bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques
Authors: Stylinski C. D. , Oechel W. C. , Gamon J. A. , Tissue D. T. , Miglietta F. , Raschi A. 
Published: March 2003

ABSTRACTLifelong exposure to elevated concentrations of atmospheric CO2 may enhance carbon assimilation of trees with unlimited rooting volume and consequently may reduce requirements for photoprotective pigments. In early summer the effects of elevated [CO2] on carboxylation and light utilization of mature Quercus pubescens trees growing under chronic [CO2] enrichment at two CO2 springs and control sites in Italy were examined. Net photosynthesis was enhanced by 36 to 77%. There was no evidence of photosynthetic downregulation early in the growing season when sink demand presumably was greatest. Specifically, maximum assimilation at saturating [CO2], electron transport capacity, and Rubisco content, activity and carboxylation capacity were not significantly different in trees growing at the CO2 springs and their respective control sites. Foliar biochemical content, leaf reflectance index of chlorophyll pigments (NDVI), and photochemical efficiency of PSII (ΔF/Fm′) also were not significantly affected by [CO2] enrichment except that starch content and ΔF/Fm′ tended to be higher at one spring (42 and 15%, respectively). Contrary to expectation, prolonged elevation of [CO2] did not reduce xanthophyll cycle pigment pools or alter mid‐day values of leaf reflectance index of xanthophyll cycle pigments (PRI), despite the enhancement of carbon assimilation. However, both these pigments and PRI were well correlated with electron transport capacity.
Excretion of two proteases by the ectomycorrhizal fungus Amanita muscaria
Authors: Nehls U. , Bock A. , Einig W. , Hampp R. 
Published: March 2003

AbstractIn the soils of mature forests, nitrogen availability is mainly the result of litter decomposition. Thus protein degradation is of major interest for nutrition. Two aspartic proteases were excreted in a pH‐dependent manner by the ectomycorrhizal fungus Amanita muscaria grown in liquid culture. AmProt1 with a molecular mass of approximately 45 kDa was mainly present at pH values up to 5·4, whereas the excretion of AmProt2 with a molecular mass of about 90 kDa was only detectable at pH values between pH 5·4 and 6·3. In addition, the pH optima of both enzymes differed significantly. AmProt1 had a narrow pH optimum around 3, whereas AmProt2 had a broad pH optimum between 3 and 5·5 and a higher affinity to the substrate methylcasein. One cDNA‐clone (AmProt1*) that presumably encodes AmProt1 was identified. Like AmProt1, this cDNA was expressed in a pH‐dependent manner. In addition, carbohydrate and to a lesser extent nitrogen depletion significantly enhanced AmProt1* expression. In fully developed Populus hyb./A. muscaria ectomycorrhizas the expression of AmProt1* was significantly higher in hyphae of the Hartig net compared with those of the fungal sheath. The role of AmProt1 and AmProt2 for fungal physiology and competitiveness is discussed.
Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors
Authors: De Beer D. , Larkum A. W. D. 
Published: March 2003

AbstractWith microsensors, we measured the steady‐state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m‐2 s‐1), Ca2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calcification cannot supply sufficient protons and CO2 to sustain photosynthesis.
Natural 15N abundance of epiphytes depends on the position within the forest canopy: source signals and isotope fractionation
Authors: Wania R. , Hietz P. , Wanek W. 
Published: March 2003

AbstractThe natural 15N abundance (δ15N) of epiphytes and its N sources were studied in the canopy of a lowland rainforest in Costa Rica. Vascular and non‐vascular epiphytes and canopy soils were collected from four canopy zones and analysed for N contents and δ15N signals. In addition, the N concentrations and δ15N signatures of bulk precipitation, throughfall and stemflow were measured during the wet and the dry season. The δ15N values of epiphyte leaves decreased significantly from the lower zones (means of −3·9 and −4·3‰) to the upper zones (means of −5·4 and −6·1‰) of the canopy. In contrast, δ15N signatures of canopy soils (average −0·3‰) differed little between the zones. Bulk deposition was enriched in 15N (+4·3‰) compared to all other potential N sources and was higher than throughfall and stemflow (+0·5 to −1·3‰). δ15N values of atmospheric deposition were inversely related to those of the epiphyte leaves, whereas N isotopic composition of canopy soils did not vary significantly. Consequently, it is concluded that the variations in foliar N isotope composition of epiphytes were not simply caused by utilization of isotopically different N sources, but by different 15N discrimination during N acquisition.
Natural variation in Arabidopsis seedling photomorphogenesis reveals a likely role for TED1 in phytochrome signalling
Authors: Pepper A. E. , Corbett R. W. , Kang N. 
Published: March 2003

