bluuebunny/crossref_metadata_2025 huggingface dataset:
Activities of plasma membrane‐bound enzymes isolated from roots of spruce (Picea abies) grown in the presence of aluminium
Authors: Widell Susanne , Asp Håkan , Jensén Paul
Published: May 2006

The effect of aluminium on plasma membrane‐bound enzymes and ion uptake was studied with spruce cuttings (Piccu abies Karst.) grown in nutrient solution, pH 4.2, for 5 weeks. The H+– ATPase and glucan synthase II activities of isolated root plasma membranes were inhibited by the presence of aluminium during growth (0.1–3 mM), with glucan synthase II being more sensitive than the ATPase. The active K+‐uptake obtained with intact roots was also inhibited by aluminium, whereas the passive uptake was stimulated ca 4‐fold by moderate amounts of aluminium (0.1 mM). The uptake of Ca2+ (passive) was severely inhibited at all external aluminium concentrations tested. Experiments were also performed with aluminium added during the assay, or in preincubations of isolated plasma membranes. Again, the glucan synthuse II activity was severely inhibited bv aluminium. There were no signs of adaptation, i.e., the activities with plasma membranes from cuttings given aluminium during growth, were equally sensitive as the control. The aluminium additions in vitro were at pH 6.5 (ATPase) or 7.2? (glucan synthase II) indicating that lor the enzymes studied, aluminium can be toxic although the pH is neutral.
Purification and properties of glutamate dehydrogenase in Scots pine (Pinus sylvestris) needles
Authors: Schlee D. , Thöringer C. , Tintemann H.
Published: May 2006

NADH‐dependent glutamate dehydrogenase (GDH. EC 1. 4. 1.2) was isolated from the needles of Scots pine (Pinus sylverstris L.) grown on a rural and on a heavily polluted industrial area, and it was purified about 500 fold. The purification procedure included salt I'ractionation, ion exchange and affinity chromatography. Miehaelis constants for 2‐oxoglularale (1.7 mM). for ammonium sultate (19 mM) and for NADH (42.5 resp. 53 μM) the pH optimum (8.5) the requirements for Ca2+ ions, the temperature dependence ofl the enzyme activity (incubation from 0 to 82°C). and the relation between forest region and electrophoretie isoenzyme pattern were determined. The possible role of GDH in the adaptation of plants to ammonia assimilation (detoxification) under stress conditions, particularly with respect to air pollution, is discussed.
Purification and characterization of phosphoglucomutase from peas
Authors: Galloway Cynthia M. , Dugger W. Mack
Published: May 2006

Phosphoglucomutase (EC 2.7.5.1) was isolated from pea seeds (Pisum sativum L. cv. Grenadier) and purified to homogeneity as determined by sodium dodecylsulfate ‐ polyacrylamide gel electrophoresis (SDS‐PAGE) analysis. The enzyme was purified by utilizing 25% polyethylene glycol 4000 precipitation, followed by Fractogel‐diethyla‐minoethyl (DEAE) 650. Fractogel‐TSK HW‐55(s). and high pressure liquid chroma‐tography (HPLC)‐(PEI) column chrornatography. The resulting enzyme had a specific activity of 157 units (mg protein)‐1. a 152‐fold increase over that of the crude plant extract. The molecular weight of the enzyme was 128 to 136 kDa. as determined by native‐PAGE and column chromatography, and when it was subjected to SDS‐PAGE analysis, it was found to be composed of two subunits having molecular weights ranging from 59 to 64 kDa. Upon SDS‐PAGE analysis of a sample purified through HPLC‐PEI chromatography. two bands of protein were found: one having a molecular weight of 64 kDa and the other 68 kDa. A pH optimum of 8.6 was found for the enzyme while it was also found that cysleine. Mg2+ and glucose 1.6‐bisphosphate were necessary for optimal activity Histidine and imidazole only partially fulfilled the cysteine requirement. A 20‐min preincubation period in the absence of glucose 1‐phosphate was necessary for optimal activity of the enzyme. Without a preincubation period, there was a pronounced lag preceding the linear portion of the reaction as well as a reduction in the Vmax. An analysis of the kinetics of the reaction showed Km values ot 3.6 × 10−5 and 1.45 × 10−5M for glucose 1‐phosphate and glucose 1.6‐bisphosphate. respectively. A K., of 7.3 × 10−5M was obtained for MgCl2.
Effect of repeated severe pruning on endogenous polyamine content in hazelnut trees
Authors: Rey Manuel , Diaz‐Sala Carmen , Rodriguez Roberto
Published: May 2006

Endogenous polyamine content was determined in leaves and buds of adult and repeatedly severe pruned hazelnut trees (Corvlus avellana L.). Polyamine content in leaves from shoots obtained by forced outgrowth of branches taken from adult and pruned trees was also determined. Variations of polyamine levels in relation to pruning treatments were observed in all the analysed, tissues. Free polyamines increased in response to pruning treatments, mostly due to an increase in free putrescine. Free spermidine and spermine seemed to decrease with pruning intensity, whereas bound polyamines did not seem to correlate with treatments. Significantly, in all the analysed tissues the putrescine to spermidine plus spermine ratio increased in the free polyamine fraction. The results indicate that polyamine metabolism could play a role as a physiological marker for juvenility and rejuvenation in relation to cloning of woody plants. The possible role of polyamines in mediating and/or regulating phase change and reinvigoration is discussed.
Influence of UV‐B radiation and nitrogen starvation on daily rhythms in phototaxis and cell shape of Euglena gracilis
Authors: Petersen‐Mahrt Silja K. , Ekelund Nils G. A. , Widell Susanne
Published: May 2006

