bluuebunny/crossref_metadata_2025 huggingface dataset:
De novo synthesis of peroxidase in cotton ovule culture medium
Authors: Mellon Jay E. , Triplett Barbara A.
Published: May 2006

The biosynthesis of cotton (Gossypium hirsutum L. ‘Stoneville 208′) peroxidase (EC 1.11.1.7) has been investigated in an organ culture system, since this enzyme may play a role in cell wall biogenesis or host defense mechanisms. Electrophoretic analysis of proteins from cotton ovule cultures indicated relatively few proteins being released into the surrounding medium. De novo synthesis of released peroxidase and other medium proteins was determined by in vivo labeling of ovule cultures with [35S]‐methionine. Analysis of labeled culture medium by denatured gel electrophoresis followed by fluorography showed incorporation of isotope into 2 major proteins with molecular weights of 30 kD and 56 kD, as well as a limited number of minor proteins. Similar analysis of native isoelectric focusing gels coupled with autoradiography demonstrated [35S]‐methionine incorporation into 2 major proteins with pI values of 4.3 and 5.0. The pI 5.0 protein was shown to have a molecular weight of 30 kD. The pI 4.3 protein had a molecular weight of 56 kD and was shown to be peroxidase by activity staining. Minor radiolabeled proteins were observed in the cationic region of the isoelectric focusing gels.
Proteins associated with salt adaptation in citrus and tomato cells: Involvement of 26 kDa polypeptides
Authors: Ben‐Hayyim Gozal , Vaadia Yoash , Williams Bill G.
Published: May 2006

Stress‐induced changes in proteins of molecular weights of 25 and 27 kDa are reported for NaCl‐adapted cells of Shamouti orange (Citrus sinensis L. Osbeck) and the cultivated VFNT cherry tomato (Lysopersicon esculentum Mill.), respectively. Salt‐adapted cell lines of both species grew much faster in the presence of salt than non‐adapted cells and their growth rate was similar to that of non‐adapted cells in the absence of salt. Sodium dodecyl sulfate‐extractable citrus and tomato polypeptides were analyzed by one‐ and two‐dimensional polyacrylamide gel electrophoresis (PAGE). The enhancement of a citrus 25 kDa protein associated with salt tolerance was actually resolved only on two‐dimensional PAGE. It is a constitutive protein, i.e. it was present in salt‐tolerant ceils whether grown in the presence or absence of salt. The NaCl‐induced changes of the tomato 27 kDa protein could be resolved on one‐dimensional PAGE. This protein was first markedly suppressed by a salt shock and the time required for its recovery was dependent on the degree of salt tolerance. Prolonged adaptation resulted in an increase of this protein. Protein profiles of citrus and tomato cells grown in the absence and presence of salt revealed that while in citrus the level of most proteins was suppressed in the presence of salt, the opposite was true for tomato proteins under similar conditions. Comparison between the changes in citrus and tomato and results already published for tobacco show that many salt‐induced changes in proteins are species‐specific and that no obvious similarities exist.
Directed mutagenesis to probe the structure and function of photosystem II
Authors: Carpenter Shelly D. , Vermaas Wim F. J.
Published: May 2006

In the last few years various advances have contributed to an increased understanding of Photosystem II (PS II). Most notably, the X‐ray diffraction analysis of crystallized bacterial reaction centers, along with the recognition that there is functional and structural homology between the bacterial reaction center and PS II, has led to detailed information regarding the potential function of individual proteins and residues in the PS II complex. In‐depth studies of PS II structure and function, however, require the availability of specific mutants in which certain proteins have been altered. Recombinant DNA technology has provided the methodology by which generation of such mutants has become feasible. This minireview focuses on methods for mutagenesis of PS II components and on the impact of mutant analysis on the understanding of PS II structure and function.
Biosynthesis and antioxidant function of glutathione in plants
Authors: Alscher Ruth Grene
Published: May 2006

Glutathione is widely distributed in plant cells. It appears to be synthesized in both the chloroplast and the cytosol and to occur in both subcellular compartments at relatively high levels. Its function is that of an antioxidant; in concert with ascorbate, it acts to protect labile macromolecules against attack by scavenging free radicals and hydrogen peroxide, which are formed as a consequence of oxidative stresses such as extremes of temperature, drought, herbicides or air pollutants. An integral part of the response of glutathione metabolism to oxidative stress appears to include an increase in the levels of the reduced form of the molecule. The possible role of glutathione as an elicitor of transcriptional events associated with stress responses is briefly discussed.
Interaction between nitrogen and photon flux density in birch seedlings at steady‐state nutrition
Authors: Ingestad T. , McDonald A. J. S.
Published: May 2006

Birch (Betula pendulaRoth.) was investigated under steady‐state nutrition and growth at different incident photon flux densities (PFD) and different relative addition rates of nitrogen. PFD had a strong influence on the relative growth rate at optimum nutrition and on the nitrogen productivity (growth rate per unit of nitrogen) but little effect on the formal relationships between nitrogen and growth, i.e. PFD and nitrogen nutrition are orthogonal growth factors. At a given suboptimum nitrogen (the same distance from optimum), increased PFD increased the relative growth rate and, therefore, the relative uptake rate and the required relative addition rate in accordance with the theoretical equality between these three parameters at steady‐state nutrition. Correspondingly, at a given suboptimum relative addition rate, increased PFD decreased nitrogen status (larger distance from optimum) at an unchanged relative growth rate. Nutrient uptake rate, dry matter content, and partitioning of biomass and nutrients are strongly influenced by nitrogen status. PFD influences these characteristics, but only to an extent corresponding to its effect on the nitrogen status. The influence of PDF on the relative growth rate at optimum and on nitrogen productivity is well described by hyperbolic relationships, similar to reported PFD/photosynthesis relationships. These expressions for plant growth as well as the productivities of leaf area and quantum appear to be valuable characteristics of plant responses to light and nutrition. Although the calculated PFD/growth relationships indicate saturation at high values of PFD, a more realistic estimate of PFD at which saturation occurs is about 30 mol m−2day−1, where the highest relative growth rate and nitrogen productivity were experimentally determined. No significant effect was observed because of day length differences between the present and previous experiments.
Time‐course of uptake of dissolved inorganic carbon through willow roots in light and in darkness
Authors: Vuorinen A. Helena , Vapaavuori Elina M. , Lapinjoki Seppo
Published: May 2006

