bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of ethylene and carbon dioxide in differentiation of shoot buds in excised cotyledons of Pinus radiata in vitro
Authors: Kumar Prakash P. , Reid David M. , Thorpe Trevor A.
Published: May 2006

The production of ethylene and carbon dioxide by Pinus radiata D. Don cotyledons cultured on shoot‐forming medium in sealed Erlenmeyer flasks was studied. To establish the role of these gases on morphogenesis three experimental approaches were used: (1) capping the flasks with serum caps on various days, and removing the serum caps at different stages of morphogenesis, (2) absorbing the gases by setting up traps singly and in combination during the various stages of differentiation and (3) incubating the cultures under continuous flow of constant gas mixtures. The results indicate that both ethylene and carbon dioxide, which build up during the first 10 to 15 days of culture, promote morphogenesis. Excessive accumulation after the initiation of buds causes some degree of dedifferentiation. When both the gases were eliminated from the flasks, bud formation and growth were inhibited. In the absence of oxygen, ethylene and carbon dioxide fail to influence growth and morphogenesis.
Changes of polyamines and ethylene in cucumber seedlings in response to chilling stress
Authors: Wang Chien Yi
Published: May 2006

Cucumber (Cucumis sativus L. cv. Victory) seedlings were exposed to chilling at 5°C and endogenous levels of polyamines and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) were measured after chilling and after warming at 20°C. The level of spermidine was higher in the chilled seedlings than in the non‐chilled seedlings. Treatment with a plant bioregulator, (2RS,3RS)‐1‐(4‐cholorophenyl)‐4,4‐dimethyl‐2‐(1,2,4‐triazol‐1‐yl)pentan‐3‐ol (paclobutrazol), reduced the chilling injury and the levels of spermidine in the chilled seedlings. The levels of ACC and production of ethylene showed sharp increases after warming following exposure to chilling. These increases were suppressed by the application of aminooxyacetic acid (AOA). However, AOA treatment did not reduce chilling injury or affect the levels of polyamines in the tissue. These data indicate that the increase in ACC and ethylene is a response of the tissue to the chilling exposure and is not a cause of the injury. The data also suggest that the syntheses of polyamines and ethylene are not competitive with each other even under chilling stress conditions.
K+(Rb+) and Ca2+ fluxes in young winter wheat plants exposed to sub‐zero temperatures
Authors: Erlandson Gunvor , von Fircks Heinrich A. , Jensén Paul
Published: May 2006

Ice crystal formation temperature was determined in the region of the crown in one group of 7‐day‐old intact unhardened high‐salt plants of winter wheat (Triticum aestivum L. cv. Weibulls Starke II) with TA (Thermal Analysis) and DTA (Differential Thermal Analysis) methods. After exposure of another group of plants, grown for the first 7 days in the same way as the first group, to various sub‐zero temperatures (‐1 to 5°C), influx in roots of Rb+(86Rb+) and Ca2+(45Ca2+) and contents of K+ and Ca2+ were determined at intervals during 7 days of recovery. Ice crystal formation in the crown tissue was probably extracellular and took place at about ‐4°C. There was a large loss of K+ from the roots after treatment at sub‐zero temperatures. This loss increased as the temperature of the sub‐zero treatment decreased. During recovery, roots of plants exposed to ‐1, ‐2 and ‐3°C gradually reabsorbed K+. Reabsorption of K+ in roots of plants exposed to ‐4°C was greatly impaired. Rb+ influx decreased and Ca2+ influx increased after sub‐zero temperature treatments of the plants. Active Rb+ influx mechanisms and active extrusion of Ca2+ were impaired or irreversibly damaged by the exposure. While Rb+ influx mechanisms were apparently repaired during recovery in plants exposed to temperatures down to ‐3°C, Ca2+ extrusion mechanisms were not. The temperature for ice crystal formation in the region of the crown tissue coincides with the temperature at which the plants lost the ability to reabsorb K+ and to repair Rb+ influx mechanisms during the recovery period. Plants were lethally damaged at temperatures below −4°C.
Whole plant aspects of heavy metal induced changes in CO2, uptake and water relations of spruce (Picea abies) seedlings
Authors: Schlegel Hedda , Godbold Douglas L. , Hüttermann Aloys
Published: May 2006

Spruce seedlings [Picea abies (L.) Karst.] were exposed to a range of concentrations of Zn, Cd, Hg and methyl‐Hg for 5 weeks. The chlorophyll and water content of the needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plant were determined using a Li‐cor portable photosynthesis measuring system. Chlorophyll and water contents of needles decreased in response to all metal treatments, as did CO2 uptake. At 1 μM Cd, 0.1 μM Hg and 30 and 60 μM Zn, the decrease in CO2 uptake could be accounted for by decreased chlorophyll concentrations. Decreased transpiration was only found at 5 μM Cd and 0.01 μM methyl‐Hg. At 5 μM Cd most of the decrease in CO2 uptake could be explained by decreased chlorophyll levels and stomatal closure induced by water stress. At 0.01 μM methyl‐Hg, besides a decrease in chlorophyll concentration and partial stomatal closure, photosynthetic reactions may have been directly affected. Respiration rates were not influenced by exposure to heavy metals.
Dependence of the quality and the in vitro translation capacity of pine ribosome assemblies on the isolation procedure
Authors: Kupila‐Ahvenniemi Sirkka , Muhonen Aija , Malinen Paula
Published: May 2006

The in vitro translation capacity of total ribosome assemblies isolated from the vegetative buds of small Scots pine (Pinus sylvestris L.) plants depends on the isolation procedure. Good yields and high values for protein synthesis were obtained in experiments in which polyvinyl pyrrolidone (PVP) was added to the grinding buffer. The polysome profiles obtained after sucrose density gradient centrifugation indicated the presence of polysomes in all samples. In addition, large ribosome aggregates were visible in the scanning electron micrographs. The use of an RNase inhibitor (RNasin) together with PVP did not improve the results, and treatment with ribonuclease (RNase, EC 3.1.27.5) destroyed the ability to synthesize protein.

