bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress tolerance in the marsh plant Spartina patens: Impact of NaCl on growth and root plasma membrane lipid composition
Authors: Wu Jinglan , Seliskar Denise M. , Gallagher John L.
Published: March 2003

The C‐4 salt marsh grass, Spartina patens, thrives in the upper portion of the marsh where soil salinities may be equal to coastal seawater. Spartina patens was grown in hydroponic culture in a greenhouse at 0, 340, and 510 mM NaCl, and measured for growth, tissue cation content, and root plasma membrane (PM) lipid composition. From 0 to 340 and 510 mM, the shoot growth decreased, but root growth was not affected. The Na+ content increased in both shoots and roots when plants were grown in salt, while the shoots had a decreased K+ content and the roots had a decreased Ca2+ content. Spartina patens root plasma membrane was isolated with an aqueous polymer two‐phase system. The purity of the plasma membrane was verified with cytochemical tests on membrane enzyme markers. Plasma membrane lipids were stable relative to the membrane protein content. Molar percentages of sterols (including free sterols) and phospholipid decreased with increasing salinity. However, glycolipid showed a statistically significant increase in the total lipid as salinity in the medium was increased from 0 to 510 mM. Even at a salinity of 510 mM, the plasma membrane sterol/phospholipid ratio was unaffected by NaCl. When the plants were grown in NaCl media, the plasma membrane had a decreased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content, but the PC/PE ratios were not affected. The plasma membrane molar percentage of sitosterol in total free sterol increased when plants were grown in salt media. The predominant membrane fatty acids were C11 and C14, and the major unsaturated one was C14:1. An increase in growth medium salinity resulted in a decreased root plasma membrane fluidity.
Circadian rhythms have insignificant effects on plant gas exchange under field conditions
Authors: Williams William E. , Gorton Holly L.
Published: March 2003

Circadian rhythms in photosynthesis and stomatal conductance have been widely observed, but their possible adaptive significance is unknown. To determine whether such rhythms have a significant effect on the daily courses of carbon gain and/or water loss under field conditions, we obtained laboratory data on circadian rhythms in gas exchange of Saururus cernuus L., a wetland perennial. Using these data we modified a widely used mathematical model of photosynthesis and stomatal conductance by introducing the observed circadian‐rhythmic variation into the maximum rates of electron transport and carboxylation. We measured photosynthesis and stomatal conductance hourly on the same species growing naturally in the field and compared measured daily courses of photosynthesis and stomatal conductance with daily courses calculated using the model as originally formulated and also as modified to include circadian rhythms. The model fit the field data only slightly better when rhythms were included: the rhythms accounted for only about 1% of the observed daily carbon gain. Thus, these rhythms probably do not affect photosynthesis and stomatal conductance in the field.
Cloning and molecular characterization of a presumptive argF, a structural gene encoding ornithine carbamoyl transferase (OCT), in the cyanobacterium Nostoc sp. PCC 73102
Authors: Jansson Eva , Lindblad Peter
Published: March 2003

Ornithine carbamoyl transferase (OCT), encoded by argF, catalyzes the formation of citrulline from ornithine and carbamoyl phosphate. A presumptive argF from the filamentous cyanobacterium Nostoc sp. PCC 73102 has been cloned and sequenced. A transcriptional terminator sequence is suggested downstream of the structural gene. Amino acids known to be involved in binding the substrate carbamoyl phosphate and ornithine were observed within the sequence. The deduced amino acid sequence showed 69% identity to the deduced amino acid sequence from Synechocystis sp. PCC 6803, but less identities (30‐46@) to OCTs from other organisms. The subunits of the deduced protein had a calculated molecular mass of 33 368 Da. Northern blot experiments demonstrated a single transcript with an approximate size of 0.95 kb.
Sulphate and micronutrients can modulate the expression levels of myrosinases in Sinapis alba plants
Authors: Visvalingam Seetha , Hønsi Torunn G. , Bones Atle M.
Published: March 2003

The myrosinase‐glucosinolate system is considered to be a major component of the preformed defence system of Brassicaceae species. This hypothesis has influenced the belief that the components of the myrosinase‐glucosinolate system are present at fixed levels which are independent of environmental factors. In the present study we show that external availability of nutrients can modulate the expression levels of myrosinase enzymes (EC 3.2.3.1). Nutrients such as sulphate, iron, copper, zinc and manganese were tested for their modulation effect on myrosinase expression levels and activity in roots, stems, cotyledons and buds of Sinapis alba seedlings at four different developmental stages. The most sensitive organ was the bud where iron deficiency approximately doubled the myrosinase activity. Removal of sulphate and all four micronutrients reduced the myrosinase activity to approximately half of the activity in plants supplemented with all these nutrients. The myrosinase polypeptides can be divided into classes based on molecular mass after reduction. The nutritional status influenced mainly the 68‐kDa class of myrosinases as revealed by western blot and laser scan densitometry of the immunolabelled blots.
Effects of the plant growth regulator abscisic acid and high osmoticum on the developmental expression of the maize catalase genes
Authors: Guan Lingqiang , Scandalios John G.
Published: March 2003