The flagellate Euglena gracilis Klebs strain Z shows phototaxis and changes cell shape between oblong and round. Both cell events show daily rhythmicity. Phototaxis was highest about 2 h after light onset with a second peak of activity 9 h later. At the same times, the cells were in their most oblong shape. During the night phase the cells were phototactically inactive and round. These rhythms were altered by environmental stress, e.g. UV‐B radiation (280–320 nm) and nitrogen deficiency. Artificial UV‐B radiation of 0.5 W m−2 caused a loss in phototaxis hut the peak of activity occurred at the same time as for control cells. The transition from round to oblong cell shape was slower after UV‐B radiation, but the difference between the roundest and the most oblong cell shape was unchanged. Nitrogen deficiency caused a total loss of phototaxis and the cells remained round all the time. The cells lost all their chlorophyll and were, therefore, photosynthetically inactive.
Abscisic acid and osmotic stress or slow drying independently induce desiccation tolerance in mutant seeds of Arabidopsis thaliana
Authors: Ooms Jaap J.J. , van der Veen Renske , Karssen Cees M.
Published: May 2006

Action of endogenous abscisic acid (ABA) is absent in the ABA‐deficient and ‐insensitive double mutant (aba‐1abi3–1) seeds of Arabidopsis thaliana. Thus, responses to osmotic stress and dehydration can be studied without interference of endogenous ABA. Seeds of this double mutunt are viable hut desiceation‐intolerant. However, desiccation tolerance can he induced by either (1) slow dehydration of immature seeds; (2) treatment of immature seeds with osmotica or; (31 due to the leakiness of the ABA‐insensitivty mutation, by application of exogenous ABA. Consequently it is concluded that either ABA or osmotic‐ or dehydration‐stress and related gene expression meets the minimal requirements for acquisition of desiccation tolerance in seeds of Arabidopsis thalianna.
Molecular cloning and characterization of vernalization‐related (ver) genes in winter wheat
Authors: Chong Kang , Wang Li‐Ping , Tan Ke‐Hui , Huang Hua‐Liang , Liang Hou‐Guo
Published: May 2006

The enriched cold‐induced cDNA library of 1 × 104 plaque‐forming units (pfu. was prepared using cDNAs from cold‐induced winter wheat, subtracted with mRNA of the control (non cold‐induced). Results of the hybridization in situ of differential screening with probes of the control, the vernalized and devernalized wheat cDNAs showed that verc 17 (verc: vernalization‐relatcd cDNA clone) is specific for the veinalization. The insert of lambda of 10 recombinant was subcloned into the sites between Bam HI and Hind III in a pUC 19 plasmid. Analysis by northern blotting with a probe from verc 17 indicated that the verc17 has negative signals for the control and the devernatized mRNA, but a positive signal for the mRNA of vernalized wheat at about 1.8 kb. The sequence had 20 restriction sites, covered by 17 enzymes. The ver 17 gene showed some homology with the P. yeolii major merozoite surface‐antigen gene.
Effect of photon fluence rate, nitrogen limitation and nitrogen recovery on the level of phycoerythrin in the unicellular alga, Rhodosorus marinus (Rhodophyceae)
Authors: Dupré Catherine , Guary Jean‐Claude , Grizeau Dominique
Published: May 2006

Studies were carried out on the effects of irradiance and nitrogen sources on phycoerythrin accumulation in the unicellular Rhodophycea. Rhodosorus marinus. The abilily of this microalgal species for natural cell aggregation was used to separate easily the biomass from the culture medium. Alter the removal of nitrogen from the growth medium, phycoerythrin content decreased with time, faster the higher the fluence rate. The results suggest that, in R. marinua. a large part of the phycoerythrin content of N‐sufficient cells is used for nitrogen storage. Restoration of nitrogen in the growth medium induced an increase of phycoerythrin content. even when cells were maintained in darkness. Different inorganic and organic nitrogen sources were shown to promote also phycoerythrin recovery in the dark.
Ion balance in tomato cultivars differing in salt tolerance. I. Sodium and potassium accumulation and fluxes under moderate salinity
Authors: Taleisnik Edith , Grunherg Karina
Published: May 2006

The magnitude of sodium and potassium fluxes in Lycopersicon escutentum cuhivars Ace and Edkawi (Edkawi is considered more sait‐tolerant I was evaluated in planls grown for 10 days in aerated Hoagland solution with the addition of 25 or 100 mM NaCl. Ion accumulatiun in different plant pans, ion concentration in xylem exudate. transpiration and membrane leakiness were measured. Both cultivars responded very similarly to these levels of salinity in terms of growth. No conspicuous differences in membrane leakiness were observed. Net uprake rates were calculated from ion contents data. Potassium uptake rates were lower in salinized planls than in controls, especially in cv. Aee. Potassium/sodium selectivity ratios were much higher in Edkawi than in Ace. and higher in shoot uptake rates than in xy lem exudate. This indicates that Edakw i has a higher capacity to retain potassium under salinity, a character which could contribute to its salt‐tolerance.
Expression of three ABA‐regulated clones and their relationship to maturation processes during the embryogenesis of chick‐pea seeds
Authors: Colorado Pilar , Nicolás Carlos , Nicolás Gregorio , Rodríguez Dolores
Published: May 2006

