism. Phototropic fluence‐response curves were obtained in this way for different dark intervals. It was confirmed that the bell‐shaped fluence‐response curve for the first pulse‐induced positive phototropism (FPIPP) shifts to higher fluences following the red‐light treatment, the maximal shift being achieved at a dark interval of 2h. We found, however, that the two arms of the Fluence‐response curve do not shift synchronously. The shift of the descending arm to higher fluences began at 15 min. The ascending arm showed a slight shift to lower fluences before a greater shift to higher flucnces. the change of the shift direction occurring at 30–40min. Accordingly, the fluence‐response curve obtained for a 30 min dark interval was comparatively wide. Although dark‐adapted coleoptiles showed only fPIPP, another bell‐shaped fluence‐response curve, representing the second pulse‐induced positive phototropism (sPIPP), appeared gradually after the red‐light treatment. These changes of the phototropic fluence– respnse curve following exposure to red light are likely to have adaptive values because they favour phototropism under brighter light.
Effects of shading in different developmental phases on biomass and grain yield of winter wheat at ambient and elevated CO2
Authors: MITCHELL R. A. C. , GIBBARD C. L. , MITCHELL V.J. , LAWLOR D. W. 
Published: April 2006

ABSTRACTWinter wheat (Triticum aestivuin cv. Mercia) was grown in a controlled‐environment facility under simulated Held conditions at ambient (360μmol mol−1) and elevated (690 μmol mol−1) CO2 concentrations. Some of the plants were shaded to mimic cloudy conditions during three periods of about 20d duration between terminal spikelet and start of grain‐fill, giving 16 treatments in all. Elevated CO2, increased grain yield by about 20%, while shading in any period decreased yield, with the greatest effect in the last period, encompassing anthesis. No interactions between these effects were significant for grain yield, but there were complex interactions for mean grain size. Observed effects of shading and elevated CO2 on biomass production were well predicted by a simulation model. Observed effects of treatments on yield could be related to effects on biomass using a simple model which assumes that yield is proportional to biomass production, with coefficients of 0.42 (g grain yield g−1 biomass) for the first two periods and 0.74 for the last period. Wheat models should therefore include developmental changes in sensitivity of yield to biomass production, but biomass changes induced by different CO2 concentrations or light environments can be treated as having equivalent effects on grain yield.
Water transport in xylem conduits with ring thickenings
Authors: Roth A. 
Published: April 2006

ABSTRACTHelical or annular wall thickenings are not only present in protoxylem, but may also he a feature of the tracheids or vessel elements of secondary wood. The frequency of their occurrence tends to be a function of climatic factors and conduit diameter. In order to obtain a functional explanation for these structures, the hydrodynamic behaviour of xylem conduits with various patterns of annular wall thickenings was investigated numerically using a commercial CFD (Computational Fluid Dynamics) package. The fluid flow phenomena are presented in detail. The calculations show that the developing pressure gradient of the structures with corrugated walls is in each case lower than that of a smooth pipe with a diameter corresponding to the distance between two opposite thickenings. Furthermore, complex flow patterns with circulation zones between the thickenings develop which are dependent on the geometry of the wall. It may be hypothesized that these circulation zones influence the lateral water flow. The results are discussed with regard to the relationships between the water conduction function of the xylem and ecological factors.
Programmed accumulation of LEA‐like proteins during desiccation and cold acclimation of overwintering grape buds
Authors: SALZMAN R. A. , BRESSAN R. A. , HASEGAWA P. M. , ASHWORTH E. N. , BORDELON B. P. 
Published: April 2006

ABSTRACTMolecular investigation of the process of cold acclimation in woody plants has been limited by the superimposition of dormancy‐related events on the process of cold tolerance development. To address this limitation, we have used the grape Vitis labruscana L. ev. Concord to develop a system in which the developmental programme of dormancy can be induced seperately from cold acclimation. Using this system we have characterized differential accumulation of several proteins in grape buds during the normally superimposed endodormancy and cold acclimation programmes, and in buds which have entered only the endodormancy programme. A set of 47 kD proteins accumulated during endodormancy without cold acclimation to a level similar to that found in endodormant and cold‐acclimated buds, but without any associated increase in bud cold‐acclimation level. However, a 27 kD LEA‐like protein accumulated only in cold acclimated buds. We conclude that expression of the 47 kD glycoprotein is endodormancy‐related, but is not strictly related to the development of cold acclimation, while the 27 kD protein appears to be more specific to cold acclimation. In addition to strengthening the association of LEA‐like proteins with cold acclimation, this system allows more specific assessment of cold acclimation‐associated phenomena in overwintering buds.
Construction cost of loblolly and ponderosa pine leaves grown with varying carbon and nitrogen availability
Authors: GRIFFIN K. L. , WINNER W. E. , STRAIN B. R. 
Published: April 2006

ABSTRACTWe grew loblolly and ponderosa pine seedlings in a factorial experiment with two CO2 partial pressures (35 and 70 Pa), and two nitrogen treatments (1.0 and 3.5 mol m−3 NH4+), for one growing season to examine the effects of carbon and nitrogen availability on leaf construction cost. Growth in elevated CO2 reduced leaf nitrogen concentrations by 17 to 40%, and increased C:N by 22 to 68%. Elevated N availability increased leaf N concentrations and decreased C:N. Non‐structural carbohydrates increased in high‐CO2‐grown loblolly seedlings, except in fascicles from low N, and in ponderosa primary and fascicle leaves grown in high N. In loblolly, increases in starch were nearly 2‐fold greater than the increases in soluble sugars. In ponderosa, only the soluble sugars were affected by CO2. Leaf construction cost (g glucose g−1 dm) varied by 9.3% across all treatments. All of the variation in loblolly leaf construction cost could be explained by changes in non‐structural carbohydrates. A model of the response of construction cost to changes in the mass of different biochemical fractions suggests that the remainder of the variation in ponderosa, not explained by non‐structural carbohydrates, is probably attributable to changes in lignin, phenolic or protein concentrations.
Changes in UV‐B radiation screening effectiveness with leaf age in Rhododendron maximum
Authors: Ruhland C. T. , Day T. A. 
Published: April 2006

ABSTRACTWe examined how ultraviolet‐B radiation (UV‐B; 300 nm) screening effectiveness changes with leaf age in Rhododendron maximum growing in a shaded understory by measuring depth of penetration and epidermal transmittance with a fibre‐optic microprobe. Depth of penetration (and epidermal transmittance) of UV‐B decreased with leaf age in 1‐ to 4‐year‐old leaves, averaging 62 (32), 52 (22), 45 (16) and 48 μm (13%), respectively. Epidermal thickness increased with age in 1‐ to 4‐year‐old leaves due to a thickening of the cuticle from an average of 20 to 29μm. Ultraviolet‐B‐absorbing compound concentrations increased with age from 1–3 to 1–5 A300 cm−2 leaf area. Concentrations of UV‐B‐absorbing compounds (area basis) were a strong predictor of depth of penetration (r2= 0.82) and epidermal transmittance (r2= 0.95) of UV‐B in mature (1–4 year‐old) foliage. Chlorophyll concentrations (area basis) increased in leaves up to 3 years of age. Current‐year leaves (30 d old) were exceptional in that while they were particularly effective at screening UV‐B (depth of penetration and epidermal transmittance averaged 39μm and 5%, respectively) they had relatively low concentrations of UV‐B‐absorbing compounds (1.3 A300 cm−2). Our findings show that UV‐B‐screening effectiveness is not necessarily related to absorbing compound concentrations on a whole‐leaf basis, possibly due to anatomical changes within the epidermis that occur with leaf age.