bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen balance for wheat canopies (Triticum aestivum cv. Veery 10) grown under elevated and ambient CO2 concentrations
Authors: Smart D. R. , Ritchie K. , Bloom A. J. , Bugbee B. B.
Published: March 2003

We examined the hypothesis that elevated CO2 concentration would increase NO3– absorption and assimilation using intact wheat canopies (Triticum aestivum cv. Veery 10). Nitrate consumption, the sum of plant absorption and nitrogen loss, was continuously monitored for 23 d following germination under two CO2 concentrations (360 and 1000 μmol mol–1 CO2) and two root zone NO3– concentrations (100 and 1000 mmol m3 NO3–). The plants were grown at high density (1780 m–2) in a 28 m3 controlled environment chamber using solution culture techniques. Wheat responded to 1000 μmol mol–1 CO2 by increasing carbon allocation to root biomass production. Elevated CO2 also increased root zone NO3– consumption, but most of this increase did not result in higher biomass nitrogen. Rather, nitrogen loss accounted for the greatest part of the difference in NO3– consumption between the elevated and ambient [CO2] treatments. The total amount of NO3–‐N absorbed by roots or the amount of NO3–‐N assimilated per unit area did not significantly differ between elevated and ambient [CO2] treatments. Instead, specific leaf organic nitrogen content declined, and NO3– accumulated in canopies growing under 1000 μmol mol–1 CO2. Our results indicated that 1000 μmol mol–1 CO2 diminished NO3– assimilation. If NO3– assimilation were impaired by high [CO2], then this offers an explanation for why organic nitrogen contents are often observed to decline in elevated [CO2] environments.
Physiological and anatomical disturbances induced by chloride salts in sensitive and tolerant citrus: beneficial and detrimental effects of cations
Authors: Romero‐Aranda R. , Moya J. L. , Tadeo F. R. , Legaz F. , Primo‐Millo E. , Talon M.
Published: March 2003

In citrus, the relative contributions of chloride and cations to growth disturbances induced by salinity are a matter of controversy. Chloride salts (15 mol m–3 CaCl2, 30 mol m–3 CaCl and 30 mol m–3 KCl) reduced growth and gas exchange parameters, increased leaf damage and abscission and produced anatomical disarrangements and mineral imbalances in seedlings of sensitive Carrizo citrange (Citrus sinensis x Poncirus trifoliata) and tolerant Cleopatra mandarin (Citrus reshni). In both cultivars, Ca2+ was more beneficial, and K+ more detrimental, for growth than sodium. Photosynthesis and growth disturbances were highly correlated (P≤ 0·001) with leaf Cl– build‐up. In the sensitive genotype, Cl– was also significantly correlated with several leaf anatomical disarrangements, such as increase in succulence. In comparison with sodium, both calcium and potassium increased leaf Cl– content (up to 25 and 69%, respectively). Protective calcium effects were not linked to improvement of photosynthesis, reduction of leaf anatomical disarrangements, or prevention of Cl– and Na+ increases. It is proposed that the ameliorative effects of calcium on citrus grown under salinity are mostly related to reduction of leaf abscission. Collectively, the data suggest a cause–effect relationship between Cl– build‐up and reduced growth, whereas chloride correlations with declines in photosynthesis or increases in succulence appear to be indirect.
Stomata of trees growing in CO2‐enriched air show reduced sensitivity to vapour pressure deficit and drought
Authors: Heath J.
Published: March 2003

Stomatal conductance (gs) and photosynthetic rate (A) were measured in young beech (Fagus sylvatica), chestnut (Castanea sativa) and oak (Quercus robur) growing in ambient or CO2‐enriched air. In oak, gs was consistently reduced in elevated CO2. However, in beech and chestnut, the stomata of trees growing in elevated CO2 failed to close normally in response to increased leaf‐to‐air vapour pressure deficit (LAVPD). Consequently, while gs was reduced in elevated CO2 on days with low LAVPD, on warm sunny days (with correspondingly high LAVPD) gs was unchanged or even slightly higher in elevated CO2. Furthermore, during drought, gs of beech and chestnut was unresponsive to [CO2], over a wide range of ambient LAVPD, whereas in oak gs was reduced by an average of 50% in elevated CO2. Stimulation of A by elevated CO2 in beech and chestnut was restricted to days with high irradiance, and was greatest in beech during drought. Hence, most of the additional carbon gain in elevated CO2 was made at the expense of water economy, at precisely those times (drought, high evaporative demand) when water conservation was most important. Such effects could have serious consequences for drought tolerance, growth and, ultimately, survival as atmospheric [CO2] increases.
Dehiscence‐related expression of an Arabidopsis thaliana gene encoding a polygalacturonase in transgenic plants of Brassica napus
Authors: JENKINS E. S. , PAUL W. , CRAZE M. , WHITELAW C. A. , WEIGAND A. , ROBERTS J. A.
Published: March 2003

