bluuebunny/crossref_metadata_2025 huggingface dataset:
Agarose embedding affects cell wall regeneration and microtubule organization in sunflower hypocotyl protoplasts
Authors: Caumont Catherine , Petitprez Michel , Woynaroski Stephan , Barthou Henri , Brière Christian , Kallerhoff Jean , Borin Christiane , Souvré André , Alibert Gilbert
Published: May 2006

Sunflower hypocotyl protoplasts (Helianthus annuus L. cv. Emil) divide symmetrically to form loosely associated microcolonies when cultured in liquid medium, whereas when embedded in agarose beads they divide asymmetrically to give rise to embryo‐like structures. To understand the relationship between protoplast embedding and cell division patterns, we studied the deposition of β‐linked glucan and the dynamics of microtubules during early phases of culture. After one day in culture, under both culture conditions, a small proportion of the protoplasts had already begun to rebuild a β‐glucan cell wall and the process reached completion in all protoplasts after 10 days. Callose deposition was faster in agarose than in liquid medium but it concerned only 30–40% of the protoplasts and was not related to either division type. No marked differences were observed in cortical arrays of microtubules. However, in embedded protoplasts perinuclear microtubules formed a well‐defined basket around the nucleus; these microtubules were never observed in liquid‐cultured protoplasts. A narrow preprophase band was present only in dividing protoplasts cultured in liquid medium. The results suggest that asymmetric division could be related to the lack of a narrow preprophase band and that protoplast embedding enhances nucleation or stabilization of microtubules.
Characterization and expression of dehydrins in water‐stressed Sorghum bicolor
Authors: Wood Andrew J. , Goldsbrough Peter B.
Published: May 2006

The effect of water deficit was compared between drought‐tolerant (P954035) and drought‐susceptible (P721N) sorghum (Sorghum bicolor [L.] Moench) genotypes. Gas analysis and leaf water potential (ΨW) measurements indicated clear phenotypic differences between the genotypes in response to water deficit. Both genotypes experienced declines in ΨW, net assimilation rate (A), transpiration rate (E) and stomatal conductance (gs) during stress. P954035, however, dried more slowly and maintained higher values for A, E and gs relative to P721N. In vivo labeling studies and immunoblot analysis using an anti‐dehydrin antibody identified a protein of Mr 21 000 which was induced by water deficit and accumulated to similar levels in both genotypes. The observed molecular changes were essentially identical in both genotypes but differed only in the timing of expression. A sorghum dehydrin cDNA, dhnl, was isolated which encodes a hydrophilic protein of approximately 16.3 kDa with a predicted pl of 10.48. The deduced polypeptide sequence contains two lysine‐rich elements (KKGIMDKIKEKLPG) and shares extensive homology with other dehydrins. DHN 1 mRNA was induced by water deficit in seedlings of both drought‐tolerant and drought‐susceptible sorghum genotypes. Water deficit also induced changes in gene expression in mature preflowering sorghum plants. The anti‐dehydrin antibody detected a protein that accumulated in leaves and roots of stressed plants. The level of DHN 1 mRNA increased in the same tissues, but the abundance of this transcript was much higher in leaves and roots of mature plants than in seedlings.
Differential accumulation of water stress‐related proteins, sucrose synthase and soluble sugars in Populus species that differ in their water stress response
Authors: Pelah Dan , Wang Wangxia , Altman Arie , Shoseyov Oded , Bartels Dorothea
Published: May 2006

Proteins inducible by dehydration and abscisic acid (ABA), have been identified in a number of species and have been suggested to play a role in desiccation tolerance. Recently, we identified a novel boiling‐stable protein (BspA) which accumulated in shoots of aspen (Populus tremula L.) cultured in vitro, in response to gradual water stress and ABA application (Pelah et al. 1995. Tree Physiol. 15: 673–678.). Accumulation of BspA, and of the water stress‐related protein dehydrin dsp‐ 16 and sucrose synthase from the resurrection plant. Craterostigma plantagineum, was examined in two greenhouse‐grown Populus species to investigate the relationship between the presence of the proteins and water stress tolerance. Detached leaves of Populus tomentosa lost more water than Populus popularis, resulting in a significant decrease in leaf water potential. Using electrolyte leakage analysis, it was found that detached leaves of Populus popularis are more tolerant to water stress than those of Populus tomentosa. Using western blots with the corresponding antibodies, we have found in Populus popularis accumulation of BspA and sucrose synthase due to water stress, and the constitutive presence of a dehydrin‐like protein. In contrast, a low expression of BspA was found in Populus tomentosa, but not of sucrose synthase and dehydrin‐like proteins. Desiccation tolerance in many tissues can be partly attributed to soluble sugars. Analysis of the amount of soluble sugars did not reveal clear‐cut differences between the two species, except for significant sucrose accumulation and glucose reduction in water‐stressed Populus tomentosa and increase in glucose in water‐stressed Populus popularis. The data obtained points to a positive correlation between increased water stress tolerance of one poplar species as compared with another and accumulation of water stress‐related proteins and sucrose synthase.
Influence of cesium on tetrapyrrole biosynthesis in etiolated and greening barley leaves
Authors: Shalygo Nikolai V. , Averina Natalija G. , Grimm Bernhard , Mock Hans‐Peter
Published: May 2006

