bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of photosynthesis by viral infection: Effect on PSII structure and function
Authors: Rahoutei Jaber , García‐Luque Isabel , Barón Matilde
Published: March 2003

The effect of viral infection on photosynthesis was investigated in Nicotiana benthamiana Gray plants infected with different strains of pepper and paprika mild mottle viruses (PMMoV and PaMMoV) and chimeric viral genomes derived from them. In both symptomatic and asymptomatic leaves of virus‐infected plants, photosynthetic electron transport in photosystem II (PSII) was reduced. In all cases analyzed, viral infection affected the polypeptide pattern of the oxygen‐evolving complex (OEC) in thylakoid membranes. The levels of both the 24 and 16 kDa proteins were reduced to a differing extent when compared with the levels in healthy control. This loss of the OEC extrinsic proteins affected the oxygen evolution rates of thylakoid membranes and leaves from infected plants. Additionally, viral coat protein (CP) was found associated with the chloroplasts and the thylakoid membranes of the infected plants. The CP accumulation level was dependent upon both the post‐infection time and the virus analyzed, but independent of the CP itself since hybrid viruses did not behave as their parental viruses with the same CP, with respect to PSII inhibition, CP accumulation rates and OEC protein levels. Modulated chlorophyll (Chl) fluorescence and oxygen evolution measurements carried out in both types of leaves showed that the quantum yield of PSII electron transport was diminished in infected plants with respect to those of control plants. The decrease in electron transport efficiency was mainly caused by a reduction in the fraction of open reaction centers. The infected plants also showed a reduction in the efficiency of excitation capture in PSII by photoprotective thermal dissipation of excess excitation energy.
Effects of moderately enhanced levels of ozone on the acyl lipid composition and dynamical properties of plasma membranes isolated from garden pea (Pisum sativum)
Authors: Hellgren Lars I. , Selldén Gun , Sandelius Anna Stina
Published: March 2003

Plasma membranes were isolated from leaves of 16‐day‐old garden pea, Pisum sativum L., that had been grown in the absence or presence of 65 nl l−1 ozone for 4 days prior to membrane isolation. Plasma membranes from ozone‐fumigated plants contained significantly more acyl lipids per protein than those from leaves of plants grown in filtered air on a molar/weight ratio. The ratio between the major acyl lipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), also increased due to the ozone fumigation, while the fatty acid unsaturation level was unaltered in total plasma membrane acyl lipids, as well as in PC and PE. The amount of free sterols per protein was unaltered, but the percentage of campesterol increased, concomitant with a decrease in stigmasterol. The dynamical properties of the isolated plasma membranes were assessed using Laurdan fluorescence spectroscopy, which monitors water penetration and mobility at the hydrophilic‐hydrophobic interface of the membrane. At 0°C, the molecular mobility was slightly lower in plasma membranes from ozone‐fumigated plants than in plasma membranes from control plants, possibly reflecting the increased PE/PC, campesterol/stigmasterol and lipid/protein ratios, and suggesting that ozone‐fumigated pea plants may be more susceptible to freezing injuries.
Plant acquisition of organic nitrogen in boreal forests
Authors: Näsholm Torgny , Persson Jörgen
Published: March 2003

Research on plant nitrogen (N) uptake and metabolism has more or less exclusively concerned inorganic N, particularly nitrate. Nevertheless, recent as well as older studies indicate that plants may have access to organic N sources. Laboratory studies have shown that ectomycorrhizal and ericoid mycorrhizal plants can degrade polymeric N and absorb the resulting products. Recent studies have also shown that some non‐mycorrhizal plants are able to absorb amino acids. Moreover, amino acid transporters have been shown to be present in both plant roots and in mycorrhizal hyphae. Although both mycorrhizal and non‐mycorrhizal plants appear to have a capacity for absorbing a range of organic N compounds, is this capacity realized in the field? Several lines of evidence show that plants are outcompeted by microorganisms for organic N sources. Such studies, however, have not addressed the issue of spatial and temporal separation between plants and microorganisms. Moreover, competition studies have not been able to separate uptake by symbiotic and non‐symbiotic microorganisms. Qualitative assessment of organic N uptake by plants has been performed with dual‐labelled glycine in several studies. These studies arrive at different conclusions: some indicate that plants do not absorb this organic N source when competing with other organisms in soil, while others conclude that significant fractions of amino acid N are absorbed as intact amino acid. These variable results may reflect species differences in the ability to absorb glycine as well as differences in experimental conditions and analytical techniques. Although theoretical calculations indicate that organic N might add significant amounts of N to plant N uptake, direct quantitative assessment of the fraction of plant N derived from uptake by organic N sources is a challenge for future research.
Changes induced by Fe deficiency and Fe resupply in the organic acid metabolism of sugar beet (Beta vulgaris) leaves
Authors: López‐Millán Ana Flor , Morales Fermín , Abadía Anunciación , Abadía Javier
Published: March 2003