Pod dehiscence in Arabidopsis thaliana is accompanied by an increase in the expression of a polygalacturonase (PG). The gene encoding this mRNA has been characterized and shown to have extensive homology to a similar PG gene from Brassica napus. The A. thaliana PG promoter was fused to β‐glucuronidase (GUS) and the expression of this reporter gene analysed in transgenic B. napus plants. The GUS activity was detected throughout the dehiscence zone of pods from 35 d after anthesis and expression was restricted to those cells that undergo cell separation. Expression was also detectable at the junction between the seed and the funicular tissue and in mature anthers of flowers. Transgenic plants containing the PG promoter fused to barnase were sterile as a consequence of the anthers failing to undergo dehiscence. Fertilization of PG‐barnase plants resulted in the development of pods that exhibited a reduced capacity to shatter. The role of PG during cell separation processes in plants is discussed.
Photosynthetic capacity of loblolly pine (Pinus taedaL.) trees during the first year of carbon dioxide enrichment in a forest ecosystem
Authors: MYERS D. A. , THOMAS R. B. , DELUCIA E. H.
Published: March 2003

Our objective was to assess the photosynthetic responses of loblolly pine trees (Pinus taedaL.) during the first full growth season (1997) at the Brookhaven National Lab/Duke University Free Air CO2Enrichment (FACE) experiment. Gas exchange, fluorescence characteristics, and leaf biochemistry of ambient CO2(control) needles and ambient + 20 Pa CO2(elevated) needles were examined five times during the year. The enhancement of photosynthesis by elevated CO2in mature loblolly pine trees varied across the season and was influenced by abiotic and biotic factors. Photosynthetic enhancement by elevated CO2was strongly correlated with leaf temperature. The magnitude of photosynthetic enhancement was zero in March but was as great as 52% later in the season. In March, reduced sink demand and lower temperatures resulted in lower net photosynthesis, lower carboxylation rates and higher excess energy dissipation from the elevated CO2needles than from control needles. The greatest photosynthetic enhancement by CO2enrichment was observed in July during a period of high temperature and low precipitation, and in September during recovery from this period of low precipitation. In July, loblolly pine trees in the control rings exhibited lower net photosynthetic rates, lower maximum rates of photosynthesis at saturating CO2and light, lower values of carboxylation and electron transport rates (modelled fromA–Cicurves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO2rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light‐ and CO2‐saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first‐year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimation to CO2occurs in these canopy loblolly pine trees growing in a forest ecosystem.
Hydraulic contribution in cell elongation of tissue‐cultured plants: growth retardation induced by osmotic and temperature stresses and addition of 2,4‐dichlorophenoxyacetic acid and benzylaminopurine
Authors: Ikeda T. , Nonami H. , Fukuyama T. , Hashimoto Y.
Published: March 2003

This work was undertaken to determine the growth parameters of Lockhart’s equation for finding which component was predominantly contributing to the cell expansion rates of plants subjected to environmental stresses under tissue‐culture conditions. Embryos isolated from soybean (Glycine max[L.] Merr.) and kidney bean (Phaseolus vulgarisL.) seeds were grown under tissue‐culture conditions. The water potential of culture media ranged from−0·02 to−0·94 MPa so that nutrient deficiency and salt stress conditions could be applied. Additionally, the temperature of culture conditions was set from 10 to 40 °C to apply low‐temperature and high‐temperature stresses on plants grown at the optimum concentration of culture medium. Cell expansion could be inhibited completely by adding 2,4‐dichlorophenoxyacetic acid and benzylaminopurine to culture media to form callus tissue. The sizes of the water potential gradient between the water source and elongating cells correlated with the speed of growth rates under nutrient deficiency, salt stress, growth retardation induced by plant hormones, low‐temperature and high‐temperature conditions in the present study, indicating that cell expansion rates were mainly associated with how much water could be absorbed by elongating cells regardless of the kinds of environmental stress conditions applied.
Observations and model simulations link stomatal inhibition to impaired hydraulic conductance following ozone exposure in cotton
Authors: Grantz David A. , Zhang Xijie , Carlson Toby
Published: March 2003

Ozone (O3) inhibits plant gas exchange and productivity. Vapour phase (gs) and liquid or hydraulic phase (K) conductances to water flux are often correlated as both change with environmental parameters. Exposure of cotton plants to tropospheric O3reducesgsthrough reversible short‐term mechanisms and by irreversible long‐term disruption of biomass allocation to roots which reducesK. We hypothesize that chronic effects of O3on gas exchange can be mediated by effects onKwithout a direct effect of O3ongsor carbon assimilation (A). Experimental observations from diverse field and exposure chamber studies, and simulations with a model of mass and energy transport, support this hypothesis. O3inhibition ofKleads to realistic simulated diurnal courses ofgsthat reproduce observations at low ambient O3concentration and maintain the positive correlation between middaygsandKobserved experimentally at higher O3concentrations. Effects mediated by reducedKmay interact with more rapid responses ofgsandAto yield the observed suite of oxidant impacts on vegetation. The model extends these physiological impacts to the extensive canopy scale. Simulated magnitudes and diurnal time courses of canopy‐scale fluxes of H2O and O3match observations under low ambient concentrations of O3. With greater simulated concentrations of O3during plant development, the model suggests potential reductions of canopy‐scale water fluxes and O3deposition. This could represent a potentially unfavourable positive feedback on tropospheric O3concentrations associated with biosphere–atmosphere exchange.
Ozone exposure results in various carry‐over effects and prolonged reduction in biomass in birch (Betula pendula Roth)
Authors: Oksanen E. , Saleem A.
Published: March 2003

