bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of ovary growth on ovule development in Cucumis sativus
Authors: Varga A. , Bruinsma J.
Published: May 2006

The requirement of ovule development for fruit growth in Cucumis sativus L. was studied using different cultivars of gherkin and cucumber. The latter, particularly, show considerable ovary growth already prior to flowering. With non‐parthenocarpic cultivars, this growth stops and the fruitlets wither in ca 2 weeks post‐anthesis if no pollination occurs, whereas ovaries of non‐pollinated, parthenocarpic varieties may develop into maturity nearly as well as pollinated ones. Fruit growth turned out to be correlated with the number and size of seeds or, in the case of parthenocarpy, of empty seed‐like structures, the pseudo‐seeds. Fruit growth is enhanced beyond the parthenocarpic level by pollination. Sectorially different fruit growth, as observed in pollinated cucumber, can be ascribed to the inability of pollen tubes to reach the ovules at the pedicel end of the elongated ovary. Experiments with irradiated pollen and with style removal indicate that fertilization of ovules is not required, physical contact with the pollen tubes suffices to stimulate ovary growth. The nature of the stimulating factor is unknown.
Abscisic add levels of individual leaf cells
Authors: Brinckmann Enno , Hartung Wolfram , Wartinger Margarete
Published: May 2006

Abscisic acid (ABA) concentrations of guard cells, subsidiary cells and epidermis cells of Comrnelina communis L. and Tradescantia virginiana L. were determined in cell sap samples extracted by means of micro glass capillaries. Concentrations up to 6.7 mM were indicated by commercial immunoassay test kits. A gradient of ABA concentration was found between guard cells (2,49 ± 1.81 mM, n = 25), subsidiary cells (1.25 ± 1.46 mM, n = 21) and epidermis cells (0.86 ± 0.76 mM, n = 20; mean values ± SD).
Effects of sodium, potassium and calcium on salt‐stressed barley. I. Growth analysis
Authors: Cramer Grant R. , Epstein Emanuel , Läuchli André
Published: May 2006

Barley (Hordeum vulgare L. cv. CM 72) was grown for a 28‐day period and stressed with treatments of 125 mol m−3 NaCl or KC1 with low Ca2+ (0.4 mol m−3 Ca2+) or high Ca2+ (10 mol m−3 Ca2+). Plants were harvested periodically so that relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) could be calculated using the functional approach to plant growth analysis. Relative growth rate declined with time for all treatments, including controls. Salinity inhibited RGR relative to control values by day 10. High Ca2+ improved the growth of salt‐stressed plants in both NaCl‐salinity and KCl‐salinity. KC1 proved more toxic than NaCl, especially for KCI‐salinity plants with low Ca2+, which died by day 28. Net assimilation rate, but not LAR, was highly correlated with RGR for all treatments. This indicates that the photosynthetic‐assimilatory machinery was limiting RGR and not the leaf area of the plant.
Stimulation of ACC‐dependent ethylene production in citrus leaf discs by light
Authors: Zacarias Lorenzo , Hidela Darius , Primo‐Millo Eduardo
Published: May 2006

The influence of light and darkness incubation on in vivo ethylene forming enzyme (EFE) activity in citrus (Citrus sinensis L. Osbeck cv. Salustiana) mature leaf discs was studied. Leaf discs incubated in light produced higher amounts of ethylene than in darkness. Transfer of discs from light to the dark resulted in a marked inhibition of EFE activity, whereas transfer of discs from the dark to light enhanced ethylene forming activity considerably. Light did not affect 1‐aminocyclopropane‐l‐carboxylie acid (ACC) uptake. Incubation in a CO2‐eniiched atmosphere enhanced EFE activity both in light and in darkness, but light stimulation of EFE activity was apparently not affected by CO2. Effects of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU, inhibitor of photosynthetic electron flow) and KCN (inhibitor of cytochrome oxidase) were studied. DCMU at 0.2 mM inhibited EFE activity in light, whereas no effect was detected in the dark. On the other hand 1 mM KCN stimulated EFE activity in the light, and no significant effect was observed in the dark. CoCl2 at 1 mM inhibited ACC‐dependent ethylene production, suggesting that ethylene production from ACC is mediated by EFE in citrus leaf discs both in light and in the dark. Cycloheximide also inhibited EFE activity in the light and no effects were detected in the dark. Therefore protein synthesis in light (perhaps EFE synthesis) could be required for the light stimulation of the in vivo EFE activity.
Synthesis of protein and mRNA is necessary for transition of suspension‐cultured Catharanthus roseus cells from the G1 to the S phase of the cell cycle
Authors: Ohnishi Naoto , Kodania Hiroaki , Ando Satoshi , Komamine Atsushi
Published: May 2006

The effects of inhibition of the synthesis of protein, mRNA or rRNA on the progression of the cell cycle have been analyzed in cultures of Catharanthus roseus in which cells were induced to divide in synchrony by the double phosphate starvation method. The partial inhibition of protein synthesis at the G1 phase by anisoniycio or cycloheximide caused the arrest of cells in the G1 phase or delayed the entry of cells into the S phase. When protein synthesis was partially inhibited at the S phase, cell division occurred to about the same extent as in the control. When asynchronously dividing cells were treated with cycloheximide, cells accumulated in the G1 phase, as shown by flow‐cytometric analysis. The partial inhibition of mRNA synthesis by α‐amanitin at the G1 phase caused the arrest of cells in the G1 phase, although partial inhibition of mRNA synthesis at the S phase had little effect on cell division. In the case of inhibition of synthesis of rRNA by actinomycin D at the G1 phase, initiation of DNA synthesis was observed, but no subsequent DNA synthesis or the division of cells occurred. However, the addition of actinomycin D during the S phase had no effect on cell division. These results suggest that specific protein(s), required for the progression of the cell cycle, are synthesized in the G1 phase, and that the mRNA(s) that encode these proteins are also synthesized at the G1 phase.
Xylogliicae‐ and cello‐oligosaccharides: Antagonists of the growth‐promoting effect of H+
Authors: Lorences Ester P. , McDougall Gordon J. , Fry Stephen C.
Published: May 2006

