bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation and polypeptide composition of l,3‐ß‐glucan synthase from plasma membranes of Brassica oleracea
Authors: Fredrikson Karin , Kjellbom Per , Larsson Christer
Published: May 2006

The l,3‐ß‐glucan synthase (callose synthase, EC 2.4.1.34) was solubilized from cauliflower (Brassica oleracea L.) plasma membranes with digitonin, and partially purified by ion exchange chromatography and gel filtration [fast protein liquid chromatography (FPLC)] using 3‐[(cholamidopropyl)dimethylammonio]‐1‐propane‐sulfonate (CHAPS) in the elution buffers. These initial steps were necessary to obtain specific precipitation of the enzyme during product entrapment, the final purification step. Five polypeptides of 32, 35, 57, 65 and 66 kDa were highly enriched in the final preparation and are thus likely components of the callose synthase complex. The purified enzyme was activated by Ca2+, spermine and cellobiose in the same way as the enzyme in situ, indicating that no essential subunits were missing. The polyglucan produced by the purified enzyme contained mainly 1,3‐linked glucose.
Oxygen concentration and ethylene production in roots and leaves of wheat: short term reaction in air after anoxic and hypoxic treatments
Authors: Tonutti Pietro , Ramina Angelo
Published: May 2006

Seven‐day old wheat seedlings (Triticum aestivum L. cv. MEC) were incubated in small jars, fluxed with gas mixtures of nitrogen‐oxygen (oxygen concentrations 0. 0.3. 1,2.5, 10%) for up to 48 h. Effects of anoxia and hypoxia on ethylene evolution and ethylene‐forming enzyme (EFE) activity were determined 1 h after the plants had been transferred to air. respectively. l‐aminocyclopropane‐l‐carboxylic acid (ACC) content was measured immediately after treatments. Results showed that the ethylene production is differently affected by oxygen deprivation in roots and leaves. The effects are more closely related to ACC accumulation than to the EFE activity. In leaves, ethylene evolution is almost unaffected by oxygen concentrations above ca 1%.
The impact of freezing during maturation on storage products in canola seeds
Authors: Johnson‐Flanagan Anne M. , Thiagarajah M. R. , Pomeroy M. Keith
Published: May 2006

Mature canoia (Brassica napus cv. Westar) seeds contain large quantities of the storage proteins cruciferin and napin and storage lipids rich in C18: 1 and C18:2 fatty acids. Both the quantity and quality of these products are altered by freezing during development. Further, the response to freezing changes during seed development. The effects include decreased fatty acid chain elongation, altered fatty acid unsaturation, higher lipid levels and lower protein levels. In addition, seeds in the pivotal moisture range (55%) may be predisposed to precocious germination, which is then inhibited by a lack of adequate seed moisture. The results indicate that freezing imparts its effect in two ways. Initially, there is a freezing (low temperature) component and this is followed by rapid desiccation of the seeds. Although most responses probably result from a combination of the stresses, it appears that inhibition of fatty acid chain elongation is caused by the freezing component and the gradual inhibition of storage protein accumulation is a result of accelerated seed desiccation.
Induced Ca2+ uptake and callose synthesis in suspension‐cultured cells of Catharanthus roseus are decreased by the protein phosphatase inhibitor okadaic acid
Authors: Kauss Heinrich , Jeblick Wolfgang
Published: May 2006

Subtoxic concentrations of the saponin digitonin. the polyene antibiotic amphotericin B and the bacterial phytotoxin syringomycin induce increased uptake of 45Ca2+ into suspension‐cultured plant cells and a rapid Ca2+‐dependent defense response, callose synthesis. Both reactions were inhibited by preincubation of the cells with okadaic acid, a specific inhibitor of type 1 and type 2A protein phosphatases. These results suggest that Ca2+ uptake induced by the above agents does not occur due to unspecific perturbation of plasma membrane permeability but involves transport proteins which are controlled by protein phosphorylation/dephosphorylation. Phosphoproteins appear also to be involved in the regulation of callose synthesis, although it remains open whether this control is effected at the level of Ca2+ transport or at the 1,3‐ß‐glucan synthase involved in deposition of the polymer.
Fatty acid composition of galactolipids and phospholipids in neoplasmatic plant tissues (cecidia) and normal leaf tissue
Authors: Bayer Margrel H.
Published: May 2006

Insect‐elicited modifications of leaf cells that produce leaf galls on higher plants are concurrent with changes at the biochemical level. The neoplasmatic alterations affect the composition and concentration of membrane phospho and galactolipids. In vitro labeling of developing leaf galls from oak [induced by cympids (Hymenoptera) on L.] with [14C]‐acetate and [3H]‐oleate was used to study the label distribution in monogalactosyldiacylglyceride, digalactosyldiacylglyceride, phospha‐tidylglycerol and phosphatidylinositol in these tissues and in the normal host organs (leaf laminae). The incorporation of both labels was higher into the leaf galactolipids than into gall galactolipids, whereas the incorporation of oleate was slightly increased in the 2 phospholipids in cynipid galls. The degree of acyl chain unsaturation of individual endogenous phosphoglycerides (phosphatidylcholine, phosphatidyletha‐nolamine. phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol) was, in most cases, higher in the gall tissues. Differences in the endogenous fatty acid composition of plant polar lipids and the molar concentrations of labeled fatty‐acid precursors in galacto‐ and phospholipids are discussed with regard to modifications of the leaf phenotype and cecidogenesis on Quercus palustris L.
Changes in invertase activities precede ovary growth induced by gibberellic acid in
Authors: Estruch Juan José , Beltrán José Pío
Published: May 2006

