bluuebunny/crossref_metadata_2025 huggingface dataset:
The Ingestad concept in ectomycorrhizal research: Possibilities and limitations
Authors: Colpaert Jan V. , Verstuyft Iris
Published: March 2003

Growing ectomycorrhizal (ECM) plants in hydroponics is not common and probably not desirable, especially with fungal partners producing hydrophobic mycelia. The addition of a solid substrate with low buffering capacity to the cultivation system permitted growth of ECM Pinus sylvestris seedlings in a more root‐ and fungus‐like environment. In such semihydroponic cultivation systems, both hydrophilic (Thelephora terrestris) and hydrophobic (Suillus luteus) fungi can grow well, provided the substrate is not continuously flooded. In the present investigation, P. sylvestris seedlings were grown at two suboptimal P addition rates. Mycorrhizal seedlings had significantly lower P contents in aboveground and higher P contents in belowground plant parts than non‐mycorrhizal (NM) pines. When mycorrhizal plants are grown under steady‐state conditions, the controlled addition of nutrients according to the Ingestad concept (Ingestad and Ågren 1995) does not take into account the nutrient requirements of the associated mycobiont. Therefore, the retention of nutrients in the mycelia can result in a decreased growth of mycorrhizal plants when compared to NM controls. Under steady‐state conditions, plant and fungal development both reach an equilibrium sustained by feedback mechanisms in the allocation patterns. The maximal growth rate of different mycobionts does not necessarily occur at the nutrient addition rate resulting in maximal growth rate of a host plant. Ergosterol concentrations in roots and in growth substrate indicate that S. luteus grew more vigorously at the lower than at the higher rate of P addition.
Characterisation of the procera mutant of tomato and the interaction of gibberellins with end‐of‐day far‐red light treatments
Authors: Van Tuinen A. , Peters A. H. L. J. , Kendrick R. E. , Zeevaart J. A. D. , Koornneef M.
Published: March 2003

The tomato (Solanum lycopersicum L.) slender mutant procera (pro) was analysed for its relationship with gibberellin (GA) by combining it with GA deficiency due to the gib‐1 mutation. The sensitivity to GA biosynthesis inhibitors and the GA content were measured in the pro gib‐1 double mutant. In the gib‐1 mutant background, the pro mutation strongly reduced the GA requirement for seed germination and stem growth and almost fully restored the morphological leaf defects of the gib‐1 mutant. An end‐of‐day far‐red light treatment, when applied to the various genotypes, indicated that GAs are required for a response to this treatment, but that it act independently of the Pro gene product.
Influence of light conditions on development, apoplastic peroxidase activities and peroxidase isoenzymes in chicory root explants
Authors: Boeuf G. , Legrand B. , Rambour S.
Published: March 2003

Cichorium intybus L. (cv. Bea) root explants grown in continuous light had a higher fresh weight, lignin and chlorophyll content than explants grown in darkness. Intermediary values were found when the light conditions were switched after 6 days. Peroxidase activities (EC 1.11.1.7) were measured in the apoplastic fluid with guaiacol, indoleacetic acid (IAA) and syringaldazine as substrates. There was an inverse relationship between specific IAA oxidase activity and explant growth. Specific syringaldazine oxidase activity (SSO) correlated with the lignin content. Analysis by isoelectric focusing (IEF) showed that the apoplastic fluid contained both cationic and anionic peroxidase isoforms, whose expression differed according to culture conditions. Isoform isoelectric point (pI) 7.0 was only detectable when the explants were cultured for 12 days in darkness. When explants were grown for the first 6 days in light, SSO and lignin content were high and the isoforms pI 4.0, 6.6, 7.6 and 8.1 were highly expressed. Conversely, when the first 6 days were in darkness, specific IAA oxidase activity was high and the isoforms pI 4.5, 6.7 and 6.8. were most strongly expressed. The isoperoxidases pI 7.8 and 7.9 were strongly expressed when the explants were cultured for at least 6 days in darkness.
Carbon and water balances for young fruits of platyopuntias
Authors: Nobel Park S. , De la Barrera Erick
Published: March 2003

Questions relating to transpired versus retained water for fruits, the xylem versus the phloem as water supplier to the fruits, and the importance of fruit photosynthesis for fruit dry mass gain were examined in the field for 6 species of platyopuntias (Nopalea cochenillifera, Opuntia ficus‐indica, O. megacantha, O. robusta, O. streptacantha and O. undulata), cacti with flattened stem segments (cladodes). For plants with fruits midway between floral bud appearance and fruit maturation, transpiration was greater at night for the cladodes, as expected for Crassulacean acid metabolism (CAM) plants, but greater during the daytime for the fruits of all 6 species. Nevertheless, net CO2 uptake by fruits of these platyopuntias occurred predominantly at night, as expected for CAM plants. The water potential of the young fruits (average of −0.41 MPa) was higher than that of the cladodes (average of −0.60 MPa), indicating that water entered the fruits via the phloem rather than via the xylem. Solution entry into the fruits via the phloem supplied the water lost by transpiration and allowed for increases in fruit fresh mass (daily transpiration averaged 3.2‐fold higher than daily water content increases), while the accumulating solutes were apparently polymerized to account for the higher water potentials of the fruits compared with the cladodes. The phloem thus acts as the sole supplier of water and the main supplier of dry mass (90%) to such young fruits of platyopuntias.
Phosphatidylcholine molecular species involved in Γ‐linolenic acid biosynthesis in microsomes from borage seeds
Authors: Galle‐Le Bastard A. M. , Demandre C. , Oursel A. , Joseph M. , Mazliak P. , Kader J. C.
Published: March 2003

