bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Isoprene 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

A 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

In 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

The 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

Dark‐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

Winter 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

Helical 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

Molecular 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

We 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

We 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.
Foliar metabolic heat rate of seedlings and mature trees ofPinus ponderosaexposed to acid rain and ozone
Authors: MOMEN B. , HELMS J. A. , CRIDDLE R. S.
Published: April 2006

We investigated the effects of acid rain and ozone on respiration rates of 1‐year‐old and current‐year foliage of half‐sib seedlings and mature clones of a ponderosa pine genotype by measurement of foliar metabolic heat rates. Two rain regimes (pH 5‐1 and 3‐0) were applied weekly to foliage only, from January to April 1992. Two ozone regimes (ambient and twice‐ambient) were applied from September 1991 to November 1992. Metabolic heat rate was measured in April on 1‐year‐old foliage, in June on both 1‐year‐old and current‐year foliage, and in November on current‐year foliage in 1992. Except for current‐year foliage in June, the metabolic heat rate was calculated per unit of both foliar dry mass and N mass. In seedlings, both measures of metabolic heat rate increased in late June for 1‐year‐old foliage exposed to twice‐ambient ozone, and in November for current‐year foliage exposed to the combination of twice‐ambient ozone and pH 3‐0 rain. In mature trees, metabolic heat rate was not affected significantly by ozone, rain acidity, or their interaction. In June, when both 1‐year‐old and current‐year tissues were examined, the metabolic heat rate of expanding, current‐year foliage was higher than that of fully expanded, 1‐year‐old foliage regardless of plant age or treatment combination.
The vacuolar localization of a basic peroxidase isoenzyme responsible for the synthesis of α‐31,41‐anhydrovinblastine in Catharanthus roseus (L.) G. Don Leaves
Authors: SOTTOMAYOR M. , de PINTO M. C. , SALEMA R. , DiCOSMO F. , PEDREÕO M. A. , ROS BARCELO A.
Published: April 2006

Partially purified protein extracts of Catharanthus roseus leaves were able to couple catharanthine and vindoline to produce α‐3′,4′‐anhydrovinblastine (AVLB) in a reaction strictly dependent on H2O2. This result, and the co‐purification of peroxidase with AVLB synthetase activity, strongly suggest a peroxidase‐like nature for the coupling enzyme. Only one peroxidase isoenzyme was detected in C. roseus leaves, and it was shown that this isoenzyme consists of a molecularly‐heterogeneous basic peroxidase (EC 1‐11‐1‐7) mainly located in the vacuole. These results suggest that a basic peroxidase located in the vacuole may be the main enzyme responsible for AVLB synthesis in C. roseus leaves. This isoenzyme was also found in cell walls where a peroxidase inhibitor was detected.
Comparison of plant and fungal gravitropic responses using imitational modelling
Authors: STOČKUS A. , MOORE D.
Published: April 2006

The mechanisms of gravity perception are still hypothetical, but there are sufficient data from experiments with plants to enable mathematical modelling to imitate the behaviour of gravitropic response systems. We have a much less complete picture of gravitropic kinetics in agaric mushrooms. However, some existing mathematical models which imitate plant responses are in principle universal because their conceptual components are not limited to any specific cellular entities. In this work we have used such models to compare plant and fungal gravitropism, using recently acquired kinetic data from the agarics Coprinus cinereius and Flammulina velutipes. The results show striking similarities between plants and fungi. First, it is evident that the basic assumptions of the plant models are logically applicable to fungi. Secondly, the mechanism of bending is the same (differential growth of opposite flanks of the growing organ). Thirdly, the distribution of growth seems very similar: in both plants and fungi growth of the organ is most intensive just behind the apex and is almost absent at the apex and at the base. Fourthly, in both fungi and plants the gravitropic response exhibits a substantial time delay suggesting that many time‐consuming processes are involved in reception, transduction and realization of gravitropic stimuli. Important differences in plant and fungal gravitropism kinetics were: (i) the agaric stem apex always returned to the vertical, whereas some plant organs show stable plagiogravitropic growth; (ii) inflections were usually seen in C. cinereus stem gravitropism time courses suggesting that a curvature compensation process delayed bending for a time; (iii) C. cinercus stems very rarely overshot or oscillated around the vertical although many plant subjects oscillate and the (limited) data for F. velutipes showed a single, exaggerated overshoot and oscillation. In this latter case, experimental modelling with parameters characteristic of a low level of perception improved the fit to the F. velutipes data, indicating that the two fungi may differ in this factor. Application of the plant models focused future research attention on the urgent need for data bearing on angle‐response and acceleration–response relationships in fungi, and their detection–level thresholds for gravitational acceleration. Since the modelling also highlighted some fundamental kinetic differences between the only two fungi for which sufficient data are available at the moment, it is also clear that detailed observations need to be made of gravitropism kinetics in a larger number and wider range of fungi.
Distribution and activity of microsomal NADPH‐dependent monooxygenases and amino acid decarboxylases in cruciferous and non‐cruciferous plants, and their relationship to foliar glucosinolate content
Authors: BENNETT R. N. , KIDDLE G. , HICK A. J. , DAWSON G. W. , WALLSGROVE R. M.
Published: April 2006

