bluuebunny/crossref_metadata_2025_split huggingface dataset:
CO2 enrichment in a maturing pine forest: are CO2 exchange and water status in the canopy affected?
Authors: ELLSWORTH D. S. 
Published: March 2003

A
net, leaf net CO2 assimilation ca, CO2 concentration of air surrounding a leaf ci, leaf intercellular CO2 concentration Δ, 13C isotope discrimination δ13C, relative stable carbon isotope content ɛ, ratio of Anet at ca = 560μmol mol–1 to Anet at ca = 360 μmol mol–1 FACE, free‐air CO2 enrichment gw, stomatal conductance to water vapour Πi, initial leaf osmotic potential Rt, relative water content at incipient turgor loss Ψl, xylem water potential of leaves Ψm, soil matric potential  Elevated CO2 is expected to reduce forest water use as a result of CO2‐induced stomatal closure, which has implications for ecosystem‐scale phenomena controlled by water availability. Leaf‐level CO2 and H2O exchange responses and plant and soil water relations were examined in a maturing loblolly pine (Pinus taeda L.) stand in a free‐air CO2 enrichment (FACE) experiment in North Carolina, USA to test if these parameters were affected by elevated CO2. Current‐year foliage in the canopy was continuously exposed to elevated CO2 (ambient CO2+200μmol mol–1) in free‐air during needle growth and development for up to 400 d. Photosynthesis in upper canopy foliage was stimulated by 50–60% by elevated CO2 compared with ambient controls. This enhancement was similar in current‐year, ambient‐grown foliage temporarily measured at elevated CO2 compared with long‐term elevated CO2 grown foliage. Significant photosynthetic enhancement by CO2 was maintained over a range of conditions except during peak drought.There was no evidence of water savings in elevated CO2 plots in FACE compared to ambient plots under drought and non‐drought conditions. This was supported by evidence from three independent measures. First, stomatal conductance was not significantly different in elevated CO2 versus ambient trees of P. taeda. Calculations of time‐integrated ci/ca ratios from analysis of foliar δ13C showed that these ratios were maintained in foliage under elevated CO2. Second, soil moisture was not significantly different between ambient and elevated CO2 plots during drought. Third, pre‐dawn and mid‐day leaf water potentials were also unaffected by the seasonal CO2 exposure, as were tissue osmotic potentials and turgor loss points. Together the results strongly support the hypothesis that maturing P. taeda trees have low stomatal responsiveness to elevated CO2. Elevated CO2 effects on water relations in loblolly pine‐dominated forest ecosystems may be absent or small apart from those mediated by leaf area. Large photosynthetic enhancements in the upper canopy of P. taeda by elevated CO2 indicate that this maturing forest may have a large carbon sequestration capacity with limiting water supply.
A relationship between humidity response, growth form and photosynthetic operating point in C3 plants
Authors: Franks P. J. , Farquhar G. D. 
Published: March 2003

ABSTRACTGas exchange experiments were performed with 13 plant species that differ from each other in growth‐form and natural habitat. These comprised three herbaceous species, two ferns, two temperate deciduous trees, five rainforest trees and one liana from wet tropical forest. The aims were to investigate whether plants of similar growth‐form and from similar habitats tended to respond similarly to a change in leaf‐to‐air vapour pressure difference (VPD), and to compare their ratio of intercellular to ambient partial pressures of CO2 for given conditions. Leaves were subjected to a step change in VPD and the initial and final steady rates of transpiration were used to calculate an index of sensitivity, φ, which enabled comparison of species. The results suggest that species of similar growth‐form and habitat respond similarly to increasing VPD, with the temperate deciduous trees undergoing a greater reduction in stomatal conductance than the herbaceous plants in well‐watered soil. Also, for these experimental conditions, the ratio of leaf internal to ambient CO2 partial pressure (pi/pa) was positively correlated with both CO2 assimilation rate and stomatal insensitivity to VPD, across the 13 species. The results are discussed in terms of growth strategies and possible advantages and limitations of hydraulic systems in different plants.
Ultraviolet‐B‐induced stress and changes in gene expression in Arabidopsis thaliana: role of signalling pathways controlled by jasmonic acid, ethylene and reactive oxygen species
Authors: A.‐H.‐Mackerness S. , Surplus S. L. , Blake P. , John C. F. , Buchanan‐Wollaston V. , Jordan B. R. , Thomas B. 
Published: March 2003

