bluuebunny/crossref_metadata_2025 huggingface dataset:
Loss of tubulin during cold treatment of cultured carrot cells
Authors: Okamura Shoji , Kakiuchi Masato , Sano Atsuko , Kawajiri Masayo
Published: May 2006

When carrot cells, Daucus carota L. cv. Kintoki, in suspension culture were chilled on ice, more than 90% of the cortical microtubules disappeared within an hour. Colchicine‐binding activity in the soluble extract decreased gradually during the prolonged cold treatment and after 4 days reached a minimum level. In SDS‐polyacrylamide gel electrophoretograms of the cold‐treated cell extracts, the bands corresponding to tubulin subunits disappeared, whereas most of the other protein bands remained. The level of tubulin was restored within a day after the cells were returned to 267deg;C. The relative ratio of the two major β‐tubulin isoforms was reversed during the cold treatment, indicating that the cold sensitivity of tubulin differs according to its molecular species. When the cells were returned to 26°C, the ratio was restored to the original state within 24 h.
The impact of homologous and heterologous nurse cells on the division capability of sparsely plated cells
Authors: Bellincampi D. , Morpurgo R. , Morpurgo G.
Published: May 2006

The growth‐promoting effects of nurse cells of carrot, tomato, patato, maize, bean, carnation and two species of tobacco were studied on carrot, tomato, tobacco and potato cells plated at low densities. In an area immediately below the nurse cells the plating efficiency was very high and found to be independent of cell density. In an area outside the nurse cells, in some cases, the plating efficiency tended to be much higher in combinations with cells from a heterologous source as compared with those from a homologous source. Moreover, in the same area with some combinations the plating efficiency decreased when cell density was lowered, while with other combinations this phenomenon did not occur. This decrease was independent of the absolute value of plating efficiency. In experiments in which the concentration of conditioning factors was presumably changed, no significant difference in the plating efficiency was noticed. We therefore suggest that different plating efficiencies observed with heterologous nurse cells were not due to a higher level of conditioning factors, but rather to the production of different types of conditioning factors that are presumably degraded with different efficiency.
Changes in peroxidase activity and in peroxidase isozymes in carrot callus
Authors: Wakamatsu Kunimitsu , Takahama Umeo
Published: May 2006

Activity of soluble peroxidase and its isozyme patterns in carrot (Daucus carota L.) callus after excision and transfer to fresh Murashige and Skoog (MS) culture medium was investigated. The activity decreased markedly until day 1 and then increased gradually during days 7–10 at room temperature. The rapid initial decrease of the activity was also observed at low temperature (2°C) as well as in the presence of cycloheximide. However, the subsequent increase in the peroxidase activity after day I was slower at low temperature than at room temperature, and was not detected in the presence of cycloheximide. Activity of catalase decreased slightly within 4 days and cycloheximide enhanced the decrease of the activity. Two cationic and one anionic peroxidase isozymes disappeared or decreased markedly within the first day and one cationic and anionic peroxidase recovered 3–6 days after excision.
Carbonic anhydrases in higher plants and aquatic microorganisms
Authors: Sültemeyer Dieter , Schmidt Claudia , Fock Heinrich P.
Published: May 2006

At physiological pH‐values CO2 and HCO−3are the dominant inorganic carbon species and the interconversion between both is catalyzed by carbonic anhydrase (EC 4.2.1.1). This enzyme is widely distributed among photosynthetic organisms. In the first part of the review, the similarities and the differences of carbonic anhydrases from plants and animals are briefly described. In the second part recent advances in molecular biology to understand the structure of carbonic anhydrase from higher terrestrial plants as well as its involvement in photosynthetic CO2 fixation are summarized. Lastly, the review deals with the presence of carbonic anhydrase in aquatic organisms including cyanobacteria, microalgae, macroalgae and angiosperms. Evidence for the presence of extracellular and intracellular isozymes in these organisms are discussed. The properties and function(s) of carbonic anhydrase during the operation of the inorganic carbon concentrating mechanism are also described.
Effect of light and 2,4‐dichlorophenoxyacetic acid on the level of mRNAs for phenylalanine ammonia‐lyase and chalcone synthase in carrot cells cultured in suspension
Authors: Takeda Junko , Abe Shunnosuke , Hirose Yukio , Ozeki Yoshihiro
Published: May 2006

Changes in the amount of mRNA for phenylalanine ammonia‐lyase (PAL, EC 4. 3. 1. 5) and chalcone synthase (CHS, EC 2. 3. 1. 74) induced by light were investigated in carrot (Daucus carota L. cv. Kurodagosun) cells cultured in suspension. Cells were cultured for 5 days in 2,4‐dichlorophenoxy acetic acid (2,4‐D)‐free medium and absolute darkness. Transcription of pal and chs genes was induced by irradiation at day 5, resulting in the induction of anthocyanin synthesis. PAL mRNA transcripts were rapidly and transiently up‐regulated within 6 h after onset of irradiation, after which they were immediately down‐regulated. Then, PAL mRNA increased again slowly, the time course being coordinated with induction of CHS transcription and anthocyanin synthesis. The semi‐quantitative polymerase chain reaction (PCR) and primer extension using gene specific oligonucleotides for pal genes revealed that two different pal genes were induced sequentially by light. The rapid and transient induction of the pal gene was not related to anthocyanin synthesis, but was identical to that induced by dilution or transfer effect. This slowly‐induced pal gene, which was induced in parallel to the chs gene, corresponded to the pal gene which was induced for anthocyanin synthesis. Anthocyanin synthesis was induced by simultaneous activation of both ant‐pal and chs genes, and both mRNAs remained at a high level during anthocyanin synthesis. Expression of ant‐pal and chs was partially repressed by either depletion of light or addition of 2,4‐D. These genes were completely repressed by addition of 2,4‐D in darkness. Therefore, the two signals may act at different points. Trn‐pal was not repressed by depletion of light or addition of 2,4‐D.
Subcellular immuno‐localization, amino acid composition and partial amino acid sequences of α‐l,4‐glucan phosphorylase of Gracilaria spp (Rhodophyta)
Authors: Yu S. , Gómez‐Pinchetti J.‐L. , Garcia‐Reina G. , Ek B. , Pedersén M.
Published: May 2006