Developing pods of pea (Pisum sativum L. cv. Alaska no 7) were used to study the enzymes of sucrose metabolism. Acid and neutral invertase (EC 3.2.1.26). sucrose synthase (SS, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14) have been localized in the soluble fraction. Acid invertase activity was also present in the insoluble fraction and in pea ovary apoplast. In pea pods, sucrose breakdown was dominated by the invertase pathway. SS specific activity only increased at late stages of parthenocarpic pod development, while SPS did so in pods obtained by pollination. Changes in time course of invertase activities have been correlated with the growth rate of fruits induced to develop either by fertilization or by exogenous application of giberellic acid (GA), 2,4‐dichloro‐phenoxy acetic acid (2,4‐D) or 6‐benzylaminopurine (6‐BAP). The soluble neutral activities might be associated with pod elongation, while the acid ones were rather related to assimilate import by the induced fruits. Application of gibberellic acid to non‐pollinated ovaries significantly enhanced the soluble neutral invertase activity before any ovary outgrowth was detected (up to 2 h after treatment). Within the same period of time. GA‐treated ovaries showed a decrease in the acid invertase activity of the soluble fraction and an increase of the acid invertase activity in the apopiast. preceding in time the increment of the acid invertase activity associated with the insoluble fraction. Our results suggest that the early GA response may be mediated through a promotion of processes of protein secretion.
Partial purification and properties of an endo‐xylanase from cucumber seeds
Authors: Mujer Cesar V. , Kretchman Dale W. , Miller A. Raymond
Published: May 2006

An endo‐xylanase. 1,4‐β‐D‐xylan xylanohydrolase (EC 3.2.1.8) from immature cucumber L. cv. Heinz 3534) seeds was partially purified using ammonium sulfate fractionation and chromatography on SP‐Sephadex and Sephadex G‐100 in order to determine its role in xylan metabolism during development. Attempts to further purify the enzyme using chromatography on DEAE‐Sephadex, Bio‐Gel HTP hydroxylapatite, Sephadex G‐200 and con A‐Sepharose 4B and native polyacrylamide gel electrophoresis resulted in a significant decrease or complete loss of enzyme activity. Endo‐xylanase had a native molecular weight of 96 kDa as determined by gel filtration, exhibited optimal activity at pH 5.0 and 48°C, and was most stable from pH 4.0 to 5.0. Using beechwood 4‐o‐methyl‐d‐glucurono‐d‐xylan dyed with Remazol Brilliant Blue R as substrate, the Km was estimated to be 0.70 mg ml−1. HgCl2 at 1 mM inhibited endo‐xylanase completely. Other metal ions inhibited the enzyme in the order Cu2+ > Fe3+ > Zn2+ > Ca2+ > Mn2+. The ethanol‐soluble products of endo‐xylanase action on beechwood xylan were isolated and characterized by consecutive chromatography on Bio‐Gel P‐10 and P‐2. The major reaction products were xylo‐oligosaccharides [degree of polymerization (dp) > 10] but traces of xylobiose and free xylose were also isolated. The formation of xylo‐oligosaccharides indicated that the reaction was catalyzed primarily by an endoxylanase. The partially pure enzyme had no activity towards other cell wall polysaccharides such as cellulose, carboxymethyl cellulose, sodium carboxyl cellulose, potato starch, orange pectin, polygalacturonic acid, arabinogalactan and β‐giucan. However, it was able to hydrolyze larchwood and oat spelts xylan and a polysaccharide component from purified cucumber cell walls. The ability to utilize a substrate from cucumber cell walls supports the hypothesis that endo‐xylanase is involved in the development of cucumber seeds.
Uptake and metabolism of 6‐benzylaminopurine in shoot cultures of
Authors: Blakesley D. , Lenton J. R. , Horgan R.
Published: May 2006

Shoots of Gerbera jamesonii Bolus, cultured in vitro were induced to multiply by the addition of 2.22 μM 6‐benzylaminopurine (BAP) to the medium. Shoots growing in the presence of [14C]‐BAP were harvested every 4 days and sub‐divided into petioles plus apices, laminae and basal callus. The 3‐ and 9‐glucosides, 9‐riboside and a novel compound, the 9‐ribosylglucoside were characterised as metabolites of BAP by mass spectrometry. The 9‐riboside was the principal metabolite formed initially in petioles plus apicies and callus but further metabolism varied depending on tissue type. After 24 days the major metabolite in the callus was the 9‐ribosylglucoside, with only trace amounts of the other metabolites present. In contrast, both 3‐glucoside and 9‐ribosylglucoside accumulated in petioles plus apices whereas the 3‐glucoside accumulated in laminae.
Genotype and composition of culture medium are factors important in the selection for transformed sunflower (Helianthus annum)callus
Authors: Escandon Alejandro S. , Hahne Gunther
Published: May 2006

