bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of plant nitrogen status on the contribution of arbuscular mycorrhizal hyphae to plant nitrogen uptake
Authors: Hawkins Heidi‐Jayne , George Eckhard
Published: March 2003

The contribution of hyphae of Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) to the acquisition of mineral nitrogen by Triticum aestivum L. cv. Hano (wheat) was tested under conditions of low P and high N (+N−P) or low N (−N−P). Mycorrhizal colonisation increased the shoot dry weight and plant tissue concentrations of P and cations. However, N tissue concentrations of mycorrhizal plants were not increased, although nitrate reductase activities were significantly higher (in vivo activity) in +N−P mycorrhizal compared to non‐mycorrhizal roots. Severe plant N deficiency reduced the percentage root length colonised (but not the percentage viable colonisation), hyphal length, total

N uptake by hyphae and dry weight of mycorrhizal plants. Although mycorrhizal colonisation did not affect the overall plant N status, hyphae transported 1% (−N−P) and 7% (+N−P) of the

N‐labelled NH4NO3 to mycorrhizal plants over 48 h. The higher rate of hyphal N uptake was apparently related to the more extensive hyphal growth at the higher level of plant N supply. However, the hyphal N supply was not sufficiently high to sustain adequate N nutrition of the plants supplied with very low amounts of N to the roots. Conversely, a sufficient N supply to the roots was important for the development of an extensive mycelium.
Expression of beta‐tubulin during dormancy induction and release in apical and axillary buds of five woody species
Authors: Bergervoet Jan H. W. , Jing Hai‐Chun , Van Den Hout John W. E. , Delmondez de Castro Renato , Kunneman Bernard P. A. M. , Bino Raoul J. , Groot Steven P. C.
Published: March 2003

Cell cycle activity was studied in apical and axillary buds of Norway maple (Acer platanoides L.), apple (Malus‘M9’), pedunculate oak (Quercus robur L.), Scots pine (Pinus sylvestris L.) and rose (Rosa corymbifera‘Laxa’) during dormancy induction and release. Flow cytometric analyses revealed that in dormant buds, cells mainly were quiescent at the G0/G1 phase, while in non‐dormant buds, a significantly higher frequency of G2 cells was found in all species. In western blots accumulation of 55 kDa beta‐tubulin was found in active growing plant material, whereas in dormant buds the accumulation was much lower or below detection level. It was observed for all species that during dormancy induction the amount of beta‐tubulin decreased, while during dormancy release a fast accumulation of beta‐tubulin occurred. The dynamics of the beta‐tubulin accumulation reflected the dormancy status of tree buds of the five species studied suggesting that the beta‐tubulin level might be useful as a marker for the dormancy status in buds of temperate woody species.
Molecular characterization and expression of starch granule‐bound starch synthase in the sink and source tissues of sweet potato
Authors: Wang Shu‐Jen , Yeh Kai‐Wun , Tsai Chia‐Yin
Published: March 2003

In an effort to study regulation of starch synthesis in the source and sink tissues, a cDNA clone for starch granule‐bound starch synthase (GBSSI), which encodes a 67‐kDa protein, was isolated from a cDNA library prepared from tuberous roots of sweet potato (Ipomoea batatas Lam. cv. Tainong 62). This GBSSI protein contains a signal peptide of 77 amino acids, and the mature protein has a molecular mass of about 59 kDa. The mature protein shares 75–85% sequence identity with GBSSIs of dicotyledonous plants and about 70% identity with those of monocotyledons. The sequence of the signal peptide, on the other hand, differs substantially from those of the dicotyledons and monocotyledons studied, although their hydropathic profiles are all similar. This GBSSI gene was well expressed in tuberous roots, leaves, and stems, but not in roots. However, mechanisms involved in regulating the expression of this gene were different between tuberous roots and leaves. In tuberous roots, the synthesis of GBSSI transcript increased coordinately with tuberous root expansion; nevertheless, accumulation rates of GBSSI protein in starch granules remained constant regardless of tuberous root sizes, suggesting an involvement of post‐transcriptional regulation for the synthesis of this protein. The levels of GBSSI transcript were investigated in photosynthetic tissues during diurnal cycles, and the results suggest that the transcription of the GBSSI gene in leaves is controlled by the endogenous circadian rhythm.
Chloroplast movement in Alocasia macrorrhiza
Authors: Gorton Holly L. , Williams William E. , Vogelmann Thomas C.
Published: March 2003

Chloroplast movements in a rainforest understory plant Alocasia macrorrhiza (L.) G. Don are striking, creating changes in leaf transmittance that are visible to the naked eye. We have characterized the light requirements for these changes and the resulting changes in light penetration to different cell layers within the leaf and through the entire thickness of the leaf. Plants were grown either in a relatively constant, growth‐chamber environment or in a variable, greenhouse environment. Irradiance‐response curves for chloroplast movement were the same for both groups of plants, saturating at about 1 000 μmol m−2 s−1, though only the greenhouse‐grown plants normally encountered light sufficient to drive the movement. Chloroplast movement caused changes in whole‐leaf transmittance on the order of a few percent across the entire visible spectrum. Transmittance changes were larger within the leaf, especially directly under the palisade layer. Chloroplast movement could be manipulated experimentally by removing blue wavelengths from the spectrum of incident light or by treating with cytochalasin D.
Differential response of a sensitive and tolerant sugarbeet line to Cercospora beticola infection and UV‐B radiation
Authors: Levall Mats W. , Bornman Janet F.
Published: March 2003