ABSTRACTTreatment with supplementary UV‐B resulted in decreases in transcripts of the photosynthetic genes Lhcb and psbA and concomitant increase in transcripts of two pathogen‐related genes, PR‐1 and PDF1·2, in Arabidopsis thaliana. UV‐B exposure caused increases in jasmonic acid (JA) levels and ethylene production. UV‐B treatment of jar1 and etr1‐1 mutants, which are insensitive to JA and ethylene, respectively, showed that the increase in PR‐1 transcripts was dependent on ethylene and PDF1·2 transcripts on both JA and ethylene. In contrast, the down‐regulation of photosynthetic transcripts was independent of both compounds. Previous studies have indicated a role for reactive oxygen species (ROS) in the UV‐B‐induced down‐regulation of the photosynthetic genes and up‐regulation of PR‐1 genes. Here we have shown that ROS are also required for the UV‐B‐induced up‐regulation of PDF1·2 genes. The results indicate that the effects of UV‐B on the three sets of genes are mediated through three distinct signal transduction pathways which are similar, but not identical, to pathways initiated in response to pathogen infection. In addition, the increased sensitivity of both jar1 and etr1‐1 mutants to UV‐B radiation, as compared with wild‐type plants, indicated that intact JA and ethylene signal pathways are required for defence against UV‐B damage.
Changes in carbon allocation and expression of carbon transporter genes inBetula pendulaRoth. colonized by the ectomycorrhizal fungusPaxillus involutus(Batsch) Fr.
Authors: Wright D. P. , Scholes J. D. , Read D. J. , Rolfe S. A. 
Published: March 2003

ABSTRACTComparative analyses of aspects of the carbon (C) physiology and the expression of C transporter genes in birch (Betula pendulaRoth.) colonized by the ectomycorrhizal fungusPaxillus involutus(Batsch) Fr. were performed using mycorrhizal (M) and non‐mycorrhizal (NM) plants of similar foliar nutrient status. After six months of growth, the biomass of M plants was significantly lower than that of NM plants. Diurnal C budgets of both sets of plants revealed that M plants exhibited higher rates of photosynthesis and root respiration expressed per unit dry weight. However, the diurnal net C gain of M and NM plants remained similar. Ectomycorrhizal roots contained higher soluble carbohydrate pools and increased activity of cell wall invertase, suggesting that additional C was allocated to these roots and their ectomycorrhizal fungi consistent with an increased sink demand for C due to the presence of the mycobiont. In M roots, the expression of two hexose and one sucrose transporter genes of birch were reduced to less than one‐third of the expression level observed in NM roots. Analysis using a probe against the birch ribosomal internal transcribed spacer region revealed that M roots contained 22% less plant RNA than NM roots. As the expression of birch hexose and sucrose transporter genes was reduced to a much greater extent, this suggests that these specific genes were down‐regulated in response to alterations in C metabolism within M roots.
Stem water storage capacity and efficiency of water transport: their functional significance in a Hawaiian dry forest
Authors: Stratton L. , Goldstein G. , Meinzer F. C. 
Published: March 2003

