bluuebunny/crossref_metadata_2025 huggingface dataset:
Turgor‐dependent unloading of assimilates from coats of developing legume seed. Assessment of the significance of the phenomenon in the whole plant
Authors: Patrick J. W.
Published: May 2006

The in vivo significance of turgor‐dependent unloading was evaluated by examining assimilate transport to and within intact developing seeds of Phaseolus vulgaris (cv. Redland Pioneer) and Vicia faba (cv. Coles Prolific). The osmotic potentials of the seed apoplast were low. As a result, the osmotic gradients to the seed coat symplast were relatively small (i.e. 0.1 to 0.3 MPa). Sap concentrations of sucrose and potassium in the seed apoplast and coat symplast accounted for some 45 to 60% of the osmotic potentials of these compartments. Estimated turnover times of potassium and sucrose in the seed apoplast of < 1 h were some 5 to 13 times faster than the respective turnover times in the coat symplast pools. The small osmotic gradient between the seed apoplast and coat symplast combined with the relatively rapid turnover of solutes in the apoplast pool, confers the potential for a small change in assimilate uptake by the cotyledons to be rapidly translated into an amplified shift in the cell turgor of the seed coat. Observed adjustments in the osmotic potentials of solutions infused between the coat and cotyledons of intact seed were consistent with the in vivo operation of turgor‐dependent unloading of solutes from the coat. Homeostatic regulation of turgor‐dependent unloading was indicated by the maintenance of apoplast osmotic potentials of intact seeds when assimilate balance was manipulated by partial defoliation or elevating pod temperature. In contrast, osmotic potentials of the coat symplast adjusted upward to new steady values over a 2 to 4 h period. The resultant downward shift in coat cell turgor could serve to integrate phloem import into the seed coat with the new rates of efflux to the seed apoplast. Circumstantial evidence for this linkage was suggested by the approximate coincidence of the turgor changes with those in stem levels of 32P used to monitor phloem transport. The results obtained provide qualified support for the in vivo operation of a turgor homeostat mechanism. It is proposed that the homeostat functions to integrate assimilate demand by the cotyledons with efflux from and phloem import into the coats of developing legume seed.
Characteristics and implications of prolonged fusicoccin‐induced growth of Avena coleoptile sections
Authors: Cleland Robert E.
Published: May 2006

A study has been made of the prolonged growth of Avena coleoptile sections in response to fusicoccin (FC), a phytotoxin that promotes apoplastic acidification. The final amount of FC‐induced growth is a function of the FC concentration. Removal of the epidermis speeds up the initial rate of elongation and shortens the duration of the response, without affecting the total amount of extension. A suboptimal FC concentration (7×10−8M) which induces the same rate of proton excretion as does optimal indoleacetic acid (IAA) (1×10−5M), causes elongation which is 60–75% of that induced by IAA in 4 h or 50–65% in 7 h. This suggests that acid‐induced extension could make a major contribution to auxin‐induced growth for at least 7 h.
Peroxidase and chitinase isoenzyme activities during root infection of Chinese cabbage with Plasmodiophora brassicae
Authors: Ludwig‐Müller Jutta , Thermann Petra , Pieper Kerstin , Hilgenberg Willy
Published: May 2006

Roots of two Chinese cabbage (Brassica campestris L. ssp. pekinensis) varieties, one tolerant and one susceptible, were inoculated with Plasmodiophora brassicae in liquid medium and in soil. Chitinase and peroxidase activities were determined in roots and shoots 1–21 days after inoculation with resting spores of Plasmodiophora and the enzyme activities compared with healthy tissue of the same age. In infected roots of the susceptible variety ‘Granat’ chitinase activity was higher than in the control 10 days after inoculation with spores. In the tolerant variety ‘Parkin’ we detected an increase in chitinase activity at the same time, which was about twice that of ‘Granat’. Chitinase activity in ‘Granat’ was also enhanced on day 13, 14 and 17 after inoculation, whereas chitinase activity in ‘Parkin’ was lower in the infected roots than in the controls during that period. In the shoots no correlation between chitinase activity and infection in the two varieties was observed. Chitinase from Chinese cabbage was further characterized and showed a pH optimum at pH 4.5–5.5 and a temperature optimum at 35–45°C. After isoelectric focusing 7 isoenzymes were discovered, but there were almost no differences between infected and healthy root extracts. Two isoenzymes with pI 8.7 and 8.8 showed cross‐reactivity with an antiserum against bean chitinases. The molecular mass of these isoenzymes was determined as 33 kDa. Total peroxidase activity was generally higher in root tissue of both varieties than in the shoots. Peroxidase activity was increased most prominently in infected ‘Granat’ roots on day 13 after inoculation and of both varieties on day 17 compared to the controls. In clubbed tissue of ‘Granat’ a specific peroxidase isoenzyme appeared the first time 21 days after inoculation and was most prominent 28–30 days after inoculation. This isoenzyme had a molecular mass of ca 24 kDa and a pI of ca 8.8. With respect to our results the strategy of the Plasmodiophorales for plant attack is discussed.
Pollination‐induced senescence in phalaenopsis petals. Relationship of ethylene sensitivity to activity of GTP‐binding proteins and protein phosphorylation
Authors: Porat R. , Borochov A. , Halevy A. H.
Published: May 2006