D, L‐Dithiothreitol (DTT) and mercaptoethanol, if used instead of or together with PVP, gave low yields and also DTT destroyed the in vitro translation capacity of the ribosome assemblies. The polysome profiles had a high peak indicating dimers and often a descending series of peaks indicating polymers. A study of the scanning electron micrographs gave the impression that the largest polymers and aggregates had broken down.

Protease K (EC 3.4.21.14) when added to the grinding buffer also destroyed the ability of the ribosomes to maintain protein synthesis in vitro. In this case, the shape of the polysome profiles gave the impression of successful isolation. Clumps of ribosomes, presumably originating from large aggregates, were visible in the scanning electron micrographs. Triton X‐100 and 0.25 M NaCl in the grinding buffer extracted chromatin, which affected the results. The material lost during the extraction and purification processes consisted mainly of monosomes and their sub‐units.

On the basis of the above results it was concluded that the preservation of large polysomes and ribosome aggregates in the isolated ribosome assemblies is necessary if they are to maintain a high translation capacity. The content of the assemblies was best revealed in the scanning electron micrographs. The shape of the polysome profiles did not always correlate with the ability of the isolated ribosomes to synthesize proteins.
Activity and distribution of enzymes that interconvert purine bases, ribosides and ribotides in the tomato plant and possible implications for cytokinin metabolism
Authors: Burch L. R. , Stuchbury T.
Published: May 2006

The activity of the enzymes 5′‐nucleotidase (EC 3.1.3.5), adenosine nucleosidase (EC 3.2.2.7), adenine phosphoribosyl transferase (EC 2.4.2.7) and acid phosphatase (EC 3.1.3.2) was determined in sections of tomato plant (Lycopersicon esculentum Mill. cv. Bellina). The distribution of the enzymes changed markedly during development and a role for these enzymes in cytokinin metabolism is suggested.
Effects of water stress on glycolate metabolism in the leaves of rice seedlings (Oryza sativa)
Authors: Goyal Arun
Published: May 2006

To investigate the effects of water stress on glycolate metabolism, seedlings of a drought‐tolerant cultivar (N‐22) and a susceptible cultivar (Jaya) of Oryza sativa L. were subjected to water stress for 5, 8 or 10 days. Increasing the duration of water‐deficit‐stress produced a proportional decrease in relative water content and leaf water potential, reduced glycolate content and catalase (EC 1.11.1.6) activity, but increased glycolate oxidase (EC 1.1.3.1) activity, hydrogen peroxide and glyoxylate contents in the leaves of both cultivars. In a radiotracer experiment, with increasing duration of water stress, the proportion of label increased in 3‐phosphoglycerate, glycolate, glycine and serine. The drought‐tolerant cultivar (N‐22) was affected less than the susceptible cultivar (Jaya). The glycolate pathway metabolism is discussed in relation to photorespiration and the effects of water stress.
Effects of hypochlorite disinfection on the response of barley aleurone layers to gibberellic acid
Authors: Goudey J. Stephen , Tittle Forrest L. , Spencer Mary S.
Published: May 2006

Although the use of hypochlorite to disinfect seeds is widespread, the effects on tissues isolated from them have been largely ignored. Disinfection of barley (Hordeum vulgare L. cv. Himalaya) half‐seeds with hypochlorite solutions of ≥1.0% (w/v) available chlorine caused the pericarp to separate from the underlying tissues. Aleurone layers isolated from these grains had lower rates of oxygen consumption and released significantly less protein, PO43− Mg2+, K+ and amylase (EC 3.2.1.1) into the medium in response to gibberellic acid (GA3) than layers isolated from grains disinfected with a 0.1% hypochlorite solution. Disinfection with 1.0% hypochlorite also quantitatively altered the spectrum of proteins released into the incubation medium by the layers in response to GA3.
Effects of Ca2+ and polyamines on Na+ and Rb+ influx in excised maize roots
Authors: Riedell Walter E.
Published: May 2006

When 1 mM spermidine or spermine was included in an absorption solution which contained 20 mM Na+ and 1 mM Rb+, Na+ influx into excised maize roots (Zea mays L. cv. Golden Cross Bantam) was reduced. Rb+ influx was reduced in the presence of spermidine and uneffected in the presence of spermine when compared with control solutions. When 1 mM Ca2+ replaced the polyamines, Na+ influx was strongly reduced and Rb+ influx was promoted. Rb+ influx from 1 mM Rb+ solutions which did not contain Na+ was also promoted by 1 mM Ca2+, but was inhibited by 1 mM spermidine. This Ca2+ promotion of Rb+ influx could be reversed by 10 times greater concentration of spermidine in the absorption solution. H+ efflux from excised roots was inhibited by spermidine when compared with Ca2+ or control solutions, however, the plasma membrane ATPase was not inhibited by spermidine. It is concluded that external Ca2+ plays two separate roles in membrane function, only one of which can be substituted for by polyamines. The first role, maintenance of membrane integrity, can be substituted for by spermidine or spermine. The second function, maintenance of the Rb+ transport mechanism, is Ca2+ specific and cannot be substituted for by spermidine or spermine. The results of this study are discussed in terms of electrostatic interactions between the plasma membrane and the Ca2+ or polyamines.
Ethylene and wound‐induced cyanide‐resistant respiration climaxes in potato: The synergistic role of CO2 and the selective role of lycorine
Authors: Laties George G.
Published: May 2006

