bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructural changes induced by sub‐zero temperatures in the plasma membrane of protoplasts from winter rye
Authors: Pihakaski‐Maunsbach Kaarina , Kukkonen Markku
Published: May 2006

Freezing of nonacclimated protoplasts close to lethal temperatures induces alterations in the macromolecular organization of the plasma membrane but the significance of these structural changes in freezing injury is still uncertain. We therefore cooled non‐acclimated protoplasts isolated from cultivars of winter rye (Secale cereale L.) to two sub‐zero temperatures using two different cooling rates and analyzed freeze‐induced plasma membrane changes by freeze‐fracture electron microscopy. When a high cooling rate was used a lipid phase transition was observed in 34% of the total membrane fracture faces of the protoplasts, while with a slow cooling rate it occurred only to a very small extent. Smooth, aparticulate lamellae were approximately three times more frequent at low than at high cooling rate. Lipid phase transition from lamellar to hexagonalII (HII) phase occurred at high cooling rate more frequently at −10°C than at −30°C in three cultivars. The results suggest that the greatly increased proportion of phase transition from bilayer to non‐bilayer phase is an artifact caused by too fast a cooling rate of protoplasts. Furthermore, lateral phase separation of the plasma membrane with segregation of intramembrane particles and the appearance of membrane associated stacks of lipid lamellae, may cause cellular death by retarding the flow of intracellular water towards extracellular ice crystals formed during freezing.
Carbon partitioning in source leaves of peach, a sorbitol‐synthesizing species, is modified by photosynthetic rate
Authors: Escobar‐Gutiérrez Abraham J. , Gaudillère Jean‐Pierre
Published: May 2006

Sorbitol, together with sucrose and starch, is a major final product of photosynthesis in most species of the Rosaceae. However, little is known concerning the factors affecting the carbon fluxes into these three carbohydrates. The aim of this study was to investigate the effect of net photosynthetic CO2 assimilation rate (NAR) on primary carbon partitioning between sorbitol, sucrose, starch and other metabolites, and on the kinetic pattern of labelling in mature leaves of peach (Prunus persica [L.] Batsch). A pulse‐chase labelling experiment was conducted on a group of peach seedlings showing a range of NAR's that were obtained by using five photosynthetic photon flux density treatments. Mature leaves undergoing one of these treatments were subjected to a 4‐min pulse of 14CO2 followed by a 2‐ to 120‐min chase under 12CO2. The radioactivity in lipids, proteins and in a residual nonsoluble fraction was negligible. After a 2‐min chase the organic ions were strongly labelled, accounting for up to 40% of the total incorporated radioactivity at NAR's below 10.4 μmol CO2 m−2 s−1. After a 30‐min chase, most label was found in sorbitol, sucrose and starch with very little radioactivity in the ionic fractions. The analysis of the partitioning of the newly‐fixed carbon showed that at low NAR the 14C flux was mostly into sorbitol rather than into sucrose (ratio=2.6) or starch. When the NAR was lower than 6.1 μmol CO2 m−2 s−1, starch was lightly labelled. As the NAR increased above 10.4 μmol CO2 m−2 s−1 the 14CO2 diverted into starch increased dramatically. This study demonstrates that at low NAR's the newly‐fixed CO2 is mainly used for sorbitol synthesis. However, as NAR increases, the participation of sucrose and starch in CO2 partitioning are favoured. These results support the hypothesis that primary carbon partitioning depends on photosynthetic rate.
Diurnal patterns of stem extension growth in peach (Prunus persica): Temperature and fluctuations in water status determine growth rate
Authors: Berman M. E. , DeJong T. M.
Published: May 2006

Field measurements of stem extension growth rate in peach (Prunus persica [L.] Batsch) exhibited a consistent diurnal pattern. Stem extension rate was lowest in the early morning and increased throughout the day. In the late afternoon, 2–3‐fold increases in extension rate occurred and were sustained for 2 to 4 h. After this growth surge, rates precipitously declined and remained low during the night. The temperature response of stem growth rate at constant water potential was determined using potted trees in a dark growth chamber. Under such conditions, stem growth rate was strongly dependent on air temperature. In the field, the observed stem growth rate deviated from that predicted on the basis of temperature. These deviations were proportional to the rate of change in stem water potential. A model was constructed to predict diurnal patterns of stem extension rate using temperature and water potential data. The model was tested using data from undisturbed trees and from trees in which water potential was artificially manipulated. Growth patterns predicted by the model were in general agreement with observed rates.
The feedback mechanism of nitrate inhibition of nitrogenase activity in soybean may involve asparagine and/or products of its metabolism
Authors: Bacanamwo Methode , Harper James E.
Published: May 2006