In the first experiment, saplings of ozone‐sensitive and a more tolerant clone of Betula pendula Roth were exposed to ambient ozone (control treatment, accumulated exposure over a threshold 40 nmol mol−1 (AOT40) exposure of 1·0 μmol mol−1 h) and 1·5 × ambient ozone (elevated‐ozone treatment, AOT40 of 17·3 μmol mol−1 h) over one growing season, 1996. After over‐wintering, the dormant elevated‐ozone saplings were transferred to the control blocks and assessed for short‐term carry‐over effects during the following growing season. In the second experiment, three sensitive, four intermediate and three tolerant clones were grown under ambient ozone (control treatment, AOT40 of 0·5–0·8 μmol mol−1 h per growing season) and 1·6–1·7 × ambient ozone (elevated‐ozone treatment, AOT40 of 18·3–18·6 μmol mol−1 h per growing season) from May 1994 until May 1996, and were assessed for long‐term carry‐over effects during growing season 1997, after a 12–16 months recovery period. Deleterious short‐term carry‐over effects of ozone exposure included reduced contents of Rubisco, chlorophyll, carotenoids, starch and nutrients in leaves, lower stomatal conductance, and decreased new shoot growth and net assimilation rate, followed by a 7·5% (shoot dry weight (DW)), 15·2% (root DW) and 23·2% (foliage area) decreased biomass accumulation and yield over the long term, including a reduced root : shoot ratio. However, a slow recovery of relative growth rates during the following two seasons without elevated ozone was apparent. Several long‐lasting structural, biochemical and stomatal acclimation, stress‐defence and compensation reactions were observed in the ozone‐tolerant clone, whereas in the sensitive clone allocation shifted from growth towards defensive phenolics such as chlorogenic acid. The results provide evidence of persistent deleterious effects of ozone which remain long after the ozone episode.
Survey and synthesis of intra‐ and interspecific variation in stomatal sensitivity to vapour pressure deficit
Authors: Oren R. , Sperry J. S. , Katul G. G. , Pataki D. E. , Ewers B. E. , Phillips N. , Schäfer K. V. R.
Published: March 2003

Responses of stomatal conductance (gs) to increasing vapour pressure deficit (D) generally follow an exponential decrease described equally well by several empirical functions. However, the magnitude of the decrease – the stomatal sensitivity – varies considerably both within and between species. Here we analysed data from a variety of sources employing both porometric and sap flux estimates of gs to evaluate the hypothesis that stomatal sensitivity is proportional to the magnitude of gs at low D (≤ 1 kPa). To test this relationship we used the function gs=gsref–m· lnD where m is the stomatal sensitivity and gsref=gs at D= 1 kPa. Regardless of species or methodology, m was highly correlated with gsref (average r2= 0·75) with a slope of approximately 0·6. We demonstrate that this empirical slope is consistent with the theoretical slope derived from a simple hydraulic model that assumes stomatal regulation of leaf water potential. The theoretical slope is robust to deviations from underlying assumptions and variation in model parameters. The relationships within and among species are close to theoretical predictions, regardless of whether the analysis is based on porometric measurements of gs in relation to leaf‐surface D (Ds), or on sap flux‐based stomatal conductance of whole trees (GSi), or stand‐level stomatal conductance (GS) in relation to D. Thus, individuals, species, and stands with high stomatal conductance at low D show a greater sensitivity to D, as required by the role of stomata in regulating leaf water potential.
Assessing photosystem I and II distribution in leaves from C4 plants using confocal laser scanning microscopy
Authors: Pfündel E. , Neubohn B.
Published: March 2003

Images of chlorophyll fluorescence emitted at wavelengths above and below 700 nm were recorded from leaf sections of C4 species using confocal laser scanning microscopy (LSM). We investigated species exhibiting both NAD‐malic enzyme (NAD‐ME) C4 photosynthesis and NADP‐malic enzyme (NADP‐ME) C4 photosynthesis. Comparing LSM fluorescence of leaf sections with flow‐cytometrically determined fluorescence from individual chloroplasts revealed that LSM fluorescence was distorted by the optical properties of leaf sections. Leaf section fluorescence, when corrected by transmission data derived from light transmission images, agreed with flow cytometry data. The corrected LSM fluorescence yielded information on the distribution of the individual photosystems in the C4 leaf sections: PSII concentrations in bundle sheath cells were elevated in NAD‐ME species but diminished in most of the NADP‐ME species investigated. The NADP‐ME species, Arundinella hirta, however, showed normal PSII and increased PSI concentration in bundle sheath chloroplasts. Finally, a gradient of PSI was observed within the bundle sheath cells from Euphorbia maculata.
Responses of maize roots to drying – limits of viability
Authors: Facette M. R. , McCully M. E. , Canny M. J.
Published: March 2003

Turgid pieces of mature maize roots were dried in air and progressive changes in their relative water content (RWC) determined. Viability was tested by reproducibility of the drying curves after dehydration to successively lower RWCs. After reaching a chosen RWC, the pieces were rehydrated (approximately 2 h), and a 2nd and 3rd dehydration curve measured. Each drying curve was characterized by two parameters (a scale parameter λ, and a shape parameter β) of a survivorship function, which is a linear function of time. The parameter λ is more informative, and does not change in successive dehydrations for RWC > 0·4, suggesting no irreversible damage to the roots. Damage and death were indicated by divergences of λ in successive dehydrations to RWC = 0·35–0·15. Cryo‐analytical microscopy confirmed these data while indicating specifically death of 50 and 100% of cortical cells at RWC 0·30 and 0·15, respectively, and survival of 50% or more of sieve tubes, pericycle and vascular parenchyma cells at root RWC as low as 0·15. This pattern of stelar cell survival may allow roots to preserve their capacity for renewal of axial conductivity and branch root development following periods of severe water stress.
Analysis of the sensing and transducing processes implicated in the stomatal responses to carbon dioxide in Commelina communis L.
Authors: Cousson A.
Published: March 2003

