bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of photosynthetic acclimation to elevated CO2 and limited nitrogen supply in soybean
Authors: Sims D. A. , Luo Y. , Seemann J. R.
Published: March 2003

Plants grown at elevated CO2 often acclimate such that their photosynthetic capacities are reduced relative to ambient CO2‐grown plants. Reductions in synthesis of photosynthetic enzymes could result either from reduced photosynthetic gene expression or from reduced availability of nitrogen‐containing substrates for enzyme synthesis. Increased carbohydrate concentrations resulting from increased photosynthetic carbon fixation at elevated CO2 concentrations have been suggested to reduce the expression of photosynthetic genes. However, recent studies have also suggested that nitrogen uptake may be depressed by elevated CO2, or at least that it is not increased enough to keep pace with increased carbohydrate production. This response could induce a nitrogen limitation in elevated‐CO2 plants that might account for the reduction in photosynthetic enzyme synthesis. If CO2 acclimation were a response to limited nitrogen uptake, the effects of elevated CO2 and limiting nitrogen supply on photosynthesis and nitrogen allocation should be similar. To test this hypothesis we grew non‐nodulating soybeans at two levels each of nitrogen and CO2 concentration and measured leaf nitrogen contents, photosynthetic capacities and Rubisco contents. Both low nitrogen and elevated CO2 reduced nitrogen as a percentage of total leaf dry mass but only low nitrogen supply produced significant decreases in nitrogen as a percentage of leaf structural dry mass. The primary effect of elevated CO2 was to increase non‐structural carbohydrate storage rather than to decrease nitrogen content. Both low nitrogen supply and elevated CO2 also decreased carboxylation capacity (Vcmax) and Rubisco content per unit leaf area. However, when Vcmax and Rubisco content were expressed per unit nitrogen, low nitrogen supply generally caused them to increase whereas elevated CO2 generally caused them to decrease. Finally, elevated CO2 significantly increased the ratio of RuBP regeneration capacity to Vcmax whereas neither nitrogen supply nor plant age had a significant effect on this parameter. We conclude that reductions in photosynthetic enzyme synthesis in elevated CO2 appear not to result from limited nitrogen supply but instead may result from feedback inhibition by increased carbohydrate contents.
Diurnal variation in xylem hydraulic conductivity in white ash (Fraxinus americana L.), red maple (Acer rubrum L.) and red spruce (Picea rubens Sarg.)
Authors: Zwieniecki M. A. , Holbrook N. M.
Published: March 2003

Xylem hydraulic conductivity and percentage loss of conductivity (PLC) were measured on a ring‐porous (Fraxinus americana L., white ash), a diffuse porous (Acer rubrum L., red maple) and a coniferous (Picea rubens Sarg., red spruce) tree species in a temperate deciduous forest in central Massachusetts, USA. Measurements were made on current and 1‐year‐old branch segments in the afternoon and on the following morning. Afternoon PLC was 45 to 70% for the current year's extension growth in both white ash and red maple. Morning PLC was significantly lower (10–40%). Conductivity also varied diurnally suggesting, on average, a 50% recovery from cavitation overnight. Red spruce showed lower PLC and conductivity and a less pronounced night‐time recovery. Diurnal variation in hydraulic conductivity and PLC suggests that embolism removal occurred in all three species despite the existence of tension within the xylem. Further evidence for embolism removal was observed with an in situ double‐staining experiment in which dyes were fed to a transpiring branch during the late afternoon and the following morning. Examination of stem cross‐sections showed that a larger number of vessels were conductive in the morning than on the preceding afternoon. Results of this study suggest that hydraulic capacity is highly dynamic and that conductivity measurements reflect a balance between two processes: cavitation and embolism removal.
Water stress induces different levels of photosynthesis and electron transport rate regulation in grapevines
Authors: FLEXAS J. , ESCALONA J. M. , MEDRANO H.
Published: March 2003