Xyloglucan‐oligosaccharides and cello‐oligosaccharides, both of which are potential products of the action of cellulase on plant cell wail polysaccharides, inhibited acid‐induced elongation in pea (Pisum sativum L. cv. Alaska) stem segments. Xyloglucan‐derived nonasaccharide (XG9; Glc4‐Xyl3)Gal‐Fuc) and decasaccharide (XG10; Glc4‐Xyl3‐Gal2‐Fue) inhibited acid‐induced growth at 1.0 and 0.1 nM, respectively, whereas the heptasaccharide (XG7; Glc4‐Xyl3) and octasaccharide (XG8; Glc4‐Xyl3‐Gal)2 which lack L‐fucose, did not. XG9 at 1 nM inhibited acid‐induced growth as effectively as it inhibits auxin‐induced elongation. This suggests that XG9's effect as an inhibitor of auxin action is not mediated by a suppresion of H+‐efflux, but rather that XG9 blocks some step that is common to the action of both auxin and H+ on growth. Cello‐oligosaccharides (degree of polymerisation 4–7) also inhibited acid‐induced growth at 10 nM; these are therefore a new class of possible oligosaccha‐rin. The inhibitory effect of xyloglucan‐ and cellooligosaccharides on acid‐induced growth was rapidly reversed by washing.
Effect of cellulase fractionation on the viability of cultured barley (Hordeum vulgare) protoplasts
Authors: Krogaard Helle , Andersen Arne Skytt
Published: May 2006

The age of the stock plants was important for the barley (Hordeum vulgare L. cv. Perth) protoplast viability. Light conditions under which the stock plants were grown also affected the viability of the protoplasts. Greenhouse‐grown plants yielded much higher number of protoplasts than dark‐grown plants, but protoplast viability was better when protoplasts were isolated from etiolated plants. Light supplied during protoplast culture affected protoplast viability within the first 24 h of culture. Cellulase R‐10 (Onozuka) was better than Cellulysin (Calbiochem) and Cellulase + Macerozyme R‐10 (Onozuka) for barley mesophyll protoplast isolation. Cellulase R‐10 (Onozuka) was fractionated on a G‐75 Sephadex column. The eluted fractions were tested for their ability to release barley mesophyll protoplasts and for their toxicity towards the protoplasts. Only a small part of the Cellulase R‐10 was necessary for protoplast isolation from barley leaves. When the fractionated cellulase was analysed by isoelectric focusing, this part of the cellolase appeared as a single band.
Effects of cold on NAD+ kinase activity in winter rape plants
Authors: Maciejewska Urszula
Published: May 2006

Low temperature (2°C) caused an increase in the activity of NAD+ kinase (EC 2.7.1.23) in leaves of winter rape plants (Brassica napus L. var. oleifera L. cv. Górezański). The enzyme activity markedly increased between day 4 and 11 of plant exposure to cold, then tended to decrease. Changes in activity of NAD+ kinase coincided with the previously observed changes in the levels of pyridine nucleotides, NADP(H) (U. Maciejewska and A. Kacperska, Physiol. Plant. 69: 687–691, 1987). As a result of cold treatment, Ca2+–calmodulin–dependent and Ca2+–calmodulin–independent NAD+ kinase activities increased to almost the same extent. It seems therefore, that the cold–induced activation of NAD+ kinase does not depend on the Ca2+–calmodulin complex.
Partial purification and some biochemical properties of nonspecific alkaline phosphatase in germinating chick‐pea (Cicer arietinum) seeds
Authors: Angosto Trinidad , Matilla Angel
Published: May 2006

A procedure for the partial purification of a non‐specific alkaline phosphatase (EC 3.1.3.1.) from the embryonic axes of chick‐pea seeds is described. Ammonium sulphate precipitation, DEAE‐cellulase chromatography, Sephacryl S‐200 chroma‐tography and polyacrylamide gel electrophoresis are the most important steps. The molecular weight of this non‐specific enzyme, as determined by Sephacryl S–200 gel filtration and SDS–polyacrylamide gel electrophoresis, was estimated as being 68 and 78 kDa respectively; the optimum pH for p‐nitrophenylphosphate hydrolysis was 7.5, and the Km for this artificial substrate was 0.5 mM. The enzyme catalyzes the hydrolysis of a variety of organic phosphate esters. The best substrates are: phos‐phoenolpymvate (Km= 2.4 mM), NADP+ (Km= 4.0 mM), 5′‐AMP (Km= 4.5 mM), 5′‐ADP (Km= 6.1 mM) and ribose‐5P (Km= 5.8 mM); but it is unable to hydrolyze 5′‐ATP, phosphocreatine and tripolyphosptiate. Phospate was a competitive inhibitor. Zn2+, K+, Hg2+ and Mo6+ were strong inhibitors, whereas F− and Ca2+ inhibited weakly; Co2+ and Ni2+ were activators.
Resistance to photodamage in evergreen conifers
Authors: Gillies Sharon L. , Vidaver William
Published: May 2006