The effects of abscisic acid (ABA) and high osmoticum on catalase (Cat) gene expression in maize have been examined. Each Cat gene responds differently to ABA and osmotic stress at different developmental stages and in different tissues. Cat1 transcript accumulates to high levels in developing and germinating embryos, and in leaves. In embryos, Cat2 and Cat3 transcripts are up‐regulated only at very high ABA concentrations during late embryogenesis and in response to various concentrations of ABA in germinating embryos. Cat3 transcript is down‐regulated by ABA and osmotic stress in leaves. Accumulation of Cat1 transcript in response to osmotic stress is a consequence of increased endogenous ABA levels. Our data suggest that two separate pathways might be involved in the ABA‐mediated induction of Cat1. The Vp1 trans‐acting factor is required for maximum induction of Cat1 transcript in wild‐type (Vp1/—) and in W64A developing embryos; however, Vp1 is not required for inducing the Cat1 transcript in vp1 mutant developing embryos, nor in W64A germinating embryos or in leaves. Given the fact that the Cat genes have a known function, we hypothesize that the increase in Cat gene products in response to ABA is due, in part, to ABA‐mediated metabolic changes leading to changes in oxygen free radical levels, which in turn, lead to the induction of the antioxidant defense system.
Characterization of proteolytic activity during senescence in daylilies
Authors: Stephenson Paul , Rubinstein Bernard
Published: March 2003

From 12 to 24 h after the opening of daylily flowers (Hemerocallis hybrid cv. Stella d'Oro), the petals begin to degrade and the protein levels of soluble, microsomal‐ and plastid‐enriched fractions decrease by 50%, on a per petal basis. To help determine some of the components for the cell death program in daylily petals, we studied the mechanisms that regulate this loss of protein. Enzyme activities capable of digesting native daylily protein, gelatin, and azocasein markedly increase after flower opening, and their appearance is inhibited by the translation inhibitor, cycloheximide. Protein hydrolysis in vitro is prevented by inhibitors of cysteine, serine and metalloproteinases. Immunoblots using antibodies to ubiquitin pathway enzymes indicate that the ubiquitin system is not senescence specific. However, ion leakage is delayed by two inhibitors of the 26S proteasome. We propose that programmed cell death in daylily petals may involve the increase in activity of at least three classes of proteinases, and discuss the possibility that these proteinases may operate in concert with the ubiquitin pathway.
The plasma membrane H+‐ATPase from maize roots is phosphorylated in the C‐terminal domain by a calcium‐dependent protein kinase
Authors: Camoni Lorenzo , Fullone Maria Rosaria , Marra Mauro , Aducci Patrizia
Published: March 2003

A protein kinase activity associated with maize root plasma membranes was partially purified and characterized. Biochemical properties, such as calcium dependence, inhibition by calmodulin antagonists, and absence of calmodulin stimulation, indicated that the enzyme belongs to the calcium‐dependent protein kinase (CDPK) family. By means of an in‐gel phosphorylation assay the molecular mass of active polypeptides was determined: two bands of 55 and 51 kDa became labelled. The same proteins were also immunodecorated by monoclonal antibodies against soybean CDPK. Results from in vitro assays demonstrated that maize H+‐ATPase was a suitable substrate for this protein kinase and that the phosphorylation site was located at the C‐terminal domain of the enzyme. This result was confirmed by using as substrate in phosphorylation assays the isolated C‐terminal domain of the H+‐ATPase expressed in Escherichia coli as a glutathione‐transferase fusion protein.
Changes in activity of antioxidative enzymes in wheat (Triticum aestivum) seedlings under cold acclimation
Authors: Scebba Francesca , Sebastiani Luca , Vitagliano Claudio
Published: March 2003

Activated oxygen species such as superoxide radicals, singlet oxygen, hydrogen peroxide and hydroxyl radicals can be produced in plants exposed to low, non‐freezing, non‐injurious temperatures. To prevent or alleviate oxidative injury, plants have evolved several mechanisms which include scavenging by natural antioxidants and enzymatic antioxidant systems such as superoxide dismutases, catalase and peroxidases.

Although overproduction of hydrogen peroxide and increased tolerance to oxidative stress can be induced in wheat by low‐temperature treatments, data concerning changes in the enzymatic antioxidant systems are almost absent.

With the aim to provide this information, antioxidant enzyme (superoxide dismutases, catalase and peroxidases) activities were analysed in leaves and roots of Triticum aestivum cvs Brasilia (frost resistant in field) and Eridano (less frost resistant in field) seedlings grown at day/night temperatures of 24/22°C (control treatment) and 12/5°C (low‐temperature treatment).

Our data showed that superoxide dismutase activities were unaffected by low‐temperature treatment both in leaves and roots. Catalase activity in leaves and roots was decreased in 12/5°C‐grown seedlings, but Brasilia maintained higher catalase activity than Eridano. Differences were also observed in guaiacol peroxidase activities between control and acclimated seedlings: Higher guaiacol peroxidase activities were found in the leaves of 12/5°C‐grown seedlings while in roots these activities were lower. Moreover, Brasilia guaiacol peroxidase activities were higher than Eridano. Superoxide dismutase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by low‐temperature treatment.

