bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature dependent redistribution of organic nitrogen during ‘dry' storage of tulip bulbs cv. Apeldoorn
Authors: Lambrechts H. , Ravestein H. , Kollöffel C. 
Published: May 2006

Tulip bulbs cv. Apeldoorn are dry stored at 5°C for 12 weeks to ensure subsequent optimal flowering when planted in the greenhouse at higher temperatures of 17–20°C. Both temperature and duration of the cold treatment determine the subsequent rate of the shoot elongation, the time until anthesis and the flower size, pigmentation and water content. In search for cold‐specific physiological changes, possibly related to the development of the potential of proper flowering (flowering preparation), we studied the redistribution of organic nitrogen in both cooled (5°C) and non‐cooled (17°C) bulbs.During 12 weeks of dry storage, the total protein‐ and free amino acid‐nitrogen content decreased in the scales, whereas the opposite was found in the basal plate (with root primordia) and the shoot. In the shoot, this occurred significantly more at 17°C than at 5°C. At the same time, there was a tissue‐specific change in the free amino acid composition in both cooled and non‐cooled bulbs. Changes specific for the 5°C treatment were only found for the alanine content, in both the basal plate (with root primordia) and the shoot, and for the proline, asparagine, threonine, glycine and isoleucine content, in the shoot only. These changes are, for the greater part, completed within the first 6–8 weeks of dry storage. Bulbs stored for such a short period of time at 5°C still show flowering disorders. Thus, flowering preparation is only partly accompanied by changes in free amino acid contents.
Paraquat toxicity in Pisum sativum: Effects on soluble and membrane‐bound proteins
Authors: Peleg Itzhak , Zer Hagit , Chevion Mordechal 
Published: May 2006

The effects of paraquat (PQ) on Pisum sativum L. proteins were investigated in vivo in a new experimental system utilizing 10‐day‐old plant cuts.A marked decrease in the specific activity of membrane‐bound Ca2+‐dependent ATPase was recorded, while that of Mg2+‐dependent ATPase remained unchanged. Concurrently with a drop in the total plant protein, the specific activities of the three cytoplasmic enzymes, malate dehydrogenase, hydroxypyruvate reductase and triose‐phosphate isomerase, were also found to decrease. The effect on various enzymes involved in cellular defense mechanisms was also studied: glutathione reductase and superoxide dismutase activities increased, while ascorbate peroxidase was not affected.These findings shed light on the selectivity of PQ‐induced injurious processes, focusing on protein homeostasis mechanisms in the membrane and cytoplasmic compartments at the cellular level, as well as on the prominent role played by enzymatic defense systems against PQ poisoning.
Partitioning of nitrogen and biomass at a range of N‐addition rates and their consequences for growth and gas exchange in two perennial grasses from inland dunes
Authors: Boot René G. A. , Schildwacht Peter M. , Lambers Hans 
Published: May 2006

This paper describes the effects of nitrgen supply on the partitioning of biomass and nitrogen of Agrostis vinealis(L.) Schreber and Corynephorus canescens(L.) Beauv., two perennial grasses of dry, nutrient‐poor inland dunes, and their consequences for growth and gas exchange. At a given plant nitrogen concentration (PNC) the two species allocate the same relative amount of dry matter and nitrogen to their leaves. However, A. vinealis allocates more dry matter and nitrogen to its roots and less to its above‐ground support tissue than C. canescens. Both the leaf weight ratio and leaf nitrogen ratio increase with increasing PNC. Despite species‐specific differences in growth form and leaf morphology, the leaf area ratio and specific leaf area of the two species are similar, both at high and low PNC. At intermediate nitrogen supply, and thus intemediate PNC, however, A. vinealis has a higher leaf area ratio and specific leaf area than C. canescens.The two species exhibit a similar positive relationship when either the rate of net photosynthesis or the rate of shoot respiration are compared to the leaf nitrogen concentration, all expressed per unit leaf weight. The rate of net photosynthesis per unit Jeafnitrogen (PNUE) of the two species increases with decreasing leaf nitrogen concentration per unit leaf weight. C. canescens has a higher PNUE at low, and a lower PNUE at high leaf nitrogen concentration per unit leaf weight than A. vinealis. At non‐limiting nitrogen supply, A. vinealis has a higher nitrogen productivity and net assimilation rate and a similar PNC and leaf area ratio as compared to C. canescens, which explains the higher relative growth rate (RGRmax) of A. vinealis. At growth‐limiting nitrogen supply C. canescens achieves a similar relative growth rate at a lower PNC than A. vinealis.
The regulation of nitrogen accumulation in the grain of wheat plants (Triticum aestivum)
Authors: Barneix Atilio J. , Arnozis Patricia A. , Guitman Maria R. 
Published: May 2006