A, net CO2 assimilation rate E, leaf transpiration ETR, electron transport rate Fs, fluorescence yield at steady state Fm and Fm', maximal fluorescence levels when all PSII reaction centres are closed in dark‐ and light‐acclimated leaves, respectively Fo and Fo', initial fluorescence levels when all PSII reaction centres are closed in dark‐ and light‐acclimated leaves, respectively Fv/Fm, efficiency of excitation capture by open PSII in dark‐adapted leaves ΔF/Fm', actual photochemical efficiency of PSII g, stomatal conductance NPQ, non‐photochemical quenching of chlorophyll fluorescence PPFD, photosynthetic photon flux density ΨPD and ΨMD, leaf water potential at pre‐dawn and midday, respectively Rl, estimated photorespiration rate I1 and I2, Irrigation treatments R, Recovery treatment D1 and D2, drought treatments HD1 and HD2, hard drought treatments  Diurnal time courses of chlorophyll fluorescence and gas‐exchange rates were measured in young potted grapevines (Vitis vinifera L. cv. Tempranillo) subjected to different conditions of water supply under Mediterranean summer conditions. The irrigated plants exhibited typical diurnal patterns for all measured parameters, showing a correspondence between electron transport rate, net CO2 assimilation and stomatal conductance. Mild decreases in soil‐water availability led to different degrees of down‐regulation of photosynthesis and increased nonphotochemical quenching of chlorophyll fluorescence. A good correspondence between electron transport rate and CO2 assimilation was still maintained, suggesting a coregulation of both photosynthetic processes. In contrast, a severe water deficit induced a drastic down‐regulation of photosynthesis and breakage of the above‐mentioned link. Both midday net CO2 assimilation and electron transport rate significantly correlated with pre‐dawn water potential (ΨPD) (r2 = 0·65 and r2 = 0·92, P < 0·001, respectively). However, when field data were analysed, the relationship between electron transport rate and ΨPD was not maintained, although net CO2 assimilation was similarly correlated with ΨPD. Interestingly, the steady‐state chlorophyll fluorescence yield was a good indicator of plant water stress.
Shoot orientation affects vessel size, shoot hydraulic conductivity and shoot growth rate in Vitis vinifera L.
Authors: SCHUBERT A. , LOVISOLO C. , PETERLUNGER E.
Published: March 2003

Vitis vinifera L. plants were grown in containers and each plant's single shoot was orientated upwards or downwards. Some plants were trained first upwards, then downwards, then again upwards (N‐shaped plants). Vegetative growth was reduced in plants trained downwards compared to that in upward and N‐shaped plants. Shoot growth rate slowed in downward shoot portions, but only after the apex had grown downwards for at least 10 internodes. Shoot hydraulic conductivity kh, measured after elimination of xylem embolisms, was lower in downward than in upward plants. In N‐shaped plants kh was higher in the upward‐growing shoot portions, and lower in the central, downward‐growing portion. Shoot‐ and leaf‐specific conductivities were also lower in downward than in upward shoot portions. Xylem cross‐sectional area and xylem structure (number of wedges, number of vessels per unit xylem area) differed little in the three orientations. In contrast, vessel diameter and the sum of vessel cross‐sectional areas were significantly smaller in downward than in upward shoot portions. These differences could explain the reduction in conductivity observed in the downward‐orientated shoot portions. The measurements taken on N‐shaped plants showed that the decreases in kh and in vessel size were a result of shoot orientation, not shoot bending.
Selecting models to predict the timing of flowering of temperate trees: implications for tree phenology modelling
Authors: CHUINE I. , COUR P. , ROUSSEAU D. D.
Published: March 2003

Classical budburst models (Spring Warming, Sequential, Parallel and Alternating) are unable to fully predict external data, partly because of the methods of optimization used to adjust them. The purpose of this study was to examine different assumptions of budburst models and select those which are best supported by the data, defining new models able to predict external data. Eight models, each differing in one assumption, were fitted and tested using external data. The dataset used to test the models was deduced from aeropalynological data at two stations in France. The results show that some of the models proposed are able to accurately predict external dates of flowering of most of the studied species. The assumptions of those models have been individually tested and shown to improve the models accuracy. Robust estimates of the best predictor models of 12 tree species are presented. The analysis of hypothetical provenance transfer of two species, Buxus sempervirens and Platanus acerifolia, between the two study sites, shows that P. acerifolia estimates are similar in both environments whereas B. sempervirens estimates are variable. This result, which agrees with the genetic characteristics of both species, shows that local adaptation of phenology can also be studied through modelling approaches.
Ethylene: a regulator of root architectural responses to soil phosphorus availability
Authors: BORCH K. , BOUMA T. J. , LYNCH J. P. , BROWN K. M.
Published: March 2003

The involvement of ethylene in root architectural responses to phosphorus availability was investigated in common bean (Phaseolus vulgaris L.) plants grown with sufficient and deficient phosphorus. Although phosphorus deficiency reduced root mass and lateral root number, main root length was unchanged by phosphorus treatment. This resulted in decreased lateral root density in phosphorus‐deficient plants. The possible involvement of ethylene in growth responses to phosphorus deficiency was investigated by inhibiting endogenous ethylene production with amino‐ethoxyvinylglycine (AVG) and aerating the root system with various concentrations of ethylene. Phosphorus deficiency doubled the root‐to‐shoot ratio, an effect which was suppressed by AVG and partially restored by exogenous ethylene. AVG increased lateral root density in phosphorus‐ deficient plants but reduced it in phosphorus‐sufficient plants. These responses could be reversed by exogenous ethylene, suggesting ethylene involvement in the regulation of main root extension and lateral root spacing. Phosphorus‐deficient roots produced twice as much ethylene per g dry matter as phosphorus‐sufficient roots. Enhanced ethylene production and altered ethylene sensitivity in phosphorus‐deficient plants may be responsible for root responses to phosphorus deficiency.
Stomatal behaviour, photosynthesis and transpiration under rising CO2
Authors: JARVIS A. J. , MANSFIELD T. A. , DAVIES W. J.
Published: March 2003

Definitions of the variables used and the units are given in Table 1  The literature reports enormous variation between species in the extent of stomatal responses to rising CO2. This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short‐term response of leaf gas exchange to increases in ambient CO2 concentration by developing the recently proposed stomatal model of Jarvis & Davies (1998). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO2 on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way. This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO2 concentration and also drought will have important effects on the relative gains to be achieved under rising CO2.