The effects of iron deficiency and iron resupply on the metabolism of leaf organic acids have been investigated in hydroponically grown sugar beet. Organic acid concentrations and activities in leaf extracts of several enzymes related to organic acid metabolism were measured. Enzymes assayed included phosphoenol pyruvate carboxylase (PEPC; EC 4.1.1.31), different Krebs cycle enzymes: malate dehydrogenase (MDH; EC 1.1.1.37), aconitase (EC 4.2.1.3), fumarase (EC 4.2.1.2), citrate synthase (CS; EC 4.1.3.7) and isocitrate dehydrogenase (ICDH; EC 1.1.1.42), glucose‐6‐phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and two enzymes related to anaerobic metabolism (lactate dehydrogenase [LDH]; EC 1.1.1.27, and pyruvate decarboxylase [PDC]; EC 4.1.1.1). Iron concentration in leaves was severely decreased by iron deficiency. Iron resupply caused an increase in iron concentrations, reaching levels similar to the controls in 96 h. Iron deficiency induced a 2.3‐fold (from 16 to 37 mmol m−2) increase in leaf total organic acid concentration. Organic anion concentrations were still 4‐fold higher than the controls 24 h after resupply and decreased to values similar to those found in the controls after 96 h. All measured enzymes had increased activities in extracts of iron‐deficient leaves when compared to the controls and generally decreased to control values 24 h after iron addition. These data provide evidence that organic acid accumulation in iron‐deficient leaves is likely not due to an enhancement in leaf carbon fixation. Instead, this accumulation could be associated with organic acid export from the roots to the leaves via xylem.
Antioxidative enzymes in seedlings of Nelumbo nucifera germinated under water
Authors: Ushimaru Takashi , Kanematsu Sumio , Katayama Masao , Tsuji Hideo
Published: March 2003

Dry seeds of anoxia‐tolerant lotus (Nelumbo nucifera Gaertn=Nelumbium speciosum Willd.) have green shoots with plastids containing chlorophyll, so photosynthesis starts even in seedlings germinated under water, namely hypoxia. Here we investigated antioxidative enzyme changes in N. nucifera seedlings responding to oxygen deficiency. The activity of superoxide dismutase (SOD; EC 1.15.1.1), dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) were lower in seedlings germinated under water (submerged condition) in darkness (SD seedlings) than those found in seedlings germinated in air and darkness (AD seedlings). In contrast, ascorbate peroxidase (APX; EC 1.11.1.11) activity was higher in SD seedlings and the activity of catalase (EC 1.11.1.6) and monodehydroascorbate reductase (MDAR; EC 1.6.5.4) in SD seedlings was nearly the same as in AD seedlings. When SD seedlings were exposed to air, the activity of SOD, DHAR and GR increased, while the activity of catalase and MDAR decreased. Seven electrophoretically distinct SOD isozymes were detectable in N. nucifera. The levels of plastidic Cu,Zn‐SODs and Fe‐SOD in SD seedlings were comparable with those found in AD seedlings, which may reflect the maintenance of green plastids in SD seedlings as well as in AD seedlings. These results were substantially different from those previously found in rice seedlings germinated under water.
Leaf cuticular waxes of potted rose cultivars as affected by plant development, drought and paclobutrazol treatments
Authors: Jenks Matthew A. , Andersen Lise , Teusink Rebecca S. , Williams Michelle H.
Published: March 2003

The present work was carried out to evaluate how plant growth and cultural practices influence the amount and composition of cuticular waxes on leaves of rose cultivars. The total amount of cuticular wax per leaf area was higher for rose cultivar Apollo Parade than for Charming Parade. Both cultivars had waxes dominated by alkanes, with the major alkanes being the C31 and C33 homologues. Primary alcohols were the next most abundant constituent class, with C26 as the dominant homologue. Compared with Charming Parade, Apollo Parade had higher proportions of its total wax load as primary alcohols but lower acids and aldehydes. The proportion of alkanes in the total load on these cultivars was similar. Commercially produced roses are routinely treated with paclobutrazol (PBZ) to retard growth. PBZ treatments caused a 10% increase in total wax load and changes in the proportions of certain wax constituents within 11 days of application. Notable was an increase in the total proportion of acids in the total load 25 days after PBZ application, primarily because of increased C28 acids. An alternative method of retarding plant growth is production of roses under limited water availability. When Apollo Parade roses experienced periods of moderate drought stress during production, the wax load per leaf area increased 14 and 8% above control levels at 24 and 38 days after imposition of drought, respectively. Drought caused similar changes in the proportions of individual wax constituents as did PBZ application.
Effect of desiccation on potassium and anion currents from young root hairs: Implication on tip growth
Authors: Dauphin Aurélien , El‐Maarouf Hayat , Vienney Nora , Rona Jean‐Pierre , Bouteau François
Published: March 2003

Little is known about the early response of roots to desiccation. Young growing root hairs of Arabidopsis thaliana, Vigna unguiculata and Phaseolus vulgaris were used to study the early response of roots to desiccation since they behave like sensors that are able to perceive environmental signals. In control conditions, root hairs were polarized around −120 mV and displayed inward rectifying K+ currents. When submitted to short‐term desiccation, root hairs stopped their tip growth and their membrane became depolarized. Under these conditions, the K+ influx carried by the inward rectifying K+ channels was not maintained and instead slow deactivating anion channels were recorded. The inhibition of K+ influx and the large anion efflux due to the activation of slow anion currents could participate in the inhibition of tip growth.
The effect of day length, vernalization and DNA demethylation on the flowering time in Arabidopsis thaliana
Authors: Lízal Pavel , Relichová Jiřina
Published: March 2003