A feedback mechanism which involves sensing of change in phloem N concentration has been proposed to control nodulation and dinitrogen fixation in the presence of external combined N. Whether this control is in response to a change in total N or in some specific signal compound(s) is not known. In the present study we reevaluated the hypothesis that control of nodulation and N2 fixation involves sensing of change in tissue N composition and attempted to identify potential signal molecule(s) involved. Two soybean (Glycine max [L.] Merr.) genotypes (Williams 82 and NOD1‐3) differing in nodule number and tolerance to nitrate were germinated in sand trays. Seven‐day‐old seedlings were inoculated with a solution of Bradyrhizobium japonicum and grown for 28 days in growth chambers, using a hydroponic system with limited N supply to promote nodulation. Half of 28‐day‐old plants were treated with 15 mM NO3−, then control and treated plants were sampled at the onset of nitrogenase inhibition (24 h following NO3−, treatment) for evaluation of nitrogenase activity and tissue concentration of total N and of each individual free amino acid. Phenylisothiocyanate‐(PITC) amino acid derivatives were separated and quantified using HPLC. The decline in nitrogenase activity following the short‐term nitrate treatment was associated with a dramatic asparagine concentration increase in the shoot and an increase in nodule aspartate and glutamate in both genotypes. Asparagine concentration in the shoot increased 35 times from a barely detectable level of 95 to 3 327 nmol g−1 fresh weight in Williams 82, and more than tripled from 509 to 1 753 nmol g−1 fresh weight in NOD1‐3. Increase in levels of free Asn and in total free amino acids in the shoot following the short‐term nitrate treatment was more pronounced in Williams 82 than in its partially nitrate‐tolerant mutant NOD1‐3. These results indicate that the feedback control of nodule activity may involve sensing changes in shoot asparagine levels and/or products of its metabolism (aspartate and glutamate) in the nodule. These results also indicate that partial‐nitrate tolerance of nodulation in the hypernodulated NOD1‐3 mutant is associated with a lesser change in tissue N following nitrate treatment.
Retranslocation of boron in broccoli and lupin during early reproductive growth
Authors: Marentes Eduardo , Shelp Barry J. , Vanderpool Richard A. , Spiers Graeme A.
Published: May 2006

The objective of the present study was to determine if boron (B) retranslocation depends on plant‐B status and external‐B supply. The stable 10B isotope was supplied to the root system of broccoli (Brassica oleracea var. italica Plenck cv. Commander) and lupin (Lupinus albus L. cv. Ultra) plants to provide a quantitative picture of B distribution during early reproductive development. Regardless of the B regime (i.e. continuous supply with luxury, sufficient or deficient B; transfer at inflorescence emergence from either a luxury‐ or sufficient‐B supply to a deficient one) and whether 10B was acquired before or during inflorescence development, a significant proportion of the B recovered in broccoli florets and lupin fruit was 10B enriched. B acquired during inflorescence development was an important source of B for reproductive structures, but the relative importance of B acquired before and after inflorescence emergence appeared to be species dependent. The occurrence of B retranslocation was not dependent upon the induction of B deficiency. The concentrations of B in phloem exudates (0.38 to 0.03 mM) were 4‐ to 23‐fold those in xylem sap, and more similar to the concentrations in the reproductive structures (0.86 to 0.07 mM) than those in source leaves (2.4 to 0.19 mM). The decreasing acropetal gradient of tissue‐B concentrations with luxury‐B supply declined dramatically or was reversed in plants grown with sufficient or deficient B. The data are consistent with B being a phloem‐mobile element, and suggest that newly acquired B is particularly important during the early reproductive growth of plants.
Gibberellin‐induced elongation and osmoregulation in internodes of floating rice
Authors: Azuma Tetsushi , Ueno Satoshi , Uchida Naotsugu , Yasuda Takeshi
Published: May 2006

Internodal elongation in floating rice (Oryza sativa L. cv. Habiganj Aman II) is known to be enhanced by treatment with ethylene or gibberellic acid (GA3) at high relative humidity (RH). However, ethylene‐induced internodal elongation is inhibited at low RH. while GA3‐induced internodal elongation is hardly affected by humidity. We examined the possible involvement of osmoregulation in the stimulation by GA3 of the elongation of internodes at low RH. Submergence and treatment with ethylene or GA33 at 100% RH increased the osmotic potential in internodes of excised stem segments, while GA3 at 20% RH maintained the osmotic potential at a low level. In internodes of stem segments that had been treated with GA3 at 20% RH, the activity of invertase and the level of soluble sugars were almost 2‐ and 1.5‐fold higher, respectively, than those in internodes that had been treated with GA3 at 100% RH. These results indicate that one of the possible mechanisms by which GA3 promotes elongation of internodes at low RH involves the osmoregulation that is achieved by promotion of the synthesis of invertase.
Inhibition of sulphur redistribution into new leaves of vegetative soybean by excision of the maturing leaf
Authors: Sunarpi  , Anderson John W.
Published: May 2006

When soybean plants are pulsed with [35S]sulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants (Glycine max [L.] Merr. cv. Stephens) were grown in 20 μM sulphate and a small portion of the root system (donor root) was pulsed with [35S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20→SO) or with 20 μM sulphate (S20→20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20→20 plants, 35S‐label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20→SO plants except that export of label from L3 was more rapid. Excision of L3 from S20→S20 plants inhibited labelling of leaves L4‐L6 but not total sulphur, whereas in S20→SO plants, excision of L3 inhibited the import of both total sulphur and 35S‐label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The 35S‐label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves.
Nitrate reductase and molybdenum cofactor in annual ryegrass as affected by salinity and nitrogen source
Authors: Sagi M. , Savidov N. A. , L'vov N. P. , Lips S. H.
Published: May 2006