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The effects of reduced and elevated CO2 and O2 on the seaweed Lomentaria articulata
Authors: Kübler Janet E. , Johnston Andrew M. , Raven John A.
Published: March 2003

We grew a non‐bicarbonate using red seaweed, Lomentaria articulata (Huds.) Lyngb., in media aerated with four O2 concentrations between 10 and 200% of current ambient [O2] and four CO2 concentrations between 67 and 500% of current ambient [CO2], in a factorial design, to determine the effects of gas composition on growth and physiology. The relative growth rate of L. articulata increased with increasing [CO2] up to 200% of current ambient [CO2] but was unaffected by [O2]. The relative growth enhancement, on a carbon basis, was 52% with a doubling of [CO2] but fell to 23% under 5× ambient [CO2]. Plants collected in winter responded more extremely to [CO2] than did plants collected in the summer, although the overall pattern was the same. Discrimination between stable carbon isotopes (Δ13C) increased with increasing [CO2] as would be expected for diffusive CO2 acquisition. Tissue C and N were inversely related to [CO2]. Growth in terms of biomass appeared to be limited by conversion of photosynthate to new biomass rather than simply by diffusion of CO2, suggesting that non‐bicarbonate‐using macroalgae, such as L. articulata, may not be directly analogous to C3 higher plants in terms of their responses to changing gas composition.
Changes in carbohydrate metabolism and assimilate export in starch‐excess mutants of Arabidopsis
Authors: Zeeman S. C. , Rees T. Ap
Published: March 2003

The aim of this work was to investigate the effects on carbohydrate metabolism of a reduction in the capacity to degrade leaf starch in Arabidopsis. The major roles of leaf starch are to provide carbon for sucrose synthesis, respiration and, in developing leaves, for biosynthesis and growth. Wild‐type plants were compared with plants of a starch‐excess mutant line (sex4) deficient in a chloroplastic isoform of endoamylase. This mutant has a reduced capacity for starch degradation, leading to an imbalance between starch synthesis and degradation and the gradual accretion of starch as the leaves age. During the night the conversion of starch into sucrose in the mutant is impaired; the leaves of the mutant contained less sucrose than those of the wild type and there was less movement of 14C‐label from starch to sucrose in radio‐labelling experiments. Furthermore, the rate of assimilate export to the roots during the night was reduced in the mutant compared with the wild type. During the day however, photosynthetic partitioning was altered in the mutant, with less photosynthate partitioned into starch and more into sugars. Although the sucrose content of the leaves of the mutant was similar to the wild type during the day, the rate of export of sucrose to the roots was increased more than two‐fold. The changes in carbohydrate metabolism in the mutant leaves during the day compensate partly for its reduced capacity to synthesize sucrose from starch during the night.
Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high light
Authors: Muraoka Hiroyuki , Tang Yanhong , Terashima Ichiro , Koizumi Hiroshi , Washitani Izumi
Published: March 2003

Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non‐diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1–A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 μmol mol−1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ‘peak’ of diurnal assimilation was 70% greater than that obtained before the ‘peak’, but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (ΔF/Fm′) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ‘peak’. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 μmol m−2 s−1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ‘peak’, but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non‐photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration.
Glycinebetaine increases chilling tolerance and reduces chilling‐induced lipid peroxidation in Zea mays L.
Authors: Chen W. P. , Li P. H. , Chen T. H. H.
Published: March 2003

Chilling tolerance was increased in suspension‐cultured cells and seedlings of maize (Zea mays L. cv ‘Black Mexican Sweet’) grown in media containing glycinebetaine (GB). A triphenyl tetrazolium chloride (TTC) reduction test indicated that after a 7 d chilling period at 4 °C, cells treated with 1 mm GB at 26 °C for 1 d had a survival rate (30%) that was twice as high as that of untreated controls. The addition of 2·5 m
M GB to the culture medium resulted in maximum chilling tolerance (40%). The results of a cell regrowth assay were consistent with viability determined by the TTC method. In suspension‐cultured cells supplemented with various concentrations of GB, accumulation of GB in the cells was proportional to the GB concentration in the medium and was saturated at a concentration of 240 μmol (g DW)−1. The degree of increased chilling tolerance was positively correlated with the level of GB accumulated in the cells. The increased chilling tolerance was time‐dependent; i.e. it was first observed 3 h after treatment and reached a plateau after 14 h. Feeding seedlings with 2·5 m
M GB through the roots also improved their chilling tolerance, as evidenced by the prevention of chlorosis after chilling for 3 d at 4 °C/2 °C. Lipid peroxidation, as expressed by the production of malondialdehyde, was significantly reduced in GB‐treated cells compared with the untreated controls during chilling. These results suggest that increased chilling tolerance may be due, in part, to the reduction of lipid peroxidation of the cell membranes in the presence of GB.
Changes in growth, porosity, and radial oxygen loss from adventitious roots of selected mono‐ and dicotyledonous wetland species with contrasting types of aerenchyma
Authors: Visser E. J. W. , Colmer T. D. , Blom C. W. P. M. , Voesenek L. A. C. J.
Published: March 2003