Boraginaceae seeds are particularly rich in Γ‐linolenic acid (6,9,12‐octadecatrienoic acid, Γ‐18:3). In microsomes, the analysis of phosphatidylcholine (PC) molecular species by HPLC led to identification of 15 different molecular species; among them 4 contained Γ‐18:3, mostly at position 2 of sn‐glycerol. Time courses of acylation and desaturation in PC molecular species were examined when [14C]oleoyl‐CoA or [14C]linoleoyl‐CoA was provided as substrates to isolated microsomes. With [14C]oleoyl‐CoA or [14C]linoleoyl‐CoA and in the absence of NADH, 3 main labelled PC molecular species were found: 18:2/[14C]18:1, 16:0/[14C]18:1 and 18:1/[14C]18:1. When NADH was present in the incubation medium, the fatty acids were progressively desaturated by the Δ12‐ and Δ6‐desaturases successively (with [14C]oleoyl‐CoA as precursor) or by the Δ6‐desaturase alone (with [14C]linoleoyl‐CoA as precursor). In both types of experiments, 7 final desaturation products in microsomes were evidenced; among them, 3 contained radioactive Γ‐18:3, i.e. 18:2/[14C]Γ‐18:3, 18:1/[14C]Γ‐18:3 and 16:0/[14C]Γ‐18:3. While the Δ12‐desaturase had no specificity for position on the glycerol backbone, labelled Γ‐linolenic acid was recovered exclusively in the sn‐2 position.
Lipid composition of somatic and zygotic embryos from Prunus avium. Effect of a cold treatment on somatic embryo quality
Authors: Reidiboym‐Talleux Lydia , Sourdioux Martine , Grenier Emmanuel , Grenier‐De March Ghislaine
Published: March 2003

In order to evaluate the quality of Prunus avium somatic embryos, a comparison of lipid composition between somatic and zygotic embryos was undertaken. In both zygotic and somatic embryos, neutral glycerolipids (NL) and phosphatidylcholine (PC) were the 2 major lipid classes. The content of NL increased over the course of development in zygotic embryos and reached 490 μg per embryo, while the PC content reached 100 μg per embryo. However, the contents of NL and PC in somatic embryos were similar to immature zygotic embryos at stage 3. Fatty acid composition of NL from both zygotic and somatic embryos revealed more unsaturated than saturated fatty acids. In somatic embryos, the saturated/unsaturated fatty acid ratios of NL and phosphatidylinositol (PI) were similar to those observed in immature zygotic embryos up to stage 6. Conversely, in phosphatidylethanolamine (PE) the ratio was similar to the ratio observed in mature zygotic embryos, at stage 7. Histological studies confirmed the immaturity of somatic embryos: no protein or lipid reserves were observed in the vacuolated cotyledonary cells. Maturation of somatic embryos was improved by a 2‐month cold period. In cold‐treated somatic embryos, both NL and PC increased to levels comparable to those observed in mature zygotic embryos, and the PE content reached 10 times the level of that in mature zygotic embryos. The cold treatment induced a large increase in the saturated/unsaturated fatty acid ratio in phospholipids but only a slight increase in that of neutral glycerolipids. Histological studies revealed a lipid accumulation at cellular level. Lipid bodies surrounded by protein bodies were observed in cotyledonary cells of cold‐treated somatic embryos. Furthermore, the cold‐treated somatic embryos developed into plantlets with a frequency of 14%, whereas no development was obtained with the non‐treated somatic embryos.
Interactions of light and ethylene in hypocotyl hook maintenance in Arabidopsis thaliana seedlings
Authors: Knee Emma M. , Hangarter Roger P. , Knee Michael
Published: March 2003

Etiolated seedlings frequently display a hypocotyl or epicotyl hook which opens on exposure to light. Ethylene has been shown to be necessary for maintenance of the hook in a number of plants in darkness. We investigated the interaction of ethylene and light in the regulation of hypocotyl hook opening in Arabidopsis thaliana. We found that hooks of Arabidopsis open in response to continuous red, far‐red or blue light in the presence of up to 100 μl l−1 ethylene. Thus a change in sensitivity to ethylene is likely to be responsible for hook opening in Arabidopsis, rather than a decrease in ethylene production in hook tissues. We used photomorphogenic mutants of Arabidopsis to demonstrate the involvement of both blue light and phytochrome photosensory systems in light‐induced hook opening in the presence of ethylene. In addition we used ethylene mutants and inhibitors of ethylene action to investigate the role of ethylene in hook maintenance in seedlings grown in light and darkness.
Characterization of an apoplastic basic thaumatin‐like protein from recalcitrant chestnut seeds
Authors: Garcia‐Casado Gloria , Collada Carmen , Allona Isabel , Soto Alvaro , Casado Rosa , Rodriguez‐Cerezo Emilio , Gomez Luis , Aragoncillo Cipriano
Published: March 2003