Antibodies have been raised against an α‐l,4‐glucan phosphorylase (EC 2. 4. 1. 1) purified from the red alga Gracilaria chilensis. Localization of α‐l,4‐glucan phosphorylase in thin sections of G. chilensis and G. tenuistipitata was performed using immuno‐gold labelling and transmission electron microscopy. The enzyme was localized in the cytosol and around the cytosolic starch granules of the algal cells. The labelling was not associated with the chloroplast or the cell wall. Amino acid composition of the red algal phosphorylase was quite similar to that of potato tuber and rabbit muscle phosphorylases. Partial amino acid sequences showed 48, 54 and 65% homology with the rabbit, potato and Escherichia coli enzymes, respectively.
Purification of a β‐galactosidase from rice shoots and its involvement in hydrolysis of the natural substrate in cell walls
Authors: Konno Haruyoshi , Tsumuki Hisaaki
Published: May 2006

Several glycosidase and glycanase activities have been detected in homogenates of rice (Oryza sativa L. cv. Nipponbare) shoots after successive extraction with K‐phosphate (pH 7. 0) and buffer containing 3 M LiCl. The major β‐D‐galactosidase (EC 3. 2. 1. 23) present in the buffer‐soluble protein fraction was purified to electrophoretic homogeneity by a combination of chromatographic techniques including DEAE‐Sepharose CL‐6B, Sephacryl S‐200HR and p‐aminophcnyl‐β‐D‐thiogalactopyranoside–Sepharose 4B. Analysis by denaturing gel electrophoresis revealed a single polypeptide chain with an apparent molecular mass of 42 kDa. Similar to the value of 40 kDa estimated for the native protein by gel‐permeation. The isoelectric point was pH 6. 0. The Km and Vmax values for p‐nitrophenyl (PNP)‐β‐D‐galactopyra‐noside were 0. 63 mM and 0. 32 mmol (mg protein)−1 h−1, respectively. Maximum activity in McIlvaine buffer occurred at pH 3. 4, and the activity was inhibited by Ag2+, Cu2+. Hg2+, p‐chloromercuribenzoate (PCMB) and D‐galactono‐l,4‐lactone. The enzyme hydrolyzed larchwood arabinogalactan in an exo‐fashion, and acted weakly on arabinosyl and galactosyl residue‐rich polymer of pectic polysaccharides and cell walls from rice shoots.
Effect of low rhizosphere oxygen on growth, nitrogen fixation and nodule morphology in lucerne
Authors: Arrese‐Igor C. , Royuela M. , de Lorenzo C. , de Felipe M. R. , Aparicio‐Tejo P. M.
Published: May 2006

Oxygen shortage in soils can occur following a wide range of natural circumstances, affecting the plant's physiology. In this paper the performance of nodulated lucerne plants under severe hypoxia is examined and the mechanisms involved to achieve this adaptation are discussed. Nodulated lucerne plants (Medicago sativa L.) were grown with their rooting medium exposed to 1 or 21 kPa oxygen. Final yield, as expressed on a shoot dry weight basis, was unaffected but root and nodule dry weights were reduced by 50%. Water content in roots and nodules was higher at 1 kPa as a result of the formation of aerenchyma. Specific acetylene reduction activity was higher in hypoxic nodules as a consequence of modified nodule structure, although they were more sensitive to the presence of acetylene or nitrate. Root respiration was insensitive to changes in external oxygen supply, therefore providing adequate support for mineral uptake. Nodule respiration rates were 5 times higher in control plants when measured as CO2 evolution, whereas no differences were observed in O2 uptake. It is suggested that adaptation of nodulated lucerne to low oxygen concentrations involves changes in photosynthate allocation and nodule morphology, which provide a more efficient nitrogen fixation.
Osmotic regulation of assimilate unloading from seed coats of Vicia faba. Role of turgor and identification of turgor‐dependent fluxes
Authors: Patrick J. W.
Published: May 2006

Osmotic regulation of assimilate efflux from excised coats of developing Vicia faba (cv. Coles Prolific) seed was examined by exposing these to bathing solutions (adjusted to –0. 02 to –0. 75 MPa with sorbitol) introduced into the cavity vacated by the embryo. 14C photosynthate efflux was found to be independent of solution osmotic potentials below –0. 63 MPa. At higher osmotic potentials, efflux was stimulated and exhibited a biphasic response to osmotic potential with apparent saturation being reached at –0. 37 MPa. Efflux could be repeatedly stimulated and slowed by exposing seed coats to solutions of high and low osmotic potentials, respectively. Manipulation of components of tissue water potential, with slowly‐ and rapidly‐permeating osmotica, demonstrated that turgor functioned as the signal regulating 14C photosynthate efflux. Com‐partmental analysis of 14C photosynthate preloaded seed coats was consistent with exchange from 4 kinetically‐distinct compartments. The kinetics of turgor‐dependent efflux exhibited characteristics consistent with the transport mechanism residing in the plasma membranes of the unloading cells. These characteristics included the rapidity (<2 min) of the efflux response to turgor increases, similar rate constants for efflux from the putative turgor‐sensitive and cytoplasmic compartments and the apparent small pool size from which turgor‐dependent efflux could repeatedly occur. In contrast, influx of [14C] sucrose across the plasma and tonoplast membranes was found to be insensitive to turgor. The plasma membrane [14C] sucrose influx was unaffected by p‐chloromercuribenzenesulfonic acid and erythrosin B and exhibited a linear dependence on the external sucrose concentration. This behaviour suggested that influx across the plasma membrane occurs by passive diffusion. Preloading excised seed coats with a range of solutes demonstrated that turgor‐dependent efflux exhibited partial solute selectivity. Based on these findings, it is proposed that turgor controls assimilate exchange from the seed coat by regulating an efflux mechanism located in the plasma membranes of the unloading cells.
Cold‐induced changes in the polysome pattern and protein synthesis in winter rye (Secale cereale) leaves
Authors: Antikainen Mervi , Pihakaski Seppo
Published: May 2006

