bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrate assimilation and nitrogen circulation in Austrian pine
Authors: Martin Francis , Chemardin Michel , Gadal Pierre 
Published: April 2006

Nitrate uptake, reduction and translocation were examined in 5‐week‐old Austrian pines (Pinus nigra Arnold var. nigricans Host.) during exposure to 5 mM NaNO3. The rate of nitrate uptake was linear during the 7 h light period. 15N‐NO3− was detected in all parts of the pine except in the needles. By the 7th hour, 43% of the absorbed nitrate had been reduced, and this increased to 64% by the 24th hour. The major part of the total reduction occurred in the roots at this growth stage. Accumulation of 15N in reduced soluble and insoluble fractions was more prevalent in roots than in shoots. In the needles, the translocated nitrogen was mainly incorporated into the insoluble fraction. It is likely that most of the nitrogen from nitrate was transported from the roots to the aerial organs as organic nitrogen; however part of the upward nitrogen flux took place as nitrate ions.An experiment in which an exposure for 24 h to 5 mM Na15NO3 was followed by 13 days exposure to Na14NO3 (pulse chase experiment) revealed a half time of about 1 day for depletion of root nitrate. A large part of this depletion was due to the loss of 15N‐NO3− to the nutrient solution. The remaining pool of 15N‐nitrate was partitioned between a metabolically inactive and an active pool. During the chase period, the simultaneous decrease of 15N‐incorporation in the soluble N fraction and increase in the insoluble N fraction in different pine parts, particularly in the needles, suggested that protein synthesis occurred mostly in young tissues of the shoot and was the major sink of the newly absorbed 15N‐NO3.
In vitro initiation of adventitious structures in relation to the abscission zone in needle explants of Picea abies: anatomical considerations
Authors: Jansson Eva , Bornman Chris H. 
Published: April 2006

A comparison of the regeneration potential of needles of different ages in Picea abies emphasized the importance of taking into account the manner of explantation as well as the state of differentiation of the abscission zone. Generally, response in terms of initiation of adventitious structures decreased progressively not only with needle age (5 to 10 to 15 mm long) but also with the distance from the abscission zone towards the tip, that is, distally. On a bud‐induction medium adventitious shoot but primordia were produced proximally and distally (except for the very tip) of the weakly‐developed abscission zone in needles ca. 5 mm and shorter. In needles between 5 and 10 mm long the various cell types of the abscission zone commenced differentiation, and adventitious structures (shoot bud and other primordia) were formed proximal and immediately distal to it. In needles ca. 15 mm long, in which the abscission zone's hyaline, separation and protective layers became well‐developed and where senescence of the distal part commenced, response was limited to proximal tissues. Divisions giving rise to adventitious primordia distal to the abscission zone arose from epidermal cells proper and, in a more acropetal position, also from subsidiary cells of the stomata. Cells of the hypodermis contributed only in the near‐distal region of the abscission zone in younger needles, and before commencing differentiation into fibres.When excised carefully, the explant consists of a leaf plus a peg‐like cushion of axillary, meristematic tissue proximal to the abscission zone and capable of ready regeneration. In view of the apparent relationship between age and the stage of development of the abscission zone, it was concluded that there exists a critical needle length which should not be exceeded when attempting in vitro induction of organ primordia.
Relations entre production et localisation de mycosporine et morphogenèses reproductrices chez le Pyrénomycète Gnomonia leptostyla
Authors: Fayret Jacques , Vito Joël 
Published: April 2006

Relations between production and localisation of mycosporin and reproductive morphogenesis in the Pyrenomycete Gnomonia leptostyla.The production of mycosporin (P310) has been analysed in Gnomonia leptostyla (FT.) Ces. et de Not. during mycelial growth and reproductive morphogenesis (macroconidiogenesis, microconidiogenesis and differentiation of perithecia). Conidiogenesis is induced in illuminated cultures while darkness promotes perithecial development. At 20°C, the cultures produce either macroconidia or perithecia with abortive sporophyte. Microconidia differentiation and perithecia maturation require low temperature (10°C). Mycosporin is, at all times, present in the thallus. However, the concentration of mycosporin in highest in the conidiogenous thallus, intermediate in the perithecial thallus. and lowest in the vegetative mycelium. In the conidiogenous thallus, macroconidia and microconidia are both sites of mycosporin accumulation. On the contrary, in the perithecial thallus, mycosporin levels are not higher in perithecia than in mycelia, even during their maturation period. The quantitative variations of mycosporin during the thallus development and its accumulation inside conidia suggest translocation from sites of synthesis towards reproductive cells.
Oak seedlings grown in different light qualities
Authors: Axelsson Lennart , Klockare Birgitta , Sundqvist Christer 
Published: April 2006