The influence of salinity on the activity of nitrate reductase (NR, EC 1.6.6.1) and the level of the molybdenum cofactor (MoCo) as affected by the source and concentration of nitrogen was studied in annual ryegrass (Lolium multiflorum cv. Westerwoldicum). Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS m−1, containing nitrogen (0.5 or 4.5 mM) in the form of NH4NO3 or NaNO3 Salinity‐treated (11.2 dS m−1) plants produced less biomass and more organic nitrogen while accumulating more NO−3 than control plants. Increased nitrogen concentration in the irrigation solutions enhanced biomass and organic nitrogen production as well as NO−3 accumulation irrespective of the electrical conductivity. Salinity inhibited shoot growth and increased shoot NR activity of plants receiving 4.5 mM NH4NO3 or NaNO3. Similar effects were observed in roots of plants grown in 4.5 mM NaNO3. Nitrate added to a complementation medium containing ryegrass MoCo and the NR apoprotein of Neurospora crassa mutant nit‐1 stimulated the activity of the reconstituted NR (NADPH‐nitrate reductase, EC 1.6.6.3). Increased salinity and nitrogen in the nutrient solutions caused an increase of MoCo content in roots and shoots. Similar results were observed for NR activity in the shoots. The increase of MoCo in response to salinity was more pronounced than that of NR, especially in the roots. We conclude that the pool size of MoCo in ryegrass is not constant, but varies in response to nutritional and environmental factors.
Phylogenetic relationships among actinorhizal plants. The impact of molecular systematics and implications for the evolution of actinorhizal symbioses
Authors: Swensen Susan M. , Mullin Beth C.
Published: May 2006

A review of recent molecular systematic studies of actinorhizal plants and their Frankia endosymbionts is presented. For comparative purposes, a discussion of recent studies pertaining to the evolution of nodulation in the legume‐rhizobium system is included. Molecular systematic studies have revealed that actinorhizal plants are more closely related than current taxonomic schemes imply. Broad‐based analyses of the chloroplast gene rbcL indicate that all symbiotic root‐nodulating higher plants belong to a single large clade. More focused molecular analyses of both legume and actinorhizal hosts within this large clade indicate that symbioses have probably arisen more than once. By comparing host phylogenies and recently published bacterial phylogenies, we consider the coevolution of bacterial symbionts with their actinorhizal hosts.
Early interactions between Alnus glutinosa and Frankia strain ArI3. Production and specificity of root hair deformation factor(s)
Authors: Ghelue Marijke Van , Løvaas Erik , Ringø Einar , Solheim Bjørn
Published: May 2006

Actinomycetes from the genus Frankia are able to form symbiotic associations with more than 200 different species of woody angiosperms, so called actinorhizal plants. Many actinorhizal plants are infected via deformed root hairs. Factor(s) eliciting root hair deformation in actinorhizal symbioses have been found to be released into the culture medium, but the factor(s) has (have) not yet been characterized. In the present work, we describe the constitutive production of factor(s) by Frankia strain ArI3 causing root hair deformation on Alnus glutinosa. Deformation was detected after 4–5 h of incubation with both Frankia cultures and their cell‐free culture filtrates. When culture filtrate was used, deformation was concentration dependent. A contact time of 2 min between culture filtrate and host roots was sufficient to induce subsequent root hair deformation. No root hair deformation on A. glutinosa could be detected with purified Nod factors from Rhizobium meliloti or R. leguminosarum biovar viciae. No correlation was found between Frankia strains belonging to different host specificity groups and their ability to deform root hairs on A. glutinosa. However, strains not able to deform root hairs on A. glutinosa were also unable to nodulate.
Regulation of nodulation in Alnus incana‐Frankia symbiosis
Authors: Wall Luis Gabriel , Huss‐Danell Kerstin
Published: May 2006

We have studied regulation of nodulation in Alnus incana (L.) Moench using double inoculations in plastic pouches and a slide technique to observe root hair deformation. Initially, the distribution of nodules between main and lateral roots appeared quite constant, independent of the concentration of inoculum (1 to 250 μg of crushed nodules plant−1). Susceptibility to infection after the second inoculation was restricted to lateral roots after the initial infections developed. When pre‐existing nodules were excised before the second inoculation, subsequent nodules appeared to arise where infections had arrested at stages earlier than actual nodule emergence. We observed that root hairs formed postinoculation were very crowded and short with a pronounced deformation. No nodules were found later on this region of the root, suggesting a loss of susceptibility in this region. Split‐root experiments with delays between inoculation of the first and second side of the root system showed irreversible, systemic inhibition of nodulation on the second side starting between 3 and 6 days after the inoculation of the first side. Only when compatible, infective strains were used in the first inoculation, was nodule formation inhibited after the second inoculation. We conclude that autoregulation of nodulation operates in Alnus incana and on a time scale similar to what is found in some legumes.
ag13 is expressed in Alnus glutinosa nodules in infected cells during endosymbiont degradation and in the nodule pericycle
Authors: Guan Changhui , Akkermans Antoon D. L. , van Kammen Ab , Bisseling Ton , Pawlowski Katharina
Published: May 2006

We isolated and characterized an Alnus glutinosa cDNA clone, pAg13, which corresponds to a gene expressed at higher levels in nodules induced by Frankia than in roots. The deduced polypeptide sequence is rich in glutamic acid and proline and contains a putative signal peptide indicating an extracellular location of Ag13. In situ hybridization showed that ag13 is expressed in the pericycle of the nodule vascular bundle and in infected cells that exhibited degradation of the endosymbiont.
Alteration of N nutrition in Myrica gale induces changes in nodule growth, nodule activity and amino acid composition
Authors: Baker Andrea , Hill Graham F. , Parsons Richard
Published: May 2006