Cold‐induced changes in the polysome pattern and protein synthesis were analyzed in winter rye, Secale cereale L. cv. Voima, during one week's cold stress treatment, which was performed by transferring the 7‐day‐old plants from the greenhouse (25°C, long‐day conditions) to 3°C and a photoperiod of 10. 5 h. Freezing resistance determined by electrolyte leakage increased significantly upon cold stress starting from LT50 value –5°C. and reaching –9°C on the day 7 of cold exposure. After 4 weeks at low temperature, plants reached an LT50 of –12°C. The polysome content increased markedly during cold stress compared to the control plants. After 2 weeks of cold treatment the polysome content decreased to the same level as that in control plants. The size‐class distribution of polysomes showed a high proportion of large protein synthesizing polysomes in cold‐stressed plants. After 2 weeks the values were comparable to those in control plants. Cold‐induced proteins were detected using 35S‐labelled methionine for in vitro translations. At least 2 new polypeptides, Mr 30000 and 18000, were induced on the first day of cold stress and continued to be expressed at low temperatures 4 weeks later.
Energy requirements for maintenance of ion concentrations in roots
Authors: Bouma T. J. , De Visser R.
Published: May 2006

Maintenance of ion gradients across plant membranes is considered to be an important process requiring respiratory energy in plant tissues. In order to test this hypothesis, roots of intact plants of potato (Solanum tuberosum L. cv. Alcmaria and cv. Pimpernel) were incubated in a closed circulation system. Electrical conductivity of the solution surrounding these roots was continuously monitored to determine total ion efflux into demineralized water. Anion efflux rate from the symplast was 35 neq (g dry weight)−1 s−1. In combination with literature data on the specific costs of ion transport, this efflux rate yields the respiration rate associated with re‐uptake balancing efflux (i. e. maintenance of cellular ion concentrations). The results suggest that energy costs associated with re‐uptake of ions may account for up to 25–50% of the total respiratory costs involved in ion influx.
Internal carbon dioxide and ethylene levels in ripening tomato fruit attached to or detached from the plant
Authors: Saltveit Mikal E.
Published: May 2006

The carbon dioxide and ethylene concentrations in tomato fruit (Lycopersicon esculentum cv. Castelmart) and their stage of ripeness (characteristic external color changes) were periodically measured in fruit attached to and detached from the plant. An external collection apparatus was attached to the surface of individual tomato fruit to permit non‐destructive sampling of internal gases. The concentration of carbon dioxide and ethylene in the collection apparatus reached 95% of the concentration in the fruit after 8 h. Gas samples were collected every 24 h. A characteristic climacteric surge in carbon dioxide (2‐fold) and ethylene (10‐fold) concentration occurred coincident with ripening of detached tomato fruit. Fruit attached to the plant exhibited a climacteric rise in ethylene (20‐fold) concentration during ripening, but only a linear increase in carbon dioxide concentration. The carbon dioxide concentration increases in attached fruit during ripening, but the increase is a continuation of the linear increase seen in both attached and detached fruit before ripening and does not exhibit the characteristic pattern normally associated with ripening climacteric fruit. In tomato fruit, it appears that a respiratory climacteric per se, which has been considered intrinsic to the ripening of certain fruit, may not be necessary for the ripening of “climacteric” fruit at all, but instead may be an artifact of using harvested fruit.
The photoactivated toxin cercosporin as a tool in fungal photobiology
Authors: Daub Margaret E. , Ehrenshaft Marilyn
Published: May 2006

Cercospora species are a highly successful group of fungi which pathogenize diverse species of economically important plants. Many Cercospora species produce a unique photoactivated and photoinduced polyketide toxin, cercosporin, which has been implicated as a pathogenicity factor. Illuminated cercosporin interacts with molecular oxygen to produce highly toxic singlet oxygen. Although nearly all organisms tested, including plants, mice and most fungi, are susceptible to cercosporin‐mediated cell damage, Cercospora species are resistant. In general, little is known about how organisms protect themselves against singlet oxygen. Studies on how Cercospora species avoid autotoxicity are proving to be a valuable model in understanding this process in other systems. Furthermore, advances are being made in the understanding of how light regulates gene expression and cercosporin synthesis in Cercospora species. These studies are helping to elucidate mechanisms of gene regulation and light signal transduction for an environmental signal important in numerous fungal developmental processes, including secondary metabolite production.
The effect of aluminum exposure on root respiration in an aluminum‐sensitive and an aluminum‐tolerant cultivar of Triticum aestivum
Authors: Collier Donald E. , Ackermann Frank , Somers Daryl J. , Cummins W. Raymond , Atkin Owen K.
Published: May 2006