Oak seedlings (Quercus robur L.) were germinated in darkness for 3 weeks and then given continuous long wavelength far‐red light (LFR; wavelengths longer than 700 nm). A control group of seedlings was kept in darkness. After 2 additional weeks the chlorophyll formation ability in red light was examined in the different seedlings. The stability of the protochlorophyll(ide) and chlorophyll(ide) forms to high intensity red irradiation was also measured.Oak seedlings grown in darkness accumulated protochlorophyll(ide) (6 μg per g fresh matter). Absorption spectra and fluorescence spectra indicated the presence of more protochlorophyll(ide)628–632 than protochlorophyllide650–657. The level of protochlorophyll(ide) was higher in leaves of plants cultivated in LFR light (13 μg per g fresh matter) than in leaves of dark grown plants. 12% of the protochlorophyll(ide) was esterified in both cases.The level of protochlorophyll(ide)628–632 in LFR grown oaks varied with the age of the leaves, being higher in the older (basal) leaves, but also in the very youngest (top‐most) leaves. The ability of the leaves to form photostable chlorophyll in red light showed a similar age dependence, being low in rather young and in older leaves. A low ability to form photostable chlorophyll thus appears to be correlated with a high content of protochlorophyll(ide)628–632.Upon irradiation only the protochlorophyllide650–657 was transformed to chlorophyllide. After this phototransformation the chlorophyllide peak at 684 nm shifted to 671 nm within about 30 min in darkness. This shift took place without any accompanying change in photostability of the chlorophyll(ide). Upon irradiation with strong red light a similar shift took place within one minute. This indicates that the chlorophyllide after phototransformation was rather loosely bound to the photoreducing enzyme. The development towards photostable chlorophyll forms consists of three phases and is discussed.
Biosynthesis of stress ethylene in soybean seedlings: Similarities to endogenous ethylene biosynthesis
Authors: Hogsett W. E. , Raba R. M. , Tingey D. T. 
Published: April 2006

The similarity of stress ethylene biosynthesis in whole plants to endogenous ethylene biosynthesis was investigated using two inhibitors of ethylene biosynthesis, aminoethoxyvinylglycine (AVG) and cobalt chloride (Co2+); and the intermediates, methionine, S‐adenosylmethionine (SAM), and 1‐aminocyclopropane‐1‐carboxylic acid (ACC), of basal ethylene biosynthesis. Stress ethylene production induced by ozone, cadmium, or 2,4‐dichlorophenoxyacetic acid was inhibited in hydroponically‐grown soybean seedlings in a concentration‐dependent manner by both AVG and CO2+. The ethylene intermediates evoked responses in intact seedlings similar to that described for endogenous ethylene production in isolated vegetative tissue. The addition of SAM to the hydroponic system relieved AVG inhibition of stress ethylene production. Feeding ACC to the seedlings resulted in increased ethylene production independent of stress application or prior AVG inhibition. Cobalt inhibition of stress ethylene production was relieved by increasing concentrations of ACC. A short lag period of 12–18 min was observed in stress ethylene production following a 30‐min ozone exposure. Addition of cycloheximide partially inhibited ozone‐induced ethylene production.These results suggest a common pathway in whole plants for stress ethylene production and endogenous ethylene biosynthesis.
Biosynthèse de la sticticine chez le lichen Lobaria laetevirens
Authors: Bernard T. , Goas G. 
Published: April 2006

Biosynthesis of sticticin in the lichen Lobaria laetevirens (Lightf.) Zahlbr.Sticticin is the most important soluble nitrogenous compound in the thallus of L. laetevirens from which it was isolated for the first time. As its concentration can exceed 1 M when thallus water content reaches 10–12%, it might play an efficient role in osmoregulation. Its biosynthesis was investigated by supplying the lichen with L‐[U‐14C]tyrosine, DL‐3,4‐dihydroxyphenyl [3‐14C]alanine and L‐[methyl‐14C]me‐thionine. The main pathway involves, first, N‐methylations of tyrosine, then a hydroxylation of the ring and finally an esterification of the acid function.
Effect of pollination or treatment with growth regulators on levels of extractable hormones in tomato ovaries and young fruits
Authors: Sjut Volkert , Bangerth Fritz 
Published: April 2006