Changes in nodule growth and activity and in the concentrations of soluble N compounds in nodules, leaves and xylem sap under conditions of altered N nutrition in the actinorhizal plant Myrica gale L. are reported. Altering the N nutrition of symbiotic plants may alter the internal regulation of combined N which in turn may regulate nodule growth and activity. Flushing nodules daily with 100% O2 caused a decline in amide concentration and an increase in nodule growth although plants had recovered some nitrogenase activity within 4 h of exposure to O2. Samples of nodules, leaves and xylem sap were derivatized and amino acids identified and quantified using either reverse phase high performance liquid chromatography or gas chromatography‐mass spectrometry in single ion monitoring mode. The ratio of asparagine in the nodules to that in the xylem was much higher in plants fed N (6.7 for NH+4‐fed and 8.3 for NO−3‐fed plants) than for N2‐fixing plants (2.5). Significant amounts of 15N added as 15NH+4 or 15NO−3 accumulated in nodules following accumulation in the shoot which is consistent with the translocation of N to the nodules via the phloem. The uptake of 15NH+4 led to the synthesis and subsequent translocation of glutamine in the xylem sap. These results are discussed in terms of the feedback mechanisms that may regulate nitrogen fixation in Myrica root nodules.
Rapid assimilation of recently fixed N2 in root nodules of Myrica gale
Authors: Baker Andrea , Parsons Richard
Published: May 2006

In Myrica gale L. plants the assimilation of ammonia released by symbiotic Frankia was observed by 15N2 labelling and subsequent analysis of the isotopic enrichment of nodule amino acids over time by single ion monitoring gas chromatography‐mass spectrometry. In detached nodules of Myrica, glutamine was the first amino acid labelled at 30 s and subsequently the amino acids glutamate, aspartate, alanine and γ‐amino butyric acid (GABA) became labelled. This pattern of labelling is consistent with the incorporation of ammonium via glutamine synthetase [GS; EC 6.3.1.2]. No evidence for the ammonium assimilation via glutamate dehydrogenase [GDH; EC 1.4.1.2] was observed as glutamate became labelled only after glutamine. Using attached nodules and pulse‐chase labelling, we observed synthesis of glutamine, glutamate, aspartate, alanine, GABA and asparagine, and followed the transport of fixed nitrogen in the xylem largely as glutamine and asparagine. Estimation of the cost of nitrogen fixation and asparagine synthesis in Myrica nodules suggests a minimum of one sucrose required per asparagine produced. Rapid translocation of recently fixed nitrogen was observed in Myrica gale nodules as 80% of the nitrogen fixed during a 1‐h period was translocated out of the nodules within 9 h. The large pool of asparagine that is present in nodules may buffer the transport of nitrogen and thus act to regulate nitrogen fixation via a feedback mechanism.
Physiological and morphological responses of red alder and sitka alder to flooding
Authors: Batzli Janet McCray , Dawson Jeffrey O.
Published: May 2006

Red alder (Alnus rubra Bong.) and sitka alder (A. viridis ssp. sinuata [Regel] Löve & Löve) are nitrogen‐fixing woody species that grow sympatrically along the Pacific coast of North America. Red alder is found in poorly drained lowlands, as well as in soils of moist upland slopes, whereas sitka alder generally colonizes well‐drained soils. To identify factors that contribute to flood tolerance, we conducted greenhouse experiments subjecting both species to a 20‐day flood and 10‐day recovery and red alder to a 50‐day flood and 20‐day recovery. We determined the effect of this stress on nitrogenase activity, root and nodule alcohol dehydrogenase (ADH) activity, lenticel and adventitious root development, relative growth rate (RGR), and leaf gas exchange. After 24 h of flooding, nitrogenase activity could not be detected in either species. Limited nitrogenase activity did return in red alder at the end of a 10‐day recovery following the 20‐day flood, but sitka alder showed no recovery of nitrogenase activity. After 50 days of continuous flooding, red alder nitrogenase activity returned to pretreatment levels. Red alder root and nodule ADH activity was more than twice that of sitka alder under flooded conditions. Sitka alder showed extensive root mortality and leaf abscission over the same 20‐day flooding period. Flooded red alder exhibited an initial decline in root RGR, but recovered between days 10 and 20 with the formation of adventitious roots. Furthermore, initiation of adventitious roots in red alder coincided with an increase in stomatal conductance without a similar recovery of carbon dioxide exchange rate. Sitka alder formed few adventitious roots, lost much of its root and leaf biomass, and showed no restoration of growth during flooding or recovery. Different responses of red and sitka alder to flooding serve as a partial explanation for the different patterns of distribution of these species and suggest some adaptations of red alder that permit flood tolerance.
Influence of soil moisture on the nodulation of post fire seedlings of Ceanothus spp. growing in the Santa Monica Mountains of Southern California
Authors: Pratt S. D. , Konopka A. S. , Murry M. A. , Ewers F. W. , Davis S. D.
Published: May 2006