Treatments of cut phalaenopsis (Phalaenopsis hybrid, cv. ‘Herbert Hager’) flowers with cholera toxin or guanosine‐5‐0‐(3‐thiotriphosphate), compounds that modulate GTP‐binding protein activity, increased the sensitivity of the flowers to ethylene. Guanosine‐5‐0‐(2‐thiodiphosphate) which does not affect the activity of GTP‐binding proteins, had no affect on the sensitivity to ethylene. Western blot analysis of microsomal proteins, revealed that a peptide with a molecular mass of ca 42 kDa cross‐reacts with antibodies against a well‐conserved amino acid sequence (Gα‐commun peptide) of mammalian G‐proteins. Calcium ions, known co‐factors of protein kinases, also increased the sensitivity of the flowers to ethylene, while EGTA, a chelator of calcium, decreased it. Phorbol 12‐myrisate 13‐acetate, a phorbol ester, had no effect on the sensitivity to ethylene. Protein phosphorylation in petal microsomal membranes was doubled in the presence of calcium ions, but was unaffected by phorbol ester. Ten h after pollination, at the peak of ethylene sensitivity, a significant increase of ca 20% was measured in the binding of GTP to the membranes. Protein phosphorylation in flowers increased significantly following pollination, with a single peptide of ca 30 kDa most heavily phosphorylated. These observations may indicate a direct involvement of GTP‐binding proteins, and protein phosphorylation, two major components of the cellular signal transduction pathway, in the regulation of pollination induced ethylene sensitivity in phalaenopsis petals.
Effects of apoplastic sucrose on carbohydrate pools and sucrose efflux of mesophyll protoplasts of pea (Pisum sativum)
Authors: Opaskornkul Chana , Greger Maria , Tillberg Jan‐Eric
Published: May 2006

The effects of the apoplastic, i.e. external, concentration of sucrose (0–30 mM) on O2 evolution, O2 consumption, starch, sucrose, glucose and fructose content, and uptake and efflux of sucrose in mesophyll protoplasts of Pisum sativum L. cv. Fenomen were studied. Neither photosynthesis, dark respiration, sucrose nor starch content change with increased apoplastic sucrose concentration. The contents of glucose and fructose in the protoplasts increase with increased apoplastic sucrose concentration. The sucrose efflux increases with increased external sucrose concentrations between 1 and 5 mM, but above this range the efflux decreases with increased external sucrose concentrations. These findings indicate that although external sucrose does not enter the protoplasts, there is a relationship between the external sucrose pool and the internal pools of sugars in the mesophyll protoplasts. The results suggest an active sucrose efflux from the protoplasts at physiological concentrations of apoplastic sucrose (max 5 mM) and a simple diffusion mechanism at higher concentrations.
The involvement of a vanadate‐sensitive ATPase in plasma membranes of a salt tolerant cyanobacterium
Authors: Gabbay‐Azaria Rachel , Pick Uri , Ben‐Hayyim Gozal , Tel‐Or Elisha
Published: May 2006

Plasma membranes of the marine cyanobacterium Spirulina subsalsa were tested for ATPase activity, and for involvement in salt stress. Transition of cells from saline to hypersaline medium enhances the respiratory activity associated with extrusion of Na+ and Cl−, and persisting salt stress induces synthesis of respiratory enzymes in the plasma membranes. The membranes possess an ATPase, specific for ATP and Mg2+ and sensitive to orthovanadate and dicyclohexylcarbodiimide. Immunoblot analysis of plasma membrane polypeptides from Spirulina subsalsa with anti‐Arabidopsis H+‐ATPase serum identified a single polypeptide of 100 kDa, which cross‐reacted with the antibodies. An unusual feature of this ATPase is a specific stimulation by Na+ ions. Prolonged adaptation of S. subsals cells to hypersaline conditions induced an increase in ATPase activity in subsequent plasma membrane preparations, as well as a higher content of the 100 kDa polypeptide. It is suggested that the ATPase investigated is an H+‐pump, which is involved in extrusion of Na+ and in conferring resistance to salt stress.
Transformed hairy roots of Mesembryantemum crystallinum: gene expression patterns upon salt stress
Authors: Andolfatto Peter , Bornhouser Angela , Bohnert Hans J. , Thomas John C.
Published: May 2006

In Mesembryanthemum crystallinum L. (common ice plant), salinity initiates a series of events that contribute to increases in osmotically active metabolites and the establishment of water conserving Crassulacean Acid Metabolism. To better understand the role of isolated root‐specific responses during salt stress, a vigorously growing root culture was needed. Thus, we took advantage of the ability of Agrobacterium rhizogenes to transform and generate growing hairy roots. Treatment of the morphologically similar hairy and nontransformed roots of whole plants with 400 mM NaCl caused an 8‐fold increase in proline levels in these tissues. A heat shock protein 70 cognate, isolated from a root specific cDNA library, was also present at simlar levels in unstressed and stressed samples of both types of roots. However, the steady state abundance of 6 other root cDNAs differed dramatically between transformed hairy and normal roots in response to salt stress. These observations suggest that several responses to salt stress are conserved between roots of whole plants and hairy roots. Additionally, a portion of transcripts reacting to salt stress may be modulated by other factors exclusive to A. rhizogenes transformed hairy root growth. The complex and hierarchical environmental stress response of this halophyte relies on several tissue‐specific interactions, and these responses are most accurately characterized in whole plant tissues.
The accumulation of solutes and water binding strength in durum wheat
Authors: Rascio A. , Platani C. , Scalfati G. , Tonti A. , Di Fonzo N.
Published: May 2006

Variations in water binding strength, water relations and the accumulation of solutes during water stress of three durum wheat (Triticum durum Desf.) cultivars are reported and discussed. Water binding strength was determined by constructing adsorption isotherms at 5 and 20°C and by calculating the differential enthalpy (ΔH) after van't Hoff.