Conifers in the temperate zone are subject to extremes in climatic conditions, such as low temperatures and water deficits. Under such conditions chloroplast antenna pigments can absorb more light energy than can be utilized in photosynthesis. If the plant is unable to dissipate this excess energy by combined radiationless decay (heat), fluorescence emission and carotenoid quenching, photodamage can result. Potentially damaging conditions exist during winter when low temperatures often occur simultaneously with intense light levels and desiccation. Photodamage is caused when regulatory controls on the production of toxic oxygen species produced in the chjoroplast and the capacity of scavenging systems to dispose of them are exceeded. By becoming cold‐hardened and dormant, conifer species can resist all but the most severe effects of the winter climates to which they are adapted. Mechanisms which protect chloroplasts from photodamage appear to be among the essential adaptations enabling temperate conifers to resist the effects of drought and low winter temperatures, especially when light levels are high.
Do we have the auxin receptor yet?
Authors: Jones Alan M.
Published: May 2006

Several auxin‐binding proteins (ABP) have now been identified using a variety of techniques. A 43‐kDa glycoprotein thought to be a dimer of 22‐kDa subunits has been identified as a strong candidate for the auxin receptor that mediates cell elongation in etiolated maize shoots. The primary sequence has been deduced and several interesting structural features have been discerned. There is indirect evidence that this 22‐kDa ABP has a receptor function, the most compelling being that antibodies directed against the ABP can block an auxin‐induced response. There is evidence that changes in auxin‐induced growth capacity in shoots correlates with changes in the abundance of the 22‐kDa ABP suggesting that in some cases the 22‐kDa ABP may be limiting growth. Confirmation of receptor function for one of these newly‐identified ABP's should open the way for genetic manipulation of crop growth.
Cold acclimation of wheat (Triticum aestivum): Properties of enzymes involved in proline metabolism
Authors: Charest Christiane , Ton Phan Chon
Published: May 2006

Two cultivars of wheat (Triticum aestivum L.), a winter wheat, Kharkov, and a spring wheat, Glenlea, were acclimated under controlled conditions at 2 temperatures, 5°C and 25°C with a 12‐h photoperiod. Water content, protein and proline concentrations were determined. Enzymatic properties (activity and apparent energy of activation) were investigated for enzymatic systems involved in 2 pathways of proline metabolism, the glutamic acid and ornithine pathways. Four enzymes were studied, proline dehydrogenase (PDH, EC 1.5.1.2), glutamate dehydrogenase (GDH, EC 1.4.1.2‐4), glutamine synthetase (GS, EC 6.3.1.2) and ornithine transaminase (OT, EC 2.6.1.13). Cold acclimation led to an accumulation of proline, a decrease in water content and an increase in soluble protein, especially in winter wheat. For both cultivars, cold acclimation modulated enzyme properties of PDH and GDH. Increased activities of GS and OT were observed as a result of cold acclimation in both cultivars, with the greatest increase in Kharkov. The apparent energy of activation of these 2 enzymes decreased, particularly for Kharkov, which accumulated proline in cold conditions.
Studies on the long‐day inhibition of flowering in Xanthium and Kalanchoe
Authors: Papafotiou Maria , Schwabe Walter W.
Published: May 2006

It is well known in short‐day plants that a leaf held in non‐inductive photoperiods inhibits flowering when interposed between the induced leaf and the apical meristem, in an analogous manner to the basal half of a leaf induced by short‐day in its distal half. This has often been explained by the inhibiting leaf or basal part of an induced leaf becoming the major source of carbohydrates to the apex, rather than the induced leaf itself; i.e. by preventing thus the co‐transported stimulus from reaching the apex. Experiments with Kalanchoe blossfeldiana Poellniz and Xanthium strumarium L. in which carbon dioxide levels were lowered or increased, or 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea injected, or sugar fed to the petioles of a debladed interposed leaf, or night‐breaks given as well as other photoperiodic treatments, all pointed to ‘carbohydrate diversion’ not being the major cause of failure of the short‐day stimulus reaching the target apex. It is tentatively concluded that instead an inhibitory action occurs in the vascular passage of the stimulus preventing co‐transport with the carrier molecule.
Oscillations of membrane potential during inhibition of cytoplasmic streaming in Characean internodes
Authors: Śpiewla Edward , Tokarska Malgorzata
Published: May 2006

Oscillatory changes in electrical parameters of cells of Nitellopsis obtusa (Desv. in Lois) J. Gr. and Nitella flexilis f. Atkahensis R. D. W., particularly in the membrane potential, were investigated with external Ag/AgCl electrodes. Three main types of oscillations were observed. The measurements were carried out on 30 cells with the application of an inhibitor of cytoplasmic streaming (procaine) and revealed that there was no direct correlation between cytoplasmic streaming and oscillations in the membrane potential.
Cysteine, γ‐glutamyl‐cysteine and glutathione contents of spinach leaves as affected by darkness and application of excess sulfur. II. Glutathione accumulation in detached leaves exposed to H2S in the absence of light is stimulated by the supply of glycine to the petiole
Authors: Buwalda F. , Stulen I. , De Kok L. J. , Kuiper P. J. C.
Published: May 2006

