PubMed Health⌕ Search

Biomedical subjects

David Weiss

Publications and source records attributed to David Weiss.

11 recordsLinked to original sources
PubMed2003

Sugars regulate sucrose transporter gene expression in citrus.

We report the isolation and characterization of two sucrose transporter cDNAs (CitSUT1 and CitSUT2) from citrus. CitSUT1 and CitSUT2 encode putative proteins (CitSUT1 and CitSUT2) of 528 and 607 amino acids, respectively. CitSUT1 and CitSUT2 share high similarities with sucrose transporters isolated from other plants. The expression of CitSUT1 in mature leaf discs is repressed by exogenous sucrose, glucose, mannose, and the glucose analog 2-deoxyglucose but not by another glucose analog 3-O-methylglucose, indicating a hexokinase (HXK)-mediated signaling pathway. CitSUT2 expression is not affected by exogenous sugars. Whereas CitSUT1 expresses strongly in source, sugar exporting organs, CitSUT2 expresses more strongly in sink, sugar importing organs, suggesting different physiological roles for these sucrose transporters.

Amino Acid Sequence↗
PubMed2003

Girdling affects carbohydrate-related gene expression in leaves, bark and roots of alternate-bearing citrus trees.

Effects of girdling on carbohydrate status and carbohydrate-related gene expression in citrus trees were investigated. Alternate-bearing 'Murcott' (a Citrus reticulata hybrid of unknown origin) trees were girdled during autumn (25 Sep. 2001) and examined 10 weeks later. Girdling brought about carbohydrate (soluble sugar and starch) accumulation in leaves and shoot bark above the girdle, in trees during their fruitless, 'off' year. Trees during their heavy fruit load, 'on' year did not accumulate carbohydrates above the girdle due to the high demand for carbohydrates by the developing fruit. Girdling caused a strong decline in soluble sugar and starch concentrations in organs below the girdle (roots), in both 'on' and 'off' trees. Expression of STPH-L and STPH-H (two isoforms of starch phosphorylase), Agps (ADP-glucose pyrophosphorylase, small subunit), AATP (plastidic ADP/ATP transporter), PGM-C (phosphoglucomutase) and CitSuS1 (sucrose synthase), all of which are associated with starch accumulation, was studied. It was found that gene expression is related to starch accumulation in all 'off' tree organs. RNA levels of all the genes examined were high in leaves and bark that accumulated high concentrations of starch, and low in roots with declining starch concentrations. It may be hypothesized that changes in specific sugars signal the up- and down-regulation of genes involved in starch synthesis.

Carbohydrate Metabolism↗
PubMed2003

Effects of carbohydrate starvation on gene expression in citrus root.

The roots of alternate-bearing citrus (Murcott, a Citrus reticulata hybrid) trees undergo extreme fluctuations of carbohydrate abundance and starvation. Using this system, we investigated the effect of root carbohydrate (total soluble sugar, sucrose and starch) depletion on carbohydrate-related gene expression. A series of genes, including those coding for starch phosphorylase ( STPH-L and STPH-H), ADP-glucose pyrophosphorylase, small subunit ( Agps), R1, plastidic ADP/ATP transporter ( AATP), phosphoglucomutase ( PGM-P and PGM-C), sucrose synthase ( CitSuS1 and CitSuSA), sucrose transporter ( SUT1 and SUT2), hexokinase ( HK) and alpha-amylase ( alpha-AMY), have been isolated and their expression analyzed. The genes were found to respond differentially to carbohydrate depletion. STPH-L, STPH-H, Agps, R1, AATP, PGM-P, PGM-C, CitSuS1 and HK were down-regulated while SUT1 and alpha-AMY were up-regulated during carbohydrate depletion. Two other genes, CitSuSA and SUT2, did not respond to carbohydrate depletion. Fruit removal, which interrupted the carbohydrate depletion induced by heavy fruiting, reversed these gene expression patterns. Trunk girdling and whole-plant darkening treatments, which brought about root carbohydrate depletion, induced the same changes in gene expression obtained in the alternate-bearing system. The possible roles of the up- and down-regulated genes in the metabolism of carbohydrate-depleted citrus roots are discussed. Although the specific signals involved have not been determined, the results support the feast/famine hypothesis of carbohydrate regulation proposed by Koch [K.E. Koch (1996) Annu Rev Plant Physiol Plant Mol Biol 47:509-540].

