bluuebunny/crossref_metadata_2025 huggingface dataset:
Membrane lipid dynamics and lipid peroxidation in the early stages of low‐temperature sweetening in tubers of Solanum tuberosum
Authors: Wismer Wendy V. , Worthing Wendy M. , Yada Rickey Y. , Marangoni Alejandro G.
Published: March 2003

Sugar accumulation and membrane lipid parameters associated with membrane permeability in chilling injury and senescence were followed in the early stages of low‐temperature sweetening in Solanum tuberosum tubers to monitor their dynamics. Norchip, a low‐temperature sweetening‐susceptible potato cultivar, and North Dakota 860‐2, a low‐temperature sweetening‐tolerant selection, were stored for 55 days at 4 and 12°C. Sugar accumulations were not linear and were characterized by fluctuations or cycles over storage time. Sucrose cycling and accumulation were greatest for Norchip tubers stored at 4°C as compared to the other treatments. Increases in membrane permeability were not detected by increases in electrolyte leakage. No significant changes in the phospholipid, galactolipid, free sterol levels or phospholipid to free sterol ratio were observed. The double bond index obtained from the fatty acid profiles of the total lipid fraction decreased significantly (decreased unsaturation) for Norchip tubers at 4°C over time. Free fatty acid and diene conjugation values fluctuated and increased over time for all treatments with greater amplitude of fluctuations observed for Norchip tubers stored at 4°C. These latter effects may be due to the high levels of lipid acyl hydrolase and lipoxygenase found in potato tubers. When free fatty acid and diene conjugation values were plotted with glucose accumulation over time, a possible relationship among the variables was revealed. The observed peroxidation products could relate low‐temperature stress and the resultant low‐temperature sweetening to chilling injury and drought stress. The anti‐oxidative potential of potato tubers should be considered for future cultivar development as a mechanism to lessen the severity or rate of low‐temperature sweetening development.
Differences in the response of carbon assimilation to summer stress (water deficits, high light and temperature) in four Mediterranean tree species
Authors: Faria T. , Silvério D. , Breia E. , Cabral R. , Abadia A. , Abadia J. , Pereira J. S. , Chaves M. M.
Published: March 2003

Daily changes in photoprotective mechanisms were studied in sun leaves of Quercus suber L., Quercus ilex L., Olea europaea L. and Eucalyptus globulus Labill. trees during the summer in Portugal. Even though stomatal closure explained most of the diurnal variation in carbon assimilation along the summer, a decline in the photochemical yield of photosystem II (F′v/F′m) also occurred, as a result of an excess of intercepted solar radiation when carbon assimilation is limited by stomatal closure due to high vapour pressure deficits and/or soil water deficits. These changes were accompanied by the conversion of violaxanthin to antheraxanthin and zeaxanthin which were correlated with thermal dissipation of excess photon energy. In spite of a common general response, differences between species were observed ‐Olea europaea, which is a slow‐growing tree, had the lowest net photosynthetic rates, the highest proportion of carotenoids in relation to chlorophyll and the highest rates of de‐epoxidation of violaxanthin. This enabled a large thermal dissipation of the excess intercepted radiation but led to rather small values of light utilisation for photochemistry (ca 20%). In contrast, in E. globulus, a fast‐growing tree, photosynthetic rates were the highest, thermal dissipation of absorbed radiation the lowest and maximal values of light utilisation for photochemistry reached ca 50%. The two Quercus species exhibited an intermediate response. A high degree of co‐ordination is apparent between stomatal behaviour, photosynthetic capacity and photoprotection mechanisms.
Carbohydrate utilisation by cell suspension cultures of Phaseolus vulgaris
Authors: Botha Frederik C. , O'Kennedy Maretha M.
Published: March 2003

Uptake of sugar by Phaseolus vulgaris cell suspension cultures from a sucrose supplemented medium is predominantly in the hexose form. This is due to a rapid cleavage of the sucrose by an apoplastic acid invertase activity and an apparent very low demand for and uptake of carbon from the medium prior to induction of cell growth and division. Glucose is preferentially taken up, leading to an accumulation of fructose in the medium. However, when the glucose is depleted the cells do take up the fructose at a rate similar to that of glucose. When glucose or fructose is supplied individually to cell cultures, both are utilised very efficiently with growth slightly better on the fructose medium. Hexose uptake is largely an active process with diffusion uptake even at the highest concentrations (> 50 mM) contributing less than 30%. The hexose uptake system of the cells has a greater affinity for glucose (Km= 240 µM) than for fructose (Km= 960 µM) but the maximum uptake (Vmax) is similar. The major difference in the kinetic properties of hexose uptake is that glucose is a strong inhibitor of fructose uptake, while fructose has little effect on glucose uptake. The differences in the kinetic properties of the uptake system for the two hexoses can largely explain the observed pattern of hexose utilisation when both glucose and fructose are present in the medium.
A cDNA encoding a proline‐rich protein from Cicer arietinum. Changes in expression during development and abiotic stresses
Authors: Muñoz Francisco J. , Dopico Berta , Labrador Emilia
Published: March 2003