The effects of aluminum (Al) exposure on intact root respiration of an Al‐sensitive (Scout‐66) and an Al‐tolerant (Atlas‐66) cultivar of Triticum aestivum were investigated. Exposure to a wide range of Al concentrations (0–900 μmol) for 4 days stimulated respiration along the energy‐conserving cytochrome pathway in both cultivars and increased the ratio of maintenance respiration to growth respiration. The maximum rate of Scout‐66 root respiration occurred after exposure to 100–200 μmol Al. Atlas‐66 root respiration peaked after exposure to 300–400 μmol Al. Similarly, calculations of theoretical adenosine 5′‐triphosphate (ATP) production indicated that maximum daily rate of ATP production also increased upon exposure to Al in both cultivars, with peak ATP production occurring during peak respiration. Maximum root respiration rates in both cultivars were related to the Al concentration that inhibited root growth. Temporal exposure to 200 μmol Al quickly stopped root growth and stimulated cytochrome pathway respiration in Scout‐66 after 4 days. Atlas‐66 root growth and respiration were unaffected by 200 μmol Al. These results suggest that Al exposure imposes a demand for additional metabolic energy. A model describing Al effects on root respiration is presented
Growth characteristics of newly initiated cladodes of Opuntia ficusindica as affected by shading, drought and elevated CO2
Authors: Luo Yiqi , Nobel Park S.
Published: May 2006

Biomass accumulation and area expansion of newly initiated cladodes of Opuntia ficus‐indica were studied to help understand the high productivity of this Crassulacean acid metabolism species. In a glasshouse, both dry weight and area increased more and more rapidly for about 30 days and then increased linearly with time up to 63 days. The relative growth rate averaged 0. 12 day‐1, comparable to values for productive C3 and C4 plants. New cladodes initiated on basal cladodes with 2‐fold higher initial dry weight grew twice as fast. Drought reduced biomass accumulation and area expansion of new cladodes by 62 and 52%, respectively. A 70% reduction in irradiation decreased biomass accumulation of new cladodes by 17% and their thickness by 11%. In a growth chamber containing 720 μmol Co2 (mol air)‐1, biomass of newly initiated cladodes was 7% higher, area was 8% less, specific mass was 16% higher and less carbohydrate was translocated from basal cladodes than for 360 μmol Co2 mol‐1. The large capacity for storage of carbohydrate and water in basal cladodes of O. ficus‐indica apparently buffered environmental stresses, thereby reducing their effects on growth of daughter cladodes
Effects of triadimefon and osmotic stress on plasma membrane composition and ATPase activity in white spruce (Picea glauca) needles
Authors: Sailerova Eva , Zwiazek Janusz J.
Published: May 2006

White spruce [Picea glauca (Moench) Voss.] seedlings were grown in solution culture and treated with 20 mg I‐1 triadimefon [1‐(chlorophenoxy)‐3,3‐dimethyl‐1‐(1,2,4‐triazol‐1‐yl)‐2‐butanol] for 4 weeks and then subjected to osmotic stress with polyethylene glycol 3350. Water potentials and electrolyte leakage were measured in control and triadimefon‐treated seedlings before and after the plants were subjected to osmotic stress. The plasma membranes were isolated from needles to study their lipid composition and the activity of plasma‐membrane bound ATPase. Triadimefon treatment reduced water potentials and increased leakage of electrolytes from seedlings. However, when the seedlings were exposed to osmotic stress, triadimefon‐treated plants maintained higher water potentials and leaked less electrolytes compared with the control plants. Both triadimefon and osmotic stress treatments inhibited the activity of plasma membrane‐bound ATPase and altered the composition of free sterols in the plasma membranes. Triadimefon‐treated plants contained traces of campesterol, which was not present in control. Osmotic stress drastically reduced phospholipid:protein and sterol:protein ratios and increased sterol:phospholipid ratios in the plasma membranes
Effect of anti‐DNA methylation drugs on growth, level of methylated DNA, peroxidase activity and ethylene production of Bryonia dioica internodes
Authors: Galaud Jean‐Philippe , Gaspar Thomas , Boyer Nicole
Published: May 2006

A previous paper (Galaud et al. 1993. Physiol. Plant. 87: 25–30) reported a rapid demethylation of DNA after mechanical rubbing of young Bryonia dioica internodes, leading to growth inhibition. In order to assess an eventual causative role of DNA demethylation in the mechanisms underlying thigmomorphogenesis, the effects of the anti‐DNA methylation drugs, 5‐azacytosine (5‐azacyt) and 5‐azacytidine (5‐azacyd) were investigated. Treatment with 5‐azacyd induced a decrease of the methylated DNA level. This was accompanied by an increase of peroxidase activity and of ethylene production. On the contrary, 5‐azacyt had no significant effect on growth, peroxidase activity and ethylene production. The use of 5‐azacyd as an inducer of DNA demethylation is discussed in relation to the control of gene expression
Transport of 1‐aminocyclopropane‐1‐carboxylic acid into isolated maize mesophyll vacuoles
Authors: Saftner Robert A. , Martin Melinda N.
Published: May 2006