AbstractNatural genetic variation present among accessions of Arabidopsis thaliana (L.) Heynh. (commonly referred to as ‘ecotypes’) is a valuable, yet under‐exploited genetic resource for the study of plant developmental, physiological. and evolutionary responses to the environment. Seedling photomorphogenic responses were surveyed in a set of 11 Arabidopsis accessions collected from a variety of edaphic habitats and geographic locations. We observed substantial variation in light‐dependent hypocotyl growth responses in a variety of light conditions (white, red, blue, far‐red enriched light). The genetic basis for differences in hypocotyl growth responses to light between the Columbia (Col‐0) and Bensheim (Be‐0) accessions was examined in an F2 population. Quantitative genetic and quantitative trait locus (QTL) analyses were consistent with a model in which differences in light responses were conditioned by a single major gene with semi‐dominant effect, located on chromosome 4. Further experiments suggested that the genetic difference governing hypocotyl variation in this cross may be allelic to ted1, an extragenic suppressor of the de‐etiolated mutant det1, that was identified as an ethylmethane sulphonate‐induced mutation. This finding supports a role for ted1 in photomorphogenic signalling.
Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communities
Authors: Martínez F. , Lazo Y. O. , Fernández‐Galiano R. M. , Merino J. A. 
Published: March 2003

AbstractThe construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non‐significant (mean value: 1·64 ± 0·13 g glucose g−1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g−1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g−1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g−1 versus 1·78 ± 0·02 g glucose g−1). The differences observed in construction cost appeared to be due more to habitat‐induced differences in chemical composition than to any intrinsic difference between the species studied.
Do anthocyanins function as antioxidants in leaves? Imaging of H2O2 in red and green leaves after mechanical injury
Authors: Gould K. S. , McKelvie J. , Markham K. R. 
Published: March 2003

AbstractPurified anthocyanin extracts show strong antioxidant properties in vitro, but it is not known whether they can scavenge reactive oxygen in living cells. The oxidative responses in red and green portions of Pseudowintera colorata leaf laminae were compared by the real‐time imaging of H2O2 in cells after mechanical injury. An oxidative burst was elicited almost immediately from chloroplasts in the palisade mesophyll, as evidenced using the fluorochromes dichlorofluorescein and scopoletin. H2O2 accumulated in green lamina regions for 10  min, and then decreased slowly. By contrast, red regions recovered rapidly, and maintained consistently low levels of H2O2. Infusion of cells with N‐acetyl‐l‐cysteine accelerated the depletion of H2O2 from green regions. Wounded leaves ultimately developed a localized necrotic lesion and an intense anthocyanic band. The red regions were enriched in anthocyanins, flavonols, dihydroflavonols, and hydroxycinnamic acids. Only the anthocyanins were suitably located to account for the enhanced rates of H2O2 scavenging. The data support the hypothesis that red cells have elevated antioxidant capabilities in vivo.
Anthocyanin accumulation in the illuminated surface of maize leaves enhances protection from photo‐inhibitory risks at low temperature, without further limitation to photosynthesis
Authors: Pietrini F. , Iannelli M. A. , Massacci A. 
Published: March 2003

AbstractAt     suboptimal     temperatures,     anthocyanins     accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo‐inhibition but also photo‐synthesis. To investigate this phenomenon, gas exchange, fluorescence,   superoxide   dismutase   activity   and  xantho‐phyll composition of anthocyanin‐containing HOPI and anthocyanin‐deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO2 supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The ΔF/Fm (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than ΔF/Fm of W22 with either light source. This probably compensated for the lower white light absorption of HOPI chloroplasts compared with W22 because of the presence of anthocyanins and led to similar rates of calculated electron transport for both genotypes. After exposure to high white light at 5 °C, xanthophyll de‐epoxidation and superoxide dismutase activity were lower in HOPI than in W22. Further, HOPI could be exposed to a much higher irradiance than W22 before Fv/Fm was reduced to that of W22.
Diurnal changes in the expressionof glutamate dehydrogenase and nitrate reductase are involved in the C/N balance of tobacco source leaves
Authors: Masclaux‐Daubresse C. , Valadier M.‐H. , Carrayol E. , Reisdorf‐Cren M. , Hirel B. 
Published: March 2003