The proline‐rich proteins (PRPs) form a class of plant cell wall structural proteins. The expression of PRP genes is organ‐ and tissue‐specific and it is induced in response to wounding, infection and other stress conditions, but the role of these proteins in the cell wall during development and stress has not yet been established. Our objective was the characterization of a cDNA clone, termed CanPRP, isolated from a cDNA library of growing epicotyls of Cicer arietinum, and the study of the relationship between its expression and cell wall modifications during growth. CanPRP differential expression was analysed by northern blot through epicotyl growth, under different growth conditions and in different organs of chickpea. CanPRP encodes a putative PRP that contains 15 alternating pentapeptide repeats: Pro‐Pro‐Val‐Tyr‐Lys and Pro‐Pro‐Val‐Glu‐Lys, typical features of cell wall PRPs. The levels of PRP transcripts are almost undetectable in young epicotyls and increase during epicotyl growth, with the highest levels of expression found once growth begins to cease and the cell wall starts to strengthen. Accordingly, the stem of chickpea displays the highest level of expression in the basal internode, with reduced growth, decreasing towards the apex. Expression of the CanPRP clone was induced by osmotic and saline stress which inhibited growth. We conclude that the protein deduced from the CanPRP clone participates in the cell wall‐hardening process in either the stress‐mediated inhibition of growth or when cell growth ceases as development takes place.
Effects of ozone and elevated atmospheric carbon dioxide on carbohydrate metabolism of spruce needles. Catabolic and detoxification pathways
Authors: Sehmer L. , Fontaine V. , Antoni F. , Dizengremel P.
Published: March 2003

We have studied the effects of ozone, carbon dioxide and ozone combined with carbon dioxide fumigations on catabolic and detoxification pathways in spruce (Picea abies[L.] Karst.) needles. The results obtained showed an increase in the activities of three enzymes involved in the detoxification pathway, superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (AscPOD, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) when trees were exposed to ozone and to ozone‐carbon dioxide treatments. In these two treatments, the fraction of SOD activity due to the chloroplastic isoform was increased (1.5‐fold). In the needles of trees exposed to ozone and to ozone‐carbon dioxide fumigation, an increase in the activities of glucose‐6‐phosphate dehydrogenase (G‐6‐PDH, EC 1.1.1.49) showed that the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 4.2.1.2], phosphofructokinase [PFK, EC 2.7.1.1] and phosphoenolpyruvate carboxylase [PEPC, EC 4.1.1.31]), was also observed making it possible for the cell to provide the reducing power necessary for detoxification as well as energy and carbon skeletons involved in the repair processes.

When carbon dioxide alone was applied, no effects could be detected on these enzyme activities. However, when carbon dioxide was combined with ozone, the effect of ozone on trees was less than that induced by ozone alone, suggesting that elevated atmospheric carbon dioxide concentrations may to some extent protect plants from ozone injury.
Heat‐shock proteins and cross‐tolerance in plants
Authors: Sabehat Adnan , Weiss David , Lurie Susan
Published: March 2003

Environmental stresses dramatically affect plant survival and productivity. Because plants are immobile, presumably different strategies are required for protection against transient stresses. Under stress, plants synthesize specific proteins, and their accumulation has a role in protecting the tissue from possible damage. An increasing number of studies show the existence of cross‐tolerance in plants: Exposure of tissue to moderate stress conditions often induces resistance to other stresses. Many varied mechanisms explaining the phenomenon of cross‐tolerance have been proposed, and they often, but not always, suggest that specific proteins are induced by one kind of stress and are involved in the protection against other kinds. Although various cross‐protections have been demonstrated in a number of plants, a common mechanism has not been found. This review discusses heat‐shock proteins and their possible roles in protecting the plant under heat and other stresses.
Purification and characterization of strongly chitin‐binding chitinases from salicylic acid‐treated leek (Allium porrum)
Authors: Vergauwen Rudy , Van Leuven Fred , Van Laere André
Published: March 2003

Six chitinases (EC 3.2.1.14) were purified from salicylate‐treated leek (Allium porrum L.). They all strongly bind to chitin and can roughly be divided into two groups. One group has blocked N‐termini, is completely inhibited by 1 mM AgNO3, has a relatively narrow pH optimum, a temperature optimum of 40°C and cannot degrade the tetramer of chitin. The other group has unblocked N‐termini showing homology to the chitin‐binding lectin WGA and is therefore considered as class I chitinases. This group is only moderately inhibited by 1 mM AgNO3 (30%), has a relatively broad pH optimum, has a higher temperature optimum (50 to 60°C) and can degrade the tetramer of chitin to dimers. Furthermore, all isoforms have molecular masses around 34 kDa as estimated by SDS‐PAGE. They have isoelectric points ranging from 4 to 8 and no detectable lysozyme activity. Two isoforms investigated in more detail differ in their antifungal potential.
Antagonistic and synergistic interactions between aluminum and manganese on growth of Vigna unguiculata at low ionic strength
Authors: Taylor Gregory J. , Blarney F. P. C. , Edwards D. G.
Published: March 2003

Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm−1). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required.
Developmentally regulated proteins during differentiation of root system and ectomycorrhiza in Scots pine (Pinus sylvestris) with Suillus bovinus
Authors: Tarkka Mika , Niini Sara S. , Raudaskoski Marjatta
Published: March 2003