The NADPH‐dependent conversion of amino acids to their aldoximes is an initial step in glucosinolate biosynthesis. A number of microsomal aldoxime‐forming monooxygenase activities were detected in leaves from a variety of glucosi‐nolate‐containing species, whereas barley, bean and tobacco leaves did not contain any such activities. The substrates for these monooxygenases in each species largely correlated with the spectrum of glucosinolates found in that species. No activity was detected that metabolized homomethionine (supposed precursor of 2‐propenylglucosinolate [sinigrin]), even in species where sinigrin was the major glucosinolate. In Sinapis species containing hydroxybenzylglucosinolate (sinalbin), activity with L‐Tyr was detected, whereas Brassica species containing sinalbin had no such activity. However, these Brassicas did contain an L‐Phe monooxygenase activity. Partial characterization of the monooxygenases indicated that in Brassica species, Nasturtium officinalis and Raphanus sativus these resembled the flavin‐linked monooxygenases previously found in oilseed rape (Brassica napus) and Chinese cabbage (Brassica campestris). The L‐Tyr‐dependent activity in Sinapis species, and the L‐Phe‐dependent activity in Tropacolum majus, had characteristics of cytochrome P450‐type enzymes. No similarity was found with any other known amino acid metabolizing enzymes (including decarboxylases, amino acid oxidases and diamine/polyamine oxidases).
Turgor regulation in Lamprothamnium papulosum. I. I/V analysis and pharmacological dissection of the hypotonic effect
Authors: BEILBY M. J. , SHEPHERD V. A.
Published: April 2006

Current‐voltage (I/V) analysis and pharmacological dissection were applied to membranes of Lamprothamnium at the time of hypotonic stress. At least three types of process were found to be involved in the response to this stress.

The first 10min of exposure to hypotonic medium resulted in a depolarization of about 50mV accompanied by a decrease or no change in conductance. This depolarization occurred with either K+ or Ca2+ (and consequently C− channels inactivated.

The CI− channels opened mainly in the first 15min of the hypotonic stress, increasing the membrane conductance by about an order of magnitude.

The K+ conductance rose as the Cl− conductance started to diminish and reached a maximum after about 40 min.

Both types of channel were strongly potential‐dependent with a conductance peak between ‐150 and 0mV. An inactivation of K+or CI− channels resulted in moving the membrane potential away from the conductance maximum toward either EK or ECI, diminishing the ion efflux (and turgor regulation). The time courses of the conductance increases remained the same, suggesting that the conductance changes are not driven by feedback to some preset turgor level. The electrophysiology of the Lamprothamnium transporters is compared to that of salt‐sensitive charophytes.
Effects of salinity on turgor pressure and fertility in Tolypella (Characeae)
Authors: WINTER U. , SOULIÉ‐MÄRSCHE I. , KIRST G. O.
Published: April 2006