Intracellular transport of the ethylene precursor, I‐aminocyclopropane‐1‐carboxylic acid (ACC) can change the ACC concentration in cell compartments and impact ethylene biosynthesis. Transport of ACC into isolated maize (Zea mays L.) mesophyll vacuoles was studied by silicon layer flotation filtering. The transport of ACC across the tonoplast was stimulated 2. 4‐ to 8. 1‐fold by 5 mM MgATP, showed saturation kinetics with an apparent Km for ACC of 20 μM, and was optimal at 25°C. Transport of ACC was sensitive to the pH of the medium, falling as external pH rose. Effectors known to inhibit proton‐translocating ATPases (N, N‐dicyclohexylcarbodiimide) and to collapse the electrical (thiocyanate, valinomycin) and chemical (carbonylcyanide m‐chlorophenylhydrazone, gramicidin) potential gradients for protons across the tonoplast all reduced ACC transport. The nonhydrolyzable MgATP analog. Mg adenylyl‐imidodiphosphate, stimulated ACC transport as effectively as MgATP. Other nucleotides (MgADP, MgCTP, MgUTP, MgGTP) and MgPPi had little or no effect. These results suggest that ACC uptake into isolated maize mesophyll vacuoles is carrier mediated, is dependent upon an electrochemical potential gradient for protons and is specifically regulated, but not necessarily energized, by MgATP
Translocation ‐ A key factor limiting the efficiency of nitrogen fixation in legume nodules
Authors: Streeter John G.
Published: May 2006

A hypothesis is presented that the availability of water for export of nitrogenous products from legume nodules is a major factor limiting the efficiency of symbiotic nitrogen fixation. Water for export of solutes in the xylem probably depends largely on the import of water and reduced carbon in the phloeum, and one function of respiration may be to dispose of reduced carbon in order to increase the supply of water. A second hypothesis presented is that control of gas diffusion in soybean nodules is largely restricted to the cortex nearby the vascular bundles, thus making possible the linkage of solute balances in xylem and phloem with resistance to diffusion. These concepts are used in a re‐examination of literature on manipulations of nodules and nodulated plants such as lowering of light levels, water stress, defoliation, stem girdling, and alteration of oxygen supply. The concept of translocation as a major factor limiting efficiency of symbiotic fixation is consistent with the failure of superior rhizobial isolates to improve N input significantly, and this limitation could also prevent exploitation of superior bacterial symbionts in the future
Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties
Authors: Martínez‐Carraseo R. , Cervantes E. , Pérez P. , Morcuende R. , Del Molino I. M. Martín
Published: May 2006

Photosynthesis and carbohydrate content of flag leaves were measured during the post‐anthesis period of three spring wheat (Triticum aestivum L.) varieties grown with two levels of nitrogen supply, with ears either left intact or with the upper halves removed at anthesis. With low nitrogen supply, removing the upper half of the ear increased photosynthesis in the varieties Shasta and Anza, but not in Yecora. With high nitrogen, removing half ears inhibited photosynthesis in Yecora but had no effect on the other two varieties. Early in grain growth, halving ears decreased the contents of glucose, fructose (hexose), fructans and starch in leaves of Shasta and Anza, and increased those of Yecora, grown with low nitrogen level. The treatment of the ear increased hexose content of leaves of the three varieties supplied with high nitrogen level but had no effect on fructan and starch contents. Neither with high nor with low nitrogen level was leaf sucrose content affected by the treatment of the ear. There were significant correlations among levels of carbohydrates, the level of hexoses being most closely related to that of fructans. The rate of photosynthesis showed a significant negative regression over hexose levels.
Implications of N acquisition from atmospheric NH3 for acid‐bAse and cation‐anion balance of Lolium perenne
Authors: Wollenweber B. , Raven J. A.
Published: May 2006

In the atmosphere, ammonia (NH3) is the third most abundant N species which, due to various natural and anthropogenic sources, can locally reach high concentrations. The acquisition of atmospheric NH3 by plant shoots will lead to two opposing effects on acid‐base balance. Absorption and dissolution of NH3 will cause an alkalinisation, while the assimilation of NH3 results in an acidification. Different rates of these processes would lead to an acid‐base imbalance with consequences for the ionic balance of the plant. As there is only a limited capacity for biochemical disposal of excess H+ in shoots, pH regulation may involve a pattern of (in)organic ion flow between shoots and roots followed by H+/OH− extrusion into the media via roots. The acquisition of NH3 as additional N source should lead to a reduction in the ratio of mol H+/OH− gained per mol N assimilated.

We have recently investigated the NH3 acquisition by Lolium perenne L. cv. Centurion and studied the effects of gas phase NH3 on growth, acid‐base balance and water‐use efficiency. The experiments, therefore, included the application of a range of 14NH3 to the shoots and of 15N as NO3−, NH4+ or NH4NO3 to the roots. After a summary of the main conclusions from those experiments, we discuss the implications of the use of atmospheric NH3 for the mineral composition of the plants.

Over the range of NH3 supplied, plants from all treatments could utilize gas‐phase NH3. Plants receiving NO3− via their roots had a higher capacity to use gaseous NH3 than those growing with NH4+. NH3 assimilation in shoots reduced both the acid load with NH4+ nutrition and the alkaline load with NO3− supply to the roots. The most significant effect of fumigation on the ion balance was an increase in K+ within all treatments, and this effect was highest in the NH4+‐fed plants. The results of the experiments support predictions of a combination of neutralizing biochemical reactions as well as transport of organic anion salts between shoots and roots as possible acid‐base regulation mechanisms of the whole plant.
Effects of N‐supply on the rates of photosynthesis and shoot and root respiration of inherently fast‐ and slow‐growing monocotyledonous species
Authors: Van Der Werf Adrie , van Nuenen Marc , Visser Andries J. , Lambers Hans
Published: May 2006

Are there intrinsic differences in the rates of photosynthesis, shoot‐ and root‐respiration between inherently fast‐ and slow‐growing monocotyledons at high and low nitrogen supply? To analyze this question we grew 5 monocotyledons, widely differing in their inherent relative growth rate at high and low nitrogen supply in a growth room. Nitrate was exponentially added to the plants, enabling us to compare inherent differences in plant characteristics, without any effect of species differences in the ability to take up nutrients.