We studied the effect of three factors on the induction of flowering in Arabidopsis thaliana, i.e. vernalization, day length and DNA demethylation. Seven natural late flowering genotypes and 13 late flowering mutants were used in the experiments. The effect of the vernalization and the short day (SD) was uniform in all genotypes used, resulting in shortening (vernalization) or extension of the period before the appearance of the first flower primordia. On the other hand, the effect of the demethylating agent (5‐azacytidine [5‐azaC]) was not uniform in the genotypes used. In all natural late genotypes (except Lu‐1), the shortening of the flowering time (FT) after 5‐azaC treatment was observed. On the contrary, only five mutants –dl, pm, M63, M73 and fca‐1– showed a shortening of the FT, while in the majority of the late flowering mutants, no significant response (earlier flowering) was found. The different response to the vernalization and demethylation treatment in late flowering mutants shows the possibility of two different pathways leading to the flowering, both of which are regulated by DNA demethylation. The different response of natural and induced late flowering genotypes after 5‐azaC treatment shows that genes that play a role in flower development are of a different nature.
Mechanism of copper‐enhanced photoinhibition in thylakoid membranes
Authors: Pätsikkä Eija , Aro Eva‐Mari , Tyystjärvi Esa
Published: March 2003

The effect of copper on photoinhibition of photosystem II (PSII) in vitro was studied in bean (Phaseolus vulgaris L. cv. Dufrix) and pumpkin (Cucurbita pepo L.) thylakoids. The thylakoids were illuminated at 200–2 000 μmol photons m−2 s−1 in the presence of 70–1 830 added Cu2+ ions per PSII. Three lines of evidence show that the irreversible damage of PSII caused by illumination of thylakoids in the presence of Cu2+ was mainly due to donor‐side photoinhibition resulting from inhibition of the PSII donor side by Cu2+. First, addition of an artificial electron donor partially restored PSII activity of thylakoids that had been illuminated in the presence of Cu2+. Second, already moderate light was enough to cause rapid inhibition of PSII, and the inhibition could be saturated by light. Third, the extrinsic polypeptides of the oxygen‐evolving complex were found to become oxidized by the combined effect of Cu2+ and light. The presence of oxygen was not necessary for the copper‐induced enhancement of photoinhibition of PSII. When the illumination was prolonged, copper caused a gradual collapse of the thylakoid structure by increasing degradation of thylakoid proteins.
Effects of leaf wetting and high humidity on stomatal function in leafy cuttings and intact plants ofCorylus maxima
Authors: Fordham Michael C. , Harrison‐Murray Richard S. , Knight Linda , Evered Carol E.
Published: March 2003

When rooted cuttings ofCorylus maximaMill. cv. Purpurea are moved from the wet and humid conditions of the rooting environment, the leaves frequently shrivel and die. Since the newly formed adventitious root system has been shown to be functional in supplying water to the shoot, stomatal behaviour inC. maximawas investigated in relation to the failure to prevent desiccation. Stomatal conductance (gs) in expanding leaves (L3) of cuttings increased almost 10‐fold over the first 14 days in the rooting environment (fog), from 70 to 650 mmol m−2s−1. In contrast, gsof expanded leaves (L1) changed little and was in the region of 300 mmol m−2s−1. Midday leaf water potential was much higher in cuttings than in leaves on the mother stock‐plant (−0.5 versus −1.2 MPa) even before any roots were visible. Despite this, leaf expansion of L3 was inhibited by >50% in cuttings and stomata showed a gradual reduction in their ability to close in response to abscisic acid (ABA). To determine whether the loss of stomatal function in cuttings was due to severance or to unnaturally low vapour pressure deficit and wetting in fog, intact plants were placed alongside cuttings in the rooting environment. The intact plants displayed reductions in leaf expansion and in the ability of stomata to close in response to dark, desiccation and ABA. However, in cuttings, the additional effect of severance resulted in smaller leaves than in intact plants and more severe reduction in stomatal closure, which was associated with a 2.5‐fold increase in stomatal density and distinctively rounded stomatal pores. The similarities between stomatal dysfunction inC. maximaand that observed in many species propagated in vitro are discussed, as is the possible mechanism of dysfunction.
Toxicity of selenium to Lemna minor in relation to sulfate concentration
Authors: Severi Aldo
Published: March 2003

The aquatic plant Lemna minor L. was treated with sodium selenite or sodium selenate to test the toxicity of these salts in relation to high or low levels of sulfate in the culture medium. Several morphophysiological aspects, such as multiplication rate (MR), ratio of the number of fronds to number of colonies (Nfr/Ncol), frond size, cell ultrastructure, pigment content and guaiacol peroxidase (EC 1.11.1.7) activity were evaluated. Their variations might be an indirect means of evaluating the degree of susceptibility or tolerance of this plant to selenium (Se). Sodium selenite or sodium selenate treatments at concentrations ranging from 1 to 256 μM generally decreased the investigated parameters. Moreover, the sulfate concentration influenced the toxicity of both Se salts. In general, with treatments in a medium containing a high sulfate (HS) content, sodium selenite appeared more toxic than sodium selenate, whereas in a low sulfate (LS) medium, sodium selenate seemed more toxic. MR was significantly increased at 1–4 μM selenite and LS or 8 μM selenate and HS levels, suggesting that Se may be an essential nutrient for this plant.
Differences in salt sensitivity of four deciduous tree species to soil or airborne salt
Authors: Paludan‐Müller Georg , Saxe Henrik , Pedersen Lars Bo , Randrup Thomas Barfoed
Published: March 2003