Reducing sugars, proline, K+ and Cl− were the major contributors to osmotic adjustment. Solutes, such as quaternary ammonium compounds, and non‐reducing sugars contributed to osmotic potential at full turgor, but did not increase in proportion to water stress. Genotypic differences have been observed for K+ accumulation capability, the water‐stressed leaves of cv. Capeiti 8 showing the largest increase. The same cultivar demonstrated the most negative ΔH values, indicative of strongly bound water, and the highest integrated enthalpy (ΔHinf) values for leaf moisture below 0.1 g H2O per g dry weight, i.e. in the isotherm region where water was presumably chemisorbed to the charged groups of macromolecules. The accumulation of ions (Cl−, K+) and proline was concurrent with an increase in the binding‐strength of tightly and weakly bound water, respectively.
Carbohydrate accumulation and utilization in soybean plants in response to altered phosphorus nutrition
Authors: Qiu Jinshu , Israel Daniel W.
Published: May 2006

We conducted a study to determine whether increased starch accumulation is the cause or the result of decreased growth in phosphorus‐deficient soybean plants (Glycine max [L.] Merr. cv. Ransom). Nitrate‐dependent plants were provided with nutrient solution containing either 0.05 or 1.00 mM phosphorus. On day 22 after transplanting the phosphorus concentration in solutions supplied to one‐half of the plants that had received 0.05 mM phosphorus was increased to 1.0 mM phosphorus and the phosphorus concentration in solutions supplied to plants that had received 1.0 mM phosphorus was decreased to 0.05 mM P. The other half of plants in each treatment remained at the same external phosphorus concentration to serve as phosphorus‐deficient or phosphorus‐sufficient controls. Onset of phosphorus deficiency decreased (1) photosynthetic capacity through negative effects on whole plant leaf area and photosynthetic rate per unit leaf area and (2) relative growth rate and leaf elongation rate. However, continuous increases in starch concentration in all organs during onset of phosphorus deficiency indicated that decreased nonstructural carbohydrate availability was not the primary cause of decreased growth. During onset of phosphorus deficiency, significant decreases in relative growth rate (3–8‐day interval) and in day and night leaf elongation rate (8 days) occurred before or at the same time as significant increases in stem, leaf and root starch concentrations. These results support the conclusion that disruption of metabolic functions associated with growth impaired utilization of available nonstructural carbohydrate in plants adjusting to phosphorus deficiency. After phosphorus‐deficient plants were transferred to the sufficient external phosphorus concentration, starch concentrations in leaves and stems decreased to those of phosphorus‐sufficient control plants within 3 days. These decreases in starch concentration in leaves and stems preceded measurable changes in relative growth rate (3–8‐day interval), day and night leaf elongation rate (8 days) or CO2 exchange rate (8 days). Therefore, when soybean plants recover from phosphorus deficiency, starch stored in leaves and stems is ready to be utilized in the synthesis of structural biomass during the time required for activation and/or development of additional photosynthetic capacity.
Cell wall‐bound trans‐ and cis‐ferulic acids in growing maize roots
Authors: Locher Roland , Martin Hilary V. , Grison René , Pilet Paul‐Emile
Published: May 2006

The levels of cell wall‐bound trans‐ and cis‐ferulic acids in roots of dark grown Zea mays cv. LG11 plants were measured. They were quantified after alkaline hydrolysis of purified cell walls by reversed phase HPLC using trans‐cinnamic acid as internal standard. The total amount of ferulic acid (trans‐ and cis‐ferulic acid) in the root base was 3–4 times higher than in the root tip. Cis‐ferulic acid represented between 2% (tip) and 18% (base) of the total ferulic acid content. The total content of trans‐ and cis‐ferulic acids was approximately the same in the stele and the cortex, but the level of cis‐ferulic acid in the stele was 5–6 times higher than in the cortex. Trans‐ and cis‐ferulic acid levels as well as the percentage of cis‐ferulic acid in the elongation zone were steady between 48 and 96 h after the beginning of germination. Slowly growing roots contained more wall‐bound ferulic acids, particularly cis‐ferulic acid, than fast growing roots. This relationship was found in the differentiation zone but not in the elongation zone. The importance of cell wall‐bound trans‐ and cis‐ferulic acids is discussed in the context of root growth and differentiation.
Adenine salvage activity during callus induction and plant growth
Authors: Lee Diana , Moffatt Barbara A.
Published: May 2006

Adenine phosphoribosyltransferase (APRT; EC 2.4.2.7) activity was monitored in crude extracts of Arabidopsis thaliana tissues and callus. Changes in APRT activity during germination were determined within different organs of the mature plant and during callus induction. APRT activity was constitutively expressed in all organs examined. There was an increase in APRT activity detected in seeds beginning 3 days following imbibition, after which the level decreased to that found in leaf tissue of mature plants. There was also an increase in APRT activity early during callus induction. A mutant that lacks APRT activity had a diminished capacity for callus induction in both the presence and absence of exogenous cytokinin. The results are consistent with the hypothesis that an increase in APRT activity is associated with actively dividing cells. The significance of these observations is discussed relative to the role of APRT in adenylate and cytokinin metabolism during plant development.
Developmental changes in carbohydrate content and sucrose degrading enzymes in tuberising stolons of potato (Solanum tuberosum)
Authors: Ross Heather A. , Davies Howard V. , Burch Lindsay R. , Viola Roberto , McRae Diane
Published: May 2006