Water stress inhibits germination of chick‐pea seeds and produces specific changes in gene expression. some of which are coincident with those induced by the exogenous application of abscisic acid (ABA). Three cDNA clones, GAB‐8, GAB‐9 and GAB‐11, were previously identified as under the regulation of ABA and osmotic stress in embryonic axes of germinating chick‐pea. Here we try to establish a relationship between the changes in gene expression induced by ABA and stress conditions during germination and those naturally occurring during the desiccation process that leads to seed maturation. Our results show that the germinative capacity of chick‐pea is related to the water content of the organ. In vitro translation of the mRNAs from developing seed reveals that in the later stages of seed maturation some polypeptides appear that previously were found to be regulated by ABA and by water deficit in germinating seeds. Hybridization by northern blot of embryogenic mRNAs with GAB‐8. GAB‐9 and GAB‐11 clones shows that the mRNAs corresponding to such clones only appear in the later phases of seed formation, coinciding with seed dehydration, and persisting until seeds became fully mature. The results suggest that these mRNAs are probably related to the response to dehydration that occurs during seed maturation, and that the pattern of expression of these ABA‐regulated clones coincides with that of the established late embryogenesis‐abundant (LEA) genes.
The accumulation of proline in Prasiola crispa during winter in Antarctica
Authors: Jackson A. E. , Seppelt R. D.
Published: May 2006

Samples of Prasiola crispa were collected in Antarctica throughout a 13‐month period and analysed for free amino acids by HPLC. There was a marked increase in the levels of proline with the onset of winter, concurrent with a decrease in the other predominant amino acids. In January, proline constituted 1.2 ± 0.1 μ mol (g dry weight)−1. whereas by mid‐April it was the major component at 28.4 ± 2.9 μ mol (g dry weight)−1. When winter samples were thawed in a growth cabinet, their proline content declined to 4.3 ± 0.5 μ mol (g dry weight)−1 after 7 days. Measurements of photosynthetic quantum yield indicated that winter samples of P. crispa also recovered photosynthetic activity upon thawing. Amino acids and other solutes are involved in the preservation of photosynthetic activities during freezing and it seems probable that proline is involved in cryoprotection in this species. In summer samples, there was no evidence that proline levels in P. crispa increased with the conductivity of the water in which they were found growing.
Interaction of boron and calcium in the cyanobacteria Anabaena and Synechococcus
Authors: Bonilla Ildefonso , Bolaños Luis , Mateo Pilar
Published: May 2006

Although some studies have reported an interaction between boron (B) and calcium (Ca2+) in higher plants, there is little evidence for a similar relationship in cyanobacteria. The present study was designed to determine the effect of a supplement of boron to Ca2+‐deficient cultures of Anabaena PCC 7119 and Synechococcus PCC 7942. Grown under Ca2+ deprivation, Anabaena had a slow growth rate and a low photosynthetic pigment content that was related to an inhibition of photosynthesis. Ca2+‐deficient cells showed a lack of cohesiveness of the heterocyst envelope layers, which was consistent with a rapid decline in nitrogenase activity. A supplement of B led to partial recovery from the effects caused by lack of Ca2+. Similarly, low Ca2+ had inhibitory effects on growth and metabolism of Synechococcus cultures. In this case, the effect of a B supplement depended on the concentration of Ca2+ in the growth medium. When Ca2+ was present at normal concentration. B was not required, at least no more than trace amounts. However, when the Ca2+ concentration decreased, B was required at increasing levels. An effect of boron on uptake and/or on the binding of Ca2+ in cyanobacteria is proposed.
Methyl jasmonate induces pigmentation and flavonoid gene expression in petunia corollas: A possible role in wound response
Authors: Tamari Guy , Borochov Amihud , Atzorn Rainer , Weiss David
Published: May 2006

We have previously shown that gibberellic acid (GA) plays an important role in the regulation of anthocyanin synthesis and flavonoid gene transcription in developing petunia corollas. The aim of the present work was to examine the possible role of methyl jasmonate (JA‐Me) in the regulation of these processes. JA‐Me induces anthocyanin biosynthesis and chalcone synthase (chs) and dihydroflavonol 4‐reductase (dfr) gene expression in detached corollas. JA‐Me promoted β‐glucuronidase (GUS) activity in corollas of transgenic plants carrying the gus gene driven by a chs promoter, indicating that it acts at the level of transcription initiation. Whereas chs induction by GA3 started after 5 h and was durable. that of JA‐Me was more rapid but transient. Anthocyanin synthesis was induced by wounding and this effect was enhanced by JA‐Me. Wounding also induced an increase in jasmonate content in detached corollas. The kinetics of chs and dfr mRNA accumulation following wounding was similar to that caused by JA‐Me but not to that caused by GA3. Our results suggest that JA‐Me does not play a role in the natural developmental regulation of corolla pigmentation but that it may mediate wound‐induced changes in flavonoid gene transcription.
Balancing photosynthetic light‐harvesting and light‐utilization capacities in potato leaf tissue during acclimation to different growth temperatures
Authors: Steffen Kenneth L. , Wheeler Raymond M. , Arora Rajeev , Palta Jiwan P. , Tibbitts Theodore W.
Published: May 2006