During the dry season (early May through September of 1994), following a fall 1993 wildfire, a survey of seedling nodulation was conducted at several sites in the Santa Monica Mountains of Southern California. Seedlings of Ceanothus spinosus, C. megacarpus, C. oliganthus, and C. cuneatus were manually excavated. During this period, only 12 of the 182 seedlings excavated were nodulated, and all of the nodulated seedlings were found in the relatively moist clay soils of a stream bank. No nodules were observed on the 170 seedlings excavated from the drier sites. An irrigation experiment was established in midsummer to assess whether water stress inhibits nodulation of post‐fire Ceanothus seedlings. Four plots with numerous seedlings of C. cuneatus and C. spinosus were irrigated with distilled water and monitored over a 9‐week period. There was a significant increase in nodulation frequency, water potential, stomatal conductance, transpiration, shoot elongation, and photosynthetic rate of irrigated seedlings compared with adjacent controls. Although these data support the hypothesis that water stress inhibits nodulation. it is unclear whether this is because of an effect of soil moisture on the nodulation capacity of the soils (i.e. on the size and physiological state of the soil Frankia population) or to a host plant response to drought which might prevent actinorhizal root infection and/or nodule development.
Formation of cluster roots and mycorrhizal status of Comptonia peregrina and Myrica pensylvanica in Maine, USA
Authors: Hurd Todd M. , Schwintzer Christa R.
Published: May 2006

Extent of cluster (proteoid) root formation in the field was examined in relation to availability of P and successional status of the site in two actinorhizal, N2‐fixing shrubs. Comptonia peregrina (L.) Coult. and Myrica pensylvanica Loisel. In C. peregrina cluster roots were present at all 13 sites and comprised between 0.2 and 19% of total fine root dry weight. Cluster root formation was most extensive at recently disturbed sites and was negatively correlated with cover of associated woody species (r =−0.85), litter depth (r =−0.81) and available (extractable) soil P (r =−0.75). In M. pensylvanica cluster roots were present at all 11 sites and comprised between 6 and 20% of total fine root dry weight. On mineral soils (n = 6), extent of cluster root formation was negatively correlated (r =−0.86) with cover of associated woody species and with litter depth (r =−0.78; P= 0.07). Comptonia peregrina and M. pensylvanica lack functional mycorrhizae at these sites because only intracellular infections were found and these lacked arbuscules. None of 22 non‐N2‐fixing, dominant woody species associated with C. peregrina and M. pensylvanica formed cluster roots. Cluster roots probably allow C. peregrina and M. pensylvanica to obtain sufficient P from nutrient‐poor soils in the absence of functional mycorrhizae. Extensive cluster root formation on disturbed, early successional sites may aid these species in colonizing these sites because they have to form only one symbiosis (with Frankia) and not two (with Frankia and a mycorrhizal fungus).
Nucleotide sequence and expression ofnifHD fromFrankiastrain EuIKl, a symbiont ofElaeagnus umbellata
Authors: Kim Ho Bang , An Chung Sun
Published: May 2006

Nucleotide sequences ofnifHD fromFrankiastrain EuIKl were determined and analysed. The 3.2‐kb and 5.5‐kbBamHI fragments of a genomic clone were previously shown to containnifHD‐like sequences and to be contiguous, based on hybridization experiments and partial sequencing data. Sequence analysis of about 3.0 kb from these fragments revealed two open reading frames and beginning of a third in the same orientation, each of which showed high degree of sequence homology withnifH,nifD andnifK, respectively. The deduced amino acid sequence of thenifH ORF, consisting of 861 bp, showed sequence similarity of about 91% with those of otherFrankiastrains, whereas that ofnifD ORF, consisting of 1458 bp, showed about 85% similarity. Intergenic sequence betweennifH andnifD was 45 bp and betweennifD andnifK was 61 bp. The 5’ofnifH revealed putative Shine‐Dalgarno sequences; however, a sequence resembling a typicalnif‐promoter or NifA binding site was not found. Northern hybridization of RNA from the nodules showed thatnifHDK were transcribed into a polycistronic mRNA in the symbiont ofElaeagnus umbellata.
Whole cell hybridization as a tool to study Frankia populations in root nodules
Authors: Hahn Dittmar , Zepp Kornelia , Zeyer Josef
Published: May 2006

Molecular methods based on DNA or rRNA hybridization are powerful tools in microbial ecology for the specific detection and enumeration of bacteria unbiased by the limitations of culturability. A promising alternative to the analysis of Frankia populations in root nodules by methods based on rRNA extraction or on DNA extraction followed by the polymerase chain reaction (PCR) is the whole cell hybridization technique. This technique includes the microscopic detection of labeled probes hybridized to specific target sequences on marker molecules such as rRNA in fixed microbial cells. The analysis of uncultured Frankia populations in root nodules can reliably be performed on a subgroup level when digoxigenin‐labeled oligonucleotide probes or in vitro transcripts directed against an actinomycetes‐specific insertion on the 23S rRNA are used. Digoxigenin‐labeled probes are more suitable for in situ detection of Frankia than fluorescent probes since the sensitivity is higher and problems arising from the autofluorescence of cells and plant material are avoided. All these strategies, however, require pretreatments to increase the permeability of vesicles, hyhae and spores.
nifV is contiguous to nifHDK in Frankia strain FaC1
Authors: Oh Bo Si , Twigg Paul G. , Hong Jeong Soo , Mullin Beth C. , An Chung Sun
Published: May 2006

