bluuebunny/crossref_metadata_2025 huggingface dataset:
CO2 assimilation, xanthophyll cycle pigments and PSII efficiency in pumpkin plants as affected by ozone fumigation
Authors: Ciompi Stefania , Castagna Antonella , Ranieri Annamaria , Nali Cristina , Lorenzini Giacomo , Soldatini Gian Franco
Published: May 2006

CO2 assimilation, xanthophyll cycle pigments and PSII efficiency were analyzed in two different ages of pumpkin leaves (Cucurbita pepo L. cv. Ambassador) exposed to 150 nmol mol‐1 of ozone (5 days, 5 h day‐1). Gas‐exchange measurements revealed a reduction in CO2 assimilation and stomatal conductance, accompanied by an increase in the intercellular CO2 concentration both in young and in mature leaves as compared to their respective controls. In both leaves, F0 remained unchanged, while Fm and the Fv/Fm ratio decreased after O3 fumigation, indicating that ozone may induce an alteration in the capability of photosystem II (PSII) to reduce the primary acceptor QA. In the mature leaves the photochemical quenching (qp) was significantly lowered by the pollutant, but this was not the case in the young leaves where qp did not change. In both mature and young ozonated pumpkin leaves, the development of non‐photochemical quenching caused a decrease in the PSII photochemical rate, as shown by the correlation between Fv/Fm and the de‐epoxidation state of dark‐adapted leaves. Decreases in the Fv/Fm ratio are generally attributed to damage to the PSII reaction centre, apart from the down‐regulation of the capacity of PSII electron transport. While in young ozonated leaves the decrease in the Fv/Fm ratio was not associated with damage to the D1 protein, in mature ozonated pumpkin leaves, the decrease in the Fv/Fm was accompanied by a significant decline in the D1 content. In conclusion, ozone exposure induces alterations in the light reactions of photosynthesis in both young and mature leaves. However, in young leaves the engagement of the xanthophyll cycle appears to counteract ozone effects against the photosynthetic apparatus as demonstrated by the absence of damage to the D1 protein. On the other hand, the loss of D1 protein in mature fumigated leaves suggests that the activation of the xanthophyll cycle is not sufficient to prevent photoinhibition, probably because a physiological state of senescence adds to the oxidative stress.
Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species
Authors: Noguchi Ko , Terashima Ichiro
Published: May 2006

Mature leaves of shade species exhibit lower respiratory rates than those of sun species. To elucidate the mechanism underlying different respiratory rates between sun and shade species, we examined respiratory properties of leaves in Spinacia oleracea L., a sun species, and Alocasia odora (Lodd.) Spach, a shade species, with special reference to changes in the respiratory rate throughout the night. In S. oleracea, rates of both CO2 efflux and O2 uptake decreased with time during the night, whereas in A. odora both rates were virtually constant at lower levels. The rates of O2 uptake in S. oleracea increased upon addition of sucrose, and the rates attained were virtually identical throughout the night. However, the addition of an uncoupler [carbonyl cyanide p‐(trifluoromethoxy)‐phenylhydrazone; FCCP] did not alter the rates. In contrast, the rates of O2 uptake in A. odora were enhanced by the addition of FCCP, but not by sucrose. The concentrations of carbohydrates in the tissue decreased throughout the night in both species and the ATP/ADP ratio was always greater in A. odora. These results indicate that, in S. oleracea, the availability of respiratory substrate determines the respiratory rate, while the low respiratory rate in A. odora is ascribed to its low demand for ATP.
Chill‐responsive dehydrins in blueberry: Are they associated with cold hardiness or dormancy transitions?
Authors: Arora Rajeev , Rowland Lisa J. , Panta Ganesh R.
Published: May 2006

To survive winters, woody perennials of temperate zones must enter into endodormancy. Resumption of spring growth requires sufficient exposure to low temperature (chill units, CUs) in winter (chilling requirement), which also plays a role in the development of cold hardiness (cold acclimation). Physiological studies on dormancy breaking have focused on identifying markers, such as appearance or disappearance of proteins in response to varying degrees of chill unit accumulation. However, whether these changes are associated with dormancy transitions or cold acclimation is not clear. In the present study, greenhouse‐grown blueberry (Vaccinium section Cyanococcus) plants were used to address this question. Three blueberry cultivars, Bluecrop, Tifblue, and Gulfcoast having chilling requirement of approximately 1 200, 900 and 600 CUs, respectively, were first exposed to 4°C for long enough to provide chill units equivalent to one‐half of their respective chilling requirement. This treatment was expected to result in cold acclimation. A fraction of plants was then subjected to a 15/12°C (light/dark) regime for 2 weeks, a treatment expected to be “dormancy‐neutral” but cause deacclimation. Before and after each treatment, cold hardiness and dormancy status of floral buds were determined; proteins were extracted from the buds collected on the same sampling date, and separated by one‐dimensional SDS‐PAGE. Dehydrin‐like proteins were identified by immunoblotting, using anti‐dehydrin antiserum. Results indicate that the chilling treatment resulted in cold acclimation as indicated by increased bud hardiness in all three cultivars. Data also indicate a distinct accumulation of three dehydrin‐like proteins of 65, 60, and 14 kDa during cold acclimation. The cold hardiness and levels of dehydrin proteins decreased during the exposure to 15/12°C for 2 weeks. Results also confirmed that this treatment had no negative effect on chill unit accumulation. Densitometric scans of protein gels indicated a close association between the abundance of dehydrins and degree of cold hardiness in these cultivars. In addition, levels of the dehydrin proteins and cold hardiness remained about the same between 100% and >100% satisfaction of chilling requirement. These results suggest that changes in dehydrin expression are more closely associated with cold hardiness than with dormancy transitions.
Endogenous abscisic acid levels are linked to decreased growth of bush bean plants treated with NaCl
Authors: Montero Elena , Cabot Catalina , Barceló Juan , Poschenrieder Charlotte
Published: May 2006