Mature chestnut seeds, with one of the highest moisture contents described to date, accumulate certain defensive proteins at unusually elevated levels. In this work a major 23‐kDa thaumatin‐like protein, termed CsTL1, has been purified from mature chestnut (Castanea sativa) cotyledons. Amino acid sequencing and characterization of its full‐length cDNA indicate that CsTL1 is synthesized as a preprotein with a signal peptide 22 amino acids in length. The mature protein contains 16 conserved cysteine residues presumably involved in disulfide bonding and has a high isoelectric point (ca. 9). Unlike most basic pathogenesis‐related (PR) proteins, mature CsTL1 is localized to the extracellular matrix, as revealed by immunoelectron microscopy studies of cotyledonary cells. The isolated protein has in vitro antifungal activity against Trichoderma viride and Fusarium oxysporum and shows strong synergistic effects with CsCh1, the most abundant chestnut cotyledon endochitinase. Moreover, both CsTL1 and CsCh1 appear to be regulated in the same manner during seed development and germination. These observations, along with the recent finding of endoglucanase activity for some TL proteins, support the notion that CsTL1 and CsCh1 are part of a complex seed defensive system against microbial growth. Another possibility is that these, and probably other seed PR proteins, have antifreeze activity. Both functions would be particularly relevant for chestnut seeds given their remarkable moisture content at maturity.
Protein phosphatase inhibitors activate defense responses in rice (Oryza sativa) leaves
Authors: Rakwal Randeep , Shii Katsuhiko , Agrawal Ganesh K. , Yonekura Masami
Published: March 2003

The protein phosphatase inhibitor cantharidin activates defense responses in rice leaves when applied exogenously at concentrations ranging from 100 to 500 μM. Responses include the accumulation of the major rice phenolic phytoalexin sakuranetin and the lactone phytoalexin momilactone A. Accumulation of sakuranetin was preceded by an induction of phenylalanine ammonia lyase (PAL) activity and an increase in the activity of naringenin 7‐O‐methyltransferase (NOMT), the key enzyme in sakuranetin biosynthesis. Cantharidin also strongly induced accumulation of the probenazole (PBZ)‐inducible protein (PBZ1) and two novel, related proteins named PBZ2 and PBZ3. Endothall, a herbicide and potent protein phosphatase inhibitor, but not its inactive analog (1,4‐dimethylendothall) also induced sakuranetin accumulation, increased activity of NOMT and accumulation of the 3 PBZ proteins. In contrast, two other protein phosphatase inhibitors, calyculin A and microcystin LR, did not activate these defense responses. Induction of NOMT and PAL activity, and sakuranetin accumulation, was completely blocked by cycloheximide. Leaf segments treated with cantharidin and endothall showed brownish and orange colored lesions, respectively, similar to the lesion mimic mutants of rice. These results indicate a direct role for protein phosphorylation/dephosphorylation events in the activation of defense responses in rice, in particular on the accumulation of antifungal phytoalexins and the PBZ proteins.
A storage protein gene from taro shows tuber‐specific expression in transgenic potato
Authors: Guimarães Rejane Lima , Marcellino Lucı´lia Helena , Grossi de Sá Maria Fátima , De Castro Monte Damares
Published: March 2003

Tarin is a family of storage proteins of Mr 12 500 that accounts for approximately 40% of the total soluble proteins in taro (Colocasia esculenta) corms. Besides its role as storage reserve, tarin may also act in defense responses. tar1, a gene encoding an isoform of tarin, was previously identified and it was shown to be expressed during corm development. To investigate the mechanisms involved in the regulation of tar1, transgenic tobacco and potato plants were produced. High levels of transcripts were found only in tubers of plants grown in the greenhouse. However, in vitro grown plants accumulated mRNA in both tubers and stems. It was also found that sucrose influenced tar1 expression in in vitro plants. Temporal expression of the tar1 gene varied, transcripts were not observed in stolons, but in all subsequent stages of potato development. These results suggest that the regulation of tar1 gene in potato mimics the regulation of potato storage protein genes. The tar1 promoter showed homology with patatin (potato storage protein) promoters. However, in transgenic tobacco, no expression was detected, indicating tuber specificity.
Endogenous gibberellins in Lolium perenne and influence of defoliation on their contents in elongating leaf bases and in leaf sheaths
Authors: Morvan‐Bertrand Annette , Ernstsen Arild , Lindgård Bente , Koshioka Masaji , Le Saos Joëlle , Boucaud Jean , Prud'homme Marie‐Pascale , Junttila Olavi
Published: March 2003

Gibberellin (GA) levels in leaf sheaths and in elongating leaf bases of perennial ryegrass (Lolium perenne L. cv. Bravo) were monitored in undefoliated and defoliated plants. Nine C‐13‐hydroxylated GAs (GA8, GA97, GA29, GA1, GA20, GA44, GA19, GA17, GA53) and one C‐13‐non‐hydroxylated GA (GA9) were identified by combined gas chromatography‐mass spectrometry in leaf extracts. The total level of GA8, GA29, GA1, GA20, GA44, GA19 and GA53, determined by selected ion monitoring, was 7 times higher in elongating leaf bases than in mature leaf sheaths. In both leaf tissues, defoliation induced an increase in GA53 level, while GA20 and GA1 levels decreased, suggesting that the GA53→GA44, as well as GA19→GA20, conversions were slowed down. The roles of GA1 in the control of leaf elongation and fructan mobilization following defoliation are discussed.
Differential aluminum tolerance in soybean: An evaluation of the role of organic acids
Authors: Silva Ivo R. , Smyth Thomas J. , Raper C. David , Carter Thomas E. , Rufty Thomas W.
Published: March 2003