Growth in stagnant, oxygen‐deficient nutrient solution increased porosity in adventitious roots of two monocotyledonous (Carex acuta and Juncus effusus) and three dicotyledonous species (Caltha palustris, Ranunculus sceleratus and Rumex palustris) wetland species from 10 to 30% under aerated conditions to 20–45%. The spatial patterns of radial oxygen loss (ROL), determined with root‐sleeving oxygen electrodes, indicated a strong constitutive ‘barrier’ to ROL in the basal root zones of the two monocotyledonous species. In contrast, roots of the dicotyledonous species showed no significant ‘barrier’ to ROL when grown in aerated solution, and only a partial ‘barrier’ when grown in stagnant conditions. This partial ‘barrier’ was strongest in C. palustris, so that ROL from basal zones of roots of R. sceleratus and R. palustris was substantial when compared to the monocotyledonous species. ROL from the basal zones would decrease longitudinal diffusion of oxygen to the root apex, and therefore limit the maximum penetration depth of these roots into anaerobic soil. Further studies of a larger number of dicotyledonous wetland species from a range of substrates are required to elucidate the ecophysiological consequences of developing a partial, rather than a strong, ‘barrier’ to ROL.
Simultaneous measurement of water flow velocity and solute transport in xylem and phloem of adult plants of Ricinus communis over a daily time course by nuclear magnetic resonance spectrometry
Authors: Peuke A. D. , Rokitta M. , Zimmermann U. , Schreiber L. , Haase A.
Published: March 2003

A new method for simultaneously quantifying rates of flow in xylem and phloem using the FLASH imaging capabilities of nuclear magnetic resonance (NMR) spectrometry was applied in this study. The method has a time resolution of up to 4 min (for the xylem) and was used to measure the velocity of flows in phloem and xylem for periods of several hours to days. For the first time, diurnal time course measurements of flow velocities and apparent volume flows in phloem and xylem in the hypocotyl of 40‐d‐old Ricinus communis L were obtained. Additional data on gas exchange and the chemical composition of leaves, xylem and phloem sap were used to assess the role of leaves as sinks for xylem sap and sources for phloem. The velocity in the phloem (0·250 ± 0·004 mm s−1) was constant over a full day and not notably affected by the light/dark cycle. Sucrose was loaded into the phloem and transported at night, owing to degradation of starch accumulated during the day. Concentrations of solutes in the phloem were generally less during the night than during the day but varied little within either the day or night. In contrast to the phloem, flow velocities in the xylem were about 1·6‐fold higher in the light (0·401 ± 0·004 mm s−1) than in the dark (0·255 ± 0·003 mm s−1) and volume flow varied commensurately. Larger delays were observed in changes to xylem flow velocity with variation in light than in gas exchange. The relative rates of solute transport during day and night were estimated on the basis of relative flow and solute concentrations in xylem and phloem. In general, changes in relative flow rates were compensated for by changes in solute concentration during the daily light/dark cycle. However, the major solutes (K+, NO3−) varied appreciably in relative concentrations. Hence the regulation of loading into transport systems seems to be more important to the overall process of solute transport than do changes in mass flow. Due to transport behaviour, the chemical composition of leaves varied during the day only with regard to starch and soluble carbohydrates.
UV‐B‐induced DNA damage and expression of defence genes under UV‐B stress: tissue‐specific molecular marker analysis in leaves
Authors: Kalbin G. , Hidema J. , Brosché M. , Kumagai T. , Bornman J. F. , Strid Å.
Published: March 2003

The aim of this study was to investigate the regulatory effect of ultraviolet‐B (UV‐B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre‐acclimation of plants to UV‐B radiation prior to exposure by UV‐B during treatment. Results showed that mRNA accumulation was similar during acute short‐term UV‐B exposure for chalcone synthase (Chs) and short‐chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV‐B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV‐B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV‐B‐induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV‐B levels resulted in significantly higher basal levels of CPDs than in non‐acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes.
Cadmium induces senescence symptoms in leaf peroxisomes of pea plants
Authors: McCarthy I. , Romero‐Puertas M. C. , Palma J. M. , Sandalio L. M. , Corpas F. J. , Gómez M. , Del Río L. A.
Published: March 2003