It has been previously debated whether CO2 would depolarize the guard cell plasma membrane through malate‐mediated activation of the anion channel. Moreover, it has been assessed that the CO2 signal would be transduced via cytosolic free Ca2+. In the present study, the CO2 sensing and transducing processes were reinvestigated in Commelina communis (L.) mainly by studying how
L‐(–)‐malic acid and Ca2+ flux modulators affected different CO2 stomatal responses.
L‐(–)‐malic acid (1 m
M) inhibited by about 50% both CO2‐induced stomatal closing and CO2‐triggered inhibition of the stomatal opening response to the auxin indolyl‐3‐butyric acid. Stomatal closing in response to atmospheric CO2 was strongly inhibited by the 1,4 dihydropyridines SDZ‐202 791 R(–) (SDZ (–)) and nifedipine, and this inhibition was attenuated by the 1,4 dihydropyridines SDZ‐202 791 S(+) and S‐(–)‐BAY K8644. Suboptimal concentrations of the slow anion channel blockers 5‐nitro‐2,3‐phenylpropyllamine benzoic acid and anthracene‐9‐carboxylic acid increased the 50% inhibition of the CO2 closing response by the Ca2+ flux modulators SDZ (–) and 1,2‐bis(o‐aminophenoxy)ethane‐N,N,N′N′‐tetraacetic acid in a stronger manner than an additive one. Together, these results support the view that CO2 is sensed through reducing proton extrusion. Moreover, they might suggest that the CO2 signal is transduced through Ca2+ signalling arising from depolarization‐mediated activation of a putative plasma membrane voltage‐gated L‐type Ca2+ channel and for which the plasma membrane slow anion channel is a potential target.
The gene sll0273 of the cyanobacterium Synechocystis sp. strain PCC6803 encodes a protein essential for growth at low Na+/K+ ratios
Authors: Mikkat S. , Milkowski C. , Hagemann M.
Published: March 2003

A mutant of Synechocystis sp. strain PCC6803 was obtained by random cartridge mutagenesis, which could not grow at low sodium concentrations. Genetic analyses revealed that partial deletion of the sll0273 gene, encoding a putative Na+/H+ exchanger, was responsible for this defect. Physiological characterization indicated that the sll0273 mutant exhibited an increased sensitivity towards K+, even at low concentrations, which was compensated for by enhanced concentrations of Na+. This enhanced Na+ demand could also be met by Li+. Furthermore, addition of monensin, an ionophore mediating electroneutral Na+/H+ exchange, supported growth of the mutant at unfavourable Na+/K+ ratios. Measurement of internal Na+ and K+ contents of wild‐type and mutant cells revealed a decreased Na+/K+ ratio in mutant cells pre‐incubated at a low external Na+/K+ ratio, while it remained at the level of the wild type after pre‐incubation at a high external Na+/K+ ratio. We conclude that the Sll0273 protein is required for Na+ influx, especially at low external Na+ concentrations or low Na+/K+ ratios. This system may be part of a sodium cycle and may permit re‐entry of Na+ into the cells, if nutrient/Na+ symporters are not functional or operating.
Zinc hyperaccumulation and cellular distribution in Arabidopsis halleri
Authors: Zhao F. J. , Lombi E. , Breedon T. , M S. P.
Published: March 2003

Although Arabidopsis halleri (=Cardaminopsis halleri) is known as a Zn hyperaccumulator, there have been no detailed studies on Zn accumulation, tolerance and cellular distribution in this species. In a hydroponic experiment, A. halleri grew healthily with Zn concentrations varying from 1 to 1000 μM, without showing phytotoxicity or reduction in root or shoot dry weights. The concentration of Zn in the shoots increased from 300 μg g−1 dry weight in the 1 μM Zn treatment to 32 000 μg g−1 in the 1000 μM Zn treatment. Approximately 60% of the total Zn in the shoots were water‐soluble, and there was no evidence of Zn and P co‐precipitation. Both citric and malic acid concentrations in the shoots were not significantly affected by the Zn treatments, whereas in the roots there was a positive response in both organic acids to increasing Zn in solution. Cellular distribution of Zn, Ca and K in frozen hydrated leaf tissues was examined using energy‐dispersive X‐ray microanalysis. Zinc was sequestered in the base of trichomes, whereas the middle and upper parts of trichomes were highly enriched with Ca. Mesophyll cells appeared to have more Zn than the epidermis, probably because the latter were very small in size. Similarities and differences between A. halleri and the other well‐known Zn hyperaccumulator, Thlaspi caerulescens, are discussed.
Naturally low carbonic anhydrase activity in C4 and C3 plants limits discrimination against C18OO during photosynthesis
Authors: Gillon J. S. , Yakir D.
Published: March 2003