Seedlings of four deciduous tree species maple (Acer pseudoplatanus), beech (Fagus sylvatica), horse chestnut (Aesculus hippocastanum) and lime (Tilia cordata) were exposed to de‐icing salt (NaCl) either through the soil or applied to the above ground plant parts. A soil solution of 1.65 g l−1 NaCl was maintained from the start of the experiment in January 1999 until termination in June 1999. The main effects caused by salt treatment through the soil were a reduction in photosynthesis of up to 50% and the development of leaf chlorosis or necrosis covering up to 50% of the total leaf area for the most sensitive species (lime and beech); maple and horse chestnut were relatively tolerant. There was no significant correlation between Cl or Na concentration in leaves and the relative sensitivity of the species. Saturated salt solution was applied to bark, buds or leaf scars on two occasions three weeks apart during the winter season. This affected the timing of bud break with delays of up to eight days compared with the controls. In the most sensitive species the above ground salt treatments partly prevented bud break (beech) or reduced photosynthesis (lime). Uptake through the bark was most important for the development of stress effects, compared with uptake through the other above ground plant parts.
Flavonol synthase gene expression during citrus fruit development
Authors: Moriguchi Takaya , Kita Masayuki , Ogawa Kazunori , Tomono Yasuhiko , Endo Tomoko , Omura Mitsuo
Published: March 2003

We isolated a cDNA clone (CitFLS) encoding flavonol synthase (FLS) from the satsuma mandarin (Citrus unshiu Marc.) fruit and investigated the steady state of CitFLS RNA expression during the fruit development. The CitFLS was 1274 bp long, encoded 335 amino acid residues, and belonged to a family of 2‐oxoglutarate‐dependent dioxygenases. The level of CitFLS transcript was higher in the young leaves than in the old leaves, and it was high at the early developmental stage and low at the mature stage in the juice sacs/segment epidermis (edible part). On the other hand, the CitFLS transcript increased in the peel during fruit maturation. These results indicated that the satsuma mandarin CitFLS was differentially regulated in the developmental stage and in a tissue‐specific manner. Additionally, satsuma mandarin peel tissues produced rutin (a flavonol glycoside) from an exogenous dihydroquercetin (taxifolin), indicating the ability of these tissues to produce flavonols.
Origin and basipetal transport of the IAA responsible for rooting of carnation cuttings
Authors: Garrido Germán , Ramón Guerrero Juan , Angel Cano Emilio , Acosta Manuel , Sánchez‐Bravo José
Published: March 2003

The origin and transport of the IAA responsible for rooting was studied in carnation (Dianthus caryophyllus L.) cuttings obtained from secondary shoots of the mother plants. The presence of mature leaves in the cuttings was essential for rooting. Removal of the apex and/or the youngest leaves did not reduce the rooting percentage as long as mature leaves remained attached. Removal of mature leaves inhibited rooting for a 24‐day period during which the basal leaves grew and reached maturity. After this period rooting progressed as in intact cuttings. Auxin (NAA + IBA) applied to the stem base of defoliated cuttings was about 60% as effective as mature leaves in stimulating rooting. Application of NPA to the basal internode resulted in full inhibition of rooting. The view, deduced from these results, that auxin from mature leaves is the main factor controlling the rooting process was reinforced by the fact that mature leaves contained IAA and exported labelled IAA to the stem. The distribution of radioactivity after application of (5–3H)‐IAA to mature leaves showed that auxin movement in the stem was basipetal and sensitive to NPA inhibition. The features of this transport were studied by applying 3H‐IAA to the apical cut surface of stem sections excised from cuttings. The intensity of the transport was lower in the oldest node than in the basal internode, probably due to the presence of vascular traces of leaves. Irrespective of the localization of the sections and the carnation cultivar used, basipetal IAA transport was severely reduced when the temperature was lowered from 25 to 4°C. The polar nature of the IAA transport in the sections was confirmed by the inhibition produced by NPA. Local application of IAA to different tissues of the sections revealed that polar auxin transport was associated with the vascular cylinder, the transport in the pith and cortex being low and apolar. The present results strongly support the conclusion that IAA originating from the leaves and transported in the stem through the polar auxin transport pathway was decisive in controlling adventitious rooting.
Lignification related enzymes in Picea abies suspension cultures
Authors: Kärkönen Anna , Koutaniemi Sanna , Mustonen Maaret , Syrjänen Kaisa , Brunow Gösta , Kilpeläinen Ilkka , Teeri Teemu H. , Simola Liisa Kaarina
Published: March 2003

Activity of a number of enzymes related to lignin formation was measured in a Picea abies (L) Karsten suspension culture that is able to produce native‐like lignin into the nutrient medium. This cell culture is an attractive model for studying lignin formation, as the process takes place independently of the complex macromolecular matrix of the native apoplast. Suspension culture proteins were fractionated into soluble cellular proteins, ionically and covalently bound cell wall proteins and nutrient medium proteins. The nutrient medium contained up to 5.3% of total coniferyl alcohol peroxidase (EC 1.11.1.7) activity and a significant NADH oxidase activity that is suggested to be responsible for hydrogen peroxide (H2O2) production. There also existed some malate dehydrogenase (EC 1.1.1.37) activity in the apoplast of suspension culture cells (in ionically and covalently bound cell wall protein fractions), possibly for the regeneration of NADH that is needed for peroxidase‐catalysed H2O2 production. However, there is no proof of the existence of NADH in the apoplast. Nutrient medium peroxidases could be classified into acidic, slightly basic and highly basic isoenzyme groups by isoelectric focusing. Only acidic peroxidases were found in the covalently bound cell wall protein fraction. Several peroxidase isoenzymes across the whole pI range were detected in the protein fraction ionically bound to cell walls and in the soluble cellular protein fraction. One laccase‐like isoenzyme with pI of approximately 8.5 was found in the nutrient medium that was able to form dehydrogenation polymer from coniferyl alcohol in the absence of H2O2. The total activity of this oxidase towards coniferyl alcohol was, however, several orders of magnitude smaller than that of peroxidases in vitro. According to 2D 1H‐13C correlation NMR spectra, most of the abundant structural units of native lignin and released suspension culture lignin are present in the oxidase produced dehydrogenation polymer but in somewhat different amounts compared to peroxidase derived synthetic lignin preparations. A coniferin β‐glucosidase (EC 3.2.1.21) was observed to be secreted into the culture medium.
Sucrose metabolism and cellulose biosynthesis in sunflower hypocotyls
Authors: Kutschera U. , Heiderich A.
Published: March 2003