Carbohydrate Metabolism↗
PubMed2003

Volatile ester formation in roses. Identification of an acetyl-coenzyme A. Geraniol/Citronellol acetyltransferase in developing rose petals.

The aroma of roses (Rosa hybrida) is due to more than 400 volatile compounds including terpenes, esters, and phenolic derivatives. 2-Phenylethyl acetate, cis-3-hexenyl acetate, geranyl acetate, and citronellyl acetate were identified as the main volatile esters emitted by the flowers of the scented rose var. "Fragrant Cloud." Cell-free extracts of petals acetylated several alcohols, utilizing acetyl-coenzyme A, to produce the corresponding acetate esters. Screening for genes similar to known plant alcohol acetyltransferases in a rose expressed sequence tag database yielded a cDNA (RhAAT1) encoding a protein with high similarity to several members of the BAHD family of acyltransferases. This cDNA was functionally expressed in Escherichia coli, and its gene product displayed acetyl-coenzyme A:geraniol acetyltransferase enzymatic activity in vitro. The RhAAT1 protein accepted other alcohols such as citronellol and 1-octanol as substrates, but 2-phenylethyl alcohol and cis-3-hexen-1-ol were poor substrates, suggesting that additional acetyltransferases are present in rose petals. The RhAAT1 protein is a polypeptide of 458 amino acids, with a calculated molecular mass of 51.8 kD, pI of 5.45, and is active as a monomer. The RhAAT1 gene was expressed exclusively in floral tissue with maximum transcript levels occurring at stage 4 of flower development, where scent emission is at its peak.

Acetyltransferases↗
PubMed2002

Producing Bose-Einstein condensates using optical lattices.

We relate the entropies of ensembles of atoms in optical lattices to atoms in simple traps. We then determine which ensembles of lattice-bound atoms will adiabatically transform into a Bose condensate. This shows a feasible approach to Bose condensation without evaporative cooling.

Journal Article↗
PubMed2002

Linkage of chromosome 13q32 to schizophrenia in a large veterans affairs cooperative study sample.

Several prior reports have suggested that chromosomal region 13q32 may harbor a schizophrenia susceptibility gene. In an attempt to replicate this finding, we assessed linkage between chromosome 13 markers and schizophrenia in 166 families, each with two or more affected members. The families, assembled from multiple centers by the Department of Veterans Affairs Cooperative Studies Program, included 392 sampled affected subjects and 216 affected sib pairs. By DSM-III-R criteria, 360 subjects (91.8%) had a diagnosis of schizophrenia and 32 (8.2%) were classified as schizoaffective disorder, depressed. The families had mixed ethnic backgrounds. The majority were northern European-American families (n = 62, 37%), but a substantial proportion were African-American kindreds (n = 60, 36%). Chromosome 13 markers, spaced at intervals of approximately 10 cM over the entire chromosome and 2-5 cM for the 13q32 region were genotyped and the data analyzed using semi-parametric affected only linkage analysis. For the combined sample (with race broadly defined and schizophrenia narrowly defined) the maximum LOD score was 1.43 (Z-score of 2.57; P = 0.01) at 79.0 cM between markers D13S1241 (76.3 cM) and D13S159 (79.5 cM). Both ethnic groups showed a peak in this region. The peak is within 3 cM of the peak reported by Brzustowicz et al. [1999: Am J Hum Genet 65:1096-1103].

Adult↗
PubMed2002

Increased anthocyanin accumulation in aster flowers at elevated temperatures due to magnesium treatment.

Temperature is one of the main external factors affecting anthocyanin accumulation in plant tissues: low temperatures cause an increase and elevated temperatures cause a decrease in anthocyanin concentration. Several metals have been shown to increase the half-life time of anthocyanins, by forming complexes with them. We studied the combined effect of elevated temperatures and increased metal concentrations on the accumulation of anthocyanins in aster 'Sungal' flowers. It has been found that magnesium treatment of aster plants or detached flower buds, partially prevents colour fading at elevated temperatures. Anthocyanin concentration of aster 'Sungal' flowers grown at 29 degrees C/21 degrees C day/night, respectively, was about half that of flowers grown at 17 degrees C/9 degrees C. The activity of phenylalanine ammonia-lyase (PAL) and chalcone isomerase (CHI) decreased as the temperature increased. Treatment of both whole plants and detached flower buds grown at elevated temperatures in the presence of magnesium salts, increased flower anthocyanin concentration by up to 80%. Measurement of magnesium following these treatments revealed an increased level of the metal in the petals, suggesting a direct effect. Magnesium treatment does not seem to cause increased synthesis of anthocyanin through a stress-related reaction, since the activities of both PAL and CHI did not increase due to this treatment. The results of this study show that increasing magnesium levels in aster petals prevents the deleterious effect of elevated temperatures on anthocyanin accumulation, thus enhancing flower colour.