When illuminated leaf discs and detached leaves of spinach (Spinacia oleracea L. cv. Estivato) were exposed to 0.4 and 0.25 μl 1‐1 H2S, respectively, pool sizes of cysteine and glutathione increased. In the dark, apart from these compounds, the level of γ‐glutamyl‐cysteine also increased. Incubation of leaf discs with 1.0 mM buthionine sulfoximine (BSO) resulted in the accumulation of cysteine only, both in the light and in darkness. When glycine was supplied to the petioles of detached leaves exposed to H2S in the dark, the accumulation of glutathione was stimulated, while γ‐glutamyl‐cysteine accumulation was prevented completely. Glycolate and glyoxylate, precursors of glycine in the glycolate pathway, had nearly the same effect as glycine. Although other amino acids were apparently taken up equally well as glycine when supplied to the petiole, they were much less effective, or not effective at all, in restoring glutathione synthesis in the dark. These results provide evidence, that H2S‐induced glutathione accumulation in spinach leaves in the dark is limited by the availability of glycine, giving rise to the accumulation of the metabolic precursor γ‐glutamyl‐cysteine.
Salt‐induced cooperativity in ATPase activity of plasma membrane‐enriched fractions from cultured Citrus cells: kinetic evidence
Authors: Ben‐Hayyim Gozal , Ran Uri
Published: May 2006

ATPase activity was studied in plasma membrane‐enriched fractions prepared from cultured Citrus sinensis L. cv. Osbeck cells. In general, properties of the plasma membrane ATPase from cultured cells, such as optimal pH and temperature. Vmax and Km were similar to those already observed in higher plants. The effects of high salt concentrations on ATPase activity were studied in membrane fractions derived from salt‐sensitive and salt‐tolerant cells grown in the presence or absence of salt. NaCl did not have an in vivo effect on Vmax and the apparent Km value for ATP. However, high concentrations of NaCl, or KCl, added in vitro, induced cooperativity in the enzyme and reduced the affinity of the enzyme for its substrate. Isoosmolar concentrations of sucrose or choline chloride failed to do so. Our results suggest that the plasma membrane ATPase of Citrus cells has more than one substrate‐binding site on the native form of the enzyme which interact in the presence of salt and act independently in its absence.
A mechanism of mitochondrial damage induced by tert‐butyl hydroperoxide and microsomes in vitro
Authors: Matsuo Tomoaki , Kashiwaki Yumiko , Itoo Saburo
Published: May 2006

Isolated potato (Solanum tuberosum L. cv. Dansyaku) tuber mitochondria showed a significant loss in respiratory activity when treated with tert‐butyl hydroperoxide (BHP), especially in the presence of microsomes. The following alterations appeared in parallel with the gradual decrease in the respiratory activity: The outer membrane became leaky, probably due to peroxidation of phospholipids. The level of sulfhydryl (SH) groups in mitochondrial proteins decreased in contrast to non‐protein SH groups. A considerable amount of phospholipids was degraded and lost. A mechanism of the mitochondrial damage induced by BHP and microsomes is discussed with respect to a significant role of free radicals which may be formed at the onset of senescence or physiological disorders.
Properties of glutamate dehydrogenase from developing maize endosperm
Authors: Šukalović Vesna Hadži‐Taškovć
Published: May 2006

Glutamate dehydrogenase (EC 1.4.1.3) activity was assayed in homogenates of maize (Zea mays L. inbred lines Oh43 and Oh43o2) endosperm during development. During the period 20–35 days after pollination anabolic (aminative) activities were higher than catabolic (deaminating) ones. In order to study the regulation of GDH activity, glutamine or glutamate were injected into the ear peduncle before sample harvesting. The amination and deamination reactions showed similar behaviour with different nitrogen sources: glutamine increased, whereas glutamate decreased, both aminative and deaminative reactions. Partially purified enzyme was active with NADH and NADPH in a ratio 9:1. In Tris‐HCl buffer a broad optimum at pH 7.6–8.9 and pH 6.8–8.9 was observed with NADH and NADPH, respectively, NADH activity was activated by Ca2+. Saturation curves for (NH4)2SO4 and NADH showed normal Michaelis‐Menten kinetics in the presence of 1 mM Ca2+, but substrate inhibition occurred without Ca2+. The enzyme was inactivated by EDTA. The effect of EDTA was reversed by Ca2+ and Mn2+, but not by Cu2+ and Mg2+.
Correlations between activated charcoal, Fe‐EDTA and other organic media ingredients in cultured anthers of Anemone canadensis
Authors: Johansson Lars B. , Calleberg Eva , Gedin Ann
Published: May 2006

The effects of activated charcoal and organic substances on embryogenesis in anther cultures of Anemone canadensis L. were studied. Embryogenesis was independent of the presence in the culture medium of glycine, nicotinic acid, pyridoxine, thiamine, folic acid, d‐biotin or myoinositol. Absence of Fe‐EDTA totally inhibited embryogenesis. Activated charcoal (AC) adsorbed Fe‐EDTA, pyridoxine, folic acid and nicotinic acid in a double‐layer medium almost completely within 24 h. If petri dishes according to the souble‐layer method were stored overnight or more, embryogenesis was totally inhibited, probably due to adsorbtion of Fe‐EDTA by AC. It was shown that AC itself released some yet unidentified substance(s) that stimulated embryogenesis. The addition of polyvinylpolypyrrolidone (PVPP) to the culture medium stimulated embryogenesis, but PVPP was not as efficient as AC. Embryogenesis was totally inhibited when AC and PVPP were applied together. Minor additions of ethanol to the culture medium stimulated embryogenesis when AC was present, but no such effect was obtained when AC was absent.
Glycosidases of apple fruit: A multi‐functional β‐galactosidase
Authors: Dick Arthur J. , Opoku‐Gyamfua Angelina , DeMarco Alphonse C.
Published: May 2006