ABSTRACTWe investigated the contribution of internal water storage and efficiency of water transport to the maintenance of water balance in six evergreen tree species in a Hawaiian dry forest. Wood‐saturated water content, a surrogate for relative water storage capacity, ranged from 70 to 105%, and was inversely related to its morphological correlate, wood density, which ranged between 0·51 and 0·65 g cm−3. Leaf‐specific conductivity (kL) measured in stem segments from terminal branches ranged from 3 to 18 mmol m−1 s−1 MPa−1, and whole‐plant hydraulic efficiency calculated as stomatal conductance (g) divided by the difference between predawn and midday leaf water potential (ΨL), ranged from 70 to 150 mmol m−2 s−1 MPa−1. Hydraulic efficiency was positively correlated with kL (r2 = 0·86). Minimum annual ΨL ranged from − 1·5 to − 4·1 MPa among the six species. Seasonal and diurnal variation in ΨL were associated with differences among species in wood‐saturated water content, wood density and kL. The species with higher wood‐saturated water content were more efficient in terms of long‐distance water transport, exhibited smaller diurnal variation in ΨL and higher maximum photosynthetic rates. Smaller diurnal variation in ΨL in species with higher wood‐saturated water content, kL and hydraulic efficiency was not associated with stomatal restriction of transpiration when soil water deficit was moderate, but avoidance of low minimum seasonal ΨL in these species was associated with a substantial seasonal decline in g. Low seasonal minimum ΨL in species with low kL, hydraulic efficiency, and wood‐saturated water content was associated with higher leaf solute content and corresponding lower leaf turgor loss point. Despite the species‐specific differences in leaf water relations characteristics, all six evergreen tree species shared a common functional relationship defined primarily by kL and stem water storage capacity.
ABA‐deficient (aba1) and ABA‐insensitive (abi1‐1, abi2‐1) mutants of Arabidopsis have a wild‐type stomatal response to humidity
Authors: Assmann Sarah M. , Snyder Jo Ann , Lee Yuh‐Ru Julie 
Published: March 2003

ABSTRACTIn most plant species, a decrease in atmospheric humidity at the leaf surface triggers a decrease in stomatal conductance. While guard cells appear to respond to humidity‐induced changes in transpiration rate, as opposed to relative humidity or vapour pressure difference, the underlying cellular mechanisms for this response remain unknown. In the present set of experiments, abscisic acid (ABA)‐deficient (aba1) and ABA‐insensitive (abi1‐1 and abi2‐1) mutants of Arabidopsis thaliana were used to test the hypothesis that the humidity signal is transduced by changes in the flux or concentration of ABA delivered to the stomatal complex in the transpiration stream. In gas exchange experiments, stomatal conductance was as sensitive to changes in vapour pressure difference in aba1, abi1‐1 and abi2‐1 mutant plants as in wild‐type plants. These experiments appear to rule out an obligate role for either the concentration or flux of ABA or ABA conjugates as mediators of the guard cell response to atmospheric water potential. The results stand in contrast to the well‐established role of ABA in mediating guard cell responses to decreases in soil water potential.
Regulation of nitrate reductase expression in leaves by nitrate and nitrogen metabolism is completely overridden when sugars fall below a critical level
Authors: Klein D. , Morcuende R. , Stitt M. , Krapp A. 
Published: March 2003

ABSTRACTThese experiments use Nia30(145), a tobacco nia1nia2 double null mutant transformed with a NIA2 construct, to define when sugar supply plays the dominating role in the regulation of nitrate reductase (NIA) expression. The null alleles of Nia30(145) are transcribed and translated to produce non‐functional NIA transcript and NIA protein, providing an endogenous reporter system to track NIA expression at the transcript and protein level. The re‐introduced NIA2 construct is expressed at low efficiency, providing a background in which the response to changes in sugar status is not complicated by simultaneous changes in the rate of nitrate assimilation and the levels of nitrate and glutamine. In an alternating light–dark regime, Nia30(145) contained high levels of nitrate and low levels of glutamine and other amino acids. This drives constitutive overexpression of NIA. After transfer of Nia30(145) to continuous darkness, nitrate remains high and glutamine low, but the NIA transcript level and NIA protein decreased significantly within 24 h and were undetectable from 48 h onwards. The decrease of the NIA transcript level was fully reversed and the decrease of NIA protein was partly reversed when leaves were detached from the pre‐darkened plants and supplied with sucrose in the dark. The decrease was not reversed by nitrate or cytokinin. The NIA transcript disappeared when the leaf sugar content fell below 4 μmol hexose equivalents g−1 FW, and recovered when sugars rose above 8 μmol hexose equivalents g−1 FW. It is concluded that low sugar represses NIA, completely overriding signals derived from nitrate and nitrogen metabolism.
Effect of mycorrhizal‐enhanced leaf phosphate status on carbon partitioning, translocation and photosynthesis in cucumber
Authors: Black K. G. , Mitchell D. T. , Osborne B. A. 
Published: March 2003

