bluuebunny/crossref_metadata_2025 huggingface dataset:
Osmoprotectant β‐alanine betaine synthesis in the Plumbaginaceae: S‐adenosyl‐	l‐methionine dependent N‐methylation of β‐alanine to its betaine is via N‐methyl and N,N‐dimethyl β‐alanines
Authors: Rathinasabapathi Bala , Sigua Celia , Ho Janice , Gage Douglas A.
Published: March 2003

β‐Alanine betaine is an osmoprotective compound accumulated by most members of the plant family Plumbaginaceae. Leaf and root tissues of Limonium latifolium known to accumulate β‐alanine betaine readily convert supplied β‐alanine to β‐alanine betaine. To identify the intermediates and the enzymes involved in β‐alanine betaine synthesis, radiotracer experiments using [

C] formate were employed. These studies demonstrate that β‐alanine betaine is synthesized from β‐alanine via N‐methyl and N,N‐dimethyl β‐alanines. A rapid and sensitive radiometric assay was developed to measure N‐methyltransferase (NMT) activities by using [methyl‐14C] or [methyl‐3H] S‐adenosyl‐
l‐methionine (AdoMet) as the methyl donor. Leaf extracts from β‐alanine betaine accumulators –Armeria maritima, L. latifolium and L. ramosissimum– had detectable NMT activities while none were found in L. perezii, a species that does not accumulate β‐alanine betaine. The NMT activities were further characterized from the leaves of L. latifolium. The activities had a pH optimum of 8.0, were soluble and inhibited by S‐adenosyl‐
l‐homocysteine. Extractable activities were similar from plants grown under control and salinity stress conditions. Radiolabeling with [

C]
l‐aspartic acid indicated that, unlike in bacteria, decarboxylation of
l‐aspartic acid is not the source of β‐alanine in the Plumbaginaceae.
Reactive oxygen species and antioxidants in legume nodules
Authors: Becana Manuel , Dalton David A. , Moran Jose F. , Iturbe‐Ormaetxe Iñaki , Matamoros Manuel A. , C. Rubio Maria
Published: March 2003

Reactive oxygen species are a ubiquitous danger for aerobic organisms. This risk is especially elevated in legume root nodules due to the strongly reducing conditions, the high rates of respiration, the tendency of leghemoglobin to autoxidize, the abundance of nonprotein Fe and the presence of several redox proteins that leak electrons to O2. Consequently, nodules are particularly rich in both quantity and diversity of antioxidant defenses. These include enzymes such as superoxide dismutase (EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) and metabolites such as ascorbate and thiol tripeptides. Nodule antioxidants have been the subject of intensive molecular, biochemical and functional studies that are reviewed here. The emerging theme is that antioxidants are especially critical for the protection and optimal functioning of N2 fixation. We hypothesize that this protection occurs at least at two levels: the O2 diffusion barrier in the nodule parenchyma (inner cortex) and the infected cells in the central zone.
Purification and characterization of an endoamylase from tulip (Tulipa gesneriana) bulbs
Authors: Ranwala Anil P. , Miller William B.
Published: March 2003

Amylase activity extracted from tulip (Tulipa gesneriana L. cv. Apeldoorn) bulbs that had been stored for 6 weeks at 4°C was resolved to 3 peaks by anion‐exchange chromatography on diethylaminoethyl‐Sephacel. These 3 amylases exhibited different relative mobilities during non‐denaturing polyacrylamide gel electrophoresis (PAGE). The most abundant amylase form (amylase I) was purified to apparent homogeneity using hydrophobic interaction chromatography, gel filtration and chromatofocusing. The apparent molecular mass of the purified amylase was estimated to be 51 kDa by sodium dodecyl sulfate‐PAGE and 45 kDa by gel filtration chromatography. The purified amylase was determined to be an endoamylase (EC 3.2.1.1) based on substrate specificity and end‐product analysis. The enzyme had a pH optimum of 6.0 and a temperature optimum of 55°C. The apparent Km value with soluble starch (potato) was 1.28 mg ml−1. The presence of Ca2+ increased the activity and thermal stability of the enzyme. The presence of dithiothreitol enhanced the activity, while β‐mercaptoethanol and reduced glutathione had no significant effect. When pre‐incubated in the absence of the substrate, N‐ethylmaleimide and 5,5′‐dithiobis‐(2‐nitrobenzoic acid) partially inhibited the enzyme. α‐cyclodextrins or β‐cyclodextrins had no effect on enzyme activity up to 10 mM. In addition to CaCl2, CoCl2 slightly enhanced activity, while MgCl2 and MnCl2 had no significant effect at a concentration of 2 mM. ZnCl2, CuSO4, AgNO3 and EDTA partially inhibited enzyme activity, while AgNO3 and HgCl2 completely inhibited it at 2.0 mM.
A novel method for growing Arabidopsis thaliana plants hydroponically
Authors: Arteca Richard N. , Arteca Jeannette M.
Published: March 2003