AbstractA novel cDNA encoding glutamate dehydrogenase (GDH) from tobacco(Nicotiana tabacum), namedgdh1,was characterized.Thegdh1mRNA was detected in roots, stems and source/senescentleaves. In order to investigate diurnal regulation ofgdh1inleaves, the content ingdh1mRNA was measured every 3 h overa 48 h period and compared toniaandgs2mRNAlevels, encoding, respectively, nitrate reductase (NR) and chloroplasticglutamine synthetase (GS2). In source leaves,gdh1mRNA levelsexhibit diurnal fluctuations. A 12 h shift was observedbetween the day–night rhythms ofgdh1andniaexpression.Metabolite contents were also measured and a shift in the day–nightfluctuations of both glutamate (GLU) andγ‐aminobutyricacid (GABA) was observed between sink and source leaves, whereasthe diurnal rhythm ofα‐ketoglutarate showed no change.A possible role of GDH in the shift of GLU and GABA contents isdiscussed. Leaf disc experiments showed thatgdh1expressionis enhanced in conditions of continuous darkness. This trend isinhibited by sucrose feeding. The opposite was observed forniaexpression.An important outcome of this work is the reverse regulation ofgdh1andniagenes.A possible role of sugars and amino acids in the co‐regulation ofgdh1andniagenesis suggested.
Phloem loading and unloading of sugars and amino acids
Authors: LALONDE S. , TEGEDER M. , THRONE‐HOLST M. , FROMMER W. B. , PATRICK J. W. 
Published: March 2003

ABSTRACTIn terrestrial higher plants, phloem transport delivers most nutrients required for growth and storage processes. Some 90% of plant biomass, transported as sugars and amino nitrogen (N) compounds in a bulk flow of solution, is propelled though the phloem by osmotically generated hydrostatic pressure differences between source (net nutrient export) and sink (net nutrient import) ends of phloem paths. Source loading and sink unloading of sugars, amino N compounds and potassium largely account for phloem sap osmotic concentrations and hence pressure differences. A symplasmic component is characteristic of most loading and unloading pathways which, in some circumstances, may be interrupted by an apoplasmic step. Raffinose series sugars appear to be loaded symplasmically. However, sucrose, and probably certain amino acids, are loaded into minor veins from source leaf apoplasms by proton symporters localized to plasma membranes of their sieve element/companion cell (se/cc) complexes. Sucrose transporters, with complementary kinetic properties, are conceived to function as membrane transporter complexes that respond to alterations in source/sink balance. In contrast, symplasmic unloading is common for many sink types. Intervention of an apoplasmic step, distal from importing phloem, is reserved for special situations. Effluxers that release sucrose and amino acids to the surrounding apoplasm in phloem loading and unloading are yet to be cloned. The physiological behaviour of effluxers is consistent with facilitated membrane transport that can be energy coupled. Roles of sucrose and amino acid transporters in phloem unloading remain to be discovered along with mechanisms regulating symplasmic transport. The latter is hypothesized to exert significant control over phloem unloading and, in some circumstances, phloem loading.
Differences between rice and wheat in ribulose‐1,5‐bisphosphate regeneration capacity per unit of leaf‐N content
Authors: SUDO E. , MAKINO A. , MAE T. 
Published: March 2003

ABSTRACTThe photosynthetic rates under saturating CO2 conditions per unit of leaf‐N content were higher in wheat than in rice. This suggested that ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity is greater in wheat. Therefore, the biochemical factor(s) for this difference were examined between rice and wheat. Soluble protein‐N, insoluble‐N, and trichloroacetic acid (TCA) soluble‐N contents were found not to differ between the two species. The activities of several Calvin cycle enzymes such as RuBP carboxylase, NADP‐glyceraldehyde‐3‐phosphate dehydrogenase, phosphoglycerate kinase and chloroplastic fructose‐1,6‐bisphosphatase (cpFBPase) activities per unit of leaf‐N content were all higher in wheat than in rice. Among them, cpFBPase activity was most highly correlated with CO2‐saturated photosynthesis. The Vmax activity of sucrose‐phosphate synthase (SPS) for UDP‐glucose was almost the same between the two species and its Km value was a little lower in rice. Chlorophyll content and its a/b ratio did not differ. Cytochrome (Cyt) f content was greater in wheat, whereas coupling factor 1 content was greater in rice. Cyt f content was highly correlated with CO2‐saturated photosynthesis, irrespective of the two species. The results thus suggested that higher RuBP regeneration capacity in wheat leaves is most closely related to a greater Cyt f content and that another candidate is cpFBPase.
Peach red marbling and peach sooty ringspot, two new virus‐like degenerative diseases of Prunus
Authors: Grasseau  , Macquaire  , Boyé  , Cornaggia  , Desvignes  
Published: March 2003