The effect of growing pea (Pisum sativum L.) plants with a toxic CdCl2 concentration (50 µm) on the metabolism and proteolytic activity of leaf peroxisomes was studied. In peroxisomes purified from plants treated with cadmium, an increase in the total protein concentration and in the activity and protein level of the photorespiratory enzyme glycolate oxidase was found. The glyoxylate cycle enzymes, malate synthase and isocitrate lyase, whose activity is normally very low in leaf peroxisomes, were enhanced by Cd treatment. The activity of the endogenous proteases of leaf peroxisomes was determined. Two leucine‐aminopeptidase isozymes (AP1‐AP2) were detected, and their activity was slightly higher in Cd‐treated plants. Five endopeptidases (EP1‐EP5) were present in pea leaf peroxisomes, and in plants grown with Cd the activity of isozymes EP1‐EP4 was increased. The ultrastructural analysis of pea leaves showed that Cd produced a disorganization of the chloroplast structure, with an increase in the number of plastoglobuli, and the formation of vesicles in the vacuoles. Taken together, these results indicate that Cd induces senescence symptoms in leaf peroxisomes, and probably a metabolic transition of leaf peroxisomes into glyoxysomes, and suggest that the peroxisomal proteases could participate in the metabolic changes produced by Cd.
Nitrogen dynamics during O3‐induced accelerated senescence in hybrid poplar
Authors: Bielenberg D. G. , Lynch J. P. , Pell E. J.
Published: March 2003

Experiments were conducted to determine the fate of nitrogen (N) remobilized as a result of ozone (O3)‐induced accelerated senescence in hybrid poplar subjected to declining N availability concurrent with O3 stress. Cuttings were grown in sand culture where the supply of N to the plant could be controlled on a daily basis and reduced in half of the plants when desired. Plants all initially received 3·57 mm N daily until approximately the 20 leaf stage after which daily supply of N was reduced to 0·71 mm. Plants were grown in open‐top chambers in the field (Rock Springs, PA, USA) and received charcoal‐filtered air, half also received supplemental O3 to a level of 0·08 µL L−1. Allocation of newly acquired N was determined with 15N. The specific allocation (mg labelled N mg−1 total N) of labelled N to upper, expanding leaf N was not affected by O3, but was strongly affected by N treatment. However, O3 increased the relative partitioning of labelled N to the expanding leaves and the roots. The balance between partitioning of newly acquired N to the upper leaves and roots was not affected by O3, but was reduced by N withdrawal. Calculated net N flux was strongly negative in the lower leaves of O3‐exposed, N withdrawal plants. Nitrogen uptake was not reduced by O3. The allometric relationships between the roots and shoots were not affected by O3 or N availability. The relative contribution of newly acquired versus remobilized N to new growth appears to be determined by N supply. Ozone exposure alters the allocation of newly acquired N via alterations in plant size, whereas N availability exerts a strong effect upon both plant size and N allocation.
Atmospheric CO2 concentration may directly affect leaf respiration measurement in tobacco, but not respiration itself*
Authors: Jahnke S. , Krewitt M.
Published: March 2003

When atmospheric CO2 concentration increases, various consequences for plant metabolism have been suggested, such as changes in photosynthesis, photorespiration or respiration which can affect growth and carbon sequestration. In addition to long‐term (indirect) effects on respiration, short‐term (direct) effects of CO2 concentration on the respiration of leaves, shoots and roots are described in the literature. In most cases, respiration is reported to be inhibited by increased CO2 concentration, but the mechanism(s) are not yet understood. It has been shown previously that, when the respective technical problems and properties of a gas exchange system are fully considered, a short‐term increase in CO2 (up to 4200 µmol mol−1) had no effect on respiration of Phaseolus or Populus leaves (Jahnke, Plant, Cell and Environment 24, 1139–1151, 2001). However, in the present study, large (apparent) CO2 effects were found with mature Nicotiana leaves whereas, in young leaves, the effect was absent. The experimental results clearly show that the observed direct CO2 effect on dark CO2 efflux in the mature tobacco leaves was caused by leakage of CO2 inside the leaves (and the magnitude of the effect was dependent on the size of the leakage). Nicotiana leaves are, in contrast to Phaseolus and Populus leaves (which are heterobaric), characterized by a homobaric anatomy in which intercellular air spaces are not compartmented and provide a continuous system of open pores in the lateral (paradermal) direction of the leaves. Mesophyll porosity increases with leaf development, which explains the differences between young and mature tobacco leaves. When internal leakage was experimentally restricted, the CO2 inhibition on CO2 efflux was no longer observed. It is concluded that the measured direct CO2 effect(s) on leaf CO2 efflux in the dark are artefactual, and that a true direct CO2 effect on leaf respiration does not exist.
Enhanced tolerances of transgenic tobacco plants expressing both superoxide dismutase and ascorbate peroxidase in chloroplasts against methyl viologen‐mediated oxidative stress
Authors: Kwon S. Y. , Jeong Y. J. , Lee H. S. , Kim J. S. , Cho K. Y. , Allen R. D. , Kwak S. S.
Published: March 2003