We investigated the effect of temperature during growth and development on the relationship between light‐harvesting capacity, indicated by chlorophyll concentration, and light‐utilization potential, indicated by light‐ and bicarbonate‐saturated photosynthetic oxygen evolution, in Solanum tuberosum L. cv. Norland. Conal plantles were transplanted and grown at 20°C for 2 weeks before transfer to 12, 16, 20, 24 and 28°C for 6 weeks. After 4 weeks of the temperature treatments, leaf tissue fresh weights per area were one‐third higher in plants grown at 12°C vs those grown at 28°C. Conversely, chlorophyll content per area in tissue grown at 12°C was less than one‐half of that of tissue grown at 28°C at 4 weeks. Photosynthetic capacity measured at a common temperature of 20°C and expressed on a chlorophyll basis was inversely proportional to growth temperature. Leaf tissue from plants grown at 12°C for 4 weeks had photosynthetic rates that were 3‐fold higher on a chlorophyll basis than comparable tissue from plants grown at 28°C. These results suggest that the relationship between light‐harvesting capacity and light‐utilization potential varies 3‐fold in response to the growth temperatures examined. The role of this response in avoidance of photoinhibition is discussed.
Enhancement of the light‐triggered electrical response in plant cells following their de‐energization with uncouplers
Authors: Bulychev Alexander A. , Vredenberg Wim J.
Published: May 2006

Light‐triggered membrane potential changes in cells of a liverwort Anthoceros are greatly enhanced by the ionophorous uncouplers nigericin and monesin. Stimulation of the light‐triggered electrical response (LTER) by nigericin occurred concomitantly with inhibition of a slow decline in the chlorophyll fluorescence, which suggests that the transmembrane pH gradient in thylakoids is not essential for generation of LTER at the plasma membrane. The extent of monensin‐stimulated LTER remained high under a diminished driving force for the ionophore‐induced proton‐cation exchange across the plasma membrane (elevation of the external Na+ concentration from 1 to 50 mM), which indicates that energy uncoupling in chloroplasts is more related to the electric response enhancement than the induction of the H+/K+(Na+) exchange at the plasma membrane. Enhancement of LTER by ionophores occurs in parallel with stimulation of light‐triggered pH changes (alkalinization) in the vicinity of the cell surface, which suggests an association of trans‐membrane H+ fluxes with LTER. The results are consistent with the hypothesis that illumination produces a temporary inhibition of the plasma membrane H+ pump with a subsequent activation of gated channels and transient rapid depolarization of the cell.
Uptake of atmospheric 15NO2 and its incorporation into free amino acids in wheat (Triticum aestivum)
Authors: Weber Paul , Nußbaum Stefan , Fuhrer Jürg , Gfeller Hans , Schlunegger Urs Peter , Brunold Christian , Rennenberg Heinz
Published: May 2006

Five‐week‐old wheat plants were exposed, under controlled environmental conditions, to 60 nl 1−115NO2 or to purified air. After 48 and 96 h of exposure, leaves, stalks and roots were analysed for 15N‐enrichment in α‐amino nitrogen of soluble, free amino acids. In addition, the in vitro nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NIR, EC 1.7.7.1) activities were determined in the leaves. NR activity in the leaves decreased continously during the 96‐h exposure to purified air. In the leaves exposed to 15NO2, NR activity increased within the first 24 h, then decreased, and reached the level of controls after 96 h. NiR activity in leaves exposed to purified air was almost constant during the 96‐h exposure. In leaves exposed to 15NO2, NiR activity increased within the first 48 h, then decreased, and reached the level of controls after 72 h, Exposure to 15NO2 enhanced the total content of soluble, free amino acids in all tissues analysed. Most of this increase was attributed to Glu in the leaves and to Asn plus Gln the α‐amino group of soluble, free amino acids was observed in the leaves, the lowest enrichment in the roots. The main labelled amino compounds were Glu (with 8.0%15N enrichment compared to the control), γ‐aminobutyric acid (GABA; 7.9%), Ala (7.2%). Ser (6.8%), Asp (5.5%) and Gln (4.6%). Appreciable incorporation of 15 into Asn was not found. After 96 h exposure to 15NO2 the 15N enrichment in the α‐amino group of soluble, free amino acids in the leaves declined as compared to the values obtained after 48 h fumigation. The possible pathway and the time course of 15N incorporation into soluble, free amino acids from the 15NO2 absorbed are discussed.
Differences in release of endogenous sugars and amino acids from attached and detached seed coats of developing pea seeds
Authors: De Jong A. , Wolswinkel P.
Published: May 2006

The effect of p‐chloromercuribenzenesulfonic acid (PCMBS), carbonylcyanide‐m‐chlorophenylhydrazone (CCCP) and a high apoplastic pH (pH 7.5 compared with pH 5.5) on the release of sugars (sucrose and glucose) and amino acids from attached and detached seed coats of Pisum sativum L. cv. Marzia into a bathing solution was measured by means of the ‘empty seed coat technique’. PCMBS reduced the release of sugars and amino acids from attached as well as from detached seed coats, suggesting that carrier‐mediated transport might be involved. CCCP reduced sugar release from attached seed coats while amino acid release was hardly affected. In experiments with detached seed coats CCCP had no effect on release of either sugar or amino acids, suggesting that it is not energy‐dependent. Raising the pH of the bathing solution from pH 5.5 to pH 7.5 slightly increased sugar release from both attached and detached seed coats while amino acid release was not affected. This might indicate a role of the apoplastic pH in regulating sugar release from the seed coat via a retrieval mechanism. The presented data indicate that there are important differences between sugars and amino acids with respect to transport processes in the seed coat. This is supported by the observation that the rate of amino acid release from the seed coat was higher than the rate of sugar release. The release data of detached seed coats were subjected to compartmental analysis in order to calculate rate constants for release from cell compartments. In the case of sugars, the half‐times for emptying the cytoplasmic and vacuolar compartment were 0.8 h and 12.5 h. respectively. For amino acids the half‐times were 0.5 h for emptying the cytoplasmic and 3.8 h for emptying the vacuolar compartment.
Metabolic changes associated with cold‐acclimation in contrasting cultivars of barley
Authors: Murelli Carla , Rizza Fulvia , Albini Franca Marinone , Dulio Andrea , Terzi Valeria , Cattivelli Luigi
Published: May 2006