In this report we describe the development of a simple system for growing individual Arabidopsis plants hydroponically under environmental conditions which are simple to maintain while maximizing growth and development. The system consists of a Life Raft Float Unit with a 14–20 mm sponge inserted into its center; this unit is placed into a Magenta GA7 vessel containing Arabidopsis nutrient solution. Plants grown in this experimental system do not require aeration, 125 μmol m−2 s−1 supports vigorous plant growth, 1/4 to 1/8 strength Arabidopsis nutrient solution promotes maximal growth while higher or lower levels have adverse effects and temperatures between 18 and 24°C were found to be optimal. Plants grown under these conditions exhibit physiological factors such as time to flowering and overall appearance similar to those grown in potting media. The low maintenance method described in this paper provides an alternative to existing hydroponic methods used to grow Arabidopsis. Adaptation of this system for growing large numbers of plants in 1 container is also discussed.
Identification of the RPS10 polypeptide encoded by the mitochondrial genome in Solanum tuberosum: translation initiates at a genomic‐encoded AUG and not at a conserved AUG codon created by RNA editing
Authors: Zanlungo S. , Quiñones V. , Holuigue L. , Jordana X.
Published: March 2003

We have previously reported the identification of a gene encoding ribosomal protein S10 (rps10) in the Solanum tuberosum mitochondrial genome and shown that its transcripts undergo processing in the form of splicing and editing. Specific antibodies were raised against recombinant potato RPS10 obtained in Escherichia coli from the corresponding cDNA. Protein blot analysis revealed that the RPS10 polypeptide is present in potato mitochondria and is assembled into the mitochondrial ribosome. Potato rps10 mRNA translation may initiate at a genomic‐encoded AUG codon, or at a downstream in‐frame AUG codon which is created by RNA editing and coincides with liverwort and pea initiation codons. A peptide corresponding to the 19 amino acid sequence between both putative initiation codons was used to raise antibodies specific for the potato RPS10 N‐terminal extension. These antibodies were able to recognise a polypeptide of 16 kDa in a potato mitochondrial fraction enriched in ribosomes. This molecular mass corresponds to that of the polypeptide detected with antibodies against recombinant RPS10 and is in agreement with the molecular weight calculated from the cDNA sequence. These results showed that potato mitochondrial rps10 gene is expressed at the protein level and that translation initiates at the first genomic‐encoded AUG codon. Potato RPS10 has an N‐terminal extension of unknown function when compared to RPS10 from other organisms.
Cytokinin‐ and wound‐inducible cytochrome P450 from Nicotianaplumbaginifolia
Authors: Mujer Cesar V. , Smigocki Ann C.
Published: March 2003

Two Nicotianaplumbaginifolia cDNA clones, CYP72A2 and npl2, with high sequence similarity to cytochrome P450 monooxygenases were isolated using reverse transcription‐polymerase chain reaction. CYP72A2 has an open reading frame of 1524 nucleotides and its deduced 508 amino acid sequence has 45% identity to Catharanthusroseus P450 CYP72A1. npl2 is similar to CYP72A2, except for an 82‐nucleotide deletion within its coding region and an internal stop codon. Southern blot analysis indicated that there are at least 3 copies of the CYP72A2 gene and that they are induced at the RNA and protein levels by mechanical wounding, insect chewing (Manducasexta) and cytokinin application. The response to feeding larvae and wounding was systemic. In N. plumbaginifolia plants transformed with a wound‐inducible cytokinin biosynthesis gene construct (PI‐II‐ipt), gene induction in response to wounding and feeding insects occurred sooner and was generally higher than in untransformed plants. The modulation of CYP72A2 expression by cytokinins and the possible role of P450 in plant defense responses are discussed.
Changes in cell‐wall polysaccharides from the mesocarp of grape berries during veraison
Authors: Yakushiji Hiroshi , Sakurai Naoki , Morinaga Kunihisa
Published: March 2003

Softening of grape berries (Vitis vinifera L.×V. labruscana cv. Kyoho) was evaluated by studying changes in composition and degradation of cell‐wall polysaccharides. The grape berry softens at the beginning of the second growth cycle many weeks before harvest. The softening stage is called ‘veraison’ by viticulturists. On day 50 after full bloom, green hard berries (before veraison [BV]), softening berries (veraison [V]) and partly peel colored berries (C) were selected from the same clusters. In addition, mature berries (M) were collected on day 78 after full bloom. Mesocarp tissues at each stage were fractionated into hot water‐soluble (WS), hot EDTA‐soluble (pectin), alkali‐soluble (hemicellulose) and residual (cellulose) fractions. Neutral and acidic sugar contents of WS and pectin fractions decreased only after the V stage, while the neutral sugar content of the hemicellulose fraction decreased from the BV to V stages. Cellulose content constantly decreased as the berry ripened, but the large decrease was found from the BV to V stages. Molecular masses of pectic and hemicellulosic polysaccharides decreased from the BV to V stages. Hemicellulosic xyloglucan was markedly depolymerized from the BV to V stages. The neutral and acidic sugar composition of each fraction changed little during the berry ripening. These data indicated that softening of berry during veraison involved the depolymerization of pectin and xyloglucan molecules and decrease in the amounts of hemicellulose and cellulose.
Differential response of antioxidant enzymes in leaves of necrotic wheat hybrids and their parents
Authors: Dalal Monika , Khanna‐Chopra Renu
Published: March 2003