Nitrogen accumulation in the ear of wheat plants (Triticum aestivum L. cv. Klein Chamaco) during ear growth was studied under 4 experimental conditions. Plants were grown in pots with Perlite or soil, and fertilized with nutrient solutions. In one experiment the plants were grown in a greenhouse and supplied with high (16mM) or low (1.6 mM) N in the nutrient solutions until anthesis, and then with or without nitrogen supply until ripening. In a second experiment the plants were grown with high N supply until anthesis, and then for half of the plants light intensity was decreased by 50%, and at the same time. N supply was terminated for half of the plants within each light treatment. A third experiment was similar to the previous one, but was carried out in a growth cabinet under 20% of the maximal irradiance in the greenhouse. In a fourth experiment half the ear was excised at anthesis in half of the plants, and these plants were then supplied with or without nitrogen.In all experiments there was a linear relation between the rate of N accumulation and the rate of ear growth. A wide range of final individual grain weights and N concentration was observed among the experiments. The same maximum N concentration was observed for all grain sizes, although the N concentration could be different between grains of the same size. The grain N concentration correlated with the rate of N accumulation per unit of ear weight increase during ear growth. It is suggested that in wheat plants there is a dependence of nitrogen transport on carbon transport to the ear, and to the ear, and that the final grain N concentration is determined by the N/C ratio exported from the vegetative tissues.
Aluminium effects on Scenedesmus obtusiusculus with different phosphorus status. I. Mineral uptake
Authors: Greger Maria , Tillberg Jan‐Eric , Johansson Monica 
Published: May 2006

Synchronously growing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 and 72 h in the presence or absence of phosphorus. Aluminium chloride (37, 74, 111, 148, 185, or 222 μmol) was added daily to 1 l cell suspension at the end of the cell division phase. As AlCl3 decreases the pH of the growth medium, controls were run in media with low pH in the absence of AlCl3. Samples for analysis of the internal (net uptake) and external (bound to cell surface) levels of Al, Mg, P, Ca, and Fe were taken every second hour during a 24 h period or once after 72 h.The investigation shows that the intracellular aluminium in Scenedesmus affects the nutrient status of the cells. A high intracellular level of Al is in consort with an enhancement of the intracellular fractions of Mg, P, Ca and Fe. The increase in net uptake of the minerals measured in the presence of Al is not due to an Al‐induced lowering of the pH, caused by Al. The concentrations of Al, Mg, P, Ca and Fe in the cells are generally lower during the dark period of the cell cycle, when the cells are dividing, than during the light period. A peak in mineral concentration of the cells could be monitored in the middle of the 24 h life cycle of the cells. The intracellular Al level is higher when the growth medium is low in P than in phosphorus‐rich medium, due to precipitation of aluminium‐phosphate both in medium and at cell surfaces. The extracellular Al and P fractions are thus higher in the presence than in the absence of P. The highest Al content monitored in the cells is about 100 nmol Al (106 cells)−1. A large fraction of Al initially taken up after addition to the medium is subsequently released from the cells during the 24 h cell cycle. The results are interpreted as Al effects on the plasma membrane, thus indirectly affecting various mechanisms for ion transport across the membrane. There are also indications that a surface covered with aluminium‐phosphate, formed at high P level in the medium, may prevent ion uptake.
Changes in the level of MACC during cold hardening and dehardening in winter wheat
Authors: Macháčková Ivana , Hanišová Alena , Krekule Jan 
Published: May 2006