The 18O content of CO2 is a powerful tracer of photosynthetic activity at the ecosystem and global scale. Due to oxygen exchange between CO2 and 18O‐enriched leaf water and retrodiffusion of most of this CO2 back to the atmosphere, leaves effectively discriminate against 18O during photosynthesis. Discrimination against 18O (Δ18O) is expected to be lower in C4 plants because of low ci and hence low retrodiffusing CO2 flux. C4 plants also generally show lower levels of carbonic anhydrase (CA) activities than C3 plants. Low CA may limit the extent of 18O exchange and further reduce Δ18O. We investigated CO2–H2O isotopic equilibrium in plants with naturally low CA activity, including two C4 (Zea mays, Sorghum bicolor) and one C3 (Phragmites australis) species. The results confirmed experimentally the occurrence of low Δ18O in C4, as well as in some C3, plants. Variations in CA activity and in the extent of CO2–H2O isotopic equilibrium (θeq) estimated from on‐line measurements of Δ18O showed large range of 0–100% isotopic equilibrium (θeq= 0–1). This was consistent with direct estimates based on assays of CA activity and measurements of CO2 concentrations and residence times in the leaves. The results demonstrate the potential usefulness of Δ18O as indicator of CA activity in vivo. Sensitivity tests indicated also that the impact of θeq< 1 (incomplete isotopic equilibrium) on 18O of atmospheric CO2 can be similar for C3 and C4 plants and in both cases it increases with natural enrichment of 18O in leaf water.
Ethanol treatment triggers a heat shock‐like response but no thermotolerance in soybean (Glycine max cv. Kaohsiung No.8) seedlings
Authors: Kuo H.‐F. , Tsai Y.‐F. , Young L.‐S. , Lin C.‐Y.
Published: March 2003

Non‐lethal heat‐shock (HS) treatment has previously been shown to induce thermotolerance in soybean (Glycine max cv. Kaohsiung No.8) seedlings. This acquired thermotolerance correlates with the de novo synthesis of heat‐shock proteins (HSPs). Interestingly, we found that ethanol treatments also elicited HS‐like responses in aetiolated soybean seedlings at their normal growth temperature of 28 °C. Northern blot analyses revealed that the expression of HS genes hsp17.5, hsp70 and hsc 70 was induced by ethanol. Radioactive amino acids were preferentially incorporated into high molecular weight (HMW) HSPs rather than class I low molecular weight (LMW) HSPs during non‐lethal ethanol treatments. Immunoblot analysis confirmed that no accumulation of class I LMW HSPs occurred after non‐lethal ethanol treatment. Pre‐treatment with a non‐lethal dose of ethanol did not provide thermotolerance, as the aetiolated soybean seedlings could not survive a subsequent heat shock of 45 °C for 2 h. In contrast, non‐lethal HS pre‐treatment, 40 °C for 2 h, conferred tolerance on aetiolated soybean seedlings to otherwise lethal treatments of 7·5% ethanol for 8 h or 10% ethanol for 4 h. These results suggest that plant class I LMW HSPs may play important roles in providing both thermotolerance and ethanol tolerance.
Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profiles
Authors: Vogelmann T. C. , Han T.
Published: March 2003

Profiles of chlorophyll fluorescence were measured in spinach leaves irradiated with monochromatic light. The characteristics of the profiles within the mesophyll were determined by the optical properties of the leaf tissue and the spectral quality of the actinic light. When leaves were infiltrated with 10−4M DCMU [3‐(3,4‐dichlorophenyl)‐1, 1‐dimethyl‐urea] or water, treatments that minimized light scattering, irradiation with 2000 μmol m−2 s−1 green light produced broad Gaussian‐shaped fluorescence profiles that spanned most of the mesophyll. Profiles for chlorophyll fluorescence in the red (680 ± 16 nm) and far red (λ > 710 nm) were similar except that there was elevated red fluorescence near the adaxial leaf surface relative to far red fluorescence. Fluorescence profiles were narrower in non‐infiltrated leaf samples where light scattering increased the light gradient. The fluorescence profile was broader when the leaf was irradiated on its adaxial versus abaxial surface due to the contrasting optical properties of the palisade and spongy mesophyll. Irradiation with blue, red and green monochromatic light produced profiles that peaked 50, 100 and 150 μm, respectively, beneath the irradiated surface. These results are consistent with previous measurements of the light gradient in spinach and they agree qualitatively with measurements of carbon fixation under monochromatic blue, red and green light. These results suggest that chlorophyll fluorescence profiles may be used to estimate the distribution of quanta that are absorbed within the leaf for photosynthesis.
Dynamics of concentrations and nutrient fluxes in the xylem of Ricinus communis– diurnal course, impact of nutrient availability and nutrient uptake
Authors: Herdel K. , Schmidt P. , Feil R. , Mohr A. , Schurr U.
Published: March 2003

Diurnal courses of nutrient transport in the xylem and their response to external availability of nutrients were studied. In soil culture, maximal concentrations in all analysed substances were observed during night‐time. Over experimental periods of up to 20 d, concentrations of some ions increased, most by accumulation in the soil. Stringent nutrient conditions were established in a novel pressure chamber. An aeroponic nutrient delivery system inside allows the sampling of xylem sap from intact plants under full control of the nutrient conditions at the root. Analysis of xylem transport under these highly defined conditions established that (1) diurnal variations in concentrations and fluxes in the xylem are dominated by plant‐internal processes; (2) concentrations of nutrients in the xylem sap are highly but specifically correlated with each other; (3) nitrate uptake and nitrate flux to the shoot are largely uncoupled; and (4) in continuous light, diurnal variations of xylem sap concentrations vanish. Step changes in nitrate concentrations of the nutrient solution established that (5) the concomitant increase in nitrate concentration and flux in the xylem is delayed by 2–3 h and is only transient. Diurnal variations of xylem sap composition and use of the new technique to elucidate xylem‐transport mechanisms are discussed.
Responses of riparian trees to interannual variation in ground water depth in a semi‐arid river basin
Authors: Horton J. L. , Kolb T. E. , Hart S. C.
Published: March 2003

