bluuebunny/crossref_metadata_2025 huggingface dataset:
Ethylene biosynthesis in peach fruitlet abscission
Authors: Ruperti B. , Bonghi C. , Tonutti P. , Ramina A.
Published: March 2003

Ethylene biosynthesis was studied in the peach (Prunus persica L. Batsch) fruitlet abscission zone (AZ), located between pedicel and pericarp and responsible for the shedding of the fruit. Explants, made up of the abscission layer and small parts of pedicel and pericarp, were flushed with air or air + propylene (500 cm3 m–3) for up to 72 h. Parameters of ethylene biosynthesis were monitored in excised zone and non‐zone tissues. Both treatments induced an increase of ethylene biosynthesis in all tissues examined and a climacteric‐like behaviour was observed: ethylene evolution peaked at 12 and 48 h in air + propylene and air, respectively. The activity of 1‐aminocyclopropane‐1‐carboxylate oxidase (ACO) and related transcript accumulation paralleled ethylene evolution. Furthermore a decreasing gradient, in terms of ethylene production, ACO activity and mRNA accumulation was in general observed moving from the distal (pericarp side) to the proximal (pedicel side) non‐zone, through the abscission zone. The content of 1‐aminocyclopropane‐1‐carboxylate (ACC) showed significant difference among treatments only at 12 h of air + propylene flushing in AZ3 and non‐zones, but no difference in terms of ACC synthase transcript and related polypeptide accumulation was observed. Endo‐β‐1,4‐glucanase (EG), the cell wall hydrolase involved in cell separation, appeared to be up‐regulated by propylene and its activity was almost exclusively confined to the abscission layer. Similarly, EG transcript accumulation occurred in zone but not in non‐zone tissues. In air‐treated and air + propylene‐treated explants the ethylene climacteric preceded the increase of EG activity and the cell separation at the level of the abscission zone.
Onset of freezing tolerance in birch (Betula pubescens Ehrh.) involves LEA proteins and osmoregulation and is impaired in an ABA‐deficient genotype
Authors: Rinne P. , Welling A. , Kaikuranta P.
Published: March 2003

In many woody plants a short photoperiod triggers the onset of cold acclimation, but the nature of this process has remained obscure. We aimed to establish which physiological and genetic factors have a role in short‐day‐induced acclimation by comparing two types of birch, Betula pubescens Ehrh. and B. pubescens f. hibernifolia Ulv., the latter being unable to increase its abscisic acid (ABA) levels. In the wild type, short‐day or natural autumn conditions in the field appeared to elevate the ABA levels before acclimation, which was accompanied by tissue desiccation, osmotic adjustments and accumulation of Group 2 LEA proteins [responsive to ABA (RAB) 16‐like; 24, 30 and 33 kDa] and Group 4 LEA proteins [late embryogenesis abundant (LEA) 14‐like; 19 kDa]. Under similar conditions the ABA‐deficient birch showed reduced water loss, defective osmoregulation, absence of inducible Group 2 LEA proteins, and delayed or reduced tolerance to freezing. In contrast, both birch genotypes showed similar seasonal production patterns of Group 4 LEA proteins. Our results demonstrate that onset of cold acclimation in birch is based on multiple mechanisms, including molecular pathways that are typical of stress responses. ABA may be important for the accurate timing of cold acclimation in trees that are sensitive to photoperiod.
Variations in the amino acid composition of xylem sap of Betula pendula Roth. trees due to remobilization of stored N in the spring
Authors: Millard P. , Wendler R. , Hepburn A. , Smith A.
Published: March 2003

Seasonal patterns of N translocation in the xylem sap of Betula pendula were studied, to determine whether specific amino acids were recovered in spring as a consequence of N remobilization. Seedlings were grown in sand culture and provided with 15NH415NO3 (at 2·2 atom percent excess) for one growing season. The following winter dormant trees were transplanted into fresh sand and given N at natural abundance thereafter. Destructive harvests were taken during bud burst and leaf growth to determine the pattern of 15N remobilization and N uptake, along with isolation of xylem sap for analysis of their amino acid profiles and 15N enrichment by GC‐MS. 15N remobilization occurred immediately following bud burst, while N derived from root uptake did not appear in the leaves until 12 d after bud burst. During N remobilization there was a 10‐fold increase in the concentration of N in the xylem sap, due predominantly to increases in citrulline and glutamine. The 15N enrichment of these two amino acids demonstrated the increase in their concentration in the xylem sap following bud burst was due to N remobilization. These results are discussed in relation to measuring N remobilization and storage capacity of trees in the field.
Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree
Authors: Livingston N. J. , Whitehead D. , Kelliher F. M. , Wang Y.‐P. , Grace J. C. , Walcroft A. S. , Byers J. N. , Mcseveny T. M. , Millard P.
Published: March 2003

The three dimensional distribution of intercepted radiation, intercellular CO2 concentration (Ci) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2‐m‐tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above‐ and below‐canopy irradiance, leaf stable carbon isotopic composition (δ13C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) Ci would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (gs), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in gs. Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ13C and needle height above ground (r2 = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and Ci (r2 = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.
The regulation of photosynthetic rate and activation of extracellular carbonic anhydrase under CO2‐limiting conditions in the marine diatom Skeletonema costatum
Authors: Nimer N. A. , Warren M. , Merrett M. J.
Published: March 2003