Extraction of Spartan apple (Malus domestica) fruit acetone powder and fractionation of the extract on DEAE‐agarose allowed detection and quantification of 10 glycosidases active toward 4‐methylumbelliferyl glycosides. Hydrolysis was measured fluorimetrically. The predominant activity, a β‐d‐galactosidase (EC 3.2.1.23), labile upon purification, was stabilized by soluble PVP. Molecular weights, measured by gel permeation HPLC, pH optima and Km values were obtained for most glycosidase activities. Multiple forms of several activities were found. The major α‐d‐ and β‐d‐galactosidases were resolved on phosphocellulose. The β‐d‐galactosidase so obtained had associated α‐l‐arabinopyranosidase and β‐d‐fucosidase activities which were retained upon GP‐HPLC. Mixed substrate kinetic analysis and inhibition analysis of this fraction indicated that the enzyme has 3 catalytic sites, 1 for each substrate, whose substrates mutually influence each other's activity positively.
The dose‐response curves for IAA induced elongation growth and acidification of the incubation medium of Zea mays coleoptile segments
Authors: Karcz W. , Stolarek J. , Pietruszka M. , Malkowski E.
Published: May 2006

The initial dose‐response curves for auxin‐induced elongation growth of Zea mays L. coleoptile segments and simultaneously measured changes of pH of the incubation medium were studied. It was found that these curves are bell‐shaped on all occasions and that at all IAA concentrations studied acidification of the incubation medium took place. The optimum response for IAA‐induced elongation growth and acidification of the incubation medium was 10−5 and 10−4M IAA, respectively. The regression curves and correlation coefficients between magnitude of the growth response and acidification of the incubation medium indicated a close relationship between these sets of data over a wide range of IAA concentrations.
The role of extracellular carbonic anhydrase for accumulation of inorganic carbon in the green alga Chlamydomonas reinhardtii. A comparison between wild‐type and cell‐wall‐less mutant cells
Authors: Palmqvist Kristin , Ramazanov Zakir , Samuelsson Göran
Published: May 2006

The role of extracellular carbonic anhydrase (CAex) for dissolved inorganic carbon (DIC) accumulation in the green alga Chlamydomonas reinhardtii was investigated. It was found that when algal cells were bubbled with ambient air, cell‐wall‐less mutant cells exhibited the same high photosynthetic affinity for CO2 as wild‐type cells despite a 10 times lower activity of CAex. It was also found that the affinity for CO2 was further increased when the total DIC concentration of the algal medium was reduced from that in equilibrium with ambient air to even lower levels. This increased affinity was not correlated with any further increase in the CAex activity.

Dextran‐bound sulfonamide (DBS. 100 μM bound ligand) completely inhibited the activity of CAex in intact, low‐DIC grown, wild‐type cells, while photosynthesis at <2 μM CO2(aq) proceeded at a far greater rate than could be maintained by CO2 supplied from the spontaneous dehydration of HCO−3. DBS‐inhibition of CAex, during the induction of the DIC‐accumulating mechanism in previously high‐DIC grown cells, only caused a 50% inhibition of photosynthesis at 10 μM CO2(aq) after 1 h of low‐DIC acclimation. It was also shown that 50 μM acetazolamide (AZ) inhibited photosynthesis at low DIC concentrations to a relatively higher degree than DBS, suggesting that AZ inhibited intracellular CA as well.

Taken together, these results suggest that low‐DIC grown cells of C. reinhardtii have the ability to transport HCO−3 across the plasma membrane in addition to the CAex‐mediated, facilitated diffusion and/or transport of CO2. It is also suggested that the relative importance of these two fluxes (CO2 or HCO−3) is dependent on the growth and experimental conditions. Facilitated CO2 uptake seems to be most prevalent, supported by HCO−3‐transport under more or less extreme situations, such as a reduction of CO2 to extremely low concentrations, leakage of CAex to the medium as in cultures of cell‐wall‐less mutant cells or when the activity of CAex has been artificially inhibited.
Chlorophyll synthetase is latent in well preserved prolamellar bodies of etiolated wheat
Authors: Lindsten Agneta , Welch Cristopher John , Schoch Siegrid , Ryberg Margareta , Rüdiger Wolfhart , Sundqvist Christer
Published: May 2006

Membrane fractions containing intact etioplasts, etioplast inner membranes, prolamellar bodies or prothylakoids from wheat (Triticum aestivum L. cv. Walde) were assayed for chlorophyll synthetase activity. Calculated on a protein basis, the etioplast inner membrane fraction showed a higher activity than the intact etioplasts. The activity was higher in the prolamellar body fraction than in the prothylakoid fraction. However, when the fractions were incubated in isolation medium with 50% (w/w) sucrose and 0.3 mM NADPH, chlorophyll synthetase activity could not be detected in the prolamellar body fraction, while the prothylakoid fraction maintained a high activity. The spectral shift to a shorter wavelength of the newly formed endogenous chlorophyllide was very rapid in the prothylakoid fraction but slow in the prolamellar body fraction. The relation between the spectral shift of chlorophyllide and the esterification activity in the fractions is discussed. Even exogenous short‐wavelength chlorophyllide could not be esterified in well preserved prolamellar bodies. This indicates that chlorophyll synthetase is present in an inactive state in the prolamellar body structure. A large‐scale method for the synthesis of geranylgeranylpyrophosphate, one of the substrates of the chlorophyll synthetase reaction, is also presented.
Response to osmotic medium and fusicoccin by seeds of radish (Raphanus sativus) in the early phase of germination
Authors: Cocucci Sergio M. , Morgutti Silvia , Abruzzese Alessandro , Alisi Chiara
Published: May 2006

