bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTOzone (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

ABSTRACTIn 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

ABSTRACTResponses 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

ABSTRACTImages 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

ABSTRACTTurgid 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

ABSTRACTIt 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

ABSTRACTA 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

ABSTRACTAlthough 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

ABSTRACTThe 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

ABSTRACTNon‐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

ABSTRACTProfiles 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

ABSTRACTDiurnal 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

ABSTRACTWe 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

ABSTRACTThe 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

ABSTRACTThe 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.