Uptake of dissolved inorganic carbon (DIC) from a nutrient solution by willow roots was measured in light and darkness and the distribution in the plant of DIC taken up by the roots was determined. It was also studied whether the transport system could be activated by preincubation with dissolved inorganic carbon.

Willow plants (Salix cv. Aquatica gigantea) grown in hydroponic culture media were preincubated for 2 days with or without 0.74 mM NaHCO3. After preincubation, either unlabelled or [14C]‐labelled NaHCO3 was injected into the media and after 1, 5, 10 and 24 h either in light or in darkness the plants were harvested in pieces into liquid nitrogen, lyophilized and burned in a combustion chamber.

14C was transported through the roots to the shoots and leaves both in light and in darkness, although incorporation of 14C in darkness was only half of that in light at the end of the 24‐h feeding period. Both in light and in darkness the amount of 14C increased in all parts of willow plants with time. In light the rate of labelling was highest into cuttings and shoots. In darkness more than half of the total label was detected in cuttings of both the non‐activated and the activated treatments.

In the shoots the middle part was most strongly labelled after 5 and 10 h, but after 24 h 14C moved towards the base of the shoot. In the leaves at all feeding times most radioactivity was incorporated into the young, fully open leaves on the upper part of the shoots. Preincubation of plants with unlabelled NaHCO3 in growth media had no clear effect on the rate of DIC uptake either in light or in darkness.
Metabolism of tritiated and deuterated gibberellins A1, A4 and A9 in Sitka spruce (Picea sitchensis) shoots during the period of cone‐bud differentiation
Authors: Moritz Thomas , Philipson J. Julian , Odén Per Christer
Published: May 2006

A mixture of tritiated and deuterated gibberellins (GAs) was injected into elongating shoots of Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts grown under environmental conditions that were either inductive (heat and drought, HD) or non‐inductive (cool and wet, CW) for flowering. The metabolites were purified by high performance liquid chromatography (HPLC), detected by liquid scintillation counting of aliquots of collected fractions and identified by gas chromatography–mass spectrometry (GC‐MS). Deuterated GA9 was converted to deuterated GA4, deuterated GA34, and deuterated GA1 in both treatments. Deuterated GA4 was metabolized to deuterated GA34 and deuterated GA1 in the CW material, but only deuterated GA1 was detected in the HD material. The amount of detected metabolites was higher in the HD material, caused by a higher rate of metabolism and/or smaller losses of the metabolites during sample purification. GA1 was converted to a polar unidentified metabolite in both treatments, but to a higher degree in the CW treatment.
Glycolate metabolism in cyanobacteria. III. Nitrogen controls excretion and metabolism of glycolate in Anabaena cylindrica
Authors: Renström‐Kellner Eva , Bergman Birgitta
Published: May 2006

The effect of nitrogen on excretion and metabolism of glycolate in Anabaena cylindrica (CCAP 1403/2a) was studied. Glycidate, an inhibitor of glutamate:glyoxylate aminotransferase (EC 2.6.1.4), reduced the L‐methionine‐DL‐sulfoximine‐induced NH4+ release by ca 40%, while net CO2 fixation and C2H2 reduction were not lowered. This indicates that at least a part of the glyoxylate synthesized in A. cylindrica is metabolized via glycine to serine. Addition of NH4Cl or glutamate to the medium reduced the excretion of glycolate. At pH 9, under air, NH4Cl reduced the excretion by 10–30% and under high pO2 (0.03 kPa CO2 in O2) by about 80–90%. At pH 7.5, under high pO2, NH4Cl and glulamate reduced the excretion by about 40 and 80%, respectively. Also, the presence of NH4Cl stimulated the animation of glyoxylate under such conditions as shown by an increased glycine pool and a decreased glutamate pool. We suggest that nitrogen regulates the capacity of A. cylindrica to retain and recycle glycolate intracellularly and that glutamate serves as an amino donor in the conversion of glyoxylate to glycine.
Dry weight accumulation and starch‐synthesis enzymes in grain of cultured ears of three winter wheat varieties
Authors: Cervantes E. , Pérez P. , Martínez‐Carrasco R.
Published: May 2006