Tuberising stolon tips of potato (Solanum tuberosum L. cv. Record) accumulate starch and sucrose but the hexose content, particularly fructose, declines rapidly. Similar changes occur in the region 2 cm behind the swelling apex but the decline in glucose is far more pronounced than in the developing tuber. Tuberisation is characterised by an apparent switch from an invertase‐dominated sucrolytic system (both acid and alkaline invertases [EC 3.2.1.26] are present) to one dominated by sucrose synthase (EC 2.4.1.13). Sucrose synthase and fructokinase (EC 2.7.1.4) activities were, at a maximum, ca 10‐ and 5‐fold higher, respectively in the swelling stolon tip compared with the non‐tuberising region. At the highest starch contents attained, the starch level in the young developing tuber was approximately double that in the adjacent non‐tuberising stolon region. Immunoblots revealed that developmental changes in sucrose synthase. fructokinase and alkaline invertase polypeptides corresponded with enzyme activities. Antibodies raised against the N‐terminal amino acid sequence of a soluble invertase purified from mature tubers did not detect significant quantities of a polypeptide in stolons and young, developing tubers. Antibodies raised against an in vitro expression product of an apoplastic invertase cloned from a leaf cDNA library detected a polypeptide in developing tubers but not in mature ones. However, expression of the protein did not correlate well with acid invertase activity during early tuber formation.
Immunological analysis of aconitase in pumpkin cotyledons: the absence of aconitase in glyoxysomes
Authors: De Bellis Luigi , Hayashi Makoto , Biagi Pier Paolo , Hara‐Nishimura Ikuko , Alpi Amedeo , Nishimura Mikio
Published: May 2006

Aconitase (EC 4.2.1.3) was purified by column chromatography and SDS‐PAGE. Specific antibodies for aconitase were prepared after affinity purification of the antiserum with purified aconitase. The antibodies reacted with purified pumpkin aconitase, and with the 98 kDa protein band after electrophoretic fractionation of extracts of pumpkin cotyledons. Immunoblot analysis revealed a protein with similar molecular mass in extracts of several plants. The intensity of the 98 kDa band increased as pumpkin cotyledons developed in darkness, and decreased thereafter upon illumination. Aconitase activity showed a similar pattern. Anion exchange chromatography of a homogenate of pumpkin cotyledons, followed by western blotting, displayed the presence of immunoreactive protein bands only in fractions showing aconitase activity. The results indicate that the antibodies were specific for aconitase. When we investigated the presence of immunoreactive bands after sucrose gradient fractionation, aconitase was detected in the supernatant fractions and in mitochondria, while a very low amount was found in glyoxysomes. These data provide additional proof that aconitase is not localized in glyoxysomes.
Fruit softening in banana: correlation among stress‐relaxation parameters, cell wall components and starch during ripening
Authors: Kojima Kiyohide , Sakurai Naoki , Kuraishi Susumu
Published: May 2006

Bananas, Musa (AAA group, Cavendish subgroup) ‘Giant Cavendish’, were ripened in a biotron at 25°C with ethylene during 4 days. Changes in mechanical properties of pulp were detected by a stress‐relaxation technique. The decrease in T0, the parameter for minimum stress‐relaxation time, began between day 0.5 and 1, while the decrease in initial stress began between day 0 and 0.5, suggesting that the decrease in elasticity and viscosity of pulp is a crucial physical event of pulp softening. Cellulose and moisture contents were about 3 and 780 mg (g fresh weight)−1, respectively, which were unchanged during ripening. The decrease in starch content of cell materials and in uronic acid content of the pectic polysaccharides of the cell walls began between day 0.5 and 1. As regards the sugar composition of the hemicellulose fraction, decreases in arabinose, mannose and galactose contents began between day 0 and 0.5. The results show that the partial decrease in hemicelluloses preceded the breakdown of starch and suggest that the coordinated degradation of pectic and hemicellulosic polysaccharides and starch is the main cause for the pulp softening process.
Plasma membrane‐bound H+‐ATPase and reductase activities in Fe‐deficient cucumber roots
Authors: Rabotti Giuseppina , Zocchi Graziano
Published: May 2006

Physiological and biochemical modifications induced by Fe‐deficiency have been studied in cucumber (Cucumis sativus L. cv. Marketer) roots, a Strategy I plant that initiates a rapid acidification of the medium and an increase in the electric potential difference when grown under Fe‐deficiency. Using the aqueous two‐phase partitioning method, a membrane fraction which has the plasmalemma characteristics was purified from roots of plants grown in the absence and in the presence of iron. The plasma membrane vesicles prepared from Fe‐deficient plants showed an H+‐ATPase activity (EC 3.6.1.35) that is twice that of the non‐deficient control. Furthermore, membranes from Fe‐deficient plants showed a higher capacity to reduce Fe3+‐chelates. The difference observed in the reductase activity was small with ferricyanide (only 30%) but was much greater with Fe3‐EDTA and Fe3‐citrate (210 and 250%, respectively). NADH was the preferred electron donor for the reduction of Fe3+ compounds. Fe3+ reduction in plasma membrane from cucumber roots seems to occur with utilisation of superoxide anion, since addition of superoxide dismutase (SOD; EC 1.15.1.1) “in vitro” decreased Fe3+ reduction by 60%.