The leaves of necrotic hybrid of wheat (Triticum aestivum L.) exhibited high superoxide content associated with increased lipid peroxidation and membrane damage in earlier studies (Khanna‐Chopra et al. 1998, Biochem Biophys Res Commun 248: 712–715; Dalal and Khanna‐Chopra 1999, Biochem Biophys Res Commun 262: 109–112). In the present study, we investigated the activities of the antioxidant enzymes in the leaves of necrotic wheat hybrids, Kalyansona×C306 (K×C) and WL711×C306 (WL×C) and their parents at different developmental stages. The K×C hybrid exhibited more severe necrosis than WL×C. In K×C, superoxide dismutase (SOD) activity showed no increase over the parents, while WL×C showed an early increase, but it was possibly insufficient to scavenge increased superoxide. Activities of guaiacol peroxidase, ascorbate peroxidase and glutathione reductase were enhanced, while catalase exhibited a decrease in activity, with the appearance of visible necrosis in both the hybrids. The isozyme profile of the antioxidant enzymes was similar in the hybrids and their parents. One existing isoform of guaiacol peroxidase showed an early appearance in the hybrid and increased in intensity with the progression of necrosis. The results reveal a differential response of antioxidant enzymes in necrotic wheat hybrids as compared to their parents. The response differed in magnitude at developmental stages of the leaves, which might be related to the intensity of necrosis expressed by the hybrids.
Elevated CO2 and ozone reduce nitrogen acquisition by Pinus halepensis from its mycorrhizal symbiont
Authors: Kytöviita Minna‐Maarit , Le Thiec Didier , Dizengremel Pierre
Published: March 2003

The effects of 700 μmol mol−1 CO2 and 200 nmol mol−1 ozone on photosynthesis in Pinus halepensis seedlings and on N translocation from its mycorrhizal symbiont, Paxillus involutus, were studied under nutrient‐poor conditions. After 79 days of exposure, ozone reduced and elevated CO2 increased net assimilation rate. However, the effect was dependent on daily accumulated exposure. No statistically significant differences in total plant mass accumulation were observed, although ozone‐treated plants tended to be smaller. Changes in atmospheric gas concentrations induced changes in allocation of resources: under elevated ozone, shoots showed high priority over roots and had significantly elevated N concentrations. As a result of different shoot N concentration and net carbon assimilation rates, photosynthetic N use efficiency was significantly increased under elevated CO2 and decreased under ozone. The differences in photosynthesis were mirrored in the growth of the fungus in symbiosis with the pine seedlings. However, exposure to CO2 and ozone both reduced the symbiosis‐mediated N uptake. The results suggest an increased carbon cost of symbiosis‐mediated N uptake under elevated CO2, while under ozone, plant N acquisition is preferentially shifted towards increased root uptake.
Response to auxin changes during maturation‐related loss of adventitious rooting competence in loblolly pine (Pinus taeda) stem cuttings
Authors: Greenwood Michael S. , Cui Xiuyu , Xu Fuyu
Published: March 2003

Hypocotyl cuttings (from 20‐ and 50‐day‐old Pinus taeda L. seedlings) rooted readily within 30 days in response to exogenous auxin, while epicotyl cuttings (from 50‐day‐old seedlings) rarely formed roots within 60 days. Responses to auxin during adventitious rooting included the induction of cell reorganization and cell division, followed by the organization of the root meristem. Explants from the bases of both epicotyl and hypocotyl cuttings readily formed callus tissue in response to a variety of auxins, but did not organize root meristems. Auxin‐induced cell division was observed in the cambial region within 4 days, and later spread to the outer cortex at the same rate in both tissues. Cells at locations that would normally form roots in foliated hypocotyl cuttings did not produce callus any differently than those in other parts of the cortex. Therefore, auxin‐induced root meristem organization appeared to occur independently of auxin‐induced cell reorganization/division. The observation that N‐(1‐naphthyl)phthalamic acid (NPA) promoted cellular reorganization and callus formation but delayed rooting implies the existence of an auxin signal transduction pathway that is specific to root meristem organization. Attempts to induce root formation in callus or explants without foliage were unsuccessful. Both the cotyledon and epicotyl foliage provided a light‐dependent product other than auxin that promoted root meristem formation in hypocotyl cuttings.
The ectopic overexpression of a citrus gibberellin 20‐oxidase enhances the non‐13‐hydroxylation pathway of gibberellin biosynthesis and induces an extremely elongated phenotype in tobacco
Authors: Vidal Ana M. , Gisbert Carmina , Talón Manuel , Primo‐Millo Eduardo , López‐Díaz Isabel , García‐Martínez José L.
Published: March 2003