Cereal plants become more resistant to freezing when first exposed to a period of cold‐acclimation. Many physiological and molecular changes have been shown to occur at low temperatures, but the role and the contribution of each to frost resistance is still poorly understood. Two cultivars of barley (Hordeum vulgare L.), the winter barley Onice and the spring barley Gitane, were acclimated under controlled conditions under an 8‐h photoperiod at 4°C (light) and 2°C (dark) for 21 days. Changes in free proline, ABA, water‐soluble carbohydrates and free fatty acids were measured to assess their involvement in cold‐acclimation and to explain the different frost‐resistant capacities of the two cultivars. Exposure of barley plants to low temperature resulted in an equal increase in proline in both cultivars. During the first days of cold acclimation, ABA levels showed a peak in the frost‐resistant cultivar, lasting about 24 h, followed by a decrease. The water soluble carbohydrates reached their highest content after 3 days of hardening, although after 14 to 21 days of acclimation the carbohydrate content was similar to that of unhardened plants. The frost‐resistant Onice had a much higher free fatty acid content than the frost‐sensitive Gitane. Furthermore in Onice 86% of free farty acids was represented by unsaturated molecular species. Inolenic acid alone being 71%. In contrast, in the frost‐sensitive cultivar only 31% of free fatty acids was unsaturated and a large amount of 9‐oxo‐nonanoic acid, a product present in the linolenic acid cascade, was also detected.

The ABA content after 2 days of hardening and the free fatty acid composition were clearly different between the two cultivars and may explain, at least in part, the different frost‐resistant capacities of Onice and Gitane.
Changes in abscisic acid and indole‐3‐acetic acid in axillary buds of Elytrigia repens released from apical dominance
Authors: Pearce David W. , Taylor John S. , Robertson J. Mason , Harker K. Neil , Daly Edward J.
Published: May 2006

Growth of axillary buds on the rhizomes of Elytrigia repens (L) Nevski is strongly dominated by the rhizome apex, by mechanisms which may involve endogenous hormones. We determined the distribution of indole‐3‐acetic acid (IAA) and abscisic acid (ABA) in rhizomes and measured (by gas‐chromatography‐mass spectrometry) their content in axillary buds after rhizomes were decapitated. The same measurements were also made in buds induced to sprout by removing their subtending scale leaves. The ABA content tended to be higher in the apical bud and in the axillary buds than in the adjacent internodes, and tended to decline basipetally in the internodes and scale leaves. IAA was similary distributed, except that there was less difference between the buds and other rhizome parts. After rhizomes were decapitated, the ABA content of the first axillary bud declined to 20% of that of control values within 24 h, while the IAA content showed no marked tendency to change. The ABA content also declined within 12 h in the first axillary bud after rhizomes were denuded, while the content of IAA tended to increase after 6 h. These changes occurred before the length of the first axillary bud increased 24–48 h after rhizomes were decapitated or denuded. We conclude that the release of axillary buds from apical dominance in E. repens does not require IAA content to be reduced, but is associated with reduced ABA content.
Peach rootstock differences in ring nematode tolerance related to effects on tree dry weight, carbohydrate and prunasin contents
Authors: Olien W. C. , Graham C. J. , Hardin M. E. , Bridges W. C.
Published: May 2006

Ring nematode (Criconemella xenoplax: Cx) predisposes peach trees to the disease peach tree short life. Peach genotypes vary widely in survival rates when they are infested with Cx, but all are suitable hosts to Cx. Differences among peach genotypes in carbohydrate depletion and release of cyanide from prunasin degradation have been correlated with sensitivity to Cx. but cause and effect relations are not known. We compared dry weight, nonstructural carbohydrates (CHO) and prunasin in a highly sensitive (Nemaguard) and a highly tolerant (BY520‐9) peach rootstock inoculated with 0 or 10 Cx (ml soil)−1 in a pot study. Plant responses to the four treatment combinations were evaluated after 11 months of incubation with and without Cx. Cx parasitism reduced dry weight and concentrations of starch and soluble carbohydrates of all organs in Nemaguard, but not in those of BY520–9. Prunasin content was not affected by Cx in either rootstock. Increased partitioning of dry weight and carbohydrate fractions from shoots to roots and shifts in proportional composition of individual sugars occurred in Nemaguard but not in BY520–9. These results are consistent with the hypothesis that Nemaguard is more sensitive to Cx than is BY520–9 because it allows more of its CHO reserves to be partitioned from shoot to root in response to Cx parasitism. When parasitism is severe, reduced levels of CHO in the aboveground portion of the tree could result in tree injury or death at levels of environmental and biological stresses that do not injure healthy trees.
Relationship of antioxidant enzymes to ozone tolerance in branches of mature ponderosa pine (Pinus ponderosa) trees exposed to long‐term, low concentration, ozone fumigation and acid precipitation
Authors: Benes Sharon E. , Murphy Terence M. , Anderson Paul D. , Houpis James L. J.
Published: May 2006