The relationships between cellulose accumulation, changes in specific activities of enzymes of sucrose catabolism, levels of UDP‐glucose and rate of dark respiration were investigated in the subapical 1 cm‐hypocotyl region of 10‐ to 14‐day‐old‐sunflower seedlings (Helianthus annuus L). The plants were grown under a light/dark regime in vermiculite that was soaked either with distilled water or half‐strength Hoagland nutrient solution. At this stage of seedling development, the hypocotyl had ceased to elongate but increased in width. Stem thickening and the rate of cellulose accumulation were promoted by nutrient solution. The levels of the soluble (vacuolar) and wall‐associated acid invertases (EC 3.2.1.26) were not correlated with these processes. However, the activities of the soluble (cytoplasmic) and membrane‐bound sucrose synthases (EC 2.4.1.13) were larger in hypocotyls that were grown in the presence of nutrient solution. The concentration of UDP‐glucose was reduced, and the rate of dark respiration was enhanced in the hypocotyls that were grown in Hoagland solution. The results support the hypothesis that both forms of the enzyme sucrose synthase play a critical role in cellulose biosynthesis of hypocotyl cells that had ceased to elongate and continue to grow by wall thickening.
Up‐regulation of arginine decarboxylase gene expression and accumulation of polyamines in mustard (Brassica juncea)in response to stress
Authors: Mo Hua , Pua Eng‐Chong
Published: March 2003

Arginine decarboxylase (ADC) is a key enzyme involved in the synthesis of polyamines, which have been implicated in a wide range of plant responses, including stress. However, regulation of polyamine levels in relation to ADC in response to stress at the molecular level is not well understood. In an attempt to address this question, we first cloned two cDNAs in mustard (Brassica juncea[L.] Czern & Coss var. Indian Mustard), designated MADC2 and MADC3, encoding predicted ADC. MADC2 and MADC3 encode polypeptides of 692 and 680 amino acid residues, respectively. A comparison of deduced amino acid sequence revealed that both were highly homologous to MADC1 (77%), a mustard ADC, and other plant ADCs (63–84%). Northern analysis revealed that ADC transcripts in mustard were generally more abundant in stem and root but were barely detectable in leaf. However, ADC expression in the leaf was up‐regulated differentially in response to stress such as chilling, salt and mannitol and to treatments with exogenous polyamines. While chilling induced expression of all three ADC genes, salt predominantly resulted in increased accumulation of MADC3 transcript. Leaves exhibited a similar response to exogenous putrescine, spermidine and spermine, all of which stimulated accumulation of MADC2 and MADC3 transcripts but not MADC1. Furthermore, exogenous putrescine also increased the endogenous levels of spermidine and spermine, while a higher endogenous putrescine and spermidine content was detected in leaf incubated with exogenous spermine. Leaves also responded to chilling, salt and mannitol by increasing the levels of the cellular polyamine content, in which the level of spermine in free and conjugated forms increased most profoundly.
Water relations and gas exchange in poplar and willow under water stress and elevated atmospheric CO2
Authors: Johnson Jon D. , Tognetti Roberto , Paris Piero
Published: March 2003

Predictions of shifts in rainfall patterns as atmospheric [CO2] increases could impact the growth of fast growing trees such as Populus spp. and Salix spp. and the interaction between elevated CO2 and water stress in these species is unknown. The objectives of this study were to characterize the responses to elevated CO2 and water stress in these two species, and to determine if elevated CO2 mitigated drought stress effects. Gas exchange, water potential components, whole plant transpiration and growth response to soil drying and recovery were assessed in hybrid poplar (clone 53–246) and willow (Salix sagitta) rooted cuttings growing in either ambient (350 µmol mol−1) or elevated (700 µmol mol−1) atmospheric CO2 concentration ([CO2]). Predawn water potential decreased with increasing water stress while midday water potentials remained unchanged (isohydric response). Turgor potentials at both predawn and midday increased in elevated [CO2], indicative of osmotic adjustment. Gas exchange was reduced by water stress while elevated [CO2] increased photosynthetic rates, reduced leaf conductance and nearly doubled instantaneous transpiration efficiency in both species. Dark respiration decreased in elevated [CO2] and water stress reduced Rd in the trees growing in ambient [CO2]. Willow had 56% lower whole plant hydraulic conductivity than poplar, and showed a 14% increase in elevated [CO2] while poplar was unresponsive. The physiological responses exhibited by poplar and willow to elevated [CO2] and water stress, singly, suggest that these species respond like other tree species. The interaction of [CO2] and water stress suggests that elevated [CO2] did mitigate the effects of water stress in willow, but not in poplar.
Aphid (Sitobion yakini) investigation suggests thin‐walled sieve tubes in barley (Hordeum vulgare) to be more functional than thick‐walled sieve tubes
Authors: Matsiliza B. , Botha C.E.J.
Published: March 2003