Levels of extractable free indolyl‐3‐acetic acid (IAA), gibberellin‐like substances (GA's), and abscisic acid (ABA) were analysed in tomato ovaries (Lycopersicon esculentum Mill.) before pollination as well as in fruits 5 and 10 days after pollination or treatment with growth regulators to induce parthenocarpic fruit development. Growth regulators applied were a naphthoquinone (bendroquinone), an auxin (4‐CPA), a morphactin (CME), and a benzothiadiazole (DU).The initial high levels of ABA (2.7 μg/g dry weight) in unpollinated ovaries decreased to one third or less after 5 and 10 days. In contrast levels of IAA increased from 80 up to 180 ng/g dry weight. Activity of GA's could be detected only in young fruits but not in unpollinated ovaries.The possible relevance of these findings for tomato fruit‐set is discussed.
Effect of cycloheximide and renewal of phosphorus supply on surface acid phosphatase activity of phosphorus deficient tomato roots
Authors: Boutin Jean‐Pierre , Provot Madeleine , Roux Louis 
Published: April 2006

Changes in surface phosphatase activity of tomato root (Lycopersicon esculentum L. cv. Marmande) have been studied in relation to its P status. Experiments were performed either with excised roots cultured in vitro or with entire plants (split root method) grown in various conditions (P deficiency, renewal of P supply). In some experiments different parts of the root were separated according to their P status during their primary growth.The surface phosphatase in different root parts depends first of all on P status during their primary growth. Moreover the cell wall phosphatase of tomato root is stable in vivo. Thus the changes in the surface phosphatase of a root system result mainly from the growth of new roots, which bear an enzyme activity that is either high if they are P deficient or low if they are P provided. The control of the cell wall phosphatase synthesis appears to be a repression‐derepression process mediated by the root cell concentration in some P compound, probably orthophosphate. Cycloheximide stops or alters the growth of excised roots, so that this inhibitor was found unsuitable to study the synthesis of cell wall phosphatase under in vivo conditions. Split root experiment shows that the increase in surface phosphatase activity may occur locally, i.e. only in the parts of the root system which are P deficient. Agricultural and ecological aspects of these findings are pointed out.
Adaptation of corn roots to exogenously applied auxin
Authors: Gougler Judy A. , Evans Michael L. 
Published: April 2006

The ability of intact primary roots of corn (Zea mays L. Bear Hybrid WF 9 × 38) to adapt to growth‐inhibitory concentrations of auxin was studied using a highly sensitive position sensor transducer to measure growth. The timing, concentration dependence and temperature dependence of adaptation were studied as well as the time course of loss of adaptation upon removal of auxin. The rate of root elongation is inhibited 80% within 40 min after application of 10−7M IAA. Within 90 min growth rate begins to recover. For concentrations of IAA equal to or greater than 10−7M, recovery of growth rate (adaptation) is incomplete. Corn roots show a similar pattern of adaptation to the synthetic auxins NAA and 2,4‐D. The Q10 for adaptation is high (3.2) and comparable to that for root growth (3.3). Upon removal of exogenous IAA, loss of adaptation occurs with full sensitivity to the hormone regained within 20 min.Based on the auxin specificity and the Q10 for adaptation it is concluded that adaptation occurs neither by a change in the auxin degradation capacity of the root nor by a diffusional redistribution of applied auxin. It is suggested that adaptation involves metabolic processes, perhaps a metabolically dependent alteration of the number or affinity of auxin binding sites.
Elastic response of the roots of field crops
Authors: Whiteley G. M. , Dexter A. R. 
Published: April 2006

The elasticity of root tips was investigated in experiments of the static clamped‐beam type. The response was non‐linear. The results were interpreted in terms of a generalized elastic modulus M, and two parameters, α and β, which account for the non‐linearity.Seminal axes and primary lateral roots of 16 crop species grown in the laboratory show significant inter‐species differences but insignificant inter‐variety differences in the elastic properties. A smaller set of results for field‐grown roots with two tillage treatments shows that, in nearly all cases, the elastic modulus is smaller and the diameter is larger than with laboratory‐grown roots. Environmental factors such as water potential, and nutrition have significant influences on the diameters and elastic behaviour of roots.
Effects of moisture stress and senescence on the synthesis of abscisic acid in the primary leaves of bean
Authors: Eze J. M. O. , Dumbroff E. B. , Thompson J. E. 
Published: April 2006