ABSTRACTAn assessment of the effects of arbuscular mycorrhizal (AM) infection on photosynthesis, carbon (C) allocation, translocation and biomass production of cucumber, grown in sand culture, was made using a previously determined phosphorus (P) supply (0·13 mol m−3 P) which had a significant impact on AM infection. Separation of a direct effect of AM infection from an indirect one due to an enhanced leaf P status was achieved using a comparable non‐mycorrhizal treatment (NAM + P) supplemented with extra P (0·19 mol m−3 P). Total leaf P concentration, specific leaf mass, photosynthetic capacity, and incorporation of 14C into non‐structural carbohydrate pools were dependent on leaf age. Both maximum and ambient photosynthetic rates were significantly higher in the youngest fully expanded leaves from AM and NAM + P plants which also had the higher leaf P concentrations. There were no differences in the total concentrations of starch, sucrose, raffinose or stachyose in young or old leaves among AM, non‐mycorrhizal (NAM) and NAM + P treatments. However, younger leaves of NAM plants showed a shift in 14C‐partitioning from stachyose and raffinose synthesis to starch accumulation. Determination of ADP‐glucose pyrophosphorylase (AGPase), sucrose synthase and sucrose phosphate synthase enzyme activities revealed that only AGPase activity was correlated with the increased incorporation rate of 14C into starch in young leaves of NAM plants. Although there were significant AM‐specific effects on C translocation to the root system, AM plants had similar rate of photosynthesis to NAM + P plants. These results suggest that the increase in photosynthetic rate in leaves of AM‐infected cucumber was due to an increased P status, rather than a consequence of a mycorrhizal ‘sink’ for assimilates.
Blue light inhibits stomatal development in soybean isolines containing kaempferol‐3‐O‐2G‐glycosyl‐gentiobioside (K9), a unique flavonoid glycoside
Authors: Liu‐Gitz L. , Britz S. J. , Wergin W. P. 
Published: March 2003

ABSTRACTStomata have a fundamental role in controlling plant photosynthesis and transpiration, but very little is known about factors controlling stomatal differentiation and development. Lines of soybean that contain a specific flavonol glycoside, kaempferol‐3‐O‐2‐glycosyl‐gentiobioside (K9), as well as greatly reduced stomatal density, especially on the adaxial epidermis, have been identified. The specific effects of blue light photoreceptors on stomatal development in K9 lines and their isoline pairs containing no K9 were studied. Low irradiances of blue light (7% of total photosynthetically active radiation) added to high irradiances from low‐pressure sodium lamps strongly inhibited stomatal development on the adaxial epidermis of K9 lines, but not in isoline pairs differing putatively in only one gene and lacking K9. Overall, blue light slightly increased stomatal density on the abaxial epidermis in all isolines, demonstrating differential regulation of stomatal development in the upper and lower epidermis. Blue light also caused an increase in leaf area in all isolines, indicating that changes in stomatal density were not the non‐specific result of alterations in leaf area. Morphological studies revealed that the blue light‐induced reduction in stomatal density in K9 lines was due to reduced stomatal initiation as well as aborted or abnormal stomatal development. As the phytochrome photostationary state was kept constant, the results indicate that one or more blue light receptors are involved in the control of stomatal development. This system should be useful for the study of mechanisms controlling stomatal development, even if the photo‐inhibitory response is unique to K9 lines.
Identification of a novel multiple environmental factor‐responsive 1‐aminocyclopropane‐1‐carboxylate synthase gene, NT‐ACS2, from tobacco
Authors: Ge L. , Liu J. Z. , Wong W. S. , Hsiao W. L. W. , Chong K. , Xu Z. K. , Yang S. F. , Kung S. D. , Li N. 
Published: March 2003

ABSTRACTMany abiotic environmental factors elicit the production of stress‐ethylene in higher plants. To elucidate the molecular mechanisms underlying the regulation of stress‐ethylene production and the physiological roles played by stress‐ethylene in stress responses of plants, we studied the gene expression of ACC synthase in tobacco plants that had been subjected to environmental stresses. Four new tobacco ACC synthase cDNA fragments, NT‐ACS2, NT‐ACS3, NT‐ACS4 and NT‐ACS5, were identified and sequenced. It was found that NT‐ACS2 could be induced by wounding, cold temperature and, especially, sunlight. NT‐ACS4 was induced at a faster kinetics by wounding. The multiple environmental stress‐responsive (MESR) NT‐ACS2 gene was found to contain three introns and four exons and encode a polypeptide of 484 amino acids, 54·6 kDa and pI 6·87. Computer analysis of the 3·4 kb 5′ flanking region upstream of the ACS coding region revealed the existence of a group of putative cis‐acting regulatory elements potentially conferring wounding, chilling, and UV light inducibility. Phylogenetic analysis of ACC synthase genes of different plant origins indicated that the chill‐inducible NT‐ACS2 gene is closely related to a chilling‐inducible citrus ACS gene.
The influence of nitrogen on rain forest dipterocarp seedlings exposed to a large increase in irradiance
Authors: Bungard R. A. , Scholes J. D. , Press M. C. 
Published: March 2003

