摘要:

ABSTRACTThe response of adaxial and abaxial stomatal conductance inRumex obtusifoliusto growth at elevated atmospheric concentrations of CO2(250 μmol mol−1above ambient) was investigated over two growing seasons. The conductance of both the adaxial and abaxial leaf surfaces was found to be reduced by elevated concentrations of CO2. Elevated CO2caused a much greater reduction in conductance for the adaxial surface than for the abaxial surface. The absence of effects upon stomatal density indicated that the reductions were probably the result of changes in stomatal aperture. Partitioning of gas exchange between the leaf surfaces revealed that increased concentrations of CO2caused increased rates of photosynthesis only via the abaxial surface. Additionally, leaf thickness was found to increase during growth at elevated concentrations of CO2. The tendency for these amphistomatous leaves to develop a distribution of conductance approaching that of hypostomatous leaves clearly reduced their maximum photosynthetic potential. This conclusion was supported by measurements of stomatal limitation, which showed greater values for the adaxial surfaces, and greater values at elevated CO2. This reduction in photosynthesis may in part be caused by higher diffusive limitations imposed because of increased leaf thickness. In an uncoupled canopy, asymmetrical stomatal responses of the kind identified here may appreciably reduce transpiration. Species which show symmetrical responses are less likely to show reduced transpirational rates, and a redistribution of water loss between species may occur. The implications of asymmetrical stomatal responses for photosynthesis and canopy transpiration are discuss

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTFour dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet‐B (UV‐B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV‐B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV‐B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV‐

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA spring wheat crop was grown at ambient and elevated (550 μmol mol−1) CO2concentrations under free‐air CO2enrichment (FACE) in the field. Four experimental blocks, each comprising 21‐m‐diameter FACE and control experimental areas, were used. CO2elevation was maintained day and night from crop emergence to final grain harvest. This experiment provided a unique opportunity to examine the hypothesis that CO2elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and lo assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age. Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS‐PAGE. For leaves at completion of emergence of the blade, growth at the elevated CO2concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined. Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3–4 further leaves formed above with continued development of the crop. By 35 d following completion of blade emergence, leaf 5 was in shade. At this point, the chlorophyllalbratio had declined by 26% both in plants grown at the control CO2concentration and in those grown at the elevated CO2concentration, which is indicative of shade acclimation. The ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO2concentration. The light‐ harvesting complex of photosystcm II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO2concentration. Following completion of the emergence of the flag‐leaf blade, the elevated‐CO2treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d. From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated‐CO2treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%. At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2concentration treatment relative to the control. By 52 d, all of these proteins showed a significant decline relative to the control. This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated‐CO2treatment, but that this was preceded by a CO2‐concentration

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTBet v 1 isoforms, the major pollen allergens of white birch (Betula verrucosa), show sequence homology to a class of pathogenesis‐related (PR) proteins identified in several other plant species. We recently reported that Bet v 1‐related mRNAs and proteins are induced by microbial pathogens in birch cell suspension cultures, which suggests that these pollen allergens and PR proteins are encoded by the same gene family. However, apart from the genes expressed in pollen, no otherBet v 1clones have been characterized until now. Here we describe the isolation, by screening with a pollenBet v 1cDNA probe, of three full‐length cDNA clones,Bet v 1‐Sc1, Sc2 and Sc3, from a cDNA library prepared from cultured birch cells grown in the presence ofPseudomonas syringae.Sequence analysis indicated that these clones are highly homologous, but different from the genes encoding the pollen isoallergens. Northern blots and RNase protection experiments showed that the three genes are transcriptionally activated, with similar kinetics, in birch cells co‐cultivated with bacteria or fungi, regardless of whether they were pathogenic for birch. Infection of leaves with the fungusTaphrina betulina, a natural pathogen of birch, also led to the coordinated activation of theBet v 1‐Scgenes, although infection withFusarium solanidid not. These results demonstrate that theBet v 1gene family of pollen allergens includes a subset of genes, different from those constitu‐tively expressed in pollen, that are induced in somatic cells upon their interaction with microorganisms. The possible implications of these results for the function ofBet v 1proteins in the defence reaction against pathogens, as well as for the incidence of Type I allergies,