Journal Article↗
PubMed2002

Gibberellin regulates post-microsporogenesis processes in petunia anthers.

Previous studies have suggested that gibberellins (GAs) are produced in petunia anthers and transported to the corolla to induce growth and pigmentation. In this work, we studied the role of GA in the regulation of anther development. When petunia plants were treated with the GA-biosynthesis inhibitor paclobutrazol, anther development was arrested. Microscopic analysis of these anthers revealed that paclobutrazol inhibits post-meiotic developmental processes. The treated anthers contained pollen grains but the connective tissue and tapetum cells were degenerated. A similar phenotype was obtained when the Arabidopsis GA-signal repressor, SPY, was over-expressed in transgenic petunia plants, i.e. anther development was arrested following microsporogenesis. The expression of the GA-induced gene, GIP, can be used in petunia as a molecular marker to study GA responses. GA3 treatment of young anthers promoted, and paclobutrazol inhibited, GIP expression, suggesting that the hormone controls the natural activation of the gene in the anthers. Analyses of GIP expression during anther development revealed that the gene is induced only after microsporogenesis. This observation further suggests a role for GA in the regulation of post-meiotic processes during petunia anther development.

Journal Article↗
PubMed2002

O-methyltransferases involved in the biosynthesis of volatile phenolic derivatives in rose petals.

Rose (Rosa hybrida) flowers produce and emit a diverse array of volatiles, characteristic to their unique scent. One of the most prominent compounds in the floral volatiles of many rose varieties is the methoxylated phenolic derivative 3,5-dimethoxytoluene (orcinol dimethyl ether). Cell-free extracts derived from developing rose petals displayed O-methyltransferase (OMT) activities toward several phenolic substrates, including 3,5-dihydroxytoluene (orcinol), 3-methoxy,5-hydroxytoluene (orcinol monomethyl ether), 1-methoxy, 2-hydroxy benezene (guaiacol), and eugenol. The activity was most prominent in rose cv Golden Gate, a variety that produces relatively high levels of orcinol dimethyl ether, as compared with rose cv Fragrant Cloud, an otherwise scented variety but which emits almost no orcinol dimethyl ether. Using a functional genomics approach, we have identified and characterized two closely related cDNAs from a rose petal library that each encode a protein capable of methylating the penultimate and immediate precursors (orcinol and orcinol monomethyl ether, respectively) to give the final orcinol dimethyl ether product. The enzymes, designated orcinol OMTs (OOMT1 and OOMT2), are closely related to other plant methyltransferases whose substrates range from isoflavones to phenylpropenes. The peak in the levels of OOMT1 and OOMT2 transcripts in the flowers coincides with peak OMT activity and with the emission of orcinol dimethyl ether.

Amino Acid Sequence↗
PubMed2002

Rose scent: genomics approach to discovering novel floral fragrance-related genes.

For centuries, rose has been the most important crop in the floriculture industry; its economic importance also lies in the use of its petals as a source of natural fragrances. Here, we used genomics approaches to identify novel scent-related genes, using rose flowers from tetraploid scented and nonscented cultivars. An annotated petal EST database of approximately 2100 unique genes from both cultivars was created, and DNA chips were prepared and used for expression analyses of selected clones. Detailed chemical analysis of volatile composition in the two cultivars, together with the identification of secondary metabolism-related genes whose expression coincides with scent production, led to the discovery of several novel flower scent-related candidate genes. The function of some of these genes, including a germacrene D synthase, was biochemically determined using an Escherichia coli expression system. This work demonstrates the advantages of using the high-throughput approaches of genomics to detail traits of interest expressed in a cultivar-specific manner in nonmodel plants. EST sequences were submitted to the GenBank database (accession numbers BQ 103855 to BQ 106728).

Alkyl and Aryl Transferases↗