Cesium chloride (CsCl) treatment of greening primary leaves of barley for 8 h inhibited chlorophyl] accumulation in a concentration‐dependent manner and led to the accumulation of excessive amounts of uroporphyrin(ogen) III (URO[gen]) and to a minor extent of heptacarboxylporphyrin(ogen). When dark‐grown leaves were incubated with CsCl, accumulation of URO(gen) was observed only after feeding of the tetrapyrrole precursor 5‐aminolevulinic acid. Western blot analysis showed no apparent difference in content of uroporphyrinogen decarboxylase (EC 4.1.1.37, UROD) or selected proteins involved in tetrapyrrole biosynthesis in extracts of CsCl‐incubated (15 mM) versus control leaves. UROD activity was drastically decreased upon CsCl treatment in leaves incubated in the dark or in the light (44 and 86%, respectively). Selected preceding enzymes of the tetrapyrrole biosynthetic pathway, 5‐aminolevulinic acid dehydratase (EC 4.2.1.24, ALAD) and porphobilinogen deaminase (EC 4.3.1.8, PBGD), were influenced only to a minor extent under standard incubation conditions (15 mMCsCl). Furthermore, the ALA synthesizing capacity did not differ in leaves incubated with and without Cs−cations. UROD activity of crude homogenates from control plants and after partial purification was reduced to 56 and 80%, respectively, upon addition of 10 mMCsCl. Equal concentrations of KCl were not inhibitory. Enzyme assays of the same barley extract in the presence of CsCl yielded no effect on ALAD and a minor loss of PBGD activity. The initial visible cytotoxic effect of CsCl appeared to be a selective inhibition of UROD resulting in accumulation of photosensitizing URO (gen). Consequences of the diminished UROD activity on early steps of the tetrapyrrole biosynthesis and its functional and regulatory significance for the porphyrin synthesis are discussed.
The expansion of maize root‐cap mucilage during hydration. 3. Changes in water potential and water content
Authors: McCully M. E. , Boyer J. S.
Published: May 2006

Root‐cap mucilage from aerial nodal roots of maize has been found to have water potential values of −11 MPa or lower when air dried. The value approaches 0 MPa within 2 min of hydration in distilled water. In this time the expanding gel absorbs only about 0.3% of the water content of fully expanded mucilage. It is concluded that the root‐cap mucilage per se has almost no capacity to retain water in the rhizosphere. Any function that it may play in the slowing of root desiccation would be indirect. For example, mucilage might decrease pore size between and within soil aggregates by pulling the particles together in a cycle of nocturnal efflux of water from the root surface, and diumal dyring during transpiration.
The interaction of high temperature and elevated CO2 on photosynthetic acclimation of single leaves of rice in situ
Authors: Lin Weihong , Ziska Lewis H. , Namuco Offilia S. , Bai Kezhi
Published: May 2006

Rice (Oryza sativa L. cv. IR72) was grown at three different CO2 concentrations (ambient, ambient + 200 μmol mol−1, ambient + 300 μmol mol−1) at two different growth temperatures (ambient, ambient + 4°C) from sowing to maturity to determine longterm photosynthetic acclimation to elevated CO2 with and without increasing temperature. Single leaves of rice showed a cooperative enhancement of photosynthetic rate with elevated CO2 and temperature during tillering, relative to the elevated CO2 condition alone. However, after flowering, the degree of photosynthetic stimulation by elevated CO2 was reduced for the ambient + 4°C treatment. This increasing insensitivity to CO2 appeared to be accompanied by a reduction in ribulose‐1.5‐bisphosphate carboxylase/oxygenase (Rubisco) activity and/or concentration as evidenced by the reduction in the assimilation (A) to internal CO2 (C1) response curve. The reproductive response (e.g. percent filled grains, panicle weight) was reduced at the higher growth temperature and presumably reflects a greater increase in floral sterility. Results indicate that while CO2 and temperature could act synergistically at the biochemical level, the direct effect of temperature on floral development with a subsequent reduction in carbon utilization may change sink strength so as to limit photosynthetic stimulation by elevated CO2 concentration.
Cytokinins from terminal buds of Euphoria longana during different growth stages
Authors: Chen Wen‐Shaw , Huang Kuang‐Liang , Yu Hsiao‐Ching
Published: May 2006

The presence of endogenous cytokinins were detected in the terminal buds of longan (Euphoria longana Lam.) after purification by ion exchange and Sephadex LH‐20 chromatography, and bioassay, enzymic degradation, high‐performance liquid chromatography and gas chromatography‐mass spectrometry. Permethylated derivatives of two highly active cytokinin glucoside compounds from dormant buds were: 6‐(4‐O‐β‐D‐glucosyl‐3‐methyl‐but‐2‐enylamino) purine (zeatin‐O‐glucoside) and 9‐β‐D‐ribofuranosyl‐6‐(4‐hydroxy‐3‐methyl‐but‐2‐enylamino) purine (zeatin riboside‐O‐glucoside). Simultaneously, four active cytokinins from buds at the stages of leaf flush and flower bud initiation were identified as 6‐(4‐hydroxy‐3‐methyl‐but‐trans‐2‐enylamino) purine (zeatin), zeatin‐9‐β‐D‐ribofuranosylpurine (zeatin riboside), 6‐(3‐methyl‐2‐butenyl) aminopurine (isopentenyladenosine, 2iPA) and N‐(3‐methyl‐2‐butenyl) adenine (isopentenyladenine, 2iP). The total cytokinin levels were low at leaf flush, with the zeatin and zeatin riboside in the buds about 70% of the total. In the transition of the terminal bud from leaf flush to dormancy, the principal cytokinins were zeatin‐O‐glucoside and zeatin riboside‐O‐glucoside. However, significant decreases in the levels of zeatin‐O‐glucoside and zeatin riboside‐O‐glucoside and increases in those of zeatin, zeatin riboside, 2iPA and 2iP were observed at flower bud initiation. It is suggested that in longan, the cytokinins that are translocated to the shoots are accumulated in the buds at the dormant stage, and that later there is a considerable increase in free cytokinins during flower bud initiation, leading to the promotion of flower bud development.
Purification and characterization of β‐amylase from leaves of potato (Solanum tuberosum)
Authors: Viksø‐Nielsen Anders , Christensen Tove M. I. E. , Bojko Maja , Marcussen Jan
Published: May 2006