The effect of increasing osmotic values of the medium (mannitol) on the growth and the response mechanisms of seeds of radish (Raphanus sativus L., cv. Ton do Rosso Quarantino) during the early phase of germination was investigated in the presence or absence of fusicoccin (FC). Decreasing the water potential in the medium inhibited the growth and the evolution of protein synthesis and enhanced H+ extrusion, net uptake of K+ and malic acid synthesis. FC, which stimulates these latter functions, counteracted the inhibitory effect of the decreasing water potential of the medium on growth and protein synthesis. Neither in the absence nor in the presence of FC did decreasing water potential of the medium enhance the synthesis of soluble sugars and amino acids to support the osmotic pressure of the seeds. The osmotic and water potentials of the seeds increased during germination. FC made the increase more rapid, while mannitol kept both potentials low. The pressure potentials of the seeds also decreased with time, and both FC and mannitol enhanced this change. If the seeds were without turgor, the development of protein synthesis was blocked. The seeds counteract the effect of decreasing water potentials in the medium by: a) enhancing H+ extrusion (and, as a consequence, wall loosening and transport mechanisms) and the synthesis of malic acid as apparent in the presence of FC; b) regulating the osmotic potentials of the cells (with a lower dilution of the osmotic compounds present in the seeds due to the diminished uptake of water); c) controlling the growth through the effects of a) and b) on the pressure potentials (internal hydrostatic pressure) of the seeds and on protein synthesis.
Heat shock proteins in willow (Salix viminalis)
Authors: Vahala Tiina , Eriksson Tage , Engström Peter
Published: May 2006

The heat shock response in three vegetatively propagated clones of Salix viminalis L. was studied. In the clone 78198, synthesis of a total of 58 proteins was induced or increased by heat shock. Of these proteins, 39 were found in both leaves and callus, 8 only in leaves, and 11 only in callus. The number of heat shock proteins differed between the three clones studied. The molecular weights of the heat shock proteins ranged from 18000 to over 94000. The optimal synthesis of heat shock proteins took place at 37–40°C, but several proteins could be induced at 25–30°C. The synthesis of the majority of the proteins present at a normal growth temperature (20°C) was not completely blocked by the heat shock. More than 12 h was needed for the reappearance of the normal protein synthesis pattern after heat shock.
Phosphate and calcium uptake in beech (Fagus sylvatica) in the presence of aluminium and natural fulvic acids
Authors: Asp Håkan , Berggren Dan
Published: May 2006

In the present study we examine the effects of Al on the uptake of Ca2+ and H2PO‐4 in beech (Fagus sylvatica L.) grown in inorganic nutrient solutions and nutrient solutions supplied with natural fulvic acids (FA). All the solutions used were chemically well characterized. The uptake of Al by roots of intact plants exposed to solutions containing 0, 0.15 or 0.3 mM AlCl3 for 24 h, was significantly less if FA (300 mg l−1) were also present in the solutions. The Ca2+(45Ca2+) uptake was less affected by Al in solutions supplied with FA than in solutions without FA. There was a strong negative correlation between the Al and Ca2+ uptake (r2=0.98). When the Al and Ca2+ (45Ca2+) uptake were plotted as a function of the Al3+ activity (or concentration of inorganic mononuclear Al), almost the same response curves were obtained for the ‐FA and +FA treatments. We conclude that FA‐complexed Al was not available for root uptake and therefore could not affect the Ca2+ uptake. The competitive effect of Al on the Ca2+ uptake was also shown in a 5‐week cultivation experiment, where the Ca concentration in shoots decreased at an AlCl3 concentration of 0.3 mM. The effect of Al on H2PO−4 uptake was more complex. The P content in roots and shoots was not significantly affected, compared with the control, by cultivation for 5 weeks in a solution supplied with 0.3 mM AlCl3, despite a reduction of the H2PO−4 concentration in the nutrient solution to about one‐tenth. At this concentration Al obviously had a positive effect on H2PO−4 uptake. The presence of FA decreased 32P‐phosphate uptake by more than 60% during 24 h, and the addition of 0.15 or 0.3 mM AlCl3 to these solutions did not alter the uptake of 32P‐phosphate.
Oxygen and the regulation of nitrogen fixation in legume nodules
Authors: Layzell David B. , Hunt Stephen
Published: May 2006

In N2‐fixing legume nodules, O2 is required in large amounts for aerobic respiration, yet nitrogenase, the bacterial enzyme that fixes N2, is O2 labile. A high rate of O2 consumptition and a cortical barrier to gas diffusion work together to maintain a low, non‐inhibitory O2 concentration in the central, infected zone of the nodule. At this low O2 concentration, cytosolic leghemoglobin is required to facilitate the diffusion of O2 through the infected cell to the bacteria. The resistance of the cortical diffusion barrier is variable and is used by legume nodules to regulate the O2 concentration in the infected cells such that it limits aerobic respiration and N2 fixation at all times. The resistance of the diffusion barrier and therefore the degree of O2 limitation seems to be regulated in response to changes in the O2 concentration of the central infected zone, the supply of phloem sap to the nodule, and the rate of N assimilation into the end products of fixation.
A simple protocol to purify fresh nuclei from milligram amounts of meristematic pea root tissue for biochemical and flow cytometry applications
Authors: Chiatante Donato , Brusa Paola , Levi Marisa , Sgorbati Sergio , Sparvoli Elio
Published: May 2006