Changes in the level of 1‐(malonylamino)‐cyclopropane‐1‐carboxylic acid (MACC) were determined in 6 winter wheat cultivars during cold hardening at 4°C. The cultivars differed by one degree of frost resistance within the range of degree II to VII of the COMECON scale. The time‐course of changes in MACC level showed a similar pattern in all 6 cultivars; i.e. increase till day 6, no changes for the next 10 days, and then a steady decrease till the end of the hardening period. There was little difference between the final and the initial levels. The increase of MACC level, expressed as per cent of the original level, was not directly correlated with either the degree of frost resistance of the actual percentage of survival. In some cultivars. mean errors exceeded the difference in MACC accumulation between cultivars closest on the resistance scale.The fate of MACC during the second half of hardening and after transfer of plants to 25°C was studied in cultivars Bezostaya and San Pastore. During the second half of the hardening period the level of MACC decreased in the leaves of both cultivars, but increased significantly in the roots. Within two days of transfer of the hardened plants to 25°C, the MACC level in leaves increased again, while that in the roots decreased. This finding, together with the preliminary evidence of very low MACC metabolism, strongly suggest that MACC accumulates in roots during the hardening period and when transferred to 25°C, it moves from roots to leaves.
Measurements of intra‐and extracellular pH in the liverwort Conocephalum conicum during action potentials
Authors: Trębacz K. 
Published: May 2006

During action potentials triggered by electricity and light, measurements of intra‐ and extracellular pH in the liverwort Conocephalum conicum L. were carried out by the use of antimony‐filled H+‐sensitive microelectrodes. Intracellular pH increased transiently by about 0.05 unit in the course of an action potential, while extracellular pH, measured at the surface of the thallus, remained unchanged. Switching the light off caused a transient increase in intracellular pH by less than 0.1 unit. Turning the light on produced a fast pH decrease by about 0.15 unit followed by a slow increase. When the light was intensive enough, the action potential thus triggered caused a slight increase in intracellular pH superimposed on the phase of a slow pH increment.The magnitude and time course of the intracellular pH changes seem insufficient for a role as messenger between action potential and the up to 100% increase in the rate of respiration that has been registered in Conocephalum conicum as a consequence of excitation.
Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in Chlamydomonas reinhardtii
Authors: Ramazanov Z. , Cárdenas J. 
Published: May 2006

Interaction between induction of carbonic anhydrase (CA) activity, induction of inorganic carbon (Ci) concentrating mechanisms and the photorespiratory glycolate pathway has been studied in wild type 6145c and photorespiratory mutant 18–7F (low in phosphoglycolate phosphatase activity) cells of C. reinhardtii. Cell transfer from high CO2 (5%, v/v) to low CO2 (0.03%) provoked an increase of extracellular and total (extracellular plus intracellular) CA in both wild type and mutant cells. During adaptation to low CO2 conditions, both strains excreted ammonium to the medium at a similar rate in the presence of l‐methionine‐d‐l‐sulfoximine (MSX), an inhibitor of glutamine synthetase (GS). MSX also provoked ammonium excretion by air adapted wild type and mutant cells, even though both strains had high levels of CA activity and of Ci concentrating activities.GS increased in both strains after transfer from high to low CO2 conditions. However, this increase was abolished by aminooxyacetate, an inhibitor of the glyoxylate‐serine aminotransferase, and by glycolaldehyde, an inhibitor of triose phosphate to ribulose 1,5‐bisphosphate conversion. CA synthesis did not occur in the presence of either aminooxyacetate or glycolaldehyde. Algae grown in high CO2 in the presence of aminooxyacetate did not induce Ci concentrating mechanisms. Integration of these three processes, i.e., CA synthesis, Ci‐concentration, and photorespiratory glycolate pathway is proposed in the framework of carbon metabolism of the alga.
The role of hormones on morphogenesis of thin layer explants from normal and transgenic tobacco plants
Authors: Altamura Maria Maddalena , Capitani Francesca 
Published: May 2006