Transformed tissues can be efficiently selected with the help of selectable markers. We studied the influence of genotype, culture medium, and chemical nature of selectable markers on the callus formation of sunflower (Helianthus annuus L.) hypocotyl explants during the selection process. Kanamycin was found not to be a suitable marker for sunflower transformation, while paromomycin and phosphinotri‐cin are both useful. Because the mechanism of action of these inhibitors is intimately connected with the physiological reactions of the cultured tissues, we investigated the influence of key media components on the efficiency of selection of transformed callus on phosphinotricin. Auxin, cytokinin, and gibberellic acid, as well as nitrate concentration, all had a strong influence on the spontaneous resistance of untrans‐formed sunflower hypocotyl explants against this herbicide. The number of transformed cells varied in function of the growth regulator balance. Possible reasons for this media dependence are discussed.
Storage protein mobilization during germination and early seedling growth of Zea mays
Authors: Hay Pamela Camp , Ramsaur Tina , Smith Carlene , Miernyk Jan A.
Published: May 2006

Changes in general protease activity and the levels of the zein storage proteins were monitored during germination and early seedling growth of maize (Zea mays L. inbred A636). General endosperm endoprotease activity, measured in vitro using azocasein as a substrate, increased continuously to day 5 and remained high thereafter. The increase was in parallel with the loss of zein protein as determined by immunoblot analysis, with a total loss of detectable zein by 10 days after inhibition of the seeds. A method was developed for the specific in vitro assay of zein degrading activity by monitoring the release of soluble radioactivity from the immobilized storage protein. The in vitro pH optimum for both general protease and zein degrading activities in homogenates prepared from isolated endosperm was 4.0. However, the curve for general protease activity was asymmetrical suggesting the presence of more than 1 protease. This was verified by activity staining of gelatin‐containing polyacrylamide gels, which suggested the presence of 3 major and 3 minor protease activities. Both general protease and zein‐specific activities were enhanced more than 2‐fold when 2‐mercaptoethanol (ME) was included in the assays, and both were inhibited by fhiol‐protease directed compounds. Most of the general protease activity but none of the zein‐specific protease activity bound to con A‐Sepharose. Both the con A‐binding and nonbinding fractions were analyzed using gelatin activity gels. The 3 minor activity bands were present in the fraction which was specifically eluted from the con A column by a‐methyl‐mannoside, while the 3 major activity bands, corresponding to the zein‐specific protease activity, did not bind to the immobilized lectin.
Gibberellins in shoots of Hordeum vulgare. A comparison between cv. Triumph and two dwarf mutants which differ in their response to gibberellin
Authors: Boolher Gillian M. , Gale Michael D. , Gaskin Paul , MacMiilan Jake , Sponsel Valerie M.
Published: May 2006

The gibberellin (GA) content of barley (Hordeum vulgare L.) cv. Triumph was analysed by full scan gas chromatography‐mass spectrometry. Developing grain contained several di‐, tri‐, and tetra‐hydroxylated GAs, with the most abundant ones being hydroxylated at C‐2, C‐3, C‐12β, and/or C‐18. In contrast, the only GAs to be detected in shoots of 9‐day old dark‐ and light‐grown seedlings of Triumph were 13‐hydroxylated C19‐GAs, namely GA1, GA8, GA20, and GA29, (all of which are components of the early 13‐hydroxylation GA biosynthetic pathway) and GA3. Feeds of [13C.3H2GA20, confirmed that GA20 is a precursor of GA1, GA8, and GA29 in barley shoots. From these results it is suggested that stem growth of barley, in common with that of several other mono‐ and dicotyledons, is controlled by GA,. Homozygous gal and gal lines were obtained after backcrossing to Triumph. These were then compared to Triumph with respect to their GA content and response to applied GAs and GA precursors. Shoots of the homozygous gal gal plants contained ca 6‐fold less GA1, than Triumph. These plants responded to all ent‐kaurenoids and 13‐hydroxylated C20‐ and C19‐GAs tested. It is concluded that the gal locus impairs the GA biosynthetic pathway prior to ent‐kaurene, most probably at ent‐kaurene synthetase. In contrast, shoots of homozygous gal gal line contained ca 10‐fold higher levels of GA, than Triumph, but failed to respond to applied GA, or GA3. The gal locus therefore confers insensitivity to both exogenous and endogenous GAs, possibly by perturbing the reception or transduction of the GA1 signal.
Elimination of flowering and most cytological changes after selective long‐day exposure of the shoot tip of Sinapis alba
Authors: Havelange A. , Bernier G.
Published: May 2006

Entire plants of Sinapis. alba exposed to a single long day were induced to flower. However, if only the shoot tip was exposed to the long, day, no flowering ensued. In the apical meristem of plants with only the shoot tip exposed to the long day, none of the ultra structural changes normally observed in the meristem of induced plants were detected, except for a marked increase in the number of mitochondria per cell. We conclude that the great majority of ultra structural changes normally occurring in the shoot meristem during floral transition are not direct effects of day length on the tip but are caused by signal(s) generated in induced leaves.
The effect of light and exogenous gibberellic acid on respiration pathways during germination of tomato seeds
Authors: Gui Mei‐Xiang , Wang Xiao‐Ming , Huang Wei‐Yu
Published: May 2006