The organization of genes with the capacity to code for four proteins involved in nitrogen fixation in Frankia strain FaC1 was determined by restriction fragment mapping and nucleotide sequence analysis. Analysis of the 44‐kb genomic cosmid clone pFAH 1. isolated from a cosmid library made from Frankia strain FaCl, resulted in the identification of a 7.2‐kb PstI fragment to which Klebsiella nifH, nifD and nifK probes hybridized. This nif‐hybridizing fragment was subcloned and analyzed by restriction fragment mapping. Further subcloning of the 7.2‐kb fragment and subsequent sequence analysis of approximately 6.8 kb revealed the presence of six open reading frames (ORFs). Four of these ORFs have the potential to code for nifV‐, nifH‐, nifD‐ and nifK‐like gene products and the two others are unidentified ORFs. The organization of the structural genes for nitrogenase is the same in this Frankia strain as it is in most other nitrogen‐fixing prokaryotes, but the positioning of the nifV‐like gene relative to the nifHDK cluster differs, A consensus nif‐promoter‐like sequence, found 5’to nifH. was not detected upstream of the nifV‐like gene. Nine copies of a 7‐bp direct repeat were found 5’to ORFA.
Direct characterization of Frankia and of close phyletic neighbors from an Alnus viridis rhizosphere
Authors: Normand Philippe , Chapelon Chrystelle
Published: May 2006

To analyze the population structure of Frankia soil populations, DNA was extracted from an Alnus viridis rhizosphere, PCR‐amplified with a primer designed to be specific, and cloned. A PCR‐RFLP analysis of the resulting clones showed that none had a pattern close to those expected from an analysis made on Frankia collection strains, on which HhaI, HpaII and HaeIII were found to be the most discriminant restriction enzymes. Sequencing was done on a subset of soil clones and these were compared to DNA data banks. Some sequences were typical of lowGC Firmicutes (Bacillus and relatives), whereas others were typical of highGC Firmicutes (Actinomycetes and relatives). Two of these sequences appear to be in the same line of descent as Frankia and Geodermatophilus and represent as yet uncharacterized soil microorganisms. This shows that the design of specific or generic primers must be refined constantly to take into account the deposition of such new sequences in DNA data banks.
Differences in the reactivation process in thermosensitive seeds of Phacelia tanacetifolia with germination inhibited by high temperature (30°C)
Authors: Pirovano Livia , Morgutti Silvia , Espen Luca , Cocucci Sergio M.
Published: May 2006

The changes in several metabolic parameters induced in thermosensitive seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair) by an inhibitory temperature of 30°C were evaluated and compared to those occurring at the optimum temperature for germination (16°C). The severe inhibition of germination (70%) at 30°C was accompanied by an inhibition of the increase in total RNA and glucose‐6‐phosphate followed by an inhibition of the increase in DNA, reducing sugars and ATP. Both transcriptional and translational activities occurred at the two temperatures, but with substantial differences. They were higher at 30 than at 16°C after 9 h of imbibition. With time, translational activity became much lower at 30°C, as indicated by the inhibition of the increases in the polysome/monosome ratio and of the levels of activities, evaluated in vitro, of glucose‐6‐phosphate dehydrogenase, pyruvate kinase, glucokinase and malate dehydrogenase. Transport also occurred at 30°C, as indicated by the positive net flux of K+ into the cells and by the electrochemical equilibrium of mobile K+ between the outside and inside of the cells. There was much less mobile K+ inside the cells at 30 than at 16°C (50 and 13%, respectively, after 24 and 72 h of imbibition). The values of cytoplasmic pH were the same at 16 and 30°C. At 30°C, the vacuolar pH did not change, whereas at 16°C it became more acidic at 72 h. The possible roles of cytoplasmic K+ concentration and pH in the control of the reactivation of metabolism during germination of Phacelia tanacetifolia seeds are discussed.
Utilization of the acetylene reduction assay to screen for tolerance of symbiotic N2 fixation to limiting P nutrition in common bean
Authors: Vadez Vincent , Beck Douglas P. , Lasso Jesus H. , Drevon Jean‐Jacques
Published: May 2006

The limitation of symbiotic nitrogen fixation due to P deficiency restricts the development of a sustainable agriculture, particularly in Mediterrancan and tropical soils. Common bean genotypes, APN18, BAT271, PVA846, POT51, G2633 and G12168, were grown in an aerated N‐free nutrient solution at low (72 μmol plant‐1 week‐1) and control P supplies (360 μmol plant‐1 week‐1). Nitrogenase activity was estimated by in situ measurements of acetylene reduction activity (ARA) in a flow‐through system. During the assays, maximum values of ARA (peak ARA) were reached between 20 and 30 min after exposure to C2H2, depending on P treatment and growth stage. Thereafter, a decline in C2H4 evolution was observed. This decline was most pronounced in low‐P plants and there was a significant genotypic effect. ARA per plant was decreased by P deficiency, mostly because nodulation was delayed and the number and mass of nodules were reduced. The ARA decrease during pod filling was also activated by P deficiency. ARA per g dry weight nodule was increased by P deficiency in G2633 and G12168, unchanged in APN18, BAT271 and POT51 and decreased in PVA846. Except for the climbing type IV G2633, total N at harvest for all P treatments was correlated with the cumulative value of peak ARA and with peak ARA at early pod‐filling which was the highest peak ARA throughout the growth cycle of type III bushy genotypes. We conclude that if phenology and growth habit are carefully considered, peak ARA is a reliable screen of genotypes for N2 fixation tolerance to P deficiency. Selection of lines with early nodulation under P deficiency is also advisable, and the effect of P deficiency on the nodule functioning needs to be considered.
A role for cytosolic glutamine synthetase in the remobilization of leaf nitrogen during water stress in tomato
Authors: Bauer Diana , Biehler Klaus , Fock Heinrich , Carrayol Elisa , Hirel Bertrand , Migge Andrea , Becker Thomas W.
Published: May 2006