In the marine diatom Skeletonema costatum, carbonic anhydrase activity exterior to the plasma membrane (CAext) was detected only when the available CO2 concentration was less than 5·0 mmol m–3, this activity being unaffected by the total dissolved inorganic carbon concentration. The inhibition of CAext by dextran bound sulphonamide (DBS) demonstrated the key role of this enzyme in maintaining photosynthetic rate under CO2‐limited conditions. Treatment with trypsin followed by affinity chromatography on p‐aminomethylbenzene‐sulphamide agarose and subsequent SDS‐PAGE analysis revealed a polypeptide from carbon‐replete cells of identical molecular mass to the CAext released by trypsin from CO2‐limited cells. Redox activity in the plasma membrane of intact cells was measured by following the light‐dependent reduction of ferricyanide or NADP, the greatest activity being shown by CO2‐limited cells. Overall the results suggest that high rates of redox activity under conditions of CO2‐limitation were required for the activation of CAext.
Two forms of sustained xanthophyll cycle‐dependent energy dissipation in overwintering Euonymus kiautschovicus
Authors: Verhoeven A. S. , Adams W. W. , Demmig‐Adams B.
Published: March 2003

Seasonal differences in PSII efficiency (Fv/Fm), the conversion state of the xanthophyll cycle (Z + A)/ (V + A + Z), and leaf adenylate status were investigated in Euonymus kiautschovicus. On very cold days in winter, Fv/Fm assessed directly in the field remained low and Z + A high throughout day and night in both sun and shade leaves. Pre‐dawn transfer of leaves from subfreezing temperatures in the field to room temperature revealed that recovery (increases in Fv/Fm and conversion of Z + A to violaxanthin) consisted of one, rapid phase in shade leaves, whereas in sun leaves a rapid phase was followed by a slow phase requiring days. The pre‐dawn ATP/ADP ratio, as well as that determined at midday, was similar when comparing overwintering leaves with those sampled in the summer, although pre‐dawn levels of ATP + ADP were elevated in all leaves during winter relative to summer. After a natural transition to warmer days during the winter, pre‐dawn Fv/Fm and Z + A in shade leaves had returned to values typical for summer, whereas in sun leaves Fv/Fm and Z + A levels remained intermediate between the cold day in winter and the summer day. Thus two distinct forms of sustained (Z + A)‐dependent energy dissipation were identified based upon their differing characteristics. The form that was sustained on cold days but relaxed rapidly upon warming occurred in all leaves and may result from maintenance of a low lumenal pH responsible for the nocturnal engagement of (Z + A)‐dependent thermal dissipation exclusively on very cold days in the winter. The form that was sustained even upon warming and correlated with slow Z + A to violaxanthin conversion occurred only in sun leaves and may represent a sustained engagement of (Z + A)‐dependent energy dissipation associated with an altered PSII protein composition. In the latter, warm‐sustained form, uncoupler or cycloheximide infiltration had no effect on the slow phase of recovery, but lincomycin infiltration inhibited the slow increase in Fv/Fm and the conversion of Z + A to violaxanthin.
Wood properties and ring width responses to long‐term atmospheric CO2enrichment in field‐grown loblolly pine (Pinus taedaL.)
Authors: TELEWSKI F. W. , SWANSON R. T. , STRAIN B. R. , BURNS J. M.
Published: March 2003

Loblolly pine (Pinus taedaL.) were grown in the field, under non‐limiting nutrient conditions, in open‐top chambers for 4 years at ambient CO2partial pressures (pCO2) and with a CO2‐enriched atmosphere (+ 30 PapCO2compared to ambient concentration). A third replicate of trees were grown without chambers at ambientpCO2. Wood anatomy, wood density and tree ring width were analysed using stem wood samples. No significant differences were observed in the cell wall to cell lumen ratio within the latewood of the third growth ring formed in 1994. No significant differences were observed in the density of resin canals or in the ratio of resin canal cross‐sectional area to xylem area within the same growth ring. Ring widths were significantly wider in the CO2‐enrichment treatment for 3 of 4 years compared to the ambient chamber control treatment. Latewood in the 1995 growth ring was significantly wider than that in the ambient control and represented a larger percentage of the total growth‐ring width. Carbon dioxide enrichment also significantly increased the total wood specific gravity (determined by displacement). However, when determined as total sample wood density by X‐ray densitometry, the density of enriched samples was not significantly higher than that of the ambient chamber controls. Only the 1993 growth ring of enriched trees had a significantly higher maximum latewood density than that of trees grown on non‐chambered plots or ambient chambered controls. No significant differences were observed in the minimum earlywood density of individual growth rings between chambered treatments. These results show that the most significant effect of CO2enrichment on wood production in loblolly pine is its influence on radial growth, measured as annual tree ring widths. This influence is most pronounced in the first year of growth and decreases with age.
The effects of nitrogen stress on the stable carbon isotope composition, productivity and water use efficiency of white spruce (Picea glauca (Moench) Voss) seedlings
Authors: LIVINGSTON N. J. , GUY R. D. , SUN Z. J. , ETHIER G. J.
Published: March 2003