Amylolytic activity is widely distributed in plants. In potato leaves (Solanum tuberosum L.) the abundant amylolytic activity was found to be β‐amylase (EC 3.2.1.2, a‐1,4‐D‐glucan maltohydrolase). β‐Amylase from potato leaves was purified to homogeneity for study of enzyme characteristics. The purification steps included ammonium sulphate precipitation, anion exchange chromatography, affinity chromatography and gel filtration. The end product of α‐1,4‐glucan degradation was maltose. The protein is a 111‐kDa homo‐dimer with a subunit molecular mass of 56 kDa and a pl of 5.6. The pH‐optimum is 6.5 using p‐nitrophenylmaltopentaoside (PNPG5) as substrate. The optimal temperature for hydrolysis is at 40°C. The enzyme is unstable at temperatures above 40°C. The Knt‐value for PNPG5 is 0.73 mM and the activity is inhibited by cyclodextrins. At a concentration of 1 mM, β‐cyclodextrin is a stronger inhibitor than α‐cyclodextrin (68 and 20% inhibition, respectively). Branched glucans (e.g. starch and amylopectin) are superior substrates as compared to long, essentially unbranched glucans (e.g. amylose). This study of the catalytic properties of β‐amylase from potato leaves indicates the importance of β‐amylase as a starch degrading enzyme.
Plasma membrane transport systems in higher plants: From black boxes to molecular physiology
Authors: Logan Helen , Basset Mireille , Véry Anne‐Aliénor , Sentenac Hervé
Published: May 2006

Considerable progress in identifying transport systems of the plant plasma membrane has been made recently. The putative systems cloned to date comprise H+‐ATPases, potassium, chloride and water channels, and carriers involved in the transport of glucose, sucrose, amino acids, peptides, potassium, nitrate, ammonium, phosphate, sulfate, iron and copper. Most of these systems were identified first in Arabidopsis thaliana. Successful cloning strategies have involved the following variety of techniques: complementation of yeast mutants, screening of Arabidopsis mutants, immunoscreening of a cDNA expression library expressed in mammalian cells, screening of genomic and cDNA libraries with probes (or degenerate oligonucleotides) derived from yeast and/or animal genes, or database screening for sequence similarity to eukaryotic counterparts. Many related transport systems have subsequently been identified either by screening libraries directly, or by systematic cDNA sequencing programs. Surprisingly large gene families have been revealed. Heterologous expression systems, such as yeast, Xenopus oocytes or insect cells, provide tools for studying the transport activities, biochemical properties and structure‐function relationships of these systems. Their expression and functions in planta are investigated using northern blot analysis, in situ hybridization, and transgenic approaches. Individual systems encoded by the same gene family can differ in their transport properties and have distinct tissue expression patterns. Such diversity might be central to the integration of solute transport at the whole plant level, allowing the differential expression of sets of transport systems specifically tailored to the requirements of each tissue.
Lipid synthesis and metabolism in the plastid envelope
Authors: Maréchal Eric , Block Maryse A. , Dorne A.‐J. , Douce Roland , Joyard Jacques
Published: May 2006

Plastid envelope membranes play a major role in the biosynthesis of glycerolipids. In addition, plastids are characterized by the occurrence of plastid‐specific membrane glycolipids (galactolipids, a sulfolipid). Plant lipid metabolism therefore has unique features, when compared to that of other eukaryotic organisms, such as animals and yeast. However, the glycerolipid biosynthetic pathway in chloroplasts is almost identical to that found in cyanobacteria, and reflects the prokaryotic origin of the chloroplast. Fatty acids generated in the plastid stroma are substrates for a whole set of enzymes involved in the synthesis of polar lipids of plastid membranes such as galactolipids, the sulfolipid, the phosphatidylglycerol. In addition, fatty acids are exported outside the plastid where they are used for extraplastidial polar lipid synthesis (phosphatidylcholine, phosphatidylethanolamine, etc.). Various desaturation steps leading to the formation of polyunsaturated fatty acids occur in various cell compartments, especially in chloroplasts, using fatty acids esterified to polar lipids as substrates. Furthermore, plant glycerolipids can be metabolized by a series of very active envelope enzymes, such as the galactolipid:galactolipid galactosyltransferase and the acyl‐galactolipid forming enzyme. The physiological significance of these enzymes is however largely unknown. One of the most active pathways involved in lipid metabolism and present in envelope membranes is the oxylipin pathway: polyunsaturated fatty acids that are released from polar lipids under various conditions (injury, pathogen attack) are converted to oxylipin. Thus, the plastid envelope membranes are also involved in the formation of signalling molecules.
Purification, characterization and stability of barley grain peroxidase BP 1, a new type of plant peroxidase
Authors: Rasmussen Christine B. , Henriksen Anette , Abelskov A. Katrine , Jensen Rikke B. , Rasmussen Søren K. , Hejgaard Jørn , Welinder Karen G.
Published: May 2006