Tomato (Lycopersicon esculenlum Mill. cv. Taiwan Red) seeds are typical lightsensitive seeds where light requirement can be substituted by gibberellic acid (GA3). During the initial stage of germination, the hexose monophosphate pathway (HMP) in seeds incubated for 24 h under white light or 12 h in 0.3 mW GA3 solution acidified with 1 M HCI for 1 h in the dark (HCl→GA3) was much greater than in seeds incubated for 24 h in the dark. The results were obtained from measurements of the respiration rate by man metric method of Warburg with or without iodoacetic acid, and from activities of glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49) and aldolase (EC 4.1.2.13). Although the HMP tended to decrease at the later stage (72 h under white light or in the dark, or 36 h in HCl→GA3), it remained greater in light‐ than in dark‐incubated seeds. CN‐resistant respiration increased from 27–30% to 57–64% of the total respiration in seeds incubated under white light or in HCI→GA3, while respiration of non‐germinating, dark‐incubated seeds remained zero. Benzohydrox–amic acid (BHAM), an inhibitor of the alternative pathway, inhibited both respiration and seed germination. It is concluded that the enhancement of HMP and the CN–resistant pathways are both controlled by Pfr, but there is no direct connection between them.
Culture of mycorrhizal tree seedlings under controlled conditions: Effects of nitrogen and aluminium
Authors: Jentschke Georg , Godbold Douglas L. , Huttermann Aloys
Published: May 2006

A sand culture system was developed for growth of mycorrhizal seedlings under monoxenic conditions, with frequently renewed nutrient solution The composition of the nutrient solution resembled that of a forest soil solution, based on long‐term measurements from forest sites at Soiling, northern Germany. Seedlings of Picea abies (L.) Karst. inoculated with Lactarius rufus (Scop.) Fr. were grown in this culture system. Plants developed rapidly, having almost totally mycorrhizal root systems. Nitrate at 2.7 mM in the nutrient solution and applied over a 13 week period had no negative effect on mycorrhizal development. Ammonium at 2.7 mM reduced the degree of mycorrhizal infection slightly, in such a way that the degree of mycorrhizal infection was reduced to a much less extent than the total number of root lips. Hence, the impact of NH+4 may be primarily on root development and not on mycorrhizal fungal colonization. When the concentrations of NO‐3 and NH+4 used in the present study are compared to those found in forest soil solutions, NO‐3 and NH4+ would not appear to influence mycorrhizal development negatively under natural conditions. Aluminium at 0.8 mM and applied over a 13 week period reduced Mg uptake into roots and needles by 52 and 64%, respectively, resulting in needle chlorosis and strongly reduced photosynthetic activity. From a comparison of this study with others, no major difference in physiological response to aluminium exposure between non‐mycorrhizal seedlings and seedlings colonized with Lactarius rufus was found.
The original basal stem section influences rooting in Pinus banksiana cuttings
Authors: Haissig Bruce E. , Riemenschneider Don E.
Published: May 2006

We tested the hypothesis that, during propagation, the basal stem of Pinus banksiana Lamb, cuttings contains a nonauxin endogenous root‐forming stimulus (ERS) whose effects are not replaced by auxin treatment; i.e., that auxin treatment of cuttings and surgical removal of their basal stems during propagation act additively on rooting, without significant interaction, as determined by analyses of variance. We studied the effects of ERS by severing the original basal (1 cm) stem from cuttings at days 3, 6 and 9 of a 30‐day period of propagation. To study treatment interaction, we applied the auxin N‐phenyl indolyl‐3‐butyramide to some surgically treated cuttings. Results for all variables (proportion of rooted cuttings, number of roots per cutting and fresh weight of basal stem plus roots, if any) indicated that removing the basal stem reduced rooting and that auxin treatment increased rooting, without significant treatment interaction. The results thus supported the hypothesis that P. banksiana seedling cuttings contain ERS. However, neither the present nor previous tests have shown that ERS is a chemical stimulus rather than, for example, a biophysical or anatomical one.
Aluminium avoidance by Mucuna pruriens
Authors: Hairiah Kurniatun , van Noordwijk Meine , Stulen Ineke , Kuiper Pieter J. C.
Published: May 2006

The hypothesis was tested that the avoidance of acid subsoil by the velvet bean Mucuna pruriens is based on a mechanism acting on the whole root system rather than on individual roots. In a split‐root experiment with circulating nutrient solution the growth of plants with Al‐containing (+/+) or Al‐free (0/0) solution on both sides of the root system was compared with that of plants which had a choice (0/+). Two levels of Al (110 and 185 μM) were tested at two levels of Ca (50 and 1250 μM). In the 185 μM Al treatment the concentration of monomeric Al varied between 53 μM, directly after refreshing the solution, and 5 μM at harvest time.

An external Al concentration of 110 μM had no effect on shoot and root dry weight, while 185 μM Al applied to both sides of the root system (+/+) increased root dry weight and reduced shoot dry weight and shoot/root ratio, compared with the 0/0 control. Application of 185 μM Al to half of the roots, ied to a significant shift in root growth in favour of the control side; this response is described here as Al avoidance. On the basis of total root length, root dry weight and root surface area, the ratio of 0/+ roots was 3.1, 2.8 and 2.4, respectively.

Al avoidance at 185 μM Al was confirmed in another experiment, in which root response was measured to a local P source, supplied in a third compartment containing only KH2PO4. A significant increase in root length and dry weight in this compartment was observed, when other roots of the same plant were growing in the presence of Al. This result indicates that Al avoidance by Mucuna roots is related to P preference.
Differential accumulation of methyl jasmonate‐induced mRNAs in response to abscisic acid and desiccation in barley (Hordeum vulgare)
Authors: Reinbothe Steffen , Reinbothe Christiane , Lehmann Jörg , Parthier Benno
Published: May 2006