A, assimilation rate a, fractionation against 13C for CO2 diffusion through air b, net fractionation against 13C during CO2 fixation Ca, ambient CO2 concentration Cc, CO2 concentration at the chloroplast Ci, intercellular CO2 concentration D, vapour pressure deficit En, needle transpiration rate Ep, whole plant water use gw, leaf internal transfer conductance to CO2 gs, stomatal conductance to water vapour L, projected leaf area NUE, nitrogen use efficiency PEP, phosphoenolpyruvate Rubisco, ribulose‐1,5‐biphosphate carboxylase TDR, time domain reflectometry WUE, water use efficiency Δ, carbon isotope discrimination δ13C, carbon isotope abundance parameter δ13Ca, carbon isotopic composition of atmospheric CO2 θ, volumetric soil water content  The effect of nitrogen stress on needle δ13C, water‐use efficiency (WUE) and biomass production in irrigated and dry land white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings, representing 10 controlled crosses, were planted in the field in individual buried sand‐filled cylinders. Two nitrogen treatments were imposed, nitrogen stressed and fertilized. The ranking of δ13C of the crosses was maintained across all combinations of water and nitrogen treatments and there was not a significant genetic versus environmental interaction. The positive relationships between needle δ13C, WUE and dry matter production demonstrate that it should be possible to use δ13C as a surrogate for WUE, and to select for increased WUE without compromising yield, even in nitrogen deficient environments. Nitrogen stressed seedlings had the lowest needle δ13C in both irrigated and dry land conditions. There was a positive correlation between needle nitrogen content and δ13C that was likely associated with increased photosynthetic capacity. There was some indication that decreased nitrogen supply led to increased stomatal conductance and hence lower WUE. There was a negative correlation between intrinsic water use efficiency and photosynthetic nitrogen use efficiency (NUE). This suggests that white spruce seedlings have the ability to maximize NUE when water becomes limited. There was significant genetic variation in NUE that was maintained across treatments. Our results suggest that in white spruce, there is no detectable effect of anaplerotic carbon fixation and that it is more appropriate to use a value of 29‰ (‘Rubisco only’) for the net discrimination against 13C during CO2 fixation. This leads to excellent correspondence between values of Ci/Ca derived from gas exchange measurements or from δ13C.
Elevated CO2 enhances stomatal responses to osmotic stress and abscisic acid in Arabidopsis thaliana
Authors: LEYMARIE J. , LASCÈVE G. , VAVASSEUR A.
Published: March 2003

A, carbon assimilation rate ABA, abscisic acid Ci, intercellular space CO2 concentration g, leaf conductance WUE, water use efficiency  Carbon dioxide and abscisic acid (ABA) are two major signals triggering stomatal closure. Their putative interaction in stomatal regulation was investigated in well‐watered air‐grown or double CO2‐grown Arabidopsis thaliana plants, using gas exchange and epidermal strip experiments. With plants grown in normal air, a doubling of the CO2 concentration resulted in a rapid and transient drop in leaf conductance followed by recovery to the pre‐treatment level after about two photoperiods. Despite the fact that plants placed in air or in double CO2 for 2 d exhibited similar levels of leaf conductance, their stomatal responses to an osmotic stress (0·16–0·24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO2. Similarly, the drop in leaf conductance triggered by 1 μM ABA applied at the root level was stronger at double CO2. Identical experiments were performed with plants fully grown at double CO2. Levels of leaf conductance and carbon assimilation rate measured at double CO2 were similar for air‐grown and elevated CO2‐grown plants. An enhanced response to ABA was still observed at high CO2 in pre‐conditioned plants. It is concluded that: (i) in the absence of stress, elevated CO2 slightly affects leaf conductance in A. thaliana; (ii) there is a strong interaction in stomatal responses to CO2 and ABA which is not modified by growth at elevated CO2.
The utilization of pre‐anthesis reserves in grain filling of wheat. Assessment by steady‐state 13CO2/12CO2 labelling
Authors: Gebbing T. , Schnyder H. , KÜhbauch W.
Published: March 2003

δ, C isotope composition relative to Pee Dee Belemnite WSC, water‐soluble carbohydrates N, nitrogen C, carbon cv, cultivar ME, efficiency of mobilized pre‐anthesis C utilization in grain filling (g C g–1C)  Significant mobilization of protein and carbohydrates in vegetative plant parts of wheat regularly occurs during grain filling. While this suggests a contribution of reserves to grain filling, the actual efficiency of mobilized assimilate conversion into grain mass (ME) is unknown. In the present study the contribution of pre‐anthesis C (C fixed prior to anthesis) to grain filling in main stem ears of two spring wheat (Triticum aestivum L.) cultivars was determined by 13C/12C steady‐state labelling. Mobilization of pre‐anthesis C in vegetative plant parts between anthesis and maturity, and the contributions of water‐soluble carbohydrates (WSC) and protein to pre‐anthesis C mobilization were also assessed. Experiments were performed with two levels of N fertilizer supply in each of 2 years. Pre‐anthesis reserves contributed 11–29% to the total mass of C in grains at maturity. Pre‐anthesis C accumulation in grains was dependent on both the mass of pre‐anthesis C mobilized in above‐ground vegetative plant parts (r2 = 0·87) and ME (defined as g pre‐anthesis C deposited in grains per g pre‐anthesis C mobilized in above‐ground vegetative plant parts; r2 = 0·40). ME varied between 0·48 and 0·75. The effects of years, N fertilizer treatments and cultivars on ME were all related to differences in the fractional contribution of WSC to pre‐anthesis C mobilization. Multiple regression analysis indicated that C from mobilized pre‐anthesis WSC may be used more efficiently in grain filling than C present in proteins at anthesis and mobilized during grain filling. Possible causes for variability of ME are discussed.
XET‐related genes and growth kinematics in barley leaves
Authors: PETERS W. S. , FRICKE W. , CHANDLER P. M.
Published: March 2003