This paper studies the relative importance of endogenous ABA and ion toxicity in the leaf growth inhibition caused by NaCl in salt‐adapted and unadapted bush beans. Adaptation to salt‐stress was achieved by germination of seeds in 75 mM NaCl, while unadapted plants were germinated in tap water. The adaptation process caused a transitory increase in leaf ABA, Na+ and Cl− concentrations, while leaf expansion was inhibited. However, when grown for 8 or 13 days in 75 mM NaCl‐containing nutrient solution, primary and first trifoliolate leaves of salt‐adapted plants had greater areas than those of unadapted plants. Concentrations of ABA, Na+ and Cl− in these leaves were lower in adapted plants, and a strong negative correlation between leaf expansion growth and either leaf Na+, Cl− or ABA concentrations could be established. However, in the second trifoliolate leaves only the ABA, but not the Na+ or Cl−, concentrations were significantly correlated with leaf expansion. Our results suggest that salt‐induced inhibition of leaf expansion growth in bush beans is mediated by ABA rather than Na+ or Cl− toxicity. Moreover, the increase of ABA, induced by the salt‐pretreatment, seems to play an important role in limiting the accumulation of Na+ and Cl− in the leaves, leading to adaptation of bush beans to salt‐stress.
Changes of endogenous hormone levels in developing seeds, zygotic embryos and megagametophytes in Picea glauca
Authors: Kong Lisheng , Attree Stephen M. , Fowke Larry C.
Published: May 2006

Endogenous free abscisic acid (ABA), indole‐3‐acetic acid (IAA) and gibberellins (GAs) were identified and quantified in whole white spruce (Picea glauca [Moench] Voss) seeds, zygotic embryos and megagametophytes by high performance liquid chromatography and gas chromatography‐selected ion monitoring‐mass spectrometry. In seeds, the ABA content was high at the early embryo developmental stage and underwent a further rapid increase at the precotyledonary stage about 4 weeks after pollination (AFP). This latter increase in ABA corresponded with an increase in seed dry weight 4–6 weeks AFP. Increases of ABA continued until the late maturation stage (8 weeks AFP). The endogenous ABA concentration on a dry weight basis was higher in embryos than in megagametophytes, but the total ABA content per structure was lower in embryos than in megagametophytes because the size and weight of these two structures were different. At the late maturation stage, ABA amounts decreased earlier in embryos (8 weeks AFP) than in megagametophytes (10 weeks AFP). Low concentrations of ABA were observed in embryos and megagametophytes of stored seeds. During development, the endogenous IAA amount in the megagametophytes declined after pollination. This was followed by an increase from 2 to 6 weeks AFP. During late maturation, the IAA content increased in megagametophytes but decreased in the embryos. Throughout seed development, GA4 slightly decreased while GA9 increased. Endogenous GA7 remained very low throughout. In stored seeds, amounts of both IAA and GAs were lower than in developing seeds. Concomitant with a rapid increase in seed dry weight, seed moisture content (MC) decreased sharply between precotyledonary stage and early cotyledonary stage (4 and 6 weeks AFP). Seeds could absorb water and germinate after a significant decrease of MC and at a high endogenous ABA content (8 weeks AFP). These results suggest that endogenous ABA, IAA and GAs are involved in white spruce embryogenesis. There are relatively high ABA and IAA contents in the embryo environment but the GAs checked in this study are low.
Frost tolerance and biochemical changes during hardening and dehardening in contrasting white clover populations
Authors: Svenning Mette M. , Røsnes Kirsti , Junttila Olavi
Published: May 2006

Successful winter survival of perennial plants, like white clover, is dependent on proper timing of both hardening and dehardening. The purpose of this study was to investigate the regulation of these processes in two cultivars (AberCrest and AberHerald) and two Norwegian ecotypes (Særheim collected at 58°46′N lat. and Bodø at 67°20′N lat.) of white clover (Trifolium repens L.). For hardening and dehardening, plants were exposed to controlled temperature conditions and frost hardiness of stolons was tested by programmed freezing at the rate of 3°C per hour. In addition, stolons were analysed for starch, soluble sugars and soluble amino acids. Cultivars AberCrest and AberHerald, selected for growth at low temperature and winter hardiness in the United Kingdom, were significantly less hardy than the Norwegian populations. After six weeks of hardening (2 weeks at 6°C and 4 weeks at 0.5°C), estimated LT50 values were −13.8, −13.0, −17.8 and −20.3°C for AberCrest, AberHerald, Saerheim and Bodø, respectively. The rate of dehardening increased with increasing temperature. At low temperature (6°C), the northern ecotype from Bodø was more resistant to dehardening than AberHerald. However, at 18°C the absolute rate of dehardening (°C day−1) was twice as high in Bodø as in AberHerald plants. Stolon elongation during dehardening was initiated at lower temperatures in AberHerald than in plants of the Bodø ecotype. The content of total soluble sugars, sucrose and the amino acids proline and arginine were significantly higher in hardy plants of Bodø than in those of AberHerald. Sucrose levels decreased during dehardening and correlations between sucrose content and LT50 during this process were statistically highly significant for both Bodø and AberHerald. The least hardy populations of white clover were characterized by thick stolons, long internodes and large leaves.
Modification of chemical properties of cell wall polysaccharides in the inner tissues by white light in relation to the decrease in tissue tension in Pisum sativum epicotyls
Authors: Miyamoto Kensuke , Mitani Yuko , Soga Kouichi , Ueda Junichi , Wakabayashi Kazuyuki , Hoson Takayuki , Kamisaka Seiichiro , Masuda Yoshio
Published: May 2006