The role of organic acids in aluminum (Al) tolerance has been the object of intensive research. In the present work, we evaluated the roles of organic acid exudation and concentrations at the root tip on Al tolerance of soybean. Exposing soybean seedlings to Al3+ activities up to 4.7 μM in solution led to different degrees of restriction of primary root elongation. Al tolerance among genotypes was associated with citrate accumulation and excretion into the external media. Citrate and malate efflux increased in all genotypes during the first 6 h of Al exposure, but only citrate efflux in Al‐tolerant genotypes was sustained for an extended period. Tolerance to Al was correlated with the concentration of citrate in root tips of 8 genotypes with a range of Al sensitivities (r2=0.75). The fluorescent stain lumogallion indicated that more Al accumulated in root tips of the Al‐sensitive genotype Young than the Al‐tolerant genotype PI 416937, suggesting that the sustained release of citrate from roots of the tolerant genotype was involved in Al exclusion. The initial stimulation of citrate and malate excretion and accumulation in the tip of all genotypes suggested the involvement of additional tolerance mechanisms. The experiments included an examination of Al effects on lateral root elongation. Extension of lateral roots was more sensitive to Al than that of tap roots, and lateral root tips accumulated more Al and had lower levels of citrate.
Overexpression of a heterologoussamgene encoding S‐adenosylmethionine synthetase in flax (Linum usitatissimum) cells: Consequences on methylation of lignin precursors and pectins
Authors: Lamblin Frédéric , Saladin Gaëlle , Dehorter Bertrand , Cronier David , Grenier Emmanuel , Lacoux Jérôme , Bruyant Philippe , Lainé Eric , Chabbert Brigitte , Girault Fabienne , Monties Bernard , Morvan Claudine , David Hélène , David Alain
Published: March 2003

TheArabidopsis thaliana sam1gene encoding S‐adenosylmethionine synthetase (EC 2.5.1.6) was transferred to flax (Linum usitatissimum) cells viaAgrobacterium tumefaciens. This enzyme catalyses the conversion of methionine to S‐adenosylmethionine (SAM), the major methyl group donor in living cells. The aim of this work was to study the consequences of an increased SAM‐synthetase (SAM‐S) activity in transgenic cell lines on both the production of mono‐ and dimethoxylated lignin monomers and the degree of methylesterification of pectins. Hypocotyls were cocultivated withAgrobacterium tumefaciensstrain GV3101 (pGV2260) harbouring the pO35SSAM binary vector carrying thesam1gene under the control of the 35S promoter and thenptIIgene for selection of putative transformed cells. Most of the transgenic cell lines exhibited a significant (up to 3.2‐fold) increase in SAM‐S activity compared to the controls. The results showed that for the cell lines analysed this transformation had no effect on caffeic acidO‐methyltransferase (COMT, EC 2.1.1.68) in vitro activity, degree of methoxylation of lignin precursors or lignin deposition, pectin methyltransferase (PMT, EC 2.1.1) in vitro activity, but led to an increase of pectin methylesterification in friable and fast‐growing transgenic cell lines.
Effect of embryonic axis removal and exogenous calcium on carboxypeptidase I of mung bean seedling cotyledons
Authors: Singh Sushmita , Wilson Karl A. , Tan‐Wilson Anna L.
Published: March 2003

Removal of the embryonic axis prevents the normal decline of carboxypeptidase (Cpase) I in mung bean seedling cotyledons. Cpase I activity and protein, the latter manifested on western blots, almost completely disappear about 24 h before the cotyledon abscises. Of the 3 proteolytic enzyme patterns, only that of Cpase I can be restored by an exogenous supply of 10 mM CaCl2 in the agar growth medium. The calcium effect is dependent on [CaCl2] and is not manifested in the presence of chelators and calcium channel blockers. For detached cotyledons to show the normal low level of Cpase I by the eighth day of growth, calcium had to be supplied during seed imbibition and throughout the entire time from removal of the axis. The difference between detached cotyledons in the absence and presence of calcium was greatest when the cotyledons were detached 4–6 days after seed imbibition. Loss of Cpase I activity and protein can be demonstrated in vitro, with the maximum level of Cpase I‐degrading activity measured 4 days after seed imbibition under the same growth conditions used to study the calcium effect. It is sensitive to pepstatin and has a pH optimum of 3, suggesting that this Cpase I‐degrading activity is due to an aspartic protease.
The promoter of a cytosolic glutamine synthetase gene from the conifer Pinus sylvestris is active in cotyledons of germinating seeds and light‐regulated in transgenic Arabidopsis thaliana
Authors: Avila Concepción , R. Cantón Francisco , Barnestein Pilar , Suárez María‐Fernanda , Marraccini Pierre , Rey Manuel , Humara Jaime M. , Ordás Ricardo , M. Cánovas Francisco
Published: March 2003

We have isolated and characterized a genomic clone encoding Scots pine (Pinus sylvestris) cytosolic glutamine synthetase (GS). The clone contains the 5′ end half of the gene including part of the coding region and 980 bp upstream of the translation initiation codon. The major transcription start site (+1) was mapped around 180 nucleotides upstream of the translation initiation codon. Sequence analysis of the 5′‐upstream region of the gene reveals the presence of putative regulatory elements including a poly‐CT consensus sequence, a purine‐rich tandem repeat and two AT‐rich regions. Fusions of the upstream gene region to uidA were shown to be transiently expressed in the cotyledons of germinating pine seeds transformed by microprojectile bombardment. Stable transformation of Arabidopsis thaliana revealed the shoot apical meristem as the major region of heterologous permanent expression in Arabidopsis, in agreement with the expression of the GS gene in Pinus. Moreover, quantitative data derived from fluorometric β‐glucuronidase assays in control and continuous light‐grown transgenic Arabidopsis plants indicate that the isolated upstream region of the gene contains regulatory sequences involved in the response to light.
Photocontrol of flowering and stem extension of the intermediate‐day plant Echinacea purpurea
Authors: Runkle Erik S. , Heins Royal D. , Cameron Arthur C. , Carlson William H.
Published: March 2003