Seasonal activity of superoxide dismutase (SOD, EC 1.15.1.1). ascorbate peroxidase (APOD, EC 1.11.1.11) and guaiacol‐oxidizing enzymes (GPODs, EC 1.11.1.7) was examined in needles of 12‐ to 15‐year‐old ponderosa pine (Pinus ponderosa Laws.) trees which received ozone (O3) and acid precipitation treatment. Individual branches were enclosed in branch exposure chambers delivering either charcoal‐filtered (O3‐reduced) air, ambient air, or air with twice ambient (2 x ambient) concentrations of O3. Acid precipitation treatments were rain of pH 3.0 or 5.1 or no rain. Changes in antioxidant enzyme activity were not a consistent response to O3 fumigation or acid precipitation, but when observed, they occurred most often in the O3‐sensitive clone and in symptomatic, fumigated branches. In the second year of fumigation. O3 fleck symptoms appeared on needles of the sensitive clone as early as July and APOD activities were significantly increased by O3 at all sampling dates. In the tolerant clone, antioxidant enzyme activities were not significantly changed by O3 in the first season of fumigation (March to December 1990), not even during an episode when ambient O3 concentrations reached 125 nl 1−1 (240 nl 1−1 in 2x ambient chambers). No foliar symptoms were observed on needles of the tolerant clone during this year. However, in the second year of fumigation (1992), O3 fleck symptoms were observed on the tolerant clone and APOD activities were significantly increased in previous‐year needles. The tolerant clone had SOD, APOD, and GPOD activities at least 40% higher than those of the sensitive clone before fumigation and 65, 178, and 119% higher, respectively, during both years of fumigation. The higher constitutive levels of these enzymes may have protected against foliar injury in 1990, however in 1992 we concluded that the stimulations in antioxidant enzyme activities observed in symptomatic branches of both clones were a consequence of O3 injury. Total (intra‐ and extracellular) activities of the antioxidant enzymes did not appear to be good indicators of O3 tolerance. Phenotypically, the O3‐tolerant clone was much more vigorous and in both years of fumigation, gas exchange rates were 30 to 71% higher than in the sensitive clone (P. D. Anderson, unpublished data). The greater vigor of the tolerant clone may allow more carbon allocation to protective and repair processes which include, but are not restricted to, the turnover of antioxidant enzymes and metabolites.
Tubulin isotypes in maize endosperm. Alterations during development and water deficit
Authors: Artlip Tim S. , Setter Tim L. , Madison James T.
Published: May 2006

Maize (Zea mays L. cv. Pioneer 3925) endosperm development is sensitive to water deficit during rapid cell division and nuclear DNA endoreduplication. To gain insight into effects of water deficit on gene‐products that are involved in these processes, we examined the accumulation of β‐tubulin, a 50‐kDa subunit of microtubules. Proteins extracted from endosperms were separated by SDS‐PAGE and immunoblotted with antibodies to β‐tubulin. In addition to the expected 50‐kDa β‐tubulin protein, monoclonal antibodies recognized a 35‐kDa protein that predominated at early stages of development and progressively disappeared coincident with the appearance of 50‐kDa β‐tubulin. Various tests demonstrated that the cross‐reacting 35‐kDa protein was not a post‐harvest artifact, but represented a group of in situ tubulin isotypes preferentially detected by the monoclonal antibodies we used. The pattern of appearance of the fragment suggested that differential expression or degradation of tubulin isotypes normally occurs during development. This expression pattern is prologed or altered during water deficit, which may affect cell division.
Copper and photosystem II: A controversial relationship
Authors: Barón Matilde , Arellano Juan B. , Gorgé Julio López
Published: May 2006

Copper is an essential micronutrient for higher plants and algae and has a direct impact on photosynthesis. It is a constituent of the primary electron donor in photosystem I, the Cu‐protein plastocyanin. Many authors have also described Cu as a constituent of photosystem II (PSII). However, high Cu concentrations inhibit the photosynthetic electron transport, especially in PSII. In addition, both Cu deficiency and Cu toxicity interfere with pigment and lipid biosynthesis and, consequently, with chloroplast ultrastructure thus negatively influencing the photosynthetic efficiency.

In this review, the different functions proposed for the metal in PSII are reviewed. With reference to the effect of toxic Cu on PSII, the polemic results concerning its mechanism of action and Cu‐binding sites are discussed. Other effects of Cu toxicity and Cu deprivation on the thylakoid membrane are also briefly described.
Chlorophyll fluorescence quenching and violaxanthin deepoxidation of FBPase antisense plants at low light intensities and low temperatures
Authors: Fisahn Joachim , Kossmann Jens , Matzke Gernot , Fuss Heidemarie , Bilger Wolfgang , Willmitzer Lothar
Published: May 2006

Genetically modified potato (Solanum tuberosum L. cv. Desiree) and tobacco (Nicotiana tabacum cv. Samsun N.N.) plants were used to analyze the effects exerted by the chloroplastic (cp) fructose‐ 1,6‐bisphosphatase (FBPase) on the regulation of light energy discrimination at the level of photosystem II. The cp‐FBPase activity was progressively inhibited by an mRNA antisense to this FBPase. The chlorophyll fluorescence quenching parameters of these transgenic plants were compared to those of wild‐type and transgenic plants that were acclimated to low temperatures. In particular various lines of the transgenic potato and tobacco plants were exposed to a temperature treatment of 10 and 20°C for 10 days. Light intensities were kept low to reduce photoinhibition so that we could analyze exclusively the effects of a modification in the carbon fixation cycle on the chlorophyll fluorescence quenching parameters. The photon flux densities (PFDs) employed at the level of the middle leaves of all plants were set to two different values of 10 μmol m−2 s−1 and 50 μmol m−2 s−1. Subsequent to this 10‐day acclimation the chlorophyll‐fluorescence parameters of all plants were measured. Photoinhibition as expressed by the Fy/Fm ratio was minor in plants subjected to a PFD of 10 μmol m−2 s−1. Higher photon fluence rates of 50 μmol m−2 s−1 at temperatures of 10°C gave rise to a significant reduction in the Fy/Fm ratios obtained from the transgenic plants which were characterized by a restriction in cp‐FBPase capacity to 20% of normal activity. Furthermore, a progressive inhibition of the cp‐FBPase activity induced an amplified nonphotochemical quenching of chlorophyll fluorescence with in the genetically manipulated species (except at 10°C and 50 μmol m−2 s−1). The increase in nonphotochemical quenching depended upon light and temperature. Photochemical quenching of light quanta within the antisense plants declined relative to that in the wild type. To further characterize the mechanisms producing higher levels of nonphotochemical fluorescence quenching. we analyzed several of the xanthophyll cycle pigments. The deepoxidation state of the xanthophyll cycle pigments in potato plants increased with attenuating FBPase activities under all conditions. For tobacco plants, this elevation of the deepoxidation state was only observed at a PFD of 50 μmol m−2 s−1.
Reconstitution of barley photosystem I reveals that the N‐terminus of the PSI‐D subunit is essential for tight binding of PSI‐C
Authors: Naver Helle , Scott M. Paul , Andersen Birgitte , Møller Birger Lindberg , Scheller Henrik Vibe
Published: May 2006