Tomato (Lycopersicon esculentum L.) responded to a prolonged period of water stress with stomatal closure followed by premature flowering and the subsequent production of small fruits containing fertile seeds. Water stress was correlated with a net loss of protein from tomato leaves and the concomitant accumulation of free amino acids, reflecting the remobilization of leaf nitrogen to meet the N‐requirement for the rapid development of reproductive organs. We show by northern blot analysis of the transcript pools, and by immunoblot analysis of the protein levels that water stress stimulates tomato cytosolic glutamine synthetase (EC 6.1.3.2; GS‐1) gene expression, while plastidic glutamine synthetase (GS‐2) gene expression remains unchanged during drought. These results suggest a role of GS‐1 in the generation of glutamine for the transport of the nitrogen that is remobilized in tomato leaves in response to chronic water stress. The remobilization of leaf N during water stress appears to be. at least in part, initiated by a specific down‐regulation of the leaf transcript pool corresponding to the small subunit of ribulose‐1,5‐bisphosphate carboxylase/oxygenase.
Peroxidase‐mediated conjugation of glutathione to unsaturated phenylpropanoids. Evidence against glutathione S‐transferase involvement
Authors: Dean John V. , Devarenne Timothy P.
Published: May 2006

A number of plant species are thought to possess a glutathione S‐transferase enzyme (GST: EC 2.5.1.18) that will conjugate glutathione (GSH) to trans‐cinnamic acid (CA) and para‐coumaric acid (4‐CA). However, we present evidence that this activity is mediated by peroxidase enzymes and not GSTs. The N‐terminal amino acid sequence of the GSH‐conjugating enzyme purified from etiolated corn shoots exhibited a strong degree of homology to cytosolic ascorbate peroxidase enzymes (APX: EC 1.11.1.11) from a number of plant species. The GSH‐conjugating and APX activities of corn could not be separated during chromatography on hydrophobic‐interaction. anion‐exchange, and gel filtration columns. Spectral analysis of the enzyme revealed that the protein had a Soret band at 405 nm. When the enzyme was reduced with dithionite, the peak was shifted to 423 nm with an additional peak at 554 nm. The spectrum of the dithionite‐reduced enzyme in the presence of 0.1 mM KCN exhibited peaks at 430, 534 and 563 nm. These spectra are consistent with the presence of a heme moiety. The GSH‐conjugating and APX activities of the enzyme were both inhibited by KCN. NaN3, p‐chloromercuribenzoate (pCMB), and iodoacetate. The APX specific activity of the enzyme was 1.5‐fold greater than the GSH‐conjugating specific activity with 4‐CA. In addition to the corn enzyme, a pea recombinant APX (rAPX) and horseradish peroxidase (HRP; EC 1.11.1.7) were also able to conjugate GSH to CA and 4‐CA. The peroxidase enzymes may generate thiyl free radicals of GSH that react with the alkyl double bond of CA and 4‐CA resulting in the formation of a GSH conjugate.
Regulation of the CO2‐concentrating mechanism in Chlorella vulgaris UAM 101 by glucose
Authors: Villarejo Arsenio , Orús Maria Isabel , Martinez Flor
Published: May 2006

In the green alga Chlorella vulgaris UAM 101, a CO2‐concentrating mechanism is induced when the cells are growing under low CO2 conditions. We have investigated the effect of glucose on the induction of this mechanism. Cells adapted to low CO2 in the presence of glucose showed a reduced ability to transport and fix external inorganic carbon. This reduction was correlated with a decrease in internal carbonic anhydrase activity. 3‐O‐methyl‐glucose, a nonmetabolizable analog of glucose, caused a more dramatic repression of these phenomena. Immunoblot analyses of total cell protein of Chlorella vulgaris UAM 101 against large subunit of ribulose‐1.5‐bisphosphate carboxylase/oxygenase and ribulose 1.5‐bisphosphate‐carboxylase/oxygenase activase polyclonal antibodies showed that the expression of these two polypeptides was affected by neither CO2 level, nor glucose or 3‐O‐methyl‐glucose. Ultrastructure studies showed that the low CO2‐induced development of the pyrenoid was also affected by glucose. Immunocytochemical data demonstrated that ribulose‐1.5‐bisphosphate carboxylase/oxygenase was exclusively located in the pyrenoid matrix. This localization and the density of labeling of the pyrenoid region were affected by neither CO2 level nor the presence of glucose.
Alternation of plasma membrane lipids in aluminum‐resistant and aluminum‐sensitive wheat genotypes in response to aluminum stress
Authors: Zhang Guichang , Slaski Jan J. , Archambault Daniel J. , Taylor Gregory J.
Published: May 2006

We have studied the effect of aluminum (A1) on lipid composition of plasma membranes from roots of an A1‐resistant (PT741) and an A1‐sensitive (Katepwa) cultivar of Triticum aestivum L. Several genotype–specific changes were observed in phospholipids and steryl lipids. While exposure to 20 μM AICI3 for 3 days had no effect on total phospholipids in either genotype, the most abundant phospholipid, phosphatidylcholine, increased significantly in the A1‐sensitive Katepwa. Aluminum also decreased steryl lipids (mainly free sterols) in PT741. Such changes were not observed in Katepwa. As a result of differential changes in lipid composition, the relative abundance of one lipid class to another changed. The ratio of steryl lipids to phospholipids decreased in PT741, with no change in Katepwa. While limited information on the relationship between membrane function and lipid composition makes it difficult to relate these changes to A1 toxicity and resistance, changes observed only in the A1–resistant genotype could contribute to continued plant growth in the face of A1 stress.
Growth analysis of wild‐type and photomorphogenic‐mutant tomato plants
Authors: Kerckhoffs L. H. J. , Sengers M. M. T. , Kendrick R. E.
Published: May 2006