The major peroxidase of barley grain (BP 1) has enzymatic and spectroscopic properties that are very differeant from those of other known plant peroxidases (EC 1.11.1.7) and can therefore contribute to the understanding of the many physiological functions ascribed to these enzymes. To study the structure‐function relationships of this unique model peroxidase, large‐scale and Jaboratory‐scale purifications have been developed. The two batches of pure BP 1 obtained were identical in their enzymatic and spectral properties, and confirmed that BP 1 is different from the prototypical horseradish peroxidase isoenzyme C (HRP C). However, when measuring the specific activity of BP 1 at pH 4.0 in the presence of 1 mM CaCl2, the enzyme was as competent as HRP C at neutral pH towards a variety of substrates (mM mg−1 min−1): coniferyl alcohol (930±48), caffeic acid (795±53), ABTS (2,2′‐azino‐di‐[3‐ethyl‐benzothiazoline‐(6)‐sulfonic acid]) (840±47), ferulic acid (415±20), p‐coumaric acid (325±12), and guaiacol (58±3). The absorption spectrum of BP 1 is blue‐shifted compared to that of HRP C with a Soret maximum of 399–402 nm, depending on pH. The prosthetic group was shown to be iron‐protoporphyrin IX, which is characteristic of plant peroxidases. BP 1 is stable from pH 3 to 11, indicating that its unusual spectral characteristics do not result from enzyme instability. The thermostability is also normal with a melting temperature of 75°C at pH 6.6, and 67°C at pH 4.0 and 8.3. It is clear that the unusual properties of BP 1 are genuine, and reflect a novel regulation of plant peroxidase function.
N‐acetylchitooligosaccharides elicit expression of a single (1→3)‐β‐glucanase gene in suspension‐cultured cells from barley (Hordeum vulgare)
Authors: Kaku Hanae , Shibuya Naoto , Xu Peilin , Aryan Arun P. , Fincher Geoffrey B.
Published: May 2006

N‐acetylchitooligosaccharides of degree of polymerization 6 to 8 elicit the synthesis of (1→3)‐β‐glucan endohydrolase (EC 3.2.1.39) activity in suspension‐cultured cells derived from immature barley (Hordeum vulgare) embryos. Corresponding de‐acety‐lated chitooligosaccharides have no effect. Concentrations ofN‐acetylchitoheptaose in the 200 nMrange are sufficient to elicit the response. A 2‐ to 3‐fold increase in (1→3)‐β‐glucanase activity is detected 24 h after the addition of the oligosaccharide. Non‐denaturing gel electrophoresis, coupled with the in situ detection of (1→3)‐β‐glucanase activity in the gels, has enabled the separation of specific isoforms of the enzyme. The increase in (1→3)‐β‐glucanase activity followingN‐acetylchitoheptaose induction is attributable predominantly to enhanced levels of isoenzyme GII, although the barley (1→3)‐β‐glucanase gene family encodes at least seven different isoforms of the enzyme. Northern hybridization analyses with gene‐specific probes confirmed the presence of mRNA encoding isoenzyme GII as the major mRNA in cells treated with the oligosaccharide elicitor. The results therefore demonstrate a specific induction of the (1→3)‐β‐glucanase isoenzyme GII gene following stimulation of barley cells with oligosaccharides of fungal cell wall origin, and further suggest that a plant's response to microbial attack involves transcription of quite specific members of the gene families that encode pathogenesis‐related proteins.
Photoperiodic induction of dormancy and freezing tolerance in Betula pubescens. Involvement of ABA and dehydrins
Authors: Welling Annikki , Kaikuranta Päivi , Rinne Päivi
Published: May 2006

In many woody plants photoperiod signals the initiation of dormancy and cold acclimation. The photoperiod‐specific physiological and molecular mechanisms have remained uncharacterised. The role of abscisic acid (ABA) and dehydrins in photope‐riod‐induced dormancy and freezing tolerance was investigated in birch, Betula pubescens Ehrh. The experiments were designed to investigate if development of dormancy and freezing tolerance under long‐day (LD) and short‐day (SD) conditions could be affected by manipulation of the endogenous ABA content, and if accumulation of dehydrin‐like proteins was correlated with SD and/or the water content of the buds. Experimentally, the internal ABA content was increased by ABA application and by water stress treatment under LD, and decreased by blocking the synthesis of ABA with fluridone under SD. Additionally, high humidity (95% RH) was applied to establish if accidental water stress was involved in SD. ABA content was monitored by gas chromatography‐mass spectrometry with selective ion monitoring (SIM). Short days induced a transient increase in ABA content, which was absent in 95% RH, whereas fluridone treatment decreased ABA. Short days induced a typical pattern of bud desiccation and growth cessation regardless of the treatment, and improved freezing tolerance except in the fluridone treatment. ABA content of the buds was significantly increased after spraying ABA on leaves and after water stress, treatments that did not induce cessation of growth and dormancy, but improved freezing tolerance. In addition to several constitutively produced dehydrins, two SD‐specific proteins of molecular masses 34 and 36 kDa were found. Photoperiod‐ and experimentally‐induced alterations in ABA contents affected freezing tolerance but not cessation of growth and dormancy. Therefore, involvement of ABA in the photoperiodic control of cold acclimation is more direct than in growth cessation and dormancy. As the typical desiccation pattern of the buds was found in all SD plants, and was not directly related to ABA content or to freezing tolerance, this pattern characterises the onset of photo‐period‐induced growth cessation and dormancy. The results provide evidence for the existence of various constitutively and two photoperiod‐induced dehydrins in buds of birch, and reveal characteristics of dormancy and freezing tolerance that may facilitate further investigations of photoperiodic control of growth in trees.
Serine synthesis in cyanobacteria by a nonphotorespiratory pathway
Authors: Colman Brian , Norman Eric G.
Published: May 2006