Total and radiolabelled proteins from Pinus sylvestris roots, ectomycorrhiza and the ectomycorrhizal fungus Suillus bovinus, were analyzed after separation by 2‐D gel electrophoresis. The purpose was to address the contribution of individual proteins to the development of ectomycorrhiza. In Pinus sylvestris, ectomycorrhiza forms only in the short roots and therefore special attention was paid to the proteins of short roots before formation of ectomycorrhiza. A main result, from comparisons of protein amounts in main and lateral root tips and short roots, was that the specialized growth pattern of short roots is associated with the production of five short root‐specific proteins, and that several proteins of the main and lateral roots are repressed in short roots. At the morphologically different stages of the ectomycorrhiza, only few changes appeared in the amounts of the host and the symbiont proteins. Only one ectomycorrhiza‐specific protein could be distinguished.
Photosynthetic parameters as early indicators of ozone injury in apple leaves
Authors: Soja Gerhard , Pfeifer Ulrike , Soja Anna‐Maria
Published: March 2003

Ozone may affect leaf photosynthesis even before visible symptoms become apparent. This study had the objective to test several parameters of chlorophyll fluorescence and leaf gas exchange for their usefulness as indicators of latent ozone injury in the field. Container‐grown apple trees (Malus domestica Borkh. cv. Golden Delicious) were exposed to four different ozone levels in open‐top chambers. Identical leaves were analyzed in fixed‐time intervals for the characteristics of fast fluorescence induction kinetics in vivo. By using high‐time resolution, characteristic parameters describing the early photochemical events could be calculated according to the JIP‐test. Parameters responsive to the different ozone treatments showed clear dependence on the accumulated ozone dose. Ozone exposure immediately preceding the measurements was more important for the extent of the physiological effects than the total accumulated ozone dose. The most sensitive parameters were the turnover number N (indicating how many times QA has to be reduced for full reduction of all acceptors; positively correlated to ozone dose) and D0, the density of reaction centres per leaf area (negatively correlated to ozone dose). Most parameters analyzed showed clearer responses to ozone on the adaxial than on the abaxial surface of the leaf. Changes in the parameter N were better correlated to ozone doses with low cut‐offs (AOT00 and AOT20), whereas changes in D0 and in the specific electron fluxes per reaction centre were mainly influenced by ozone doses with high cut‐offs (AOT80 and AOT100). Leaf gas exchange analyses revealed a higher ozone sensitivity in carboxylation efficiency than in light utilization efficiency and in the rate of light‐saturated net photosynthesis. All ozone‐induced photosynthetic effects were observed in leaves showing no sign of visible leaf injury. This study identified fluorescence parameters that could be useful for rapid monitoring and early detection of latent leaf injury by ozone.
Inactivation by gene disruption of 2‐cysteine‐peroxiredoxin in Synechocystis sp. PCC 6803 leads to increased stress sensitivity
Authors: Klughammer Barbara , Baier Margarete , Dietz Karl‐Josef
Published: March 2003

2‐Cysteine‐peroxiredoxins (2‐CP) constitute a ubiquitous group of enzymes which reduce toxic alkyl hydroperoxides. In higher plants it was shown that the nuclear encoded 2‐CPs are posttranslationally imported into the chloroplasts, the site of most active oxidative metabolism in plants (Baier and Dietz 1997, Plant J. 12; 179‐190). The genome of the bluegreen alga Synechocystis (EMBL acc. # D64000) encodes a 2‐CP which shares 60% homology to higher plant 2‐CPs on the gene level and about 70% on the level of the mature protein. In order to elucidate the physiological significance of 2‐CPs for photosynthetic organisms, the 2‐CP gene was mutated in Synechocystis sp. PCC 6803 by insertion of a kanamycin gene cartridge. Following complete segregation mutant lines were analyzed for growth and photosynthetic parameters. The mutants revealed decreased growth rates as compared to the wild type. Growth inhibition was relieved after lowering the concentration of Fe or trace elements in the growth medium. Chlorophyll a fluorescence transients as induced by saturating light pulses were used as indicator for the state of photosynthesis. The effective quantum yield decreased at lower light intensities in the mutants as compared to the wild type Synechocystis. Simultaneously, electron transport rates saturated at lower light intensities in the mutants. These data provide the first evidence that 2‐CPs play a pivotal protective role in photosynthesis.
Photosynthesis of two poplar clones under long‐term exposure to ozone
Authors: Soldatini Gian Franco , Lorenzini Giacomo , Filippi Ferruccio , Nali Cristina , Guidi Lucia
Published: March 2003

The photosynthetic response was studied in two clones (Populus deltoides × maximowiczii Eridano and Populus × euramericana I‐214), known for their differential response to ozone (O3) in terms of visible symptoms, when exposed to O3 (60 nl l−1 5 h day−1, 7 and 15 days). The photosynthetic ability was tested using gas exchange and chlorophyll fluorescence analysis. O3 caused a decrease in the CO2 assimilation rate at light saturation level in mature leaves of both clones. Alterations of Chl fluorescence parameters, in particular the Fv/Fm ratio and non‐photochemical quenching were also observed. The effects were similar for both clones and it could not be concluded that differential effects on electron transport capacity were responsible for the observed reduction in photosynthesis. The reduction of photosynthetic rate in Eridano was due mainly to a reduced mesophyll activity, as evidenced by the increase in intercellular CO2 concentration and the minimal changes in stomatal conductance. In contrast, in I‐214, stomatal effects were primarily responsible, although effects on the mesophyll cannot be excluded. Data obtained indicate that the effects observed at the mesophyll level may be attributed to indirect effects caused by membrane disorders.
Peroxisomal manganese superoxide dismutase: Purification and properties of the isozyme from pea leaves
Authors: Palma José M. , López‐Huertas Eduardo , Corpas Francisco J. , Sandalio Luisa M. , Gómez Manuel , Del Río Luis A.
Published: March 2003