Transgenic plants of Nicotiana tabacum overexpressing a gibberellin (GA) 20‐oxidase cDNA (CcGA20ox1) from citrus, under the control of the 35S promoter, were taller (up to twice) and had larger inflorescences and longer flower peduncles than those of control plants. Hypocotyls of transgenic seedlings were also longer (up to 4 times), and neither the seedlings nor the growing plants elongated further after application of GA3. Hypocotyl and stem lengths were reduced by application of paclobutrazol, and this inhibition was reversed by exogenous GA3. The ectopic overexpression of CcGA20ox1 enhanced the non‐13‐hydroxylation pathway of GA biosynthesis leading to GA4, apparently at the expense of the early‐13‐hydroxylation pathway. The level of GA4 (the active GA from the non‐13‐hydroxylation pathway) in the shoot of transgenic plants was 3–4 times higher than in control plants, whereas that of GA1, formed via the early‐13‐hydroxylation pathway (the main GA biosynthesis pathway in tobacco), decreased or was not affected. GA4 applied to the culture medium or to the expanding leaves was found to be at least equally active as GA1 on stimulating hypocotyl and stem elongation of tobacco plants. The results suggest that the tall phenotype of tobacco transgenic plants was due to their higher content of GA4, and that the GA response was saturated by the presence of the transgene.
Ozone treatment affects pigment precursor metabolism in pine seedlings
Authors: Shamay Y. , Raskin V. I. , Brandis A. S. , Steinberger H. E. , Marder J. B. , Schwartz A.
Published: March 2003

Five‐week‐old seedlings of Pinus halepensis Mill. and Pinus brutia Ten. were exposed to air polluted with ozone (O3) (250 nl l−1, 12 h day−1 for 4 days) or to ambient air containing ca 10–20 nl l−1 O3, in the light (180 μmol m−2 s−1 photosynthetic photon flux density [PPFD], 12 h day−1) and then fed for 24 h in the light (100 μmol m−2 s−1 PPFD) with various radioactive precursors of chlorophyll (Chl) and carotene biosynthesis: 5‐[4‐14C]‐aminolevulinic acid (14C‐ALA), l‐[14C(U)]‐glutamic acid (14C‐Glu), or d,l‐[2‐14C]‐mevalonic acid (14C‐MVA). Pigments were then extracted from cotyledons and fully expanded needles. Chl a and carotene were separated by thin‐layer chromatography and high‐performance liquid chromatography and their specific activities were determined. 14C‐ALA and 14C‐Glu labels were incorporated into Chl a and carotene. Exposure to O3 did not inhibit incorporation of 14C‐ALA into Chl a molecules, but hydrolysis of Chl a showed that O3 inhibited phytol labelling of Chl a. Labelling of carotene was also inhibited by O3, but not when 14C‐MVA was used as the label. These data suggest that O3 treatment inhibits (directly or indirectly) the biosynthesis of isoprenoids from products of ALA and Glu metabolism in the plastid, but not from MVA in the cytosol. This inhibition was more prominent when 14C‐ALA was used as the label than when 14C‐Glu was the labelling precursor. A significant increase in pheophorbide a, a tetrapyrrole component of Chl a labelling, and a concomitant decrease in phytol labelling was observed following incubation of O3‐treated pine seedlings with 14C‐ALA and 14C‐Glu. Stronger inhibition of carotene biosynthesis and activation of Chl a tetrapyrrole labelling by 14C‐ALA (in comparison with 14C‐Glu) indicated that exposure to O3 inhibits the conversion of ALA to Glu as the first step in ALA catabolism. These results also suggested a more intensive Glu metabolism (in comparison with ALA) for carotene biosynthesis in the cytosol, as well as cooperation between two pathways of isopentenyl diphosphate biosynthesis.
Stimulation of plant plasma membrane Ca2+‐ATPase activity by acidic phospholipids
Authors: Bonza Maria Cristina , Luoni Laura , De Michelis Maria Ida
Published: March 2003

The effect of phospholipids on the activity of the plasma membrane (PM) Ca2+‐ATPase was evaluated in PM isolated from germinating radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) seeds after removal of endogenous calmodulin (CaM) by washing the PM vesicles with EDTA.  Acidic phospholipids stimulated the basal Ca2+‐ATPase activity in the following order of efficiency: phosphatidylinositol 4,5‐diphosphate (PIP2)≈phosphatidylinositol 4‐monophosphate>phosphatidylinositol≈phosphatidylserine≈phosphatidic acid. Neutral phospholipids as phosphatidylcholine and phosphatidylethanolamine were essentially ineffective. When the assays were performed in the presence of optimal free Ca2+ concentrations (10 μM) acidic phospholipids did not affect the Ca2+‐ATPase activated by CaM or by a controlled trypsin treatment of the PM, which cleaved the CaM‐binding domain of the enzyme. Analysis of the dependence of Ca2+‐ATPase activity on free Ca2+ concentration showed that acidic phospholipids increased Vmax and lowered the apparent Km for free Ca2+ below the value measured upon tryptic cleavage of the CaM‐binding domain; in particular, PIP2 was shown to lower the apparent Km for free Ca2+ of the Ca2+‐ATPase also in trypsin‐treated PM.  These results indicate that acidic phospholipids activate the plant PM Ca2+‐ATPase through a mechanism only partially overlapping that of CaM, and thus involving a phospholipid‐binding site in the Ca2+‐ATPase distinct from the CaM‐binding domain. The physiological implications of these results are discussed.
Control of plant development by limiting factors: A nutritional perspective
Authors: McIntyre Gordon I.
Published: March 2003