We investigated the physiological and growth responses of native (Populus fremontii S. Wats. and Salix gooddingii Ball) and exotic (Tamarix chinensis Lour.) riparian trees to ground water availability at the free‐flowing Hassayampa River, Arizona, during dry (1997) and wet (1998) years. In the drier year, all species experienced considerable water stress, as evidenced by low shoot water potentials, low leaf gas exchange rates and large amounts of canopy dieback. These parameters were significantly related to depth of ground water (DGW) in the native species, but not in T. chinensis, in 1997. Canopy dieback was greater in the native species than in T. chinensis when ground water was deep in 1997, and dieback increased rapidly at DGW > 2·5–3·0 m for the native species. Analysis of combined data from wet and dry years for T. chinensis tentatively suggests a similar physiological sensitivity to water availability and a similar DGW threshold for canopy dieback. In 1998, shoot water potential and leaf gas exchange rates were higher and canopy dieback was lower for all species because of increased water availability. However, T. chinensis showed a much larger increase in leaf gas exchange rates in the wet year than the native species. High leaf gas exchange rates, growth when water is abundant, drought tolerance and the maintenance of a viable canopy under dry conditions are characteristics that help explain the ability of T. chinensis to thrive in riparian ecosystems in the south‐western United States.
N content of phloem and xylem exudates during the transition to flowering in Sinapis alba and Arabidopsis thaliana
Authors: Corbesier L. , Havelange A. , Lejeune P. , Bernier G. , Périlleux C.
Published: March 2003

The involvement of nitrogenous substances in the transition to flowering was investigated in Sinapis alba and Arabidopsis thaliana (Columbia). Both species grown in short days (SD) are induced to flower by one long day (LD). In S. alba, the phloem sap (leaf and apical exudates) and the xylem sap (root exudate) were analysed in LD versus SD. In A. thaliana, only the leaf exudate could be analysed but an alternative system for inducing flowering without day‐length extension was used: the displaced SD (DSD). Significant results are: (i) in both species, the leaf exudate was enriched in Gln during the inductive LD, at a time compatible with export of the floral stimulus; (ii) in S. alba, the root export of amino acids decreased in LD, whereas the nitrate remained unchanged – thus the extra‐Gln found in the leaf exudate should originate from the leaves; (iii) extra‐Gln was also found very early in the apical exudate of S. alba in LD, together with more Glu; (iv) in A. thaliana induced by one DSD, the leaf export of Asn increased sharply, instead of Gln in LD. This agrees with Asn prevalence in C‐limited plants. The putative role of amino acids in the transition to flowering is discussed.
A variety of wheat tolerant to deep‐seeding conditions: elongation of the first internode depends on the response to gibberellin and potassium
Authors: Chen L. , Nishizawa T. , Higashitani A. , Suge H. , Wakui Y. , Takeda K. , Takahashi H.
Published: March 2003

The addition of gibberellin A3 (GA3) to culture media induced a dramatic elongation of the first internode in Hong Mang Mai, a wheat variety tolerant to deep‐seeding conditions. The length of the first internode in the GA3‐treated seedlings reached approximately 45 cm, which is twice as long as that of the control, whereas first internodes of other varieties were 3 to 12 cm long and hardly affected by GA3. The level of endogenous gibberellins (GA) in Hong Mang Mai was not greater than that of other wheat varieties. The expression of GAMyb, a transcription factor, was abundant in the first internode and substantially increased by GA3 application in Hong Mang Mai, compared with other wheat varieties. These results suggest that the first internode of Hong Mang Mai is more sensitive to GA in inducing strong elongation. The presence of potassium in the culture media was indispensable for the first internode elongation. Application of GA3 enhanced the uptake of potassium in Hong Mang Mai. Higher sensitivity of the first internode to GA could cause strong elongation by increasing the amount of osmotic solute, which plays an important role in the tolerance mechanism of Hong Mang Mai to deep‐seeding conditions.
Evaluating different soil and plant hydraulic constraints on tree function using a model and sap flow data from ponderosa pine
Authors: Williams M. , Bond B. J. , Ryan M. G.
Published: March 2003