Upon treatment with abscisic acid (ABA) or as a result of water stress (desiccation) detached leaf segments of barley (Hordeum vulgare L. cv. Salome) synthesized proteins of Mr 66000, 37000, 30000 and 23000 which had previously been characterized as abundant methyl jasmonate (JaMe)‐induced proteins. The time course of appearance of mRNAs encoding JaMe‐induced proteins was compared under the three different treatments, i.e. JaMe, ABA and desiccation. From the overall analysis by in vitro translation, a complex alteration in the leaf mRNA population became evident that depended on the treatment employed. mRNAs likewise induced by the various treatments could be discriminated from mRNAs appearing specifically after JaMe‐ or ABA‐treatment or in response to desiccation. For two mRNAs induced by JaMe, ABA and desiccation, sequence homology was suggested to transcripts encoding late embryogenesis abundant (LEA) proteins. The two transcript species of 2.17 kb and 1.28 kb detected with a synthetic Lea gene‐specific probe in northern blot hybridizations appeared with different time courses and accumulated to different extents under the various treatments, highlighting the obvious diversity of Lea gene expression in response to ABA, JaMe and desiccation. We suggest a role of jasmonates in mediating water stress reactions in vegetative tissues of barley.
Effects of ethidium bromide and chloramphenicol on the mitochondrial nucleoids in Euglena gracilis
Authors: Hayashi Yasuko , Ueda Katsumi
Published: May 2006

The effects of ethidium bromide (EB) at 0.13 mM and of chloramphenicol (CAP) at 46 mM on the mitochondria and mitochondrial nucleoids in Euglena gracilis. Z strain, were examined by fluorescence microscopy and by electron microscopy. Ethidium bromide stopped the multiplication of cells and decreased their respiratory activity by 55% after treatment for 10 days. Most of the mitochondria became slender with few cristae and some became cup‐shaped with stacked cristac. Mitochondrial nucleoids decreased markedly in number after treatment with EB for more than 2 days. After treatment for 3 days with EB, mitochondrial nucleoids could not be detected in about half of all cells examined. Treatment with CAP for 10 days reduced the respiratory activity by 47%. Chloramphenicol did not decrease the number of mitochondrial nucleoids but it increased the number of cristae and the volume of mitochondria.
Effects of pH on proton transport by vacuolar pumps from maize roots
Authors: Brauer David , Conner DeNea , Tu Shu‐I
Published: May 2006

Protons pumps of the tonoplast may be involved in the regulation of cytosolic pH, but the effects of pH on the coupled activities of these transporters are poorly understood. The effects of pH on the activities of the H+‐translocating pyrophosphatase (PPiase) and vacuolar‐type H+‐translocating adenosine triphosphatase (H+‐ATPase) from maize (Zea mays L. cv. FRB 73) root membranes were assessed by model that simultaneously considers proton transport by the pump and those processes that reduce net transport. The addition of either pyrophosphate or ATP to either microsomal or tonoplast membranes generated a pH gradient. The pH gradient generated in the presence of both substrates was not the sum of the gradients produced by the two substrates added separately. When membranes were separated by sucrose density gradient centrifugation, pyrophosphate (PPi)‐dependent proton transport was associated with light density membranes having tonoplast H+‐ATPase activity. These results indicate that some portion of the PPiase was located on the same membrane system as the tonoplast ATPase; however, tonoplast vesicles may be heterogeneous, differing slightly in the ratio of ATP‐ to PPi‐dependent transport. Proton transport by both the PPiase and ATPase had maximal activity at pH 7.0 to 8.0 Decreases in proton transport by the ATPase at pH above the optimum were associated with increases in the processes that reduce net transport. Such an association was not observed at pH values below the optimum. These results are discussed in terms of in situ regulation of cytoplasmic pH by the two pumps.
Cellular and morphological changes at the terminal shoot apex of the short‐day plant Pharbitis nil during the transition to flowering
Authors: Herbert Robert J. , Francis Dennis , Ormrod John C.
Published: May 2006

Changes in morphology and measurements of cell doubling time were recorded for the first time in the terminal shoot apex of the short‐day plant, Pharbitis nil Chois. (Ipomea nil L.) cv. Violet, undergoing the floral transition. A treatment comprising 48 h darkness given to 4‐day‐old plants resulted in 100% flowering at the shoot terminal meristem. An inhibitory treatment comprising two 5 min red night‐breaks during the 48 h dark period was used to discriminate between events essential for flowering, and those changes resulting from shifts from light to darkness and vice versa. Morphology was studied using both light microscopy and scanning electron microscopy. Cell doubling times were measured using the colchicine accumulation of metaphases method. An increase in the rate of primordial initiation, a change in the divergence angle and a change in phyllotaxis occurred during the floral transition. Moreover, the apex widened and flattened following the inductive dark treatment; the cell doubling time decreased in the peripheral zone and increased in the central zone of these pre‐floral meristems.
Modified solvent partitioning scheme providing increased specificity and rapidity of immunoassay for indole‐3‐acetic acid
Authors: Veselov Stanislav Yu. , Kudoyarova Guzel R. , Egutkin Naum L. , Gyuli‐Zade Vaid Z. , Mustafina Aelita R. , Kof Ella M.
Published: May 2006

Based on the distribution constant of IAA, the efficiency of solvent partitioning has been improved by modifying the proportions of the solvents. IAA is recovered almost quantitatively by this method which also renders further sample reduction superfluous. Selective IAA recovery is supported by the distribution of immunoreactive materials on chromatograms. This modified scheme simplifies prepurification of samples for more reliable immunoassay.
Temperature dependent redistribution of organic nitrogen during ‘dry' storage of tulip bulbs cv. Apeldoorn
Authors: Lambrechts H. , Ravestein H. , Kollöffel C.
Published: May 2006

Tulip bulbs cv. Apeldoorn are dry stored at 5°C for 12 weeks to ensure subsequent optimal flowering when planted in the greenhouse at higher temperatures of 17–20°C. Both temperature and duration of the cold treatment determine the subsequent rate of the shoot elongation, the time until anthesis and the flower size, pigmentation and water content. In search for cold‐specific physiological changes, possibly related to the development of the potential of proper flowering (flowering preparation), we studied the redistribution of organic nitrogen in both cooled (5°C) and non‐cooled (17°C) bulbs.