Increased ultraviolet‐B (UV‐B, 280–320 nm) radiation, due to depletion of stratospheric ozone, is an increasing threat to living organisms. Furthermore, increased ground level temperatures as a consequence of global warming may favour development of pathogens, such as Cercospora beticola, that thrive at high temperatures. This study evaluates the effect of combined UV stress and Cercospora leaf‐spot disease on young sugarbeet plants (Beta vulgaris L.). An inoculum consisting of twelve European isolates of C. beticola Sacc. was used in the experiments. One Cercospora‐sensitive and one Cercospora‐tolerant sugarbeet line were analysed from growth regimes where plants were grown either under visible radiation alone or with supplemental UV‐B. Photosynthetic pigments and partial reactions of photosynthesis, including potential yield and quantum yield under illumination, non‐photochemical quenching (qNPQ) and photochemical quenching (qP), were measured to assess plant response. The combination of Cercospora and supplemental UV‐B radiation in the sensitive line resulted in a decreased photosynthetic efficiency, shown by qNPQ and quantum yield under illumination as compared with that for either stress applied alone. The Fv/Fm was unchanged for plants subjected to UV‐B radiation without infection, although the qNPQ decreased. The Cercospora‐tolerant line showed no significant differences under the different treatments. Thus, the line tolerant to Cercospora infection also proved to be tolerant to UV‐B radiation alone and in combination with the infection.
Evaluation of the importance of lactate for the activation of ethanolic fermentation in lettuce roots in anoxia
Authors: Kato‐Noguchi Hisashi
Published: March 2003

According to the Davies–Roberts hypothesis, plants primarily respond to oxygen limitation by a burst of lactate production and the resulting pH drop in the cytoplasm activates ethanolic fermentation. To evaluate this system in lettuce (Lactuca sativa L.), seedlings were subjected to anoxia and in vitro activities of alcohol dehydrogenase (ADH, EC 1.1.1.1), pyruvate decarboxylase (PDC, EC 4.1.1.1) and lactate dehydrogenase (LDH, EC 1.1.1.27) and concentrations of ethanol, acetaldehyde and lactate were determined in roots of the seedlings. The in vitro activities of ADH and PDC in the roots increase in anoxia, whereas no significant increase was measured in LDH activity. At 6 h, the ADH and PDC activities in the roots kept in anoxia were 2.8‐ and 2.9‐fold greater than those in air, respectively. Ethanol and acetaldehyde in the roots accumulated rapidly in anoxia and increased 8‐ and 4‐fold compared with those in air by 6 h, respectively. However, lactate concentration did not increase and an initial burst of lactate production was not found. Thus, ethanol and acetaldehyde production occurred without an increase in lactate synthesis. Treatments with antimycin A and salicylhydroxamic acid, which are respiratory inhibitors, to the lettuce seedlings in the presence of oxygen increased the concentrations of ethanol and acetaldehyde but not of lactate. These results suggest that ethanolic fermentation may be activated without preceding activation of lactate fermentation and may be not regulated by oxygen concentration directly.
Responses to cadmium in leaves of transformed poplars overexpressing Γ‐glutamylcysteine synthetase
Authors: Arisi A.‐C. M. , Mocquot B. , Lagriffoul A. , Mench M. , Foyer C. H. , Jouanin L.
Published: March 2003

Poplars overexpressing a bacterial Γ‐glutamylcysteine synthetase (Γ‐ECS) in the cytosol (lines ggs11 and ggs28) had a 30‐fold increase in foliar Γ‐ECS activity relative to untransformed controls. Foliar Γ‐glutamylcysteine (Γ‐EC) was increased by 10‐fold while foliar glutathione accumulation increased by up to 3.5‐fold in the leaves of the transformants. Untransformed and transformed poplars were grown with different soil concentrations of cadmium (0–1100 μg g−1 soil) for 2 weeks. Cadmium accumulated in the leaves of both transformed and untransformed poplars and growth was inhibited. Growth inhibition and foliar cadmium accumulation were greatest at the highest soil cadmium concentrations in all lines. Exposure to cadmium enhanced the foliar cysteine, Γ‐EC and glutathione pools in all lines but less glutathione was present in the leaves of the untransformed controls than the transformants under all growth conditions. Cadmium‐induced changes in the activities of malic enzyme, isocitrate dehydrogenase and guaiacol peroxidase were less pronounced in the leaves of the transformed poplars overexpressing Γ‐ECS than in the untransformed controls. Glutamate dehydrogenase and glutathione reductase activities were unchanged by exposure to cadmium. We conclude that overexpression of Γ‐ECS activity and foliar glutathione accumulation in transformed poplar allows greater tissue cadmium accumulation but has only a marginal effect on cadmium tolerance in poplar.
Sugars enhance the expression of gibberellin‐induced genes in developing petunia flowers
Authors: Neta‐Sharir Inbal , Shoseyov Oded , Weiss David
Published: March 2003

Sugar is essential for the development of detached Petunia hybrida flowers. We have shown that sucrose (Suc) and gibberellic acid (GA3) are required for anthocyanin accumulation and the expression of various genes in developing petunia corollas. The effect of GA3 on the expression of the gibberellin‐induced gene and chalcone synthase gene, in detached corollas, was promoted by metabolic sugars such as Suc, glucose (Glc) and fructose, but not by the nonmetabolized 3‐O‐methylglucose and the sugar alcohol, mannitol. Several pieces of evidence support sugars’ signaling role in the corollas and the possible involvement of hexokinase as the sugar sensor. Mannose, which is inefficiently metabolized but is phosphorylated by hexokinase at efficiency similar to Glc, was as effective as Glc in promoting gene expression and pigmentation. 2‐Deoxyglucose, which is a substrate for hexokinase but is not metabolized in glycolysis, also promoted gene expression. On the other hand, mannoheptulose, a competitive inhibitor of hexokinase, completely abolished the promotive effect of Glc. We suggest that sugar‐phosphorylation‐related signal transduction interacts with the gibberellin signal to induce gene expression and anthocyanin accumulation in developing petunia corollas.
The xanthophyll cycle is induced by light irrespective of water status in field‐grown lavender (Lavandula stoechas) plants
Authors: Munné‐Bosch Sergi , Alegre Leonor
Published: March 2003