The organogenic potential of thin layer stem explants of non‐reproductive tobacco plants was tested on a hormone‐free medium and under various hormonal conditions. A comparison was made between thin layers excised from normal and transgenic plants at the same developmental stage. The transgenic plants were transformed by insertion of TR‐ and TL‐DNA from Agrobacterium rhizogenes 1855 root‐inducing plasmid. The aim was to identify hormonal conditions capable of stimulating the expression of the flowering competence present in the differentiated stem tissues at the induced stage before any visible sign of transition to reproductive development. Flower neoformation, observed at the end of the culture period (day 25), occurred on untransformed thin layers only with kinetin treatment. Explants from transgenic plants showed flower bud regeneration on hormone‐free medium, indoleacetic acid alone (1 μM), kinetin alone (1 μM), and most abundantly on indoleacetic acid plus kinetin (1 μM each). No flower formation was observed on indolebutyric acid plus kinetin (10 μM and 0.1 μM, respectively) in both normal and transgenic explants. The latter treatment enhanced rooting instead, above all in the transgenic explants. On hormone‐free medium vegetative bud formation was well expressed both by untransformed and transgenic explants, and enhanced by the combined, equimolar concentrations of indoleacetic acid and kinetin.The results show that cytokinin allows flowering in florally determined stem explants from normal plants. In the transgenic explants, the flowering response increases when indoleacetic acid is added to cytokinin, thus suggesting a role for auxin in enhancing the expression of the florally determined state in thin cell layers of non‐reproductive plants.
Flow cytometry and plant protoplast cell biology
Authors: Bergounioux Catherine , Brown Spencer C. , Petit Patrice X. 
Published: May 2006

Flow cytometry, which requires individualized or single cell preparations, is particularly adapted to studies of protoplast biology. It has been developed at three levels: descriptions of populations, measurement of cell function, and positive or negative selection of rare protoplast types. It enables measurement of several parameters in single protoplasts at a high rate of analysis. Without protoplast purification, excellent resolution of subpopulations is still possible. The quantitative data obtained on each protoplast normally have relative units but absolute calibration of intensity scale is available. Specific probes allow one to correlate multiparameter data on each cell. DNA, RNA, proteins, metabolites, organelles, virus and plasmid content of protoplasts have been described.The essential conceptual advantage of flow cytometry is the processing of heterogeneous material, typical of biological samples, but inadequately handled through overall mean values. Biological properties of protoplast subpopulations are followed using fluorescence intensity as a measure of DNA versus RNA or protein synthesis, cytoplasmic and nuclear antigens, membrane potentials, membrane viscosity, cell wall regeneration and pH.
Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution
Authors: Irigoyen J. J. , Emerich D. W. , Sánchez‐Díaz M. 
Published: May 2006

Exchange rates of CO2 and H2O and metabolism of hydrogen peroxide have been measured in leaves of alfalfa ev. Aragón) under drought stress. The inhibitory effect of drought upon photosynthesis depended on the severity of the stress treatment. Leaf water potential (Ψleaf) down to,‐2.8 MPa reduced CO2 availability due to stomatal closure and inhibited the rate of photosynthesis. Leaf water potential lower than,‐2.8 MPa directly affected CO2 fixation, although CO2 was not limiting. Transpiration was more affected by stornatal closure than photosynthesis, which led to am apparent improvement in WUE (water use efficiency). Alfalfa leaves with Ψleaf lower than,‐2.0 MPa had an increased quantum requirement, probably due to the severe stress effect on photoenergetic reactions.Ethylene evolution from alfalfa leaves increased when they were subjected to Ψleaf of,‐ 1.6 MPa. Under more severe stress, the leaves showed low or almost no ethylene production. In parallel with the increase in ethyiene production, alfalfa leaves exhibited an increased membrane lipid peroxidation index (maloridialdehyde content) and an increased peroxide content. Superoxide disinutase activity (SOD; EC 1.15.1.1) was not affected by drought stress. Catalase (EC 1.11.1.6) was inhibited at slight stress, but significantly increased at a Ψleaf of ‐2.0 MPa. Peroxidase (EC 1.11.1.7) was progressively inhibited as drought stress developed. The possible implication of reactive O2 intermediates in drought stress‐induced senescence of alfalfa leaves is discussed in the light of the pattern of enzymatic scavenging systems.
The effect of exposure to microgravity on the development and structural organisation of plant protoplasts flown on Biokosmos 9
Authors: Rasmussen O. , Klimchuk D. A. , Kordyum E. L. , Danevich L. A. , Tarnavskaya E. B. , Lozovaya V. V. , Tairbekov M.G. , Baggemd C. , Iversen T. ‐H. 
Published: May 2006