At high nitrogen supply, the fast‐growing species from productive habitats had a higher photosynthetic nitrogen use efficiency and rate of root respiration than the slow‐growing ones from unproductive habitats. Only minor differences were observed in their rates of photosynthesis and shoot respiration per unit leaf area. At low nitrogen supply, the rates of photosynthesis and shoot‐ and root respiration decreased for all species, even though there were no longer any differences in these processes between inherently fast‐ and slow‐growing species. The photosynthetic nitrogen use efficiency increased for all species, and no differences were found among species.

Differences in the photosynthetic nitrogen use efficiency among species and nitrogen treatments are discussed in terms of the utilization of the photosynthetic apparatus, whereas differences in respiration rate are discussed in terms of the energy demand for growth, maintenance and ion uptake and their related specific respiratory energy costs. It is concluded that the relatively high abundance of slow‐growing species compared to fast‐growing ones in unproductive habitats is unlikely to be explained by differences in rates of photosynthesis and respiration or in photosynthetic nitrogen use efficiency.
Nitrate permease from Azotobacter chroococcum
Authors: Paneque A. , Muñoz‐Centeno M. C. , Ruiz M. T. , Cejudo F. J.
Published: May 2006

Active transport systems in bacteria can be divided into two groups: those that are osmotic shock‐resistant with one single membrane protein, and those that are shock‐sensitive and have a membrane‐bound protein complex plus a soluble periplasmic protein. Whether the bacterial assimilatory nitrate transport falls into the one or the other of these two groups has not been studied before. We report that nitrate uptake by the strictly aerobic, N2‐fixing heterotrophic bacterium Azotobacter chroococcum is sensitive to osmotic shock. The polypeptide composition of cytoplasmic membranes changes in response to the nitrogen source available to the cells. Incorporation of [35S]‐methionine into proteins as well as use of the A. chroococcum TRI mutant, which is defective in nitrate transport, and the A. choococcum MCD1 strain, a mutant unable to use nitrate as a nitrogen source, suggest that nitrate transport into A. chroococcum cells is mediated by a multicomponent system tightly bound to the cytoplasmic membrane.
Nitrite in the root zone and its effects on ion uptake and growth of wheat seedlings
Authors: Zsoldos Ferenc , Haunold Ernst , Vashegyi Ágnes , Herger Peter
Published: May 2006

The immediate and posteffects of various concentrations of NaNO2 on ion uptake of wheat (Triticum aestivum L. cv. GK Öthalom) seedlings were studied at different pH values. Without pretreatment, the higher the concentration of NaNO2 the greater was the decrease in uptake of K+ into the roots, both at pH 4 and pH 6. At pH 6 but not at pH 4 the reverse was true when the seedlings were pretreated with NaNO2. Due to the high Na+ content of the roots, an effect of Na+ in this process cannot be excluded. Nitrite was taken up by the roots more rapidly than nitrate. Nitrite at 0.1 mM in the medium induced the development of an uptake system for both NO−2 and NO−3 in wheat roots. At higher concentrations pretreatment with NO−2 decreased NO−3 uptake by the roots, but NO3 did not inhibit the uptake of NO2. The toxic effect of NO−2 was strongly pH dependent. Lower pH of the external solution led to an increased inhibition by NO−2 of both ion uptake and growth of seedlings. The inhibitory effect of NO−2 differed considerably for roots and shoots. The roots and especially the root hairs were particularly sensitive to NO−2 treatment.
Effect of N‐nutrition and irrigation on fruit production of carob (Ceratonia siliqua)
Authors: Correia P. J. , Martins‐Loução M. A.
Published: May 2006

A combined fertilization and irrigation experiment was initiated in order to see whether such treatment could improve the productivity of carob (Ceratonia siliqua L. cv. Mulata) on Mediterranean marginal lands. Mature carob trees (20–30 years old) were submitted to 3 different irrigation levels (100%;, 50%; and 0%;) based on daily standard evaporation values, measured with a class A pan. For each water level either 21 or 63 kg N ha−1 was applied as ammonium nitrate. The results reported here refer to a two‐year experiment, and show that the productivity of the trees could be improved due to a positive interaction between water and N application. In addition, they suggest that also under the normal dry conditions of these Mediterranean systems nitrogen application is effective, even without irrigation.
Abscisic acid induced stress‐like polyamine pattern in wheat seedlings, and its reversal by potassium ions
Authors: Aurisano Nicoletta , Bertani Alcidc , Mattana Monica , Reggiani Remo
Published: May 2006

In 3‐day‐old wheat (Triticum aestivum L. cv. Marinat) seedlings, 100 μM ABA blocked the growth and altered the level of K+ in both the shoot and root. The presence of ABA increased the putrescine titer during a 24‐h treatment. Increasing the endogenous level of K+ by the addition of 10 mM KCl to the ABA‐treated seedlings, inhibited the effect of ABA on growth and putrescine level. In both tissues, ABA increased putrescine content at low concentrations (1 μM), reaching the maximal effect at 100 μM. Putrescine increase induced by ABA was inhibited by both α‐difluoromethylarginine (DFMA) and α‐difluoromethylornithine (DFMO) in shoots while only the inhibitor of arginine decarboxylase was effective in the root. The presence of ABA modulated, in opposite ways, ornithine and arginine decarboxylase activities. These results are discussed in relation to ion balance under stress.
Studies on energy status and mitochondrial respiration during growth and senescence of mung bean cotyledons
Authors: Wen Jiang‐Qi , Liang Hou‐Gou
Published: May 2006