The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O2 in controlling the Fe3+/Fe2+ ratio in the rhizosphere are discussed.
Artificial associations between Daucus and nitrogen‐fixing Azotobacter cells in vitro
Authors: Varga Sz. S. , Korányi P. , Preininger É. , Gyurján I.
Published: May 2006

Symbiotic associations were established between nitrogen‐fixing Azotobacter zettuovii (CRS‐H6) cells and carrot (Daucus carota L. cv. ‘Rother’ Half Long) tissues based on the induced carbon and energy dependency of diazotrophs on plant metabolic activity. Symbiotic associations were grown on nitrogen‐free media for four years. Plant regeneration was achieved from callus‐bacterium associations on nitrogen‐containing media. Light and electron micrographs are used to show the localization of bacteria in intercellular spaces of callus and regenerated plant tissues. The nitrogen‐fixing ability of the partnership was proved on nitrogen‐free media.
The role of acid phosphatases in plant phosphorus metabolism
Authors: Duff Stephen M. G. , Sarath Gautam , Plaxton William C.
Published: May 2006

Hydrolysis of phosphate esters is a critical process in the energy metabolism and metabolic regulation of plant cells. This review summarizes the characteristics and putative roles of plant acid phosphatase (APase). Although immunologically closely related, plant APases display remarkable heterogeneity with regards to their kinetic and molecular properties, and subcellular location. The secreted APases of roots and cell cultures are relatively non‐specific enzymes that appear to be important in the hydrolysis and mobilization of Pi from extracellular phosphomonoesters for plant nutrition. Intracellular APases are undoubtedly involved in the routine utilization of Pi reserves or other Pi‐containing compounds. A special class of intracellular APase exists that demonstrate a clear‐cut (but generally nonabsolute) substrate selectivity. These APases are hypothesized to have distinct metabolic functions and include: phytase, phosphoglycolate phosphatase, 3‐phosphoglycerate phosphatase, phosphoenolpyruvate phosphatase, and phosphotyrosyl‐protein phosphatase. APase expression is regulated by a variety of developmental and environmental factors. Pi starvation induces de novo synthesis of extra‐ and intracellular APases in cell cultures as well as in whole plants. Recommendations are made to achieve uniformity in the analyses of the different APase isoforms normally encountered within and between different plant tissues.
Comparison of properties of leaf and root glutathione reductases from spinach
Authors: Tanaka Kiyoshi , Sano Tomoko , Ishizuka Kozo , Kitta Kazumi , Kawamura Yukio
Published: May 2006

Glutathione reductase (GR; EC 1.6.4.2) was purified from spinach roots (rGR) to homogeneity in terms of SDS‐PAGE, and its properties were compared with those of the enzyme from spinach leaves (IGR). The two enzymes had similar native molecular (118000) and subunit masses (58000) and immunochemical properties, but different pH optima (ca pH 7.8 for IGR, ca pH 7.2 for rGR) and amino acid compositions. Peptide maps of two GRs showed that they differed from each other. The N‐terminal amino acid of the IGR was glycine and that of the rGR was blocked. The partial amino acid sequence of the N‐terminal region of the IGR was determined to the 11 th residue and it was found that the sequence of 8 amino acids of the IGR had 100% homology with that of the putative chloroplast GR from Arabidopsis and pea.
Carbon economy in walnut seedlings during the acquisition of autotrophy studied by long‐term labelling with 13CO2
Authors: Maillard P. , Deléens E. , Daudet F.A. , Lacointe A. , Frossard J.S.
Published: May 2006

A closed growth chamber was designed to study the acquisition of autotrophy by seedlings of walnut (Juglans regia L. cv. Lara) in controlled conditions (22°C, 12‐h photoperiod) during the first two months of growth. The chamber consisted of two airtight compartments, in which continuous gas exchange was measured on the aerial and subterranean parts of several batches of tree seedlings. Long‐term labelling with 13CO2 was used in the chamber to study the import, distribution, and respiratory losses of photoassimilates (autotrophic carbon) in relation to the partitioning and use of reserves of the maternal seed (heterotrophic carbon). The carbon economy of walnut seedlings was estimated by measurements of gas exchange, carbon content, and 13C/12C isotopic ratio in dry matter and respiratory CO2. The seedlings were entirely heterotrophic for energy and structural growth during the first 21 days after sowing. From day 22, photosynthesis appeared. At day 29, autotrophic carbon accounted for 25% and 30% of respiration in the root and shoot respectively; these proportions increased to 45% and 65% at day 54. The autotrophic carbon was incorporated into the dry matter of the shoot from day 32 but only after day 40 into the dry matter of the taproot. From day 32, the total contribution of heterotrophic carbon decreased regularly, and until day 43, it was essentially used for root growth. Thereafter, the contribution of heterotrophic carbon was negligible, and at day 54 the walnut seedlings were entirely autotrophic.
Removal of nuclear contaminants and of non‐specifically photosystem II‐bound copper from photosystem II preparations
Authors: Arellano Juan B. , Schröder Wolfgang P. , Sandmann Gerhard , Chueca Ana , Barón Matilde
Published: May 2006

In conventional photosystem II preparation high amounts of Cu are found. After fractionation by centrifugation, Cu can be completely removed from photosystem II without affecting either its photosynthetic activity or the composition of its specific proteins. We could demonstrate that the Cu was associated with nuclear contaminants in the starch fraction. Among the contaminants, several histones were identified by specific antisera and by N‐terminal sequencing. In order to obtain homogeneous BBY preparations of PSII a procedure is employed that involves a 10000 g centrifugation step and which eliminates non‐specifically bound metals, nucleic acids and histones with the starch pellet. The resulting starch‐free BBY (BBYs‐), which is free of these nuclear contaminants, is an appropriate preparation for biophysical studies or for those of metal interactions with PSII.
Development of a cold hardiness model for deciduous woody plants
Authors: Aniśko Tomasz , Lindstrom Orville M. , Hoogenboom Gerrit
Published: May 2006