Intermediate‐day plants (IDP) flower most rapidly and completely under intermediate photoperiods (e.g., 12–14 h of light), but few species have been identified and their flowering responses are not well understood. We identified Echinacea purpurea Moench as an IDP and, based on our results, propose a novel mechanism for flowering of IDP. Two genotypes of E. purpurea (‘Bravado’ and ‘Magnus’) flowered most completely (≥79%) and rapidly and at the youngest physiological age under intermediate photoperiods of 13–15 h. Few (≤14%) plants flowered under 10‐ or 24‐h photoperiods, indicating E. purpurea is a strongly quantitative IDP. Plants were also induced to flower when 15‐h dark periods were interrupted with as few as 7.5 min of low‐intensity lighting (night interruption, NI). Flowering was progressively earlier as the NI increased to 1 h, but was delayed when the NI was extended to 4 h. Stem length increased by ≥230% as the photoperiod or NI duration increased, until plants received a saturating duration (at 14 or 1 h, respectively). Flowering was inhibited when 16‐h photoperiods were deficient in red (R, 600–700 nm) light, and was promoted when photoperiods were deficient in far‐red (FR, 700–800 nm) light. Because of our results, we propose the flowering behavior of IDP such as E. purpurea is composed of two mechanisms: a light‐dependent response operating through light‐labile (type I) phytochrome in which flowering is inhibited by an LD, and a light‐stable (type II) phytochrome (i.e., phyB, D and E) response in which flowering is promoted by a short‐night.
Ubiquitin‐ and proteasome‐dependent proteolysis in plants
Authors: Ingvardsen Christina , Veierskov Bjarke
Published: March 2003

In recent years it has become obvious that protein degradation is an important catabolic process during development in plants and animals. One very conserved degradative system is the ubiquitin‐ and proteasome‐dependent proteolytic pathway, which is found in all eukaryotes from yeast to mammals and plants. The pathway consists of two parts, one in which chains of ubiquitin are conjugated to substrate proteins, and one in which these substrate proteins are either degraded by the 26S proteasome or are de‐ubiquitinated. The ubiquitin‐ and proteasome‐dependent pathway degrades a wide range of proteins in the nucleus and cytoplasm. It is highly specific, but controls a large number of cellular events due to the diversity in the conjugating enzymes. This pathway is important for removal of abnormal/damaged proteins that have had their recognition sites exposed as well as for control of specific transcription factors and cell cycle regulators. In plants, ubiquitin‐ and proteasome‐dependent proteolysis is known to be involved in regulation of the cell cycle and transcription factors as well as endoplasmic reticulum‐associated protein degradation, stress response and developmental processes, such as xylogenesis and senescence.
Contrasting responses of photosynthesis and carbon metabolism to low temperatures in tall fescue and clovers
Authors: Pérez Pilar , Morcuende Rosa , Martín del Molino Isabel , Sánchez de la Puente Luis , Martínez‐Carrasco Rafael
Published: March 2003

Growth, photosynthesis and carbohydrate metabolism in plants of two grassland species, clover (Trifolium subterraneum L. cv. Areces and Gaitan) and tall fescue (Festuca arundinacea Schreb.), shifted from 25 to 12°C for 1 day or developed at 12°C were compared with controls kept at 25°C. Cold development produced a larger inhibition of growth in fescue than in clovers. In contrast, transferring plants from high to low temperature inhibited photosynthesis to a lesser extent in fescue than in clovers, this difference being associated with an increase in the activation state of Calvin cycle enzymes in fescue, but not in the clovers, a decreased cytosolic fructose‐1,6‐bisphosphatase (cFBPase, EC 3.1.3.11) activity in clovers, and an accumulation of hexose phosphates only in fescue. Development at 12°C partly relieved the inhibition of photosynthesis in clovers, in contrast with fescue, which correlated with increases in total ribulose‐1,5‐bisphosphate carboxylase oxygenase (Rubisco, EC 4.1.1.39) activity only in clovers, and with greater increases in total stromal FBPase (sFBPase) activity in clovers than in fescue. The activity of sucrose synthesis enzymes was increased in the two clovers and fescue developed in the cold, while carbohydrate accumulation was much bigger in cold‐developed fescue than in clovers because of a 5‐fold increase in fructan contents in the former. The contents of phosphorylated intermediates increased in clovers but decreased in fescue grown at 12°C. Our results suggest that restricted ribulose‐1,5‐bisphosphate (RuBP) regeneration limited the recovery of photosynthetic capacity in cold‐developed fescue.
Polyphenol oxidase and herbivore defense in trembling aspen (Populus tremuloides): cDNA cloning, expression, and potential substrates
Authors: Haruta Miyoshi , Pedersen Jens A. , Constabel C. Peter
Published: March 2003

The biochemical anti‐herbivore defense of trembling aspen (Populustremuloides Michx.) was investigated in a molecular analysis of polyphenol oxidase (PPO; EC 1.10.3.2). A PPO cDNA was isolated from a trembling aspen wounded leaf cDNA library and its nucleotide sequence determined. Southern analysis indicated the presence of two PPO genes in the trembling aspen genome. Expression of PPO was found to be induced after herbivory by forest tent caterpillar, by wounding, and by methyl jasmonate treatment. Wound induction was systemic, and occurred in unwounded leaves on wounded plants. This pattern of expression is consistent with a role of this enzyme in insect defense. A search for potential PPO substrates in ethanolic aspen leaf extracts using electron spin resonance (ESR) found no pre‐existing diphenolic compounds. However, following a brief delay and several additions of oxygen, an ESR signal specific for catechol was detected. The source of this catechol was most likely the aspen phenolic glycosides tremulacin or salicortin which decomposed during ESR experiments. This was subsequently confirmed in experiments using pure salicortin.
Current molecular understanding of the genetically programmed process of leaf senescence
Authors: Chandlee Joel M.
Published: March 2003