Relationships between tree size and physiological processes such as transpiration may have important implications for plant and ecosystem function, but as yet are poorly understood. We used a process‐based model of the soil–plant–atmosphere continuum to investigate patterns of whole‐tree sap flow in ponderosa pine trees of different size and age (36 m and ∼250 years versus 13 m and 10–50 years) over a developing summer drought. We examined three different hypothetical controls on hydraulic resistance, and found that size‐related differences in sap flow could be best explained by absolute differences in plant resistance related to path length (hypothesis 1) rather than through different dynamic relationships between plant resistance and leaf water potential (hypothesis 2), or alterations in rates of cumulative inducement and repair of cavitation (hypothesis 3). Reductions in sap flow over time could be best explained by rising soil–root resistance (hypothesis 1), rather than by a combination of rising plant and soil–root resistance (hypothesis 2), or by rising plant resistance alone (hypothesis 3). Comparing hourly predictions with observed sap flow, we found that a direct relationship between plant resistance and leaf water potential (hypothesis 2) led to unrealistic bimodal patterns of sap flow within a day. Explaining seasonal reduction in sap flow purely through rising plant resistance (hypothesis 3) was effective but failed to explain the observed decline in pre‐dawn leaf water potential for small trees. Thus, hypothesis 1 was best corroborated. A sensitivity analysis revealed a significant difference in the response to drought‐relieving rains; precipitation induced a strong recovery in sap flow in the hypothetical case of limiting soil–root resistance (hypothesis 1), and an insignificant response in the case of limiting plant resistance (hypothesis 3). Longer term monitoring and manipulation experiments are thus likely to resolve the uncertainties in hydraulic constraints on plant function.
Developmental and seasonal changes of stress responsiveness in beech leaves (Fagus sylvatica L.)
Authors: Polle A. , Schwanz P. , Rudolf C.
Published: March 2003

The development of beech leaves (Fagus sylvatica L.) was characterized by determination of the pigment and electrolyte concentrations as well as the accumulation of dry mass and specific leaf mass from bud break to senescence. To test the hypothesis that stress tolerance and responsiveness of defences show developmental and/or seasonal changes, leaf discs were either incubated in the absence (control) or presence of paraquat to induce oxidative stress. Controls displayed developmental changes in stress susceptibility ranging from less than 15% of maximum electrolyte leakage in mature leaves to more than 20% leakage in senescent and 36–46% in immature leaves. Paraquat concentrations were chosen to result in about 95% of maximum electrolyte conductivity within 24 h in all developmental stages. Paraquat accumulation was about two‐fold lower in senescent as compared with immature leaves, whereas stress susceptibility, as characterized by the kinetics of the increase in relative leakage, was similar in these developmental stages with 50% of maximum electrolyte conductivity (EC50) = 6·5 h in immature and 7·5 h in senescent leaves. In mature leaves with intermediate paraquat accumulation rates, two classes of stress‐sensitivity were distinguished, namely stress‐resistant and stress‐susceptible leaves with EC50= 9·5 and 5·2 h, respectively. Stress‐resistance of mature leaves was accompanied by a rapid, approximately two‐fold induction of superoxide dismutase activity. Stress‐sensitive mature leaves initially contained high superoxide dismutase activities but showed a rapid, more than six‐ fold loss in activity in 24 h. Correlation of meteorological data with leakage rates suggested that high air temperatures and low precipitation might have been predisposing for loss of resistance against oxidative stress in beech leaves.
Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplings
Authors: Usami T. , Lee J. , Oikawa T.
Published: March 2003

The interactive effects of increased temperature and CO2 enrichment on the growth of 2‐year‐old saplings of Quercus myrsinaefolia, an evergreen broad‐leaved oak, were studied throughout an entire year in the vicinity of their northernmost distribution. Saplings were grown under different conditions in two chambers: (1) a temperature gradient chamber at ambient temperature, 3 and 5 °C warmer conditions with an ambient CO2 concentration, and (2) in a CO2 temperature gradient chamber at 3 °C warmer conditions with 1·5 times the normal CO2 concentration, and 5 °C warmer conditions with doubled CO2 concentration. The 3 and 5 °C warmer conditions enhanced the relative growth rate during almost the entire year, producing 53 and 47% increases in annual biomass production, 27 and 44% enhancement of root growth during shoot dormancy and 3 and 5 week prolongation of the shoot growing period, respectively. However, a daily mean air temperature exceeding 30 °C under the 5 °C warmer condition caused a marked reduction in net assimilation rate (NAR) from July to September. The CO2 enrichment further enhanced the positive effects of warming in spring and the resulting increases in NAR almost completely compensated for the negative effect of warming during summer. From autumn to winter, attenuation of the effects of CO2 was compensated by the increased sink strength produced by the warming. The annual biomass production was more than doubled by the combination of temperature elevation and CO2 enrichment.
Signalling drought in guard cells
Authors: Luan S.
Published: March 2003

A number of environmental conditions including drought, low humidity, cold and salinity subject plants to osmotic stress. A rapid plant response to such stress conditions is stomatal closure to reduce water loss from plants. From an external stress signal to stomatal closure, many molecular components constitute a signal transduction network that couples the stimulus to the response. Numerous studies have been directed to resolving the framework and molecular details of stress signalling pathways in plants. In guard cells, studies focus on the regulation of ion channels by abscisic acid (ABA), a chemical messenger for osmotic stress. Calcium, protein kinases and phosphatases, and membrane trafficking components have been shown to play a role in ABA signalling process in guard cells. Studies also implicate ABA‐independent regulation of ion channels by osmotic stress. In particular, a direct osmosensing pathway for ion channel regulation in guard cells has been identified. These pathways form a complex signalling web that monitors water status in the environment and initiates responses in stomatal movements.
Chromium ions inactivate electron transport and enhance superoxide generation in vivo in pea (Pisum sativum L. cv. Azad) root mitochondria
Authors: Dixit V. , Pandey V. , Shyam R.
Published: March 2003