The peroxisomal manganese superoxide dismutase (perMn‐SOD; EC 1.15.1.1) was purified to homogeneity for the first time from peroxisomes of pea (Pisum sativum L.) leaves. Peroxisomes were isolated from pea leaves by sucrose density‐gradient centrifugation, and then perMn‐SOD was purified from these organelles by two purification steps involving anion‐exchange and gel‐filtration fast protein liquid chromatography. Pure peroxisomal Mn‐SOD had a specific activity of 2 880 units per mg protein and was purified 3 000‐fold, with a yield of about 7 µg enzyme per kg pea leaves. The relative molecular mass determined for perMn‐SOD was 92 000, and it was composed of four equal subunits of 27 kDa. Ultraviolet and visible absorption spectra of the enzyme showed two absorption maxima at 278 and 483 nm, respectively, and two shoulders at 290 and 542 nm. By isoelectric focusing (pH 5‐7), an isoelectric point of 5.53 was determined for perMn‐SOD. In immunoblot assays, purified Mn‐SOD was recognized by a polyclonal antibody against mitochondrial Mn‐SOD (mitMn‐SOD) from pea leaves. The amino acid sequence of the N‐terminal region of the purified peroxisomal enzyme was determined. A 100% identity was found with the mitMn‐SOD from pea leaves, and high identities were also found with Mn‐SODs from other plant species.
Desaturation of fatty acids as an adaptive response to shifts in light intensity 1
Authors: Klyachko‐Gurvich Geda L. , Tsoglin Lev N. , Doucha Jiři , Kopetskii Jiři , Shebalina (ryabykh) Irina B. , Semenenko Victor E.
Published: March 2003

The comparative study of various unicellular algae, characterised by different carbon chain lengths and different numbers of double bonds per fatty acid (FA) chain, exhibited some similarity in the mechanisms of their response to changes in light conditions, in terms of FA metabolism. In all cases, the optimisation of photosynthetic process resulted in some increase in the relative content of the most unsaturated FA, i.e. C16:3Ω3 and C18:3Ω3 acids in Chlorella cells, C16:4Ω3 and C18:3Ω3 in Dunaliella and Chlamydomonas, C20:5Ω3 in Porphyridium, and C18:2Ω6 in Synechocystis sp. As a rule, these FA were esterified to monogalactosyldiacylglycerols (MGDG), the predominant lipids of thylakoid membranes. Such an increase in the relative content of the polyunsaturated FA usually occurred during the period when the photosynthesis, as well as the biosynthesis of FA de novo, were transiently inhibited following shifts in environmental conditions even at their optimisation. The increase in the relative content of the most unsaturated FA could be performed via desaturation of their immediate precursors. In turn, the deterioration of life conditions (decrease in the light intensity, ageing of cells or cultures, and others) resulted in the accumulation of these precursors. As a result, the cell could change its FA composition without alteration of the whole multistage process but only at the rate of this end reaction of polyunsaturated FA biosynthesis. In the majority of algae, these polyunsaturated acids were Ω3‐homologues, regardless of the difference in their structures, but in some cyanobacteria (e.g. Synechocystis) the relative content of Ω6‐FA increased. The acceleration of Ω3‐FA biosynthesis could be observed, regardless of changes in the total index of unsaturation. This FA desaturation was shown to correlate with the activity of photosystem I (PSI). The specificity of this reaction enables us to assume it to be an adaptive response which provides alterations to lipid‐protein interactions in the membrane that may be important for the self‐assembly of active chlorophyll‐protein complexes for photosynthetic akpparatus.
Coffee seeds contain 11S storage proteins
Authors: Acuña Ricardo , Bassüner Ronald , Beilinson Vadim , Cortina Hernando , Cadena‐Gómez Gabriel , Montes Virginia , Nielsen Niels C.
Published: March 2003

A legumin‐like seed protein was purified from the endosperm of coffee (Coffea arabica L. cv. Colombia). In contrast to legumes, where efficient storage globulin extraction requires buffered saline solutions well above the acidic pKI of the globulins, coffee legumin is readily extracted with acidic aqueous buffers. The coffee legumin migrates like other 11S storage globulins in sucrose gradients. Subunits of coffee legumin have an apparent molecular mass of about 55 kDa after one‐dimensional SDS‐polyacrylamide gel electrophoresis in the absence of a reducing agent. In the presence of 2‐mercaptoethanol, two polypeptides appear that have apparent molecular masses of 33 and 24 kDa. Two full‐length cDNAs were generated from mRNA of developing seeds that were more than 98% homologous. They had open reading frames of 1 458 and 1 467 bp. Each encoded legumin precursors of 486 and 489 amino acids, respectively (Mr=54 136 and 54 818). Examination of a 5′ promoter region from a coffee legumin gene revealed a putative legumin‐box. Genomic DNA from C. arabica was digested with six different restriction endonucleases. After separation of the fragments by electrophoresis, single discrete fragments on DNA blots hybridized strongly to a cDNA probe for the acidic chain. Other fragments that hybridized weakly with this probe were visible after hybridization at very low stringency. DNA from other species and commercially important cultivars that comprise the genus Coffea produced similar results. Immunocytochemical studies revealed that some legumin was detected in the cytoplasm in mature coffee seeds, but that the majority of it was in large storage vacuoles that accounted for most of the cell volume.
Structure‐activity relationships of ABA analogs based on their effects on the gas exchange of clonal white spruce (Picea glauca) emblings
Authors: Fuchs Edgar E. , Livingston N. J. , Abrams S. R. , Rose P. A.
Published: March 2003