Removal of the peripheral subunits PSI‐C, ‐D and ‐E from the photosystem I (PSI) complex of barley requires a urea treatment much harsher than required to remove the similar subunits from cyanobacterial PSI. The resulting PSI barley core was reconstituted by addition of the E. coli expressed subunits PSI‐C and ‐D, and PSI‐E isolated from barley. Western blotting, flash photolysis and NADP+ photoreduction measurements demonstrated complete and specific removal of the three subunits from the core and efficient reconstitution of the complex after addition of PSI‐C, ‐D and ‐E. Flash photolysis reveals that PSI‐D is essential for binding of functional PSI‐C to the PSI core. An N‐terminally truncated barley PSI‐D lacking 24 amino acid residues and thus being without the N‐terminal extension characteristic for higher plant PSI‐D proteins reconstitutes the PSI core to 50% of the level obtained with intact PSI‐D as demonstrated by flash photolysis and NADP+ photoreduction measurements. Cyanobacterial PSI‐D is functionally equivalent to truncated barley PSI‐D with respect to its activity to reconstitute the PSI core. This shows that the N‐terminal extension of plant PSI‐D plays a key role in binding PSI‐C to the core. The plant‐specific N‐terminus of PSI‐D is hypothesized to execute its function through interaction with a plant‐specific PSI subunit, possibly PSI‐H. An anchoring function of the N‐terminus of PSI‐D would also explain the harsh treatment needed to obtain a plant PSI core. PSI‐E is important for efficient NADP+ reduction but does not influence electron transfer to iron‐sulphur centres A/B nor binding of PSI‐C. The enhancing effect of PSI‐E on NADP+ reduction is independent of the presence of the N‐terminus of PSI‐D.
Gravitropic responses of the Avena coleoptile in space and on clinostats. I. Gravitropic response thresholds
Authors: Brown Allan H. , Chapman David K. , Johnsson Anders , Heathcote David
Published: May 2006

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g‐force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow‐speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.1 and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostal experiments on earth using the same apparatus.

Characteristic gravitropistic response patterns of Avena were not substantially different from those observed in ground‐based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than 0.1 g.
Influence of nitrogen supply and sink strength on changes in leaf nitrogen compounds during senescence in two wheat cultivars
Authors: Martín del Molino I. M. , Martínez‐Carrasco R. , Pérez P. , Hernández L. , Morcuende R. , Sánchez de la Puente L.
Published: May 2006

Changes in various nitrogen compounds during senescence of the fourth leaf were studied in two cultivars of spring wheat (Triticum aestivum L.). One of the cultivars (Yecora) was supplied with two N levels; the other (Tauro) was grown with the high N level and pruned above the fourth leaf, whereas the control was left intact. In both cultivars grown with high N supply, net nitrogen export from the fourth leaf did not occur until 35 days after sowing (DAS). Loss of leaf soluble proteins started earlier than that of chlorophylis, and coincided initially with an increase in insoluble protein. In N deficient plants the level of total N, soluble protein, and the activity of nitrate reductase (NRA. EC 1.6.6.1) started to decrease about 5 days earlier, and along with chlorophyll, continued to decrease at a faster rate, than in high N plants. Also, with low N supply, the large subunit (LSU, 58 kDa) of ribulose‐1.5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) decreased in greater proportion than other soluble proteins, while with high N supply the decrease in Rubisco LSU was similar to that of other soluble proteins. Nitrogen deficiency caused a greater decrease in soluble proteins than in insoluble proteins, and NRA relative to soluble proteins. The faster senescing Tauro cultivar had lower levels of most parameters, especially NRA, soluble protein and, after 35 DAS. Rubisco LSU as a proportion of soluble protein. The decrease in sink strength due to shoot pruning did generally not affect the level of the various nitrogenous compounds until 35 DAS; thereafter the levels of most parameters, especially soluble protein, Rubisco LSU and, at late stages of senescence, insoluble protein, were higher in pruned than in control shoots. Thus, shoot pruning slows down senescence. The 56‐ and 78‐kDa polypeptides increased, rather than decreased, with leaf age; the level of these two polypeptides showed a negative relationship with Rubisco LSU (r = ‐0.933 and r = ‐0.758, respectively).
Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods
Authors: Moritz T.
Published: May 2006