A custom designed growth‐measuring apparatus, controlled by a microcomputer has been used to study extension growth kinetics of wild‐type and photomorphogenic‐mutant tomato (Lycopersicon esculentum Mill.) plants with and without end‐of‐day farred light (EODFR). The following photomorphogenic mutants were used. Far‐red insensitive (fri.1): deficient in phytochrome A (phyA); temporarily red light‐insensitive (tri.3): deficient in phytochrome Bl (phyB1), and their isogenic wild type (WT) cv. MoneyMaker. aurea (au): deficient in phytochrome chromophore biosynthesis; high‐pigment‐1 (hp‐1): exhibiting exaggerated phytochrome responses, and their isogenic WT cv. Ailsa Craig. The stem elongation rate (SER) during a 24‐h period of all the genotypes studied shows a similar pattern, having two dramatic transients, one shortly after the onset of the light period (a sharp decline in SER) and another shortly after the start of the dark period (a sharp increase in SER). These transients are probably associated with water relations as a consequence of opening and closure of the stomata. The fastest SER occurs during the dramatic oscillations early in the dark period. Between the genotypes there are large quantitative differences in SER. All the genotypes tested exhibited a strong EODFR response, resulting in a relative promotion of SER during the first period after the start of EODFR and in the subsequent light and dark periods. These results indicate that phyA, absent in the fri.1 mutant, does not play a major role in SER of light‐grown tomato plants, whereas phyB 1, absent in the tri.3 mutant, is partly responsible for the compact stature of WT plants. An additional phytochrome other than phy A and phy B1 must therefore be capable of eliciting the EODFR response.
A spruce gene, af70, constitutively expressed in somatic embryos and induced by ABA and low temperature in seedlings
Authors: Sabala Izabela , Franzén Helena , von Arnold Sara
Published: May 2006

We have previously shown that abscisic acid (ABA) specifically induces the secretion of a protein (AF70) in well‐developed group A somatic embryos of Picea abies (Sabala et al. 1996). In the present work the gene for this protein has been isolated and completely sequenced. Homology in amino acid sequence of the AF70 protein and deduced amino acid sequence from the af70 clone and results from Southern blot analysis suggest that the clone codes for the AF70 protein isolated previously. There are strong indications that the AF70 protein undergoes several post‐transcriptional modifications characteristic of secreted proteins. The af70 gene is expressed in group A and group B somatic embryos as well as in nonembryogenic calluses, but the expression in somatic embryos is not regulated by ABA. In contrast, seedlings of Picea abies do not express this gene under normal conditions, but do so in response to cold treatment as well as to ABA treatment. Furthermore, during cold acclimation, achieved when the seedlings are cultured at 20°C under long night conditions, the gene is expressed.
The case for chloroplast thylakoid carbonic anhydrase
Authors: Stemler Alan J.
Published: May 2006

Washed thylakoid membranes and photosystem II‐enriched membrane fragments from cyanobacteria, green algae, and chloroplasts from both C3 and C4 plants possess the ability to reversibly hydrate CO2. That is, the membranes have an intrinsic carbonic anhydrase activity. The present review outlines the discovery of thylakoid carbonic anhydrase and presents the evidence that it is a unique isozyme, distinct from other cellular carbonic anhydrases. It appears that at least some thylakoid carbonic anhydrase is closely associated with photosystem II and may be required for electron transport. This would explain why all inhibitors of carbonic anhydrase also inhibit photosystem II. Several speculative functions of thylakoid carbonic anhydrase are discussed. These include a possible role in carbon metabolism, in the protonation of plastoquinone, and/or in oxygen evolution.
The Development of Same‐ and Opposite‐Sex Social Relations Among Adolescents: An Analogue Study
Authors: Hops Hyman , Alpert Anthony , Davis Betsy
Published: May 2006

The present study, utilizing an analogue procedure and a short‐term longitudinal design, examined the relative strength of observed behavior in predicting mid‐ to late‐adolescents' ratings of that behavior. Direct observations were made of 89 adolescents during videotaped problem‐solving interactions with groups of unfamiliar peers. Within 6‐member peer groups, counterbalanced for gender, the adolescents participated in a series of problem‐solving and discussion tasks. Peer groups met one hour daily for six consecutive days. The interactions were coded with the LIFE code and three behavioral constructs were assessed: facilitative, problem‐solving, and aggressive. Same‐ and opposite‐sex peer ratings of three factors, sociable, aggressive, and withdrawn, were obtained at the end of the second and sixth days. Hierarchical linear modeling analyses revealed that same‐sex sociability ratings were predicted by prosocial behaviors of both girls and boys whereas boys' aggressive behavior also predicted these ratings across gender. In contrast, aggressive behavior displayed by girls predicted boys' ratings of girls' aggression. Withdrawal ratings were related to low levels of all behaviors. The results provide further evidence that peer perceptions may be driven by characteristics associated with gender that have been determined by culturally proscribed practices and socialization efforts.