Barley, like most other grasses that have been studied, contains two kinds of sieve tube. The first formed are called thin‐walled sieve tubes because of their thin wall compared to the late‐formed, and are associated with companion cells. The late‐formed are thick‐walled sieve tubes, which differentiate next to the metaxylem vessels and lack companion cells. Aphid (Sitobion yakini (Eastop) feeding was studied using light microscopy to determine if they preferentially feed from thin‐ or thick‐walled sieve tubes in the barley leaf. Penetration of the stylets through the leaf epidermis and mesophyll was largely intercellular, becoming partly intercellular and, partly, intracellular inside the vascular bundle. Sixteen of 19 pairs of stylets (84%), and 293 of 317 (92%) stylet tracks terminated at the thin‐walled sieve tubes, suggesting that Sitobion yakini feeds preferentially on the thin‐walled sieve tubes which seem to be more attractive to the aphid. These thin‐walled sieve tubes are thus probably the most functional in terms of phloem loading and transport.
Endosperm‐specific expression of green fluorescent protein driven by the hordein promoter is stably inherited in transgenic barley (Hordeum vulgare) plants
Authors: Cho Myeong‐Je , Choi Hae‐Woon , Jiang Wen , Ha Chi D. , Lemaux Peggy G.
Published: March 2003

The expression of green fluorescent protein (GFP) and its inheritance were studied in transgenic barley (Hordeum vulgare L.) plants transformed with a synthetic green fluorescent protein gene [sgfp(S65T)] driven by either a rice actin promoter or a barley endosperm‐specific d‐hordein promoter. The gene encoding phosphinothricin acetyltransferase (bar), driven by the maize ubiquitin promoter and intron, was used as a selectable marker to identify transgenic tissues. Strong GFP expression driven by the rice actin promoter was observed in callus cells and in a variety of tissues of T0 plants transformed with the sgfp(S65T)‐containing construct. GFP expression, driven by the rice actin promoter, was observed in 14 out of 17 independent regenerable transgenic callus lines; however, expression was gradually lost in T0 and later generation progeny of diploid lines. Stable GFP expression was observed in T2 progeny from only 6 out of the 14 (43%) independent GFP‐expressing callus lines. Four of the 8 lines not expressing GFP in T2 progeny, lost GFP expression during T0 plant regeneration from calli; one lost GFP expression in the transition from the T0 to T1 generations and three lines were sterile. Similarly, expression of bar driven by the maize ubiquitin promoter was lost in T1 progeny; only 21 out of 26 (81%) independent lines were Basta‐resistant. In contrast to actin‐driven expression, GFP expression driven by the d‐hordein promoter exhibited endosperm‐specificity. All seven lines transformed with d‐hordein‐driven GFP (100%) expressed GFP in the T1 and T2 generations, regardless of ploidy levels, and expression segregated in a Mendelian fashion. We conclude that the sgfp(S65T) gene was successfully transformed into barley and that GFP expression driven by the d‐hordein promoter was more stable in its inheritance pattern in T1 and T2 progeny than that driven by the rice actin promoter or the bar gene driven by the maize ubiquitin promoter.
Auxin stimulates S6 ribosomal protein phosphorylation in maize thereby affecting protein synthesis regulation
Authors: Beltrán‐Peña Elda , Aguilar Raúl , Ortíz‐López Adriana , Dinkova Tzvetanka D. , De Jiménez Estela Sánchez
Published: March 2003

Auxin is known to stimulate protein synthesis in many plant tissues, but the mechanisms involved in this process are unknown. The present research inquires whether auxin might regulate selective translation of mRNAs by inducing S6 ribosomal protein phosphorylation on the 40S ribosomal subunit in maize (Zea mays L.). Maize embryonic axes auxin‐stimulated by natural (IAA) or synthetic (Dicamba or 1‐NAA) auxins, selectively increased ribosomal protein synthesis. This effect was not reproduced by auxin inactive analogue 2‐NAA. Enhanced S6 ribosomal protein phosphorylation on the 40S ribosomal subunit was also observed after auxin stimulation, as measured by [32P] incorporation into this protein. This increment did not occur when stimulation was performed with the inactive auxin analogue. Further, increased recruitment into polysomes of two 5′TOP‐like mRNAs, encoding for the initiation translation factor eIF‐iso4E and the S6 ribosomal protein, was also found after auxin stimulation of maize axes. A positive correlation was established between the levels of S6 ribosomal protein phosphorylation and the S6 ribosomal protein transcript recruitment into polysomes by means of okadaic acid or heat shock application to maize axes. These data indicate that auxin stimulates S6 ribosomal protein phosphorylation on maize ribosomes, concomitant to the recruitment of specific mRNAs (5′TOP‐like mRNAs) into polysomes for translation. It is proposed that by this mechanism auxin regulate the synthesis of specific proteins in maize tissues.
Pea rms6 mutants exhibit increased basal branching
Authors: Rameau Catherine , Murfet Ian C. , Laucou Valerie , Floyd Robert S. , Morris Suzanne E. , Beveridge Christine A.
Published: March 2003