The pathway of serine synthesis was investigated in six species of cyanobacteria: Anabaena cylindrica, A. variabilis, A. flos‐aquae, Coccochloris peniocystis, Gleo‐capsa alpicola and Phormidium molle. Activity of the enzymes phosphoglycerate (PGA) dehydrogenase (EC 1.1.1.95), phosphoserine transaminase (EC 2.6.1.52) and phosphoserine phosphatase (EC 3.1.3.3) was detected in vitro in all species, but no PGA phosphatase (EC 3.1.3.20) or hydroxypyruvate reductase (EC 1.1.1.26) activity could be detected. Metabolism of [1‐14C]PGA by cell‐free extracts of C. peniocystis resulted in the labelling of serine, alanine and aspartate, which represented 84, 11 and 4% of the labelled amino acid pool, respectively, Labelled serine isolated from these experiments was 100% carboxyl‐labelled indicating that it was formed directly from PGA. The labelling of serine was markedly reduced by 5 mM phosphoserine. These in vitro findings indicate that cyanobacteria are capable of synthesizing serine directly from PGA, independent of ribulose‐1.5‐bisphosphate oxidation, and that the route of serine synthesis via phosphohydroxypyruvate and phosphoserine is the predominant pathway in these organisms.
cDNAs induced by ozone from Atriplex canescens (saltbush) and their response to sulfur dioxide and water‐deficit
Authors: No Eun‐Gyu , Flagler Richard B. , Swize Martha A. , Cairney John , Newton Ronald J.
Published: May 2006

Ozone effects on plant water relations have been reported to be similar to those of water‐deficit. The objective was to identify ozone‐inducible (OI) clones from Atriplex canescens (saltbush) and determine if they were also responsive to water‐deficit as well as SO2. cDNA clones derived from four different polyA RNAs which accumulate in 8‐month‐old shrub leaves exposed to ozone (0.2 μl I−1, 6 h day−1, 7 days) were isolated by differential screening, analyzed by northern blots, sequenced, and gene product homologies with other plant genes were determined. Clone OI12A‐3 has homology with wound‐inducible proteinase inhibitors, whereas clone OI8–3 protein is homologous to thiol proteases. Clones OI2–2 and OI14–3 putatively code for glycine‐rich proteins with repeated motifs (Gly‐Gly‐Gly‐Tyr‐Gly‐His)n and putative cell‐wall‐targeting signal peptides. Clone OI2–2 and particularly clone OI14–3 were also induced by both SO2 and water‐deficit. These data indicate that woody plant genes associated with cell wall protein production and whose expression is induced by several stress factors may be responding to common oxidative stress pathways.
Shikimate dehydrogenase from pepper (Capsicum annuum) seedlings. Purification and properties
Authors: Díaz José , Merino Fuencisla
Published: May 2006

Shikimate dehydrogenase (SKDH, EC 1.1.1.25) was extracted from seedlings of pepper (Capsicum annuum L.) and purified 347‐fold. The purification procedure included precipitation with ammonium sulphate and chromatography in columns of Reactive Red‐agarose, Q‐Sepharose and Sephadex G‐100. Pepper SKDH isozymes are separable only using PAGE. The purified enzyme has a relative molecular mass of 67 000 as estimated by gel filtration. The optimum pH of enzyme activity is 10.5 and the optimum temperature is 50°C, but the enzyme is quickly inactivated at temperatures higher than 40°C. The purified enzyme exhibited typical Michaelis‐Menten kinetics and Km values are 0.087 mM for shikimic acid and 0.017 mM for NADP. The mechanism of reaction is sequential considering NADP as a cosubstrate. Ions such as Ca2+, Mg2+ and Mn2+ activate the enzyme, but Zn2+ and Cu2+ are strong inhibitors. Some phenolic compounds such as guaiacol, protocatechuic acid and 2,4‐D are competitive inhibitors of pepper SKDH, showing Ki values of 0.38 mM, 0.27 mM and 0.16 mM, respectively.
Desiccation increases sucrose levels in Ramonda and Haberlea, two genera of resurrection plants in the Gesneriaceae
Authors: Müller Joachim , Sprenger Norbert , Bortlik Karlheinz , Boller Thomas , Wiemken Andres
Published: May 2006

A few genera of angiosperms are known as ‘resurrection plants’ since their leaves withstand complete desiccation. In many organisms, including some resurrection plants, desiccation tolerance is associated with the accumulation of special carbohydrates. We examined whether this is also true for the two European angiosperm genera of resurrection plants, Ramonda and Haberlea in the Gesneriaceae. Using gas chromatography, non‐structural carbohydrates were determined as a percentage of the dry weight in leaves of Ramonda nathaliae subjected to various desiccation regimes. Sucrose was the predominant soluble carbohydrate in all samples, and its level steadily increased from 2 to 10% during desiccation. Starch amounted to ca 2% in control leaves and disappeared completely within 8 days of desiccation. Considerable amounts (1–2.5%) of raffinose and smaller amounts of its precursor galactinol (1‐a‐galactosyl‐myo‐inositol) were present in control leaves; these carbohydrates showed only minor changes upon desiccation. Similar results were obtained when excised leaves of Ramonda nathaliae, Ramonda myconi and Haberlea rhodopensis were subjected to desiccation. These data indicate that sucrose accumulation is connected to desiccation tolerance in Gesneriaceae; the presence of raffinose may be a pre‐adaptation since this sugar prevents crystallization of sucrose during drying.
Role of the alternative oxidase in limiting superoxide production by plant mitochondria
Authors: Purvis Albert C.
Published: May 2006