Changes in the activities of antioxidant enzymes induced by cold acclimation support the hypothesis that a frost‐resistant wheat cultivar, in comparison with a less frost‐resistant one, maintains a better defence against activated oxygen species during low‐temperature treatment.
Decreased ascorbic acid levels and brown core development in pears (Pyrus communis L. cv. Conference)
Authors: Veltman R. H. , Sanders M. G. , Persijn S. T. , Pemppelenbos H. W. , Oosterhaven J.
Published: March 2003

Changes in ascorbic acid content are measured in the cortex tissue of Conference pears stored at various compositions of carbon dioxide and oxygen. Enhanced carbon dioxide levels cause ascorbic acid concentrations to decline. Soon after ascorbic acid has declined below a certain value, browning of the core tissue can be observed. Reducing carbon dioxide levels before this value is reached causes ascorbic acid levels to increase again and prevents browning to a great extent. In preliminary experiments with a photoacoustic laser‐based detection system, it was shown that pears that show browning produce ethane, which is most likely a result of membrane peroxidation. Storage conditions, ascorbic acid levels and browning in pears are discussed in relation to diffusion characteristics, energy metabolism and energy maintenance levels of the fruit.
Evidence for enzyme complexes in the phenylpropanoid and flavonoid pathways
Authors: Winkel‐Shirley Brenda
Published: March 2003

A growing body of evidence indicates that phenylpropanoid and flavonoid metabolism is catalyzed, not by free‐floating ‘soluble’ enzymes, but via one or more membrane‐associated multienzyme complexes. This type of macromolecular organization has important implications for the overall efficiency, specificity, and regulation of these pathways. Classical biochemical studies of phenylpropanoid and flavonoid metabolism have laid a solid foundation for this model, providing evidence of the channeling of intermediates between enzyme active sites and co‐localization of enzymes in cell membranes. This work is now being extended using transgenic plants to determine how the partitioning of metabolites within these pathways is controlled, as well as applying sensitive methods to define specific interactions among the individual enzymes. Information from these studies promises to provide new insights into the structuring of biosynthetic pathways within cells, which should lead to more effective means for engineering the production of plant metabolites with nutritional and agronomic importance.
Temporal and spatial regulation of the expression of 1‐aminocyclopropane‐1‐carboxylate oxidase by ethylene in mung bean (Vigna radiata)
Authors: Jin EonSeon , Lee Jae‐Hyeok , Park Jong‐A , Kim* Woo Taek
Published: March 2003

Ethylene induced an increase in the level of 1‐aminocyclopropane‐1‐carboxylate oxidase (VR‐ACO1) transcript in mung bean hypocotyls. Time course study revealed that the level of the VR‐ACO1 mRNA in excised mung bean hypocotyls increased after 2‐h ethylene treatment and much higher mRNA levels were observed thereafter, while the basal level of transcript was slightly decreased in control tissues. The in vivo ACC oxidase activity increased from 31 nl g−1 h−1 at zero time to maximum activity of 62 nl g−1 h−1 at 10‐h ethylene treatment. Polyclonal antibody against VR‐ACO1 protein expressed in E. coli cells was generated. Immunoblot analysis using the resulting antiserum showed that the induction pattern of ACC oxidase polypeptide was in parallel with that of enzyme activity during the incubation with ethylene. Thus, ethylene increases the levels of the VR‐ACO1 mRNA and ACC oxidase protein as well as enzyme activity in mung bean hypocotyls. The abundance of the VR‐ACO1 transcript and protein was also induced in all parts of light‐grown mung bean seedlings by ethylene treatment. However, both the basal levels and the magnitudes of ethylene‐induction of VR‐ACO1 were markedly different in different tissues, with the roots being the most sensitive to ethylene. These results suggest that the different part of mung bean seedlings has a distinct potential to respond to ethylene with regard to ACC oxidase gene activation. Furthermore, our data suggest that the induction of VR‐ACO1 by ethylene is subject not only to transcriptional control but also to posttranscriptional control in hypocotyls, whereas ethylene regulates the VR‐ACO1 gene expression mainly at the transcriptional level in roots. The possible molecular mechanism of regulation of ACC oxidase gene expression by ethylene and its significance are discussed.
Growth, photosynthesis, and respiration of Chlorella sorokiniana after N‐starvation. Interactions between light, CO2 and NH4+ supply
Authors: Vona Vincenza , Di Martino Rigano Vittoria , Esposito Sergio , Carillo Petronia , Carfagna Simona , Rigano Carmelo
Published: March 2003

N‐sufficient cells of Chlorella sorokiniana Shihira and Krauss, strain 211/8k, absorbed NH4+ under light plus CO2 conditions, when growth occurred, but not in darkness or in the absence of CO2, when growth was inhibited. N‐sufficient cells subjected to conditions of N‐starvation for a 24‐h period showed a marked loss of photosynthetic activity. Upon supply of NH4+, N‐starved cells sufflated with CO2 air exhibited a time‐dependent recovery of photosynthetic activity, both when suspended in light and in darkness. By contrast, growth only occurred in cells suspended in light. N‐starved cells absorbed NH4+ in darkness, but at a lower rate than in light. All of these data suggest that dark NH4+ uptake is driven by N assimilation to recover from N‐starvation and that the light‐dependent NH4+ uptake is driven by growth, being then influenced by conditions that affect recovery or growth. Unlike CO2 conditions, in a CO2‐free atmosphere, absorption of NH4+ by N‐starved cells occurred at a higher rate in darkness than in light. Accordingly, resumption of photosynthetic potential after NH4+ supply occurred in darkened cells, but not in illuminated cells. Respiratory activity of N‐starved cells was enhanced up to 3‐fold by NH4+ and 2‐fold by methylammonium, with different patterns, suggesting that respiratory enzymes were affected by N‐metabolism, especially through short‐term control mechanisms triggered by the expenditure of metabolic energy involved in N‐metabolism.
Changes in ascorbate oxidase gene expression and ascorbate levels in cell division and cell elongation in tobacco cells
Authors: Kato Naohiro , Esaka Muneharu
Published: March 2003