Detached ears of three winter wheat (Triticum aestivum L.) varieties were cultured in solution for 12 days with sucrose levels varying from 36.5 to 292 mM. The dry weight and starch content of grains increased asymptotically with the sucrose level in the solution. At 4 days of culture, glucose phosphate isomerase (EC 5.3.1.9) activity grain−1 was lower with 36.5 mM than with higher sucrose levels in the medium; at 8 days, adenosinc diphosphoglucose pyrophosphorylase (EC 2.7.7.27) and (soluble plus bound) starch synthase (EC 2.4.1.21) activities grain−1 were higher with 146 and 292 mM sucrose than with 36.5 and 73 mM sucrose. The multiple regression of starch content over these enzyme activities showed that starch synthase was relatively more important as an independent variable. The dry weight and starch content of grains were higher in the variety Maris Huntsman than in Splendeur and Hobbit. The water content of grains was lower in Splendeur than in the other two varieties. At 4 days the glucose phosphate isomerase, adenosine diphosphoglucose pyrophosphorylase and starch synthase activities grain−1 were smaller in Splendeur than in Hobbit and Maris Huntsman and al 8 days they were higher in Maris Huntsman than in Hobbit and Splendeur. The varietal differences in starch content of grains were related to the activities of glucose phosphate isomerase and especially of starch synthase.
Polygalacturonase activity and variation in ripening of papaya fruit with tissue depth and heat treatment
Authors: Lazan Hamid , Ali Zainon Mohd. , Liang Kam Soon , Yee Kwec Lin
Published: May 2006

Effects of tissue position (viz. outer vs inner mesocarp) and heat treatment (48°C, 20 min) on variations in polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activity and ripening of fruits of Carica papaya L. cv. Backcross Solo were investigated. Polygalacturonase activity increased during ripening concomitantly with an increase in tissue softness and soluble polyuronide level. Throughout ripening, inner mesocarp tissue was softer and contained higher polygalacturonase activity than outer mesocarp tissue. Titratable acidity as well as ß‐galactosidase (EC 3.2.1.23) activity also increased during ripening; however, unlike polygalacturonase, their level or activity was lower in inner than in outer mesocarp. Ascorbic acid could partially account for the increase in titratable acidity during ripening but contributed very little to the differences in titratable acid levels between outer and inner mesocarp. Heat treatment had no effect on either fruit softness or titratable acidity, but it markedly reduced the increase in ascorbic acid and polygalacturonase activity during ripening. Ripening, as reflected by changes in tissue softness and polygalacturonase activity, progressed outwardly from the interior towards the exterior of the fruit. The effect of heat treatment in suppressing polygalacturonase activity was relatively greater in inner than in outer mesocarp, suggesting that sensitivity of the enzyme to heat treatment may vary with stage of ripeness of the tissue.
Growth and root hydraulic conductivity of several citrus rootstocks under salt and polyethylene glycol stresses
Authors: Zekri Mongi , Parsons Lawrence R.
Published: May 2006

The water relations responses to salt of several important citrus rootstocks such as Swingle citrumelo, sour orange, and Milam lemon have not been studied in detail before. Studies were set up to compare growth and root hydraulic properties of these rootstocks to other citrus rootstocks by exposing them to NaCl and polyethylene glycol (PEG) stresses.

Seedlings of 7 citrus rootstocks were irrigated for 5 months with nutrient solutions containing NaCl or PEG that had been adjusted to osmotic potentials of ‐0.10, ‐0.20 or ‐0.35 MPa. The 7 rootstocks studied were sour orange (Citrus aurantium), Cleopatra mandarin (Citrus reticulata Blanco), Swingle citrumelo (C. paradisi x P. trifoliata), Carrizo citrange (C. sinensis x P. trifoliata), rough lemon (Citrus jambhiri Lush), Milam lemon (C. jambhiri hybrid), and trifoliate orange (Poncirus trifoliata [L.] Raf.). In both shoot and root growth, Cleopatra mandarin and sour orange were the least sensitive to salt, Milam and trifoliate orange were the most sensitive, and rough lemon, Swingle, and Carrizo were intermediate in sensitivity. Even though the roots were exposed to solutions of equal osmotic potentials, plant growth and root conductivity were reduced more by the PEG treatments than the corresponding NaCl treatments. At ‐0.10 and ‐0.20 MPa, shoot and root dry weights were reduced 16 to 55% by NaCl and 24 to 68% by PEG. Shoot root ratio was lowered at the higher concentrations, particularly by PEG.

There was a major decrease in root conductivity caused by NaCl at ‐0.10 MPa (19 to 30% in sour orange and Cleopatra mandarin and 78 to 85% in trifoliate orange and Milam). Conductivity decreased more at ‐0.20 and ‐0.35 MPa, but not proportionally as much as at ‐0.10 MPa. Root weight per unit length increased at the higher salt levels, particularly in trifoliate orange. Water flow rate through root systems followed the same trend as root conductivity; salt affected sour orange and Cleopatra mandarin the least and trifoliate orange and Milam the most. However, reductions in fibrous root length by salt treatment differed. Root lengths of Swingle and Carrizo were least affected by salt while sour orange. Milam, and rough lemon were the most affected. Hence, even though sour orange and Cleopatra mandarin were more tolerant than the other rootstocks in terms of water flow rate or root conductivity, these 2 rootstocks showed a proportionally greater decrease in root length than Carrizo, Swingle, or trifoliate orange.
Different effects of supplied ammonium on glutamine synthetase activity in mustard (Sinapis alba) and pine (Pinus sylvestris) seedlings
Authors: Vollbrecht P. , Klein E. , Kasemir H.
Published: May 2006

The activity of glutamine synthetase (GS) in mustard (Sinapis alba L.) and Scots pine (Pinus sylvestris L.) seedlings was used as an index to evaluate the capacity to cope with excessive ammonium supply. In these 2 species GS activity was differently affected by the application of nitrogen compounds (NH4+ or NO3−). Mustard seedlings older than 5 days showed a considerable increase in GS activity after NH4+ or NO3− application. This response was independent of the energy flux, but GS activity in general was positively affected by light. Endogenous NH4+ did not accumulate greatly after nitrogen supply. In contrast, seedlings of Scots pine accumulated NH4+ in cotyledons and roots and showed no stimulation of GS activity after the application of ammonium. In addition, root growth was drastically reduced. Thus, the pine seedlings seem to have insufficient capacity to assimilate exogenously supplied ammonium. NO3−, however, did not lead to any harmful effects.
Changes in leaf water status associated with salinity in mature, field grown Prunus salicina
Authors: Ziska Lewis H. , Hutmacher Robert B. , Hoffman Glen J. , DeJong Theodore M.
Published: May 2006

Seasonal and diurnal measurements of leaf water potential (ψ1), relative water content (RWC) and stomatal conductance (gs) were made in the field on 19‐year old Prunus salicina (L.) cv. Santa Rosa, a deciduous fruit tree species, irrigated with 3 different concentrations of saline water over a 3 year period (1985‐1987). With the exception of stage III of fruit growth, little or no treatment difference in Φ1, leaf turgor potential (Φp), or RWC was noted during the day. Seasonal averages of morning (0700‐0900) and afternoon (1500‐1700) Φp did not decline with increasing salinity, indicating long‐term osmotic adjustment in this species. Maintenance of leaf water status under saline conditions was in part a consequence of increased stomatal closure, with a subsequent reduction in leaf transpiration rate. However, during stage III of fruit growth, an increase in mean afternoon (1200‐1700) stomatal conductance of 26‐117%, independent of salinity treatment, was observed in 1985 and again in 1987. Higher conductance values during this period may be associated with rapid fruit expansion and greater assimilate demand. The observed increase in conductance resulted in greater leaf water loss and larger measured differences in midday ψ1 between salinity treatments. This research indicates that for Prunus salicina in the field, salinity stress resulted in leaf water deficits only during the final period of fruit expansion and ripening.
Regulation of Rubisco activity in vivo
Authors: Salvucci Michael E.
Published: May 2006

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) is not able to achieve and maintain adequate CO2 and Mg2+ activation under physiological conditions. Higher plants and green algae contain Rubisco activase, a soluble protein which not only facilitates Rubisco activation in situ but also regulates enzyme activity in response to irradiance and other factors. Regulation of Rubisco activity by modulation of activation state coordinates the rate of CO2 fixation with the rate of substrate regeneration. This regulation may be required to ensure that the levels of photosynthetic metabolites in the chloroplast are optimal for photosynthesis under a variety of environrmental conditions. Some plant species also appear to regulate Rubisco activity by synthesizing 2‐carboxyarabinitol 1‐phosphate, an inhibitor of Rubisco in the dark. This inhibitor may function primarily as a regulator of metabolite binding in the dark rather than as a modulator of Rubisco activity in the light.
The effects of low water contents on physiological activities of seeds
Authors: Vertucci Christina W.
Published: May 2006

Physiological activity changes in seeds when water content is changed from 0 to 40%. The limited metabolism of dry seeds allows for studies of the role of water in the biochemical reactions of living systems. At very low water contents, seeds exhibit limited biochemical activity, however light reactions and some oxidative processes are possible. As water content is increased, enzymatic reactions are increasingly facilitated. At moisture contents of about 24% mitochondrial electron transport is detectable. Changes in the physiological activity of seeds occur at discrete moisture levels that are reflective of discrete changes in the thermodynamic properties of water.
Glycolate metabolism in cyanobacteria
Authors: Renström Eva , Rai Amar N. , Bergman Birgitta
Published: May 2006

The mechanism for uptake of glycolate in the cyanobacterium Anabaena 7120 and its capacity to metabolize glycolate were examined. The uptake of [14C]‐glycolate in light, at pH 7, consisted of an initial rapid phase (≤60s) and a second slower phase. The latter obviously represents metabolism as the glycolate dehydrogenase inhibitor 2‐pyridylhydroxymethanesulfonic acid (HPMS) did not affect the initial uptake phase while the second phase was strongly reduced. The sulfhydryl reagent N‐ethylmaleimide (NEM) inhibited uptake of glycolate and the uptake was reduced by lactate, glycerate and glyoxylate, Treatment with triphenylmethylphosphonium (TPMP+), a lipophilic cation collapsing ΔΨ only slightly reduced the uptake of glycolate. At pH 7.0, the F0F1‐ATPase inhibitor N, N′‐dicyclohexylcarbodiimide (DCCD) and the uncoupler carbonylcyanide m‐chlorophenylhydrazone (CCCP) abolished the uptake. Inhibition of photophosphorylation by dark‐treatment and presence of 3‐(3′,4′‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU) also reduced the uptake. Decreasing the pH in the range of 10 to 5.5 increased the uptake. In contrast to the situation at pH 7. CCCP did not affect the initial glycolate uptake at pH 5.5. We conclude that the uptake of glycolate is a carrier‐mediated process which, at pH 7, is dependent on a H+‐ATPase to create the ΔpH across the membranes needed for uptake, while at pH 5.5 the uptake of glycolate is not ATP‐dependent. The capacity to metabolize glycolate was at least 50 μmol (mg chl a)−1 h−1 in young cultures. In older cultures the rate was nearly 50% lower.
Dormancy and spring development of lateral buds in mulberry (Morus alba)
Authors: Suzuki Takeo , Kitano Minoru
Published: May 2006

Patterns of spring development of lateral buds of mulberry (Morus alba L. cv. Shin‐ichinose) coppice shoots on 11‐year‐old low‐pruned stumps varied in response to girdling, pruning and arching. The erect controls showed a weak acrotonic (apex‐favoring) growth habit, in which the majority of the buds, including the basal ones, sprouted and elongated in mid‐ and late April, and hence there was a prolonged imposition of dominance on the upper laterals in mid‐ and late May. In contrast, early spring girdling or pruning enhanced the activity of the upper buds of the proximal (lower) halves of the girdled stems or of the pruned stems, resulting in considerable dominance of the laterals from such buds in late April. Arching markedly inhibited buds on the under side of the arched stems, leading to poor shoots. By late April, the buds on the adaxial (upper) side readily grew into new vertical shoots, which dominated over the lateral ones.

When studied by a multiple‐node‐cutting test, increased length of segments of post‐dormant mulberry stems was accompanied by decreased bud activity of the segments and by decreased breaking ability of the lower buds within the segments, suggesting the importance of roots in the weak acrotonic habit of the erect stem in spring. By contrast, the acropetal influences of the attached stems can in part affect dominance relationships, perhaps mediated through competition for factors translocated from the roots. Continuous basal applications of abscisic acid inhibited bud break and shoot growth of the postdormant stem segments, but these inhibitory effects could be reversed by applied gibberellic acid A3 (GA3).

Two phases of lateral bud dormancy in erect mulberry coppice shoots were identified. The first was characterized by a smaller breaking capacity in the upper buds than in the lower ones and hence by a basitonic (base‐favoring) gradient in bud growth potential. The second phase corresponded to a restoration of these capabilities in the upper buds and to a change towards a linear gradient in bud growth potential, with disappearance of the dormant condition, in February and March. This gradient change during dormancy release may represent the physiological basis for the weak acrotonic habit of erect mulberry stems in spring.
Effects of copper on active and passive Rb+ influx in roots of winter wheat
Authors: Jensén Paul , Aòalsteinsson Sveinn
Published: May 2006

The effects of copper (CuCl2) on active and passive Rb+(86Rb+) influx in roots of winter wheat grown in water culture for 1 week were studied. External copper concentrations in the range of 10–500 μM in the uptake nutrient solution reduced active Rb+ influx by 20–70%, while passive influx was unaffected (ca 10% of the Rb+ influx in the Cu‐free solution). At external Rb+ concentrations of up to 1 mM, Cu exposure (50 μM decreased Vmax to less than half and increased Km to twice the value of the control. Short Cu exposure reduced the K+ concentration in roots of low K+ status. Pretreatment for 5 min in 50 μM CuCl2 prior to uptake experiments reduced Rb+ influx by 26%. After 60 min pretreatment with Cu, the corresponding reduction was 63%. Cu in the cultivation solution impeded growth, especially of the roots. The Cu concentration in the roots increased linearly with external Cu concentration (0–100 μM) while Cu concentration in the shoots was relatively unchanged. The K+ concentration in both roots and shoots decreased significantly with increased Cu in the cultivation solutions. Possible effects of Cu on membranes and ion transport mechanisms are discussed.
Quantitative aspects of triacylglycerol metabolism and sterol synthesis from 14C‐acetate in etiolated seedlings of Euphorbia lambii
Authors: Groeneveld Henri W. , Elings Jopie C. , Jorge Blanco Magdalena Soda , Bramwell David
Published: May 2006

Triacylglycerols occur in both the endosperm and embryo of Euphorbia lambii seeds. Upon germination, the amount of these neutral lipids in the endosperm decreased with 1.06 mg fatty acid day‐1. The embryo contained 1.4 mg fatty acids in the triacylglycerols and this value declined slowly to 0.4 mg seedling‐1 during the 8 day period of endosperm depletion. Radioactive acetate was rapidly taken up by the cotyledons of intact seedlings, translocated throughout the entire seedling, and up to 10.5% of the 14C proceeded to the sterols and latex triterpenols. Maximum uptake values of 1.4 μmol seedling‐1 day‐1 of acetate were measured. Acetate uptake and subsequent incorporation into sterols and triterpenols decreased substantially in the presence of increasing amounts of sucrose (up to 0.3 M). Traces of acetate did not effect [14C]‐sucrose uptake and corresponding synthesis of [14C]‐sterols and triterpenols, but increased concentrations of acetate (0.05 M and up) reduced both uptake of sucrose and its conversion into unsaponifiable lipids.

The uptake capacity of the cotyledons for [14C]‐glycerol exceeded the daily production in the endosperm, but only a small amount of label proceeded to the sterols and triterpenols. [14C]‐Triacylglycerols were never detected in the seedling, regardless of the labeled substrate used. Although acetate is an efficient precursor in triterpenol and sterol synthesis, the uptake capacity of the cotyledons for this metabolite is too small in relation to the daily production of water soluble substrates in the endosperm. If acetate is released by the endosperm, only a marginal contribution towards triterpenol and sterol synthesis in the seedling is to be anticipated from this substrate.
NADH‐dependent Fe3+EDTA and oxygen reduction by plasma membrane vesicles from barley roots
Authors: Brüggemann Wolfgang , Moog Petra R.
Published: May 2006

Brüggemann, W. and Moog, P. R. 1989. NADH‐dependent Fe3+EDTA and oxygen reduction by plasma membrane vesicles from barley roots.

Biochemical properties of pyridine‐dinucleotide‐dependent Fe3+‐EDTA reductase were analysed in purified plasma membranes (PM) from barley (Hordeum vulgare L. cv. Marinka) roots. The enzymatic activity preferred NADH over NADPH as electron donor and it was 3‐fold increased in the presence of detergent. The reductase showed a pH optimum of 6.8 and saturable kinetics for NADH with Km (NADH) of 125 μM and Vmax of 143 nmol Fe (mg protein)‐1 min‐1 in the presence of 500 μM Fe3+EDTA. For the dependence of the reaction rate on the iron compound, Km(Fe3+EDTA) of 120 μM and Vmax of 184 nmol (mg protein)‐1 min‐1 were obtained. The activity was insensitive to superoxide dismutase (SOD; EC 1.15.1.1), catalase (EC 1.11.1.6) and antimycin A, but stimulated by an oxygen‐free reaction medium. It could be solubilized by 0.25% (w/v) Triton X‐100. The solubilized enzyme revealed one band in native polyacrylamide gel electrophoresis (PAGE) and in isoelectric focussing (IEF) at pl 7.4 by enzyme staining. Major polypeptides with molecular weights of 94, 106, 120 and 205 kDa corresponded to the enzyme‐stained band from native PAGE.

Analysis of oxygen consumption by the membranes revealed the existence of NADH:CK oxidoreductase activity, which was stimulated by salicylhydroxamic acid (SHAM), chinhydron, Fe3+EDTA and Fe3+EDTA but not by K3 [Fe(CN)6] or K4[Fe (CN)6). The stimulating effect of the iron chelates on oxygen consumption was due to Fe2+ and could be suppressed by bathophenanthroline disulfonate (BPDS), SOD and p‐chloromercurophenylsulfonic acid (PCMS). The results are discussed with respect to the nature of the stimulation.
Abscisic acid and temperature modify the levels of calmodulin in embryonic axes of Cicer arietinum
Authors: Hernández‐Nistal Josefina , Rodriguez Dolores , Nicolás Gregorio , Aldasoro Juan José
Published: May 2006

Changes in calmodulin (CaM) levels in embryonic axes of Cicer arietinum L. cv. Castellana germinated under three different conditions were measured. Abscisic acid (ABA) and a temperature of 30°C, which delay chick‐pea germination, respectively decreased and increased the concentration of CaM compared to the values obtained under normal germinating conditions (H2O‐25°C). The CaM concentration was higher in those zones of the axes undergoing an active cell division.

The compartmentalization of CaM in 36‐h‐old embryonic axes grown under these three conditions was also measured. Cytosolic and mitochondrial CaM was higher in axes where a delayed germination occurred as well as in the cell walls of normally grown ones. On the other hand, CaM was higher in nuclear and microsomal fractions extracted from H2‐O‐25°C‐treated axes. From these data we postulate that delayed germination could be an effect of altered CaM distribution in chick‐pea embryonic axes.
Growth and respiration in two mangrove species at a range of salinities
Authors: Burchett M. D. , Clarke C. J. , Field C. D. , Pulkownik A.
Published: May 2006

Growth and dark respiration rates were measured in leaves and roots of seedlings of Avicennia marina (Forsk.) Vierh, (grey mangrove), and Aegiceras corniculatum (L.) Blanco (river mangrove). Plants were grown in a soil mixture at ambient temperatures and watered with 0.25 and 100% sea‐water. Oxygen uptake was measured in excised root and leaf samples. In both species growth was maximal in 25% sea‐water, and root respiration was lowest in 100% sea‐water. Differences were found between the two species in the responses of leaf respiration to salinity. In A. corniculatum leaf respiration was raised in both 25 and 100% sea‐water, while in A. marina only leaves in 100% sea‐water showed higher rates of respiration. These results are consistent with the view that A. marina is the more salt‐tolerant of the two species. In A. corniculatum the respiration rates of the hypocotyl were also measured, and were much higher in 100% sea‐water than in the other two treatments. The results suggest that at high salinities there is a high metabolic cost in the shoots of both species, and that at such salinities rates of root respiration may be limited by the supply of substrate from the shoots.
Structure, biosynthesis, and function of asparagine‐linked glycans on plant glycoproteins
Authors: Faye Loïc , Johnson Kenneth D. , Sturm Arnd , Chrispeels Maarten J.
Published: May 2006

In plants, glycoproteins with asparagine‐linked glycans (oligosaccharides) are found in vacuoles, in the extracellular space or matrix, and associated with the endo‐membrane system (endoplasmic reticulum, Golgi apparatus, plasma membrane, tonoplast). These glycans are of the high‐mannose type, with a structure identical to that found in other organisms (mammals, yeast), or of the complex type with a β1–2 linked xylosyl residue not found in mammalian complex glycans. Asparagine‐linked glycans play multiple roles by modifying the physicochemical properties of the polypeptides to which they are attached.
Wheat aging: the contribution of embryonic and non‐embryonic lesions to loss of seed viability
Authors: Petruzzelli Luciana , Taranto Giovanni
Published: May 2006

A study has been made to identify the contribution of senescent changes occurring in embryonic and non‐embryonic (endosperm and aleurone layer) tissues on germination of wheat (Triticum durum L. cv. Appulo) seed lots of 97, 93 and 70% viability. Measurements of germination and rates of macromolecular synthesis of embryos excised from dry seeds showed that as seed viability declined from 97 to ca 93%, there was a decrease in the capacity of embryos to grow and synthesise protein, RNA and DNA. However, no significant differences were observed between embryos from 93 and 70% viability seed stocks. Changes in nutrients, fresh and dry weights of embryonic and non‐embryonic tissues and electrophoretic patterns of endosperm proteins by sodium dodecyl‐sulfate polyacrylamide gel electrophoresis showed a reduced mobilisation of reserve material in 70%‐viable seeds. α‐Amylase (EC 3.2.1.1) production was also decreased. It is suggested that alterations occurring in non‐embryonic structures play a significant role in seed viability loss. This role might be mediated by failing nutrient supply, but the involvement of some inhibitor or toxic substance is also possible.
Relationships among cytokinins, ethylene and poly amines during the stratification‐germination process in seeds of Acer saccharum
Authors: Walker Mark A. , Roberts Dane R. , Waite Janet L. , Dumbroff Erwin B.
Published: May 2006

Relatively high levels of dihydrozeatin and trans‐zeatin were detected in unstratified seeds of Acer saccharum Marsh. Both cytokinins increased substantially over the first 20 days of stratification at 5°C and then fell rapidly to values well below original levels by first germination on day 55. In seeds held at 20°C, a non‐afterripening temperature, cytokinin levels remained constant for the first 10 days and then declined to their lowest levels by day 20. Levels of putrescine, spermidine and spermine in the radicles and cotyledons did not change during the full course of the afterripening process, but large increments were noted during radicle emergence. A large increase in ethylene production at germination suggests that competition for S‐adenosyl‐methionine by the ethylene and polyamine biosynthetic pathways did not inhibit synthesis of ethylene or polyamines during seedling emergence and establishment. In seeds stratified at 20°C, ethylene showed an exceptionally large peak early in the stratification period, but polyamine contents remained low throughout the test. The present results are consistent with the hypothesis that cytokinins play a significant role in overcoming the metabolic block present in dormant seeds. This conclusion is supported by data showing that high levels of cytokinins develop concurrently with the start of tissue differentiation and at the time when abscisic acid and phenolic inhibitors decline in stratifying seeds. Changes in ethylene and polyamine contents did not correlate with any events in the afterripening process; however, large increases in levels of these substances were closely associated with the germinative process and, in the case of polyamines, specifically with the start of cell division.
Diagnostic parameters for selecting against novel spruce (Picea abies) decline: I. Tree morphology and photosynthesis response to acute SO2 exposures
Authors: Saxe Henrik , Murali N. S.
Published: May 2006

The dose‐ and time‐response effects of single 4‐h day‐exposures to 0.50, 0.79, 1.28, 1.58, 2.38 or 3.35 μl l−1 (ppm) SO2 followed by single 3‐h night‐exposures of 0.60, 0.87, 1.54, 1.91, 2.91 or 3.98 μl l−1 SO2 on photosynthesis, transpiration and dark respiration were examined for nine East European (Carpatho‐Ukrainian, ‘Rachovo’) half‐sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season.

Even the lowest SO2 concentration reduced photosynthesis and transpiration within 1 h. Photosynthesis of the different spruce types was affected significantly differently, the most sensitive spruce being suppressed 2.5 times more than the most tolerant spruce. ‘Westerhof’ was more resistant to SO2 than the average ‘Rachovo’ half‐sibs. Neither transpiration (stomatal reaction), which was affected alike by all SO2 concentrations, nor SO2 uptake, explained adequately the effects on photosynthesis. Night transpiration, but not dark respiratin, was stimulated by night SO2 preceded by day SO2 exposure.

The gradient of different SO2 sensitivities among young trees from the half‐sib families demonstrated a significant negative correlation with the gradient of different sensitivities to novel decline symptoms of their parents growing in a rural seed orchard in Denmark, and with the gradients of four morphology parameters, (height, branching, branch density and the number of Lammas shoots) of the young trees, which in turn demonstrated a positive correlation with decline sensitivity in the seed orchard. The relative photosynthesis sensitivity and the morphology of half‐sibs may serve as diagnostic parameters for laboratory selection of the most resistent trees to novel spruce decline in the field. There was a positive correlation between SO2 induced scorching of Lammas shoots and the inhibition of photosynthesis, but not between the severity of SO2 scorching and symptoms of novel spruce decline. The two visible types of symptoms looked very different.
Diagnostic parameters for selecting against novel spruce (Picea abies) decline: II. Response of photosynthesis and transpiration to acute NOx exposures
Authors: Saxe Henrik , Murali N. S.
Published: May 2006

The dose‐ and time‐response effects of sequential 3 h+3 h NO→NO2 day time exposures [0–9 μl l−1 (ppm) NO, 0–7.5 μl l−1 NO2] followed by 3 h+3 h NO→NO2 night‐time exposures (0–9.5 μl l−1 NO, 0–9 μl l−1 NO2) on photosynthesis, transpiration and dark respiration were examined for nine Carpatho‐Ukrainian (‘Rachovo’) half‐sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. In a second exposure series the exposure sequence was reversed. None of the treatments induced needle scorching.

The higher NOx (NO or NO2) concentrations reduced photosynthesis and transpiration within 1 h. The physiology of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 6.6 times and its transpiration 5.5 times more than the most tolerant. ‘Westerhof’ was more sensitive to NO2 than the average ‘Rachovo’ half‐sibs.

The gradients of different photosynthesis and transpiration sensitivities among the half‐sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, but significant negative correlations with the gradient of novel decline symptoms among their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivies may thus serve as diagnostic parameters for laboratory selection of the most resistant trees to novel spruce decline.

The average NO2 flux density was three times larger than the average NO flux density. Only for NO2 and in light was stomatal NOx uptake larger than the total NOx uptake. Both night transpiration and dark respiration were stimulated by high concentrations of night NOx, preceded by day NOx exposures.
Diagnostic parameters for selecting against novel spruce (Picea abies) decline: IV. Response of photosynthesis and transpiration to SO2+NO2 exposures
Authors: Saxe Henrik
Published: May 2006

The dose‐ and time‐response effects of 3 days of 6 h day‐time sequential exposures to NO2, SO2 and SO2+NO2 of 0.45–1.81 μl l−1 (ppm) SO2 and 1.50–7.65 μl l−1 NO2 on photosynthesis, transpiration and dark respiration were examined for nine Carpatho‐Ukrainian half‐sib families and a population from the GFR (‘Westerhof’) of Norway spruce [Piecea abies (L.) Karst.], all in their 5th growing season.