When treated with ethylene in O2, conditioned potato (Solanum tuberosum L. cv. Russet Burbank) tubers – that is, tubers kept at room temperature for 10 days or more – yield slices that are CN− resistant. Ten % CO2 in the gas mixture not only synergizes the effect of ethylene, but replaces the need for conditioning as well. The response to CO2 is more pronounced with increasing time from harvest. By contrast fresh slices from untreated tubers are CN− sensitive, as are slices from tubers incubated in O2 or O2 plus CO2. The suggestion is made that CN− resistance is constitutive, and that treatment with ethylene/CO2 in O2 confers on potato tuber tissue a resistance to the extensive degradation of membrane phospholipids that normally attends slicing and leads to the loss of CN− resistance. In this connection respiration inhibition by imidazole, an inhibitor of fatty acid α‐oxidation, is extensive in slices of untreated tubers, and sharply diminished in slices of ethylene‐treated tubers in proportion to their CN− resistance.

The coextensive rise of respiration rate and CN− resistance in aged potato slices has led to the presumption that the CN−‐resistant path mediates the respiration climax. Accordingly the alkaloid, lycorine, has been considered to inhibit the development of CN− resistance in aging potato slices because it curtails the wound‐induced respiration. A comparison was carried out on the effect of lycorine on CN−‐sensitive and CN−‐resistant fresh slices – the latter obtained from ethylene/CO2‐treated tubers. Lycorine suppressed the development of the wound‐induced respiration without restricting the development of CN− resistance.
Nitrate reductase activity in nodules of pea inoculated with hydrogenase positive and hydrogenase negative strains of Rhizobium leguminosarum
Authors: Ligero F. , Lluch C. , Olivares J. , Bedmar E. J.
Published: May 2006

The nitrate reductase (NR, EC 1.6.6.1) activity in root nodules formed by hydrogenase positive (Hup+) and hydrogenase negative (Hup−) Rhizobium leguminosarum strains was examined in symbioses with the pea cultivar Alaska (Pisum sativum L.), Rates of activity were determined by the in vivo assay in nodules from plants that were only N2‐dependent or grown in the presence of 2 mM KNO3. The rates varied widely among strains, regardless of the Hup phenotype of the R. leguminosarum strain used for inoculation, but the overall results indicated that nodules formed by Hup− strains accumulated more nitrite in the incubation medium than did those with Hup− phenotypes. Total plant dry weight and reduced nitrogen content of pea plants grown in the presence of 2 mM KNO3 and inoculated with single Hup+ and Hup−R. leguminosarum strains were statistically different among some strains. These observations suggest that the possible advantages derived from the presence of the Hup system on whole plant growth may be counteracted by the higher rates of NR activity in the Hup− strains in the R. leguminosarum‐pea symbiosis.
Survival and division in protoplasts from tobacco (Nicotiana tabacum) depends on the physiological state of the individual donor plant
Authors: Cassells Alan C. , Tamma Lakshmi
Published: May 2006

Variation in the survival potential of protoplasts isolated from different leaf positions and from individuals within a batch of N. tabacum L. cv. Xanthi‐ne is reported. Foliar application of growth regulators and nutrients to unstressed, waterlogged and waterstressed donor plants, demonstrates the prophylactic role of such treatments. It is suggested that intrabatch variation may be related to fluctuations in water supply to the individual donor plants. Vegetative propagation via buds in vitro improved the quality of donors compared with seed raised plants. Further, tissue culture progeny were more tolerant of in vivo waterlogging. The high osmotic pressure of the tissue culture medium may induce this tolerance. The results are discussed in the context of an overall strategy to control the quality of donor plants for protoplast isolation.
Active, inactive and in vitro synthesized forms of polyphenoloxidase during leaf development
Authors: Lanker Thomas , King Thomas G. , Arnold Steven W. , Flurkey William H.
Published: May 2006

Polyphenoloxidase (PPO; EC 1.14.18.1) activity decreased 8‐fold from young to mature Vicia faba L. Moensch (cv. Long pod) leaves. The Km for catechol remained relatively constant from young to mature leaves. Electrophoretic separation and analysis showed that only one active form was present in extracts from various leaf sizes. The amount of this form appeared to decrease with leaf size/age. In extracts which had not tanned, electroblotting and immunostaining indicated that one enzyme form was present with a molecular mass of 45 kDa. Two leaf categories contained greater amounts of this immunological cross‐reacting PPO than other leaf categories. When extracts were allowed to darken, immunoblotting detected three enzyme forms with molecular masses of 45, 59 and 63 kDa. The latter two immunological crossracting species had no detectable enzyme activity. Poly‐A+ mRNA was isolated from six leaf sizes and translated in vitro. A product corresponding to PPO was present in all leaf categories. Greater amounts of this translation product were observed in medium‐sized leaves than in very young or mature leaves. These results suggest that: (1) enzymatic assays for PPO are not reliable indicators of the total amount of PPO protein present in developing leaves, (2) immunoblotting can detect inactive enzyme forms, (3) only one active form of the enzyme is present at all developmental stages, and (4) mRNA corresponding to PPO is present at all developmental stages but appears to be more abundant in certain leaf sizes/ages.
Comparative studies of sucrose and mannitol utilization in celery (Apium graveolens)
Authors: Fellman J. K. , Loescher W. H.
Published: May 2006