Mitochondria isolated from the pericarp tissue of green bell pepper (Capsicum annuum L.) fruit and purified on a Percoll gradient produced superoxide in buffers aerated with oxygen. ADP and uncouplers of the electron transport chain reduced superoxide production. Disulfiram, an inhibitor of the alternative oxidase, enhanced superoxide production. Inhibitors of complex III had little effect on superoxide production by mitochondria which were insensitive to cyanide. Less superoxide was produced when dithiothreitol was used to reduce the sulfhydryl groups of the alternative oxidase protein and the enzyme was activated with pyruvate than when the sulfhydryl groups were oxidized with diamide. A role for the alternative oxidase in limiting the level of reactive oxygen species produced in stressed and senescing plant tissues is suggested.
Proteinase A‐like enzyme from germinated kidney bean seeds. Its action on phaseolin and vicilin
Authors: Rotari Vitalyi , Senyuk Vitalyi , Horstmann Christian , Jivotovskaya Antonina , Vaintraub Iosif
Published: May 2006

A cysteine proteinase that possibly participates in the degradation of phaseolin, the main storage protein of kidney bean (Phaseolus vulgaris L. cv. Moldavian) was isolated from germinating kidney bean seeds and partially characterized. According to its properties it may be classified as a member of a group of homologous cysteine proteinases A, also present in germinating seeds of a number of other plants. The proteinase of this group hydrolyze storage proteins to short peptides. Similarly, the kidney bean proteinase hydrolyzes vicilin, the reserve protein of vetch (Vicia sativa). However, its action on phaseolin is limited to the cleavage of subunits into two approximately equal parts and to the splitting off a small number of short peptides. An explanation of phaseolin resistance to the action of this proteinase is proposed on the basis of the differences of its structure from that of other homologous 7S proteins.
Up‐regulation of two cDNA clones encoding metallothionein‐like proteins in apple fruit during cool storage
Authors: Reid Suzanne J. , Ross Gavin S.
Published: May 2006

We are investigating the molecular basis of low temperature responses in apples, by identifying and characterising fruit genes which show altered expression in response to cool‐storage, Two independent cold‐regulated clones (pAMTI and pAMT2) were isolated from a cDNA library derived from cool‐stored apple (Malus domestics Borkh. cv. Granny Smith) fruit. These clones share only 27% amino acid identity with each other, but both show high similarity to plant metallothionein (MT)‐like proteins. The polypeptide encoded by pAMTI shares similarity with type 2 MT‐like sequences, while that encoded by pAMT2 is similar to others which share a different distribution of cysteine residues. We suggest, these form a ‘type 3’ group of MT‐like clones. Genomic Southern analysis confirmed that there is a family of MT‐like genes in apple. There are differing patterns of pAMTI and pAMT2 expression during apple fruit development, amt 1 RNA was abundant in flowers and during the early stages of development, and decreased as the fruit approached maturity, while amt2 RNA was barely detectable in flowers and young fruit and accumulated with fruit development. In ripe fruit. amt 1. expression was up‐regulated, while amt2 expression was down‐regulated. In leaves, both genes showed increased expression with leaf age. In Granny Smith, Cox's Orange Pippin and Braeburn apple cultivars. both genes were up‐regulated in cool‐stored fruit. In Granny Smith contical tissue, amt RNA levels were elevated within the first 45 min at both 0.5°C and 4°C, but not at 12.5°C. The different patterns of amt1 and amt2 expression during fruit development and in different tissues suggest that the respective genes have distinct controlling elements and may be functionally different. The in vivo roles of the encoded polypeptides, particularly in relation to chilling tolerance or acclimation, are as yet unknown.
Concepts of plant biotic stress. Some insights into the stress physiology of virus‐infected plants, from the perspective of photosynthesis
Authors: Balachandran S. , Hurry V. M. , Kelley S. E. , Osmond C. B. , Robinson S. A. , Rohozinski J. , Seaton G. G. R. , Sims D. A.
Published: May 2006

The consequences of biotic stress have been poorly understood, partly because its application is difficult to control and partly because its physiological consequences are highly variable. Many plant viruses are recognised on the basis of leaf symptoms that depend on localised changes to chloroplast structure and function. This paper reviews recent progress in understanding early interactions between plant viruses and the photosynthetic apparatus, using chlorophyll fluorescence analysis of novel, defined algal‐virus systems and using high resolution imaging of chlorophyll fluorescence and other photosynthetic processes in higher plant systems. We then consider the consequences of viral effects on photosynthetic functioning for whole plants and populations with an emphasis on the potential interactions with other environmental factors. Early responses indicated by increase in both non‐photochemical quenching of fluorescence and increased reduction state of the primary electron transport acceptor QA suggest that, not surprisingly, both photoprotective and photoinhibitory processes contribute to the accelerated local demise of the photosynthetic apparatus and symptom development. In other cases, localised accumulations of carbohydrate and source‐sink imbalance following infection may inhibit gene expression, leading to altered levels of chloroplast protein complexes and enzymes of photosynthetic metabolism coincident with symptom development. Recent experiments suggest that much of the variability in plant responses to biotic stress may result from interactions with other environmental factors, such as light intensity and nutrition. Experiments suggest that virus infections may have greater effects on fitness and competitive ability in low N, high light environments than in shaded, high nutrient conditions. Some ecological implications of these observations are discussed.
Reactive oxygen species and antioxidants: Relationships in green cells
Authors: Alscher Ruth G. , Donahue Janet L. , Cramer Carole L.
Published: May 2006