DV, displacement velocity GA3, gibberellic acid REGR, relative elemental growth rate XET, xyloglucan‐endotransglycosylase  Recently Schünmann et al. (1997; Plant, Cell and Environment 20, 1439–1450) investigated the correlation of spatial patterns of xyloglucan‐endotransglycosylase (XET) activity, XET‐related mRNAs, and growth in elongating barley (Hordeum vulgare L.) leaves. Here, methodological difficulties in the kinematic growth analysis are discussed, and it is concluded that the role that XET‐related gene activity plays in the control of spatial growth patterns remains undetermined.
Light acclimation, CO2 response and long‐term capacity of underwater photosynthesis in three terrestrial plant species
Authors: Vervuren P. J. A. , Beurskens S. M. J. H. , Blom C. W. P. M.
Published: March 2003

To characterize underwater photosynthetic performance in some terrestrial plants, we determined (i) underwater light acclimation (ii) underwater photosynthetic response to dissolved CO2, and (iii) underwater photosynthetic capacity during prolonged submergence in three species that differ in submergence tolerance: Phalaris arundinacea, Rumex crispus (both submergence‐tolerant) and Arrhenatherum elatius (submergence‐intolerant). None of the species had adjusted to low irradiance after 1 week of submergence. Under non‐submerged (control) conditions, only R. crispus displayed shade acclimation. Submergence increased the apparent quantum yield in this species, presumably because of the enhanced CO2 affinity of the elongated leaves. In control plants of the grass species P. arundinacea and A. elatius, CO2 affinities were higher than for R. crispus. The underwater photosynthetic capacity of R. crispus increased during 1 month of submergence. In P. arundinacea photosynthesis remained constant during 1 month of submergence at normal irradiance; at low irradiance a reduction in photosynthetic capacity was observed after 2 weeks, although there was no tissue degeneration. In contrast, underwater photosynthesis of the submergence‐intolerant species A. elatius collapsed rapidly under both irradiances, and this was accompanied by leaf decay. To describe photosynthesis versus irradiance curves, four models were evaluated. The hyperbolic tangent produced the best goodness‐of‐fit, whereas the rectangular hyperbola (Michaelis‐Menten model) gave relatively poor results.
Three new osmotic stress‐regulated cDNAs identified by differential display polymerase chain reaction in rapeseed leaf discs
Authors: Deleu C. , Coustaut M. , Niogret M.‐F. , Larher F.
Published: March 2003

Plant osmotic stress responses are associated with changes in gene expression. Osmotic stress‐regulated genes (OR genes) have been isolated by various approaches such as differential screening of cDNA libraries or by complementation. We have used differential display of mRNA to isolate partial cDNAs corresponding to transcripts differentially expressed in leaf discs from osmotically stressed rapeseed. The cloning and the sequencing of three OR genes (MC12, MC43 and MC24) isolated by this method are reported here. Differences in corresponding mRNA levels during the first hours of stress were confirmed by Northern blot analysis. The deduced amino acid sequence of the MC12 and MC43 clones, for which mRNA accumulation was detected under osmotic stress, shows significant similarities to saccharopine dehydrogenase and linker histone H1‐3 genes, respectively. Furthermore these up‐ regulated genes are induced by ABA. The nucleotide sequence of MC24 shows strong homology with a chloroplast gene (rps12) encoding a ribosomal protein. mRNA hybridization with MC24 led to a multiple banding pattern resulting from maturation of polycistronic precursor transcripts. Levels of different sized transcript hybridizing with MC24 decreased during osmotic stress, suggesting that rps12 chloroplast gene is down‐regulated by osmotic stress. Interestingly, up‐regulation of a gene encoding an enzyme involved in lysine catabolism suggests that products from this pathway could be of interest for the adaptation of rapeseed leaf explants subjected to osmotic upshock in vitro. This discovery opens new insights into metabolic adjustment mechanisms under stress.
Diffusion and reaction of oxygen in the central tissue of ureide‐producing legume nodules
Authors: Thumfort P. P. , Layzell D. B. , Atkins C. A.
Published: March 2003