ABA analog structure‐function relationships were determined by testing an array of 19 different ABA analogs on 1‐year‐old clonal white spruce (Picea glauca [Moench.] Voss) raised from somatic embryos. The contribution of specific structural features to analog activity was determined from the relative effect of aeroponically applied analog solutions (10−3M) on seedling gas exchange. Seedling transpiration rate (E) and carbon assimilation rate (A) were measured continuously during treatment by means of a whole plant cuvette system. The analogs were racemic about the C‐1′ chiral center and were derived from changes imposed on six regions of the ABA molecule. The activity of optically pure (+)‐S‐ABA and (−)‐R‐ABA were also determined. Analog activity was reduced by changing the oxidation level at C‐1 from the carboxylic acid. The ring C‐2′, C‐3′ double bond was important but not essential to activity. The activity lost through changes in ring structure and C‐1 oxidation level was, in many cases, almost fully restored by replacing the C‐4, C‐5 double bond with a triple bond. Therefore, analogs with a triple bond at C‐4 were more active than their equivalents with a dienoic side chain. Fluorination of the C‐7′ methyl caused a relatively moderate reduction in analog activity. Truncation of C‐1 and C‐2 from the side chain reduced activity to near zero. The unnatural (−)‐ABA enantiomer was inactive.
Involvement of intracellular Ca2+ in blue light‐dependent proton pumping in guard cell protoplasts from Vicia faba
Authors: Shimazaki K. , Goh C.‐H. , Kinoshita T.
Published: March 2003

Recent studies have suggested that Ca2+/calmodulin (CaM) or CaM‐like proteins may be involved in blue light (BL)‐dependent proton pumping in guard cells. As the increase in cytosolic concentration of Ca2+ is required for the activation of CaM and CaM‐like proteins, the origin of the Ca2+ was investigated by measuring BL‐dependent proton pumping with various treatments using guard cell protoplasts (GCPs) from Vicia faba. BL‐dependent proton pumping was affected neither by Ca2+ channel blockers nor by changes of Ca2+ concentration in the medium used for the GCPs. Addition of Ca2+ ionophores and an agonist to GCPs did not induce proton pumping. However, BL‐dependent proton pumping was inhibited by 10 mM caffeine, which releases Ca2+ from the intracellular stores, and by 10 μM 2,5‐di‐(tert‐butyl)‐1,4‐benzohydroquinone (BHQ) and 10 μM cyclopiazonic acid (CPA), inhibitors of Ca2+‐ATPase in the sarcoplasmic and endoplasmic reticulum (ER). By contrast, the inhibitions were not observed by 10 μM thapsigargin, an inhibitor of animal ER‐type Ca2+‐ATPase. The inhibitions by caffeine and BHQ were reversible. Light‐dependent stomatal opening in the epidermis of Vicia was inhibited by caffeine, BHQ, and CPA. From these results, we conclude that the Ca2+ thought to be required for BL‐dependent proton pumping may originate from intracellular Ca2+ stores, most likely from ER in guard cells, and that this origin of Ca2+ may generate a stimulus‐specific Ca2+ signal for stomatal opening.
Light‐triggered electrical events in the thylakoid membrane of plant chloroplasts
Authors: Bulychev Alexander A. , Vredenberg Wim J.
Published: March 2003

An overview is given of electrical events that occur in plant chloroplasts in association with their energization and subsequent photosynthetic performance. Special emphasis is given to the measuring techniques, in particular application of patch‐clamp methods, which enable comparison of light‐induced photocurrent and ‐potential kinetics of the thylakoid with kinetics of changes in chlorophyll fluorescence yield.
Role of bicarbonate in photosystem II, the water‐plastoquinone oxido‐reductase of plant photosynthesis
Authors: Van Rensen Jack J. S. , Xu Chunhe , Govindjee
Published: March 2003

Depletion of bicarbonate (carbon dioxide) from oxygenic cells or organelles not only causes cessation of carbon dioxide fixation, but also a strong decrease in the activity of photosystem II; the photosystem II activity can be restored by readdition of bicarbonate. Effects of bicarbonate exist on both the acceptor as well as on the donor side of photosystem II. The influence on the acceptor side is located between the primary and secondary quinone electron acceptor of photosystem II, and can be demonstrated in intact cells or leaves as well as in isolated thylakoids and reaction center preparations. At physiological pH, bicarbonate ions are suggested to form hydrogen bonds to several amino acids on both D1 and D2 proteins, the reaction center subunits of photosystem II, as well as to form ligands to the non‐heme iron between the D1 and D2 proteins. Bicarbonate, at physiological pH, has an important role in the water‐plastoquinone oxido‐reductase: on the one hand it may stabilize, by conformational means, the reaction center protein of photosystem II that allows efficient electron flow and protonation of certain amino acids near the secondary quinone electron acceptor of photosystem II; and, on the other hand, it akppears to play a significant role in the assembly or functioning of the manganese complex at the donor side. Functional roles of bicarbonate in vivo, including protection against photoinhibition, are also discussed.
The microtubule cytoskeleton does not integrate auxin transport and gravitropism in maize roots
Authors: Hasenstein K. H. , Blancaflor E. B. , Lee J. S.
Published: March 2003