Short photoperiod induces growth cessation in seedlings of Norway spruce (Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA9 and GA20 can not induce growth. In contrast application of GA, and GA4 induced shoot elongation. The results indicate that 3β‐hydroxylation of GA9 to GA4 and of GA20 to GA1 is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA1, GA3, GA4, GA7, GA9, GA12, GA15, GA15, GA20, GA29, GA34 and GA51 were identified by combined gas chromatography‐mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and 14C‐labelled GAs as intermal standards. In short days, the amounts of GA9, GA4 and GA1 are less than in plants grown in continuous light. There is no significant difference in the amounts of GA3, GA12, and GA20 between the different photoperiods. The lack of accumulation of GA9 and GA20 under short days is discussed.
Endogenous levels of polyamines and abscisic acid in pepper fruits during growth and ripening
Authors: Serrano Maria , Martínez‐Madrid María Concepción , Riquelme Fernando , Romojaro Félix
Published: May 2006

The levels of polyamines (PA) and abscisic acid (ABA) in the pericarp of California variety pepper fruit (Capsicum annuum L.) were analyzed during development and ripening. Putrescine level was 2.75 μmol g−1 fresh weight 7 days after fruit set and fell during the exponential stage of growth to 1.05 μmol g−1 fresh weight. During the second growth stage. PA and ABA levels remained stable and fell sharply at the beginning of maturation. The levels of spermidine and spermine decreased throughout fruit development and maturation from 0.61 to 0.05 and 0.31 to 0.02 μmol g−1 fresh weight, respectively, but no changes were associated with the onset of maturation. ABA levels remained high (0.70‐0.80 μg g−1 fresh weight) during the stages of fruit growth and fell at the beginning of maturation to 0.12 μg g−1 fresh weight, before rising again during the last stages of maturation and senescence. The decrease in putrescine and ABA levels and the subsequent increase in the latter may be responsible for controlling the processes of ripening in pepper fruit.
Regulation of phenylpropanoid metabolism by exogenous precursors in axenic cultures of Sphagnum fallax
Authors: Rasmussen Susanne , Peters Gotje , Rudolph Hansjörg
Published: May 2006

Sphagnum plantlets, cultivated in continuous‐feed bioreactors, are characterised by high levels of free endogenous phenolics and a pronounced excretion of some phenolics into the effluent culture medium. The transfer of Sphagnum fallax, precultivated in continuous‐feed bioreactors, to batch cultures resulted in an increased flux through phenylpropanoid metabolism and an accumulation of p‐coumaric acid to 0.1 μM and of trans‐sphagnum acid up to 0.5 μM in the external medium [3H]‐labelled L‐phenylalanine (7.7 GBq mol−1) was rapidly taken up, resulting in an enhanced synthesis and excretion of p‐coumaric and trans‐sphagnum acid. Specific activities were 6.9 and 5.4 GBq mol−1, respectively, for these cinnamic acids excreted into the external medium. Endogenous pools of trans‐cinnamic and p‐coumaric acid did not increase and no labelling could be detected in these compounds. Cell wall‐bound activity amounted to ca 14% of the applied activity after 48 h of incubation, 59% of which was recovered in dioxane/2 M HCl extracts of the cell wall. Exogenously applied trans‐cinnamic acid (0.1 mM) was taken up to 46% and resulted in a transient endogenous accumulation of trans‐cinnamic acid, the level of free endogenous p‐coumaric and trans‐sphagnum acid was found to have decreased. The concentrations of p‐coumaric and trans‐sphagnum acid in the culture medium rose to 17 and 2.4 μM, respectively, after 48 h of incubation in 0.1 mMtrans‐cinnamic acid. Exogenously applied p‐coumaric acid (0.1 mM) was taken up to 79% from the incubation solution but not stored endogenously, as metabolic products trans‐sphagnum acid and an unknown p‐coumaric acid‐conjugate accumulated in the external medium and endogenously. These results give evidence for the biosynthetical route from phenylalanine to sphagnum acid and a channelling of pathway intermediates by the enzymes L‐phenylalanine ammonia‐lyase (EC 4.3.1.5) and cinnamic acid 4‐hydroxylase (EC 1.14.13.11).
β‐Galactosidase, polygalacturonase and pectinesterase in differential softening and cell wall modification during papaya fruit ripening
Authors: Lazan Hamid , Selamat Mohd. Kasim , Ali Zainon Mohd.
Published: May 2006

Papaya (Carica papaya L. cv. Eksotika) fruit softens differentially in relation to position of the tissue. The inner mesocarp tissue is softer, and its firmness decreases more rapidly during ripening than that of the outer mesocarp tissue. As the fruit ripens, pectin solubility and depolymerisation increase. Hemicellulose, too, appears to be depolymerised but, unlike pectins, this apparent degradation of hemicellulose is associated with an increase rather than a decrease in its level. Pectin and hemicellulose depolymerisation began in the inner mesocarp tissue at about the same time as β‐galactosidase (EC 3.2,1.23) activity started to increase and tissue firmness began to decrease more rapidly. In contrast, pectin solubilisation in both outer and inner mesocarp tissues occurred steadily throughout ripening at a comparable rate and paralleled closely the increase of polygalacturonase (PG; EC 3.2.1.67) and pectinesterase (EC 3.1.1.11). In general, irrespective of enzyme distribution, tissue softening during ripening was more closely related to changes in β‐galactosidase activity than to PG or pectinesterase activity. Papaya, β‐galactosidase appears to be an important wall degrading enzyme and may contribute significantly to differential softening, perhaps by complementing the action of polygalacturonase. Polygalacturonase activity increased with increasing depth of the mesocarp tissue, as did softening of the fruit.