The imposition of oxidative stress leads to increased production of reactive oxygen species (ROS) in plant cells. Orchestrated defense processes ensue that have much in common between stresses, yet are also particular to the site of action of the stress and its concentration. Possible functional roles of these responses include, but are not restricted to, the protection of the photosynthetic machinery, the preservation of membrane integrity and the protection of DNA and proteins. Superimposed upon our understanding of cellular mechanisms for protection against abiotic stress is a newly discovered role of ROS in signalling and defense response to pathogens (J. L. Dangl, R. A. Dietrich and M. S. Richberg. 1996. Plant Cell 8: 1793–1807). Evidence to date suggests a coordinated response to ROS among different members of the superoxide dismutase (SOD) gene families. A further layer of complexity is afforded by reports of coordination of expression between ascorbate peroxidase and SOD genes. Our understanding of the signalling mechanisms that underlie these coordinated events is in its infancy. An exciting future lies ahead in which the orchestration of successful antioxidant stress responses will be gradually revealed. Current data suggest that complex regulatory mechanisms function at both the gene and protein level to coordinate antioxidant responses and that a critical role is played by organellar localization and inter‐compartment coordination.
Plant glutathione peroxidases
Authors: Eshdat Yuval , Holland Doron , Faltin Zehava , Ben‐Hayyim Gozal
Published: May 2006

Oxidative stress in plants causes the induction of several enzymes, including superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2). The first two are responsible for converting superoxide to H2O2 and its subsequent reduction to H2O, and the third is involved in recycling of ascorbate. Glutathione peroxidases (GPXs, EC 1.11.1.9) are a family of key enzymes involved in scavenging oxyradicals in animals. Only recently, indications for the existence of this enzyme in plants were reported. Genes with significant sequence homology to one member of the animal GPX family, namely phospholipid hydroperoxide glutathione peroxidase (PHGPX), were isolated from several plants. Cit‐SAP, the protein product encoded by the citrus csa gene, which is induced by salt‐stress, is so far the only plant PHGPX that has been isolated and characterized. This protein differs from the animal PHGPX in its rate of enzymatic activity and in containing a Cys instead of selenocysteine (Sec) as its presumed catalytic residue. The physiological role of Cit‐SAP and its homologs in other plants is not yet known.
Hydrogen peroxide‐ and glutathione‐associated mechanisms of acclimatory stress tolerance and signalling
Authors: Foyer Christine H. , Lopez‐Delgado Humberto , Dat James F. , Scott Ian M.
Published: May 2006

Plants adapt to environmental stresses through specific genetic responses. The molecular mechanisms associated with signal transduction, leading to changes in gene expression early in the stress response, are largely unknown. It is clear, however, that gene expression associated with acclimatory responses is sensitive to the redox state of the cell. Of the many components which contribute to the redox balance of the cell, two factors have been shown to be crucial in mediating stress responses. Thiol/disulphide exchange reactions, particularly involving the glutathione pool and the generation of the oxidant H2O2, are central components of signal transduction in both environmental and biotic stresses. These molecules are multifunctional triggers, modulating metabolism and gene expression. Both are able to cross biological membranes and diffuse or be transported long distances from their sites of origin. Glutathione and H2O2 may act alone or in unison, in intracellular and systemic signalling systems, to achieve acclimation and tolerance to biotic and abiotic stresses.
Changes in the biochemical status of plant cells induced by the environmental pollutant ozone
Authors: Schraudner Martina , Langebartels Christian , Sandermann Heinrich
Published: May 2006

Tropospheric ozone will increase during the next decades and will reach the critical threshold concentration of 40 nl l−1 more often in rural regions than in urban areas. Damage inflicted on plants by ozone can be divided into chronic and acute damage, reflecting different defence strategies of the plants. Chronic damage, somewhat similar to a premature senescence, follows disturbances in sugar metabolism, inhibition of photosynthesis, disbalances in the redox‐status and ROS‐production in the chloroplast stroma. The acute damage resembles the hypersensitive response which occurs after a pathogen attack. Either the accumulation of reactive oxygen species (ROS) or the efficiency of scavenging systems in the apoplast may govern the spread of cell death. Probably, different signalling pathways mediate the plant responses, such as ethylene, salicylate and ROS. ROS production and lipid peroxidation take place either on the plasma membrane or in the chloroplastic membrane and lipid hydroperoxides and derivatives, such as jasmonate, can act as signals for subsequent plant reactions. Both kinds of plant responses, i.e., acute as well as chronic damage, can affect the plants' abilities to respond to further stress attacks.
Effects of increased UV‐B radiation and elevated levels of tropospheric ozone on physiological processes in European beech (Fagus sylvatica)
Authors: Zeuthen Jakob , Mikkelsen Teis N. , Paludan‐Müller Georg , Ro‐Poulsen Helge
Published: May 2006

As a consequence of the ongoing reduction of the stratospheric ozone layer, the vegetation is exposed to increasing levels of UV‐B radiation (280–320 nm). In addition ozone in the troposphere is a pollutant and also capable of affecting the photosynthetic machinery.