In order to better understand the role of antioxidant enzymes in plant stress protection mechanisms, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants were developed that overexpress both superoxide dismutase (SOD) and ascorbate peroxidase (APX) in chloroplasts. These plants were evaluated for protection against methyl viologen (MV, paraquat)‐mediated oxidative damage both in leaf discs and whole plants. Transgenic plants that express either chloroplast‐targeted CuZnSOD (C) or MnSOD (M) and APX (A) were developed (referred to as CA plants and AM plants, respectively). These plant lines were crossed to produce plants that express all three transgenes (CMA plants and AMC plants). These plants had higher total APX and SOD activities than non‐transgenic (NT) plants and exhibit novel APX and SOD isoenzymes not detected in NT plants. As expected, transgenic plants that expressed single SODs showed levels of protection from MV that were only slightly improved compared to NT plants. The expression of either SOD isoform along with APX led to increased protection while expression of both SODs and APX provided the highest levels of protection against membrane damage in leaf discs and visual symptoms in whole plants.
Cucumber mosaic virus movement protein affects sugar metabolism and transport in tobacco and melon plants
Authors: Shalitin D. , Wang Y. , Omid A. , Gal‐On A. , Wolf S.
Published: March 2003

In addition to its influence on plasmodesmal function, tobacco mosaic virus movement protein (TMV‐MP) causes an alteration in carbon metabolism in source leaves and in resource partitioning among the various plant organs. The present study was aimed at characterizing the influence of cucumber mosaic virus (CMV)‐MP on carbohydrate metabolism and transport in both tobacco and melon plants. Transgenic tobacco plants expressing the CMV‐MP had reduced levels of soluble sugars and starch in their source leaves and a significantly reduced root‐to‐shoot ratio in comparison with control plants. A novel virus‐vector system was employed to express the CMV‐coat protein (CP), the CMV‐MP or the TMV‐MP in melon plants. This set of experiments indicated that the viral MPs cause a significant elevation in the proportion of sucrose in the phloem sap collected from petioles of source leaves, whereas this sugar was at very low levels or even absent from the sap of control melon plants. The mode by which the CMV‐MP exerts its effect on phloem‐sap sugar composition is discussed in terms of possible alterations in the mechanism of phloem loading.
Profiles of light absorption and chlorophyll within spinach leaves from chlorophyll fluorescence
Authors: Vogelmann T. C. , Evans J. R.
Published: March 2003

Chlorophyll fluorescence was used to estimate profiles of absorbed light within chlorophyll solutions and leaves. For chlorophyll solutions, the intensity of the emitted fluorescence declined in a log–linear manner with the distance from  the  irradiated  surface  as  predicted  by  Beer's  law. The amount of fluorescence was proportional to chlorophyll  concentration  for  chlorophyll  solutions  given  epi‐illumination on a microscope slide. These relationships appeared to hold for more optically complex spinach leaves. The profile of chlorophyll fluorescence emitted by leaf cross sections given epi‐illumination corresponded to chlorophyll content measured in extracts of leaf paradermal sections. Thus epifluorescence was used to estimate relative chlorophyll content through leaf tissues. Fluorescence profiles across leaves depended on wavelength and orientation, reaching a peak at 50–70 µm depth. By infiltrating leaves with water, the pathlengthening due to scattering at the airspace : cell wall interfaces was calculated. Surprisingly, the palisade and spongy mesophyll had similar values for pathlengthening with the value being greatest for green light (550 > 650 > 450 nm). By combining fluorescence profiles with chlorophyll distribution across the leaf, the profile of the apparent extinction coefficient was calculated. The light profiles within spinach leaves could be well approximated by an apparent extinction coefficient and the Beer–Lambert/Bouguer laws. Light was absorbed at greater depths than predicted from fibre optic measurements, with 50% of blue and green light reaching 125 and 240 µm deep, respectively.
Photosynthetic parameters in seedlings of Eucalyptus grandis as affected by rate of nitrogen supply
Authors: GRASSI G. , MEIR P. , CROMER R. , TOMPKINS D. , JARVIS P. G.
Published: March 2003

Seedlings of Eucalyptus grandis were grown at five different rates of nitrogen supply. Once steady‐state growth rates were established, a detailed set of CO2 and water vapour exchange measurements were made to investigate the effects of leaf nitrogen content (N), as determined by nitrogen supply rate, on leaf structural, photosynthetic, respiratory and stomatal properties. Gas exchange data were used to parametrize the Farquhar–von Caemmerer photosynthesis model. Leaf mass per area (LMA) was negatively correlated to N. A positive correlation was observed between both day (Rd) and night respiration (Rn) and N when they were expressed on a leaf mass basis, but no correlation was found on a leaf area basis. An Rd/Rn ratio of 0·59 indicated a significant inhibition of dark respiration by light. The maximum net CO2 assimilation rate at ambient CO2 concentration (Amax), the maximum rate of potential electron transport (Jmax) and the maximum rate of carboxylation (Vcmax) significantly increased with N, particularly when expressed on a mass basis. Although the maximum stomatal conductance to CO2 (gscmax) was positively correlated with Amax, there was no relationship between gscmax and N. Leaf N content influenced the allocation of nitrogen to photosynthetic processes, resulting in a decrease of the Jmax/Vcmax ratio with increasing N. It was concluded that leaf nitrogen concentration is a major determinant of photosynthetic capacity in Eucalyptus grandis seedlings and, to a lesser extent, of leaf respiration and nitrogen partitioning among photosynthetic processes, but not of stomatal conductance.
Limits to xylem refilling under negative pressure in Laurus nobilis and Acer negundo
Authors: HACKE U. G. , SPERRY J. S.
Published: March 2003