Previous simulation models for the diffusion and reaction of oxygen in legume nodules were based on infected cells and neglected adjacent uninfected cells. This study uses a three‐dimensional model of the central zone of legume nodules made up of the two cell types represented by a geometrically defined, space‐filling, binary combination of polyhedra, each with bevelled edges to allow for a network of intercellular gas spaces. The model predicted a distinctively compartmentalized distribution of [O2] between uninfected and infected cells; with high O2 concentrations for an uninfected cell being consistent with, and necessary for, efficient operation of uricase and ureide synthesis and low O2 concentrations across most of the infected cell providing a suitable environment for N2‐fixation. Compartmentalization of O2 also predicted significant O2 fluxes between cell types, compromising maintenance of low [O2] in infected cells, as well as high [O2] in uninfected cells. The results predict that there might be significant resistance to O2 diffusion across the cell : cell interface due to the plasmalemma and cell walls.
Manganese application alleviates the water deficit‐induced decline of N2 fixation
Authors: Vadez V. , Sinclair T. R. , Serraj R. , Purcell L. C.
Published: March 2003

Water deficit is a very serious constraint on N2 fixation rates and grain yield of soybean (Glycine max Merr.). Ureides are transported from the nodules and they accumulate in the leaves during soil drying. This accumulation appears responsible for a feedback mechanism on nitrogen fixation, and it is hypothesized to result from a decreased ureide degradation in the leaf. One enzyme involved in the ureide degradation, allantoate amidohydrolase, is manganese (Mn) dependent. As Mn deficiency can occur in soils where soybean is grown, this deficiency may aggravate soybean sensitivity to water deficit. In situ ureide breakdown was measured by incubating soybean leaves in a 5 mol m−3 allantoic acid solution for 9 h before sampling leaf discs in which remnant ureide was measured over time. In situ ureide breakdown was dramatically decreased in leaves from plants grown without Mn. At the plant level, allantoic acid application in the nutrient solution of hydroponically grown soybean resulted in a higher accumulation of ureide in leaves and lower acetylene reduction activity (ARA) by plants grown with 0 mol m−3 Mn than those grown with 6·6 mol m−3 Mn. Those plants grown with 6·6 mol m−3 Mn in comparison with those grown with 52·8 mol m−3 Mn had, in turn, higher accumulated ureide and lower ARA. To determine if Mn level also influenced N2 fixation sensitivity to water deficit, a dry‐down experiment was carried out by slowly dehydrating plants that were grown in soil under four different Mn nutritions. Plants receiving no Mn had the lowest leaf Mn concentration, 11·9 mg kg−1, and had N2 fixation more sensitive to water deficit than plants treated with Mn in which leaf Mn concentration was in the range of 21–33 mg kg−1. The highest Mn treatments increased leaf Mn concentration to 37·5 mg kg−1 and above but did not delay the decline of ARA with soil drying, although these plants showed a significant increase in ARA under well‐watered conditions.
Protection against the photo‐induced inactivation of the photosystem II complex by abscisic acid
Authors: Saradhi P. Pardha , Suzuki I. , Katoh A. , Sakamoto A. , Sharmila P. , Shi D.‐J. , Murata N.
Published: March 2003

To examine the effect of abscisic acid (ABA) on the photo‐induced inactivation of the photosystem II (PSII) complex, a suspension culture of Chlamydomonas reinhardtii was treated with ABA for 24 h in darkness and then, after removal of ABA, the cells were exposed to strong light at a photon flux density of 2000 μmol m−2 s−1 at various temperatures. The activity of PSII, as estimated in terms of chlorophyll fluorescence and the evolution of oxygen, decreased significantly during the exposure of cells to the strong light, and the extent of the photo‐induced decrease in PSII activity was much greater at lower temperatures. Irrespective of temperature, the decrease in PSII activity in ABA‐treated cells was significantly smaller than that in control cells. Moreover, the recovery of PSII activity from the photo‐inactivated state in ABA‐treated cells was significantly faster than that in control cells. The recovery of PSII activity in both ABA‐treated and control cells was almost entirely prevented by the presence of chloramphenicol. These results indicate that ABA protects the PSII complex in C. reinhardtii against photo‐induced inactivation by accelerating the recovery of this complex.
Strategy differences of two potato species in response to nitrogen starvation. Do plants have a genetic switch for nitrogen signalling?
Authors: Davies Corinne S.
Published: March 2003

Survival responses to nitrogen starvation are well known in micro‐organisms but little studied in plants. To construct a framework for study of the plant responses, we investigated the strategy differences of tubers from two closely related potato species. Solanum tuberosum conserves tuber nitrogen by inhibiting shoot growth, but S. phureja mobilizes tuber nitrogen to grow shoots, flowers and seeds. Genetic analysis of progeny from S. phureja–haploid S. tuberosum crosses uncovered segregation of a single dominant gene for the S. tuberosum inhibition strategy. Within S. tuberosum, haploid progeny closely resembled their tetraploid parents, suggesting strong genetic control of the inhibition. Growth of the inhibited shoots was proportional to sub‐optimal levels of added nitrate, and was triggered by exogenous gibberellic acid (GA3). These observations support the notion that potato plants can closely tie shoot growth to ambient nitrogen levels – probably by a root–shoot nitrogen signal transduction pathway, and that this can be overridden by emergency mobilization of nitrogen reserves, perhaps by GA signalling from the tuber. Furthermore, genes for such developmental switches can be identified by classical genetic analysis of closely related species, such as S. tuberosum and S. phureja, that exhibit opposite survival strategies.
Effects of light on respiration and oxygen isotope fractionation in soybean cotyledons
Authors: Ribas‐Carbo M. , Robinson S. A. , Gonzàlez‐Meler M. A. , Lennon A. M. , Giles L. , Siedow J. N. , Berry J. A.
Published: March 2003