The water relations, the photosynthetic capacity and the pigment content of leaves, i.e. chlorophylls, carotenes and xanthophylls, were analysed during the summer drought and recovery after autumn rainfalls in lavender (Lavandula stoechas L.) plants grown in Mediterranean field conditions. Summer drought caused photoinhibition of photosynthesis and significant decreases in chlorophylls (by ca 75%), β‐carotene (by ca 65%), and lutein and neoxanthin (by ca 50%), although their contents remained unaltered between predawn and midday, suggesting a progressive decrease in response to drought. In contrast, the levels of violaxanthin decreased from predawn to midday, giving rise to enhanced formation of zeaxanthin and antheraxanthin in high light. Zeaxanthin and antheraxanthin formation was not induced by water deficit. Although the levels of photosynthetic pigments were severely affected by water deficit, carotenoids decreased less than chlorophylls, which resulted in increased levels of carotenoids per unit of chlorophyll. We conclude that the enhanced formation of zeaxanthin in high light and the increased levels of carotenoids per unit of chlorophyll observed in water‐stressed plants may help to avoid photoinhibitory damage to the photosynthetic apparatus.
Effect of N source on concentration of Rubisco in Eucalyptus diversicolor, as measured by capillary electrophoresis
Authors: Warren Charles R. , Chen Zu‐Liang , Adams Mark A.
Published: March 2003

Proteins in plant tissues have been extensively characterised by conventional methods such as liquid chromatography and polyacrylamide gel electrophoresis – methods that are tedious and time‐consuming. Capillary electrophoresis is potentially a more simple and cost‐effective method (with respect to time and consumables) but needs substantial development, especially for native plants which are frequently poor in protein and rich in interfering substances (oils, tannins, phenols). We report here the development of capillary electrophoresis (CE) for the separation of SDS‐protein complexes (by molecular mass) and their quantification in plant tissues. In leaf extracts, two peaks dominated the electropherograms, these peaks had migration times corresponding to the small and large subunits of Rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase; EC 4.1.1.39) and co‐migrated with added purified Rubisco. Linearity of peak area, reproducibility of migration time and peak areas for the small and large subunit were excellent, suggesting Rubisco could be quantified with a high degree of accuracy. We determined how the concentration (0.5 or 4 mM) and form of N applied (nitrate versus ammonium) affects partitioning of N to Rubisco in seedlings of Eucalyptus diversicolor. Analysis of extracts from leaves of Eucalyptus diversicolor was only possible after precipitation of proteins with trichloroacetic acid (TCA). Precipitation with TCA was highly reproducible and recovery of added Rubisco through procedures of extraction, precipitation and analysis were close to 100% for both subunits. An 8‐fold difference in the concentration of N applied did not affect total N, the concentration of Rubisco or the fraction of N present as Rubisco. The similarity of total N may well reflect faster rates of growth in those plants receiving 4 mM N, and a subsequent ‘dilution’ of tissue N. The N source did not affect total N, the concentration of Rubisco or the fraction of N present as Rubisco. Despite similar Rubisco concentrations, the total concentration of soluble proteins was greater in ammonium‐grown plants.
Proliferating cell nuclear antigen expression in maize seed development and germination: Regulation by phytohormones and its association with putative cell cycle proteins
Authors: Herrera Ivonne , De La Paz Sánchez María , Molina Juan , Plasencia Javier , Vázquez‐Ramos Jorge M.
Published: March 2003

The proliferating cell nuclear antigen (PCNA) plays a fundamental role in DNA replication and repair and recently, it has been found associated to proteins that control the G1 phase of the cell cycle, such as cyclin D. Maize PCNA cDNA has been cloned and overexpressed in order to raise antibodies. The expression of PCNA has been followed during seed development and seed germination using the homologous antibodies. The protein was found at a constant level during seed development up to 48 days after pollination (DAP) and then the amount declined to very low levels, similar to those found in dry seeds. Upon germination, PCNA levels rose gradually reaching a peak by 20 h germination. Imbibition in the presence of cytokinins (Benzyladenine, BA) produced a sharp increase in amount during the first 3–6 h germination, whereas imbibition in the presence of abscisic acid (ABA) did not alter the pattern of expression as compared with control seeds. Immunoprecipitation experiments showed that PCNA was associated to a putative cyclin D protein during germination and this association was altered by phytohormones. While the complex PCNA‐cyclin D‐like protein was present along the first 15 h of germination under control conditions, it was dissociated after 6 h if embryo axes germinated in the presence of BA or ABA. However, complex dissociation in the presence of BA was due to degradation of the putative cyclin D protein while in the presence of ABA the putative cyclin D was still present. These results are discussed in the context of seed germination and the cell cycle.
Differential sensitivity to ozone in two poplar clones.
Authors: Ranieri Annamaria , Serini Roberta , Castagna Antonella , Nali Cristina , Baldan Barbara , Lorenzini Giacomo , Soldatini Gian Franco
Published: March 2003