Preparatory experiments for the IML‐1 (International Microgravity Laboratory) mission to be flown on the Space Shuttle in January, 1992, were performed on a 14 day flight on Biokosmos 9 (Kosmos 2044) in September 1989. The purpose of the experiment was to study the effect of weightlessness on protoplast regeneration. Problems, with late access to the space vehicle meant that the newly isolated protoplasts from hypocotyl cells of rapeseed (Brassica napus L. cv Niklas) and suspension cultures of carrot (Daucus carota L. cv Nobo) had to be stored at 4°C for 36 h prior to the launch of the biosatellite, in order to delay cell wall regeneration until the samples were in orbit. In the flight samples and the ground controls, a portion of the total number of protoplasts regenerated cell walls. The growth of flight rapeseed cells was only 56% compared to the ground control; the respective growth of carrot cells in orbit was 82% of the ground control. Analysis demonstrated that the peroxidase activity and the amount of protein was lower in the flight samples than in the ground controls. The number of different isoenzymes was also decreased in the flight samples. A 54% decrease in the production of cellulose was found in rapeseed, and a 71% decrease in carrot. Hemicellulose production was also decreased in the flight samples compared to the ground controls.Ultrastructural analysis of the cell aggregates from the protoplasts cultured in orbit, demonstrated that hydrolysis and disappearance of reserve starcb occurred in the flight cell plastids. The mitochondria were more varied in appearance in the flight samples than in the ground control cells. An increased frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds was also observed. Fluorescence analysis showed a decrease of the calcium content in cell cultures under space flight compared to the ground controls.One general effect of the stay onboard the space vehicle was a retardation of the regeneration processes. Callus cultures obtained from the flight samples grew very slowly compared to callus regenerated from the ground controls, and two years after the Biokosmos 9 flight there appears to be no further growth in the samples exposed to microgravity. Callus cultures from the ground controls, however, continue to grow well. A simulation experiment for IML‐1 performed in January 1990 at ESTEC (European Space Technology Center), The Netherlands, has resulted in regenerated plants. These observations are discussed and compared to the results obtained on Biokosmos 9.
Theories and methods on plant nutrition and growth
Authors: Ingestad Torsten , I. Ågren Gõran 
Published: May 2006

A theory comprising two basic concepts relating nutrition and growth is presented. The first concept is a nutrient flux model and is based upon studies of plants at constant internal nutrient concentrations, where a formal mathematical derivation shows that the relative uptake rate (RU) and the relative growth rate (RG) are equal. Deviations from equality are results of experimental insufficiencies and errors. The second concept is based on the observation that RG is linearly related to the internal nutrient concentration. The slope represents nutrient productivity (Pn), an important parameter expressing growth rate per unit of nutrient. Light and the plant genome, for example, influence the value of the proportionality factor, Pn, but not the formal relationship between the internal nutrient concentration and RGNot only the theory itself but many results and conclusions are very different from those obtained with traditional methods. In experiments where RU was controlled during the exponential period of growth, the relationships between treatment (the relative addition rate, RA), nutrient uptake (RU) and growth (RG) were reproduced with extremely low variability. In agreement with theory, internal nutrient concentration and RG remained stable over time (steady‐state).An extension of the theory is based upon the empirical assumption that after exponential growth, self‐shading and ageing reduce Pn in proportion to biomass. This assumption has been successfully applied in predicting growth of forest stands, but the nature of the growth reduction is little understood. The generalized model has few parameters and can easily be rewritten to suit different experimental aims, for example to establish reference values and to model changes in soil fertility. Further extension and understanding of the model and different interpretations of the parameters are discussed.