The Cholodny‐Went hypothesis of gravitropism suggests that the graviresponse is controlled by the distribution of auxin. However, the mechanism of auxin transport during the graviresponse of roots is still unresolved. To determine whether the microtubule (MT) cytoskeleton is participating in auxin transport, the cytoskeleton was examined and the movement of H‐IAA measured in intact and excised taxol, oryzalin, and naphthylphthalamic acid (NPA)‐treated roots of Zea mays cv. Merit. Taxol and oryzalin did not inhibit the graviresponse of roots but the auxin transport inhibitor NPA greatly inhibited both auxin transport and graviresponse. NPA had no effect on MT organization in vertical roots, but caused MT reorientation in horizontally placed roots. Regardless of treatment, the organization of MTs in intact roots differed from that in root segments. The MT inhibitors, taxol and oryzalin had opposite effects on the MTs, namely, depolymerization (oryzalin) and stabilization and thickening (taxol), but both treatments caused swelling of the roots. The data indicate that the MT cytoskeleton does not directly interfere with auxin transport or auxin‐mediated growth responses in maize roots.
Tricolorin A, a potent natural uncoupler and inhibitor of photosystem II acceptor side of spinach chloroplasts
Authors: Achnine Lahoucine , Pereda‐Miranda Rogelio , Iglesias‐Prieto Roberto , Moreno‐Sánchez Rafael , Lotina‐Hennsen Blas
Published: March 2003

Tricolorin A, (11S)‐11‐hydroxyhexadecanoic acid 11‐O‐α‐
l‐ rhamnopyranosyl‐(1?3)‐O‐α‐
l‐{2‐O‐(2S‐methylbutanoyl)‐4‐O‐(2S‐methylbutanoyl)}‐rhamnopyranosil‐(1?2)‐O‐β‐
d‐glucopyranosil‐(1?2)‐β‐fucopyranoside‐(1,3′′‐lactone), the major phytogrowth inhibitor isolated from Ipomoea tricolor Cav. (Convolvulaceae) was found to be a potent uncoupler (U50=0.33 μM) of photophosphorylation in spinach chloroplasts. Tricolorin A inhibited H+‐uptake and adenosine 5′‐triphosphate (ATP) synthesis, and stimulated basal and phosphorylating electron flows. Using a combination of two well‐known fluorescent ΔpH probes, 9‐aminoacridine and 9‐amino‐6‐chloro‐2‐methoxyacridine, the uncoupling behavior of tricolorin A was also demonstrated for submitochondrial particles. Polarographic data showed that high concentrations (20 μM) of tricolorin A inhibited photosystem II (PSII) electron flow at the level of plastoquinone B (QB). Chlorophyll (Chl) a fluorescence analysis showed that tricolorin A induced accumulation of QA− and strongly decreased the electron transport capacity, suggesting that the target of this molecule was located at the QB level. The macrocyclic lactone‐type structure of this allelopathic agent proved to be an important structural requirement for uncoupling activity since its hydrolysis caused loss of the inhibitory potential.
Autoinhibition of indoleacetic acid transport in the shoots of two‐branched pea (Pisum sativum) plants and its relationship to correlative dominance
Authors: Li Chun‐Jian , Bangerth Fritz
Published: March 2003

Two‐branched pea plants (Pisum sativum L. cv. Lisa ZS) with different dominance degrees, obtained by removing the epicotyl shortly after germination, were used to study the interaction between the polar transport of indoleacetic acid (IAA) in both branches of the plants and its relationship to correlative dominance. The dominant shoot had higher transport capacity for C‐IAA applied to the cut stump of one side of the Y‐form explant was used, the stronger the H‐IAA transport was inhibited and the more the transported IAA was conjugated above the junction on the other side. The results of these experiments support the autoinhibition hypothesis at junctions. The relationship between elongation growth and IAA export/transport in the two‐branch pea plants is considered.
Low temperature‐wheat‐fungal interactions: A carbohydrate connection
Authors: Gaudet Denis A. , Laroche André , Yoshida Midori
Published: March 2003

Winter annual and perennial crop species grown in the northern boreal ecosystem must survive periods of protracted snow cover and low temperatures during the winter. In deep snow regions, plants are susceptible to winter stresses caused by both snow molds and low temperatures. Therefore, high levels of tolerance to freezing and snow molds are requisite for crops adapted to these regions. Accumulation of soluble carbohydrates in winter wheat during the autumn is linked to both hardening and resistance to attack by snow molds. Snow mold‐resistant cultivars accumulate higher levels of carbohydrate and metabolize them at slower rates than susceptible cultivars. The quantity and quality of carbohydrates, particularly fructans, remaining in the spring after snow mold attack appear important for survival of winter wheat. However, the total accumulation of carbohydrates is dependent on the stage of development of the winter cereal plant at the beginning of the winter. Recent research findings have shown that sugars are pivotal metabolic activators of the sugar‐sensing enzyme, hexokinase, which initiates signal transduction and activation of numerous metabolic genes including host defense genes. Thus, an understanding of the metabolism of soluble carbohydrates, particularly fructans, during plant growth, hardening, and snow mold infection, is essential to the elucidation of survival mechanisms in plants subjected to these winter stresses.
Photoinhibition of photosystem II in tobacco plants overexpressing glutathione reductase and poplars overexpressing superoxide dismutase
Authors: Tyystjärvi Esa , Riikonen Marjukka , Arisi Ana‐Carolina M. , Kettunen Reetta , Jouanin Lise , Foyer Christine H.
Published: March 2003