Natural leaf senescence proceeds through an orderly program of events referred to, generally, as the ‘senescence syndrome’. Leaf senescence consists of primarily, but not exclusively, a set of degradative and remobilization activities that salvage valuable nutrients by reallocation to the seeds or other viable parts of the plant. The program requires changes in gene expression and eventually culminates in death of the leaf or whole plant. Leaf/whole plant senescence has now been scrutinized extensively using molecular genetic approaches and a clearer picture of the events that comprise the developmental program is beginning to emerge. However, while understandings of the phenomenological aspects of the program have become apparent, the mechanistic aspects, particularly with regard to the processes required for induction and regulation of the program, are still far from clear. Molecular evidence suggests the process is complex in terms of the wide array of genes and activities expressed, and in terms of the overall regulation of progression of the events of the syndrome. This article attempts to review our current understanding of leaf senescence and includes a brief discussion of aspects of the process that require clarification if we are to more fully understand this complex developmental program.
Characterization of aluminium‐induced citrate secretion in aluminium‐tolerant soybean (Glycine max) plants
Authors: Yang Zhen Ming , Nian Hai , Sivaguru Mayandi , Tanakamaru Shigemi , Matsumoto Hideaki
Published: March 2003

Recently, we showed that secretion of citrate in an aluminium (Al) tolerant cultivar soybean (Glycine max) (cv. Suzunari) is a specific response to Al stress [Yang et al. (2000) Physiol Plant 110: 72–77]. Here we investigated the intrinsic mechanisms behind the secretion of citrate induced by Al. The amount of citrate secreted during the 24‐h Al treatment period increased with increasing concentration of Al (0–70 μM). We analysed citrate secretion basically under 3 conditions: (1) by varying light‐exposure, (2) with intact or excised shoots and (3) by using a divided chamber technique. Further, the content of organic acids in the tissue and the activity of enzymes involved in organic acid metabolism were analysed and evaluated. The results indicate that high rate of citrate secretion in soybean requires a 4‐h induction period. Al had a continuous effect on the citrate secretion when Al was removed from the treatment solution. Citrate secretion increased steadily under exposure to continuous light. However, when the shoots were excised the citrate secretion rate dropped to 3–6 times that of their control counterparts. Results of root manipulation experiments revealed that citrate secretion required the direct contact of Al. In other words, only the Al‐treated root portions secreted citrate. All these observations suggest that the shoots play a role in Al‐induced citrate secretion. Although shoots may not supply citrate for the secretion upon Al treatment, it seems that they may provide the carbon source and/or energy for citrate synthesis in the root. On the other hand, the root organic acid content (1‐cm apex) indicated that malate might contribute to citrate secretion by keeping the balance between citrate synthesis and release in the root apices. Quantification of enzymes involved in organic acid metabolism showed only a 16% increase in citrate synthase activity upon Al treatments (6 h) with no differences in other enzymes. Hence, we could not rule out completely the potential contribution of citrate from shoots and the results are discussed in the light of shoots contributing either energy or citrate itself for enhanced citrate secretion in the Al‐tolerant plant roots.
Chilling‐induced leaf abscission of Ixora coccinea plants. III. Enhancement by high light via increased oxidative processes
Authors: Michaeli Rina , Philosoph‐Hadas Sonia , Riov Joseph , Shahak Yosepha , Ratner Kira , Meir Shimon
Published: March 2003

The role of increased oxidation induced by successive stresses of chilling and high light in the induction of leaf abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7°C for 3 days) to high light (500–700 μmol m−2 s−1 photosynthetically active radiation) for 5 h at 20–25°C enhanced chilling‐induced leaf abscission. This abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, α‐naphthaleneacetic acid or the ethylene action inhibitor, 1‐methylcyclopropene. The oxidative processes initiated during the low light period following the dark chilling period, such as indoleacetic acid (IAA) decarboxylation and lipid peroxidation, were further enhanced by subsequent exposure to high light. Photoinhibition, expressed by the reduction of the chlorophyll fluorescence parameter Fv/Fm, was evident following exposure to high light, irrespective of the temperature of the pretreatment, but this reduction persisted only in chilled plants. This suggests that oxidative processes generated during and after the chilling period might have inhibited the recovery from photoinhibition. The chilling stress under darkness induced a 60% reduction in superoxide dismutase (SOD) activity and significant increases (130–600%) in the activities of several other antioxidative enzymes. These data suggest that the chilling‐induced reduction in SOD activity may well be responsible for the increase in the oxidative stress induced by the subsequent light treatment, as expressed by the increased enzymatic activities. Taken together, this study provides further support for the involvement of oxidative processes in the events occurring in tissues exposed to sequential chilling and light stresses, leading to reduction in free IAA content in the abscission zone and to leaf abscission.
Vernalization, photoperiod and GA3 interact to affect flowering of Japanese radish (Raphanus sativus Chinese Radish Jumbo Scarlet)
Authors: Erwin John E. , Warner Ryan M. , Smith Alan G.
Published: March 2003