More than 600 Prunus samples were examined by using a nonradioactive digoxigenin‐labelled RNA probe specific for hop stunt viroid (HSVd). Prunus salicina and Prunus armeniaca appeared to be better hosts than Prunus persica. The weak viroid concentration in flowers and young leaves of peach trees growing in the field did not permit its detection in such samples. The diagnosis was more reliable (about 85%) with bark and leaves aged 4 months and more, from regrowths of GF 305 peach seedlings inoculated and kept in the greenhouse. Detection of HSVd in leaves and bark of apricot and Japanese plum plants aged 3 months or more also proved reliable (about 80% and 90%, respectively). HSVd could be transmitted in apricot, peach and plum nucleic acid preparations to GF 305 peach seedlings by repeated stem slashing, and to cherries (Prunus avium and Prunus serrulata) by approach grafting with an infected P. salicina source. The viroid was eliminated from 18% of the clones obtained after thermotherapy.In the course of this study, 25 selected Prunus accessions suspected to be infected by unusual diseases were analysed by hybridization with a HSVd‐specific probe and by indexing on GF 305 peach seedlings in the greenhouse. Fifteen of these accessions were found to be infected by HSVd, 19 induced reddish marbling, and four induced small blackish spots on the leaves aged about 4 months. Repeated assays showed that these foliar symptoms were not caused by the viroid. Peach red marbling (PRMa) has not been associated with any known virus and seems to be caused by an infectious agent not yet described. That could also be the case with the agent of peach sooty ringspot (PSRS). PRMa and PSRS symptoms were reproduced by grafting and indexing, and their causal agents eliminated by thermotherapy in a significant fraction of the treated plants. They behave like viral agents and can infect the different Prunus species studied.
Factors affecting diseases of winter wheat in England and Wales, 1989–98
Authors: Hardwick N. V. , Jones D. R. , Slough J. E. 
Published: March 2003

The above article was published without a number of the author's corrections included. The publisher offers their unreserved apology for this and the sections affected are reprinted below in their entirety.Samples from 360 to 450 randomly selected winter wheat crops in England and Wales were collected annually during the milky ripe development stages (GS 73–75) from 1989 to 1998. The number of samples from each region was proportional to the area of winter wheat grown. The percentage area affected by disease was assessed on the top two leaves and the ear, and the incidence and severity of stem base diseases were also recorded. An estimate of the percentage area of the crop affected by Barley yellow dwarf virus (BYDV) and take‐all (Gaeumannomyces graminis) was made in the field. Septoria leaf blotch (Septoria tritici, teleomorph Mycosphaerella graminicola) was the major foliar disease recorded, with an average maximum severity of 7·8% of the area of leaf 2 affected in 1998. Eyespot (Tapesia spp.) was the major stem base disease, with the highest incidence of stems falling into the damaging moderate plus severe categories (18·9%) in 1998. Levels of powdery mildew (Blumeria graminis) showed a decline from 0·4% of the area of leaf 2 in 1989 to 0·1% in 1998. This fall was associated with a reduction in the proportion of disease‐susceptible cultivars grown. There were significant regional differences in levels of septoria leaf blotch, brown rust (Puccinia recondita), eyespot, sharp eyespot (Rhizoctonia cerealis) and BYDV. The percentage of crops treated with a fungicide rose from 96% in 1989 to 98% in 1998 and the mean number of spray applications per crop rose during this period from 2·1 to 2·5. A higher proportion of crops was treated with fungicides between the end of tillering and fifth node detectable (GS 29–35) than around flag leaf emergence (GS 36–48) or ear emergence (GS 49–71). Prior to 1994, the majority of late fungicide sprays was applied at, or after, ear emergence, but from 1994, the majority was applied around flag leaf emergence. The value and socioeconomic implications of the results are discussed.
Survival of Clavibacter michiganensis ssp. michiganensis in infected tomato stems under natural field conditions in California, Ohio and Morocco
Authors: Fatmi M. , Schaad N. W. 
Published: March 2003

The survival and half‐life of Clavibacter michiganensis ssp. michiganensis (C. michiganensis), the causal agent of bacterial canker of tomato, were determined in infected plant debris under natural field conditions in California, Ohio and Morocco using a semiselective agar medium. The organism survived significantly longer in tomato stems left on the soil surface than in stems buried in the soil at all locations studied. The pathogen was recovered in high amounts from tomato stems left on the soil surface for 314 days in Ohio and California, USA, and for 194 and 132 days in Melk Zhar and Aït Melloul, Morocco, respectively; it was recovered from stems buried in the soil for up to 314 days in Ohio, up to 240 days in California, and up to 60 days in Aït Melloul and Melk Zhar. The half‐life of the pathogen in stems left on the soil surface ranged from 23·2 to 24·8 days in the USA, and from 7·8 to 12·3 days in Morocco, whereas the half‐life in buried stems ranged from 14·0 to 16·7 days in the USA and from 3·7 to 9·5 days in Morocco. Based on the half‐life data, the predicted survival times of C. michiganensis in stems on the soil surface in Ohio, California, Melk Zhar and Aït Melloul would be up to 822, 770, 424 and 261 days, respectively, while the predicted survival times in stems buried in the soil would be 541, 497, 305 and 128 days, respectively. These results show that the survival and half‐life of C. michiganensis in plant debris are relatively long and are influenced by both tissue exposure and geographic location.