Light effects on electron flow through the cyanide‐resistant respiratory pathway, oxygen isotope fractionation and total respiration were studied in soybean (Glycine max L.) cotyledons. During the first 12 h of illumination there was an increase in both electron partitioning through the alternative pathway and oxygen isotope fractionation by the alternative oxidase. The latter probably indicates a change in the properties of the alternative oxidase. There was no engagement of the alternative oxidase in darkness and its fractionation was 27‰. In green cotyledons 60% of the respiration flux was through the alternative pathway and the alternative oxidase fractionation was 32‰. Exposing previously illuminated tissue to continuous darkness induced a decrease in the electron partitioning through the alternative pathway. However, this decrease was not directly linked with the low cellular sugar concentration resulting from the lack of light because 5 min of light every 12 h was sufficient to keep the alternative pathway engaged to the same extent as plants grown under control conditions.
Heat‐induced protection against death of suspension‐cultured apple fruit cells exposed to low temperature
Authors: Wang C. Y. , Bowen J. H. , Weir I. E. , Allan A. C. , Ferguson I. B.
Published: March 2003

Death of suspension‐cultured apple fruit cells (Malus domestica Borkh. cv. Braeburn), resulting from exposure to low temperature (1 °C), was reduced by a prior 1 h/38 °C treatment. Pre‐heated chilled cells produced less ethylene, indicating lower chilling injury. Heat treatment resulted in increased transcripts for a low molecular weight (hsp17) and a 70 kDa heat shock protein (hsp), but expression weakened within 24 h following the transfer of cells to 25 °C. When cells were instead transferred to 1 °C after heat, elevated hsp gene expression persisted for up to 3 d. Flow cytometric analysis of apple cell protoplasts showed that the 1 °C treatment resulted in a subpopulation of protoplasts undergoing cell death, not observed with the 38 °C pre‐treatment. Chromatin condensation did not occur with the heat treatments. These results suggest that heat‐induced reduction of cell death at low temperatures may involve persistence of hsps, and low‐temperature susceptibility is less likely to be associated with programmed cell death. All cells do not respond in the same way, their tolerance being associated with different states of metabolism or of the cell cycle.
Will rising CO2 protect plants from the midday sun? A study of photoinhibition of Quercus myrtifolia in a scrub‐oak community in two seasons
Authors: Hymus G. J. , Dijkstra P. , Baker N. R. , Drake B. G. , Long S. P.
Published: March 2003

Over a large part of the photoperiod, light energy absorbed by upper canopy leaves saturates photosynthesis and exceeds the energetic requirements for light‐saturated linear electron flow through photosystem II (JPSII), so that photoinhibition results. From a theoretical consideration of the response of light‐saturated photosynthesis to elevated atmospheric CO2 partial pressure (pCO2) it may be predicted that, where light‐saturated photosynthesis is Rubisco‐limited, an increase in pCO2 will stimulate JPSII. Therefore, the proportion of absorbed quanta dissipated photochemically will increase and the potential for photoinhibition of photosynthesis will decrease. This was tested by measuring modulated chlorophyll a fluorescence from Quercus myrtifolia Willd. growing in the field in open‐top chambers, at either current ambient or elevated (ambient + 35 Pa) pCO2 on Merritt Island, Florida, USA. During spring and summer, light‐saturated photosynthesis at current ambient pCO2 was Rubisco‐limited. Consistent with theoretical prediction, JPSII was increased and photoinhibition decreased by elevated pCO2 in spring. In the summer, when growth had largely ceased, an acclimatory decrease in the maximum Ribulose 1,5 bisphosphate saturated carboxylation capacity (Vc max) removed the stimulation of JPSII seen in the spring, and photoinhibition was increased in elevated pCO2. It is concluded that, for Q. myrtifolia growing in the field, the effects of elevated pCO2 on JPSII and photoinhibition will reflect seasonal differences in photosynthetic acclimation to elevated pCO2 in a predictable manner.
The identification of a pollen‐specific LEA‐like protein in Lilium longiflorum
Authors: Mogami N. , Shiota H. , Tanaka I.
Published: March 2003

A novel pollen‐specific LEA‐like protein, LP28, was detected in Lilium longiflorum using two‐dimensional polyacrylamide gel electrophoresis (2D‐PAGE). Immunoblot analysis using antiserum raised against LP28 revealed that the protein was not found in somatic tissues or uninucleate microspores, but accumulated gradually in developing pollen following microspore mitosis. Furthermore, LP28 was abundant in germinated pollen after hydration. The cDNA clone corresponding to LP28 encoded a putative protein of 238 amino acids with a calculated molecular mass of 24·2 kDa and a pI of 4·7. The amino acid sequence is highly hydrophilic except for the N‐terminal hydrophobic signal peptide. The sequence has similarities with group 3 LEA (late embryogenesis abundant) proteins. Immunocytochemical analyses demonstrated that LP28 was mainly found in cytoplasmic granules of the vegetative cell until pollen maturation, but after hydration it appeared in the elongating pollen tube wall. LP28 might be a unique pollen‐specific protein that is transported to the pollen tube wall after germination. Therefore, it is assumed that LP28 plays a role not only in pollen maturation, but also in the growth of the pollen tube, which penetrates the stylar matrix.
Increases of 3‐phosphoglyceric acid in potato plants through antisense reduction of cytoplasmic phosphoglycerate mutase impairs photosynthesis and growth, but does not increase starch contents
Authors: Westram A. , Lloyd J. R. , Roessner U. , Riesmeier J. W. , Kossmann J.
Published: March 2003