The objective of the present study was to develop an empirical cold hardiness model applicable to several taxa of deciduous trees. Cold hardiness expressed as lowest survival temperature of Acer rubrum, Betula nigra, Liquidambar styracifiua, Fraxinus pennsylvanica, Prunus serotina and Quercus alba was evaluated at approximately weekly intervals during the winters of three consecutive years. Plant samples and meteorological data were collected from Georgia Experiment Station, Griffin, Georgia. Maximum, minimum and average temperatures, hourly chill and heat accumulation. day length and time of year were used as input variables for model development. The statistical method of stepwise procedure of regression analysis was employed to select variables for the model. Based on the assumption that model components should be the same for all taxa included in this study and all three winters, the following independent model variables were selected as valid inputs: day length, number of accumulated hours with temperature above 20°C and number of accumulated hours with temperature below 10°C. Equation coefficients of species‐specific models were determined for each species. Cold hardiness predictions were compared to actual observations for each species. The model components were interpreted as representing two processes: (1) internally regulated and independent of actual temperature, and (2) externally regulated and dependent on the amount of accumulated chill or heat. The model allowed for comparisons of cold hardening and dehardening between the studied taxa and between years.
NaCl‐induced changes in protoplasmic characteristics of Hordeum vulgare cultivars differing in salt tolerance
Authors: Mansour M. M. F. , Stadelmann E. J.
Published: May 2006

Water permeability and cytoplasmic viscosity and streaming were investigated in seedlings of two Hordeum vulgare cultivars differing in salt tolerance. Six‐day‐old seedlings were grown for 4 additional days in Hoagland solution with and without 100 mM NaCl added.

Observations and measurements were made in subepidermal cells of the coleoptile using plasmolytic and centrifugation methods and recordings of the speed of movement of microsomes.

Water permeability was about the same in controls of both cultivars, and was decreased by NaCl stress, but decreased less in the tolerant cultivar. Cells from control plants of the stress tolerant variety had a higher cytoplasmic viscosity than cells from the moderately sensitive cultivar. Cytoplasmic viscosity in both cultivars decreased due to NaCl stress, and more so in the sensitive one. Cytoplasmic streaming was faster in the controls of the salt sensitive cultivar than in controls of the salt tolerant cultivar; NaCl had no significant effect on cytoplasmic streaming in both cultivars.

The specific responses of the cytoplasm of the sensitive and tolerant cultivars to the salt treatment reflect differences in its structure and composition. These differences in the cytoplasm already exist before exposure to salt stress but some alterations of cytoplasmic parameters (e.g. water permeability) were induced by the saline environment.
Inhibition of the degradation of chloroplast membranes during senescence in nuclear ‘stay green’ mutants of soybean
Authors: Guiamét Juan J. , Giannibelli M. Cristina
Published: May 2006

Near‐isogenic lines of soybean (Glycine max [L.] Merr.) cv. Clark carrying nuclear ‘stay green’ genes were examined to determine the effects of these genes on the breakdown of thylakoid membranes during senescence. In order to accelerate their senescence, mature leaves were excised and incubated in darkness for 7 days. The homozygous combination of the recessive alleles d1 and d2 (at two different nuclear loci), with or without G (a dominant allele in another locus that causes green seed coat) inhibited the loss of chlorophyll and thylakoid proteins during senescence. Electron micrographs of leaves of cv. Clark during the yellowing process showed chloroplasts in various stages of disintegration; their thylakoid network was disrupted and abundant osmiophilic globuli formed. These senescent leaves also showed evident signs of deterioration of the plasma membrane, including discontinuities, invaginations and membrane ‘whorls’. In contrast, leaves carrying d1d1d2d2 and GGd1d1d2d2 did not show signs of plasma membrane degradation, and their chloroplasts appeared intact, with a continuous, unbroken thylakoid network and tightly stacked grana.

Exogenous applications of abscisic acid (1 and 10 μM), methyl jasmonate (10 μM) or ethylene (1 and 10 μl]−1) accelerated chlorophyll degradation in cv. Clark, but had no appreciable effect in d1d1d2d2 and GGd1d1d2d2, which indicates that their pheno‐types are not due to a deficiency in any of these hormones. The nuclear ‘stay green’ genotypes d1d1d2d2 and GGd1d1d2d2 exhibit a general incompetence for the degradation of chloroplast membranes and, thus, they may constitute useful tools in the study of the biochemistry and regulation of leaf senescence.
Photosynthesis in cold acclimated leaves of plants with various degrees of freezing tolerance
Authors: Bauer Helmut , Nagele Monika , Comploj Monica , Galler Verena , Mair Monika , Unterpertinger Edith
Published: May 2006

The objective of this study was to compare the photosynthetic changes during cold acclimation in various plant types able to acquire different degrees of freezing tolerance. Four herbaceous and six woody plants were hardened under natural or artificial conditions and – after determination of their frost resistance (LT50) – the net photosynthetic rate at an ambient CO2 of 33 Pa (Pn33), the dependencies of Pn to light and to CO2 and the room temperature chlorophyll a fluorescence were recorded under optimal conditions.