The biological function of ascorbate oxidase (AAO) was not yet clarified, although it was suggested that AAO may be involved in cell growth. We investigated AAO expression and ascorbate metabolism during non‐synchronous, synchronous, and elongation cultures of tobacco BY‐2 cells. In non‐synchronous culture, AAO mRNA was abundant in logarithmic growth phase. Ascorbate content greatly increased during the growth, whereas dehydroascorbate content was slightly increased. In synchronous division culture, AAO mRNA was detected in all phases, but the levels were quite low in G1 phase. Ascorbate content was high in all phases, whereas dehydroascorbate content was low, especially in G1 phase. In elongation culture, the levels of AAO mRNA increased during elongation of the cells. AAO activity in the culture medium, as well as ascorbate and dehydroascorbate contents in the cells, also increased during the elongation. We propose that AAO expression and production of dehydroascorbate are under the control of the cell cycle and that AAO may function apoplastically as an ascorbate oxidizer in the process of cell elongation.
NaCl effects on proline metabolism in rice (Oryza sativa) seedlings
Authors: Lutts S. , Majerus V. , Kinet J.‐M.
Published: March 2003

Salt‐stress effects on osmotic adjustment, ion and proline concentrations as well as proline metabolizing enzyme activities were studied in two rice (Oryza sativa L.) cultivars differing in salinity resistance: I Kong Pao (IKP; salt‐sensitive) and Nona Bokra (salt‐resistant). The salt‐sensitive cultivar exposed to 50 and 100 mM NaCl in nutritive solution for 3 and 10 days accumulated higher levels of sodium and proline than the salt‐resistant cultivar and displayed lower levels of osmotic adjustment. Proline accumulation was not related to proteolysis and could not be explained by stress‐induced modifications in Δ1‐pyrroline‐5‐carboxylate reductase (P5CR; EC 1.5.1.2) or proline dehydrogenase (PDH; EC 1.5.1.2) activities recorded in vitro. The extracted ornithine Δ‐aminotransferase (OAT; EC 2.6.1.13) activity was increased by salt stress in the salt‐sensitive cultivar only. In both genotypes, salt stress induced an increase in the aminating activity of root glutamate dehydrogenase (GDH; EC 1.4.1.2) while deaminating activity was reduced in the leaves of the salt‐sensitive cultivar. The total extracted glutamine synthetase activity (GS; EC 6.3.1.2) was reduced in response to salinity but NaCl had contrasting effects on GS1 and GS2 isoforms in salt‐sensitive IKP. Salinity increased the activity of ferredoxin‐dependent glutamate synthase (Fd‐GOGAT; EC 1.4.7.1) extracted from leaves of both genotypes and increased the activity of NADH‐dependent glutamate synthase (NADH‐GOGAT; EC 1.4.1.14) in the salt‐sensitive cultivar. It is suggested that proline accumulation is a symptom of salt‐stress injury in rice and that its accumulation in salt‐sensitive plants results from an increase in OAT activity and an increase in the endogenous pool of its precursor glutamate. The physiological significance of the recorded changes are analyzed in relation to the functions of these enzymes in plant metabolism.
Photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica
Authors: Xiong F. S. , Ruhland Christopher T. , Day Thomas A.
Published: March 2003

The photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica was examined by measuring whole‐canopy CO2 gas exchange and chlorophyll (Chl) a fluorescence of plants growing near Palmer Station along the Antarctic Peninsula. Both species had negligible midday net photosynthetic rates (Pn) on warm, usually sunny, days (canopy air temperature [Tc]> 20°C), but had relatively high Pn on cool days (Tc<10°C). Laboratory measurements of light and temperature responses of Pn showed that high temperature, not visible irradiance, was responsible for depressions in Pn on warm sunny days. The optimal leaf temperatures (Tl) for Pn in C. quitensis and D. antarctica were 14 and 10°C, respectively. Both species had substantial positive Pn at 0°C Tl, which were 28 (C. quitensis) and 32% (D. antarctica) of their maximal Pn, and we estimate that their low‐temperature compensation points occurred at −2°C Tl (C. quitensis) and −3°C (D. antarctica). Because of the strong warming trend along the peninsula over recent decades and predictions that this will continue, we were particularly interested in the mechanisms responsible for their negligible rates of Pn on warm days and their unusually low high‐temperature compensation points (i.e., 26°C in C. quitensis and 22°C in D. antarctica). Low Pn at supraoptimal temperature (25°C) appeared to be largely due to high rates of temperature‐enhanced respiration. However, there was also evidence for direct impairment of the photosynthetic apparatus at supraoptimal temperature, based on Chl fluorescence and Pn/intercellular CO2 concentration (ci) response curve analyses. The breakpoint or critical temperature (Tcr) of minimal fluorescence (Fo) was ≈42°C in both species, which was well above the temperatures where reductions in Pn were evident, indicating that thylakoid membranes were structurally intact at supraoptimal temperatures for Pn. The optimal Tl for photochemical quenching (qp) and the quantum yield of photosystem II (PSII) electron transfer (φPSII) were 9 and 7°C in C. quitensis and D. antarctica, respectively. Supraoptimal temperatures resulted in lower qp and greater non‐photochemical quenching (qNP), but had little effect on Fo, maximal fluorescence (Fm) or the ratio of variable to maximal fluorescence (Fv/Fm) in both species. In addition, carboxylation efficiencies or initial slopes of their Pn/ci response were lower at supraoptimal temperatures, suggesting reduced activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco). Although continued warming along the peninsula will increase the frequency of supraoptimal temperatures, Tc at our field site averaged 4.3°C and was below the temperature optima for Pn in these species for the majority of diurnal periods (86%) during the growing season, suggesting that continued warming will usually improve their rates of Pn.
Metal toxicity and ectomycorrhizas
Authors: Jentschke G. , Godbold D. L.
Published: March 2003