In this study, 5‐year‐old European beech trees were exposed from 1 July to October 1993 to two levels of UV‐B radiation and two levels of ozone, alone and in combination, in open‐top chambers equipped with lamps. The simulated UV‐B levels corresponded to either clear sky ambient level or a 14% decrease in the stratospheric ozone column over eastern Denmark, resulting in a 23% difference in biologically effective UV‐B (UV‐BBE) irradiance. The maximum UV‐Bbe given was 8.61 kJ m−2 day−1. The ozone levels were either the ambient (average 32 nl l−1) or ambient with ozone addition (average resulting concentration 71 nl l−1). Compared to the control treatment (ambient UV‐B, ambient O3) the elevated levels of UV‐B and O3 affected the trees negatively, expressed as declines in net photosynthesis (Pn), stomatal conductance (gs), chlorophyll fluorescence (Fv/Fm) and acceleration of senescence, measured as yellowing of the leaves. The UV‐B treatment induced stomatal closure before the other treatments did. The magnitude of the decreases in Pn and Fv/Fm occurred in the order: control <UV‐B <O3 <UV‐B and O3. Compared to the control, the combination treatment with high levels accelerated the visual senescence processes by ca 27 days, while for high UV‐B and O3 alone, there was an acceleration by 14 and 21 days, respectively. UV‐B and O3 in combination enhanced the negative effects compared with UV‐B and O3 alone. The Pn and Fv/Fm results could be related to this acceleration process. The chamber effect was investigated by comparing the control plots with a plot without open‐top chamber. The trees in the chambers showed a higher Pn and Fv/Fm and a 14‐day delayed senescence compared to the trees outside, probably caused by higher temperatures, a more protected environment and altered conditions inside the chambers.
Heat treatment to decrease chilling injury in tomato fruit. Effects on lipids, pericarp lesions and fungal growth
Authors: Lurie Susan , Laamim Mostafa , Lapsker Zoria , Fallik Elazar
Published: May 2006

Tomato fruits are sensitive to low temperature and develop chilling injury, while at nonchilling temperatures they ripen rapidly. Previously, a hot‐air treatment was found to reduce the sensitivity of the fruit to low temperatures. In the present study hot air was compared to hot water and their effects on reducing chilling injury and fungal decay were investigated. Tomatoes (Lycopersicon esculentum cv. Daniella) at the breaker stage were subjected to hot air, 48 h at 38°C, or various hot water dips, 30 min at 40°C or 2 min at 46, 48 or 50°C, before holding at 2°C. The unheated tomatoes developed chilling injury and fungal infections at 2°C, but not at 12°C. All the heat treatments reduced chilling injury and decay in tomatoes held for 3 weeks at 2°C. The outer pericarp tissue of heated tomatoes had higher phospholipid and lower sterol contents than unheated tomatoes. Heated tomatoes also had less saturated fatty acids than unheated tomatoes held at 2°C, but not at 12°C. Scanning electron micrograph observations showed that all the fruits had microcracks in their surface, but the unheated chilled tomatoes had also fungal growth in the cracks, while those of the heated tomato fruit did not. In the areas of chilling injury collapsed cells were present under the peel and could also support pathogen development. It is suggested that the heat treatment institutes a response to high temperature stress in the fruit tissue that leads to strengthened membranes. This prevents the loss of function and cell collapse which was found in the chilling‐injured areas of affected fruit.
Tissue specific modulation of salt inducible gene expression: Callus versus whole plant response in salt tolerant alfalfa
Authors: Winicov Hga , Shirzadegan Magid
Published: May 2006

We have cloned several genes that were continuously induced by salt in our salt‐tolerant alfalfa (Medicago sativa L.) callus. These genes were not induced by 24 h salt stress in the parent salt‐sensitive cell line. To investigate the extent to which salt‐stress regulation of these genes is influenced by a program of tissue specific regulation we have characterized another one of the cloned cDNAs, pA18, determined the expression of the transcript it encodes and compared its salt‐inducible tissue‐specific expression in plants with MsPRP2, another single or low copy gene induced in the salt‐tolerant cells. While pA18 and MsPRP2 transcripts are similarly salt‐induced in callus, comparisons of tissue specific expression between these two genes demonstrate that regulated tissue specific expression can override salt inducibility of mRNA accumulation for individual genes.
Stress responses of tobacco cells to high temperature and salinity. Proline accumulation and phosphorylation of polypeptides
Authors: Kuznetsov Vladimir V. , Shevyakova Nina I.
Published: May 2006

Stress responses to high temperatures (35–48°C) and salinity (170–340 mM NaCl) and thermotolerance were investigated for the salt‐sensitive wild type and the salt‐tolerant NrEs‐1 strain of Nicotiana sylvestris L. using suspension‐cultured cells. Under saline conditions, NrEs‐1 strain cells accumulated proline, polyamine (putrescine and spermidine) and betaine in contrast to wild‐type cells. The simultaneous treatment of salt‐tolerant cells with high temperature (40°C) and NaCl (170 or 340 mM) resulted in a transient overproduction of proline accompanied by an increase in their thermotolerance. At the high temperature, the synthesis of polypeptides and the accumulation of heat shock protein HSP70 mRNA were not affected by salinity. The higher thermotolerance of the NaCl‐tolerant cells could not be related to osmoprotecting sugar‐starch interconversions but could rather be associated with selective phosphorylation of several polypeptides (23–24, 27, 31–32, 47 kDa) prior to the accumulation of proline. The possible role of polyamines and polypeptide phosphorylation in this respect is discussed.