When white light irradiation inhibits shoot growth in derooted pea (Pisum sativum L. cv. Alaska) cuttings, it decreases tissue tension, a driving force for shoot growth, by making the cell wall of the inner tissues mechanically rigid. To elucidate the mechanism by which light affects the mechanical properties of the cell wall in the inner tissues, its effect on the chemical properties of the cell walls was studied by analyzing qualitatively and quantitatively cell wall polysaccharides in the epdidermis and inner tissue of pea epicotyls grown in both dark and light. The amount of polysaccharides per subhook in the cell walls of both tissues increased during a 4‐h dark incubation. Light suppressed the increase in hemicellulosic (HC)‐II and cellulosic polysaccharides in the inner tissues, while it did not affect the increase in other wall fractions in either the epidermal or subepidermal tissues. No light effect was observed on the neutral sugar compositions of pectin, HC‐I or HC‐II fractions in either of the tissues. Light increased the mass‐average molecular mass of xyloglucan and rhamnoarabinogalactan in HC‐II fractions in the inner tissues, while such an effect was not observed in the epidermis. These facts suggest that the light‐induced decrease in the tissue tension in pea epicotyls is caused by an increase in the molecular size of xyloglucan, rhamnoarabinogalactan in the HC‐II fraction and/or the suppression of the synthesis of HC‐II and cellulosic polysaccharides in the inner tissues.
Carbohydrate solutilization of tomato locule tissue cell walls: Parallels with locule tissue liquefaction during ripening
Authors: Cheng Guiwen W. , Huber Donald J.
Published: May 2006

Carbohydrate solubilization and glycosidase activities were investigated in tomato (Lycopersicon esculentum Mill. cv. Solar Set) locule cell walls to identity processes involved in the liquefaction of this tissue. Cell walls were prepared from the locule tissue of fruit at the immature green, mature green, and breaker stages of development. Enzymically active walls incubated in dilute buffer released high molecular mass pectins, oligomeric carbohydrate, and the neutral sugars rhamnose, glucose, galactose, arabinose, xylose, and mannose. The release was sustained for at least 50 h at 34°C and was inhibited more than 50% by 1 mM Hg2+. Pectins released from the cell walls of locule tissue at progressive stages of liquefaction were similar in molecular mass and showed no evidence of downshifts on a Sepharose CL–2B–300 column during prolonged incubation. A cell‐free protein extract prepared from the locule tissue of mature‐green fruit promoted a net release of polymeric and monomeric carbohydrates from high‐temperature inactivated cell walls. Polygalacturonase activity was not detected in locule protein although glycosidases including β‐mannosidase (EC 3.2.1.25), α‐ and β‐galactosidases (EC 3.2.1.22–23), β‐arabinosidase (EC 3.2.1.56) and β‐glucosidase (EC 3.2.1.21) were present. Pectinmethylesterase (EC 3.1.1.1 1) activity was detected at the immature‐green stage but declined to negligible levels in mature‐green and breaker locule tissue. Parallels between the in vitro solubilization of carbohydrate from locule tissue cell walls and the changes occurring during locule liquefaction are discussed.
Photosynthetic carbon acquisition in the lichen photobionts Coccomyxa and Trebouxia (Chlorophyta)
Authors: Palmqvist Kristin , de Los Rios Asuncion , Ascaso Carmen , Samuelsson Göran
Published: May 2006

Processes involved in photosynthetic CO2 acquisition were characterised for the isolated lichen photobiont Trebouxia erici (Chlorophyta, Trebouxiophyceae) and compared with Coccomyxa (Chlorophyta), a lichen photobiont without a photosynthetic CO2‐concentrating mechanism. Comparisons of ultrastructure and immuno‐gold labelling of ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco; EC 4.1.1.39) showed that the chloroplast was larger in T. erici and that the majority of Rubisco was located in its centrally located pyrenoid. Coccomyxa had no pyrenoid and Rubisco was evenly distributed in its chloroplast. Both species preferred CO2 rather than HCO3− as an external substrate for photosynthesis, but T. erici was able to use CO2 concentrations below 10–12 μM more efficiently than Coccomyxa. In T. erici, the lipid‐insoluble carbonic anhydrase (CA; EC 4.2.1.1) inhibitor acetazolamide (AZA) inhibited photosynthesis at CO2 concentrations below 1 μM, while the lipid‐soluble CA inhibitor ethoxyzolamide (EZA) inhibited CO2‐dependent O2 evolution over the whole CO2 range. EZA inhibited photosynthesis also in Coccomyxa, but to a much lesser extent below 10–12 μM CO2. The internal CA activity of Trebouxia, per unit chlorophyll (Chl), was ca 10% of that of Coccomyxa. Internal CA activity was also detected in homogenates from T. erici and two Trebouxia‐lichens (Lasallia hispanica and Cladina rangiferina). In all three, the predominating CA had α‐type characteristics and was significantly inhibited by low concentrations of AZA, having an I50 below 10–20 nM. In Coccomyxa a β‐type CA predominates, which is much less sensitive to AZA. Thus, the two photobionts differed in three major characteristics with respect to CO2 acquisition, the subcellular location of Rubisco, the relative requirement of CA and the biochemical characteristics of their predominating internal CA. These differences may be linked to the ability of Trebouxia to accumulate dissolved inorganic carbon internally, enhancing their CO2 use efficiency at and below air‐equilibrium concentrations (10–12 μM CO2) in comparison with Coccomyxa.
Ubiquitin conjugation to endogenous proteins in the dormant tuber of Helianthus tuberosus and during the first cell cycle
Authors: Scoccianti Valeria , Corsi Dario , Magnani Mauro
Published: May 2006