Raphanus sativus L. Chinese Radish Jumbo Scarlet has characteristics that make it an excellent plant model for vernalization studies. This study further characterizes flower induction of R. sativus Chinese Radish Jumbo Scarlet. Seed were imbibed in distilled water containing 0, 10−5M or 10−3M GA3 for 24 h and were then exposed to 6 ± 0.5°C (vernalized) for 0, 2, 4, 6, or 8 days. Seedlings were then grown under a short‐ (8 h) or long‐day photoperiod (8 h with or without a 4‐h night interruption; 2200–0200 h). Of unvernalized plants grown under long‐ and short‐day conditions, 45 and 3% flowered, respectively. Saturation of the vernalization response occurred after a 4‐ or 8‐day vernalization treatment when plants were placed under long‐ or short‐days, respectively. Basal leaf number and days to anthesis decreased when seeds were cooled for 2 or 4 days and were imbibed with 10−3M GA3 compared to distilled water only. These data indicate that R. sativus Chinese Jumbo Scarlet has principally an obligate vernalization requirement when grown under short‐days. GA3 application only facilitated flowering when the length of the vernalization treatment was marginal. Taken together, these data support the use of this plant as a model plant for identifying vernalization responses under short‐day conditions.
Uncoupling brassinosteroid levels and de‐etiolation in pea
Authors: Symons Gregory M. , Schultz Lee , Kerckhoffs L. Huub J. , Davies Noel W. , Gregory Davina , Reid James B.
Published: March 2003

The suggestion that brassinosteroids (BRs) have a negative regulatory role in de‐etiolation is based largely on correlative evidence, which includes the de‐etiolated phenotypes of, and increased expression of light‐regulated genes in, dark‐grown mutants defective in BR biosynthesis or response. However, we have obtained the first direct evidence which shows that endogenous BR levels in light‐grown pea seedlings are increased, not decreased, in comparison with those grown in the dark. Similarly, we found no evidence of a decrease in castasterone (CS) levels in seedlings that were transferred from the dark to the light for 24 h. Furthermore, CS levels in the constitutively de‐etiolated lip1 mutant are similar to those in wild‐type plants, and are not reduced as is the case in the BR‐deficient lkb plants. Unlike lip1, the pea BR‐deficient mutants lk and lkb are not de‐etiolated at the morphological or molecular level, as they exhibit neither a de‐etiolated phenotype or altered expression of light‐regulated genes when grown in the dark. Similarly, dark‐grown WT plants treated with the BR biosynthesis inhibitor, Brz, do not exhibit a de‐etiolated phenotype. In addition, analysis of the lip1lkb double mutant revealed an additive phenotype indicative of the two genes acting in independent pathways. Together these results strongly suggest that BR levels do not play a negative‐regulatory role in de‐etiolation in pea.
Water entry into detached root systems saturates with increasing externally applied pressure; a result inconsistent with models of simple passive diffusion
Authors: Emery R. J. Neil , Salon Christophe
Published: March 2003

The most widely accepted model of radial water entry from the soil into the xylem of roots is based on principles of ordinary passive diffusion. However, long‐standing problems with this model remain unresolved, which concern variable intrinsic properties of conductivity, Lp, changing reflection coefficients, σ, and inaccurate resolution of osmotic differentials between the soil and xylem. Our study re‐examined pressure flow relationships in isolated roots of tomato (Lycopersicon esculentum Mill. cv. Montfavet), pea (Pisum sativum cv. Baccara) and soybean (Glycine max L. Merryl cv. Essor) manipulated in a pressure chamber. In addition to problems previously recognized with the simple passive diffusion model, a new conflict, flow saturation, was observed at high pressures. Experiments revealed that the plateau in flow, Jmax seen at high pressures followed natural rhythms diurnally and developmentally, and was not due to root damage or unnatural flow restriction. Near the end of the photoperiod, Jmax closely correlated with root dry mass. The above inconsistencies between observations in pressure‐flow kinetics and ordinary passive diffusion indicate that either the current model should be adjusted or a new model should be proposed.
Stimulation of respiration by Pb2+ in detached leaves and mitochondria of C3 and C4 plants
Authors: Romanowska Elżbieta , Igamberdiev Abir U. , Parys Eugeniusz , Gardeström Per
Published: March 2003

The exposure of detached leaves of C3 plants (pea, barley) and C4 plant (maize) to 5 mM Pb (NO3)2 for 24 h caused a reduction of their photosynthetic activity by 40–60%, whereas the respiratory rate was stimulated by 20–50%. Mitochondria isolated from Pb2+‐treated pea leaves oxidized substrates (glycine, succinate, malate) at higher rates than mitochondria from control leaves. The respiratory control (RCR) and the ADP/O ratio were not affected. Pb2+ caused an increase in ATP content and the ATP/ADP ratio in pea and maize leaves. Rapid fractionation of barley protoplasts incubated at low and high CO2 conditions, indicated that the increased ATP/ADP ratio in Pb2+‐treated leaves resulted mainly from the production of mitochondrial ATP. The measurements of membrane potential of mitochondria with a TPP+‐sensitive electrode further showed that mitochondria isolated from Pb2+‐treated leaves had at least as high membrane potential as mitochondria from control leaves. The activity of NAD‐malate dehydrogenase in the protoplasts from barley leaves treated with Pb2+ was 3‐fold higher than in protoplasts from control leaves. The activities of photorespiratory enzymes NADH‐hydroxypyruvate reductase and glycolate oxidase as well as of NAD‐malic enzyme were not affected. The presented data indicate that stimulation of respiration in leaves treated by lead is in a close relationship with activation of malate dehydrogenase and stimulation of the mitochondrial ATP production. Thus, respiration might fulfil a protective role during heavy metal exposure.
Isolation of an ethylene‐responsive gene (ERAF16) for a putative methyltransferase and correlation of ERAF16 gene expression with female flower formation in cucumber plants (Cucumis sativus)
Authors: Ando Sugihiro , Sakai Shingo
Published: March 2003