The ability of juvenile Laurus nobilis and Acer negundo plants to refill embolized xylem vessels was tested under conditions of soil drought when xylem sap pressure was substantially negative, thus violating the expected condition that pressure must rise to near atmospheric for refilling. Intact potted plants were dried to a stem water potential (ΣW) corresponding with approximately 80% loss of hydraulic conductivity (PLC) in shoots. Then plants were re‐watered and kept at a less negative target ΨW for 1–48 h. The ΨW was measured continuously with stem psychrometers. Rewatered L. nobilis held at the target ΨW for 1 h showed no evidence for refilling unless ΨW was within a few tenths of a MPa of zero. In contrast, re‐watered L. nobilis held for 24 and 48 h at water potentials well below zero showed a significant reduction in PLC. The recovery was highly variable, being complete in some stem segments, and scarcely evident in others. Embolism repair was accompanied by a significant but moderate decrease in the osmotic potential (Ψ) of the bulk xylem sap (Ψ = −67 kPa in recovering plants versus −31 kPa in controls). In contrast, embolized and re‐watered A. negundo plants held for 24 h at target ΨW of −0·9 and −0·3 MPa showed no embolism reversal. The mechanism allowing L. nobilis plants to refill under negative pressure is unknown, but does not appear to operate in A. negundo, and is slower to act for drought‐induced embolism than when embolism was artificially induced by air injection as previously shown for L. nobilis.
Spatial and temporal spread of powdery mildew (Erysiphe pisi) in peas (Pisum sativum) varying in quantitative resistance
Authors: Viljanen‐Rollinson S. L. H. , Frampton C. M. A. , Gaunt R. E. , Falloon R. E. , McNeil D. L.
Published: March 2003

A field experiment was conducted to assess the progress in time and spread in space of powdery mildew (caused by Erysiphe pisi) in pea (Pisum sativum) cultivars differing in resistance to the disease. Disease severity (proportion of leaf area infected) was measured in 19 × 23 m plots of cultivars Pania and Bolero (both susceptible) and Quantum (quantitatively resistant). Inoculum on infected plants was introduced into the centre of each plot. Leaves (nodes) were divided into three groups within the canopy (lower, middle, upper) at each assessment because of the large range in disease severity vertically within the plants. Disease severity on leaves at upper nodes was less than 4% until the final assessment 35 days after inoculation. Exponential disease progress curves were fitted to disease severity data from leaves at middle nodes. The mean disease relative growth rate was greater on Quantum than on Pania or Bolero, but it was delayed, resulting in an overall lower disease severity on Quantum. Gompertz growth curves were fitted to disease progress on leaves at lower nodes. Disease progress on Quantum was delayed compared with Pania and Bolero. The average daily rates of increase in disease severity from Gompertz curves did not differ between the cultivars on these leaves. Disease gradients in the plots from the inoculum focus to 12 m were detected at early stages of the epidemic, but the effects of background inoculum inputs and the rate of disease progress meant that these gradients decreased with time as the disease epidemic intensified. Spread was rapid, and there were no statistically significant differences between cultivar isopathic rates (Pania 2.2, Quantum 2.9 and Bolero 4.0 m d−1).
Sensitive and specific detection of Clavibacter xyli subsp. xyli, causal agent of ratoon stunting disease of sugarcane, with a polymerase chain reaction‐based assay
Authors: Fegan M. , Croft B. J. , Teakle D. S. , Hayward A. C. , Smith G. R.
Published: March 2003

A sensitive, specific polymerase chain reaction‐based assay was developed for the detection of the causal agent of ratoon stunting disease of sugarcane, Clavibacter xyli subsp. xyli. This assay uses oligonucleotide primers derived from the internal transcribed spacer region between the 16S and 23S rRNA genes of the bacterial rRNA operon. The assay is specific for C. xyli subsp. xyli and does not produce an amplification product from the template of the closely related bacterium C. xyli subsp. cynodontis, nor from other bacterial species. The assay was successfully applied to the detection of C. xyli subsp. xyli in fibrovascular fluid extracted from sugarcane and was sensitive to approximately 22 cells per PCR assay. A multiplex PCR test was also developed which identified and differentiated C. xyli subsp. xyli and C. xyli subsp. cynodontis in a single PCR assay.
Relationships between seed germination, fumonisin content, and Fusarium verticillioides infection in selected maize samples from different regions of Costa Rica
Authors: Danielsen  , Funck Jensen
Published: March 2003