Ubiquitin is a small protein involved in an ATP‐dependent proteolytic pathway in all eukaryotes. This pathway has been demonstrated to be required for both the bulk degradation of cellular proteins and the targeted proteolysis of specific regulatory proteins. We have investigated the presence of ubiquitin (Ub) and the ubiquitin‐conjugating system in dormant and activated tubers of Helianthus tuberosus L. cv. OB 1 that represent a widely used model system for studies on the cell cycle in plants. Immunoblot experiments revealed the presence of free ubiquitin and ubiquitin conjugates. Furthermore, the presence of an active ubiquitin‐conjugating system, both time‐ and ATP‐dependent, was demonstrated by incubation with 125I‐labeled ubiquitin. A few proteins able to form thiol esters with 125I‐Ub and probably corresponding to ubiquitin‐conjugating enzymes, E1 and E2s, were also found. During the first cell cycle, several proteins become ubiquitinated. In particular a large amount of protein conjugates was present at 6 h when the lowest content of free ubiquitin was found. Subsequently, a dramatic decrease in ubiquitin conjugates occurred. It is well known that cell cycle progression in eukaryotes depends on cyclin levels and cyclin B degradation is ubiquitin‐ and ATP‐dependent. By immunoblot experiments we showed that cyclin B in H. tuberosus is present as at least two protein bands of 50 and 54 kDa and that their amounts undergo profound changes during the cell cycle. The 54‐kDa band was also recognized by an anti‐ubiquitin antibody. These data seem to indicate that in H. tuberosus activated tuber slices, the ATP‐dependent ubiquitin proteolytic pathway is involved in the dedifferentiation process occurring after the artificial break of dormancy when the cells acquire the characteristics linked to the meristematic state.
Changes in in vivo chlorophyll fluorescence quenching in lichen thalli as a function of water content and suggestion of zeaxanthin‐associated photoprotection
Authors: Calatayud Angeles , Deltoro Vicente I. , Barreno Eva , Valle‐Tascon Secundino del
Published: May 2006

The function of photosystem II (PSII) during desiccation was investigated via analysis of Chl a fluorescence emission in thalli from Parmelia quercina (Willd.) Vainio, Parmelia acetabulum (Necker) Duby, Ramalina farinacea (L.) Ach., Pseudevernia furfuracea (L.) Zopf., and Evernia prunastri (L.) Ach. Water loss followed the same exponential pattern in all these species, the half time being dependent on species. Desiccation affected the fluorescence parameters. Dark‐adapted maximum fluorescence (Fm), instantaneous fluorescence (Fo) and the ratio of variable (Fm–Fo) to Fm were dependent on water content and decreased in two distinct phases: a slow and apparently linear phase, followed by a more steep decline at low water content. Actual PSII photochemical yield (φPSII), non‐photochemical quenching (NPQ), efficiency of photon capture (φexc), and photochemical quenching (qp) remained nearly constant until 30% relative water content (RWC), decreasing rapidly thereafter. In contrast, increased NPQ appeared to occur only at water content values lower than 20%. Treatment of thalli with dithiothreitol (DTT) effectively reduced NPQ during desiccation and increased susceptibility to photoinhibition caused by exposure to high light as measured by dark recovery of the FvFm ratio. HPLC analysis showed that the level of the de‐epoxidized xanthophyll cycle pigments antheraxanthin (Anth) and zeaxanthin (Zea) increased during lichen desiccation. The results point towards the existence of a photoprotective mechanism with the involvement of Zea and Anth in non‐radiative dissipation of the desiccation‐induced excess of energy.
Nitrate reductase is inhibited in leaves of Triticum aestivum treated with high levels of copper
Authors: Luna Celina M. , Casano Leonardo M. , Trippi Victorio S.
Published: May 2006

Copper is a potent sulfhydryl reagent which can also catalyse the generation of active oxygen. Since nitrate reductase (EC 1.6.6.1) is an SH‐enzyme sensitive to oxidative environments, the relations among copper, active oxygen species and nitrate reductase (NR) activity are of interest. Foliar segments of wheat (Triticum aestivum cv. Oasis) were floated on CuSO4 solutions (up to 250 μM) for 24 h under continuous light. Copper decreased NR activity before affecting active oxygen generation as estimated by changes in oxidative parameters, including malondialdehyde, K+ leakage and chlorophyll degradation. Cysteine and Na‐benzoate counteracted this decrease, suggesting an oxidative damage of the enzyme in leaves exposed to high copper levels. Copper‐induced NR inactivation was further studied in the partially purified enzyme. Preincubation with CuSO4 inhibited NR. Copper inhibition was reversed by subsequent incubation with EDTA, indicating that the metal bonded to key ‐SH groups of the enzyme. In addition, an ˙OH‐generating system (composed of CuSO4, ascorbate and H2O2) irreversibly decreased the activity of purified NR to a greater extent than copper alone. Our results show that copper affects nitrogen metabolism by diminishing NR activity, involving a direct effect on key SH‐groups and an indirect effect via attack by active oxygen species induced by the metal.
Ultrastructural aspects of the cytoplasmic origin and accumulation of oil in olive fruit (Olea europaea)
Authors: Rangel B. , Platt K. A. , Thomson W. W.
Published: May 2006