The effect of acute O3 exposure (5 h at 150 ppb) on photosynthetic electron transport and the thylakoid polypeptide pattern has been studied in 2‐month‐old cuttings of two poplar clones (Populus deltoides×maximowiczii clone Eridano and P.×euramericana clone I‐214), known for their differential response to O3 in terms of visible symptoms. The more sensitive Eridano developed severe blackish bifacial necrosis concentrated in the interveinal areas of the basal and intermediate leaves, while in the less sensitive I‐214 clone, visible symptoms were slight or entirely absent. A generalized, significant decrease in leaf pigment content was shown by both of the stressed clones, although the decline in β‐carotene content was much more marked in Eridano than in I‐214. Activation of the xanthophyll cycle was not detected in either clone. In both clones, immunoblot analysis of the thylakoid proteins showed a decrease in the levels of all the PSII polypeptides tested following O3 exposure, whereas the PsaA/B protein in the PSI core was more severely affected in Eridano than in I‐214. No changes in the chloroplast structure could be seen on electron microscopic study in either clone. The only visible difference was a great accumulation of starch grains in Eridano. All of these results suggest that O3 exposure induces alterations in the photosynthetic apparatus in both poplar clones, Eridano being affected to a greater extent than I‐214.
Detection and seasonal expression pattern of a pathogenesis‐related protein (PR‐10) in Douglas‐fir (Pseudotsuga menziesii) tissues
Authors: Ekramoddoullah Abul K. M. , Yu Xueshu , Sturrock Rona , Zamani Arezoo , Taylor Doug
Published: March 2003

Previously, a PR‐10 protein Pin m III was described in western white pine. In this study, primers based on cDNA of Pin m III were utilized to obtain the genomic sequence of a Pin m III homologue –Pse m I – in Douglas‐fir. A comparative analysis of a deduced amino acid sequence of Pin m III and Pse m I genes indicated about 80% similarity between the two protein sequences, and a consensus 20 amino acid sequence located around the p‐loop sequence was used to synthesize a peptide of 20 amino acids. An antibody to this synthetic peptide was able to detect the Pse m I protein in Douglas‐fir. The anti‐Pse m I antibody was used in a western immunoblot to monitor seasonal variation of the Pse m I in Douglas‐fir needles and its level was shown to increase with overwintering of Douglas‐fir seedlings. However, unlike the Pin m III, there is no indication that the Pse m I is associated with frost hardiness. Analysis of infected Douglas‐fir roots showed a possible trend to up‐regulation of Pse m I by pathogens such as the laminated root rot fungus, Phellinus weirii. The expression of Pse m I protein in Douglas‐fir seedlings is very low compared to the expression of Pin m III protein in western white pine seedlings. In addition, a light‐harvesting complex I protein, PSI‐F, was identified in Douglas‐fir by N‐terminal amino acid sequencing.
Androgenesis: Affecting the fate of the male gametophyte
Authors: Pechan Paul M. , Smykal Petr
Published: March 2003

Embryogenesis can be initiated directly from microspores or pollen grains. This process is known as androgenesis and is dependent on elicitation of a stress response in microspores and pollen grains. The cell response to stress includes the synthesis of small molecular weight heat shock protein proteins (smHSPs), the predominant heat shock protein family in plants. smHSPs are synthesized in all microspores and pollen grains subjected to stress, whether or not they are potentially androgenic. smHSPs serve as a marker indicating that cells have responded to a stress stimulus. Apart from the need of the stress response, induction of androgenesis is also developmentally regulated. Thus, microspores and pollen grains that are predominantly at the late uninucleate to early bicellular stage of development, around the first pollen mitosis, can be induced to undergo androgenesis. Younger or older cells are unlikely to be induced to undergo this process. For example, once pollen maturation gene products begin to accumulate, bicellular pollen grains become fully committed to the pollen maturation process. Even under stress, such cells cannot be induced to undergo androgenesis. In early bicellular pollen, androgenesis is initiated from the vegetative cell (VC). In contrast to the situation during pollen maturation, the VC, when stressed, continues to synthesize DNA. This is one of the prerequisites for pollen‐derived embryogenesis. The generative cell does not contribute to this process. Reorganization of the cytoskeleton and its polar axis can be observed during androgenesis induction. The first division is usually symmetrical. Based on the time difference between the removal of stress, the first cellular division and the synthesis of the cell wall, the first microspore or pollen grain cell division in Brassica napus can already be termed androgenesis‐related.
Decreased root hydraulic conductivity reduces leaf water potential, initiates stomatal closure and slows leaf expansion in flooded plants of castor oil (Ricinus communis) despite diminished delivery of ABA from the roots to shoots in xylem sap
Authors: Else Mark A. , Coupland David , Dutton Lindsay , Jackson Michael B.
Published: March 2003