The capacity for ABA synthesis during moisture stress of primary leaves of bean (Phaseolus vulgaris cv. Kinghorn) was defined in terms of leaf age and associated changes in several physiological parameters. The leaves were fully expanded within 9 days after emergence. Fresh and dry weights per unit of leaf area fell during all 5 weeks of the study, from leaf expansion through advanced senescence. The most significant losses in weight occurred during the third and fourth weeks and coincided with a sharp drop in protein content that began immediately after full‐leaf. Chlorophyll concentrations declined rapidly during leaf expansion and then more slowly through the end of the fifth week when the leaves were ready to abscise. The ratio of chlorophyll a to b rose steeply over the first 4 weeks of the study.Although a rapid loss of protein provided the most definitive indication of the early stages of leaf senescence, a marked decline in the ability to synthesize ABA was more closely associated with the termination of rapid leaf growth. This relationship between leaf expansion and the capacity for ABA synthesis during moisture stress remained unchanged when ABA content was expressed on a per unit chlorophyll, protein or dry weight basis.A water deficit between 5 and 10% of fresh weight, representing a drop in water potential of less than 150 kPa, was sufficient to initiate accumulation of ABA in young leaves. Slightly more intensive levels of stress were required to stimulate ABA synthesis in senescent leaves, but total accumulation was less than one‐tenth of the amount recorded in the younger tissue.
Effects of varied nitrogen stress on growth and nutrition in three Salix clones
Authors: Ericsson Tom 
Published: April 2006

The ability of Salix aquatica Smith, S. fragilis L. and S. viminalis L. to absorb nitrogen at varied growth rates was investigated in nutrient solutions. The effects of five nitrogen addition rates on growth rates, nitrogen contents of the plants, nitrogen concentration of the media, and dry matter distribution between roots, stems and leaves, were studied.These clones are highly efficient in absorbing nitrogen at low concentrations in the root medium, independent of growth rate. Strong linear regressions were found between any two of the three factors: relative rate of nitrogen supply (RN), nitrogen content (plant), and relative growth rate (R). Dry matter production per unit nitrogen taken up and unit time (N‐productivity) and per unit nitrogen taken up independent of time (N‐efficiency) was closely correlated to the nitrogen status of the plant. Root development was favoured in the sub‐optimum treatments, and leaf development in the optimum treatments. With regard to their ability to absorb nitrogen, these Salix clones appear satisfactory for efficient short rotation energy forestry.
Purification and molecular properties of nitrite reductase from Anabaena sp. 7119
Authors: Mendez José M. , Vega José M. 
Published: April 2006

Ferredoxin‐nitrite reductase (EC 1.7.7.1.) from the cyanobacteria Anabaena sp. 7119 has been purified 763‐fold with a specific activity of 21.5 units/nig protein (0.358 μkatals/mg). The enzyme has a molecular mass of 52,000 daltons with a Stokes radius of 3.09 nm and a sedimentation coefficient of 4.07 S. The cellular level of nitrite reductase activity gradually increases in response to the addition of increasing amounts of iron to the culture medium.When partially purified nitrite reductase preparations are subjected to sucrose‐density‐gradient centrifugation there is a dose correspondence between nitrite reductase activity and absorbance at 400 nm. This suggests the association of a heme chromophore with the enzyme. Furthermore, the presence of an iron‐sulfur center is suggested by a close association of acid‐labile sulfide with nitrite reductase activity. Carbon monoxide inhibits nitrite reductase activity. The nature and kinetics of this reaction are comparable to other siroheme‐containing nitrite reductases.
The apparent viscosity of the protoplasm of subepidermal stem basis cells of Pisum sativum. Relation to aging, drought tolerance and water stress
Authors: Lee‐Stadelmann Ok Young , Hulme Dale A. , Stadelmann Eduard J. 
Published: April 2006