A simple protocol to purify fresh nuclei from very small amounts (mg) of Pisum sativum (cv. Lincoln) root tissue is presented. The protocol is reliable and has been repeated many times; it can be performed within a few hours and needs only a simple modification of common glassware for tissue homogenization. Similar yields of purified nuclei are obtained both with meristematic and adult root tissues using a detergent‐free glyeerol buffer. Purified nuclei can be stored at –20°C for several weeks without any appreciable loss of integrity. The high yield of purified nuclei enables us to use our preparations for biochemical and cytometric investigations.
Ethylene, ethanol, acetaldehyde and carbon dioxide released by Prunus avium shoot cultures
Authors: Righetti B. , Magnanini E. , Infante R. , Predieri S.
Published: May 2006

Wild cherry (Prunus avium L.) shoots were cultured in closed vessels on a proliferation medium and the volatile substances released during incubation at photosynthetic photon flux density of 30 μmol m–2 S–1 were determined. Ethylene and CO2 started forming at the beginning of the incubation period and a linear relationship between their formation was observed even at high CO2 concentrations. After 30 days of culture, CO2 reached a concentration of 30%. Shoots released elhanol and acetaldehyde after several days of incubation.
Changes in gene expression of Scots pine buds during the winter and under experimentally altered light and temperature conditions
Authors: Nuotio S. , Häggman H. , Kupila‐Ahvenniemi S.
Published: May 2006

Vegetative buds of Scots pine (Pinus sylvestris L.) were collected during the apparently dormant phase in January and February and at the beginning of the growth phase in May. Wintering Scots pine plants were placed in climate chambers in which either the daily photoperiod or the temperature simulated the situation in early spring, whereas the other conditions were characteristic of midwinter.

The amount of total ribosome populations and their in vitro translation capacities were independent of the height of the tree or place of collection, but both were dependent on the season; the amount of ribosomes per fresh weight of buds was lower in spring than in winter, whereas the translation capacity in spring exceeded that in winter. Poly(A)+ RNA was purified from the ribosomes and translated in vitro and the translation products were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The polypeptide patterns proved that changes in gene expression can occur in plants growing outdoors even during the season of severe cold. In the climate chamber experiments, lengthening of the daily photoperiod increased the in vitro translation capacity of the buds within 7 days even at temperatures below 0°C, whereas a rise in temperature seemed to cause a more transient stress effect. Both treatments induced alterations in the pattern of in vitro polypeptide synthesis. It is suggested that while improvements in both light and temperature hastened the development of the buds under experimental growth conditions, the lengthening of the day may be the factor which induces a change in wintertime metabolism under natural conditions.
Rice callus physiology – Identification of volatile emissions and their effects on culture growth
Authors: Adkins S. W. , Shiraishi T. , McComb J. A.
Published: May 2006

Rice (Oryza sativa L.) callus cultures modified the atmosphere of the headspace of the vessel used for culture maintenance by producing carbon dioxide, ethanol and ethylene, while utilizing oxygen. Small quantities of acetaldehyde and ethane were also measured in one cultivar. Under these conditions of culture maintenance, callus from some cultivars were much more difficult to keep alive than callus from others. The largest proportion of necrotic callus was produced from cultures growing under conditions of high ethylene production and low oxygen utilization. When callus was exposed to a controlled flowing gas mixture similar to that accumulated above necrotic callus, growth of 2 necrosis‐susceptible cultivars was more strongly inhibited than growth of 2 necrosis‐tolerant cultivars. The poor callus growth was associated with higher ethylene production and a lower rate of oxygen utilization.
Root growth and statocyte polarity in lentil seedling roots grown in microgravity or on a slowly rotating clinostat
Authors: Lorenzi Giovanna , Perbal Gérald
Published: May 2006

The ability of clinostats to simulate microgravity was evaluated by comparing lentil (Lens culinnrias L. cv. Verte du Puy) seedlings grown in space (Spacelab D1 Mission) with seedlings grown on a slowly rotating elinostat. Seeds were germinated and incubated for 25.5 h at 22°C (1) in microgravity, (2) on a 1g‐centrifuge in space. (3) on a slowly rotating elinostat and (4) on the ground. Morphological (root length and orientation) and ultrastructural (distribution of amyloplasts, location of the nucleus in statocytes) parameters were studied. For clinostat experiments, two different configurations were employed: the longitudinal axis of the root was parallel (horizontal elinorotation) or perpendicular (vertical elinorotation) to the axis of rotation. the same configurations were used for the lg‐controls. Root length and orientation were similar for roots grown on the clinostat and in microgravity. The amyloplasts were identically distributed in statocytes of horizontally clinorolated roots and in statocytes differentiated in microgravity. However, the location of the nucleus was similar in vertically rotated roots and microgravity samples. Since the involvement of the nucleus in graviperception is not known, it can be concluded that horizontal clinorotation simulates microgravity better than vertical elinorotation.
Alterations of gene expression in potato (Solanum commersonii) during cold acclimation
Authors: Tseng M. J. , Li P. H.
Published: May 2006

Plantlets of Solanum commersonii stem‐culture were acclimated at 5°C day/night temperature for 14 days. Cold hardiness increased from – 3.5°C to – 8.6°C. During the course of acclimation, the synthesis of polypeptides was investigated and poly (A+) RNA was isolated. Translation products of poly(A+) RNA in a rabbit rcticulocyte lysate system were then analyzed. During the 14 days of acclimation, 23 cold‐induced polypeptides were identified. Most of them disappeared following 1 day of de‐acclimation at a 20/15°C day/night regime. The synthesis of one group of polypeptides is prominent and stable throughout the acclimation period. The other group is transient. The most prominent and stable polypeptides have molecular weights of 21, 22, 31 and 83 kDa.