We studied photoinhibition in two cultivars of tobacco (Nicotiana tabacum L.) expressing the bacterial gor gene in the cytosol and in four lines of poplar (Populus tremula×P. alba) expressing the FeSOD gene of Arabidopsis thaliana in the chloroplast. The respective total activities of glutathione reductase (EC 1.6.4.2) in leaves of gor tobaccos and superoxide dismutase (EC 1.15.1.1) in the FeSOD poplars were 5–8 times higher than in the respective untransformed control plants. Leaves of control and transformed plants were subjected to high‐light stress at 20°C, and photoinhibition of photosystem II (PSII) was measured by oxygen evolution and chlorophyll fluorescence. The leaves were illuminated both in the presence and absence of lincomycin, which inhibits chloroplast protein synthesis. In both cases, the time course of loss of PSII activity was identical in plants overproducing superoxide dismutase (SOD) and in the untransformed controls, suggesting that the ability to convert superoxide to hydrogen peroxide is not a limiting factor in protection against photoinhibition, or in the repair of photoinhibitory damage or that the site of O2− production is not accessible to the transgene product. The rate constant of photoinhibition, measured in lincomycin‐treated leaves, was smaller in glutathione reductase (GR) overproducing tobacco cv. Samsun than in the respective wild‐type, but this difference was not seen in cv. Bel W3. The steady‐state level of PSII activity measured when the PSII repair cycle was allowed to equilibrate with photoinhibitory damage under high light was not higher in the GR overproducing cv. Samsun, suggesting that the repair of photoinhibitory damage was not enhanced in plants overproducing GR in the cytosol.
The role of gibberellin biosynthesis in the control of growth and flowering in Matthiola incana
Authors: Hisamatsu Tamotsu , Koshioka Masaji , Kubota Satoshi , Fujime Yukihiro , King Rod W. , Mander Lewis N.
Published: March 2003

Recently, it was found that stem elongation and flowering of stock Matthiola incana (L.) R. Br. are promoted by exogenous gibberellins (GAs), including GA4, and also by acylcyclohexanedione inhibitors of GA biosynthesis, such as prohexadione‐calcium (PCa) and trinexapac‐ethyl (TNE). Here, because it was unclear how GA biosynthetic inhibitors could promote stem elongation and flowering, their effect on GA biosynthesis has been examined by quantifying endogenous GA levels; also, the sensitivity of stem elongation and flowering to various GAs in combination with the inhibitors was examined. Stem elongation and flowering were most effectively promoted by GA4 when combined with PCa and, next in order, by 2,2‐dimethyl‐GA4, PCa, GA4+TNE, TNE, GA9+PCa and by GA4. There was little or no promotion by GA1, GA3, GA9, GA13, GA20 and 3‐epi‐2,2‐dimethyl‐GA4. Both the promotive effects of the acylcyclohexanediones on stem elongation and flowering, particularly when applied with GA4, and the fact that TNE caused a build‐up of endogenous GA4 imply that one effect of TNE at the lower dose involved an inhibition of 2β‐hydroxylation of GA4 rather than an inhibition of 20‐oxidation and 3β‐hydroxylation of GAs which were precursors of GA4. Overall, these results indicate that: (1) GAs with 3β‐OH and without 13‐OH groups (e.g. GA4) are the most important for stem elongation and flowering in M. incana; (2) growth promotion rather than inhibition can result if an acylcyclohexanedione acts predominantly to slow 2β‐hydroxylation and so slows inactivation of active gibbberellins, including GA4. It follows that a low dose of an acylcyclohexanedione can be a ‘growth enhancer’ for any applied GA that is liable to inactivation by 2β‐hydroxylation.
Non‐invasive measurements of leaf epidermal transmittance of UV radiation using chlorophyll fluorescence: field and laboratory studies
Authors: Barnes Paul W. , Searles Peter S. , Ballaré Carlos L. , Ryel Ronald J. , Caldwell Martyn M.
Published: March 2003

Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe‐PAM fluorometer to test the utility of this technique as a means of non‐intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris, grown under controlled‐environmental conditions, F(UV‐B)/F(BG) was negatively correlated with whole‐leaf UV‐B‐absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r2=0.77 [UV‐B]; 0.85 [UV‐A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field‐grown Glycine max exposed to near‐ambient solar UV‐B at a mid‐latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV‐B)/F(BG) values (i.e., lower UV‐B epidermal transmittance) than those exposed to attenuated UV‐B, but solar UV‐B reduction had a minimal effect on F(UV‐B)/F(BG) in plants growing at a high‐latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV‐B)/F(BG) when exposed to very high supplemental UV‐B (biologically effective UV‐B=14–15 kJ m−2 day−1) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica, showed significant increases in F(UV‐B)/F(BG) relative to those receiving ambient UV‐B. These anomalous fluorescence changes were associated with increases in BG‐absorbing pigments (anthocyanins), but not UV‐B‐absorbing pigments. These results indicate that non‐invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV‐B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG‐absorbing pigments that interfere with these indirect measurements of UV‐transmittance.
Protochlorophyllide‐independent import of two NADPH:Pchlide oxidoreductase proteins (PORA and PORB) from barley into isolated plastids
Authors: Dahlin Clas , Aronsson Henrik , Almkvist Jenny , Sundqvist Christer
Published: March 2003