Our studies on two branching mutants of pea (Pisum sativum L.) have identified a further Ramosus locus, Rms6, with two recessive or partially recessive mutant alleles: rms6‐1 (type line S2‐271) and rms6‐2 (type line K586). Mutants rms6‐1 and rms6‐2 were derived from dwarf and tall cultivars, Solara and Torsdag, respectively. The rms6 mutants are characterized by increased branching from basal nodes. In contrast, mutants rms1 through rms5 have increased branching from both basal and aerial (upper stem) nodes. Buds at the cotyledonary node of wild‐type (WT) plants remain dormant but in rms6 plants these buds were usually released from dormancy. Their growth was either subsequently inhibited, sometimes even prior to emergence above ground, or they grew into secondary stems. The mutant phenotype was strongest for rms6‐1 on the dwarf background. Although rms6‐2 had a weak single‐mutant phenotype, the rms3‐1 rms6‐2 double mutant showed clear transgression and an additive branching phenotype, with a total lateral length almost 2‐fold greater than rms3‐1 and nearly 5‐fold greater than rms6‐2. Grafting studies between WT and rms6‐1 plants demonstrated the primary action of Rms6 may be confined to the shoot. Young WT and rms6‐1 shoots had similar auxin levels, and decapitated plants had a similar magnitude of response to applied auxin. Abscisic acid levels were elevated 2‐fold at node 2 of young rms6‐1 plants. The Rms6 locus mapped to the R to Gp segment of linkage group V (chromosome 3). The rms6 mutants will be useful for basic research and also have possible agronomical value.
Ecophysiology of Antarctic vascular plants
Authors: Alberdi Miren , Bravo León A. , Gutiérrez Ana , Gidekel Manuel , Corcuera Luis J.
Published: March 2003

Most of the ice and snow‐free land in the Antarctic summer is found along the Antarctic Peninsula and adjacent islands and coastal areas of the continent. This is the area where most of the Antarctic vegetation is found. Mean air temperature tends to be above zero during the summer in parts of the Maritime Antarctic. The most commonly found photosynthetic organisms in the Maritime Antarctic and continental edge are lichens (around 380 species) and bryophytes (130 species). Only two vascular plants, Deschampsia antarctica Desv. and Colobanthus quitensis (Kunth) Bartl., have been able to colonize some of the coastal areas. This low species diversity, compared with the Arctic, may be due to permanent low temperature and isolation from continental sources of propagules. The existence of these plants in such a permanent harsh environment makes them of particular interest for the study of adaptations to cold environments and mechanisms of cold resistance in plants. Among these adaptations are high freezing resistance, high resistance to light stress and high photosynthetic capacity at low temperature. In this paper, the ecophysiology of the two vascular plants is reviewed, including habitat characteristics, photosynthetic properties, cold resistance, and biochemical adaptations to cold.
Boron requirement in the Discaria trinervis (Rhamnaceae) and Frankia symbiotic relationship. Its essentiality for Frankia BCU110501 growth and nitrogen fixation
Authors: Bolaños Luis , Redondo‐Nieto Miguel , Bonilla Ildefonso , Wall Luis G.
Published: March 2003

The essentiality of boron (B) for nitrogen fixation in heterocystous cyanobacteria and rhizobial symbioses has been widely established. However, nothing is known about the possible involvement of the micronutrient in actinorhizal symbioses. Therefore, the effect of boron (B) deficiency on the establishment of the Discaria trinervis‐Frankia BCU110501 symbiosis was investigated. Nodulation was diminished in B‐deficient D. trinervis or in plants inoculated with Frankia grown in the absence of B. These poorly nodulated plants showed a reduction of shoot and root weight and small size. Because depletion of the micronutrient during growth of the actinomycete altered the infection capacity of Frankia, we also studied growth, structure and nitrogen fixation of free‐living Frankia BCU110501. Growth was delayed in B‐deficient BAP media (+N cultures), and completely inhibited in B‐deprived N‐free BAP media (–N cultures), suggesting that B is required to enhance growth of Frankia and essential for the development of nitrogen fixing activity. Ultrastructural study of B‐deficient cells showed an alteration of filament walls both in +N and especially in –N cultures, indicating a possible role of the microelement in the maintenance of these structures. Moreover, the stability of vesicle envelopes was impaired in the absence of B and, hence, nitrogenase occurrence and nitrogen fixation were totally absent. The results show that B is required for both partners to establish an effective symbiosis.
Isolation and characterization of a Chlamydomonas gene that encodes a putative blue‐light photoreceptor of the phototropin family
Authors: Huang Kaiyao , Merkle Thomas , Beck Christoph F.
Published: March 2003

In the search for a Chlamydomonas reinhardtii photoreceptor that may mediate blue‐light‐induced responses we identified a gene that encodes a protein with a structure typical for that of members of the phototropin family, i.e. two LOV domains that may function in flavin mononucleotide binding and a ser/thr kinase domain. The amino acid sequences of these domains are closely related to those of higher plant phototropins. This single‐copy gene (Phot) encodes a protein with a calculated molecular mass of 81.4 kDa which is distinctly smaller than the homologous proteins of higher plants that exhibit molecular masses around 120 kDa. Expression analyses revealed rather constant levels of Phot mRNA and Phot protein in vegetative cells incubated in the dark and in cells undergoing gametogenesis. Only vegetative cells in the light showed a reduced expression of the Phot gene. Cell fractionation studies revealed that the protein is membrane‐associated. In higher plants, phototropins were shown to be bound to the plasma membrane. However, the expression of a Phot‐GFP gene fusion in tobacco protoplasts revealed an association of the fusion protein with the endogenous membrane network of the cell.
Serpins of oat (Avena sativa) grain with distinct reactive centres and inhibitory specificity
Authors: Hejgaard Jørn , Hauge Sidsel
Published: March 2003