Utilization of sucrose and mannitol, the major forms of translocatable assimilate in celery (Apium graveolens L. cv. Giant Pascal), was investigated in intact plants, excised leaves and leaf discs by estimating the soluble carbohydrate pools, starch levels and oxidation of [14C]‐sucrose or mannitol in the light and after extended dark treatments. In detached mature fully‐expanded leaves, mannitol pools remained constant, while sucrose decreased during a 48 h dark treatment. In attached leaves on plants trimmed to a single compound leaf, however, mannitol levels decreased after a dark treatment. In leaf discs floated on bathing solutions containing [14C]‐sucrose or [14C]‐mannitol, oxidation of mannitol was restricted to young leaf tissues, whereas sucrose was metabolized to CO2 regardless of leaf age. Uptake of labelled mannitol, however, was greater than that of sucrose in the light in leaves of every age. Although both mannitol and sucrose are translocated out of leaf tissues, leaf age differences indicate that, unlike sucrose, mannitol utilization is restricted to active sink tissues. The results suggest different roles for mannitol and sucrose with mannitol representing a more rigorously sequestered transport carbohydrate.
Inhibitory and promotive effects of gibberellic acid on floral initiation and development in Poa pratensis and Bromus inermis
Authors: Heide O. M. , Bush M. G. , Evans L. T.
Published: May 2006

Flowering in Poa pratensis L. cv. Holt and Bromus inermis Leyss. cv. Manchar requires exposure to short days (SD) for primary induction to occur, followed by long days (LD) to allow the inflorescence to develop. Weekly sprays with gibberellic acid (GA3) during primary induction inhibited flower initiation in both P. pratensis and B. inermis. With 10−4M GA3 flowering of P. pratensis was suppressed even after an induction period of 10 weeks. Since both GA3 and non‐inductive LD conditions greatly stimulate leaf elongation, the degree of primary induction was closely negatively correlated with plant height (leaf sheath and blade length) at the end of the induction period. GA3 application or the interpolation of LD during SD induction were most inhibitory during the later middle part of the SD period, whereas they were stimulatory near the beginning or immediately before the SD period. We suggest that changes in the portfolio or levels of endogenous gibberellins mediate photoperiodic control of growth and floral initiation in these plants. However, GA3 sprays could not substitute for LD in causing heading and culm elongation in SD induced plants of the two species. The results are discussed in the light of results with other plants with dual floral induction requirements.
Ethylene production in habituated and auxin‐requiring tobacco callus cultures. Does ethylene play a role in the habituation?
Authors: Köves Erzsébet , Szabó Margit
Published: May 2006

Ethylene production of habituated and auxin‐requiring tobacco (Nicotiana tabacum L. cv. Xanthi) callus cultures were compared. More ethylene was produced by auxinrequiring i.e. auxin‐heterotrophic cultures than by habituated ones. Treatment with 2,4‐dichlorophenoxyacetic acid increased the ethylene evolution of habituated cultures over the range 10−7 to 10−4M, which suggests that the higher ethylene production of auxin‐dependent callus is caused by the 2,4‐D in the medium. The IAA levels depended on the age of both types of callus cultures.
Hormone directed sucrose transport during fruit set induced by gibberellins in Pisum sativum
Authors: Peretó Juli G. , Beltrán José P.
Published: May 2006

A new system has been developed to study hormone‐directed transport in intact plants during parthenocarpic fruit set induced by gibberellins. Gibberellic acid (GA3) and gibberellin A1 (GA1) applied to unpollinated ovaries of pea (Pisum sativum L. cv. Alaska) promoted sucrose transport from the leaf to the site of hormone application. In vivo experiments showed an early (30 min) accumulation of [14C]‐sucrose in ovaries of pea stimulated by gibberellins. This activation of sucrose transport appears to be mediated by gibberellins (GA1, GA3), increasing both loading of phloem with sucrose in the leaf (source) and sucrose unloading in the ovary (sink). The ability of pea tissue segments to take up sucrose in vitro was not affected by the hormonal treatment.
Characterization of cyclic nucleotide phosphodiesterase activity in Phaseolus vulgaris
Authors: Dupon M. , Van Onckelen H. A. , De Greef J. A.
Published: May 2006

Cyclic nucleotide phosphodiesterase (3′,5′‐cyclic nucleotide nucleotidohydrolase, EC 3.1.4.17) activity isolated from Phaseolus vulgaris L. cv. Limberg seedlings was partially purified and characterized by fractional (NH4)2SO4 precipitation, DEAE‐cellulose chromatography, chromatography on 3′,5′‐cAMP‐agarose, gel permeation chromatography and chromatofocusing. A crude enzyme preparation, a 30–65% (NH4)2SO4 pellet, showed an acidic pH optimum. The enzyme activity was stimulated by imidazole and divalent cations such as Ca2+, Mg2+ and Mn2+, whereas NaF, PPi and Fe3+ were inhibitory. Isobutylmethylxanthine had no significant effect on the plant enzyme. An MI of 42 000 was estimated by gel permeation high performance liquid chromatography. By chromatography on 3′,5′‐cAMP‐agarose a phosphodiesterase was resolved that produced 5′‐AMP as sole reaction product.
The contribution of fructose 2,6‐bisphosphate to the regulation of sucrose synthesis during photosynthesis
Authors: Stitt M. , Gerhardt R. , Wilke I. , Heldt H. W.
Published: May 2006