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTStands ofScirpus olneyi, a native saltmarsh sedge with C3photosynthesis, had been exposed to normal ambient and elevated atmospheric CO2concentrations (Ca) in their native habitat since 1987. The objective of this investigation was to characterize the acclimation of photosynthesis ofScirpus olneyistems, the photosynthesizing organs of this species, to long‐term elevatedCatreatment in relation to the concentrations of Rubisco and non‐structural carbohydrates. Measurements were made on intact stems in the Held under existing natural conditions and in the laboratory under controlled conditions on stems excised in the field early in the morning. Plants grown at elevatedCahad a significantly higher (30–59%) net CO2assimilation rate (A) than those grown at ambientCawhen measurements were performed on excised stems at the respective growthCa. However, when measurements were made at normal ambientCa,Awas smaller (45–53%) in plants grown at elevatedCathan in those grown at ambientCa. The reductions inAat normal ambientCa, carboxylation efficiency andin situcarboxylase activity were caused by a decreased Rubisco concentration (30–58%) in plants grown at elevatedCa; these plants also contained less soluble protein (39–52%). The Rubisco content was 43 to 58% of soluble protein, and this relationship was not significantly altered by the growth CO2concentrations. The Rubisco activation state increased slightly, but thein situcarboxylase activity decreased substantially in plants grown at elevatedCa. When measurements were made on intact stems in the field, the elevatedCatreatment caused a greater stimulation of,A(100%) and a smaller reduction in carboxylation efficiency (which was not statistically significant) than when measurements were made on excised stems in the laboratory. The possible reasons for this arc discussed.Plants grown at elevatedCacontained more non‐structural carbohydrates (25–53%) than those grown at ambientCa. Plants grown at elevatedCaappear to have sufficient sink capacity to utilize the additional carbohydrates formed during photosynthesis.Overall, our results are in agreement with the hypothesis that elevated Caleads to an increased carbohydrate concentration and the ensuing acclimation of the photo‐synthetic apparatus in C3plants results in a reduction in the protein complement, especially Rubisco, which reduces the photosynthetic capacity in plants grown at elevated Ca, relative to plants grown at normal ambient Ca. Nevertheless, when compared at their respective growth Ca, Scirpus olneyi plants grown at elevated Cain their native habitat maintained a substantially higher rate of photosynthesis than those grown at normal ambient Caeven after 8 years of grow

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTRoot architecture is described for intact root systems of cultivated (Lactuca sativa L.) and wild (L. serriola L.) lettuce, grown for 5 to 6 weeks in greenhouse pot and cylinder experiments in coarse‐textured soil.L. sativacv. Salinas and a sclinas line of L. serriola attained the same biomass at 4 to 6 weeks after planting. Root biomass allocation was also similar, but root architecture differed. In the top zone along the tap root (0 to 5 cm), Salinas tended to produce more laterals, a greater total root length, and more external links (segments that originate at a branch point and end in a meristem) than wild lettuce. In the 5 to 55cm zone of the tap root, these measures were greater in the wild species. These patterns of root structure were generally corroborated by a second cylinder study with a different pair of L. sativa and L. serriola. Regressions of root structural traits were made against total root dry weight as a means to compare root architecture independently of the size of the root system. Regressions demonstrated that production of root segments differed between the two species; for example the slope for the regression of summed external link length in the top 0 to 5 cm with total root dry weight was significantly higher for Salinas, indicating that the rate of construction in the top 0 to 5cm was greater for cultivated than for wild lettuce. Yet, from 5 cm depth to the tap root tip, the rate of construction of external link length was greater in L. serriola. For many of these types of regression, r2and mean slope ± SE suggested that more variation occurred in cultivated than wild lettuce, yet genetic heterogeneity was probably low within the studied taxa. Inadvertent selection may have occurred in the breeding of cultivated lettuce varieties for increased root growth in the surface zone where water and fertilizer are applied, and for greater plasticity in construction of root segments, which might maximize the efficiency of exploitation of soil moisture and nutrien