During 12 weeks of dry storage, the total protein‐ and free amino acid‐nitrogen content decreased in the scales, whereas the opposite was found in the basal plate (with root primordia) and the shoot. In the shoot, this occurred significantly more at 17°C than at 5°C. At the same time, there was a tissue‐specific change in the free amino acid composition in both cooled and non‐cooled bulbs. Changes specific for the 5°C treatment were only found for the alanine content, in both the basal plate (with root primordia) and the shoot, and for the proline, asparagine, threonine, glycine and isoleucine content, in the shoot only. These changes are, for the greater part, completed within the first 6–8 weeks of dry storage. Bulbs stored for such a short period of time at 5°C still show flowering disorders. Thus, flowering preparation is only partly accompanied by changes in free amino acid contents.
Purification of a tonoplast polypeptide with sucrose transport properties
Authors: Thom Margaret , Getz Hans Peter , Maretzki Andrew
Published: May 2006

Sucrose uptake into vacuoles of sugarcane parenchyma cells is mediated by a transporter. A polypeptide fitting that description has been partially purified from solubilized tonoplast by gel filtration and ion exchange chromatography. Purification of the relevant polypeptide was followed by reconstitution of fractions into liposomes and measurement of sucrose uptake into the proteoliposomes. In addition, a mono‐clonal antibody raised against tonoplast inhibited sucrose uptake. Western blots showed that the monoclonal antibody was relatively nonspecific but was suitable for monitoring the sucrose transport‐related polypeptide during purification. The mono‐clonal antibody bound a polypeptide of approximately 40 kDa, and this band was found in the fraction with sucrose uptake activity.
Internode length in Pisum. A new allele at the Lh locus
Authors: Swain Stephen M. , Reid James B.
Published: May 2006

A new allele at the Lh locus has been identified in Pisum sativum L. and named lhi. This allele results in reduced GA levels in young shoots, and a dwarf phenotype. Gas chromatography‐selected ion monitoring (GC‐SIM) with dideuterated internal standards has been used to demonstrate a quantitative relationship between the level of endogenous GA1 and internode length using the three alleles (Lh, lh and lhi) at the Lh locus. These results are consistent with previous findings in peas (for alleles at the Le locus) and other species possessing a predominant early 13‐hydroxylation pathway for GA biosynthesis and support the role of GA1 as the major native GA in peas with biological activity in its own right. However, in contrast to alleles at the Le locus, GA20 levels are also reduced in lh and lhi plants. The lhi allele also has possible pleiotropic effects on seed abortion, leading to a reduction in seed yield compared to plants homozygous for the previously characterised Lh or lh alleles.
Paraquat toxicity in Pisum sativum: Effects on soluble and membrane‐bound proteins
Authors: Peleg Itzhak , Zer Hagit , Chevion Mordechal
Published: May 2006

The effects of paraquat (PQ) on Pisum sativum L. proteins were investigated in vivo in a new experimental system utilizing 10‐day‐old plant cuts.A marked decrease in the specific activity of membrane‐bound Ca2+‐dependent ATPase was recorded, while that of Mg2+‐dependent ATPase remained unchanged. Concurrently with a drop in the total plant protein, the specific activities of the three cytoplasmic enzymes, malate dehydrogenase, hydroxypyruvate reductase and triose‐phosphate isomerase, were also found to decrease. The effect on various enzymes involved in cellular defense mechanisms was also studied: glutathione reductase and superoxide dismutase activities increased, while ascorbate peroxidase was not affected.

These findings shed light on the selectivity of PQ‐induced injurious processes, focusing on protein homeostasis mechanisms in the membrane and cytoplasmic compartments at the cellular level, as well as on the prominent role played by enzymatic defense systems against PQ poisoning.
Xyloglucan structure and post‐germinative metabolism in seeds of Copaifera langsdorfii from savanna and forest populations
Authors: Buckeridge Marcos S. , Rocha Dalva C. , Reid J. S. Grant , Dietrich Sonia M. C.
Published: May 2006

The cotyledons of Copaifera langsdorfii Desf, have been shown to contain a water‐soluble xyloglucan (amyloid), which represents about 40% of the seed's dry weight. On acid hydrolysis its composition (Glc:Xyl:Gal = 4.0:2.8–2.9:1.5–1.7) was similar to that of the well‐characterized xyloglucan of Tamarindus indica L. (Glc:Xyl:Gal = 4.0:3.0–3.1:1.4). On hydrolysis with pure Trichoderma viride cellulase, both C. langsdorfii and T. indica xyloglucan gave the same xyloglucan oligosaccharides:

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but in significantly different proportions A:B1:B2:C = 1:0.4–0.5:2.1–2.2:3.1–3.4 in T. indica, and 1:1.1:1.8:7.4 and 1:1.3:2.6:12 for C. langsdorfii, savanna and forest populations respectively. This demonstrated a difference in fine molecular structure, notably in the distribution of the terminal non‐reducing galactose substituents, between the xyloglucans of the two species and indicated differences in the specificities of their biosynthetic mechanisms. The xyloglucans obtained from C. langsdorfii seeds harvested from savanna and forest environments were slightly different, one from the other, in their sugar‐residue composition (Glc:Xyl:Gal = 4.0:2.9:1.5 and 4.0:2.8:1.7, respectively), and were significantly different in the relative proportions of the xyloglucan oligosaccharides released on cellulase hydrolysis (above). Using light microscopy and biochemical methods, no difference in the pattern or rate of postgerminative xyloglucan metabolism was detected in seeds of savanna and forest origin. This is the first clear experimental evidence for differences in a storage xyloglucan structure between populations of the same species. It may indicate environmental influences on xyloglucan biosynthesis.
Partitioning of nitrogen and biomass at a range of N‐addition rates and their consequences for growth and gas exchange in two perennial grasses from inland dunes
Authors: Boot René G. A. , Schildwacht Peter M. , Lambers Hans
Published: May 2006

This paper describes the effects of nitrgen supply on the partitioning of biomass and nitrogen of Agrostis vinealis(L.) Schreber and Corynephorus canescens(L.) Beauv., two perennial grasses of dry, nutrient‐poor inland dunes, and their consequences for growth and gas exchange. At a given plant nitrogen concentration (PNC) the two species allocate the same relative amount of dry matter and nitrogen to their leaves. However, A. vinealis allocates more dry matter and nitrogen to its roots and less to its above‐ground support tissue than C. canescens. Both the leaf weight ratio and leaf nitrogen ratio increase with increasing PNC. Despite species‐specific differences in growth form and leaf morphology, the leaf area ratio and specific leaf area of the two species are similar, both at high and low PNC. At intermediate nitrogen supply, and thus intemediate PNC, however, A. vinealis has a higher leaf area ratio and specific leaf area than C. canescens.

The two species exhibit a similar positive relationship when either the rate of net photosynthesis or the rate of shoot respiration are compared to the leaf nitrogen concentration, all expressed per unit leaf weight. The rate of net photosynthesis per unit Jeafnitrogen (PNUE) of the two species increases with decreasing leaf nitrogen concentration per unit leaf weight. C. canescens has a higher PNUE at low, and a lower PNUE at high leaf nitrogen concentration per unit leaf weight than A. vinealis. At non‐limiting nitrogen supply, A. vinealis has a higher nitrogen productivity and net assimilation rate and a similar PNC and leaf area ratio as compared to C. canescens, which explains the higher relative growth rate (RGRmax) of A. vinealis. At growth‐limiting nitrogen supply C. canescens achieves a similar relative growth rate at a lower PNC than A. vinealis.
Seed dormancy patterns in Epipactis palustris (Orchidaceae): Requirements for germination and establishment of mycorrhiza
Authors: Rasmussen Hanne N.
Published: May 2006

Some terrestrial orchid species, including Epipactis palustris (L.) Crantz, are considered extremely difficult to germinate and cultivate in vitro. Observations of orchids germinating in nature are very few, and the timing and requirements for seedling establishment are unknown for most species. Seeds of E. palustris were incubated in vitro with an appropriate fungus, but germination was poor unless several other conditions were also met: scarification of the testa in Ca(OCL)2, an initial incubation for several weeks at 27°C, and a subsequent cold stratification for 8–12 weeks at 4–8°C, With these pretreatments, germnation responses exceeded 50% after incubation for 4 weeks at 20°C. Healthy protocorms with normal organ development were only produced by symbiotic culture following this lengthy seed preparation. The findings suggest that under natural conditions the seeds need some after‐ripening, and the testa needs to be partially decomposed before germination. The requirement for chilling suggests that germination of seeds in situ occurs in spring.
Relationship between photosystem II activity and CO2 fixation in leaves
Authors: Krall John P. , Edwards Gerald E.
Published: May 2006

There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO2 fixed. A measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady‐state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals ΦII times incident light intensity times the fraction of incident light absorbed by PSII. In C4 plants, there is a linear relationship between PSII activity and CO2 fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C4 species. In C3 plants, both CO2 fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO2, or per O2 reacting with RuBP). The rates of PSII activity associated with photosynthesis in C3 plants, based on estimates of the rates of carboxylation (vo) and oxygenation (vo) at various levels of CO2 and O2, largely account for the PSII activity determined from fluorescence measurements. Thus, in C3 plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO2 fixation.
The effects of endogenous cytokinin content on benzyladenineenhanced nitrate reductase induction
Authors: Banowetz Gary M.
Published: May 2006