The development of oil bodies and oil droplets in fruits of olive was examined at the ultrastructural level. Both oil bodies that form in young fruits and oil droplets that develop with fruit maturation are cytoplasmic bodies. The formation of the small oil bodies occurs in localized regions of the cytoplasm. These bodies are closely associated and fuse together, forming a small oil droplet that protruded against and indented the vacuolar membrane. As the fruit matures, new oil bodies appear to form and fuse with the oil droplet, resulting in the formation of a single large oil droplet of about 30 μm in diameter in most mature mesocarp cells. The cytoplasmic region where the oil bodies formed had a granulate, ultrastructural appearance, and cytoplasmic components such as membranes and ribosomes were noticeably absent in these regions. The granulate material coated the oil bodies and oil droplets, and appeared as a thin, compressed band between the round inner surface of the droplets and the indented tonoplast. We suggest that this granulate material is involved in the synthesis of the oil and, with enlargement of the oil bodies, this coat becomes thinner in regions where they are closely associated, resulting in zones where confluence of the oil occurs.
Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II. The interaction of light environment and soil fertility on seedling physiology
Authors: Johnson Jon D. , Tognetti Roberto , Michelozzi Marco , Pinzauti Simone , Minotta Gianfranco , Borghetti Marco
Published: May 2006

The survival and growth of natural beech regeneration after canopy removal is variable and little is known about ecophysiological mechanisms of these responses. Biomass, nonstructural carbohydrate levels and nitrogen concentrations were measured in an Italian population of European beech seedlings. Seedlings were container‐grown in two types of soil, organic and mineral, collected at the study site. The seedlings were grown under three light treatments: under full beech canopy (understory), exposed to full sun only during midday (gap) and under full sun (clearing). Leaf gas exchange and chlorophyll a fluorescence parameters were measured and then foliar analyses were conducted for chlorophyll, phenolic and tannin levels. Biomass and allocation were significantly affected by light and soil treatments. The clearing seedlings and those in organic soil were larger than seedlings in the other light treatments or soil type. Total nonstructural carbohydrate concentrations were lower in the understory seedlings and significant differences between soil types were present in the gap and clearing seedlings. Nitrogen concentrations were higher in the understory seedlings and those growing in the organic soil compared to the other treatments. Gas exchange rates were highest in clearing and the organic soil seedlings. Gap seedlings exhibited photosynthetic acclimation that allowed them to utilize high light of midday and any sunflecks during the morning and afternoon. Relative fluorescence was significantly influenced by both light treatment and soil type, with the highest values observed in the gap seedlings. Light response curves showed decreasing apparent maximum quantum efficiency from the understory to clearing, while maximum photosynthetic rate was highest in the gap seedlings. Chlorophyll concentration was highest in understory seedlings and those growing in organic soil and higher in seedlings growing in organic than in mineral soil. Both foliar tannin and phenolic levels were highest in clearing seedlings, and only tannin concentrations were affected by soil type. Understory seedlings had the highest mortality and insect herbivory; the latter was found to be inversely related to tannin concentration. Overall, growth and photosynthesis in beech seedlings responded positively to high light associated with small canopy gaps. Organic soil increased seedling size, particularly in the gap and clearing environments. We conclude that forest gaps are favorable for photosynthesis and growth of European beech seedlings.
Influence of bicarbonate and metal ions on the development of root Fe(III) reducing capacity by Fe‐deficient cucumber (Cucumis sativus) plants
Authors: Romera Francisco J. , Alcántara Esteban , de, la Guardia Manuel Díaz
Published: May 2006

The effect of bicarbonate and selected metal ions on the development of enhanced root Fe(III) reducing capacity (a response to Fe deficiency of dicotyledons) was studied in young plants of cucumber (Cucumis sativus L. cv. Ashley) grown in nutrient solution. Pretreatment of 11‐day‐old Fe‐deficient cucumber plants with 20 mM NaHCO3, for at least 23 h prior to determination of root Fe(III) reducing capacity, markedly inhibited this response. The inhibitory effect of bicarbonate could be partly reversed by a 4‐ to 8‐h treatment with either 10 μM MnSO4, 10 μM FeEDDHA, 2 μM ZnSO4, 0.5 μM NiCl2, or 0.25 μM, or CoSO4 (final concentrations), added to the nutrient solution. By contrast, the addition of other salts of metal ions, like CuSO4 and Cd(NO3)2, at 0.25, 0.5 or 1 μM, or MgSO4, at 0.5, 1 or 2 mM (final concentrations), had no beneficial effect. The results suggest that bicarbonate may inhibit the development of root Fe(III) reducing capacity by diminishing the availability of certain metal ions required for this response.
Spatial and temporal responses of the maize catalases to low temperature
Authors: Auh Chung‐Kyoon , Scandalios John G.
Published: May 2006

Catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) is a primary antioxidant enzyme that can remove H2H2 rapidly and prevent the formation of reactive oxygen species. The maize (Zea mays L.) catalase genes are regulated in their expression spatially and temporally. Using embryos from germinating seeds and developing kernels from the maize standard inbred line W64A, which expresses all three Cat genes, and the CAT‐2 null line A338F, we have examined the response of the three catalase genes to low temperatures (14°C, 4°C, or 14/4°C). Total catalase activity increased in response to low temperatures in germinating embryos of both maize lines. Zymogram analysis showed that the increase in total catalase activity was due to accumulation of the CAT‐1 and CAT‐2 isozymes in the scutella and embryonic axes of germinating embryos. In both lines, CAT‐3 activity decreased in the embryonic axes of germinating embryos in response to low temperatures. The steady‐state levels of Cat transcripts did not parallel the pattern of the corresponding catalase proteins, indicating the involvement of post‐transcriptional control mechanisms. In contrast to germinating embryos and excepting an increase at 4°C in A338F, total catalase activity decreased in response to low temperatures in scutella of developing embryos of both lines. CAT‐2 activity (in W64A) and CAT‐3 activity (in A338F) decreased in response to low temperatures and their corresponding steady‐state levels of mRNA also decreased. Only CAT‐1 activity increased dramatically at 4°C in A338F, but Cat I transcript level did not change. Our data indicate that the three maize catalase genes respond differentially to low temperatures at two different developmental stages.
Purification of plasma membranes from dry maize embryos
Authors: Sánchez‐Nieto Sobeida , García‐Rubio Oscar , Pacheco‐Moisés Fermín , Carballo Aquiles , Rodríguez‐Sotres Rogelio , Gavilanes‐Ruíz Marina
Published: May 2006

Isolation of subcellular fractions from dry structures such as seeds or their tissues is difficult. In the present work, plasma membranes were isolated from dry maize (Zea mays L.) embryos with an enrichment of 11‐fold as estimated by glucan synthase II (GSII, EC 2.4.1.34) activity and a purity of 78 to 90% as judged by the sensitivity of ATP hydrolysis to vanadate, a specific inhibitor of the plasma membrane H+‐ATPase (EC 3.6.1.35). The procedure involved a double homogenization of the dry embryos and the addition of a 1500‐g supernatant to an aqueous polyethyleneglycol‐dextran two‐phase partitioning system; the optimal ratio of polyethyleneglycol‐dextran for purification of plasma membranes from dry seeds was 6.8/6.8% (w/w). In the isolated membranes a trace of a tonoplast enzyme marker (tonoplast H+‐ATPase, EC 3.6.1.3) could be detected, but there were negligible amounts of mitochondrial and rough endoplasmic reticulum markers, H+‐ATPase (EC 3.6.1.34) and diacylglycerol acyltrans‐ferase (EC 2.3.1.20), respectively. The technique could also be used in hydrated embryos. The entire procedure can be carried out in 5 to 6 h. The resulting preparation is stable for at least 2 months at −70°C. The membranes of dry and hydrated embryos exhibited a high level of vanadate‐sensitive ATPase activity that was increased by lysophosphatidylcholine.
The contribution of drought‐related decreases in foliar nitrogen concentration to decreases in photosynthetic capacity during and after drought in prairie grasses
Authors: Heckathorn Scott A. , DeLucia Evan H. , Zielinski Raymond E.
Published: May 2006

While stomatal closure usually limits photosynthesis during drought, our previous results suggest that drought‐related decreases in foliar nitrogen concentration (NL) limit photosynthesis during recovery from drought in prairie grasses. Here we estimate the importance of decreases in NL to decreased photosynthetic capacity (PScap) during drought and a subsequent recovery period in three perennial C4 prairie grasses. PScap (O2 evolution at light and CO2 saturation) decreased 69 to 78% during drought in these grasses, and full recovery of PScap required 8 to 12 days, until younger leaves were expanded or older leaves were repaired, depending on species. Decreases in NL explained 38 to 51% of the loss of PScap during drought and accounted for 51 to 69% of the total loss of PScap integrated over the post‐drought recovery period. N‐related loss of PScap appeared to result more from decreases in ribulose‐1,5‐bisphosphate carboxylase/oxygenase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (4.1.1.31), and other soluble photosynthetic enzymes, than from decreases in thylakoid N‐containing compounds. Decreases in quantum yield of O2 evolution and Fv/Fm (variable‐to‐maximum fluorescence of dark‐adapted leaves) during drought were small, so we assumed that little damage to photsystem II (PSII) and thylakoid membrane function occurred. Further, F0 (minimum F) decreased or remained unchanged, dark F0 was greater than light F0, and decreases in photochemical quenching (the fraction of oxidized PSII) were reversed within 1–3 days after drought. Therefore, prolonged increases in non‐photochemical quenching (qn; thermal dissipation of excess light energy) during and after drought were indicative of protective downregulation and were likely associated with disproportionate loss of soluble photosynthetic proteins during drought. In support of this, post‐drought recovery of qn paralleled recovery of NL and PScap. Thus, in C4 prairie grasses, loss of PScap during drought is largely the result of decreases in shoot NL and of associated protective downregulation, decreasing carbon assimilation for 1–2 weeks after drought.
Thidiazuron‐induced morphogenesis of Regal geranium (Pelargonium domesticum): A potential stress response
Authors: Murch Susan J. , KrishnaRaj Sankaran , Saxena Praveen K.
Published: May 2006