Most proteinase inhibitors from plant seeds are assumed to contribute to broad‐spectrum protection against pests and pathogens. In oat (Avena sativa L.) grain the main serine proteinase inhibitors were found to be serpins, which utilize a unique mechanism of irreversible inhibition. Four distinct inhibitors of the serpin superfamily were detected by native PAGE as major seed albumins and purified by thiophilic adsorption and anion exchange chromatography. The four serpins OSZa–d are the first proteinase inhibitors characterized from this cereal. An amino acid sequence close to the blocked N‐terminus, a reactive centre loop sequence, and the second order association rate constant (ka′) for irreversible complex formation with pancreas serine proteinases at 24°C were determined for each inhibitor. OSZa and OSZb, both with the reactive centre scissile bond P1‐P1′ Thr↓Ser, were efficient inhibitors of pancreas elastase (ka′ > 105M−1 s−1). Only OSZb was also an inhibitor of chymotrypsin at the same site (ka′ = 0.9 × 105M−1 s−1). OSZc was a fast inhibitor of trypsin at P1‐P1′ Arg↓Ser (ka′ = 4 × 106M−1 s−1); however, the OSZc‐trypsin complex was short‐lived with a first order dissociation rate constant kd = 1.4 × 10−4 s−1. OSZc was also an inhibitor of chymotrypsin (ka′ > 106M−1 s−1), presumably at the overlapping site P2‐P1 Ala↓Arg, but > 90% of the serpin was cleaved as substrate. OSZd was cleaved by chymotrypsin at the putative reactive centre bond P1‐P1′ Tyr↓Ser, and no inhibition was detected. Together the oat grain serpins have a broader inhibitory specificity against digestive serine proteinases than represented by the major serpins of wheat, rye or barley grain. Presumably the serpins compensate for the low content of reversible inhibitors of serine proteinases in oats in protection of the grain against pests or pathogens.
Decrease in sunflower (Helianthus annuus) seed viability caused by high temperature as related to energy metabolism, membrane damage and lipid composition
Authors: Corbineau Françoise , Gay‐Mathieu Chantal , Vinel Dominique , Côme Daniel
Published: March 2003

The aim of the present work was to investigate whether loss of germination ability and viability of sunflower (Helianthus annuus L.) seeds during incubation at a high temperature (45°C) was related to changes in energy metabolism, loss of membrane integrity, and/or changes in lipid composition. Pre‐treatment of seeds at 45°C progressively reduced subsequent germination at the optimal temperature (25°C). Seeds did not germinate at 45°C and almost all of them were dead after 72 h of soaking at this high temperature. This loss of seed viability was associated with a large increase in leakage of K+ and total electrolytes into the incubation medium, and with production of malondialdehyde in the embryonic axis and cotyledons, suggesting a loss of membrane integrity probably due to lipid peroxidation. ATP and ADP levels increased sharply during the first hours of imbibition at 45°C, remained high for about 24 h and then decreased. As a consequence, the energy charge followed a similar pattern. If the treatment at 45°C did not exceed 48 h, seeds recovered an apparently normal energy metabolism after transfer to 25°C, even though they lost their ability to germinate at this temperature. Therefore, energy metabolism at the whole embryo level cannot be considered as an indicator of germination ability. Incubation of seeds at 45°C resulted in an increase in triacylglycerols and diacylglycerols without a significant change in their fatty acid composition. It also induced a slight increase in phospholipid content with an increase in C16:0, C18:0 and C18:1, but with no change in C18:2. In phospholipids, the C18:2/C18:1 and (C18:1 + C18:2)/ (C16:0 + C18:0) ratios thus declined during treatment at 45°C. The results obtained suggest that deterioration of sunflower seeds during incubation at a high temperature is mainly related to membrane damage and alteration of energy metabolism, and that accumulation of malondialdehyde, which is an index of lipid peroxidation, does not correspond to a decrease in total lipids and phospholipids nor to a significant change in fatty acid composition, except in PL in which the C18:2/C18:1 and (C18:1 + C18:2)/ (C16:0 + C18:0) ratios slightly declined.
Changes in leaf hydraulics and stomatal conductance following drought stress and irrigation in Ceratonia siliqua (Carob tree)
Authors: Lo Gullo Maria A. , Nardini Andrea , Trifilò Patrizia , Salleo Sebastiano
Published: March 2003

Changes in leaf hydraulic conductance (K) were measured using the vacuum chamber technique during dehydration and rehydration of potted plants of Ceratonia siliqua. K of whole, compound leaves as well as that of rachides and leaflets decreased by 20–30% at leaf water potentials (ΨL) of −1.5 and −2.0 MPa, i.e. at ΨL values commonly recorded in field‐growing plants of the species. Higher K losses (up to 50%) were measured for leaves at ΨL of −2.5 and −3.0 MPa, i.e. near or beyond the leaf turgor loss point. Leaves of plants rehydrated while in the dark for 30 min, 90 min and 12 h recovered from K loss with characteristic times and to extents inversely proportional to the initial water stress applied. Leaf conductance to water vapour of plants dehydrated to decreasing ΨL and rehydrated at low transpiration was inversely related to loss of K, thus suggesting that leaf vein embolism and refilling (and related changes in leaf hydraulics) may play a significant role in the stomatal response.