Metal toxicity (Al and heavy metals) is a major constraint affecting root growth in a number of natural or managed ecosystems. Fine roots of the majority of plant species are associated with mycorrhizal fungi, which may modify the sensitivity of roots to metal stress. In this review, we summarise the available evidence demonstrating beneficial effects of ectomycorrhizas in alleviation of metal toxicity in forest tree seedlings. We identify experimental shortcomings of past research (e.g. the use of shoot metal concentrations as a measure of metal uptake, use of microanalytical techniques biased by element redistribution) that may confound major conclusions drawn from these experiments. Although there is no doubt that in many cases ectomycorrhizal fungi indeed ameliorate metal stress in their host plants, the mechanism(s) involved remain(s) unclear. The role of metal sorption on fungal tissues thought to reduce metal exposure of the host plant is critically reviewed. As direct evidence (both under artificial and soil conditions) supporting a unique role of fungal immobilisation of metals is lacking so far, there is an urgent need to also test alternative tolerance mechanisms such as the release of metal chelating substances, or nutritional and hormonal effects mediated by mycorrhizal fungi.
Exogenous abscisic acid fate during maturation of hybrid larch (Larix×leptoeuropaea) somatic embryos
Authors: Label Philippe , Lelu Marie‐Anne
Published: March 2003

The maturation of somatic embryogenesis of hybrid larch is an essential step for plantlet production. ABA controls not only synchronicity of maturation, but has important consequences on eventual viability of the plantlet. To gain understanding of the role of this plant growth regulator during the maturation process of hybrid larch somatic embryos, we studied the incorporation of [ H]‐(±)‐abscisic acid [tritiated (±)‐ABA] over 6 weeks of culture. Results showed a rapid incorporation of label into the tissues directly in contact with the culture medium. Accumulation of tritiated (±)‐ABA occurred mainly in the maturing somatic embryos found at the periphery of the embryogenic mass but not in direct contact with the culture medium. Tritiated (±)‐ABA was mainly conjugated as a glucose ester form. Rates of tritium incorporation indicated a significant build‐up in tritiated (±)‐ABA metabolization at the third week of culture. The weekly measurement of labelling in the culture medium over 6 weeks showed no localized exhaustion of tritiated (±)‐ABA in positions where the embryogenic masses were placed in Petri dishes. The calculated ABA internal content of the maturing somatic embryos was similar to published ELISA measurements of ABA. This result suggests an absence of endogenous ABA synthesis by somatic embryos of hybrid larch during maturation.
Aluminium tolerance is achieved by exudation of citric acid from roots of soybean (Glycine max)
Authors: Yang Zhen Ming , Sivaguru Mayandi , Horst Walter J. , Matsumoto Hideaki
Published: March 2003

Fourteen soybean (Glycine max [L.] Merr.) cultivars were analysed and found to differ considerably in aluminium (Al) resistance. The cultivars Suzunari (Al‐resistant) and Shishio (Al‐sensitive) were selected for further analysis of physiological mechanisms of Al‐resistance. The relative root growth of Shishio was 48% compared to 76% for Suzunari in response to 15 μM Al (24 h). Aluminium accumulation and Al‐induced callose formation in root apices were 50 and 25% of that in Suzunari, respectively. Al inhibited both Suzunari and Shishio during the first 6 h of exposure. However, the root growth inhibition was further increased in Shishio but not in Suzunari, suggesting an Al‐induced Al‐resistant mechanism operating in Suzunari. Organic acid analysis in root exudates of both cultivars revealed that they specifically exuded citrate in response to Al. However, the citrate exudation rate was significantly higher in Suzunari during the 6 h/24 h Al treatment, which was 52/330 compared to Shishio's 26/118 (nmol [g root fresh weight]−1 [6 h]−1), respectively. This Al‐induced citric acid exudation was found to be specific for Al, as several other metals failed to induce citrate exudation in both cultivars. Fourteen days of P deficiency did not elicit citrate excretion in both cultivars, while application of Al to P‐deficient plants rapidly induced citrate exudation in both cultivars, confirming the specificity of the response of these soybean cultivars to Al. To our knowledge, this is the first report demonstrating an Al‐exclusion mechanism in soybean cultivars, which is conferred by enhanced and specific Al‐induced exudation of citrate.
Expression of a phytoene synthase gene and characteristic carotenoid accumulation during citrus fruit development
Authors: Ikoma Yoshinori , Komatsu Akira , Kita Masayuki , Ogawa Kazunori , Omura Mitsuo , Yano Masamichi , Moriguchi Takaya
Published: March 2003

A cDNA clone encoding a protein homologue to phytoene synthase (PSY, CitPSY1) was isolated from Satsuma mandarin (Citrus unshiu Marc.) fruit. Expression analysis revealed the presence of the CitPSY1 transcript in flowers and leaves, with a higher level detected in the mature than in the young leaves. In fruit, the transcript was present in a low quantity in the flavedo (peel) and juice sacs/segment epidermis (edible part) at an early developmental stage. Later, it began to accumulate towards fruit maturation in both parts. These fluctuations were in accordance with carotenoid accumulation and chlorophyll disappearance. We suggest that CitPSY1 plays an important role in carotenoid accumulation. We also propose a possible pathway in carotenoid biosynthesis that is based on the fluctuation of the characteristic carotenoid composition during Satsuma mandarin development.
Effects of light quality on somatic embryogenesis in Araujia sericifera
Authors: Torné Josep M. , Moysset Luisa , Santos Mireya , Simón Esther
Published: March 2003