We present the first experimental results on salinity tolerance and regulation mechanisms in the genus Tolypella. The two species investigated, T. nidifica and T. glomerata, regulate turgor pressure with almost complete effectiveness by adjustment of K+ and CT concentrations. Sucrose is also involved. The mechanism is basically identical to the mechanism of turgor pressure regulation previously identified in representatives of the genera Chara and Lamprothamnium. Since Chara and Lamprothamnium on the one hand and Tolypella on the other belong to different phylogenetic branches that separated early in the geological history of the Characeae, the K+ regulation mechanism can be assumed to represent an ancient pattern derived from a salt‐tolerant common ancestor. Furthermore, our experiments provide evidence that salinity is a limiting factor for fertility in both T. nidifica and T. glomerata. Although the onset of gametangia covers the whole range of salinities tested here (0–29 psu), 12psu was the inhibitory level for the formation of mature oospores. Fertilization is probably disturbed by an increase in salinity. An inability to reproduce sexually under euryhaline conditions could explain why the distribution of the two species is restricted to oligo‐ and mesohaline environments, despite the wide range of salinity tolerance of their vegetative apparatus.
Prevention of aluminium toxicity with supplemental boron. I. Maintenance of root elongation and cellular structure
Authors: LENOBLE M. E. , BLEVINS D. G. , SHARP R. E. , CUMBIE B. G.
Published: April 2006

Aluminium toxicity is an important factor limiting plant growth mi acid soils. Symptoms of B deficiency and Al toxicity are very similar and generally associated with impaired membrane Function and root growth. Thus the objective of this study was to determine whether supplemental B prevents Al inhibition of root growth and development. Squash (Cucurbita pepo L. cv. Sunbar) was grown in hydroponic nutrient media with 44 mmol m−3 free Al and B concentrations extending from 5 to 100 mmol m−3. Our results establish that B protects against Al inhibition of root growth. Protection was apparent at all levels of organization examined: primary root and lateral root lengths; primary root cell elongation, cell production rate, tissue organization and cell structure; primary root morphology and maturation. Protection against Al inhibition was also apparent for shoot growth. These studies were undertaken in solution culture to limit the variables examined; however, the underlying motivation for this study is the problem of worldwide Al toxicity in soils. Therefore, the effect of adding additional B to a high‐Al soil was also investigated and is the subject of the companion paper (Le Noble. Blevins & Miles 1996, Plant, Cell and Environment 19, 1143–1148).
Prevention of aluminium toxicity with supplemental boron. II. Stimulation of root growth in an acidic, high‐aluminium subsoil
Authors: LENOBLE M. E. , BLEVINS D. G. , MILES R. J.
Published: April 2006

Root growth inhibition is an early symptom of Al toxicity and B deficiency. Our hypothesis is that Al toxicity may induce B deficiency, and it was our objective to determine if incorporation of supplemental B would promote root penetration into an acidic, high‐Al subsoil. Alfalfa (Medicago sativa L. cv. Hy‐Phy) was grown in slanted tubes with a Plexiglas window along their length. The top half of the tub contained silt loam soil and the bottom half contained subsoil from the Bt1 horizon (26% Al saturation) of a Creldon silty clay loam. Both soils originally contained 0–9 kg B ha−1. When root growth was measured in the bottom half of the high‐A1 subsoil, all measurements—depth of rooting, total root growth, final root lengths and root dry weight—demonstrated greater root growth in treatments where additional B was incorporated into the high‐Al subsoil. Results from this soil study extend those obtained in our hydroponic study in which supplemental B presented Al inhibition of root growth. Boron concentrations may need to he increased under acidic ‘high‐Al’ soil conditions to promote root penetration into these soil zones, and this could be especially important during periods of drought stress.
Gravitropism of maize and rice coleoptiles: dependence on the stimulation angle
Authors: IINO M. , TARUI Y. , UEMATSU C.
Published: April 2006

Gravitropism of maize and rice coleoptiles was investigated with respect to its dependence on the angle of displacement or the initial stimulation angle (ISA). Close examination of curvature kinetics and the response to a drop in stimulation angle (SA) indicated that the gravitropic response during an early but substantial part of curvature development is directly related to the ISA, there being no effect of the reduction of SA resulting from the curvature response itself. On the basis of this finding, the relationship between the steady SA and the curvature rate was determined. In maize, the curvature rate increased linearly with the sines of SAs up to an SA of 90°. Rice coleoptiles. however, showed a saturation curve in the same range of SAs. The saturation profile was nearly identical between coleoptiles grown in air and those submerged in water, although the latter elongated much faster. Rice coleoptiles appeared to be far more sensitive to gravity than maize coleoptiles. It is concluded that the sensitivity to gravity, assessed through dependence on ISA, is a property inherent to a given gravitropic organ. Long‐term measurements of curvature indicated that the coleoptiles bend back past the vertical. This overshooting was marked in submerged rice coleoptiles.
Shoot and root physiological responses to localized zones of soil moisture in cultivated and wild lettuce (Lactuca spp.)
Authors: GALLARDO M. , JACKSON L.E. , THOMPSON R.B.
Published: April 2006