Thidiazuron (TDZ), a phenylurea derivative with cytokinin‐like activity, induced the development of outgrowths on root tissue of vegetatively propagated geraniums (Pelargonium × hortorum, Pelargonium domesticum and Pelargonium graveolens). Root outgrowths developed as globular or elongated structures following treatment with 10–30 μM TDZ and many of these structures differentiated to produce shoots. Analysis of root and shoot samples, collected daily during the outgrowth induction phase and at the end of the treatment period, revealed significant changes in accumulation of manganese, iron, copper, calcium, magnesium and potassium. The markers of a stress response, proline, abscisic acid and 4‐aminobutyrate, accumulated in the TDZ‐treated roots during the first week of induction. Assessment of the adenylate phosphate pool sizes of the TDZ‐treated plants indicated a sequential increase in the endogenous levels of ATP, ADP and AMP following each application of TDZ. The energy charge ratio was also significantly higher in TDZ‐treated plants indicating an increase in ATP utilizing systems. Similarily, pyridine nucleotide pool size analyses revealed that TDZ‐treated plants had a higher level of endogenous NADP+ in the initial 24‐h period following each treatment and the level of NADPH increased following the third application of TDZ. The ratio of NADPH/NADP+ was significantly higher in TDZ‐treated plants throughout the treatment period. We hypothesize that the primary effect of TDZ was through induction of a stress response in the geranium plants. In order to overcome this stress, the plants accumulated significantly higher levels of proline, ABA and 4‐aminobutyrate. Moreover, the plants also exhibited modified metabolic processes which in turn led to increased availability of energy and reducing power required for subsequent growth and to initiate stress adaptation mechanisms including modified cellular processes and regenerative outgrowth development.
Winter hardening and glutathione status in the bilberry (Vaccinium myrtillus) in response to trace gases (CO2, O3) and nitrogen fertilization
Authors: Taulavuori Erja , Taulavuori Kari , Laine Kari , Pakonen Tuulikki , Saari Esko
Published: May 2006

Bilberry plants (Vaccinium myrtillus L.) at a field site in northern Finland (65°N) were subjected to nitrogen fertilization [6.5 mmol m−2 NH4NO3× Ca(OH)2] at the beginning of 3 growing seasons in late May and to trace gas fumigation (CO2 and O3) for 5 months (May–September) in 1993–1995 in order to investigate frost resistance and glutathione concentrations during the winter hardening period, and to assess the correlation between these variables. Harvesting was performed twice in the autumn of both 1994 and 1995, and the two‐year data for each harvest were pooled. The frost resistance of the bilberry stems increased by about 10°C during the hardening period between the two harvests. Nitrogen fertilization increased the frost resistance towards late autumn. The fumigation treatments had no marked effect on it. The combination of elevated CO2 and nitrogen fertilization induced a decrease in frost resistance. Increases in total glutathione concentrations and the proportion of reduced glutathione (GSH) in the stems were evident during hardening. Nitrogen fertilization positively affected the total glutathione concentration and the proportion of GSH at the beginning of the hardening period but the effect disappeared during the hardening process. Trace gas fumigation as such had no marked effect on glutathione concentration. Increases in glutathione concentrations during hardening did not correlate with frost resistance, possibly due to different timing of the appearence of the response to fertilization treatment, i.e., glutathione responded in the beginning of hardening while frost resistance at the end. The lack of correlation with frost resistance, and especially the different responses to nitrogen fertilization, may reflect the indirect role of glutathione in the development of winter hardening, as a transport and storage form of reduced nitrogen and sulphur. In conclusion, winter hardening and glutathione status in the bilberry seems to be sensitive to nitrogen fertilization, and not affected by elevated CO2 and O3.
Cloning, characterization and transcriptional studies of ferredoxin genes from the mesophilic cyanobacterium Synechocystis sp. PCC 6803 and the thermophilic cyanobacterium Synechococcus vulcanus
Authors: Nakamoto Hitoshi , Suzuki Toyoko
Published: May 2006

Genes encoding ferredoxins from the transformable unicellular cyanobacterium Synechocystis sp. PCC 6803 and the thermophilic unicellular cyanobacterium Synechococcus vulcanus were cloned and sequenced. Southern blot hybridization detected a single copy of the ferredoxin sequences in both cyanobacterial genomes. Northern blot hybridization analyses indicated RNA transcripts of approximately 440 bases for Synechocystis sp. PCC 6803 and 460 bases for Synechococcus vulcanus. The accumulation of transcripts of the two cyanobacteria was three to four times greater in cells grown in iron‐rich medium than in cells grown in iron‐deficient medium.
Free and conjugated polyamines in embryogenic and non‐embryogenic leaf regions of camellia leaves before and during direct somatic embryogenesis
Authors: Pedroso M. C. , Primikirios N. , Roubelakis‐Angelakis K. A. , Pais M. S.
Published: May 2006

Contents of endogenous free and conjugated polyamines were determined in embryogenic and non‐embryogenic leaf regions of Camellia japonica leaf explants, before (day 0), and 20 and 45 days after the induction of direct somatic embryogenesis, to clarify whether or not polyamines are linked to the specific morphogenic responses previously reported in the leaf regions. The analysis was carried out by high‐performance liquid chromatography. The results showed that there were no significant differences in the endogenous free and conjugated putrescine (Put), spermidine (Spd) and spermine (Spm) contents between the embryogenic and non‐embryogenic leaf regions of the same leaf. Thus, leaf region‐specific embryogenic response in C. japonica is not being determined/conditioned by the endogenous levels of Put, Spd and/or Spm. However, soluble and insoluble conjugated Put and soluble conjugated Spd seem to be related to the formation and development of globular embryos.
Photosynthetic responses of Coffea arabica leaves to a short‐term high light exposure in relation to N availability
Authors: Ramalho José C. , Pons Thijs L. , Groeneveld Henri W. , Nunes M. Antonieta
Published: May 2006