The effects of photoperiod, light quality and end‐of‐day (EOD) phytochrome photoconversion on somatic embryogenesis (SE) of Araujia sericifera petals have been studied. Petals from immature flowers were cultured under 8‐ and 16‐h photoperiods using Gro‐lux fluorescent lamps. The photon fluence rate was 90–100 μmol m−2 s−1 and the red (R):far‐red (FR) ratio was 98. R, FR, R followed by FR (R‐FR) and FR followed by R (FR‐R) light treatments were applied for 3 weeks at the end of the photoperiods. In a set of experiments, dl‐α‐difluoromethylarginine (DFMA) or methylglyoxal bis(guanylhydrazone) (MGBG), both inhibitors of polyamine biosynthesis, were added to the culture medium in order to study the involvement of polyamine metabolism. The level of SE was the same in long (LD) and short (SD) days. Thus, the light effect was accomplished after 8 h. All EOD treatments that decreased the Pfr level inhibited SE when applied after SD, but not after LD. The FR‐R treatment after LD caused an additional stimulatory effect on SE, even in the presence of polyamine inhibitors. DFMA inhibited SE in both SD and LD, but MGBG did not modify SE in either SD or LD. The R, FR and R‐FR treatments did not alter the level of SE when applied after LD in the presence of DFMA or MGBG. However, these treatments decreased SE after SD when the medium contained polyamine inhibitors. Our results suggest that Gro‐lux lamps, which produce an extremely high R:FR ratio, promote SE in A. sericifera and a timing response to phytochrome photoconversion during photoperiodic induction. Thus, our data corroborate the involvement of phytochromes and polyamines in SE in A. sericifera, which responded as a light‐dominant long‐day plant.
The role of photorespiration in redox and energy balance of photosynthetic plant cells: A study with a barley mutant deficient in glycine decarboxylase
Authors: Igamberdiev Abir U. , Bykova Natalia V. , Lea Peter J. , Gardeström Per
Published: March 2003

Protoplasts and mitochondria were isolated from leaves of homozygous barley (Hordeum vulgare L.) mutant deficient in glycine decarboxylase complex (GDC, EC 2.1.2.10) and wild‐type plants. The photosynthetic rates of isolated protoplasts from the mutant and wild‐type plants under saturating CO2 were similar, but the respiratory rate of the mutant was two‐fold higher. Respiration in the mutant plants was much more strongly inhibited by antimycin A than in wild‐type plants and a low level of the alternative oxidase protein was found in mitochondria. The activities of NADP‐ and NAD‐dependent malate dehydrogenases were also increased in mutant plants, suggesting an activation of the malate‐oxaloacetate exchange for redox transfer between organelles. Mutant plants had elevated activities of NADH‐ and NADPH‐dependent glyoxylate/hydroxypyruvate reductases, which may be involved in oxidizing excess NAD(P)H and the scavenging of glyoxylate. We estimated distribution of pools of adenylates, NAD(H) and NADP(H) between chloroplasts, cytosol and mitochondria. Under photorespiratory conditions, ATP/ADP and NADPH/NADP ratios in the mutant were higher in chloroplasts as compared to wild‐type plants. The cytosolic NADH/NAD ratio was increased, whereas the ratio in mitochondria decreased. It is concluded that photorespiration serves as an effective redox transfer mechanism from the chloroplast. Plants with a lowered GDC content are deficient in this mechanism, which leads to over‐reduction and over‐energization of the chloroplasts.
Role of gibberellins in parthenocarpic fruit development induced by the genetic systempat‐3/pat‐4in tomato
Authors: Fos Mariano , Proaño Karina , Nuez Fernando , García‐Martínez José L.
Published: March 2003

The role of gibberellins (GAs) in the induction of parthenocarpic fruit‐set and growth by thepat‐3/pat‐4genetic system in tomato (Lycopersicon esculentumMill.) was investigated using wild type (WT; Cuarenteno) and a near‐isogenic line derived from the German line RP75/59 (the source ofpat‐3/pat‐4parthenocarpy). Unpollinated WT ovaries degenerated but GA3application induced parthenocarpic fruit growth. On the contrary, parthenocarpic growth ofpat‐3/pat‐4fruits, which occurs in the absence of pollination and hormone treatment, was not affected by applied GA3. Unpollinatedpat‐3/pat‐4fruit growth was negated by paclobutrazol, an inhibitor ofent‐kaurene oxidase, and this inhibitory effect was negated by GA3. The quantification of the main GAs of the early 13‐hydroxylation pathway (GA1, GA8, GA19, GA20, GA29and GA44) in unpollinated ovaries at 3 developmental stages (flower bud, FB; pre‐anthesis, PR; and anthesis, AN), by gas chromatography‐selected ion monitoring, showed that the concentration of most of them was higher inpat‐3/pat‐4than in WT ovaries at PR and AN stages. The concentration of GA1, suggested previously to be the active GA in tomate, was 2–4 times higher. Unpollinatedpat‐3/pat‐4ovaries at FB, PR and AN stages also contained relatively high amounts (5–12 ng g−1) of GA3, a GA found at less than 0.5 ng g−1in WT ovaries. It is concluded that the mutationspat‐3/pat‐4may induce natural facultative parthenocarpy capacity in tomato by increasing the concentration of GA1and GA3in the ovaries before pollination.
Effects of climatic warming on cold hardiness of some northern woody plants assessed from simulation experiments
Authors: Ögren Erling
Published: March 2003