A full‐length cDNA encoding cytosolic phosphoglycerate mutase (PGAM; E.C. 5.4.2.1) from potato (Solanum tuberosum L.) was isolated. RNA blots indicated that the accumulation of PGAM transcript was similar in all organs studied. Transgenic potato plants with either constitutive, or tuber‐specific, decreases in PGAM expression were created. Constitutive reduction of enzyme activity of down to 25% of the control resulted in increased 3‐PGA contents of up to 30% in leaves, but also led to reduced growth rates, probably due to a reduction of photosynthetic activity. Soluble carbohydrates and starch in leaves were reduced, and the tuber yield of the plants was lowered. Plants with 30% of the wild‐type PGAM activity in leaves and 55% in tubers showed reduced amounts of starch in tubers also. Tuber‐specific reduction of PGAM expression in transgenic potato plants had no effect on starch metabolism and tuber yield, although the 3‐PGA level was increased. This indicates that 3‐PGA concentrations in potato tubers are not important for regulating ADP‐glucose pyrophosphorylase activity in the production of starch under some environmental conditions.
Altered metabolic fluxes result from shifts in metabolite levels in sucrose phosphorylase‐expressing potato tubers
Authors: Fernie A. R. , Tiessen A. , Stitt M. , Willmitzer L. , Geigenberger P.
Published: March 2003

As reported in a previous paper (Plant, Cell and Environment 24, 357–365, 2001), introduction of sucrose phosphorylase into the cytosol of potato results in increased respiration, an inhibition of starch accumulation and decreased tuber yield. Herein a more detailed investigation into the effect of sucrose phosphorylase expression on tuber metabolism, in order to understand why storage and growth are impaired is described. (1) Although the activity of the introduced sucrose phosphorylase was low and accounted for less than 10% of that of sucrose synthase its expression led to a decrease in the activities of enzymes of starch synthesis relative to enzymes of glycolysis and relative to total amylolytic activity. (2) Incubation of tuber discs in [14C]glucose revealed that the transformants display a two‐fold increase of the unidirectional rate of sucrose breakdown. However this was largely compensated by a large stimulation of sucrose re‐synthesis and therefore the net rate of sucrose breakdown was not greatly affected. Despite this fact major shifts in tuber metabolism, including depletion of sucrose to very low levels, higher rates of glycolysis, and larger pools of amino acids were observed in these lines. (3) Expression of sucrose phosphorylase led to a decrease of the cellular ATP/ADP ratio and energy charge in intact growing tubers. It was estimated that at least 30% of the ATP formed during respiration is consumed as a result of the large acceleration of the cycle of sucrose breakdown and re‐synthesis in the transformants. Although the absolute rate of starch synthesis in short‐term labelling experiments with discs rose, starch synthesis fell relative to other fluxes including respiration, and the overall starch content of the tubers was lower than in wild‐type tubers. (4) External supply of amino acids to replace sucrose as an osmoticum led to a feed‐back inhibition of glycolysis, but did not restore allocation to starch. (5) However, an external supply of the non‐metabolizable sucrose analogue palatinose – but not sucrose itself – stimulated flux to starch in the transformants. (6) The results indicate that the impaired performance of sucrose phosphorylase‐expressing tubers is attributable to decreased levels of sucrose and increased energy consumption during sucrose futile cycling, and imply that sucrose degradation via sucrose synthase is important to maintain a relatively large sucrose pool and to minimize the ATP consumption required for normal metabolic function in the wild type.
Growth responses of yellow‐poplar(Liriodendron tulipifera L.) exposed to 5 years of O3 aloneor combined with elevated CO2
Authors: Rebbeck J. , Scherzer A. J.
Published: March 2003

Field‐grown yellow‐poplar (Liriodendron tulipifera L.) werefumigated from May to October in 1992–96 within open‐topchambers to determine the impact of ozone (O3) aloneor combined with elevated carbon dioxide (CO2) on saplinggrowth. Treatments were replicated three times and included: charcoal‐filteredair (CF); 1 × ambient ozone (1 × O3);1·5 × ambient ozone (1·5 × O3);1·5 × ambient ozone plus 350 p.p.m.carbon dioxide (1·5 × O3 + CO2)(target of 700 p.p.m. CO2); and open‐air chamberlessplot (OA). After five seasons, the total cumulative O3 exposure (SUM00 = sumof hourly O3 concentrations during the study) rangedfrom 145 (CF) to 861 (1·5 × O3) p.p.m. × h (partsper million hour). Ozone had no statistically significant effecton yellow‐poplar growth or biomass, even though total root biomasswas reduced by 13% in the 1·5 × O3‐exposedsaplings relative to CF controls. Although exposure to 1·5 × O3 + CO2 hada stimulatory effect on yearly basal area growth increment aftertwo seasons, significant increases in shoot and root biomass (∼ 60% increaserelative to all others) were not detected until the fifth season.After five seasons, the yearly basal area growth increment of saplingsexposed to 1·5 × O3 + CO2‐air increasedby 41% relative to all others. Based on this multi‐yearstudy, it appears that chronic O3 effects on yellow‐poplargrowth are limited and slow to manifest, and are consistent withprevious studies that show yellow‐poplar growth is not highly responsiveto O3 exposure. In addition, these results show thatenriched CO2 may ameliorate the negative effects of elevatedO3 on yellow‐poplar shoot growth and root biomass underfield conditions.
Photosystem II energy use,non‐photochemical quenching and the xanthophyll cycle in Sorghumbicolor grown under drought and free‐air CO2 enrichment(FACE) conditions
Authors: Cousins A. B. , Adam N. R. , Wall G. W. , Kimball B. A. , Pinter P. J. , Ottman M. J. , Leavitt S. W. , Webber A. N.
Published: March 2003