Cultivated crisphead lettuce (Lactuca sativa L.) has a shallower root system than its wild relative, Lactuca serriola L. The effects of localized soil water, at depth, on plant water relations, gas exchange and root distribution were examined in the two species using soil columns with the soil hydraulic‐ally separated into two layers, at (0–20 cm and 20–81) cm, but permitting root growth between the layers. Three treatments were imposed on 7‐week‐old plants, and maintained for 4 weeks: (i) watering, both layers to field capacity; (ii) drying the upper layer while watering the lower layer to field capacity, and (iii) drying both layers.

Drying only 0–20 cm of soil had no effect on leaf water status, net photosynthesis, stomatal conductance or biomass production in L. serriola compared to a well‐watered control, but caused a short‐term reduction (10 d) in leaf water status and photosynthesis in L. sativa that reduced final shoot production. The different responses may be explained by differences in root distribution. Just before the treatments commenced, L. serriola had 50% of total root length at 20–80 cm compared to 35% in L. sativa. Allocation of total biomass to roots in L. serriola was approximately double that in L. sativa. The wild species could provide germplasm for cultivated lettuces to extract more soil water from depth, which may improve irrigation efficiency.
Stomata from growth‐chamber‐grown Vicia faba have an enhanced sensitivity to CO2*
Authors: TALBOTT L. D. , SRIVASTAVA A. , ZEIGER E.
Published: April 2006

Abaxial stomata from Vicia faba leaves grown in a growth chamber under constant light, temperature and humidity showed an elaborate pattern of aperture changes over the course of a light cycle. These aperture changes were tightly correlated with changes in chamber CO2 concentration (r2=0.83). Changes in chamber [CO2] resulted, in turn, from substantial daily fluctuations in ambient [CO2], typical of the Los Angeles environment with a constant offset caused by photosynthesis and respiration of the plants within the chamber. The dominant role of the stomatal response to CO2 in the control of aperture was confirmed by manipulation of chamber [CO2]. Fast (15 min) increases and decreases in [CO2] caused rapid decreases and increases in aperture, while constant |CO2] resulted in constant aperture. In contrast, aperture changes in comparable plants grown under greenhouse conditions were tightly correlated with changes in incident solar radiation (r2=0.80), and poorly correlated with changes in [CO2] (r2=0.09). Greenhouse‐grown plants transferred to growth chamber conditions showed no apparent response to CO2. These data indicate that growth‐chamber‐grown V, faba leaves provide an experimental system optimally suited for the study of the stomatal response to CO2, and suggest that acclimation to environmental conditions alters the sensitivity of stomata to CO2.
Gravisensitivity of cress roots: investigations of threshold values under specific conditions of sensor physiology in microgravity*
Authors: VOLKMANN D. , TEWINKEL M.
Published: April 2006

The minimum dose (dose = stimulus × time), one of three threshold values related to gravity, was determined under microgravity conditions for cress roots. Seedlings were cultivated on a 1g centrifuge in orbit and under microgravity, respectively. After continous stimulation on a threshold centrifuge, minimum doses of 20–30 gs for microgravity roots and 50–60 gs for roots grown on a 1g centrifuge were estimated, which indicated that micro‐gravity roots have a higher sensitivity than 1g roots. These results do not confirm the threshold value of 12gs which was determined for cress roots using the slow rotating clinostat. Following application of intermittent stimuli to microgravity‐grown roots, gravitropic responses were observed after two stimuli of 13‐5 gs separated by a stimulus‐free interval of 118 s. Generally, this demonstrates that higher plants are able to ‘sum up’ stimuli which are below the threshold value. Microscopic investigations of the cellular structure corresponding to stimulations in the range of the threshold value demonstrated a small displacement of statoliths in root statocytes. No significant correlation was observed between gravitropic curvature and statolith displacement. If the statolith theory is accepted, it can be concluded that stimulus transformation must occur in the cytoplasm in the near vicinity of the statoliths and that this transformation system – probably involving cytoskeletal elements – must have been affected during microgravity seedling cultivation.
Photosystem II and oxygen regulation in Sesbania rostrata stem nodules
Authors: JAMES E.K. , IANNETTA P.P.M , NIXON P.J. , WHISTON A.J. , PEAT L. , CRAWFORD R.M.M , SPRENT J.I. , BREWIN N.J.
Published: April 2006