Effects of climatic warming on cold hardiness were investigated for some northern woody plants. In the first experiment, seedlings of Norway spruce (Picea abies [L.] Karst.), Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were exposed to naturally fluctuating temperatures averaging −6°C (ambient) and 0°C (elevated) for 16 weeks in midwinter before they were thawed and re‐saturated with water. In lodgepole pine, needle sugar concentrations had decreased by 15%, and the temperature needed to induce 10% injury to needles in terms of electrolyte leakage had increased by 6°C following treatment to elevated as compared with control temperatures. In contrast, Norway spruce and Scots pine showed no effects. The lack of an effect for Scots pine was ascribed to seedlings containing unusually large energy reserves that buffered respiratory expenditure of sugars. A strong, linear relationship between levels of cold hardiness, assessed by the electrolyte leakage method, and sugars was found when combining data from this and previous, similar experiments. In the second experiment, the evergreen dwarf shrub Empetrum hermaphroditum Hagerup was analysed for leaf cold hardiness, using the electrolyte leakage method, and sugar concentrations in late spring and late autumn during the third year of a warming experiment in a subarctic dwarf shrub community. The objective was to test the hypothesis that warming in the growing season alters hardening/dehardening cycles by increasing soil nitrogen mineralization and plant growth. Data found, however, suggested that cold hardening/dehardening cycles were unaffected by warming.
In vivo sucrose stimulation of colour change in citrus fruit epicarps: Interactions between nutritional and hormonal signals
Authors: Iglesias Domingo J. , Tadeo Francisco R. , Legaz Francisco , Primo‐Millo Eduardo , Talon Manuel
Published: March 2003

During ripening, citrus fruit‐peel undergoes ‘colour break’, a process characterized by the conversion of chloroplast to chromoplast. The process involves the progressive loss of chlorophylls and the gain of carotenoids, changing peel colour from green to orange. In the present work, the in vivo and in vitro effects of supplemented nutrients (sucrose and nitrogen) and phytohormones (gibberellins [GA] and ethylene) on colour change in fruit epicarp of Satsuma mandarin (Citrus unshiu (Mak.) Marc., cv. Okitsu), were studied. The rate of colour break was correlated positively with sucrose content and negatively with nitrogen content. The removal of leaves blocked natural sucrose build‐up and nitrogen reduction in the peel. Defoliation also inhibited chlorophyll disappearance and carotenoid accumulation, thereby preventing colour break. In vivo sucrose supplementation promoted sucrose accumulation and advanced colour break. In both in vivo and in vitro experiments, colour change promoted by sucrose was unaffected by ethylene but delayed by GA3. In non‐supplemented plants, ethylene accelerated colour break while GA3 had no detectable effects. Ethylene inhibitors effectively counteracted the sucrose effects on colour change. Collectively, these results suggest that the chloroplast to chromoplast conversion in citrus fruit epicarps is stimulated by sucrose accumulation. The sugar regulation appears to operate via ethylene, whereas GA may act as a repressor of the sucrose‐ethylene stimulation.
Canopy development of a model herbaceous community exposed to elevated atmospheric CO2 and soil nutrients
Authors: Hartz‐Rubin Jennifer S. , DeLucia Evan H.
Published: March 2003

To test the prediction that elevated CO2 increases the maximum leaf area index (LAI) through a stimulation of photosynthesis, we exposed model herbaceous communities to two levels of CO2 crossed with two levels of soil fertility. Elevated CO2 stimulated the initial rate of canopy development and increased cumulative LAI integrated over the growth period, but it had no effect on the maximum LAI. In contrast to CO2, increased soil nutrient availability caused a substantial increase in maximum LAI. Elevated CO2 caused a slight increase in leaf area and nitrogen allocated to upper canopy layers and may have stimulated leaf turnover deep in the canopy. Gas exchange measurements of intact communities made near the time of maximum LAI indicated that soil nutrient availability, but not CO2 enrichment, caused a substantial stimulation of net ecosystem carbon exchange. These data do not support our prediction of a higher maximum LAI by elevated CO2 because the initial stimulation of LAI diminished by the end of the growth period. However, early in development, leaf area and carbon assimilation of communities may have been greatly enhanced. These results suggest that the rate of canopy development in annual communities may be accelerated with future increases in atmospheric CO2 but that maximum LAI is set by soil fertility.
Enhanced photochemical light utilization and decreased chilling‐induced photoinhibition of photosystem II in cotton overexpressing genes encoding chloroplast‐targeted antioxidant enzymes
Authors: Kornyeyev Dmytro , Logan Barry A. , Payton Paxton , Allen Randy D. , Holaday A. Scott
Published: March 2003

The aim of this study was to determine whether increases in stromal superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) via transformation could reduce photosystem (PS) II photoinhibition at low temperature for cotton (Gossypiumhirsutum L.) plants and to determine by what mechanism this protection may be realized. During 3‐h exposures of lincomycin‐treated leaf discs to 10°C and a photon flux density of 500 μmol m−2 s−1, all transgenic plants exhibited significantly greater PSII activity and O2 evolution than did wild‐type plants. Also, the rate constant of PSII photoinactivation was significantly lower for all transgenic plants than for wild‐type plants. No significant differences existed between genotypes in non‐photochemical quenching of chlorophyll a fluorescence and the regulated component of the thermal dissipation of excitation energy. The relationship between changes in variable to maximum chlorophyll fluorescence (Fv/Fm) and the time‐dependent averaged excessive light exposure was similar for all genotypes. This observation excluded the possibility that differences in PSII photodamage were due to improvements in the direct protection of PSII from active oxygen by antioxidant enzyme overproduction. Similar decreases in Fv/Fm during the stress treatment for all genotypes when leaves were pre‐treated with 3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) suggested that the effect of overproduction involved events downstream of PSII in the electron transfer pathway. Since all transgenic plants exhibited a significantly higher photochemical quenching of chlorophyll fluorescence during the chilling treatment, we concluded that, under the conditions used in this study, the enhancement of the protection of PSII from photodamage by increasing the stromal antioxidant enzyme activity in cotton leaves was due to the maintenance of a higher rate of electron transport and, consequently, a lower reduction state of QA.
Plant Hsp70 molecular chaperones: Protein structure, gene family, expression and function
Authors: Sung Dong‐Yul , Kaplan Fatma , Guy Charles L.
Published: March 2003