Thirty‐five maize seed samples from three geographic regions of Costa Rica were analysed for fumonisin content, germinability, and Fusarium verticillioides infection with and without surface disinfection. The concentration of fumonisins in the maize samples varied from 4 ng g−1 to 16 000 ng g−1 with an all over‐all average of 2500 ng g−1. There was a significant difference in fumonisin content between samples from Alajuela and Guanacaste. Germination of the seed samples ranged from 12% to 98% with significant differences between regions. F. verticillioides infection was 12–98% and 13–97% for surface‐disinfected and nondisinfected seeds, respectively. There was a significant negative correlation (r = ‐0.52) between fumonisin content and seed germination, but no significant correlation was found between fumonisin content and F. verticillioides infection, or between F. verticillioides infection and seed germination. Most of the high fumonisin seed samples had some mechanical or insect damage. Whether or not the fumonisins had a direct effect on germination was not further established. It is concluded that the large differences in fumonisin content of maize seeds within and between regions are primarily caused by differences in seed quality, genetic diversity of F. verticillioides strains in natural populations, climatic differences between regions, and varietal differences. Some of the fumonisin levels found in this study coincide with levels associated with risks to humans and animals in other countries.
Effects of timing and method of application of Penicillium oxalicum on efficacy and duration of control of Fusarium wilt of tomato
Authors: De Cal  , García‐Lepe  , Pascual  , Melgarejo
Published: March 2003

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45–49% and in glasshouse experiments by 22–69%. Disease suppression was maintained for 60–100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.
Indian peanut clump virus (IPCV) infection on wheat and barley: symptoms, yield loss and transmission through seed
Authors: Delfosse  , Reddy  , Legrève  , Devi  , Thirumala Devi  , Maraite  , Reddy
Published: March 2003

Wheat and barley crops were shown to be susceptible to Indian peanut clump virus (IPCV) under field conditions. In wheat, the Hyderabad isolate of IPCV (IPCV‐H) induced symptoms resembling the rosette caused by soil‐borne wheat mosaic virus, and these were apparent only three weeks after emergence. Early‐infected plants were severely stunted and dark green, with chlorotic streaks on the youngest leaves, which turned necrotic as the plants aged; most of these plants died. Late‐infected plants were also stunted and were conspicuous in the field because of their dark green appearance as a result of delayed maturity. The virus was detected by ELISA and nucleic acid hybridization in all plants with symptoms. These plants usually produced fewer tillers than healthy ones. Spikes were malformed, often did not emerge from the flag leaf, and they contained few, shrivelled seeds. Grain yield was decreased, on average, by 58%. In barley, IPCV‐H caused severe stunting and general leaf chlorosis. As the plants aged, the leaves became necrotic and the few infected plants that reached maturity produced small spikes. IPCV‐H antigens were detected by ELISA in every wheat seed from infected plants and the virus was transmitted through wheat seed at a frequency of 0.5–1.3%. Storage at 4°C for more than a year did not affect seed transmission frequency. The virus was detected in leaves and roots of seed‐transmitted plants. Seed transmission was not detected in barley. The Durgapura isolate (IPCV‐D) was detected in wheat crops (cv. RR‐21) at 3 different locations in Rajasthan State, India. Infected plants showed reduced growth without any overt symptoms.
A new blast resistance gene identified in the Indian native rice cultivar Aus373 through allelism and linkage tests
Authors: Pan  , Wang  , Tanisaka
Published: March 2003

Blast, caused by Pyricularia grisea, is a major constraint on rice production. To widen genetic diversity for disease resistance, the Indian native rice cultivar Aus373 was screened by F2 segregation analyses to investigate the genetic basis of its high resistance. Aus373 was crossed with a series of Japanese differential cultivars (JDCs) and the Chinese susceptible cultivar Lijiangxintuanheigu (LTH). The resistance ratios of subsequent F2 progenies were used to determine the number of blast‐resistance loci present as well as allelic relationships with known loci. Resistance of Aus373 was governed by dominant alleles at two loci, one at the Pi‐k locus and the second apparently at a new locus linked to an isozyme gene Amp‐1 with a recombination fraction of 37.9 ± 3.0% on chromosome 2. This putative new locus and allele were designated Pi16(t).
Biodiversity, plant pathogens and conservation
Authors: Ingram
Published: March 2003

I speak from the perspective of the director of a major botanic garden ( Fig. 1a) with a programme of research on plant and microbial biodiversity, world‐wide, and as a plant pathologist. What I say is not intended as a comprehensive review of an academic subject. My aim, quite simply, is to place on the agenda of the 7th International Congress of Plant Pathology the subjects of biodiversity and conservation, and to suggest that the British Society for Plant Pathology and the International Society for Plant Pathology urgently consider the formulation of conservation policies for plants and their pathogens. First I shall consider the threats to plant diversity. Next I shall discuss the importance of conserving that diversity and will assess progress to date. This will lead on to the controversial subject of the conservation of plant pathogen diversity, both ex situ and in situ. Finally, I shall stress the importance of education to the conservation effort.