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTOzone pollution may reduce net carbon gain in forests, yet data from mature trees are rare and the effects of irradiance on the response of photosynthesis to ozone remain untested. We used an open‐air system to expose 10 branches within the upper canopy of an 18‐m‐tall stand of sugar maple (Acer saccharumMarsh.) to twice‐ambient concentrations of ozone (95nmol mol−1, 0900 to 1700, 1 h mean) relative to 10 paired, untreated controls (45nmol mol−1) over 3 months. The branch pairs were selected along a gradient from relatively high irradiance (PPFD 14.5 mol m−2d−1) to deep shade (0.7mol m−2d−1). Ozone reduced light‐saturated rates of net photosynthesis (Asat) and increased dark respiration by as much as 56 and 40%, respectively. Compared to sun leaves, shade leaves exhibited greater proportional reductions in Asatand had lower chlorophyll concentrations, quantum efficiencies, and leaf absorptances when treated with ozone relative to controls. With increasing ozone dose over time, Asatbecame uncoupled from stomatal conductance as ratios of internal to external concentrations of carbon dioxide increased, reducing water‐use efficiency. Ozone reduced net photosynthesis and impaired stomatal function, with these effects depending on the irradiance environment of the canopy leaves. Increased ozone sensitivity of shade leaves compared to sun leaves has consequences for net

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00598.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe absolute pressure in conducting xylem vessels of roots of 2‐week‐old, slowly transpiring intact maize plants (bathed in nutrition medium) was determined to be +0·024 ± 0·044 MPa using the xylem pressure probe. When the roots were subjected to osmotic stress (NaCI, KCI or sucrose), the xylem pressure decreased immediately and became more negative. However, the response of xylem pressure to osmotic stress was considerably attenuated, indicating that the radial reflection coefficients, σ13of the maize root for these solutes were rather low (between 0·2 and 0·4 depending on the concentration of the osmoticum). The low values of a, may be caused (partly) by unstirred layer effects. In repeated osmoticum/nutrition regimes a complex pattern of changes in xylem pressure was observed which was apparently linked to the interplay between transpiration and (passive and/or active) solute loading of the xylem. These processes were not observed when the roots were subjected to osmotic stress after excision. In this case, a biphasic response was observed comparable to that found for excised roots using the root press

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00599.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTMass spectromelry has been used to investigate the uptake of CO2by two marine diatoms,Phaeodactylum tricornutumandCyclotellasp. The time course of CO2formation in the dark after addition of 100 mmol m−3dissolved inorganic carbon (DIC) to cell suspensions showed that external carbonic anhydrase (CA) was not present in cells of P. tricornutum but was present inCyclotellasp. In the absence of external CA, or when it was inhibited by 5 mmol m−3acetazolamide, cells of both species preincubated with 100 mmol m−3DIG rapidly depleted almost all of the free CO2(3·2mmol m−31 at pH7·5) from the suspending medium within seconds of illumination and prior to the onset of steady‐state photosynthesis. Addition of bovine CA quickly restored the HCO3−–CO2equilibrium in the medium, indicating that the initial depletion of CO2resulted from the selective uptake of CO2rather than uptake of all DIG species. Transfer of cells to the dark caused a rapid increase in the CO2concentration in the medium, largely as a result of the efflux of unfixed inorganic carbon from the cells. The measured CO2uptake rates for both species accounted for 50% of the total DIG uptake at HCO3−–CO2equilibrium, indicating that HCOHCO3−was also being taken up. These results indicate that both Phaeodactylum tricornutum and Cyclotella sp. have the capacity to transport CO2actively against concentra

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00600.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSome physiological characteristics of photosynthetic inorganic carbon uptake have been examined in the marine diatomsPhaeodactylum tricornutumandCyclotellasp. Both species demonstrated a high affinity for inorganic carbon in photosynthesis at pH7.5, having K1/2(CO2) in the range 1.0 to 4.0mmol m−3and O2−and temperature‐insensitive CO2compensation concentrations in the range 10.8 to 17.6 cm3m−3. Intracellular accumulation of inorganic carbon was found to occur in the light; at an external pH of 7.5 the concentration inP. tricornutumwas twice, and that inCyclotella3.5 times, the concentration in the suspending medium. Carbonic anhydrase (CA) was detected in intactCyclotellacells but not inP. tricornutum, although internal CA was detected in both species. The rates of photosynthesis at pH 8.0 ofP. tricornutumcells andCyclotellacells treated with 0.1 mol m−3acetazolamide, a CA inhibitor, were 1.5‐ to 5‐fold the rate of CO2supply, indicating that both species have the capacity to take up HCO3−as a source of substrate for photosynthesis. No Na+dependence for HCO3−could be detected in either species. These results indicate that these two marine diatoms have the capacity to accumulate inorganic carbon in the light as a consequence, in part, of the active upta

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00601.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY