bluuebunny/crossref_metadata_2025 huggingface dataset:
Binding properties of NADPH‐protochlorophyllide oxidoreductase as revealed by detergent and ion treatments of isolated and immobilized prolamellar bodies
Authors: Grevby Cecilia , Engdahl Sheila , Ryberg Margareta , Sundqvist Christer
Published: May 2006

Prolamellar bodies were isolated from dark‐grown leaves of 6.5‐day‐old wheat (Triticum aestivumL. cv. Walde). The prolamellar bodies were immobilized in agarose beads to get a material suitable for studies on pigment and protein release, and to protect the membranes from mechanical breakage. The beads were treated with detergents and salt solutions of different ionic strengths and the eluates collected. Protochlorophyllide in the eluate was determined by fluorescence spectroscopy. Dot‐blot tests were used to estimate the amount of released NADPH‐protochlorophyllide oxidoreductase (E.C. 1.6.99.1.). Changes in ultrastructure of the treated prolamellar bodies were analysed. Release of both membrane constituents increased by treatment with detergents. With 0.2% (w/v) Triton X‐100, 60% of the fluorescence from the immobilized prolamellar bodies was eluted within 30 min. Salt solutions with increasing ionic strength increased the release from 3 to 7%. The detergent treatment resulted in a complete (Triton X‐100) or partial ([3‐(3‐cholamidopropyl)‐dimethylammonio]‐1‐propanesulfonate, CHAPS; 1‐octyl β‐d‐glucopyranoside, octylglucoside) loss of the highly regular structure of the prolamellar bodies. Immunogold labelling of ultrathin sections revealed the absence of NADPH‐protochlorophyllide oxidoreductase when the regular structure was dissolved into single membranes. The regular appearance of the prolamellar bodies was altered by treatment with 0.1MCaCl3and 0.1MKSCN, respectively, but not with 0.1MKCl. Immunogold labelling showed that that enzyme was still present in the prolamellar bodies after these treatments. Despite the ultrastructural changes, the spectral properties were unchanged. Thus we conclude that NADPH‐protochlorophyllide oxidoreductase is firmly attached to the prolamellar body membranes and that the regular ultrastructure of the prolamellar body is partly controlled by the ionic environment.
Endogenous abscisic acid and wheat germ agglutinin content in wheat grains during development
Authors: Morris Peter‐Christian
Published: May 2006

Abscisic acid (ABA) and wheat germ agglutinin content of immature wheat grains and embryos was determined by immunoassay throughout the development of a field‐grown wheat crop (Triticum aestivum cv. Timmo). Wheat germ agglutinin accumulation in the embryo was not preceded by an increase in endogenous abscisic acid amount or concentration in either embryos or grains. At a later stage in development the endogenous concentration of abscisic acid in both embryos and grains was found to be two orders of magnitude lower than the endogenous levels required to inhibit precocious germination and promote wheat germ agglutinin accumulation in excised embryos cultured in vitro. These findings are discussed in the context of the control of embryo development in vivo by both ABA and the water status of the grain and embryo.
Effects of exogenously applied growth regulators on shoot growth of inbred lines of Plantago major differing in relative growth rate: differential response to gibberellic acid and (2‐chloroethyl)‐trimethyl‐ammonium chloride
Authors: Dijkstra Paul , Kuiper Pieter J. C.
Published: May 2006

The possibility of modulating shoot growth charaeteristics of seedlings of two inbred lines of Plantago major L., differing in relative growth rate (RGR), by exogenously applied 6‐benzylaminopurine (BA), α‐naphthalene acetic acid (NAA), (gibberellic acid (GA3) and (2‐chloroethyl)‐trimethyl‐ammonium chloride (CCC) was investigated. BA completely inhibited growth of the shoot at a concentration of 1 mM, while lower concentrations had no effect. NAA reduced growth of the shoot at 10 üM, while 1 mM completely inhibited growth. Addition of 10 μM GA3 or higher stimulated shoot fresh weight up to 20% and leaf area up to 30% for the slow growing inbred line (W9), but less for the fast growing line (A4). Application of 1 mM CCC, an inhibitor of gibberellin metabolism, reduced growth of both inbred lines, but to a larger extent in the fast growing seedlings.

The lower shoot growth of W9 was associated with a lower specific leaf area (SLA) and a higher dry matter percentage of the shoot, as compared with A4. NAA reduced growth by reducing SLA and increasing leaf thickness, but the percentage dry matter of the leaves was unaffected. Stimulation of the shoot growth by GA3 application was associated with higher SLA and lower dry matter percentage. Application of CCC had opposite effects on SLA and dry matter percentage as compared with GA3. GA seems to be involved in the regulation of at least part of the genetic difference in RGR in Plantago major.
Kinetics of efflux of K+ from cultured rose cells treated with ultraviolet light
Authors: Huerta Alfredo J. , Murphy Terence M.
Published: May 2006

Irradiation of cultured rose (Rosa damascena Mill. cv. Gloire de Guilan) cells with ultraviolet light caused of loss of K+, which occurred with sigmoid kinetics. The kinetics of loss of K+ were not changed when the extracellular concentration of K+ was held constant during the period of efflux. Furthermore, the rate of loss of K+ was approximately the same even though the K+ concentration in the medium was increased from 0.1 to 10 mM. The kinetics of uptake of the lipophilic methyltriphenylphosphonium cation, an indicator of the plasma membrane potential, were linear throughout the period of K+ efflux, suggesting that the starting and stopping of K+ efflux do not reflect a passive response to changes in the membrane potential of the cells. The results are interpreted in terms of activation and inactivation of an efflux channel or pump for K+.
Mechanisms of chloride partitioning in the leaves of salt‐stressed Sorghum bicolor L.
Authors: Boursier P. , Läuchli A.
Published: May 2006

Chloride transport in sheath and blade tissue and the cellular distribution of Cl‐ were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl‐ in sheaths of salt‐stressed sorghum (Sorghum bicolor L.). Import and export of 36Cl‐ in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X‐ray microanalysis of frozen‐hydrated bulk tissue samples was used to determine the accumulation of Cl‐ and other elements in the vacuoles of sheath and blade cells.

Sheath tissue accumulated Cl‐ despite a relatively high Cl‐ turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl‐, blade tissue regulated Cl‐ levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl‐ to approximately the same concentration as sheath epidermal cells. The Cl‐ concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low.

Thus, the partitioning of Cl‐ previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl‐ at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl‐.
Responses to internal nitrogen and phosphorus concentrations of two Taraxacum microspecies of contrasting mineral ecology: critical N and P concentrations of whole plants
Authors: Hommels C. H. , Tanczos O. G. , Kuiper P. J. C.
Published: May 2006

Of the two Taraxacum microspecies used. Taraxacum sellandii Dahlst. usually occurs in grasslands with a high nutrient level; Taraxacum nordstedtii Dahlst. is generally restricted to undisturbed and mineral‐poor habitats. Growth response curves for internal N and P were established, based on relative yield of (whole) plant tissue water and (whole plant) internal mineral concentration on a tissue water basis. Critical nutrient concentrations of N and P were determined from the response curves derived. For both macroelements, T. nordstedtii showed lower critical nutrient concentrations. The difference in critical N concentrations coincided with differences in internal NO3‐3 concentrations between the microspecies. Finally, we discuss the use of tissue water as a (whole) plant growth parameter and internal mineral concentration on tissue water basis as a parameter describing the mineral status.
Responses to internal potassium ion concentrations of two Taraxacum microspecies of contrasting mineral ecology: The role of inorganic ions in growth
Authors: Hommels C. H. , Kuiper P. J. C. , Haan A. de
Published: May 2006

The two microspecies were Taraxacum sellandii Dahlst., which usually occurs in heavily fertilized grasslands, and Taraxacum nordstedtii Dahlst., which on the whole is restricted to undisturbed and mineral‐poor habitats. Growth response curves were established, depicting the relative yield of (whole) plant tissue water and the internal K+ concentration (on a whole plant basis). The critical K+ concentration, i.e. the lowest [K+]i associated with maximal growth, was derived from the response curve. T. nordstedtii, the microspecies with the low maximal growth, showed a distinctly lower critical K+ concentration than T. sellandii. A relationship between growth potential and critical K+ concentration is proposed. Responses to a declining [K+]i differed between the two microspecies. The roots of T. nordstedtii stopped functioning as a sink for inulin, and mobilized additional carbohydrates for maintaining osmotic potential and growth. The productive strategy of the fast‐growing T. sellantlii is lacking such a mechanism to buffer effects of a declining [K+]i.

Various changes were noted as regards the internal concentrations of other inorganic ions, measured as a function of [K+]i, With declining [K+]i, internal NO‐3 decreased considerably in shoot and roots, especially in T. nordstedtii, while Mg2+ accumulated, especially in the roots of T. sellandii. The interactions between growth potential and the accumulation of inorganic ions are discussed.
Luxury consumption and specific utilization rates of three macroelements in two Taraxacum microspecies of contrasting mineral ecology
Authors: Hommels C. H. , Kuiper P. J. C. , Tanczos O. G.
Published: May 2006

Plants of Taraxacum sellandii Dahlst., a microspecies adapted to fertile, and Taraxacum nordstedtii Dahlst., adapted to infertile soils, were cultured hydroponically, either on a complete nutrient solution or on one deprived of nitrogen, phosphorus, or potassium ions. For all four treatments, the growth and internal mineral concentration of the plants was monitored. For plants cultured on a complete nutrient solution, the uptake rates of nitrate, phosphate, and potassium ions were determined. Luxury consumption of the three macronutrients was computed as the excess of ion absorption over the ion uptake rates minimally required to sustain maximum growth. In these calculations the critical N, P, or K+ concentrations, earlier derived, were used as parameters describing the mineral status minimally required to allow maximum growth. Efficiency in use of the three macroelements at various levels of mineral accumulation was also computed. Finally, the response to phosphate starvation as related to phosphate uptake capacity and the accumulation of P was investigated.

The physiological properies investigated provide a causal background for the superior adaptation of T. nordstedtii as compared to T. sellandii to infertile sites. Taraxacum nordstedtii had a higher relative luxury consumption of NO3–, H2PO‐4, and K+, a higher efficiency in N and P use at N– and (severe) P‐deficiency, respectively; and, after phosphate starvation, a relatively high preservation of phosphate uptake capacity and an enlargement of P storage. In combination with the low potential growth, luxury consumption will be particularly effective in T. nordstedtii in preventing or minimizing mineral deficiency. The distribution of minerals between cytoplasm and vacuoles as a factor in mineral use efficiency is discussed.
Nodule physiology of a supernodulating pea mutant
Authors: Rosendahl Lis , Vance Carroll P. , Miller Susan S. , Jacobsen Evert
Published: May 2006

Physiological and biochemical parameters of the supernodulating pea (Pisum sativumL.) mutantnod3were compared to those of its wild‐type parent cv. Rondo in a nil nitrate environment. Plants of cv. Rondo produced more biomass and accumulated more N than plants ofnod3. Accordingly, seed yield of the wild type was twice that of the supernodulating mutant. Although the nodule number ofnod3was 10‐fold that of cv. Rondo, the nodule mass ofnod3was only twice that of cv. Rondo as individual nodules were smaller innod3than in cv. Rondo. The maximum rate of acetylene reduction activity, determined in an open flow‐through gas system, was higher in the wild type than innod3when expressed on a nodule dry weight basis. However, when expressed on a whole plant basis, the nitrogenase activity (acetylene reduction) was similar in the two symbioses. The net carbon costs of nitrogenase activity was 25% lower innod3than in cv. Rondo. An equal proportion of the net CO2efflux from the root system was for growth and maintenance of the tissue in the two symbioses. However, growth and maintenance respiration was higher innod3than in cv. Rondo per gram dry weight of the nodulated root system. The nodules ofnod3had a reduced soluble protein concentration as compared to those of the wild type. The specific activities of nodule glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.14) and asparagine synthetase (EC 6.3.5.4) were lower innod3than in cv. Rondo. The root bleeding sap ofnod3contained lower amounts of glutamine and higher amounts of asparagine than that of cv. Rondo. The results suggest that the use of carbon directly related to the dinitrogen fixation and nitrogen assimilation may be less innod3than in cv. Rondo, and that there may be differences between the two symbioses in the pathway for assimilation of fixed nitrogen.
Purification of NADPH‐specific indole‐3‐acetaldehyde reductase from Cucumis sativus by two‐dimensional native polyacrylamide gel electrophoresis
Authors: Ludwig‐Müller Jutta , Hilgenberg Willy
Published: May 2006

NADPH‐specific indole‐3‐acetaldehyde (IAAId) reductase from cucumber (Cucumis sativus L. <cv. Delikatess) was purified by several purification steps to one spot on a two‐dimensional polyacrylamide gel. The purification was 2000‐fold. IAAId reductase was shown to be a cytoplasmic enzyme by differential centrifugation and subsequent marker enzyme analysis. The substrates IAAId and dihydroxyacetone (DHA) do not seem to be converted by the same enzyme.
Cauliflower Mosaic Virus as a probe for studying gene expression in plants
Authors: Pfeiffer Pierre , Hohn Thomas
Published: May 2006

Cauliflower Mosaic Virus (CaMV) represents a natural set of cloned genes, which have to replicate and be expressed in plant cells. Because CaMV DNA cloned in a plasmid is infectious, the viral genome can be assayed for dispensable regions and used as an episomal vector for the introduction and expression of foreign genes in host plants; however, its usefulness is restricted by the limited payload it can accommodate and by the existence of a reverse transcription step in the viral replication cycle. Direct gene transfer and viral infection mediated by Agrobacterium have now extended the possibilities of manipulating CaMV DNA to non‐hosts and allowed regeneration of transgenic plants, which should permit dissection of the functions of the various viral genes. Analysis of CaMV promoters has also defined enhancer sequences that maximize expression of foreign genes in transgenic plants. Finally, the translational strategy of CaMV is now being investigated by direct introduction into protoplasts of DNA constructs that contain combinations of sequences thought to regulate translation of the viral transcripts.
Photosynthetic carbon partitioning: its regulation and possibilities for manipulation
Authors: Stitt Mark , Quick W. Paul
Published: May 2006

The regulation of photosynthetic sucrose synthesis and partitioning is reviewed with particular emphasis on the role of fructose‐2,6‐bisphosphate and sucrose phosphate synthase. It is concluded that a hierachy of regulatory mechanisms exist, which allows partitioning to be changed without this necessarily leading to a reduction in the rate of photosynthesis. Nevertheless, experimental conditions can be defined in which photosynthesis is limited by the rate of end‐product synthesis. These systems can be used to screen for genetic mutants or specific inhibitors, and to investigate a shift in sink demand or environmental factors that specifically act on carbon partitioning and/or the rate of endproduct synthesis.
Winter hardening in first‐year black spruce (Picea mariana) seedlings
Authors: Colombo S. J. , Glerum C. , Webb D. P.
Published: May 2006

Winter hardening of first‐year black spruce [Picea mariana (Mill.) B.S.P.] seedlings was studied by assessing a number of morphological and physiological changes under three hardening regimes: 1) early removal (ER), in which seedlings were exposed to natural daylengths and low ambient temperatures outside. 2) extended greenhouse culture (EG), in which seedlings were exposed to natural daylengths and warm temperatures, and 3) short day (SD), in which seedlings were exposed to short daylengths and low ambient temperatures outside. Measurements included needle primordia initiation, embryonic shoot volume, terminal bud mitotic index, embryonic shoot average cell volume, and shoot tip frost hardiness. EG seedlings formed buds containing 4 times as many needle primordia as ER stock. Embryonic shoot volume increased with number of needle primordia initiated, until late in the hardening period, when significant reductions in meristem volumes of SD and EG stock were observed. Frost hardiness increased sooner in seedlings which set bud in response to short days, but SD treatment did not result in significantly greater frost hardiness at the end of the trial. Frost hardiness was correlated with mitotic index of the embryonic shoot. Cell size in the embryonic shoot declined in seedlings of all treatments during hardening, however, EG seedlings had significantly lower cell volumes by the end of the trial in comparison to ER and SD seedlings.
Indole‐3‐acetic acid production by bacteroids from soybean root nodules
Authors: Hunter William J.
Published: May 2006

This study examined the question: do bacteroids within the nodule have the ability to produce indole‐3–acetic acid (IAA) and does their IAA‐producing ability correlate with the amount of IAA contained in the nodule? Soybean [Glycine max, (L.) Merr. cv. Tracy] plants were inoculated with a wild‐type clone of Bradyrhizobium japonicum, 1–110 known to form nodules that contain low amounts of IAA or with 5‐methyltryptophan‐resistant B. japonicum, clones known to form nodules that contain large amounts of IAA. The resulting bacteroids were isolated from the nodules and examined for their ability to synthesize IAA. IAA production by wild‐type bacteroids was 90 pmole IAA (mg protein)−1 h−1 and IAA production by mutant bacteroids was 620 to 690 pmole IAA (mg protein)−1 h−1. These data indicate that bacteroids from high IAA‐containing nodules have an enhanced ability to produce IAA, implying that bacteroid‐produced IAA accumulates in the nodule.
Neutral growth inhibitors in light‐grown dwarf pea shoots –separation, identification and growth regulation
Authors: Noguchi Hisashi , Tsurumi Seiji , Takeuchi Yasuyoshi , Hashimoto Tohru
Published: May 2006

To correlate endogenous growth inhibitors of dwarf pea to its dwarfism a thorough search of growth inhibitors was made in the neutral fraction of an acetone extract from the shoots of light‐grown seedlings of Pisum sativum L. cvs Progress No 9 and Alaska. From both cultivars six inhibitors were separated and named A‐1, A‐2, A‐3, B‐1, B‐2 and B‐3 based on their order of elution from the silica gel column. Their contents as determined by cress root bioassay were: in cv. Progress 0.40, 16.5, 6.36, 1.02, 0.11 and 0.10, and in cv. Alaska 0.33, 2.35, 3.51, 0.95, 0.10 and 0.09 cress units (g fresh weight)−1. Their contributions to growth regulation of the relevant pea plants were estimated as the products of the above‐stated contents times the ratios of the specific activities of each standard sample in the cress roots and the relevant pea cultivars, and they were; in cv. Progress A‐2, 5.44 and A‐3, 2.10, and in cv. Alaska A‐2, 0.68 and A‐3, 0.88, those of A‐2 and A‐3 constituting more than 90% of the total contribution of the six inhibitors in either cultivar. The great differences in the content and contribution to growth regulation of A‐2 and A‐3 between the two cultivars suggest that the higher contents of and greater responsiveness to the two inhibitors in cv. Progress may be causes of dwarfism of this cultivar. A‐l and A‐3 were spectroscopically identified with pisatin and a mixture of cis, trans–, and trans, trans xanthoxins.
The effect of UV‐B and UV‐C radiation onHibiscusleaves determined by ultraweak luminescence and fluorescence induction
Authors: Panagopoulos Ioannis , Bornman Janet F. , Björn Lars Olof
Published: May 2006

The effects of UV‐C (254 nm) and UV‐B (280‐320 nm) on chlorophyll fluorescence induction and ultraweak luminescence (UL) in detached leaves ofHibiscus rosa‐sinensisL. were investigated. UL from leaves exposed to UV‐B and UV‐C radiation reached a maximum 72 h after irradiation. In both cases most of the light was of a wavelength over 600 nm. An increase in the percentage of long wavelength light with time was detected. UV radiation increased peroxidase activity, which also reached a maximum 72 h after irradiation. UV‐B and UV‐C both reduced variable chlorophyll fluorescence. No effect on the amount of chlorophyll or UV screening pigments was observed with the short‐term irradiation used in this investigation.
Lateral bud development and shoot growth in low‐pruned Morus alba as affected by stem orientation
Authors: Suzuki Takeo , Kitano Minoru
Published: May 2006

Two phases of bud activity were identified in the new growth of one‐year‐old erect coppice shoots on 11‐year‐old low‐pruned stumps of mulberry (Morus alba L. cv. Shin‐ichinose) in spring, the sprouting phase in which the majority of the buds, including the basal ones, sprout and elongate, and the dominance phase (starting 4–5 weeks after sprouting) during which the upper laterals begin to assert dominance and suppress the growth of lower laterals, becoming new leading shoots. In contrast, arching before sprouting markedly inhibited buds on the under side, leading to poor shoots. By late April, the sprouts on the upper side grew readily into new erect shoots, resulting in considerable dominance over those from the lateral sides. Of these erect shoots, those located closer to the stem base grew more in May and June. The effects of arching made during the sprouting phase (late April) on bud activity and shoot lengths were generally similar to those of earlier archings before spring bud bursting. Separation of the shoots from the upper and under sides by longitudinal, horizontal splitting of the arched stems in late April did not affect the inhibited elongation of the shoots from the under side. These results suggest that in the response to arching before and in late April, the effects are related to spring bud bursting and gravimorphism. In contrast, arching during and after the dominance phase (May) had no gravimorphic effects on growth of the shoots on the upper side, although there was a stimulation of outbreak of the buds on the upper side, which remained dormant during spring bud bursting.

Continuous basal applications of abscisic acid in aqueous solution inhibited bud break and shoot growth of the postdormant erect stem segments, and defoliation of the new shoots markedly. In contrast, similar applications of an ethylene‐releasing compound, Ethephon, depressed shoot elongation slightly, but enhanced defoliation greatly. Gibberellic acid (GA3) stimulated shoot elongation, but depressed leaf enlargement.
Reduction in the free indole‐3‐acetic acid levels in Alaska pea toy the gibberellin biosynthesis inhibitor uniconazol
Authors: Law David M. , Hamilton R. H.
Published: May 2006

The gibberellin biosynthesis inhibitor uniconazol reduces both the elongation and indole‐3‐acetic acid content of growing Pisum sativum cv. Alaska intemodes. Both internode growth and indole‐3‐acetic acid content in uniconazol‐treated plants can be elevated by gibberellin A3 treatment. The lengths of the growing intemodes are directly related to the indole‐3‐acetic acid contents.
Kinetic properties of phosphoenolpyruvate carboxylase from lupin nodules and roots
Authors: Marczewski Waldemar
Published: May 2006

The kinetic properties of two forms of phosphoenolpyruvate carboxylase (PEPC I and PEPC II, EC 4.1, 1.31) from lupin (Lupinus luteus L. cv. Ventus) nodules and one enzyme form (PEPC III) from roots were studied. The Michaelis constant (Km) values for PEP, Mg2+ and especially HCO3−were lower for PEPC I. Kinetic studies showed that aspartate is a competitive inhibitor at pH 7.2 and inhibitor constant (Ki) values are different for the three forms of PEPC. Malate is a competitive inhibitor for PEPC I and PEPC III and shows mixed‐type inhibition for PEPC II. Malate inhibition is dependent upon the pH of the assay. Different effect of several metabolites was also observed. The temperature optimum was near 39°C for PEPC I and around 43°C for PEPC II and PEPC III. PEPC I appeared to be the most thermolabile. It is suggested that PEPC I from lupin nodules is closely associated with N2 fixation.
Proteolysis and the diurnal decrease of asparaginase activity
Authors: Sieciechowicz K. A. , Ireland R. J.
Published: May 2006

The mechanism responsible for the decrease in asparaginase (EC 3.5.1.1) activity in darkened leaves of Pisum sativum L. cv. Little Marvel was investigated. Asparaginase activity, obtained from half‐expanded leaves harvested at the end of the dark period, or during the light periods, was inactivated by bromelain (EC 3.4.22.4), ficin (EC 3.4.22.3), both thiol proteases, and trypsin (EC 3.4.21.4), a serine protease. Thrombin (EC 3.4.21.5), pepsin (EC 3.4.23.1), or carboxypeptidase A (EC 3.4.17.1) had no effect on dark‐ or light‐harvested asparaginase preparations. Inactivation of asparaginase activity in crude or purified preparations by ficin was not observed in the presence of leupeptin (an inhibitor of thiol proteases). Supplying leupeptin to detached half‐expanded leaves had no effect on the increase of asparaginase observed at the start of the light period, while it maintained asparaginase activity at high levels in leaves excised during or at the end of the light period. These results suggest that decreased asparaginase activity in vivo is brought about by thiol‐dependent proteases.
Isoenzyme pattern of superoxide dismutase in different varieties of citrus plants
Authors: Almansa María S , del Río Luis A. , Alcaraz Carlos F. , Sevilla Francisca
Published: May 2006

Superoxide dismutases (SOD; EC 1.15.1.1) in leaves from different cultivars of citrus plants were characterized using isoelectric focusing in polyacrylamide gels. The plants studied included Citrus limonum R. (cvs Verna, Fino, and Eureka), C. paradisi Mac (cvs Red Blush and Marsh), C. aurantium L. (cv. Comun), C. sinensis L. Osbeck (cvs Navel, Valencia, and Salustiano), and C. reticulata B. (cv. Satsuma). The three molecular forms of SOD were distinguished from each other by their different sensitivity to cyanide and H2O2. In C. limonum leaves, four Cu,Zn‐SODs, three Fe‐SODs and two Mn‐SODs were present. However, in leaves from different varieties of C. sinensis, C. paradisi, C. aurantium and C. reticulata the activity and number of Fe‐SOD isoenzymes were lower than in lemon leaves, whereas the number of MN‐SOD isozymes was increased. Cu,Zn‐SODs did not show significant variations in the different species and cultivars. The identification of Fe‐SODs in several species of the plant family Rutaceae extends the small number of higher plants where the presence of these Fe‐containing metalloenzymes has been demonstrated. Results obtained may be useful from an evolutionary viewpoint and also in mineral nutrition studies using SOD isozymes as markers of functional metals.
The relation between cell size, ploidy level and nitrate concentration in lettuce
Authors: Reinink Kees , Biom‐Zandstra Margaretha
Published: May 2006

In two experiments the relation between cell size, ploidy level and nitrate concentration of genotypes of lettuce (Lactuca saliva L.) was investigated. Artificial increase of cell size by application of gibberellic acid to young plants decreased the percentage dry weight and the concentration of organic acids in the plant sap and increased the nitrate concentration of the shoot. Application of chlormequat chloride caused the opposite effects. Tetraploid genotypes of lettuce had larger cells, a lower nitrate concentration and a higher concentration of organic solutes than diploid genotypes. Genotypical differences in nitrate concentration could not be explained by differences in cell size, but were consistently related to differences in concentration of organic acids in plant sap. The percentage dry weight of genotypes was positively correlated with the concentration of organic acids in plant sap. However, differences in nitrate concentration were also found among genotypes with comparable dry matter content. These differences could be caused by differences in partitioning of photosynthates over structural components and organic acids in the vacuoles. Mono‐saccharides seem to be less important than organic acids for explaining genotypical differences in nitrate level, because the concentration of monosaccharides was much lower than that of organic acids and because a negative relation between the concentration of monosaccharides and of nitrate was not found in every case. Genotypical differences in nitrate accumulation were not related to differences in osmolarity.
Levels of ethylene, ACC, MACC, ABA and proline as indicators of cold hardening and frost resistance in winter wheat
Authors: Macháčcková Ivana , Hanišová Alena , Krekule Jan
Published: May 2006

Changes in ethylene production and in the contents of 1‐aminocydopropane‐1‐carboxylic acid (ACC), 1‐(malonylamin6)‐cyclopropane‐1‐carboxylic acid (MACC), abscisic acid (ABA) and L‐proline were determined after 40 days of cold hardening at 4°C in three wheat cultivars differing in frost resistance. Proline and especially ABA accumulated with hardening in all varieties in parallel with the degree of frost resistance, e.g. proline and ABA increases in the non‐resistant cv. Slávia were 2x and 5x, whilst in the resistant cv. Mironovská 808 increases were 4X and 20X. Ethylene production and MACC level showed no significant changes with hardening in any of the cultivars after 40 d, but ACC levels did increase with hardening. The production of ethylene, ACC and MACC was studied during hardening. Ethylene production decreased sharply at low temperature and rose rapidly (within 1 day) on return to normal temperature, while ACC production reacted in the opposite direction. MACC levels rose rapidly during the first 4 days of cold, then more slowly for about 2 weeks, thereafter decreasing again steadily. The only varietal differences occurring at maximum levels were correlated with the degree of frost resistance.
Antibodies as probes for the study of location and metabolism of (1→3), (1→4)‐β‐D‐glucans
Authors: Hoson Takayuki , Nevins Donald J.
Published: May 2006

Polyclonal antibodies, raised against ((1→3), (1→4)‐β‐D‐glucans from oat (Avena sativa L.) caryopsis, were used to investigate the location and the metabolism of mixed‐linked β‐D‐glucans. The binding of these antibodies to the cell walls of oat coleoptiles was shown by an indirect fluorescence method. Distinct fluorescent regions were observed along the inner layers of the walls of each cell. The preimmune serum or antibodies pretreated with oat caryopsis β‐D‐glucans did not react with the cell walls. Glucan antibodies were bound to the walls of other Poaceae coleoptiles as well as to those from oat mesocotyls and roots, whereas they were not bound to the walls of some dicotyledons tested. The relative glucan content of the cell walls of oat coleoptiles as determined by β‐D‐glucanase (EC 3.2.1.73) treatment was maximum between day 3 and 4 after soaking, but it declined during further elongation. A rapid decrease in glucan content was observed in excised coleoptiles when auxin or β‐D‐glucanase was present. There was a clear correlation between the glucan content expressed on a basis of cell wall polysaccharides and the amount of the antibodies bound to the cell walls. These results indicate that the antibodies are useful probes to detect and determine (1→3), (1→4)‐β‐D‐glucans of cell walls.
ATP‐driven Ca2+ transport in sealed plasma membrane vesicles prepared by aqueous two‐phase partitioning from leaves of Commelina communis
Authors: Gräf Peter , Weiler Elmar W.
Published: May 2006

Sealed plasma membrane vesicles were obtained in high purity from leaves of Commelina communis L. by aqueous two‐phase partitioning. Based on the analysis of a range of markers, the preparations (U3+U3′ phases) were shown to be devoid of tonoplast, Golgi and thylakoid membranes, and showed only trace mitochondrial contamination. One‐third of the vesicles were oriented inside out and exhibited ATP‐driven 45Ca2+ transport [? 15 pkat (mg protein)−1]. Ca2+ uptake into the vesicles had a pH optimum of 7.2 and apparent Km values for Ca2+ of 4.4 μM and for Mg‐ATP of 300 μM. Ca2+ uptake, K+, Mg2+‐ATPase (EC 3.6.1.3) activity as well as glucan synthase II (EC 2.4.1.34) activity were all maximal at the same equilibrium density (1.17 g cm−3) on continuous sucrose density gradients. The protonophore carbonylcyanide m‐chlorophenylhydrazone (CCCP) did not inhibit the ATP‐dependent Ca2+ transport into the vesicles, excluding a Ca2+/H+ exchange driven by a proton gradient. ATP‐dependent Ca2+ uptake was inhibited by erythrosin B (I50= 0.1 μM), ruthenium red (I50= 30 μM), La3+ (I50= 10 μM) and vanadate (I50= 500 μM), but not by azide, cyanide and oligomycin. The calmodulin antagonists, trifluoperazine (I50= 70 μM) and W‐7 (I50= 100 μM) were also inhibitory, However, this inhibition was not overcome by calmodulin. Trifluoperazine and W‐7, on the other hand, stimulated Ca2+ efflux from the vesicles rather than inhibit Ca2+ uptake. Our results demonstrate the presence of a Ca2+‐ATPase in the plasma membrane of C. communis. In the intact cell, the enzyme would pump Ca2+ out of the cell. Its high affinity for Ca2+ makes it a likely component involved in adjusting low cytoplasmic Ca2+ levels. No indications for a secondary active Ca2+/H+ transport mechanism in the plasma membrane of C. communis were obtained. Both, the nucleotide specificity and the sensitivity towards vanadate. distinguish the Ca2+‐ATPase from the H+‐translocating K+. Mg2+‐ATPase in C. communis plasma membranes.
Cellulases, hemicelluloses and auxin‐stimulated growth: a possible relationship
Authors: Fry Stephen C.
Published: May 2006

The plant growth promoter, auxin, may loosen the primary cell wall by increasing the activity of extracellular cellulases – a group of enzymes that cleave hemicellulose chains in the walls of both monocotyledons and dicotyledons. Evidence is reviewed that suggests that these hemicellulose chains tether adjacent microfibrils, and that by cleaving such chains the cellulases facilitate cell expansion. On the basis of this structural arrangement a mechanism for elastic and plastic wall extension is proposed.
Cytochromes of plant plasma membranes. Characterization by absorbance difference spectrophotometry and redox titration
Authors: Askerlund Per , Larsson Christer , Widell Susanne
Published: May 2006

The cytochrome composition of plasma membranes (PM) obtained by phase partitioning of microsomal fractions from spinach leaves (Spinacea oleracea L. cv. Medania), cauliflower inflorescences (Brassica oleracea L.), sugar beer leaves (Beta vulgaris L.) and barley (Hordeum vulgare L. cv. Kristina) roots and leaves was characterized by absorbance difference spectrophotometry at different reducing conditions at 20 and – 196°C, by redox titration, and by heme staining of polypeptide bands after lithium dodecyl sulfate polyacrylamide gel electrophoresis (LDS‐PAGE). The location of the α‐bands in the difference spectra and the loss of heme after treatment with LDS indicated that predominantly cytochromes of the b‐type were present in all species tested. The total concentration of cytochrome was ca 0.35 nmol (mg protein)−1. The main component (ca 70% of total) was completely reduced by ascorbate and partly by NADH and had a midpoint potential of ca 150 mV. At – 196°C, ascorbate reduction revealed a symmetrical α‐band at ca 557 nm with PM from spinach leaves, cauliflower and sugar beet leaves, but with barley root and leaf PM ascorbate reduction resulted in an asymmetrical α‐band (shoulder at 552, maximum at 559 nm). In the dithionite‐reduced minus ascorbate‐reduced spectrum at –196°C a split α‐band (552 + 558 nm) was seen with PM from all species. This minor component had a midpoint potential of ca – 50 mV and is probably identical to cytochrome b5, the presence of which would explain the relatively high NADH‐cytochrome c reductase activities observed with plant PM. With PM from cauliflower, CO‐difference spectra indicated that cytochromes P‐420 and P‐450 were present at concentrations up to 0.06 and 0.03 nmol (mg protein)−1, respectively. Visualization of cytochromes by heme staining after LDS‐PAGE was complicated by endogenous peroxidase activity and by loss of heme during solubilisation. A presumptive b‐cytochrome (heme‐stained band at 94 kDa) was only detected with barley leaf PM.
Localisation of β‐oxidation enzymes in peroxisomes of rice coleoptiles
Authors: Pistelli Laura , Rascio Nicoletta , De Bellis Luigi , Alpi Amedeo
Published: May 2006

Enzymes of the β‐oxidation pathway in rice (Oryza sativa L., cv. Arborio) coleoptiles were investigated. The coleoptiles contain acyl‐CoA oxidase (EC 1.3.99.3), 3‐hydroxyacyl‐CoA dehydrogenase (EC 1.1.1.35), enoyl‐CoA hydratase (EC 4.2.1.17) and thiolase (EC 2.3.1.9). Analysis of coleoptile homogenates by sucrose density fractionation showed a preferential distribution of these enzymes in the unspecialized peroxisomes. The enzymatic activity found in the mitochondrial fraction was due to peroxisomal contamination since electron micrographs show the peroxisomes to be intact and pure whereas the mitochondrial fraction was contaminated by other organelles. It appears that the β‐oxidation pathway is localized in the unspecialized peroxisomes of rice coleoptiles, extending the number of plant species in which such a localization has been observed.
Changes in activities of superoxide dismutases during aging of petals of cut carnations (Dianthus caryophyllus)
Authors: Droillard Marie‐Jo , Bureau Danielle , Paulin André
Published: May 2006

Between the end of blooming and the withering of petals of cut carnations (Dianthus caryophyllus L. cv. Ember), the total superoxide dismutase activity decreased. The three forms of superoxide dismutase (Cu, Zn‐SOD, Fe‐SOD and Mn‐SOD. EC1. 15. 1. 1) identified on polyacrylamide gel exhibited several isozymes, the activities of which decreased sooner or later during aging. The important activity of the Mn‐SOD decreased at the beginning of withering to become undetectable, while the weak activity of Fe‐SODs declined only at the end of withering. It is suggested that the localization of SODs in the cell may explain these differences. Hypothesis are proposed to understand the decreased activity of SODs during aging.
Internode length in Pisum. Biochemical expression of the le gene in darkness
Authors: Ross John J. , Reid James B.
Published: May 2006

Ross, J. J. and Reid, J. B. 1989. Internode length in Pisum. Biochemical expression of the Le gene in darkness.

The Le gene appears to be biochemically expressed in dark‐grown pea (Pisum sativum L.) plants since the previously reported difference in metabolism of [3H]‐GA30 between light‐grown Le and Le plants was also observed in darkness. Furthermore, both light‐ and dark‐grown Le plants contained more endogenous GA1, ‐like substance than did comparable Le plants. Darkness did not appear to significantly increase the accumulation of GA1, in either Le or Le plants, although confirmation of GA1 levels by gas chromatography‐selected ion monitoring is still required. The results support previous findings that the overall metabolism of [3H]‐GA20, is accelerated by darkness. The evidence presented here supports previous suggestions that darkness acts on internode length by increasing some aspect of GA sensitivity.
Influence of soil O2 and CO2 on root respiration for Agave deserti
Authors: Palta Jairo A. , Nobel Park S.
Published: May 2006

Respiration measured as CO2 efflux was determined at various soil O2 and CO2 concentrations for individual, attached roots of a succulent perennial from the Sonoran Desert, Agave deserti Engelm. The respiration rate increased with increasing O2 concentration up to about 16% O2 for established roots and 5% O2 for rain roots (fine branch roots on established roots induced by wetting of the soil) and then remained fairly constant up to 21% O2. When O2 was decreased from 21 to 0%, the respiration rates were similar to those obtained with increasing O2 concentration. The CO2 concentration in the root zone, which for the shallow‐rooted A. deserti in the field was about 1 000 μl l‐1, did not affect root respiration at concentrations up to 2 000 μl l‐1, but higher concentrations reduced it, respiration being abolished at 20 000 μl l‐1 (2%) CO2 for both established and rain roots. Upon lowering CO2 to 1 000 μl l‐1 after exposure to concentrations up to 10000 μl l‐1 CO2, inhibition of respiration was reversible. Uptake of the vital stain neutral red by root cortical cells was reduced to zero, indicating cell death, in about 4 h at 2% CO2, substantiating the detrimental effects of high soil CO2 concentrations on roots of A. deserti. This CO2 response may explain why roots of desert succulents tend to occur in porous, well‐aerated soils.
An in vivo analysis of the effect of SO2 fumigation on photosynthesis in Zea mays.
Authors: Price Sarah , Long Steve P.
Published: May 2006

Fumigation of leaves with SO2 can reduce the capacity for photosynthetic CO2 uptake even in the absence of visible symptoms of damage. In vitro studies suggest that this invisible injury to intact leaves could be affected by damage to each of the main stages in the photosynthetic process. Reduced stomatal apertures may also reduce photosynthesis following SO2 fumigation. The responses of CO2 uptake by leaves to intercellular CO2 concentration and to absorbed light provide information for quantitative separation of the in vivo contribution of the different stages of photosynthesis to reduction in overall rate. This study uses these techniques to examine the basis of reduction in CO2 uptake in Zea mays cv. LG11 leaves following short‐term fumigation with SO2. Fumigation with 33 μmol m–3 SO2 for 30 min reduced light saturated CO2 uptake by about one‐third. An even greater reduction in light limited CO2 uptake was observed and with no significant change in light absorptance this was attributed to a reduced quantum yield of photosynthesis. The light saturated CO2 uptake rate and the stomatal conductance decreased in parallel. However, the relationship of CO2 uptake to the intercellular CO2 concentration suggested that the reduced stomatal conductance did not account for the reduced rate of CO2 uptake following fumigation. Both the initial slope and plateau of this relationship were significantly reduced, suggesting that both carboxylation efficiency and capacity for regeneration of CO2 acceptor were diminished by SO2 fumigation. The operating intercellular CO2 concentration indicated that both processes were co‐limiting, before and after fumigation. The time required for induction of photosynthetic CO2 uptake on illumination was approximately doubled following SO2 fumigation, showing that fumigation impairs the ability of the photosynthetic apparatus to adapt to fluctuations in light level.
Control of thiophene accumulation in calli of two Tagetes species
Authors: Croes A. F. , Aarts A. M. , Bosveld M. , Breteler H. , Wullems G. J.
Published: May 2006

The relation between root differentiation and accumulation of biocidal thiophenes was studied in stem calli of two Tagetes species. Disorganized tissues of T. erecta were low in thiophene production. A sharp rise in thiophene content coincided with the emergence of roots on the calli. Root regeneration and the amount of thiophenes produced were found to be quantitatively related. Callus tissues of T. minuta did not differentiate into organs. Nevertheless, they accumulated thiophenes throughout the incubation period. Light at 12 W m‐ stimulated thiophene production in T. erecta without having an apparent effect on root regeneration. In T. minuta even low irradiance levels (2 W m∼2) strongly inhibited thiophene accumulation. Under favorable conditions thiophene concentrations in calli of both species were comparable to or somewhat lower than the levels in roots on the plants and in excised, cultured roots of T. erecta. We conclude that in calli of T. erecta thiophene accumulation is coupled to root regeneration whereas a different control mechanism allowing for accumulation in disorganized tissues is operative in T. minuta.
Effect of hydrogen peroxide on nitrate reductase activity in detached oat leaves in darkness
Authors: Kenis J. D. , Morlans J. D. , Trippi V. S.
Published: May 2006

Nitrate reductase (NR, EC 1.6.6.1) is sensitive to O2 concentration, and therefore it was of interest to study the action of H2O2, a normal substance in plant metabolism, on NR activity in segments of 7‐, 14‐ and 17‐day‐old leaves of oat (Avena sativa L. ev. Suregrain). After 4 h of treatment in the dark, H2O2 decreased NR activity as measured with the in vivo assay. The effect was stronger in 14‐ and 17‐ than in 7‐day‐old leaves. Vacuum infiltration of cysteine did not prevent this decrease. When NR was determined with the in vitro assay, H2O2 did not seem to affect the activity after the 4 h treatment. but NR decreased when crude extracts prepared from untreated 14‐day‐old leaves were incubated directly with H2O2. This effect was prevented by addition of cysteine, ascorbate or reduced glutathione to the extracts. In order to study the possibility that low activity of the system for defense against oxidations could account for the age‐dependent response of NR to H2O2 in the in vivo test, activities of catalase, ascorbate peroxidase and glutathione reductase were measured during leaf development and after a 4‐h treatment with H2O2 in the dark. No clear correlation was found between the activities of those enzymes and changes in in vivo NR activity caused by H2O2. The results suggest that H2O2 might affect NR both directly by oxidizing SH‐groups and indirectly by decreasing reductant availability as a result of NADH oxidation. The age‐dependent response of NR to H2O2 treatment could also be explained in terms of decreased NADH availability in the tissues due to decreased NADH synthesis and/or increased degradation.