It is known that the coffee (Coffea arabica L.) plant which is originally from shade habitats would have a limited ability to grow under full sun. Previous work has shown that nitrogen fertilisation can reduce the leaf damage when the plants are exposed to high light intensities during several days. In the present work we aimed to study the effects of the high irradiance during the first hours and evaluate the positive contribution of nitrogen fertilisation in the case of short‐term exposure to strong light. Young plants (1.5–2 years old) grown in 1.5 kg of a mixed soil were supplemented with a nutrient solution containing 15 mM nitrogen in the form of NH4NO3, every 7 days (2N treatment), 15 days (1N treatment) and 45 days (0N treatment). Top mature leaves were exposed to a photosynthetic photon flux density of 1 500 μmol m−2 s−1 for a maximal period of 8 h, and changes in photosynthesis and pigment composition were monitored along the period of high light exposure. Photosynthetic capacity, leaf conductance to water vapour, electron transport capacity and maximum carboxylation activity, as well as some leaf fluorescence parameters (minimal fluorescence, photochemical efficiency of PSII and quantum yield of photosynthetic electron transport) were reduced by the stress, with a generally stronger impact observed in the 0N plants. The photochemical quenching was affected only in the 0N plants, while the non‐photochemical quenching increased in 2N plants but decreased in the 0N ones. The results showed that 2N plants presented a better initial status of the photosynthetic parameters and of the content of photoprotective pigments. Those plants showed ability to trigger some protective mechanisms, as observed by the tendency to increase the xanthophyll pool content, specially in zeaxanthin and in non‐photochemical quenching. Also, protein content presented a tendency to increase after 1.5 h, which was maintained until the end of the high light period. We conclude that nitrogen availability is a key factor in the acclimation process to high light.
Moderately increased constitutive proline does not alter osmotic stress tolerance
Authors: Maggio Albino , Bressan Ray A. , Hasegawa Paul M. , Locy Robert D.
Published: May 2006

Proline‐overproducing carrot cell lines were isolated by selection in medium containing hydroxyproline, a toxic analogue of proline. During growth of the cells in culture, length of lag phase, doubling time, and maximum fresh weight were the same for the hydroxyproline‐resistant cell line (HP) and the wild‐type cell line (JW). Proline content and resistance to hydroxyproline in the HP and JW lines were not strictly correlated indicating that another reason besides the constitutive level of proline is involved in hydroxyproline resistance. Tolerance to polyethylene glycol‐induced desiccation stress was not different between the two lines except perhaps at the early stages of culture growth when the proline levels of the two cell lines were nearly the same. The complexity of the relationship between proline accumulation and osmotolerance is discussed and strategies to achieve constitutive high levels of proline accumulation in plants are proposed.
IAA breakdown and its effect on auxin‐induced cell wall acidification in maize coleoptile segments
Authors: Peters Winfried S. , Lommel Christa , Felle Hubert
Published: May 2006

In excised Zea maus L. coleoptiles incubated in aerated media at high fresh weight per volume ratios, indole‐3‐acetic acid induces transient drops of extracellular pH. Based on the quantitative dependency of the response on the initial auxin concentration we developed a novel auxin bioassay, which allows reliable estimation of IAA concentrations between 10−85 and 10−5M. Using the bioassay and complementary concentration measurements by IAA fluorescence we found the transient IAA‐induced pH response paralleled by a decrease of auxin activity and concentration in the medium. This decline is rapid and starts immediately upon auxin addition, and insofar differs from the well known IAA degradation by epiphytic bacteria in long‐term auxin tests. We conclude that the transient character of the auxin pH response is due to rapid IAA metabolism. The effect occurs under those experimental conditions that are necessary for reliable estimations of auxin‐induced shifts of cell wall pH, which considerably complicates the interpretation of the results.
Auxin perception and signal transduction
Authors: Macdonald Heather
Published: May 2006

The action of auxin on whole plants is very complex, but we are starting to understand how some of the earliest events are signalled in single cells. There is now good evidence that auxin induces rapid events at the plasma membrane by binding to a population of the auxin‐binding protein ABPI, which is associated with a membrane‐spanning docking protein, possibly a G‐protein‐coupled receptor (GPCR). ABPI is targeted to the endoplasmic reticulum (ER) lumen, but it does not appear to bind auxin within the ER and its function (if any) in this location is unknown. It is also not known how the protein reaches the cell surface, but it is possible that it is exported together with its docking protein. Binding of auxin causes a conformational change affecting the C‐terminus of ABPI and it is likely that this change serves to activate the receptor at the plasma membrane. The signal transduction pathway appears to involve activation of phospholipase A2(PLA2) leading to the production of lipid second messengers which activate the plasma membrane proton ATPase (H−‐ATPase) by a phosphorylation‐dependent mechanism. Branch points exist that could potentially lead from this pathway to responses in the nucleus, but there is not yet any firm evidence that ABP1 is involved in such responses. Since intracellular auxin concentrations are correlated with sensitivity in some cases, it is possible that there is also a site of auxin perception inside the cell.
Auxin metabolism
Authors: Normanly Jennifer
Published: May 2006

Auxin metabolism encompasses transport, conjugation, deconjugation, conversion, and catabolism. The balance between auxin metabolism and biosynthesis determines the actual level of the hormone in a given cell and consequently plays an important role in many developmental processes from seed germination to fruit ripening. Mass spectrometry used in conjunction with stable isotope labeling studies has enabled comprehensive examination of auxin biosynthesis and turnover along with the identification of many auxin conjugate. It appears that the conjugate moiety may signal the metabolic fate (e.g. storage and eventual hydrolysis to free hormone, or catabolism). Recently identified auxin‐metabolizing enzymes are encoded by gene families which vary in specificity for auxin metabolites. The expression patterns of these genes will reveal a great deal about the mechanics of auxin metabolism.