The present study was carried out to test the hypothesis thatelevated atmospheric CO2 (Ca) will alleviate over‐excitationof the C4 photosynthetic apparatus and decrease non‐photochemicalquenching (NPQ) during periods of limited water availability. Chlorophyll a fluorescencewas monitored in Sorghum bicolor plants grown under a free‐aircarbon‐dioxide enrichment (FACE) by water‐stress (Dry) experiment.Under Dry conditions elevated Ca increased the quantum yield ofphotosystem II (φPSII) throughout the day throughincreases in both photochemical quenching coefficient (qp)and the efficiency with which absorbed quanta are transferred toopen PSII reaction centres (Fv′/Fm′).However, in the well‐watered plants (Wets) FACE enhanced φPSIIonly at midday and was entirely attributed to changes in Fv′/Fm′. Underfield conditions, decreases in φPSII under Dry treatmentsand ambient Ca corresponded to increases in NPQ but the de‐epoxidation stateof the xanthophyll pool (DPS) showed no effects. Water‐stress didnot lead to long‐term damage to the photosynthetic apparatus asindicated by φPSII and carbon assimilation measuredafter removal of stress conditions. We conclude that elevated Caenhances photochemical light energy usage in C4 photosynthesisduring drought and/or midday conditions. Additionally,NPQ protects against photo‐inhibition and photodamage. However,NPQ and the xanthophyll cycle were affected differently by elevatedCa and water‐stress.
Modelling the discrimination of 13CO2 above and within a temperate broad‐leaved forest canopy on hourly to seasonal time scales
Authors: BALDOCCHI D. D. , BOWLING D. R.
Published: March 2003

Fluxes and concentrations of carbon dioxide and 13CO2 provide information about ecosystem physiological processes and their response to environmental variation. The biophysical model, CANOAK, was adapted to compute concentration profiles and fluxes of 13CO2 within and above a temperate deciduous forest (Walker Branch Watershed, Tennessee, USA). Modifications to the model are described and the ability of the new model (CANISOTOPE) to simulate concentration profiles of 13CO2, its flux density across the canopy–atmosphere interface and leaf‐level photosynthetic discrimination against 13CO2 is demonstrated by comparison with field measurements. The model was used to investigate several aspects of carbon isotope exchange between a forest ecosystem and the atmosphere. During the 1998 growing season, the mean photosynthetic discrimination against 13CO2, by the deciduous forest canopy (Δcanopy), was computed to be 22·4‰, but it varied between 18 and 27‰. On a diurnal basis, the greatest discrimination occurred during the early morning and late afternoon. On a seasonal time scale, the greatest diurnal range in Δcanopy occurred early and late in the growing season. Diurnal and seasonal variations in Δcanopy resulted from a strong dependence of Δcanopy on photosynthetically active radiation and vapour pressure deficit of air. Model calculations also revealed that the relationship between canopy‐scale water use efficiency (CO2 assimilation/transpiration) and Δcanopy was positive due to complex feedbacks among fluxes, leaf temperature and vapour pressure deficit, a finding that is counter to what is predicted for leaves exposed to well‐mixed environments.
Colonization of roots of subterranean clover cultivars by virulent and avirulent races of Phytophthora clandestina
Authors: Purwantara A. , Flett S. P. , Keane P. J.
Published: March 2003

The colonization of the roots of four cultivars of subterranean clover by isolates representing four races of Phytophthora clandestina was studied. There was a highly significant race × cultivar interaction in the growth of inoculated tap roots and the degree of colonization of roots by the pathogen. While all races were able to infect the roots of all cultivars tested, roots of the susceptible cultivars were colonized more rapidly and extensively than those of the resistant cultivars. In compatible combinations, fungal colonization extended for a few centimetres in the tap root and lateral roots in the moderately susceptible cultivars Trikkala and Meteora, or throughout the whole root system leading to the death of the host in the very susceptible cultivar Woogenellup. In contrast, limited fungal colonization of the tap root and lack of extension of the fungus into lateral roots was typical of incompatible combinations. In all cultivars, lateral roots were as susceptible to infection as tap roots. The number of lateral roots of Woogenellup was significantly reduced by infection. However, neither the rate of lateral root formation nor the total number of lateral roots of Seaton Park, Meteora and Trikkala was reduced by infection with virulent or avirulent races of the pathogen.