This review discusses (a) how the concentration of fructose 2,6‐bisphosphate is controlled in spinach leaves, (b) how fructose 2,6‐bisphosphate and cytosolic metabolites control the cytosolic fructose‐1,6‐bisphosphatase (EC 3.1.3.11), and (c) how the activities of the fructose‐1,6‐bisphosphatase and of sucrose phosphate synthase (EC 2.3.1.14) are coordinated. These features provide the elements of a fine control network that regulates sucrose synthesis during photosynthesis. The rate of sucrose synthesis is coordinated with the supply of photosynthate, so that concentrations of metabolites and phosphate are maintained at a level in the chloroplast which allows rapid CO2 fixation. The rate of sucrose synthesis can also be modified to alter the amount of photosynthate that remains in the chloroplast for conversion to starch.
Regulation and roles for alternative pathways of hexose metabolism in plants
Authors: Black Clanton C. , Mustardy Laszlo , Sung S. S. , Kormaník P. P. , Xu D.‐P. , Paz Nachman
Published: May 2006

Plant cells have two cytoplasmic pathways of glycolysis and gluconeogenesis for the reversible interconversion of fructose 6‐phosphate (F‐6‐P) and fructose 1,6‐bisphosphate (F‐1,6‐P2). One pathway is described as a maintenance pathway that is catalyzed by a nucleotide triphosphate‐dependent phosphofructokinase (EC 2.7.1.11; ATP‐PFK) glycolytically and a F‐1,6 bisphosphatase (EC 3.1.3.11) gluconeogenically. These are non‐equilibrium reactions that are energy consuming. The second pathway, described as an adaptive pathway, is catalyzed by a readily reversible pyrophosphate‐dependent phosphofructokinase (EC 2.7.1.90; PP‐PFK) in an equilibrium reaction that conserves energy through the utilization and the synthesis of pyrophosphate. A constitutive regulator cycle is also present for the synthesis and hydrolysis of fructose 2,6‐bisphosphate (F‐2,6‐P2) via a 2‐kinase and a 2‐phosphatase, respectively. The pathway catalyzed by the ATP‐PFK and F‐1,6‐bisphosphatase, the maintenance pathway, is fairly constant in maximum activity in various plant tissues and shows less regulation by F‐2,6‐P2. Plants use F‐2,6‐P2 initially to regulate the adaptive pathway at the reversible PPi‐PFK step. The adaptive pathway, catalyzed by PPi‐PFK, varies in maximum activity with a variety of phenomena such as plant development or changing biological and physical environments. Plants can change F‐2,6‐P2 levels rapidly, in less than 1 min when subjected to rapid environmental change, or change levels slowly over periods of hours and days as tissues develop. Both types of change enable plants to cope with the environmental and developmental changes that occur during their lifetimes. The two pathways of sugar metabolism can be efficiently linked by the cycling of uridylates and pyrophosphate required for sucrose breakdown via a proposed sucrose synthase pathway. The breakdown of sucrose via the sucrose synthase pathway requires half the net energy of breakdown via the invertase pathway. Pyrophosphate occurs in plant tissues as a substrate pool for biosynthetic reactions such as the PPi‐PFK or uridine diphosphate glucose pyrophosphorylase (EC 2.7.7.9; UDPG pyrophosphorylase) that function in the breakdown of imported sucrose. Also, pyrophosphate links the two glycolytic/gluco‐neogenic pathways; and in a reciprocal manner pyrophosphate is produced as an energy source during gluconeogenic carbon flow from F‐1,6‐P2 toward sucrose synthesis.
Spore germination and phytochrome biosynthesis in the fern Lygodium japonicum as affected by gabaculine and cycloheximide
Authors: Manabe Katsushi , Ibushi Norifumi , Nakayama Akisato , Takaya Shin‐ichi , Sugai Michizo
Published: May 2006

We investigated whether the gradual increase in phytochrome content in the fern Lygodium japonicum (Thunb.) Sw. during dark imbibition results from hydration or from biosynthesis of phytochrome. Addition of gabaculine or cycloheximide to the culture medium caused inhibitions of both red light‐induced spore germination and of the appearance of phytochrome in the spores. Fifty percent inhibition of both red light‐induced germination and of the appearance of phytochrome in the spores occurred at ca 10−7 M cycloheximide. Red light‐induced germination and phytochrome appearance were markedly inhibited by 10−4 M and completely by 10−3 M gabaculine, but germination induced by gibberellic acid was unaffected. Phytochrome was not detected in spores after forced hydration. These results suggest that the increase in phytochrome during imbibition was mainly due to de novo synthesis of the phytochrome apoprotein and to synthesis of the chromophore and/or proteins required for phytochrome formation, rather than to hydration of preexisting phytochrome molecules.
Activity of glyceraldehyde‐3‐phosphate dehydrogenase isozymes during photoperiodic floral induction in spinach leaves
Authors: Bonzon Marc , Simon Patrice , Agosti Robert Degli , Greppin Hubert , Wagner Edgar
Published: May 2006

The activity of NAD+ and NADP+‐dependent glyceraldehyde‐3‐phosphate dehydrogenase isozymes (EC 1.2.1.12 and EC 1.2.1.13, respectively) were measured in spinach (Spinacia oleracea L. cv. Nobel) leaves grown under different photoperiodic treatments in order to discriminate between the early events of floral induction and processes related to acclimation. Glycolysis‐linked isozyme activities were increased not only during floral induction and acclimation, but also during acclimation alone, suggesting that the changes in cytosolic activities were most probably associated with acclimation. In contrast, the chloroplast‐linked isozyme activities only increased during flower induction and appeared to be specifically associated with the initiation of the flowering process. The relative activity changes in the chloroplast and cytosol compartments may thus be supposed to be among the first signs of translation of the photoperiodic signal into cytosolic and cellular metabolic adaptation, whereby the leaf moves rapidly into a new metabolic state.
Mg2+‐ATPase activity in wheat root plasma membrane vesicles: Time‐dependence and effect of sucrose and detergents
Authors: Bérczi Alajos , Møller Ian M.
Published: May 2006

Purified plasma membrane vesicles were isolated in the presence of 250 mM sucrose from 7‐day‐old roots of Triticum aestivum L. cv. Drabant by aqueous polymer two‐phase partitioning. When added to a low‐salt medium containing 9‐aminoacridine (9‐AA), the vesicles caused a much larger total decrease in 9‐AA fluorescence when sucrose was absent than when sucrose was present. A slow component of the decrease was also larger in the absence of sucrose. Triton X‐100 reduced the decrease in 9‐AA fluorescence upon vesicle addition and abolished completely the slow component of the decrease. There was no correlation between the time‐dependence of 9‐AA fluorescence and that of the Mg2+‐ATPase described below.