Acclimation alters translatable mRNA population during the development of cold hardiness. Two mRNAs encoding in vitro translation products at 26 and 27 kDa were identified during the course of acclimation. These proteins may play important roles in the overall programming for the development of cold hardiness in tuber‐bearing S. commersonii.
Interference from xylem sap in an enzyme‐linked immunosorbent assay for zeatin riboside
Authors: Neuman Dawn S. , Smit Barbara A.
Published: May 2006

The extent of interference from xylem sap in an enzyme‐linked immunosorbent assay was determined for a woody perennial [Populus trichocarpa Torr. & Gray x P deltoides Bart, ex Marsh (Hybrid 1l–ll)] and a herbaceous annual (Phasesolus vulgaris L. cv. Contender). Crude xylem sap collected from excised roots from both species interfered with the assay for zeatin riboside. Assays for zeatin riboside in xylem sap collected from Popidus overestimated endogenous levels, and added standards could not be accurately measured from a range of sap dilutions. When Phaseolus plants were grown under various nutrient regimens, interference in the assay was dependent on nutrient availability. Of xylem sap components (inorganic minerals, amino acids and sucrose) which may vary with environmental conditions or among species, only sucrose interfered at the concentrations tested. Since the pH of xylem sap varies it was necessary to buffer samples prior to analysis. Partial purification using anion exchange columns and Sep‐Paks cffectively eliminated interference. These results demonstrate that estimates of plant growth regulators in xylem sap by the ELISA (enzyme‐linked immunosorbant assay) method can be influenced by species and environmental conditions such as plant nutritional status.
Sucrose and fructan metabolism of different wheat cultivars at chilling temperatures
Authors: Tognetti J. A. , Salerno C. L. , Crespi M. D. , Pontis H. G.
Published: May 2006

Four wheat (Triticum aestivum L.) varieties cultivated in different climates from subtropics to North Patagonia were used to study sucrose and fructan metabolism in plants when submitted to a cold period. Higher levels of sugars were found in the more cold tolerant cultivars. Sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14) activities showed a 2–3 fold increase when plants were grown at 4°C for 10 days. The more cold‐tolerant wheat cultivars also showed the higher levels of enzyme activities. These metabolical changes were not due to anatomical or morphological differences produced during growth at 4°C
Vanadate inhibits fructose‐2,6‐bisphosphatase and leads to an inhibition of sucrose synthesis in barley leaves
Authors: Brauer Monika , Stitt Mark
Published: May 2006

Vanadate (0.1–1 mM) was supplied to leaves of barley (Hordeum vulgare var. Roland) via the transpiration stream. It led to a selective inhibition of the rate of photosynthesis at high light without altering the initial slope of the light response curve, produced markedly biphasic photosynthesis induction kinetics, and selectively decreased sucrose synthesis compared to starch synthesis. There was a 3‐fold increase of the steady state level of the signal metabolite fructose‐2,6‐bisphosphate in near saturating light. Fructose‐2,6‐bisphosphate is a potent inhibitor of cytosolic fruc‐tose‐l,6‐bisphosphatase and, in agreement, the fructose‐1,6‐bisphosphatc level doubled. The increase of fructose‐2,6‐bisphosphate could not be accounted for by the known regulation of fructose‐6‐phosphate,2‐kinase and fructose 2,6‐bisphosphatase by 3‐phosphoglycerate and fiuctose‐6‐phosphate, because these metabolites remained constant or even changed in the opposite direction to that required to generate an increase of fructose‐2,6‐bisphosphate. Instead, vanadate strongly inhibited the hydrolysis of fructose‐2,6‐bisphosphate in extracts, producing a half maximal inhibition at 2 \nM and 50 \iM in assays designed to preferentially measure the high‐and low‐affinity forms of fructose‐2,6‐bisphosphatase, respectively. Vanadale had no effect on fructosc‐6‐phosphate,2‐kinase activity at these concentrations. Vanadate also led to a deactivation of sucrose phosphate synthase. The results are discussed in relation to the role of fructose‐2,6‐bisphosphate in regulating sucrose synthesis, and its interaction with the ‘coarse’ control of sucrose phosphate synthase.
Effects of UV‐B radiation on growth and motility of four phytoplankton species
Authors: Ekelund Nils G. A.
Published: May 2006

A depletion of the stratospheric ozone layer would result in an increased UV‐B radiation, which could have harmful effects on marine organisms. The aim of this study was to determine the effects of an enhanced UV‐B radiation (280–320 nin) on the motility and growth in four Swedish phytoplanklon species. The different plankton species were exposed to different doses of UV‐B radiation during growth. The growth of the motile dinoflagellates, Gyronidium aureolum Hulburt (Ba 6), and Prorocentrum minimum (Pav.) P. Schiller (Ba 12), was more sensitive to UV‐B radiation than the non‐motile diatoms Dityhim brightwellii (P. West) Grun (Ba 15) and Phaeodactylum tricornutum Bohlin (Ba 16). One week of UV‐B radiation 2 h daily (159 J m−2 day−1), had a dramatic effect on the growth of the dinoflagellates, while the diatoms were nearly unaffected. On the other hand, when given higher intensity of UV‐B radiation (312, 468 and 624 J m−2 day−1) during the initial phase of growth, also the growth of the diatom, D. brightwellii, was inhibited. Not only the growth but also the swimming speed of the dinoflagellates C. aureolum and P. minimum were affected by UV‐B radiation. The speed decreased rapidly after 1–2 h of UV‐B radiation (312 J m−2 day−1), and after longer irradiation times the dinoflagellates lost their motility. G. aureolum exposed to UV‐B radiation, regained normal speed after two weeks of visible light.