Soil flooding reduced stomatal conductance (gs) and slowed transpiration, CO2uptake and leaf elongation inRicinus communiswithin 2–6 h. These flood‐induced responses developed further over the next 21 h. They were not associated with increased delivery of abscisic acid (ABA) in xylem sap. Instead, ABA delivery from flooded roots decreased 6‐fold within 3 h, and remained low thereafter. Root hydraulic conductance (Lp) was depressed 47% below control values within 2 h of soil flooding, and declined further during the next 21 h. The smaller Lp temporarily decreased leaf water potentials (ΨL) by up to −0.4 MPa, and caused visible wilting 3 h into the flooding treatment at 80% relative humidity. Consequently, ABA concentrations in the shoot were increased, as indicated by analyses of phloem sap. Wilting, fall in ΨL and a reduction in gs were delayed for 6 h when 0.6 MPa pneumatic pressure (technical maximum) was applied to the roots. In flooded plants, phloem sap ABA concentrations returned to normal after 24 h. The initial stomatal closure, caused by soil flooding inR. communis, is attributed to decreased leaf hydration arising from the reduced LP of oxygen‐deficient roots. Continued stomatal closure and slow leaf expansion beyond 24 h were presumably achieved by non‐hydraulic means.
A Gβ ‐like protein from soybean
Authors: Nielsen Niels C. , Beilinson Vadim , Bassüner Ronald , Reverdatto Sergei
Published: March 2003

A cDNA clone that encodes a Gβ‐like protein was isolated from germinating soybeans. The deduced amino acid sequence for this protein is similar to other Gβ‐like proteins isolated from plants and animals and contains 7 copies of the WD‐40 repeat. RNA blots and reverse transcriptase polymerase chain reaction (PCR) revealed that mRNA for the soybean Gβ‐like protein is present during seed development and germination, periods during seed ontogeny that are associated with high levels of biosynthetic activity. DNA blot analysis suggested there are only one or two copies of this gene in the soybean genome. Antibodies were raised against recombinant soybean Gβ‐like protein expressed in bacteria. The antibodies reacted with a 35‐kDa soybean protein that was present in minor amounts in developing seeds. The precise functions of Gβ‐like proteins are unknown, but there are indications that they are involved in signal transduction pathways and in this way participate in control of seed growth and development.
Changes in phenylpropanoid metabolites associated with homology‐dependent silencing of phenylalanine ammonia‐lyase and its somatic reversion in tobacco
Authors: Korth Kenneth L. , Blount Jack W. , Chen Fang , Rasmussen Susanne , Lamb Chris , Dixon Richard A.
Published: March 2003

Gene silencing of phenylalanine ammonia‐lyase (PAL) in transgenic tobacco (Nicotiana tabacumL.) is manifested phenotypically by reduced growth, altered leaf morphology, and reduced levels of phenylpropanoid compounds. Here we report the rare event of somatic reversion from silencing to PAL over‐expression in tobacco harboring the beanPAL2gene. This phenomenon allows the comparison of the effects of PAL under‐ and over‐expression in the same plant. A comparison of gene silenced and revertant tissues reveals striking differences in lignin content and monomer composition, and both qualitative and quantitative differences in soluble and cell wall bound phenylpropanoid compounds in the recovered sector.
Oxidative burst in Chenopodium rubrum suspension cells:
Authors: Pfeiffer Wolfgang , Höftberger Margit
Published: March 2003

Lowering of the osmotic value of the medium has been reported previously to induce an oxidative burst in plant cells. This has been explained by a sequence of events, including solute influx, cellular swelling and the activation of stretch‐regulated channels, triggering the production of reactive oxygen species. Moreover, it is known that the plant growth hormone auxin induces protoplast swelling. Together, these findings prompted the hypothesis that plant cells can respond to auxin‐treatment with an oxidative burst. We tested this hypothesis using suspension cultured cells from Chenopodium rubrum L. and 2,7‐dichlorodihydrofluorescein as the indicator for reactive oxygen species. An auxin‐induced oxidative burst was found similar to an osmotically induced burst. Osmotic treatment consisted of a shift from 110 mOsm to 40 mOsm. The naturally occurring halogenated auxin 4‐chloroindole‐3‐acetic acid was the most active compound tested, giving maximum rates of indicator oxidation corresponding to the formation of 4 x 10−15 mol H2O2 cell−1 min−1. Auxin analogous (10 μM) exhibited the following order of effectiveness: 4‐chloride indoleacetic acid (100%), indoleacetic acid (80%), 2,4‐dichlorophenoxyacetic acid (75%), 2‐naphthylacetic acid (52%) and 1‐naphthylacetic acid (47%). Benzoic acid (23%) was used as a control. Fusicoccin (35%) showed only slight stimulation in conjunction with complex kinetics. The detection of oxidative burst responses to 10 nM indoleacetic acid revealed a high sensitivity of the assay for auxin. Cell‐free medium from aged batch cultures and light were also found to stimulate the production of reactive oxygen species. These data indicate that reactive oxygen species can transduce and integrate developmental and environmental signals and thus play a general role in plant growth regulation.
DNA fragmentation in cereal roots indicative of programmed root cortical cell death
Authors: Liljeroth Erland , Bryngelsson Tomas
Published: March 2003

In cereals, a progressively increasing root cortical cell death (RCD) occurs from the root tip and upwards when measured with vital staining methods. In this study, nuclear DNA fragmentation was studied in seminal root segments of wheat and barley in order to investigate if the cell death resembled apoptosis. The fraction of cells with TUNEL‐positive nuclei increased gradually with increasing root age in both the cortex and the stele. Southern analysis showed a typical ladder pattern, indicating nucleosomal fragmentation already in 2‐day‐old root segments, and this became more pronounced in older root segments. DNA fragmentation appeared to be more extensive in wheat than in barley roots. These results confirm earlier studies, where RCD has been found to be earlier initiated and to proceed at a faster rate in wheat. The characteristic DNA fragmentation found in the roots indicates programmed cell death with mechanistic similarities to apoptosis. Ultrastructural examination of nuclei in cortex cells with transmission electron microscopy revealed an increased chromatin condensation in older roots, particularly in wheat.