The time course of Mg2+‐ATPase activity was followed by sampling at short intervals (down to 10 s) and analyzing for P, released. In the absence of detergent, the rates of P, release were linear from zero minutes, whether 250 mM sucrose was present or not, but the rate was 10−50% higher in the absence of sucrose than in its presence. Sucrose (250 mM) added during a minus‐sucrose assay lowered Mg2+‐ATPase activity within 2 min to the level observed with 250 mM sucrose present from the start. The effect of 25‐1 100 mM sucrose was tested and there was little or no effect below KM) mM. Above 100 mM sucrose the rate of P, release decreased drastically; at 1 100 mM sucrose the rate was ca 20% the rate at 25 mM sucrose. The inhibitory effect of sucrose was not alleviated by increased concentrations of Mg2+ and/or ATP. nor was it affected by the presence or absence of Triton X‐100. We conclude that sucrose somehow inhibits the Mg2+‐ATPase directly or affects the conformation of the plasma membrane in such a way as to inhibit the enzyme.

The presence of detergents increased Mg2+‐ATPase activity in the order Triton X‐100 (4–5‐fold) > Zwittergent 3–14 = Na‐cholate = octylglucoside > digitonin (2‐fold). In all cases optimal activity was observed at detergent concentrations at or below the critical micellar concentration. The detergent concentration curves could be simulated by the sum of a stimulatory and an inhibitory reaction. At the optimal concentration, digitonin gave a linear time‐course of P, release, whereas all the other detergents showed a distinct lag of 1–3 min before maximal rates were attained. The problems of using detergents in polarity assays are discussed.
Phenolamides during the ripening of dormant and non‐dormant seeds in different Petunia lines
Authors: Jassey Yves , Monin Jeannine
Published: May 2006

Phenolamides were extracted from reproductive organs and different capsule parts (fruit wall, placenta and seeds) of dormant and non‐dormant lines derived from the species Petunia hybrida hort,. Petunia axillaries Lam. B.S.P. and Petunia parodii Steere. The different compounds were separated by high‐pressure liquid chromatography and analyzed before pollination, during ripening, at ripeness and after 2 weeks of after‐ripening of the seeds. The extracts were examined particularly for the presence of an alkaline compound (X), which is a phenolic derivative of tryptophanamide and appears to be a biochemical marker for the dormancy of ripe dry seeds of Petunia. During capsule growth and seed ripening, compound X was not a marker for dormancy, although it occurred in the reproductive organs of seed‐parent plants. After pollination and fertilization, accumulation of compound X started mainly in the fruit wall, but in ripe dry capsules it was present entirely in the seeds. In contrast to compound X, neutral phenolamides were not detected in extracts from the fruit wall: and from the early stages of the capsule growth substantial accumulation took place only in the seeds.

Absence of compound X from ripe dry seeds appears as a necessary but not a sufficient condition for non‐dormancy.
Compound 48/80, a calmodulin antagonist, inhibits ion‐porter function in plant roots
Authors: Jacoby Benjamin , Rudich Braha
Published: May 2006

A rather specific inhibitor of calmodulin‐regulated functions, compound 48/80. inhibited 36Cl−, 86Rb+ and 22Na+ absorption by Hordeum vulgare, Phaseolus mungo and Zea mays roots. The compound did not inhibit plasmalemma or tonoplast Mg:2‐ATPase activity; neither did it inhibit or uncouple respiration, or affect ATP content and seemed also not to cause depolarization of the membrane potential of roots cells. Compound 48/80 inhibited the ΔpH‐mediated Cl−‐H+ symport in ATP‐depleted roots.
An abbreviated method for the isolation of mitochondria from storage tissues of oil seedlings
Authors: Luster Douglas G. , Fites Roger C.
Published: May 2006

High yields of metabolically active mitochondria can be rapidly isolated from reserve storage tissues of castor bean (Ricinus communis L.), cucumber (Cucumis sativus L., cv. Early Green Cluster), cotton (Gossypium hirsutum L., cv. Coker 711), and soybean (Glycine max L., cvs Forrest and Centennial) seedlings by application of crude homogenates to discontinuous sucrose gradients, allowing for a rapid separation of organelles from detrimental factors present in cell homogenates.
Gibberellin‐enhanced indole‐3‐acetic acid biosynthesis: D‐Tryptophan as the precursor of indole‐3‐acetic acid
Authors: Law David M.
Published: May 2006