It is postulated that limiting nutritional factors play a major role in the regulation of some aspects of plant development, and can provide an alternative to mechanisms based on the concept of hormonal control. This hypothesis is consistent with experimental evidence of the role of water as a limiting factor in (1) seed maturation and viviparous germination, (2) the elongation and phototropism of hypocotyls and coleoptiles, (3) the NO3−‐induced germination of dormant seeds, and (4) the release of buds from correlative inhibition. Studies on the influence of nutrition on morphogenesis have shown that the relative amounts of nitrogen and carbohydrate can determine the path of bud development as a shoot or rhizome. There is also evidence that either NO3− or sugar can limit lateral root initiation, and it is postulated that they may influence this process by a combination of osmotic and nutritional effects. The close correlation between environmentally induced developmental responses and the associated changes in the water or nutritional status of the responsive tissues, together with increasing evidence of the role of water and nutrients as transmitted signals and as regulators of gene expression, are in good agreement with their postulated role as limiting factors in the regulation of plant development.
Sprouting of the fructan‐ and starch‐storing geophyte Lachenalia minima: Effects on carbohydrate and water content within the bulbs
Authors: Orthen Birgit
Published: March 2003

The carbohydrate pool within the bulbs of Lachenalia minima W.F. Barker (Hyacinthaceae) consists of similar amounts of fructans and starch. This study was conducted to examine the changes within the pool of non‐structural carbohydrates that occur during sprouting under field conditions. The bulbs were watered over a period of 23 days to simulate the onset of the rainy season. Even though there was no significant change of the total fructan content, the distribution and the composition of the fructan fraction within the different leaf scales of the bulbs altered during sprouting. The major changes occurred in the innermost scales, the total fructan content increased from 300 (day 0) to 607 (day 23) g kg−1 dry mass and high‐performance anion‐exchange chromatography analysis revealed a significant increase of fructans with low degree of polymerization (DP). With respect to starch, the most pronounced difference accompanying the transition to growth was also in the innermost scales. In contrast to fructans, starch content decreased from 241 (day 0) to 60 (day 14) g kg−1 dry mass. These results demonstrate that starch, and not fructan, is used as the carbon and energy source for sprouting. The water content data suggest the involvement of fructans in water relations. The preferential accumulation of low DP fructans and sucrose within the innermost scales directs the water flow to where it is most needed for growth. Similar changes were obtained for bulbs in the dry soil, but transformation rates were much slower and occurred to a lesser extent, indicating that these reactions were not triggered but were accelerated by water.
What are the driving forces for water lifting in the xylem conduit?
Authors: Zimmermann Ulrich , Schneider Heike , Wegner Lars H. , Wagner Hans‐Jürgen , Szimtenings Michael , Haase Axel , Bentrup Friedrich‐Wilhelm
Published: March 2003

After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal‐ and non‐invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high‐resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to − 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel‐ and gas bubble‐supported interfacial gradients. The multiforce theory overcomes the problem of the Cohesion Theory that life on earth depends on water being in a highly metastable state.
Adenine phosphoribosyltransferase isoforms of Arabidopsis and their potential contributions to adenine and cytokinin metabolism
Authors: Allen Michael , Qin Wensheng , Moreau François , Moffatt Barbara
Published: March 2003

Adenine phosphoribosyltransferase (APT; EC 2.4.2.7) is a constitutively expressed enzyme involved in the one‐step salvage of adenine to AMP. The Arabidopsis thaliana genome contains five sequences annotated as encoding APT or APT‐like enzymes. Three of these have now been cloned, over‐expressed and compared using kinetic analyses. At a cytosolic pH, all bind adenine efficiently based on their Km values (0.8–2.6 µM), although APT1 metabolizes adenine at a rate 31–53 times faster than APT2 and APT3, respectively. Since APT also has a possible role in the interconversion of cytokinin bases to nucleotides, we characterized the activity of each isoform on zeatin, isopentenyladenine and benzyladenine. Based on their Km values, APT2 and APT3 had much higher affinities than APT1 for all three cytokinins (15–440 µM for APT2 and 3 vs. 1.8–2.5 mM for APT1); conversely the Vmax values for APT2 and APT3 on these CK substrates showed the opposite trend, being 4‐ to 19‐fold lower than those of APT1. Anti‐peptide antibodies for APT1, APT2, and APT3 were prepared and used to examine the subcellular localization of each isoform. Based on these results, APT1 and APT3 appear to be cytosolic, while the localization of APT2 was inconclusive although sequence analysis implies that APT2 is also cytosolic. Each isoform was modelled against the crystal structure of APT from Leishmania donovani, and structural differences in substrate specificity‐determining domains have been found. The estimated kinetic activities of these APTs suggest that they contribute primarily to adenine recycling, although an involvement in cytokinin interconversion cannot be discounted.
Influence of CO2 and sucrose on photosynthesis and transpiration of Actinidia deliciosa explants cultured in vitro
Authors: Arigita Luis , González Aida , Tamés Ricardo Sánchez
Published: March 2003