The tropical wetland legume Sesbania rostrata Brem. produces nitrogen‐fixing stem nodules which are green and contain chlorophyll, the chloroplasts being concentrated in a hand in the inner and mid‐cortex close to the nitrogen‐fixing cells. The photosystem II thylakoid membrane proteins D1, D2 and PsbO, which are essential for photo‐synthetic O2 evolution, were shown by immunoblotting to be present in extracts of leaves and stem nodules. Immunogold labelling confirmed their presence on stem nodule thylakoids and showed that labelling was most intense in well‐developed chloroplasts in the mid‐cortex and least intense in the smaller, less‐abundant chloroplasts adjacent to the nitrogen‐fixing cells. Concentrations of the oxygen‐carrying protein leghaemoglobin (Lb) did not differ between stem and S. rostrata root nodules, and Lb was localized in bacteroid‐containing cells, including those immediately adjacent to the cortex, in both nodule types. Moreover, nitrogenase component 2 was localized in bacteroids within the outermost layers of infected cells, suggesting that a low pO2 was maintained, despite the nearby chloroplasts. Nodule extracts examined by ELISA and immunoblots, using the monoclonal antibody MAC265, showed greatly enhanced expression of a 139 kDa glycoprotein in stem compared to root nodules. Immunogold labelling showed that material containing the MAC265 antigen occluded intercellular spaces, and was present in cell walls, throughout the cortex of stem nodules (particularly in the chloroplasl‐rich inner and mid‐cortex), but was considerably less evident in root nodules.
Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree
Authors: WHITEHEAD D. , LIVINGSTON N. J. , KELLIHER P.M. , HOGAN K. P. , PEPIN S. , MCSEVENY T.M. , BYERS J.N.
Published: April 2006

Sudden but transient changes in the fraction or illuminated foliage area in a well‐watered 7‐year‐old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (gt), stomatal conductance (gs) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in gt. However, when tree conductance was normalized with respect to the illuminated leaf area (gt'), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in gs and A up to 59 and 24%, respectively, for needles in the top third of (he crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.
Differential expression during drought conditioning of a root‐specific S‐adenosylmethionine synthetase from jack pine (Pinus banksiana Lamb.) seedlings
Authors: MAYNE M. B. , COLEMAN J. R. , BLUMWALD E.
Published: April 2006

Differential screening of a cDNA library constructed from root mRNA from jack pine (Pinus banksiana Lamb.) seedlings exposed to two cycles of drought conditioning identified a S‐adenosylmethionine synthetase (sam‐s) cDNA. A cDNA encoding the entire open reading frame of SAM‐S was identified and characterized. Analysis of the full‐length sam‐s cDNA revealed that it was 1675 bp, encoded an open reading frame of 393 amino acids and had a predicted protein mass of 43 kDa. Jack pine sam‐s was found to be highly similar to several other plant sam‐s genes. RNA gel blot analysis showed that sam‐s mRNA abundance increased following two cycles of drought conditioning and remained abundant after 3 d of rewatering. Expression of this gene appears to be root‐specific. Quantitative slot blot analysis showed that two cycles of drought conditioning caused a 6‐fold increase in sam‐s mRNA abundance whereas heat shock, cold stress and anoxia did not result in the accumulation of sam‐s mRNA. SAM‐S enzyme activity increased 2‐fold following two cycles of drought conditioning. The increase in the rate of SAM‐s enzyme activity was also correlated with changes in rates of ethylene and betaine synthesis, biosynthetic pathways that utilize SAM as a substrate. Ethylene evolution and betaine abundance increased following two cycles of drought conditioning.
Chemical differences between wildtype and gibberellin mutants of tomato determined by pyrolysis‐mass spectrometry
Authors: NIEMANN G. J. , EIJKEL G. B. , KONINGS H. , PUREVEEN J. B. M. , BOON J. J.
Published: April 2006