ABSTRACTDipterocarps dominate the canopy of lowland tropical rain forest in South‐east Asia. Seedlings of these species form diverse assemblages on the forest floor where low irradiance severely limits their growth. Further growth depends largely upon the increased irradiance that can occur with the creation of canopy gaps. However, the response of dipterocarp seedlings to increased irradiance and their subsequent establishment in the canopy may be influenced by the availability of other resources, such as nutrient availability. We investigated the influence of nitrogen supply on aspects of the photosynthetic physiology and growth of seedlings of four dipterocarp species (Shorea leprosula,Shorea johorensis,Shorea oleosaandDryobalanops lanceolata) growing under low irradiance, during transfer from low to high irradiance, and during subsequent growth at high irradiance. All four species increased growth and photosynthetic capacity in response to N‐supply at high irradiances but not at low irradiance approximating that which can be expected to occur in the forest understorey. When seedlings grown at low irradiances and varying N‐supply were exposed to a large increase in irradiance, all species showed some degree of initial photodamage (measured through chlorophyll fluorescence), the extent of which was similar between species but differed markedly depending on the pre‐exposure growth irradiance and N‐supply. Greater photodamage occurred in seedlings grown at lower compared with higher N‐supply and irradiance. Despite these initial difference in the extent of this photodamage, all seedlings demonstrated a similar capacity to recover from damage. However, the alterations in the photosynthetic physiology of leaves during this recovery differed between species and depended on N‐supply. Under high N‐supply all species apart fromS. oleosaincreased photosynthetic capacity per unit chlorophyll following exposure to high irradiance by increasing photosynthetic capacity per unit leaf area while, under low N‐supply, an increase in photosynthetic capacity per unit leaf only occurred inD. lanceolata. Our results suggest that variations in N‐availability may have a much greater impact on the relative competitiveness of dipterocarp seedlings during the regenerative phase following canopy gap formation than physiological differences between seedlings. Our results demonstrate a potentially significant role for N‐availability in the regeneration dynamics and distribution of canopy‐dominating dipterocarp species.
Changes in Rubisco and Rubisco activase gene expression and polypeptide content in Pinus halepensis M. subjected to ozone and drought
Authors: Pelloux J. , Jolivet Y. , Fontaine V. , Banvoy J. , Dizengremel P. 
Published: March 2003

ABSTRACTThe regulation of ribulose‐1,5‐biphosphate carboxlase/oxygenase (Rubisco) and Rubisco activase was followed for 3 months in an experiment studying the effects of ozone and water stress on Aleppo pine. Rubisco activity was shown to be reduced by 30% in the presence of ozone, whereas no significant effect of water stress was noticed. The effect of combined stresses on Rubisco activity was similar to the effect of ozone. The changes in protein quantity of Rubisco large subunit (LSU) and Rubisco activase (RCA), compared with control plants, were similar to that of the Rubisco activity. Using homologous probes obtained by reverse transcription (RT)‐polymerase chain reaction (PCR), rbcL and rca transcript quantities were quantified during the course of the experiment. RbcL and rca mRNA quantities decreased in ozone and after drought. Changes in rbcL transcript quantity in needles subjected to the combination of ozone and drought were similar to the ones detected when drought was applied alone. On the contrary, the pattern of rca changes under the combination of the two stresses was similar to that of ozone applied alone. A positive correlation existed between the effects of ozone on Rubisco activase and Rubisco LSU protein quantities, which was not so obvious by comparing transcript quantities. This could suggest a potential post‐transcriptional coordinated regulation of the two proteins under stress‐imposed conditions.