Explants of Actinidia deliciosa Chev. Liang and Ferguson var. Hayward were cultured in controlled CO2 atmospheres in the presence of different sucrose concentrations. Organogenesis was measured after 45 days in explants from the different assays, and quantification of photosynthesis, transpiration, chlorophylls, RUBISCO and total soluble protein content was performed in leaves from the different treatments. The best results were those of explants cultured at 600 µmol CO2 mol−1 on 20 g l−1 of sucrose for the first 20 days and then transferred to sucrose‐free medium until the end of the culture period. Increasing CO2 to 2000 µmol CO2 mol−1 in the atmosphere of the culture vessel reduced all the parameters studied. Photosynthesis of autotrophically developed explants trebled that of the reference heterotrophic explants, as there was an apparent inverse relationship between photosynthesis and transpiration. Photosynthesis was saturated at 300 µmol m−2 s−1 PPFD and 600 µmol CO2 mol−1. Chlorophylls and RUBISCO presented differences between treatments, mainly between different CO2 concentrations, with the highest values in autotrophically cultured explants. Explants grown at 2000 µmol CO2 mol−1 showed the lowest RUBISCO/Prots ratio, probably due to negative adaptation of RUBISCO to long‐term high CO2. In short, explants grown in a controlled microenvironment, with increased CO2 and under autotrophic conditions, developed wholly functional photosynthetic apparatus well prepared to be transferred to ex vitro conditions, which has many advantages in micropropagation.
Consequences of elevated CO2, augmented nitrogen‐deposition and soil type on the soluble nitrogen and sulphur in the phloem of beech (Fagus sylvatica) and spruce (Picea abies) in a competitive situation
Authors: Schraml Carmen , Herschbach Cornelia , Eiblmeier Monika , Rennenberg Heinz
Published: March 2003

Mixed spruce‐beech plantations grown in large open‐top chambers (OTC) were used to study consequences of elevated CO2, nitrogen‐deposition and soil type on plant internal nitrogen and sulphur cycling of juvenile beech (Fagus sylvatica L.) and spruce (Picea abies Karst.) in a competitive situation. Processes of re‐cycling as a consequence of protein turnover during leaf senescence in autumn were of further interest. For this purpose, phloem sap was collected in September 1998 and analysed for the composition and concentrations of organic and inorganic nitrogen and sulphur compounds. The phloem exudate of spruce showed higher total soluble non‐protein nitrogen (TSNN) concentration on calcareous soil than on acidic soil, independent of the treatment. N‐fertilization increased the N‐concentration of phloem exudate significantly on both soil types, mainly by an increase of Arg and Gln concentrations. Elevated CO2 slightly increased TSNN on calcareous, but not on acidic soil. The combination of elevated CO2 and augmented N‐deposition induced a further increase of TSNN on calcareous soil, but caused a lower N‐effect on TSNN on acidic soil. Arg, the main TSNN component in phloem exudate, mediated this effect. Since Arg is considered to be a major nitrogen storage compound, it is concluded that in autumn elevated CO2 and augmented N‐deposition, influence storage of N rather than N‐supply of spruce. An effect of elevated CO2 and augmented N‐deposition on GSH and sulphate concentrations in phloem exudate of spruce was not observed on acidic soil. On calcareous soil augmented N‐deposition enhanced, elevated CO2 decreased phloem exudate GSH contents. In combination, elevated CO2 compensated the positive effect of N‐deposition. The effects of elevated CO2 and augmented N‐deposition on phloem sap N‐ and S‐contents described above were not observed for beech trees. Apparently, elevated CO2 and augmented N‐deposition did not affect plants internal S and N cycling of beech grown in spruce‐beech plantations.
Identification and quantification of three active auxins in different tissues of Tropaeolum majus
Authors: Ludwig‐Müller Jutta , Cohen Jerry D.
Published: March 2003

Indole‐3‐acetic acid (IAA), indole‐3‐butyric acid (IBA) and phenylacetic acid (PAA) were identified as endogenous compounds with auxin activity in nasturtium (Tropaeolum majus L.) by full scan gas chromatography‐mass spectrometry. The endogenous concentrations of the three auxins were measured by GC‐selected ion monitoring‐MS and isotope dilution analysis using stable labelled isotopes. PAA was present at concentrations about 10‐ to 100‐fold lower than IAA, whereas IBA was found to be in the same concentration range as IAA. Free IAA was highest in roots followed by young leaves. IBA was also highest in the roots, and relatively high concentrations were found in young leaves and flowers. The distribution of PAA was quite different from that found for IBA. No PAA could be detected in young leaves and flowers, and in all other tissues studied the concentrations were well below those of the other two auxin compounds. The presence of a nitrilase gene family and nitrilase activity in extracts from T. majus suggests that PAA might be synthesized by the nitrilase pathway using benzylglucosinolate as precursor.
Characterization of a novel rice gene OsATX and modulation of its expression by components of the stress signalling pathways
Authors: Agrawal Ganesh K. , Rakwal Randeep , Jwa N‐S , Agrawal Vishwanath P.
Published: March 2003