The Hsp70 molecular chaperones of plants are encoded by a multi‐gene family whose members are developmentally regulated and differentially expressed in response to temperature stress and other conditions that interrupt normal protein folding or favor protein denaturation. Under non‐stressful conditions, Hsp70 cognates function in concert with a variety of co‐chaperones to facilitate folding of de novo synthesized proteins, assist in transport of precursor proteins into organelles and to help target damaged proteins for degradation. Stress‐induced Hsp70s function to mitigate aggregation of stress‐denatured proteins and to refold non‐native proteins restoring their biological function through iterative cycles of adenine nucleotide hydrolysis‐dependent peptide binding and release. Much of what is known about how plant Hsp70s function comes from the study of Hsp70s from other types of organisms. Owing to their unique biology, much remains to be learned about the many functions Hsp70s play in plants.
Cross‐linking between chloroplast fructose‐1,6‐bisphosphatase and thioredoxin f
Authors: Ocón Ester , Hermoso Rosario , Chueca Ana , Lázaro Juan José
Published: March 2003

The interaction between chloroplast fructose‐1,6‐bisphosphatase (FBPase) and thioredoxin (Trx) f, two plant proteins involved in the Benson‐Calvin cycle, is mainly of an electrostatic nature [Hermoso et al. (1996) Plant Mol Biol 30: 455–465; Reche et al. (1997) Physiol Plant 101: 463–470; Sahrawy et al. (1997) J Mol Biol 269: 623–630; Hermoso et al. (1999) Physiol Plant 105: 756–762], possibly involving carboxyl groups of the enzyme and amino groups of Trx f. We carried out the covalent stabilization of that ionic complex, for the purpose of studying the interaction between both proteins and the factors that influence it. We have used 1‐ethyl‐3‐[3‐(dimethylamino)propyl]carbodiimide, a reagent able to cross‐link carboxyl and amino groups, which allows the formation of covalent bonds between the groups that, in solution, form ionic bonds. A stable functional complex between both proteins was formed. The efficiency in the formation of that complex depends on the redox state of Trx f, ionic strength and pH, showing a strong correlation with the Trx f‐dependent enzyme activity. The complex also retains enzyme activity. This suggests that the formation of the covalent complex requires the previous stabilization of a specific functional ionic complex between both proteins, and that in this functional complex carboxyl groups of the enzyme and primary amines of Trx f are involved. This complex is not stable in a tetrameric structure of the enzyme. We could also detect covalent aggregates of FBPase subunits, which indicates the implication of ionic interactions in the stabilization of the tetrameric structure of the enzyme; besides, as molecular filtration experiments and electrophoresis suggest, hydrophobic forces would also be implicated in the enzyme structure.
Foliar phenolic composition of European white birch during bud unfolding and leaf development
Authors: Laitinen Marja‐Leena , Julkunen‐Tiitto Riitta , Rousi Matti
Published: March 2003

We studied the between‐tree and within‐tree variation in the composition and content of foliar low‐molecular‐weight phenolics (LMWP) of European white birch (Betula pendula Roth) during the unfolding of vegetative buds and during early leaf development. In buds, the major groups of phenolic compounds were hydrolysable tannins and flavonoid aglycones, whereas, later during leaf development, the flavonoid glycosides accounted for most of the total LMWP. The content of total LMWP, as well as individual compounds, varied largely among individual trees, while variation within an individual tree was low. The biosynthetic origin of individual compounds or compound groups is discussed in order to explain the main patterns in leaf chemistry during bud unfolding and early leaf development.
The synergistic effects of sugar and abscisic acid on myo‐inositol‐1‐phosphate synthase expression
Authors: Yoshida Kaoru T. , Fujiwara Toru , Naito Satoshi
Published: March 2003

1L‐myo‐inositol‐1‐phosphate [Ins(1)P1] synthase (EC 5.5.1.4) catalyses the formation of Ins(1)P1 from glucose‐6‐phosphate, the first step in the biosynthesis of myo‐inositol. Ins(1)P1 is a precursor of phytin (inositol hexakisphosphate), a storage form of phosphate and cations in seeds. Since sucrose and abscisic acid (ABA) are known to affect synthesis of storage compounds in seeds, we investigated the effects of ABA and sucrose on Ins(1)P1 synthase gene (RINO1) expression in cultured cells derived from the scutellum of mature rice seeds. Higher levels of RINO1 transcript accumulation were evident after treatment with either sucrose (10–100 mM) or ABA (10−8M to 10−4M). Glucose was also effective in the upregulation, whereas mannitol was not, suggesting that sucrose and glucose acted as metabolizable sugars and not as osmotica. Treatment with ABA and sucrose together resulted in much higher levels of transcript accumulation, suggesting a synergistic induction of the Ins(1)P1 synthase gene.