Plants of Pisum sativum L. cv. Alaska wilt resistant were subjected to two different water stress regimes under controlled environment conditions: watering was stopped either on the 7th day (early stress) or on the 21st day (late stress) after planting. Plants under the early stress regime developed drought tolerance (adapted), while those under late stress did not. The apparent viscosity of the protoplasm of subepidermal stem basis cells was analyzed by the centrifugation and plasmolysis form method during the entire growth period.The apparent viscosity of the subepidermal stem basis cells changed with plant age and was highest in 3‐week‐old plants. In controls the relation of apparent viscosity to age was the same when measured under full turgor and in relaxed state. Under early stress condition, however, the pattern of the viscosity changes with plant age was significantly different for turgescent and relaxed cells. In four week old plants, a higher apparent viscosity was measured in relaxed adapted cells than in relaxed control cells. It is suggested that the higher apparent viscosity is the result of a delayed cell aging.Apparent viscosity was inversely proportional to soil moisture content and the osmotic potential of the cell sap for the cells of late stress plants, whereas no clear relation was found for the cells of early stress plants. This difference may indicate two mechanisms of viscosity changes: 1) osmotic dehydration of the protoplasm under water stress (passive viscosity change), 2) changes in the amount, hydration or architecture of macromolecules present in the cytoplasm (active viscosity change). Whereas differences in the apparent viscosity between control and stressed cells may not be the cause of drought tolerance, they seem to indicate the development of drought tolerance. Water stress history and plant age were the most critical factors controlling the apparent viscosity changes observed.
Distribution of ATPases in wheat root membranes separated by phase partition
Authors: Lundborg Tomas , Widell Susanne , Larsson Christer 
Published: April 2006

The distribution of divalent cation stimulated ATPase activity in relation to the distribution of other enzyme activities was studied for membrane fractions from wheat roots (Tritium aestivum L. cv. Svenno). A homogenate from dark grown plants was fractionated by differential centrifugation at 1000 g, 10,000 g, 30,000 g and 60,000 g (1, 10, 30 and 60 KP fractions), followed by partition in an aqueous polymer two‐phase system, using polyethylene glycol 4000/dextran T500 concentrations of 5.7/5.7, 5.9/5.9, 6.1/6.1, 6.3/6.3 and 6.5/6.5% (w/w). The 30 KP fraction was also separated by counter‐current distribution id a 6.3/6.3% two‐phase system. Protein and activities of Ca2+, Mg2+, and Mn2+ stimulated ATPases. cytochrome oxidase, light induced absorbance change (LIAC) related to cyt b reductions, inosine diphosphatase and NADH dependent antimycin A insensitive cytochrome c reductase were measured.The partition of ATPase activities stimulated by Ca2+, Mg2+ or Mn2+ was similar at all polymer concentrations tested, indicating: a low cation specificity of the dominating ATPases. The distribution of ATPases. agreed with different marker enzymes in different centrifuge fractions. Divalent cation stimulated ATPases were evidently related to several of the organelles. In the different fractions the distribution of ATPase activity should then follow that of the marker enzyme of the dominant organelle. From studies with different polymer concentrations the 6.3/6.3‐system was selected for further separation of the membranes in the 30 KP fraction by counter‐current distribution. By this method one fraction was obtained, which probably consisted of plasmalemma and was free from mitochondrial material. Indications for plasmalemma in this fraction were a) similar partition as protoplasts and b) high LIAC activity.
8‐14C‐Zeatin metabolites and their transport from leaf to phloem exudate of Yucca
Authors: Vonk C. R. , Davelaar E. 
Published: April 2006

Transport and metabolism of 8‐14 C‐zeatin, applied to an attached de‐tipped one‐year‐old mature leaf of a Yucca plant bearing a bleeding inflorescent stalk, has been studied. Radioactive zeatin ribotide was found in the exudate of the bleeding inflorescence, which was collected over a period of 5 days. Radioactive zeatin ribotide was mainly extracted from the fed leaf. Minor conversion products in this leaf were zeatin ribotide, zeatin‐o‐β‐glucoside and zeatinriboside o‐β‐glucoside.In not zeatin fed plants, zeatin‐o‐β‐glucoside was tentatively identified as the main endogenous cytokinin in one‐year‐old mature leaves. In the bleeding sap of not treated plants no free bases of zeatin or zeatin ribosides were found. After alkaline phosphatase treatment zeatin‐riboside was detected by combined gas chromatography‐mass spectrometry, indicating the presence of zeatin ribotide in the bleeding sap. High β‐glucosidase activity was found in the stern.Results suggest that stared cytokinin glucosides from Yucca leaves are, converted by β‐glucosidase in leaves and stem, transported through the inflorescent stalk as zeatin nucleotides.