Herbaceous plants acquired freezing tolerances to temperatures between −10 and −15°C when hardened at temperatures around 0°C. Most leaves fully developed prior to frost hardening exhibited typical symptoms of senescence after frost hardening. In non‐senescing leaves Pn33 was reduced by 15 to 50% mainly due to a reduced stomatal conductance. After hardening at temperatures around −10°C Brassica survived down to −24°C, but Pn33 was almost abolished as a result of disturbances in the chloroplasts. After transferring the plants to 20/15°C Pn33 recovered completely within a few days. Woody plants hardened at temperatures around 0°C tolerated – 15 to −36°C: Pn33 was reduced by 25 to 60% and hardly recovered at 20/15°C. Hardening at −10°C induced a tolerance of −32 to <−80°C. Pn33 was almost totally blocked, but at 20/15°C it returned to the values of the plants hardened at 0°C within a few days. In woody plants disturbances were invariably localized in the chloroplasts.

Thus, conifers, and especially Pinus cembra, can survive much lower temperatures than herbaceous plants and, at the same level of freezing tolerance, exhibit appreciably less restriction in relative Pn33.
The effects of continuous illumination on southern and northern Micrasterias strains
Authors: Lehtonen Juhani A. , Volanto‐Lumppio Katja , Vuorio Päivi
Published: May 2006

Different strains of Micrasterias (Chlorophyta, Conjugatophyceae); M. rotata (Grev.) Ralfs ex. Ralfs and M. denticulata Breb. ex. Ralfs var. angulosa (Hantzsch) W. & G. S. West from northern and southern Finland were treated with continuous illumination in order to study the cellular effects of the treatment and whether the tolerance to continuous light of the northern Finnish strains is related to the different daylenght conditions in northern and southern areas. During the growing season the Finnish strains normally live in long‐day conditions or even in continuous light (between 60 and 70°N), and they also tolerated continuous illumination in the laboratory. Ultrastructural changes were found especially in the chloroplasts, where formation of calcium precipitates of different forms and sizes and also formation of plastoglobuli containing lipids appeared. However, even in 4‐week treatments the ultrastructure of cells of these northern strains was not totally disrupted, contrary to what was found in southern M. torreyi, studied earlier. Southern and northern strains tolerated continuous illumination in different ways. They seem to differ from each other physiologically, and the differences are possibly located in their ionic metabolism and regulation. The injuries sustained during continuous illumination of Micrasterias may largely be caused by the accumulation of Ca2+ in cytoplasm and organelles, especially in the chloroplasts.
Appearance of nitrate reductase, nitrite reductase and glutamine synthetase in different organs of the Scots pine (Pinus sylvestris) seedling as affected by light, nitrate and ammonium
Authors: Seith Bettina , Setzer Bernhard , Flaig Holger , Mohr Hans
Published: May 2006

Appearance of nitrate reductase (NR, EC 1.6.6.1–3), nitrite reductase (NiR, EC 1.7.7.1) and glutamine synthetase (GS, EC 6.3.1.2) under the control of nitrate, ammonium and light was studied in roots, hypocotyls and needles (cotyledonary whorl) of the Scots pine (Pinus sylvestris L.) seedling. It was found that appearance of NiR was mainly controlled by nitrate whereas appearance of GS was strongly controlled by light. In principle, the NR activity level showed the same dependency on nitrate and light as that of NiR. In the root, both nitrate and ammonium had a stimulatory effect on GS activity whereas in the whorl the induction was minor. The level of NiR (NR) activity is high in the root and hypocotyl and low in the cotyledonary whorl, whereas the GS activity level per organ increases strongly from the root to the whorl. Thus, in any particular organ the operation of the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle is not closely connected to the operation of the nitrate reduction pathway. The strong control of GS/GOGAT by light and the minor sensitivity to induction by nitrate or ammonium indicate a major role of the GS/GOGAT cycle in reassimilation of endogeniously generated ammonium.
Boron uptake by sunflower, squash and cultured tobacco cells
Authors: Brown Patrick H. , Hu Hening
Published: May 2006

Boron uptake was studied in sunflower (Helianthus annuus cv. Ha301), squash (Cucurbita pepo cv. Early prolific straight neck) and cultured tobacco (Nicotiana tobacum L. cv. TXD Monsanto cell line) cells with the use of stable B isotopes and inductively coupled plasma mass spectrometry. Boron uptake increased linearly with increasing B concentrations in the uptake medium, did not exhibit multiphasic kinetics and was not saturable over a wide concentration range. The addition of respiratory inhibitors to the uptake solution or exposure to low (2°C) or high (42°C) temperatures did not inhibit B uptake. The majority of the B within the plants, including recently absorbed B, was present in a nonexchangeable form and could not be removed by repeated rinsing with deionized water or exchange with B isotope. These results demonstrate that in these species B uptake is a passive, nonmetabolic process and that the formation of nonexchangeable B‐complexes within the cytoplasm and cell wall is a key factor in determining the uptake of B by plants.
Effects of ATP analogs on the proton pumping by the vacuolar H+‐ATPase from maize roots
Authors: Brauer David , Tu Shu‐I
Published: May 2006