In our search to identify gene(s) involved in the rice self‐defense responses, we cloned a novel rice (Oryza sativa L. cv. Nipponbare) gene, OsATX, a single copy gene, from the JA treated rice seedling leaves cDNA library. This gene encodes a 69 amino acid polypeptide with a predicted molecular mass of 7649.7 and a pI of 5.6. OsATX was responsive to cutting (wounding by cutting the excised leaf), over its weak constitutive expression in the healthy leaves. The critical signalling molecules, jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), and hydrogen peroxide, together with protein phosphatase inhibitors, effectively up‐regulated the OsATX expression with time, over the excised leaf cut control, whereas ethylene had no affect. Furthermore, copper, a heavy metal, also up‐regulated OsATX expression. Moreover, induced expression of OsATX mRNA was influenced by light signal(s), and showed a requirement for de novo synthesized protein factors. Additionally, co‐application of either JA or ABA with SA drastically suppressed the induced OsATX mRNA level. Finally, the blast pathogen, Magnaporthe grisea, triggered OsATX mRNA accumulation. These results strongly suggest a function/role(s) for OsATX in defense/stress responses in rice.
Studies on callose and cutin during the expression of competence and determination for organogenic nodule formation from internodes of Humulus lupulus var. Nugget
Authors: Fortes Ana M. , Testillano Pilar S. , Del Carmen Risueño Maria , Pais Maria S.
Published: March 2003

Callose and cutin deposition were followed by staining with Aniline Blue and Nile Red and by immunolocalization using antibodies raised against callose. Along with morphogenesis induction from internodes of Humulus lupulus var. Nugget, a temporal and spatial differential deposition of callose and cutin was observed. A cutin layer showing bright yellow autofluorescence appears, surrounding cells or groups of cells committed to express morphogenic competence. This cutin layer that evolves to a randomly organized network appeared underneath a callose layer and may create a specific cellular environment with altered permeability and altered receptors providing conditions for entering the cell cycle. The incipient callose accumulation in control explants cultured on basal medium suggests the involvement of callose in the initiation of the morphogenic programme leading to nodule formation. A scanning electron microscopic study during the organogenic process showed that before shoot bud regeneration, the cutin layer increases in thickness and acquires a smooth texture. This cutin layer is specific to nodular organogenic regions and disappeared with plantlet regeneration. This layer may control permeability to water and solute transfer throughout plantlet regeneration.
Regulation of the xanthophyll cycle pool size in duckweed (Lemna minor) plants
Authors: García‐Plazaola José Ignacio , Hernández Antonio , Artetxe Unai , Becerril José María
Published: March 2003

Duckweed (Lemna minor L.) plants grown under high light are characterized, when compared to low light acclimated plants, by a higher xanthophyll cycle (VAZ) pool content, but also by a higher proportion of photoconvertible violaxanthin and a superior ability to synthesize VAZ pigments. When duckweed plants were transferred to a high light environment a general response was the quick adjustment of the carotenoid composition, mainly xanthophyll cycle pigments. These changes resulted from a balance between a process of continuous light‐independent carotenoid degradation and a light‐induced accumulation. The use of norflurazon, an inhibitor of carotenogenesis, allowed us to demonstrate that the observed light induced increase of the VAZ pool was mainly caused by de novo synthesis through carotenogenesis. The extent of light‐induced carotenogenesis was proportional to the light treatment and also to the operation of the VAZ cycle since it was partly abolished by treatments leading to a low activity of the VAZ cycle, such as low light, DTT or DCMU. These results suggest that not only the light itself, but also a mechanism triggered by a factor associated with the de‐epoxidation state of the VAZ cycle controls carotenogenesis at some point before phytoene formation in the terpenoid biosynthesis pathway.
Effect of anti‐auxins on maturation of embryogenic tissue cultures of Nordmanns fir (Abies nordmanniana)
Authors: Find Jens , Grace Lynette , Krogstrup Peter
Published: March 2003

The present study was conducted to improve the transition from proliferation to maturation in embryogenic cultures of Nordmanns fir. For that reason, chemicals reported to affect endogenous levels or activity of auxin were included in the growth media during maturation. The auxin antagonist PCIB reduced proliferation and promoted the development of numerous high‐quality mature embryos in the tested cell lines. PCIB could not substitute for exogenously supplied ABA and the positive effect was only found when PCIB and ABA were used in combination. The effect of PCIB was dependent on the concentration and the application period. The auxin transport inhibitor TIBA also reduced proliferation, but had no positive effect on maturation. The auxin synergist phloroglucinol had the opposite effect of PCIB; proliferation was increased and no maturation was initiated. A lowered concentration of boron had no effect on proliferation but had some positive effect on maturation. The optimum protocol for PCIB application was strongly genotype dependent, and a general scheme that covered the tested cell lines could not be found. Overexposure to PCIB during maturation caused abnormal development of the mature embryos, which was revealed by a reduced number of cotyledons. These results suggest that endogenously produced auxin may be one reason for low or failing maturation of embryogenic cultures of Nordmanns fir, but also imply that auxin may play a critical role for proper development of cotyledons during the later stages of embryo maturation.
Germination and growth of lettuce (Lactuca sativa) at low atmospheric pressure
Authors: Spanarkel Robert , Drew Malcolm C.
Published: March 2003