Stem segments excised from light‐grown Pisum sativum L. (cv. Little Marvel) plants elongated in the presence of indole‐3‐acetic acid and its precursors, except for L‐tryptophan, which required the addition of gibberellin A, for induction of growth. Segment elongation was promoted by D‐tryptophan without a requirement for gibberellin, and growth in the presence of both D‐tryptophan and L‐tryptophan with gibberellin A3, was inhibited by the D‐aminotransferase inhibitor D‐cycloserine. Tryp‐tophan racemase activity was detected in apices and promoted conversion of L‐tryptophan to the D isomer; this activity was enhanced by gibberellin A3. When applied to apices of intact untreated plants, radiolabeled D‐tryptophan was converted to indole‐3‐acetic acid and indoleacetylaspartic acid much more readily than L‐tryptophan. Treatment of plants with gibberellin A3, 3 days prior to application of labeled tryptophan increased conversion of L‐tryptophan to the free auxin and its conjugate by more than 3‐fold, and led to labeling of N‐malonyl‐D‐tryptophan. It is proposed that gibberellin increases the biosynthesis of indole‐3‐acetic acid by regulating the conversion of L‐tryptophan to D‐tryptophan, which is then converted to the auxin.
Autolysis in vitro of cotton (Gossypium hirsutum) fibre cell walls
Authors: Bucheli P. , Buchala A. J. , Meier H.
Published: May 2006

Cotton (Gossypium hirsutum L. ev. Stoneville No. 406) fibres possess several types of cell wall‐bound (1→3)‐β‐glucanase activities and a significant amount of the (1→3)‐β‐glucan callose. When fibre cell wall fragments are incubated in vitro, free glucose is released. Such autolysis is barely measurable at the primary cell wall stage of development when the endogenous (1→3)‐β‐3‐glucan content is low. At the beginning of secondary cell wall formation, when the (1→3)‐β‐glucan is at a maximum, the rate of autolysis increases markedly and then remains more or less constant. Nojirimycin, a specific inhibitor of β‐glucosidase, decreases the amount of free glucose released and results in the production of a corresponding amount of (1→3)‐β‐linked oligosaccharides.
Gas exchange studies in two Portuguese grapevine cultivars
Authors: Chaves M. Manuela , Harley Peter C. , Tenhunen John D. , Lange Otto L.
Published: May 2006

Gas exchange characteristics of leaves of Vitis vinifera L. cvs Tinta Amarela and Periquita, two grapevine cultivars grown in distinct climatic regions of Portugal, were studied under natural and controlled conditions. Daily time courses of gas exchange were measured on both a hot, sunny day and a cooler, partly cloudy day. Responses of net photosynthesis to irradiance and internal partial pressure of CO2, were also obtained. A strong correlation between net photosynthesis (PN) and leaf conductance (gs) was found during the diurnal time courses of gas exchange, as well as a relatively constant internal partial pressure of CO2 (Pi), even under non‐steady‐state conditions. On the cloudless day, both PN and gs were lower in the afternoon than in the morning, despite similar conditions of leaf temperature, air to leaf water vapor deficit and irradiance. The response curves of net photosynthesis to internal CO2 showed linearity up to pi values of 50 Pa, possibly indicating a substantial excess of photosynthetic capacity. When measured at low partial pressures of O2 (1 kPa), PN became inhibited at high CO2 levels. Inhibition of PN at high CO2 was absent under normal levels of O2 (21 kPa). Significant differences in gas exchange characteristics were found between the two cultivars, with T. Amarela having higher rates under similar measurement conditions. In particular, the superior performance of T. Amarela at high temperatures may represent adaptation to the warmer conditions at its place of origin.
Distribution of free and bound forms of cis‐trans and trans‐trans abscisic acid in broad‐bean plants in relation to apical dominance
Authors: Everat‐Bourbouloux Andrée
Published: May 2006

Levels of endogenous abscisic acid (ABA; free and bound forms) have been determined by gas chromatography in stems and buds of broad‐bean plants (Vicia faba L. cv. Aguadulce) in relation to apical dominance. A downward gradient of free cis‐trans ABA occurred along the stem, from the apical bud to the roots. Except for the actively growing apical bud the levels of free cis‐trans ABA were higher in the buds than in the corresponding nodes. An inverse correlation can be set up between levels of free cis‐trans ABA and growth of buds, except for the cotyledonary ones. High levels of bound ABA (cis‐trans form) are correlated with the growth of the apical bud and that of the axillary bud ax1. The hormonal regulation of the growth of the cotyledonary buds, which contained high levels of trans‐trans ABA in bound forms, is apparently different from that of the other buds.
Isolation and characterization of multiple forms of maize leaf sucrose‐phosphate synthase
Authors: Kalt‐Torres W. , Kerr P. S. , Huber S. C.
Published: May 2006

Sucrose‐phosphate synthase SPS; (EC 2.4.1.14) from maize (Zea mays L. cv. Pioneer 3184) leaves was partially purified and kinetically characterized. Maize SPS was activated by glucose‐6‐phosphate (G‐6‐P) due to an increase in Vmax and a decrease in the Km for UDP‐glucose. The UDP‐glucose saturation profile was biphasic; thus two Km values for UDP‐glucose were calculated. Inhibition by inorganic phosphate was observed only in the presence of G‐6‐P. Chromatography of partially purified maize leaf extracts on hydroxyapatite resolved two forms of SPS activity, which differed in their affinity for UDP‐glucose and in the degree of activation by G‐6‐P. SPS was partially purified from maize leaves that were harvested in the light and in the dark. The light enzyme had a higher specific activity than the enzyme isolated from dark harvested leaves, and this difference persisted during enzyme purification. The apparent molecular weight (Stokes radius) of the light enzyme was 547 kDa, which was greater than that of the dark enzyme (457 kDa). Light and dark SPS differed in their affinities for UDP‐glucose in the absence G‐6‐P. Both the light and the dark SPS were activated by G‐6‐P; the Km for UDP‐glucose of the light enzyme was lowered by G‐6‐P, while the Km for UDP‐glucose for the dark enzyme remained unchanged. These results suggest that light activation involves a conformational change that results in differences in maximum velocity, substrate affinities and regulation by metabolites. Chromatography of either the light or dark SPS on hydroxyapatite yielded two peaks of enzyme activity, suggesting that the occurrence of the two activity peaks was not due to an interconversion of the light and dark forms.
Leaf senescence in a non‐yellowing mutant of Festuca pratensis: Degradation of carotenoids
Authors: Gut Hans , Rutz Charlotte , Matile Philippe , Thomas Howard
Published: May 2006