The enzyme catalysing the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), NADPH:Pchlide oxidoreductase (POR; EC 1.6.99.1), is a nuclear‐encoded protein that is post‐translationally imported to the plastid. In barley and Arabidopsis thaliana, the reduction of Pchlide is controlled by two different PORs, PORA and PORB. To characterise the possible Pchlide dependency for the import reaction, radiolabelled precursor proteins of barley PORA and PORB (pPORA and pPORB, respectively) were used for in vitro assays with isolated plastids of barley and pea with different contents of Pchlide. To obtain plastids with different endogenous levels of Pchlide, several methods were used. Barley plants were grown in darkness or in greenhouse conditions for 6 days. Alternatively, greenhouse‐grown pea plants were incubated for 4 days in darkness before plastid isolation, or chloroplasts isolated from greenhouse‐grown plants were incubated with Δ‐aminolevulinic acid (ALA), an early precursor in the Chl biosynthesis resulting in elevated Pchlide contents in the plastids. Both barley pPORA and pPORB were effectively imported into barley and pea chloroplasts isolated from the differentially treated plants, including those isolated from greenhouse‐grown plants. The absence or presence of Pchlide did not significantly affect the import capacity of barley pPORA or pPORB. Assays performed on stroma‐enriched fractions from chloroplasts and etioplasts of barley indicated that no post‐import degradation of the proteins occurred in the stroma, irrespective of whether the incubation was performed in darkness or in light.
Soluble proteins and dehydrins in nitrogen‐fertilized Scots pine seedlings during deacclimation and the onset of growth
Authors: Kontunen‐Soppela Sari , Taulavuori Kari , Taulavuori Erja , Lähdesmäki Pekka , Laine Kari
Published: March 2003

Deacclimation of Scots pine (Pinus sylvestris) in northern Finland (65°N) was studied from the perspective of protein metabolism, which was related to nitrogen fertilization. Two‐year‐old seedlings were fertilized with calcium ammonium nitrate (0, 442 and 884 kg N ha−1) in the summer prior to the study. Needles were harvested for analyses at 3‐week intervals during the natural deacclimation period from mid‐March to the beginning of June 1998. Deacclimation was followed by monitoring various physiological variables: freezing resistance decreased and osmotic potential increased during the experiment and needle dry weight increased from bud flushing onwards. The concentration of soluble proteins in needles was higher in fertilized seedlings but decreased transiently in the 884 kg N ha−1 fertilized seedlings before budbreak. The abundance of several small polypeptides (17–32 kDa) decreased in the spring. A 60‐kDa protein, identified by immunoblotting as a dehydrin, was detected in all treatments. The quantity of this dehydrin decreased with resumption of growth, along with the appearance of 50‐ and 56‐kDa dehydrins. The concentration of these dehydrins decreased during dehardening more rapidly in fertilized seedlings than in the control plants. The fertilized seedlings started to grow earlier than the unfertilized plants. In conclusion, nitrogen fertilization provided good reserves for new growth but did not affect deacclimation of pine needles.
Antioxidant metabolite levels in ozone‐sensitive and tolerant genotypes of snap bean
Authors: Burkey Kent O. , Wei Caimiao , Eason Gwendolyn , Ghosh Parthasarathi , Fenner Gregory P.
Published: March 2003

Ozone‐sensitive and tolerant genotypes of snap bean (Phaseolus vulgaris L.) were compared for differences in leaf ascorbic acid (vitamin C), glutathione and α‐tocopherol (vitamin E) content to determine whether antioxidant levels were related to ozone tolerance. Seven genotypes were grown in pots under field conditions during the months of June and July. Open top chambers were used to establish either a charcoal filtered (CF) air control (36 nmol mol−1 ozone) or a treatment where CF air was supplemented with ozone from 8:00 to 20:00 h with a daily 12 h mean of 77 nmol mol−1. Fully expanded leaves were analyzed for ascorbic acid, chlorophyll, glutathione, guaiacol peroxidase (EC 1.11.1.7) and α‐tocopherol. Leaf ascorbic acid was the only variable identified as a potential factor in ozone tolerance. Tolerant genotypes contained more ascorbic acid than sensitive lines, but the differences were not always statistically significant. Genetic differences in glutathione and α‐tocopherol were also observed, but no relationship with ozone tolerance was found. Guaiacol peroxidase activity and leaf α‐tocopherol content increased in all genotypes following a one week ozone exposure, indicative of a general ozone stress response. Ozone had little effect on the other variables tested. Overall, ozone sensitive and tolerant plants were not clearly distinguished by differences in leaf antioxidant content. The evidence suggests that screening for ozone tolerance based on antioxidant content is not a reliable approach.