The response of lettuce (Lactuca sativa L. cv. Waldmann's Green) to low atmospheric pressure was examined during the initial 5 days of germination and emergence, and also during subsequent growth to vegetative maturity at 30 days. Growth took place inside a 66‐l‐volume low pressure chamber maintained at 70 kPa, and plant response was compared to that of plants in a second, matching chamber that was at ambient pressure (approximately 101 kPa) as a control. In other experiments, to determine short‐term effects of low pressure transients, plants were grown at ambient pressure until maturity and then subjected to alternating periods of 24 h of low and ambient atmospheric pressures. In all treatments the partial pressure of O2 was maintained at 21 kPa (approximately the partial pressure in air at normal pressure), and the partial pressure of CO2 was in the range 66.5–73.5 Pa (about twice that in normal air) in both chambers, with the addition of CO2 during the light phase. With continuous exposure to low pressure, shoot and root growth was at least as rapid as at ambient pressure, with an overall trend towards slightly greater performance at the lower pressure. Dark respiration rates were greater at low pressure. Transient periods at low pressure decreased transpiration and increased dark respiration but only during the period of exposure to low pressure. We conclude that long‐term or short‐term exposure to subambient pressure (70 kPa) was without detectable detriment to vegetative growth and development.
Effects of season‐dependent irradiance levels and nitrogen‐deficiency on photosynthesis and photoinhibition in field‐grown rice (Oryza sativa)
Authors: Chen Yizhu , Murchie Erik H , Hubbart Stella , Horton Peter , Peng Shaobing
Published: March 2003

Photoinhibition and acclimation of photosynthesis in rice plants grown under N‐sufficient (NS) and N‐deficient (ND) field conditions were investigated during the tropical wet (WS) and dry (DS) seasons in the Philippines. Diurnal patterns of CO2 assimilation were examined. There was a transient peak in CO2 assimilation in the leaves of the NS plants in the early morning during the DS and the WS, which was not seen in the ND plants in either season. ND leaves had lower Ribulose bisphosphate carboxylase/oxygenase (Rubisco) contents and lower chlorophyll contents. A lowered quantum yield of photosystem II (φPSII) was observed in the ND plants at an intermediate irradiance though no differences between N treatments were seen at high irradiance. Analysis of carotenoids indicated a small increase in the de‐epoxidation state of the xanthophyll cycle (DES) at mid‐day in the ND leaves compared to NS. Photoinhibition was greater in ND leaves when incident mid‐day irradiance was increased by altering the leaf angle. Although Rubisco contents were lower in ND plants, photosynthesis in situ did not decline proportionally. For NS plants, Chlorophyll content, but not Rubisco content, was season‐dependent and results are discussed in terms of the interaction between irradiance use and N content of rice leaves.
Measurements of photosynthesis and respiration in plants
Authors: Hunt Stephen
Published: March 2003

Methods for measuring the rates of photosynthesis and respiration in plants are reviewed. Closed systems that involve manometric techniques, 14CO2 fixation, O2 electrodes and other methods for measuring dissolved and gas phase O2 are described. These methods typically provide time‐integrated rate measurements, and limitations to their use are discussed. Open gas exchange systems that use infra‐red CO2 gas analysers and differential O2 analysers for measuring instantaneous rates of CO2 and O2 exchange are described. Important features of the analysers, design features of gas exchange systems, and sources of potential error are considered. The analysis of chlorophyll fluorescence parameters for estimating the quantum yield for O2 evolution and CO2 fixation is described in relation to new fluorescence imaging systems for large scale screening of photosynthetic phenotypes, and the microimaging of individual chloroplasts.
The biology of Epstein–Barr virus in post‐transplant lymphoproliferative disease
Authors: Hsieh W.‐S. , Lemas M.V. , Ambinder R.F.
Published: March 2003

Post‐transplant lymphoproliferative disease (PTLD) is a B cell proliferative disorder that is associated with Epstein–Barr virus (EBV), an ubiquitous herpesvirus. EBV‐seronegative organ transplant recipients are at highest risk. EBV infection in PTLD lesions exists in a latent rather than lytic state, making tumor regression in response to antiviral agents unlikely. Viral latency proteins drive proliferation of T cells but also allow T cells to target PTLD lesions for destruction. Augmentation of the cellular immune response via the infusion of EBV‐specific cytotoxic T cells has yielded promising results in the prevention and treatment of PTLD in bone marrow transplant recipients. Efforts to extend this strategy to solid organ transplant recipients are ongoing.

Editor’s comment:The spectrum of post‐transplant lymphoproliferative disease includes both B‐ and T‐cell malignancies. While the vast majority are EBV‐associated, there is a growing subset without obvious EBV markers. Given the present state of the art, which is summarized in this paper, we are incapable of stratifying patients in terms of prognosis or the likelihood of clinical response to reduction in immune suppression or to chemotherapy. The goal for multicenter trials must include the development of uniform definitions for the clinical and virologic manifestations of PTLD, as well as further attempts to define the natural history of this group of diseases.

Jay A. Fishman, M.D.