Leaf, stem and root material of wild‐type and gibberellin (GA)‐deficient mutants of tomato (Lycopersicum esculentum L.) were analysed by pyrolysis‐mass spectrometry for possible differentiation in chemical allocation pattern among cell wall and cytoplasm. GA‐deficiency is accompanied by changes in the relative growth rate (RGR). RGR‐correlated changes were found in leaves in the comparative amounts of cellulose‐ and protein‐derived fragments. The low‐RGR genotypes contained more protein and nucleic acid, the high‐RGR ones more cellulose. In root material, a higher contribution of cellulose, hemicellulose and G‐ and S‐lignin was found for the lower‐RGR plants and comparatively high protein in the high‐RGR genotypes. For stems, less clear results were obtained, possibly because of variation in the ratio of syringyl‐ and guaiacyl‐lignin. Part of the results might be explained by a GA‐dependent change in cell size.
Enhanced ethylene production by primary roots of Zea mays L. in response to sub‐ambient partial pressures of oxygen
Authors: BRAILSFORD R. W. , VOESENEK L. A. C. J. , BLOM C. W. P. M. , SMITH A. R. , HALL M. A. , JACKSON M. B.
Published: April 2006

Ethylene production by primary roots of 72–h‐old intact seedlings of Zea mays L. cv. LG11 was studied under ambient and sub‐ambient oxygen partial pressures (pO2) using a gas flow‐through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting‐up, ethylene production in air was faster during the first 6h than later, in association with a small temporary swelling of the roots. When roots were switched from air (20–8kPa O2) to 3 or 5kPa O2 after 6h, ethylene production increased within 2—3 h. When, the roots were returned to air 16 h later, ethylene production decreased within 2—3 h. The presence of 10kPa CO2 did not interfere with the effect of 3kPa O2. Transferring roots from air to 12–5kPa did not change ethylene production, while a reduction to 1 kPa O2 induced a small increase. The extra ethylene formed in 3 and 5 kPa O2 was associated with plagiotropism, swelling, root hair production, and after 72 h, increased amounts of intercellular space (aerenchyma) in the root cortex. Root extension was also slowed down, but the pattern of response to oxygen shortage did not always match that of ethylene production. On return to air, subsequent growth patterns became normal within a few hours. In the complete absence of oxygen, no ethylene production was detected, even when anaerobic roots were returned to air after 16 h.
Response of small birch plants (Betula pendula Roth.) to elevated CO2 and nitrogen supply
Authors: PETTERSSON R. , McDONALD A. J. S. , STADENBERG I.
Published: April 2006

Small birch plants were grown for up to 80 d in a climate chamber at varied relative addition rates of nitrogen in culture solution, and at ambient (350 μmol mol‐1) or elevated (700 μmol mol‐1) concentrations of CO2. The relative addition rate of nitrogen controlled relative growth rate accurately and independently of CO2 concentration at sub‐optimum levels. During free access to nutrients, relative growth rate was higher at elevated CO2. Higher values of relative growth rate and net assimilation rate were associated with higher values of plant N‐concentration. At all N‐supply rates, elevated CO2 resulted in higher values of net assimilation rate, whereas leaf weight ratio was independent of CO2. Specific leaf area (and leaf area ratio) was less at higher CO2 and at lower rates of N‐supply. Lower values of specific leaf area were partly because of starch accumulation. Nitrogen productivity (growth rate per unit plant nitrogen) was higher at elevated CO2. At sub‐optimal N‐supply, the higher net assimilation rate at elevated CO2 was offset by a lower leaf area ratio. Carbon dioxide did not affect root/shoot ratio, but a higher fraction of plant dry weight was found in roots at lower N‐supply. In the treatment with lowest N‐supply, five times as much root length was produced per amount of plant nitrogen in comparison with optimum plants. The specific fine root length at all N‐supplies was greater at elevated CO2. These responses of the root system to lower N‐supply and elevated CO2 may have a considerable bearing on the acquisition of nutrients in depleted soils at elevated CO2. The advantage of maintaining steady‐state nutrition in small plants while investigating the effects of elevated CO2 on growth is emphasized.
A branch bag and CO2 control system for long‐term CO2 enrichment of mature Sitka spruce [Picea sitchensis (Bong.) Carr.]
Authors: BARTON C. V. M. , LEE H. S. J. , JARVIS P. G.
Published: April 2006