Foliar application of benzyladenine (BA) has been shown to enhance nitrate‐dependent induction of nitrate reductase (NR; EC 1.6.6.1) in etiolated wheat (Triticum aestivum L.) seedlings. Whether similar enhancement occurs in light‐grown plants, or whether endogenous cytokinin content affects this enhancement is unknown. Since the cytokinin content of etiolated plants probably differs from that of light‐grown seedlings, the NR response of each to exogenous root‐ or shoot‐applied BA in wheat (cv. Red Bob) was examined. Endogenous cytokinins present in untreated control tissues prior to BA application and changes that occurred after a 22 h (12 h dark followed by 10 h of light) period were determined using a combined HPLC‐immunoassay method. Shoot application of BA enhanced the induction of NR in etiolated seedlings in a concentration‐dependent manner but failed to enhance NR induction in light‐grown plants. Root‐applied BA enhanced NR induction in both etiolated and light‐grown seedlings. Endogenous root cytokinin levels were similar in both etiolated and light‐grown plants. In contrast, shoots of 6 day‐old light‐grown seedlings contained at least 20 times the amount of total cytokinins measured in shoots from etiolated plants of the same age. Total cytokinin content of the light‐grown plants diminished after the 22‐h period while that measured in etiolated seedlings increased. The responsiveness of seedlings to BA was correlated with endogenous cytokinin levels in that enhancement of NR induction by exogenous BA was low in tissues which contained high concentrations of cytokinin at the time of BA application. These results may prove useful in interpretation of gene responses to exogenous plant growth regulators.
Depression of carbon flow to the glycogen pool induced by nitrogen assimilation in intact cells of Anacystis nidulans
Authors: García‐González Mercedes , Sivak Mirta N. , Guerrero Miguel G. , Preiss Jack , Lara Catalina
Published: May 2006

The influence of nitrate and ammonium assimilation on glycogen metabolism has been determined in intact Anacystis nidulans cell actively fixing CO2. Assimilation of nitrate or ammonium resulted in significant decreases in both the incorporation into glycogen of newly fixed carbon and the accumulation of glycogen by the cells, the magnitude of these effects depending on the light intensity. The depression in glycogen synthesis induced by nitrogen assimilation was more marked at low light intensity, and especially when ammonium was the nitrogen source. Under these conditions, specific radioactivity of the glycogen pool was particularly high, indicating enhanced turnover of glycogen. Thus, in addition to a more general depressing effect of nitrogen assimilation on the carbon flow to glycogen, degradation of glycogen appears to be stimulated by ammonium assimilation at low (but not at high) light intensity.
Changes in protein synthesis during stratification and dormancy release in embryos of sugar maple (Acer saccharum)
Authors: Hance Beth A. , Bevington John M.
Published: May 2006

Protein synthesis in dormant embryos of sugar maple (Acer saccharum) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [35S]‐methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two‐dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the cotyledons.
Cytokinin biochemistry in relation to leaf senescence. VIII. Translocation, metabolism and biosynthesis of cytokinins in relation to sequential leaf senescence of tobacco
Authors: Singh Santokh , Letham D. S. , Palni L. M. S.
Published: May 2006

Cytokinin bases (zeatin and dihydrozeatin) and ribosides (zeatin riboside and dihydrozeatin riboside) were identified as major cytokinins in tobacco xylem sap by radioimmunoassay. When 3H‐labelled zeatin riboside or dihydrozeatin riboside were supplied to tobacco plants via the xylem, leaves of differing maturity did not differ appreciably in level of radioactivity or in metabolism of the cytokinin. The major metabolites of zeatin riboside in leaves were adenine, adenosine and adenine nucleotides, whereas that of dihydrozeatin riboside was dihydrozeatin 7‐glucoside. Incorporation of [14C]adenine into zeatin was evident in upper green leaves. indicating that young leaves have the capacity to synthesize cytokinins in situ. In contrast, fully expanded green leaves and senescing tobacco leaves exhibited little or no incorporation of [14C]adenine into cytokinins. This difference in cytokinin biosynthetic capacity may contribute to the differing cytokinin levels in leaves of different matirity, and may participate in control of sequential leaf senescence in tobacco.
Kinetics of the purified plasma membrane H+‐ATPase from red beet (Beta vulgaris)
Authors: de la Vara Luis E. González , Baizabal‐Aguirre Víctor M. , Medina Guadalupe
Published: May 2006

The plasma membrane H+‐ATPase (EC 3.6.1.35) was purified by washing red beet (Beta vulgaris L.) plasma membranes with sodium deoxycholate and separating the ATPase, solubilized with lysophosphatidylcholine, by centrifugation in a glycerol gradient. The purified H+‐ATPase had a sedimentation coefficient of about 8S. In the absence of exogenous protein substrates, the purified ATPase preparation did not present protein kinase activity. Compared with the H+‐ATPase in the plasma membrane, the purified ATPase presented a higher affinity for adenosine 5′‐triphosphate (ATP) and a lower sensitivity to the inhibitors vanadate and inorganic phosphate. These changes in the kinetics of the ATPase could also be observed by treating the membranes with lysophosphatidylcholine, without purifying the enzyme. These results can be explained assuming that lysophosphatidylcholine interacts with the ATPase altering its kinetics probably by stimulating the transformation from the inhibitor‐binding conformation E2 into the ATP‐binding conformation E1.
Ultraviolet‐B radiation absorbing capacity of leaf hairs
Authors: Karabourniotis George , Papadopoulos Kostas , Papamarkou Maria , Manetas Yiannis
Published: May 2006

Pubescence layers with their native structure and orientation were isolated from the leaves of Olea europaea L. and Olea chrysophylla L. They were almost transparent in the visible, but considerable absorptance was evident in the ultraviolet‐B region (UV‐B), with maximum at 310 nm. Methanolic extracts of hairs from Olea and a variety of other pubescent species consistently showed the existence of UV‐screening pigments. Absorptance of trichomes varied, but a trend towards more effective UV‐B radiation attenuation in the sub‐alpine Verbascum species may be claimed. In all cases, pigments were located within hair cells and in Olea they were characterized as phenolics with considerable flavonoid contribution. It is suggested that leaf hairs, besides other functions, may constitute a shield against UV‐B radiation.