In addition, we found nucleosomal DNA ladders in young leaf tissue from wheat but not from barley.
Stability of barley aleurone transcripts: Dependence on protein synthesis, influence of the starchy endosperm and destabilization by GA3
Authors: Aalen R. B. , Salehian Z. , Steinum T. M.
Published: March 2003

We have studied the stability of Barley aleurone and embryo expressed (Balem) transcripts in aleurone layers. The Per1,Ole1 and Ole2 transcripts are abundant during desiccation and in dry resting seeds, while B12D and B22E transcripts are expressed mainly during seed maturation and germination. From 21 to 40 days post anthesis (DPA) incubation of aleurone layers resulted in a substantial, but differential reduction in the levels of these transcripts. In contrast, Balem transcript levels in aleurone layers of incubated embryoless grains were (except for B22E) similar to those of freshly dissected layers. Cycloheximide lowered transcript levels significantly. This indicates that a protein‐synthesis‐dependent mRNA‐stabilizing mechanism is active in the aleurone cells when attached to the starchy endosperm. At the onset of seed desiccation (40 DPA), half‐lives of transcripts to be stored in the dry seed were up to several days longer than the half‐life of B22E, which decreases during seed maturation. While the Per1,Ole1 and Ole2 transcript levels decline rapidly in the aleurone layers of mature, germinating seeds, the genes are actively transcribed and their transcripts highly stable in the aleurone of incubated embryoless seeds. The expression of Ole1 and Ole2, as well as Per1, can be repressed 100–1 000‐fold by gibberellic acid (GA3) in a dose‐dependent manner. Abscisic acid can counteract the GA3 repression. Incubations with transcriptional and translational inhibitors indicate that GA3 inhibits the transcription of these genes and at the same time induces a protein‐synthesis‐dependent mechanism destabilizing their mRNA molecules present.
Regulation by light and metabolites of ferredoxin‐dependent glutamate synthase in maize
Authors: Suzuki Akira , Rioual Serge , Lemarchand Sylvie , Godfroy Nelly , Roux Yvette , Boutin Jean‐Pierre , Rothstein Steven
Published: March 2003

The regulation of Fd‐glutamate synthase (Fd‐GOGAT, EC 1.4.1.7) and NADH‐glutamate synthase (NADH‐GOGAT, EC 1.4.1.14) was investigated in maize (Zea mays L. cv. DEA) (1) during development starting from 7‐ to 11‐day‐old seedlings, (2) by treatment of 7‐day‐old etiolated leaves with intermittent light pulses to activate (red) and inactivate (far‐red) phytochromes and (3) in 7‐day‐old green leaves grown under 16‐h light/8‐h dark cycles. Fd‐GOGAT mRNA accumulated 4‐fold, and the enzyme polypeptide (3‐fold) and activity (3‐fold) also increased in leaf cells, while NADH‐GOGAT activity remained constantly low. Leaf‐specific induction of Fd‐GOGAT mRNA (3‐fold) occurred in etiolated leaves by low fluence red light, and far‐red light reversibly repressed the mRNA accumulation. Red/far‐red reversible induction also occurred for Fd‐GOGAT polypeptide (2‐fold) and activity (2‐fold), implicating the phytochrome‐dependent induction of Fd‐GOGAT. In contrast, NADH‐GOGAT activity remained constant, irrespective of red/far‐red light treatments. Fd‐GOGAT showed diurnal changes under light/dark cycles with the maximum early in the morning and the minimum in the afternoon at the levels of mRNA, enzyme polypeptide and activity. Gln diurnally changed in parallel with Fd‐GOGAT mRNA. The induction of Fd‐GOGAT provides evidence that light and metabolites are the major signal for the Gln and Glu formation in maize leaf cells.
Physiological response of Pinus halepensis needles under ozone and water stress conditions
Authors: Manes Fausto , Donato Eugenio , Vitale Marcello
Published: March 2003

The aim of this study was to evaluate how physiological processes of potted Pinus halepensis plants, grown under controlled conditions, were affected by ozone (O3) and/or water stress, integrating the gas exchange and biochemical data with fluorescence OJIP polyphasic transient data. Plants submitted to only water stress (T1) and with ozone (T3) showed a strong decrease in stomatal conductance and gas exchange, coinciding with a reduction of maximum yield of photochemistry (ϕpo) and very negative values of leaf water potential. Simultaneously, a great increase of both PSII antenna size, indicated by absorption per reaction centre, and electron transport per reaction centre were found. The reduction of photosynthesis in the O3‐treated plants (T2) by a slowing down of the Calvin cycle was supported by the increase of related fluorescence parameters such as relative variable fluorescence, heat de‐excitation constant, energy de‐excitation by spillover, and the decrease of ϕpo. We suggest an antagonistic effect between the two stresses to explain the delayed ozone‐induced decrease of stomatal conductance values for T3 with respect to T1 plants, by an alteration of the physiological mechanisms of stomatal opening, which involve the increase of intra‐cellular free‐calcium induced by ABA under co‐occurring water shortage. We emphasise the importance of considering the intensity of the individual stress factor in studies concerning the interaction of stresses.
A GC‐MS method for determination of amino acid uptake by plants
Authors: Persson Jörgen , Näsholm Torgny
Published: March 2003