Understanding the regulatory properties of the activities of the V‐type adenosine triphosphatase (ATPase) on tonoplast membranes is important in determining the mechanisms by which this enzyme controls cytoplasmic and vacuolar pH. The possible existence of a regulatory site for adenine nucleotides was examined by comparing the effects of ADP, adenylylimidodiphosphate (AMP‐PNP) and 3′‐o‐(4‐benzoyl) benzoyladenine 5′‐triphosphate (BzATP) to those of the 2′,3′‐dialdehyde derivative of AMP (oAMP) and ATP by using highly purified tonoplast vesicles from maize (Zea mays L. cv. FRB 73) roots. The addition of either AMP‐PNP or BzATP reversibly inhibited the initial rate of proton transport catalyzed by the H+‐ATPase in a concentration‐dependent manner. Less than 20 μM AMP‐PNP or 50 μM BzATP was sufficient to inhibit half the initial rate of proton transport in the presence of 2 mM ATP and an excess of Mg. Both analogs increased the Km for ATP and reduced the maximum enzyme velocity. The presence of ADP also inhibited proton transport. The characteristics of ADP‐induced inhibition were similar to those of BzATP and AMP‐PNP. The addition of the periodated derivative of AMP (oAMP) irreversibly inhibited the ATPase in a concentration and time‐dependent manner similar to that reported previously (Chow et al. 1992, Plant Physiology 98: 44–52). Irreversible inhibition by oAMP reduced the maximum velocity of the tonoplast ATPase and was prevented by the addition of ATP. The presence of ADP, AMP‐PNP or BzATP had no effect on irreversible inhibition by oAMP. The effects of ADP, AMP‐PNP and BzATP on the kinetics of ATP utilization and the lack of protection against inhibition by oAMP argue in favor of at least two types of nucleotide binding sites on the V‐type ATPase from maize root tonoplast membranes.
Effect of the physical nature of the culture medium on the metabolism of benzyladenine and endogenous cytokinins in Actinida deliciosa tissues cultured in vitro
Authors: Feito I. , Rodríguez A. , Centeno M.L. , Sánchez‐Tamés R. , Fernández B.
Published: May 2006

Endogenous cytokinin and benzyladenine (BA) metabolites were studied in kiwifruit explants grown on solidified and liquid Murashige and Skoog media supplemented with BA. The same proliferation rate was observed in both media. However, in the liquid medium the release from apical dominance was faster and the growth rate was higher than on solid medium. At the same time the number of vitrified shoots increased considerably in the liquid cultures. Exogenous BA was transformed into 9‐β‐D‐glucopyranosyl‐BA ([9G]BA), 7‐β‐D‐glucopyranosyl‐BA ([7G]BA). 7‐β‐D‐ribofura‐nosyl‐BA ([9R]BA) and the 51‐monophosphate of [9R]BA ([9R‐51P]BA). The proportion of active forms (BA, [9R‐51P]BA and [9R]BA) in respect to total BA metabolites, was generally higher in shoots from liquid than from solid media. An exception was found at day 20 when this balance was inverted. Endogenous cytokinins in kiwifruit shoots were measured by enzyme‐linked immuno sorbent assay (ELISA). The content of natural cytokinins was influenced by the levels of active forms of BA.
Abscisic acid and stress regulate gene expression during germination of chick‐pea seeds. Possible role of calcium
Authors: Colorado Pilar , Rodríguez Antonio , Nicolás Gregorio , Rodríguez Dolores
Published: May 2006

A cDNA library has been constructed using poly (A+) RNA isolated from embryonic axes of chick‐pea (Cicer arietinum L. cv. Castellana) seeds germinated for 12 h in 50 μM abscisic acid (ABA). By differential screening three clones (designated GAB‐8, GAB‐9, GAB‐11) regulated by ABA were identified. Northern analysis of these clones revealed that their transcripts decline early during normal germination but are maintained or even increased by exogenous ABA. The levels of these transcripts were analyzed after subjecting seeds to stressful conditions (low and high temperature, osmotic and saline stress). Each of them responded differently to the conditions used. Only effects of high temperature and osmotic stress on transcript levels could be correlated with the effect of ABA in the seed. The possible role of calcium on mRNA accumulation was studied, revealing that the expression of the ABA‐regulated clones seems to depend on the presence of calcium ions, suggesting that calcium is involved in the response of the seeds to ABA.
Evidence that short‐term regulation of nodule permeability does not occur in the inner cortex
Authors: Van Cauwenberghe Owen R. , Hunt Stephen , Newcomb William , Canny Martin J. , Layzell David B.
Published: May 2006

Regulation of nodule permeability in response to short‐term changes in environmental and physiological conditions is thought to occur by occlusion of intercellular spaces in the nodule inner cortex. To test this hypothesis, the permeability of legume nodules was altered by adapting them to either 20 or 80% O2 over a 2.5‐h period. The nodules were then rapidly frozen, cryo‐planed and examined under cryo‐scanning electron microscopy for differences in the number, area or shape factor of intercellular spaces. Comparisons were made between whole nodules and specific nodule zones (outer cortex, middle cortex, inner cortex and central zone) in each treatment. Gas analysis measurements indicated that nodules equilibrated at 20% O2 had a 6.6‐fold higher permeability than those equilibrated at 80% O2 However, no significant differences were observed between pO2 treatments in the number of open intercellular spaces, the cross‐sectional area of those spaces, or the proportion of the tissue area present as open space in whole nodules or any nodule zone. Also, although nodules in both treatments possessed a boundary layer of tightly packed cells in the inner cortex, the total area of intercellular spaces between cells bordering this layer did not differ between treatments. Together these observations do not support the currently favored hypothesis that nodule permeability is regulated by opening or occlusion of intercellular spaces in the nodule inner cortex. Highly significant differences (P= 0.0006) were observed between O2 treatments in the shape factor of the open intercellular spaces in all nodule zones. Nodules equilibrated at 80% O2 had significantly more isodiametric spaces while those equilibrated at 20% O2 had more long, narrow spaces. This observation suggests that the critical step in the regulation of nodule permeability to O2 may be localized in the central, infected zone and involve changes in the ratio of the surface area of the intercellular space to the volume of the infected cell.