The effect in vivo of hexavalent chromium (Cr6+) on the respiratory electron transport activity and production of superoxide (O2–) radicals, was studied in submitochondrial particles (SMPs) prepared from mitochondria isolated from roots of 15‐day‐old pea (Pisum sativum L. cv. Azad) plants exposed to environmentally relevant (20 µm) and acute (200 µm) concentrations of chromium for 7 d. A concentration ‐dependent inactivation of electron transport activity from both NADH to O2 (NADH oxidase) and succinate to O2 (succinate oxidase) was observed. The electron transport activity was more sensitive to Cr6+ with NADH as the substrate than with succinate as the substrate. Although NADH dehydrogenase and succinate dehydrogenase were less affected, NADH: cytochrome c oxidoreductase and succinate: cytochrome c oxidoreductase activities were prominently affected by Cr6+. Cytochrome oxidase was the most susceptible complex of mitochondrial membranes to Cr6+, exhibiting maximal inactivation of activity both at 20 and 200 µm chromium concentrations. Cr6+ increased the generation of O2– radicals. This effect was more evident at 200 than at 20 µm. A significant increase in lipid peroxidation of mitochondrial membranes at 200 µm Cr6+ was the physiological impact of the metal‐induced enhanced generation of O2– radicals. An increase in superoxide dismutase (SOD) activity at 20 µm Cr6+ towards enhanced production of O2– radicals appeared to be a defence response in pea root mitochondria that, however, could not be sustained at 200 µm Cr6+. The results obtained concerning inactivation of mitochondrial electron transport and subsequent enhancement in the generation of O2– radicals suggest that root mitochondria are an important target of Cr6+‐induced oxidative stress in pea.
Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast‐ and slow‐growing plant species
Authors: Loveys B. R. , Scheurwater I. , Pons T. L. , Fitter A. H. , Atkin O. K.
Published: March 2003

We examined the effect of growth temperature on the underlying components of growth in a range of inherently fast‐ and slow‐growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 °C. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter‐specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 °C but were not related to variations in RGR at 18 °C. When grown at 18 °C, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 °C used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 °C‐grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.
Interactions between atmospheric CO2 concentration and phosphorus nutrition on the formation of proteoid roots in white lupin (Lupinus albus L.)
Authors: Campbell C. D. , Sage R. F.
Published: March 2003

Atmospheric [CO2] affects photosynthesis and therefore should affect the supply of carbon to roots. To evaluate interactions between carbon supply and nutrient acquisition, the [CO2] effects on root growth, proteoid root formation and phosphorus (P) uptake capacity were studied in white lupin (Lupinus albus L.) grown hydroponically at 200, 410 and 750 µmol mol−1 CO2, under sufficient (0·25 mm P) and deficient (0·69 µm P) phosphorus. Plant size increased with increasing [CO2] only at high P. Both P deficiency and increasing [CO2] increased the production of proteoid clusters; the increase in response to increased [CO2] was proportionally greater from low to ambient [CO2] than from ambient to high. The activity of phosphoenol pyruvate carboxylase in the proteoid root, the exudation of organic acids from the roots, and the specific uptake of P increased with P deficiency, but were unaffected by [CO2]. Increasing [CO2] from Pleistocene levels to those predicted for the next century increased plant size and allocation to proteoid roots, but did not change the specific P uptake capacity per unit root mass. Hence, rising [CO2] should promote nutrient uptake by allowing lupins to mine greater volumes of soil.
Time lags for xylem and stem diameter variations in a Scots pine tree
Authors: Sevanto S. , Vesala T. , Perämäki M. , Nikinmaa E.
Published: March 2003

Diameter variations in the xylem and whole stem (i.e. over bark) stem of a Scots pine (Pinus sylvestris L.) tree were measured at four heights over a 23 d period at 5 min intervals. Cross‐correlation analysis was used to calculate time lags between the measurements. Xylem diameter measurements at the different heights had time lags varying from 10 to 50 min, measurements at the lower heights lagging behind the most. This result was in good agreement with the cohesion theory of transpiration. For the whole stem diameter measurements, the treetop lagged behind all other heights and the shortest lags were midway along the stem. Changes in whole stem diameter always lagged behind those of xylem stem diameter (30–110 min), and at all heights. The considerable differences in the behaviour of xylem and whole stem diameter support the Münch hypothesis of phloem flow. Time lags calculated separately for the shrinkage (morning) and swelling (afternoon) periods indicated shorter time lags during the swelling periods. The non‐destructive methods used show promise in the simultaneous study of flow dynamics of xylem and phloem in trees.
Carbon dioxide transport inxylem causes errors in estimation of rates of respiration in stemsand branches of trees
Authors: Teskey R. O. , Mcguire M. A.
Published: March 2003

Complementary laboratory and field experiments showed that theinternal transport of carbon dioxide (CO2) in the xylemof trees is an important pathway for carbon movement. Carbon dioxidereleased by respiration dissolves in sap and moves upward in thetranspirational stream. The concentration of CO2 in xylemsap can be up to three orders of magnitude greater than that foundin the atmosphere. In the present experiments, diffusion outwardof a portion of xylem‐transported CO2 caused a substantialoverestimation of the apparent rate of stem and branch respiration.Rates of CO2 efflux were linearly related to sap CO2 concentration.Direct manipulations of xylem sap CO2 concentration producedrapid and reversible changes in CO2 efflux from stemsand branches, in some cases quadrupling the rate of efflux. Theseresults demonstrated that apparent rates of stem and branch respirationof trees are in large part a by‐product of the rate of CO2 diffusionfrom xylem sap.