Several characteristics of mitochondrial respiration and energy status have been studied during growth and senescence of mung bean (Phaseolus radiatus L.) cotyledons. The results showed that mitochondrial oxygen consumption, respiratory control, ADP:O ratios, and energy charge changed in the cotyledons during germination and growth of the seedlings. The respiration rate of intact cotyledons approximately reflected the trend of the oxidative activities of the isolated mitochondria. An increase was observed in both whole cotyledon respiration and mitochondrial oxygen uptake at the onset of senescence of mung bean cotyledons (day 3 after germination), which thereafter declined gradually. The capacity and activity of the alternative pathway increased markedly in mitochondria isolated from senescent cotyledons. After the onset of senescence, the mung bean cotyledon mitochondria exhibited a decrease both in the respiratory control ratios and ADP:O ratios, and the cotyledons exhibited a gradual decline in energy charge. All these results showed an irreversible deterioration of energy conservation in mung bean cotyledons. The role(s) of the alternative pathway in senescent mung bean cotyledons is discussed.
Nitrogen fixation and carbon metabolism by nodules and bacteroids of pea plants under sodium chloride stress
Authors: Delgado M.J. , Garrido J.M. , Ligero F. , Lluch C.
Published: May 2006

Acetylene reduction activity (ARA) and leghemoglobin (Lb) content in nodules were sigificantly reduced when pea (Pisum sativum L. cv. Lincoln) plants were subjected to 50 mM sodium chloride stress for 3 weeks. C2H2 reduction activity by bacteriods isolated from pea nodules was drastically inhibited by saline stress, and malate appeared to be a more appropriate substrate than glucose or succinate in maintaining this activity. Salt added directly to the incubation mixture of bacteriods or to the culture medium of plants inhibited O2 uptake by bacteroids. Nodule cytosolic phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and bacteriod malate dehydrogenase (MDH; EC 1.1.1.37) activities were strongly enhanced by salt stress. Under these conditions, malate concentration was depressed in bacteroids and cytosol, whereas total soluble sugar (TSS)content slightly increased in both fractions. The effect of salt stress on TSS and malate content suggests that the utilization of carbohydrate within nodules could be inhibited during salt stress. The inhibitory effect of NaCl on N2 fixation activity of bacteroids and to the decrease in bacteroid respiration. The stimulation of fermentative metabolism induced by salinity suggests some reduction in O2 availability within the nodule. Salt stress was also responsible for a decrease of the cytosolic protein content, specifically of leghemoglobin, in the nodules.
Flavor volatilcs, sugars and color development in ripening in vitro‐cultured tomato fruit and calyx
Authors: Ishida Betty K. , Baldwin Elizabeth A. , Buttery Ron G. , Chui Suzanne H. , Ling Louisa C.
Published: May 2006

Previous studies showed that the developmental program of calyces of a tomato cultivar (Lycopersicon esculentum, cv. VFNT Cherry) changed in many aspects to that of fruit when cultured in vitro. The calyces turned red, produced ethylene, had increased tissue content of 1‐aminocyclopropane‐1‐carboxylic acid, had increased levels of the mRNA of polygalacturonase and developed ultrastructural changes in their cell walls that were indistinguishable from those of ripe tomato fruit tissue. We report in the present study the synthesis of volatile flavor compounds, changes in sugar concentrations and color development in cultured calyces that are characteristic of ripening tomato fruit. These ripening parameters of in vitro‐cultured tomato fruit were also compared to those of fruit grown in the greenhouse.
Nonstructural carbohydrates in dormant and afterripened wild oat caryopses
Authors: Nichols Maxine B. , Bancal Marie‐Odile , Foley Michael E. , Volenec Jeffrey J.
Published: May 2006

Nonstructural carbohydrates were determined in both embryo and endosperm of dormant (nongerminating) and afterripened (germinating) intact caryopses of wild oat (Avena fatua L.). No changes in endosperm starch or soluble sugar were observed at the onset of germination (18 h). No changes in glucose, fructose, sucrose or starch within dormant or afterripened embryos correlated with onset of visual germination. In afterripened embryos, depletion of raffinose (18 h), stachyose (18 h) and galactose (24 h) was correlated with germination. In contrast, raffinose‐family oligosaccharide levels in dormant embryos remained constant for 7 days following imbibition. Germination of isolated dormant embryos on 88 mM galactose‐containing media was accompanied by decreased endogenous levels of raffinose and stachyose. Isolated embryos from dormant caryopses incorporated 14C from 14C‐fructose into both raffinose and stachyose during 24 h of imbibition. In contrast, no 14C incorporation into stachyose was observed in embryos from afterripened caryopses. No 14C incorporation into raffinose was observed at 18 and 24 h. When in vitro activities of α galactosidase were measured, no temporal differences between dormant or afterripened caryopses were detected in either embryo or endosperm tissue. Although the mechanism associated with differences in utilization of raffinose and stachyose is yet unidentified, alterations in raffinose‐family oligosaccharide metabolism in the embryo appear to be a unique prerequisite for afterripening‐induced germination.
Inhibition of anthocyanin synthesis and phenylalanine ammonialyase activity by Co2+ in leaf disks of Terminalia catappa
Authors: Dube Alok , Bharti S. , Laloraya M. M.
Published: May 2006