The loss of pigments was assessed in detached leaves of Festuca pratensis Huds. kept in permanent darkness. Two genotypes, a normal yellowing cultivar Rossa and a non‐yellowing mutant Bf 993 were compared with each other. Analysis of individual pigments, chlorophylls. β‐carotene, lutein, violaxanthin and neoxanthin was performed using HPLC. In the non‐yellowing genotype the high retention of chlorophylls was associated with an equally high retention of total carotenoids. Although the two genotypes differ markedly with regard to the rate of pigment loss, the ratios of yellow to green pigments did not change significantly during dark‐induced senescence. At the end of the senescence period β‐carotene was retained to a higher degree than the xanthophylls, particularly in the yellowing genotype. In the mutant leaves the ratio of chlorophyll a to b remained nearly constant, whereas in leaves of the normal genotype a preferential retention of chlorophyll b was observed towards the end of the senescence period. It is concluded that the thylakoids of the non‐yellowing genotype retain all the principal components of protein‐pigment complexes, i.e. chlorophylls, carotenoids and apoproteins. Possible explanations for the stability of these complexes in the mutant are discussed.
Starch content and distribution in excised watermelon cotyledons treated with benzyladenine
Authors: Longo Giovanna P. , Bracale Marcella , Valtorta Orestina
Published: May 2006

We have examined the effect of benzyladenine (BA) on amyloplast number and distribution in semithin cross‐sections of excised watermelon (Citrullus vulgaris Schrad., cv. Fairfax) cotyledons grown in the dark. The sections were stained with Lugol solution and observed with an immersion objective. In control cotyledons, amyloplasts were always more abundant and contain more starch grains than in BA‐treated cotyledons. The higher starch content was correlated with a higher ratio between starch synthetase (EC 2.4.1.21) and amylase (EC 3.2.1.1) activities in the controls. In the central zone of the mesophyll, the amyloplasts contained more starch grains than in the abaxial and adaxial (palisade) zones. The average number of amyloplasts per cell was different in the three zones, and followed a different time course in control and treated cotyledons. BA decreased this number, particularly in the adaxial zones. Our data seem to indicate a different function of starch in the central and in adaxial zone of the mesophyll. In the central zone starch is probably used as a source of carbohydrates for export to the embryo axis, while in the adaxial zone, where the transformation from amyloplast to etioplast is particularly pronounced, starch may be a reserve for organelle differentiation. BA stimulates the utilization of starch for both functions.
The regulation of respiration and growth of potato tuber callus by endogenous ethylene. Suppression of ethylene action by 2,5‐norbornadiene
Authors: Gude Henk , Rietveld Ellen , van der Plas Linus H. W.
Published: May 2006

The growth (fresh and dry weight increase) of potato tuber (Solanum tuberosum L. cv. Bintje) callus discs was stimulated by incubation in air with 500 ppm 2,5‐norbornadiene (NBD, a competitive inhibitor of ethylene action) and inhibited by incubation in air with 4 000 ppm NBD. Ethylene formation by the callus was stimulated by NBD. The development of the alternative pathway, measured in isolated mitochondria was inhibited by NBD in a concentration‐dependent way. The alternative pathway capacity, measured in vivo, was inhibited by 4 000 ppm NBD, but not by 500 ppm. Uninhibited in vivo respiration, which consists of cytochrome path activity and alternative path activity, was stimulated by the treatment with 500 ppm NBD. The main contribution to this stimulation was made by the cytochrome pathway. In 4 000 ppm NBD‐treated callus, uninhibited respiration seemed to be unaffected as a consequence of an inhibited cytochrome path activity, which was compensated by a stimulated alternative path activity. Both in 500 and 4 OIK) ppm NBD‐treated callus the alternative path activity in vivo was stimulated.

The regulatory role for endogenous ethylene in potato tuber callus is discussed in relation to: 1) The induction of respiratory pathways, 2) the supply of reduction equivalents in vivo and 3) growth.
Uptake and metabolism of taurine in the green alga Chlorella fusca
Authors: Biedlingmaier Susanne , Schmidt Ahlert
Published: May 2006

Taurine entered the alga Chlorella fusca Shihira et Krauss strain 21l‐8b via a pH and energy‐dependent system (“permease”). Transport followed triphasic kinetics from 10−6 to 10−2 M with Km values for taurine of 5.4 × 10−5, 4.1 × l0−4 and l.5 × 10−3 M. This uptake system was specific for sulfonic acids and showed no affinity for α‐ and β ‐amino acids or Na+; thus the permease of C. fusca is different from all known taurine transport systems with respect to structural specificity and lack of Na+ ‐dependence. Uptake was not observed in sulfate‐grown algae but developed as a response to sulfate limitation within 2 h. Sulfate addition caused a rapid decline in taurine transport capacity. Labeled taurine was rapidly metabolized in C. fusca to sulfate and ethanolamine, suggesting oxidative hydrolysis as the mechanism of C‐S bond cleavage. Further incorporation of these catabolic products in C ‐ and S ‐metabolism was demonstrated. Taurine catabolism was also detected in other green algae and some cyanobacteria.