In this study, we present a rapid, robust and sensitive method for quantification of plant amino acid uptake using universally (U) (13C, 15N)‐labelled amino acids and gas chromatography‐mass spectrometry (GC‐MS). Amino acids were analysed as their tert‐butyldimethylsilyl (tBDMS) derivatives and displayed detection limits in the range 10–100 fmol on column, depending on the amino acid. The technique allows for simultaneous detection and quantification of both unlabelled and isotopically labelled species of amino acids. This makes simple quantification of plant amino acid uptake from an isotopically labelled source possible. The analytical variation was low, concerning total amino acid concentrations (relative standard deviation, rsd, less than 5.3%) as well as enrichment of U‐13C, 15N‐labelled glycine (Gly), arginine (Arg) and glutamic acid (Glu) (rsd<2.1%). An application of the GC‐MS method was conducted on non‐mycorrhizal Pinus sylvestris roots supplied with U‐13C, 15N‐labelled amino acids. Intact, labelled amino acids were traced in root extracts. This provided conclusive evidence of plant root uptake of intact amino acids. Uptake rates of the three amino acids Gly, Glu and Arg in the range 0.5–37.9 μmol g−1 dry weight h−1 were recorded. These rates are comparable with those recorded in earlier studies of amino acid uptake, using other methods, as well as uptake rates measured for nitrate and ammonium.
Steady‐state chlorophyll fluorescence (Fs) measurements as a tool to follow variations of net CO2 assimilation and stomatal conductance during water‐stress in C3 plants
Authors: Flexas Jaume , Escalona José Mariano , Evain Sebastian , Gulías Javier , Moya Ismaël , Osmond Charles Barry , Medrano Hipólito
Published: March 2003

Water stress experiments were performed with grapevines (Vitis vinifera L.) and other C3 plants in the field, in potted plants in the laboratory, and with detached leaves. It was found that, in all cases, the ratio of steady state chlorophyll fluorescence (Fs) normalized to dark‐adapted intrinsic fluorescence (Fo) inversely correlated with non‐photochemical quenching (NPQ). Also, at high irradiance, the ratio Fs/Fo was positively correlated with CO2 assimilation in air, with electron transport rate calculated from fluorescence, and with stomatal conductance, but no clear correlation was observed with qP. The significance of these relationships is discussed. The ratio Fs/Fo, measured with a portable instrument (PAM‐2000) or with a remote sensing FIPAM system, provides a good method for the early detection of water stress, and may become a useful guide to irrigation requirements.
Purification and characterization of the raffinose oligosaccharide chain elongation enzyme, galactan : galactan galactosyltransferase (GGT), from Ajuga reptans leaves
Authors: Haab Canan Inan , Keller Felix
Published: March 2003

Galactan: galactan galactosyltransferase (GGT), an enzyme involved in the biosynthesis of the long‐chain raffinose family of oligosaccharides (RFOs) in Ajuga reptans, catalyses the transfer of an α‐galactosyl residue from one molecule of RFO to another one resulting in the next higher RFO oligomer. This novel galactinol (α‐galactosyl‐myo‐inositol)‐independent α‐galactosyltransferase is responsible for the accumulation of long‐chain RFOs in vivo. Warm treatment (20°C) of excised leaves resulted in a 34‐fold increase of RFO concentration and a 200‐fold increase of GGT activity after 28 days. Cold treatment (10°C/3°C day/night) resulted in a 26‐ and 130‐fold increase, respectively. These data support the role of GGT as a key enzyme in the synthesis and accumulation of long‐chain RFOs. GGT was purified from leaves in a 4‐step procedure which involved fractionated precipitation with ammonium sulphate as well as lectin affinity, anion exchange, and size‐exclusion chromatography and resulted in a 200‐fold purification. Purified GGT had an isoelectric point of 4.7, a pH optimum around 5, and its transferase reaction displayed saturable concentration dependence for both raffinose (Km = 42 mM) and stachyose (Km = 58 mM). GGT is a glycoprotein with a 10% glycan portion. The native molecular mass was 212 kDa as determined by size‐exclusion chromatography. Purified GGT showed one single active band after native PAGE or IEF separation, respectively, which separated into three bands on SDS‐PAGE at 48 kDa, 66 kDa, and 60 kDa. The amino acid sequence of four tryptic peptides obtained from the major 48‐kDa band showed a high homology to plant α‐galactosidase (EC 3.2.1.22) sequences. GGT differed, however, in its substrate specificity from α‐galactosidases; it neither hydrolysed nor transferred α‐galactosyl‐groups from melibiose, galactinol, UDP‐galactose, manninotriose, and manninotetrose. Galactinol, sucrose, and galactose inhibited the GGT reaction considerably at 10–50 mM.
Joint action of phenolic acid mixtures and its significance in allelopathy research
Authors:   Inderjit, Streibig Jens C. , Olofsdotter Maria
Published: March 2003

Although the ecological significance of mixtures of phytotoxins is recognized in research on chemical plant interference (allelopathy), few studies convincingly demonstrate the joint action of phytotoxin mixtures, key to understanding the ecological impact of these materials, using established models from other biological disciplines, e.g. toxicology and pharmacology. Addressing this need, the present study investigates the joint action of the phenolic acids, p‐hydroxybenzoic, p‐coumaric and ferulic acids on root growth inhibition of perennial ryegrass (Lolium perenne L). The Additive Dose Model (ADM) isobole and estimated concentration of phenolic acid mixture were calculated on ED20, ED50 and ED80 from the dose–response curves for the phenolic acids applied alone or in mixtures of fixed ratios. The binary combination of three selected phenolic acids is generally antagonistic relative to the ADM. No evidence for synergistic activities of phenolic acids in the mixture was noted. Since allelopathic activities in nature are largely due to the presence of several compounds in a mixture, the present study advances understanding of the joint action of binary combination of allelochemicals in a mixture.
Genetic transformation of cauliflower (Brassica oleracea var. botrytis) by direct DNA uptake into mesophyll protoplasts
Authors: Radchuk Volodymyr V. , Ryschka Ulrich , Schumann Günter , Klocke Evelyn
Published: March 2003