Treatment with sucrose induced anthocyanin synthesis and phenylalanine ammonialyase (PAL, EC 4. 3. 1. 5) activity in leaf disks of Indian almond (Terminalia catappa L. Duthie). Co2+, an inhibitor of ethylene biosynthesis, inhibited anthocyanin synthesis and PAL activity when given together with sucrose. Ethephon (an exogenous source of ethylene) given along with sucrose, promoted anthocyanin synthesis and PAL activity, but in the presence of Co2+ its effectiveness decreased. In an attempt to understand the inhibitory action of Co2+ in the presence of ethephon, the effect of Co2+ on PAL activity was studied in vitro. A kinetic study showed an uncompetitive type of inhibition of PAL by Co2+, which was not time dependent. Addition of 2‐mercaptoethanol, cysteine or glutathione overcame the in vitro effect of Co2+, and 2‐mercaptoethanol also restored the activity of PAL extracted from Co2+‐treated leaf disks. It is suggested that sulfhydryl group(s) might be involved in the inactivation of PAL by Co2+. The effects of N‐ethylmaleimide (NEM) and HgCl2 (other sulfhydryl reagents) were also studied. Both NEM and Hg2+ competitively inhibited PAL activity in vitro, and the inhibition could be reversed by sulfhydryl compounds.
Role of short‐chain saturated fatty acids in the control of ethylene sensitivity in senescing carnation flowers
Authors: Whitehead C. S. , Vasiljevic D.
Published: May 2006

In cut carnations (Dianthus caryophyllus L. cv. Cally). petal senescence was associated with a climacteric pattern in ethylene production and an increase in ethylene sensitivity during the preclimacteric stage. The increase in ethylene sensitivity was caused by short‐chain saturated fatty acids (C7 to C10) produced in the petals during the early stages of senescence. Pollination or application of octanoic acid to the styles of unpollinated flowers resulted in a sudden increase in ethylene sensitivity and a marked acceleration of senescence. Treatment with silver thiosulfate (STS) resulted in a suppression of ethylene sensitivity and a marked reduction in the levels of these fatty acids. However, even in STS‐treated flowers pollination or treatment with octanoic acid gave rise to a drastic increase in ethylene sensitivity. Exposure of carnation flowers to 2. 5‐norbornadicne (NBD) vapours resulted in a dramatic suppression of ethylene sensitivity which was also overridden by stylar application of octanoic acid. Exposure to NBD suppressed the increase in ethylene sensitivity caused by treatment with octanoic acid. It appears that short‐chain saturated fatty acids increased ethylene sensitivity by increasing the ability of the tissue to bind ethylene.
Differential expression of DAHP synthase and chorismate mutase isozymes during rhizogenesis of Brassica juncea cultured in vitro
Authors: Sharma Ranjana , Bhatnagar Raj K. , Sarin Neera Bhalla
Published: May 2006

The regulatory patterns of two of the enzymes of the shikimate pathway. 3‐deoxy‐D‐arabino‐heptulosonate‐7‐phosphate synthase (DAHP synthase or DS. EC 4. 1. 2. 15) and chorismate motase (CM, EC 5. 4. 99. 5), were investigated using in vitro cultures of Brassica juncea at two stages, viz. undifferentiated, proliferating callus and the root‐forming callus. Our studies revealed the presence of the two isozymes of DAHP synthase, DS‐Mn and DS‐Co. in undifferentiated callus. However, during the rhizogenesis of the callus DS‐Mn was absent. Similarly, for chorismate mutase, whereas both the isozymes CM‐1 and CM‐2 were present in undifferentiated callus only CM‐2 was detected at rhizogenesis. The possible involvement of these isozymes in callus growth and rhizogenesis is discussed.
Plant metal content, growth responses and some photosynthetic measurements on field‐cultivated wheat growing on ore bodies enriched in Cu
Authors: Lanaras T. , Moustakas M. , Symeonidis L. , Diamantoglou S. , Karataglis S.
Published: May 2006

Some elemental levels, morphological and photosynthetic characteristics and cellular metabolites of wheat plants (Triticum aestivum L. cv. Vergina) growing in the field on an ore body (Cu concentration in the soil 3050 ug g−1) were compared to control plants growing in the same environment where the Cu concentration in the soil was 140 μg g1. The concentrations of Cu, K, Pb, Zn, Mg and Fe were higher in the ore plants but Ca was lower. Growth of the ore plants was inhibited, with decreased height (25%), weight (5%), leaf area (7%) and leaf dry weight (5%) compared to the control plants. Leaf protein concentration of the ore plants was 16. 2 mg cm2 leaf area, 63% of that of the control plants. The ore plants were chlorotic and chlorophyll concentration was 3. 8 μg cm−2 leaf area, 6. 4 times lower than that in the control plants. Ribulose 1. 5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4. 1. 1. 39) activity was 13. 4 μmol CO2 fixed (mg dry weight)−1 min−1, 164% of the activity in control plants. Therefore, growth inhibition did not appear to result from inhibition of the dark reactions of photosynthesis. High Rubisco activity appears to be maintained to permit maximal CO2 fixation rates whenever energy is available. Parameters of chlorophyll fluorescence Fm, Fv, I1/2 and Fv/Fm were lower in the ore‐grown plants than in control plants; Fm was higher. These values indicate that there is a decrease in the pool size of the electron acceptors on the reducing side of photosystem II (PSII), a destruction of PSII centres and interference in the photochemistry of PSII. The nitrogen content, soluble sugars, starch and lipid content were lower in ore‐grown plants. Lower carbohydrate levels appear to result from low photosynthetic activity. The fatty acid composition of lipids was similar in both groups. A lower proportion of polyunsaturated fatty acids was found in the ore‐grown plants. Stress caused by high Cu concentration in the soil appears to affect the light reactions of photosynthesis leading to growth inhibition.