This paper describes the construction and performance of branch bags and a CO2 control system used to fumigate branches of mature Sitka spruce trees with air enriched in CO2 (700 μmolmol‐1). It contains some examples of results obtained using the system over the course of the first two growing seasons. The branch bags have run continuously for 2 years with very few problems. CO2 concentrations were within 20 μmol mol‐1 of the target concentration for more than 90% of the time. Temperatures within the bags were slightly higher than ambient (1–2 °C) and this had some effect on phenology. Attenuation of quantum flux density (photosynthetically active radiation) was 10–15%. The branch bag system has enabled investigation into the effects of elevated CO2 on mature tissue without the problems and expense of fumigating whole trees. Growth in elevated CO2 resulted in an increase in starch and a decrease in soluble protein content of needles. Stomatal conductance was higher in elevated CO2 grown needles, and there was some evidence of an increase in photosynthetic capacity.
Cell Physiological Studies on the Avena Coleoptile Treated with Ribonuclease
Authors: Masuda Yoshio
Published: April 2006

It was revealed with excised Avena coleoptile that the growth promoting effect of indole‐3‐acetic acid was inhibited by pretreatment with ribonuclease (Masuda 1959a, b). This effect of ribonuclease was presumed to involve its digestive action on the ribonucleic acid at the protoplasmic surface (Masuda 1959b). Ribonuclease treatment decreases the cation binding capacity of the ribonucleic acid at the protoplasmic surface (Masuda 1959a).

On the other hand, it has been confirmed that indole‐3‐acetic acid bas a remarkable effect on the physico‐chemical properties of protoplasmic surface such as permeability (Masuda 1955) and adhesiveness of protoplasm to the cell wall (Masuda 1957, Masuda and Takada 1957).

The purpose of the present study is to see the effect of ribonuclease on some protoplasmic properties of cells of Avena coleoptile and substantiate the authors view on the participation of ribonucleic acid in the cell elongation.
The Production of Fruit Bodies in Collybia velutipes III. Influence of the quality of light
Authors: Aschan‐Åberg Karin
Published: April 2006

Collybia velutipes is known to develop primordia as well as stipes in darkness while the growth of the pileus is greatly stimulated even by weak light (Akai 1940, Plunkett 1953, 1956, Aschan 1954, Takemuru 1954). In those cases where similar effects in other basidiomycetes have been studied in respect to their wave‐length dependence blue light has generally been found most effective (see Marsh et al. 1959). The present author has observed well developed pilei in (Collybia cultures receiving only occasional illumination from a weak incandescent lamp. Such irradiance contains a rather low proportion of blue light, so that the question arose whether this fungus might deviate from the rule.
Permeability of the Plasmalemma as Compared with that of the Tonoplast
Authors: Haapala Eva
Published: April 2006

In recent years there has been an increasing tendency to regard the tonoplast as the decisive diffusion barrier of the protoplast. The plasmalemma has been assumed to be more or less freely permeable, especially to ions (Brooks 4, Arisz 1, Epstein 8, Briggs and Robertson 3, Sutcliffe 12). This view is, however, based on observations which are far from unequivocal.

In the following we shall try to elucidate the question of the relative permeability and susceptibility of the two plasma membranes towards sodium hydroxide and sodium carbonate. The tests were made on internodal cells of Nitellopsis obtusa, staminal hairs of Tradescantia virginiana and T. zcbrina and epidermal cells of Allium cepa var. sanguinetim. These cells show protoplasmic streaming and either contain anthocyanins or were stained with neutral red.

In these experiments the plasmalemma, or some other layer outside the streaming part of the protoplasm, is assumed to be more or less impermeable towards sodium hydroxide as long as protoplasmic streaming is going on in the cells lying in the strongly alkaline solution. On the other hand, by the time the colour of the cell sap changes a considerable amount of NaOH must have passed through the whole protoplast, including both plasmalemma and tonoplast. The principal object of the experiments was, therefore, to compare (a) the time necessary to stop the protoplasmic streaming, irreversibly, with (b) the time required for the colour of the vacuole to change either to yellow (neutral red) or to blue (anthocyanin).