Ethylene regulates sex expression in cucumber plants (Cucumis sativus L.). To clarify ethylene‐mediated regulation of sex expression, we previously used differential display technology to identify 20 ethylene‐responsive genes in the apices of cucumber plants. In this study, we report the analysis of the full‐length cDNA from clone #16 and its corresponding gene (designated as ERAF16), which encodes a methyltransferase. This type of methyltransferase has recently been identified, and some of them methylate signalling molecules in plants, which include salicylic acid and jasmonic acid. However, the substrate of the ERAF16 protein has not been revealed. We examined the ERAF16 expression pattern using RNA gel blot analysis of total RNA preparations from the apices of a monoecious cucumber (cv. Shimoshirazu‐jibai) and a gynoecious cultivar (Rensei). The levels of ERAF16 expression in these cultivars were correlated with the development of female flowers. The induction of ERAF16 transcription by ethephon occurred within 4 h of the start of treatment. The expression of ERAF16 in immature floral buds of the gynoecious cultivar was stronger than in those of the monoecious cultivar. These results suggest that ERAF16 is included in the ethylene‐induced formation of female flowers. However, ERAF16 was expressed in opened flowers and vegetative tissues. Therefore, we speculate that the role of ERAF16 protein varies, depending on the tissue and developmental stage.
Blue‐light‐control of the uptake of amino acids and of ammonia in Chlorella mutants
Authors: Kamiya Akio , Saitoh Takeshi
Published: March 2003

In non‐photosynthetic, yellow or colourless mutant cells of Chlorella kessleri, grown with nitrate as sole nitrogen source, blue light inhibited the uptake of the amino acids glycine, proline and arginine and of ammonia in growing cells, while it enhanced the uptake of these amino acids in resting cells. On the other hand, in cells grown with ammonia as the only nitrogen source without nitrate reductase activity, blue light did not influence the uptake of amino acids and of ammonia in growing cells, while it enhanced the uptake of amino acids in resting cells. Addition of methionine sulphoximine, a potent inhibitor of glutamine synthetase, to growing cells, resulted in intracellular ammonia‐accumulation and inhibition of uptake of glycine and of ammonia. For the colourless mutant, blue light was shown to activate purified nitrate reductase. These results indicate that in the mutant cells of Chlorella examined, uptake of ammonia seems to be influenced by nitrate reductase and the uptake of amino acids was influenced by both nitrate reductase and an unknown blue‐light‐receptor(s). The uptake of urea in mutant cells is not influenced by the irradiation with blue light. Uptake of glycine was also increased after addition of glucose (hexose) in the dark. Because blue light is known to enhance the breakdown of starch, a reaction producing glucose for oxidative degradation in the algae used, the role of glucose (hexose) in the blue light‐affected uptake of amino acids is discussed.
Anthocyanins facilitate tungsten accumulation in Brassica
Authors: Hale Kerry L. , Tufan Hale A. , Pickering Ingrid J. , George Graham N. , Terry Norman , Pilon Marinus , Pilon‐Smits Elizabeth A. H.
Published: March 2003

Accumulation of molybdenum in Brassica was recently found to be correlated with anthocyanin content, involving the formation of a blue complex. Here the role of anthocyanins in tungsten sequestration was investigated using three species of Brassica: B. rapa (cv. Fast plants), B. juncea (Indian mustard) and B. oleracea (red cabbage). Seedlings of B. rapa and B. juncea turned blue when supplied with colourless tungstate. The blue compound co‐localized with anthocyanins in the peripheral cell layers, and the degree of blueness was correlated with anthocyanin content. The direct involvement of anthocyanins in the blue coloration was evident when purified anthocyanins showed a colour change from pink to blue in vitro upon addition of tungstate, over a wide pH range. Anthocyanin production was upregulated 3‐fold by W in B. juncea, possibly reflecting a function for anthocyanins in W tolerance or sequestration. The presence of anthocyanins facilitated W accumulation in B. rapa: anthocyanin‐containing seedlings accumulated 3‐fold more W than an anthocyaninless mutant. There was no correlation between anthocyanin content and W tolerance under these conditions. The nature of the interaction between anthocyanins and tungstate was investigated. X‐ray absorption spectroscopy showed no change in the local chemical environment of W upon uptake of tungstate by the plant; HPLC analysis of purified anthocyanin with or without tungstate showed no peak shift after metal treatment.
Regulation of photosynthesis through source: sink imbalance in citrus is mediated by carbohydrate content in leaves
Authors: Iglesias Domingo J. , Lliso Ignacio , Tadeo Francisco R. , Talon Manuel
Published: March 2003

In citrus, the occurrence of a sink effect on photosynthesis (A) is controversial. Leaf carbohydrates and photosynthetic rates in field‐grown trees of Satsuma mandarin (Citrus unshiu[Mak.] Marc.) cv. Okitsu, were measured to elucidate whether or not the demand for photoassimilates regulates A. The data indicated that the source‐sink imbalances induced by different treatments altered both soluble (sucrose, glucose and fructose) and insoluble carbohydrates in leaves, as well as photosynthetic rates. In general, girdling and defruiting increased starch and reduced photosynthesis, whereas source‐limiting conditions imposed through partial defoliations had the opposite effect. These results are compatible with the assumption that a lack of sink activity leads to carbohydrate accumulation and feedback inhibition of A, and vice versa. Further evidence supporting a source‐sink effect on A was provided by measurements of the dry matter:leaf area ratio, since defoliations, for example, increased this ratio. The in vivo sucrose supplementation to plants with different source:sink ratios (control, defoliated, girdled and defruited plants) increased carbohydrates and reduced photosynthesis. This suggests that sugars may have, per se, the potential to repress photosynthetic rates in intact plants with active sinks. Based on these results we propose that sugar accumulation in citrus leaves causes a feedback inhibition of A.