SO2+NO2 inhibited photosynthesis and transpiration and stimulated dark respiration more than SO2 alone. SO2 and SO2+NO2 at the lowest concentrations inhibited night transpiration, but increased it at the highest concentration, the strongest effects being obtained with combined exposures. Photosynthesis of the different half‐sib families was affected significantly differently by SO2+NO2 exposures. NO2 alone had no effects.

Sensitivity to transpiration decline correlated negatively with branch density. Height of trees correlated postitively with decline sensitivity in the seed orchard. The distribution of photosynthesis and transpiration sensitivities over all tested half‐sib families correlated negatively with the distribution of decline sensitivity of their parents in a rural Danish seed orchard. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters for selecting against novel spruce decline.
Response of genetic dwarf apple plants to GA3
Authors: Steffens G. L. , Jacobs F. W. , Engelhaupt M. E.
Published: May 2006

High temperature has been implicated as the major factor responsible for dwarfing of selected apple (Malus domestica Borkh.) trees of a hybrid population of cv. Goldspur Delicious x cv. Redspur Delicious. Dwarf plants grew only 2.2 cm in 63 days under a ramped temperature regime (night 15°C, day ramped up to 38°C, held for 2 h and ramped down to 15°C—14 h daylength), whereas semi‐dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi‐dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi‐dwarf plants grew nearly 50 cm. The gibberellin biosynthesis inhibitor, paclobutrazol, retarded growth of semi‐dwarf plants in both ramped and constant environments and dwarf plants in the constant 27°C environment. It did not further reduce the size of dwarf plants growing under the ramped regime. Gibberellin (GA3) treatment reversed the inhibition of growth caused by paclobutrazol for all plants except it did not restore growth of dwarf plants in the ramped environment. These data suggest that neither pacobutrazoltreated nor untreated dwarf plants growing in the ramped environment (or in the orchard during hot summer months) are able to respond to GA3. In constrast, GA3 was utilized by the paclobutrazol‐inhibited dwarf plants growing at constant 27°C, enabling shoot elongation to take place. It appears that high temperature may have caused alterations in GA target tissues in dwarf plants so that they no longer had the capacity to respond to GA.
Immunogold localization of LHC II proteins in chloroplasts with different degrees of grana stacking induced by SAN‐9789.
Authors: Dahlin Clas
Published: May 2006

The amount and distribution of proteins of the light‐harvesting complex associated with photosystem II (PS II) were investigated using immunogold labelling of chloroplasts of wheat (Triticum aestivumL. cv. Walde). The seedlings were grown in weak red light (16 mW m−2) after imbibition of grains with SAN‐9789 (Norflurazon, 0.028 to 28 mg I−1). Chloroplasts of these plants exhibited thylakoids with different degrees of stacking. Thylakoids of untreated plants grown in a greenhouse had most gold particles per unit membrane length in both appressed and non‐appressed regions compared to red light grown plants. The ratios of labelling between appressed and non‐appressed membranes were fairly constant in red light‐ and greenhouse‐grown plants. The labelling densities were 2.5–3 times higher in the appressed thylakoids compared to the non‐appressed thylakoids. However, at a SAN concentration of 2.8 mg I−1there was a sharp decrease in thylakoid appressions and in labelling density of both appressed and non‐appressed membranes. The total amount of particles per chloroplast was also much lower as compared to that at lower SAN concentrations. Plants treated with the highest concentration of SAN (28 mg I−1) contained chloroplasts devoid of normal grana structures. In these plastids, the thylakoids were elongated and single. The labelling density in these membranes was ca 50% of that observed at 2.8 mg I−1. This paper thus supports earlier observations that proteins of the light‐harvesting complex of PS II (LHC II) are mainly localized in the appressed regions of the grana membranes, and may be involved in the formation of grana.
Growth and solute leakage in Hordeum vulgaris exposed to long‐term fumigation with low concentrations of SO2
Authors: Navari‐Izzo Flavia , Izzo Riccardo , Quartacci Mike F. , Lorenzini Giacomo
Published: May 2006

Plants of three commercial cultivars of Hordeum vulgaris L. (Barberousse, Gerbel, Panda) were continuously exposed to two concentrations of SO2 (40±5 and 117±20 ppb) against a control (charcoal‐filtered air). Experiments were performed in fumigation chambers. Fumigation was started 9 days after seeding and plant material was harvested after 48 days. In none of the three cultivars did visible symptoms of injury appear on the leaves after exposure to SO2, while they all showed a reduction in plant height and dry matter of shoots and roots and a significant increase in the shoot/root dry weight ratios depending on the cultivars. The time course of conductivity, and K+ Ca2+ and sugar effluxes were determined for 24 h. Leaves from cvs Gerbel and Panda exposed to SO2 exhibited a progressive increase in conductivity, and in Ca2+ and sugar efflux (expressed as percentages of their total effluxes). Plusmn; efflux of the three cultivars and conductivity in cv. Barberousse increased only after 24 h incubation. A relative leakage ratio (RLR) was calculated from the UV absorption at 280 nm after 24 h incubation of the leaf strips and the total 280 nm UV absorption, obtained after liquid N2 killing of the tissues. The RLR was well correlated with the total amino acids and sugars found in the leachate and can be used as a test for determining the tissue response to SO2.