Mesophyll protoplasts of Brassica oleracea var. botrytis were successfully transformed using polyethylene glycol (PEG). The success of plant transformation depended on both gene transfer and plant regeneration. Parameters, such as PEG and vector concentrations and heat shock conditions were tested in experiments on transient expression of the β‐glucuronidase (EC 3.2.1.31) gene and the most suitable conditions for DNA uptake were determined. Two antibiotic resistance marker genes for neomycin phosphotransferase (EC 2.7.1.95) and hygromycin phosphotransferase (EC 2.7.1.104), and three vector plasmids with different lengths were used to obtain stable transformants.
Reduced gravitropism in inflorescence stems and hypocotyls, but not roots, of Arabidopsis mutants with large plastids
Authors: Yamamoto Kazuyoshi , Pyke Kevin A. , Kiss John Z.
Published: March 2003

The sites of gravity perception are columella cells in roots and endodermal cells in hypocotyls and inflorescence stems. Since plastids are likely to play a role in graviperception, we investigated gravitropism in plastid mutants of Arabidopsis. Previous studies have shown that the arc6 and arc12 (accumulation and replication of chloroplasts) mutants have an average of two large plastids per leaf mesophyll cell. In this study, we found that these arc mutants have altered plastid morphology throughout the entire plant body, including the cells involved in gravity perception. There were no major differences in total starch content per cell in endodermal and columella cells of the wild‐type (WT) compared to arc6 and arc12 as assayed by iodine staining. Thus, the total mass of plastids per cell in arc6 and arc12 is similar to their respective WT strains. Results from time course of curvature studies demonstrated that the plastid mutation affected gravitropism only of inflorescence stems and hypocotyls, but not roots. Thus, roots appear to have different mechanisms of gravitropism compared to stems and hypocotyls. Time course of curvature studies with light‐grown seedlings were performed in the presence of latrunculin B (Lat‐B), an actin‐depolymerizing drug. Lat‐B promoted gravitropic curvature in hypocotyls of both the WT and arc6 but had little or no effect on gravitropism in roots of both strains. These results suggest that F‐actin is not required for hypocotyl gravitropism.
Rhizobium colonization induced changes in membrane‐bound and soluble hydroxyproline‐rich glycoprotein composition in pea
Authors: Olsson Pål Axel , Kjellbom Per , Rosendahl Lis
Published: March 2003

Abundance and distribution of plant cell surface proteins of the hydroxyproline‐rich glycoprotein (HRGP) class were studied in the pea‐Rhizobium symbiosis using immunoblot analysis. The MAC 265‐epitope was especially abundant in pea root nodules containing nitrogen‐fixing Rhizobium bacteria. A 180‐kDa MAC 265‐HRGP dominated in pea shoot plasma membranes, while almost no MAC 265‐HRGP was detected in root plasma membranes. We show here that a major difference between the plant‐derived peribacteroid membrane of the symbiosomes and the root plasma membrane was the presence of a 100‐kDa MAC 265‐HRGP in the former. Arabinogalactan proteins (AGPs), as recognized by the monoclonal antibodies MAC 207 and JIM 8, were not detected in the peribacteroid membrane, while two isoforms (100 and 220 kDa) were detected in shoot and root plasma membranes. Specific MAC 265‐HRGP isoforms were found in the peribacteroid space fraction of the symbiosomes and thus as soluble proteins in the interface between the symbionts. The abundance of the MAC 265‐epitope was much reduced in non‐nitrogen‐fixing nodules when this phenotype resulted from a dicarboxylate transport mutation in Rhizobium. There was no reduction in the abundance of the MAC 265‐epitope in non‐fixing phenotypes resulting from a mutation in the plant. The results suggest that bacterial signals related to the bacterial ability to fix nitrogen, might be responsible for the regulation of HRGP expression in root nodules.
Expression of nitrate transporter genes in tomato colonized by an arbuscular mycorrhizal fungus
Authors: Hildebrandt Ulrich , Schmelzer Elmon , Bothe Hermann
Published: March 2003

PCR amplifications using tomato DNA and degenerate oligonucleotide primers allowed identification of a new putative nitrate transporter, termed NRT2;3. Its sequence showed typical motifs of a high affinity nitrate transporter of the Major Facilitator Superfamily (MFS). The formation of its mRNA was positively controlled by nitrate, and negatively by ammonium, but not by glutamine. In situ hybridization experiments showed that this transporter was mainly expressed in rhizodermal cells. Results from expression studies with two other nitrate transporters, LeNRT1;1 and LeNRT2;1, were essentially in accord with data of the literature. In roots colonized by the arbuscular mycorrhizal fungus Glomus intraradices Sy167, transcript formation of NRT2;3 extended to the inner cortical cells where the fungal structures, arbuscules and vesicles, were concentrated. Northern analyses indicated that the expression of only NRT2;3 among the transporters assayed was higher in AMF colonized tomato roots than in non‐colonized controls. AMF‐colonization caused a significant expression of a nitrate reductase gene of G. intraradices. The results may mean that AMF‐colonization positively affects nitrate uptake from soil and nitrate allocation to the plant partner, probably mediated preferentially by LeNRT2;3. In addition, part of the nitrate taken up is reduced by the fungal partner itself and may then be transferred, when in excess, as glutamine to the plant symbiotic partner.