bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Two Genes Encoding Starch-Branching Enzymes IIa and IIb Are Differentially Expressed in Barley1
Authors: Sun Chuanxin , Sathish Puthigae , Ahlandsberg Staffan , Jansson Christer 
Published: July 2002

AbstractThe sbeIIa andsbeIIb genes, encoding starch-branching enzyme (SBE) IIa and SBEIIb in barley (Hordeum vulgare L.), have been isolated. The 5′ portions of the two genes are strongly divergent, primarily due to the 2064-nucleotide-long intron 2 insbeIIb. The sequence of this intron shows that it contains a retro-transposon-like element. Expression ofsbeIIb but not sbeIIa was found to be endosperm specific. The temporal expression patterns forsbeIIa and sbeIIb were similar and peaked around 12 d after pollination. DNA gel-blot analysis demonstrated that sbeIIa and sbeIIb are both single-copy genes in the barley genome. By fluorescence in situ hybridization, the sbeIIa and sbeIIbgenes were mapped to chromosomes 2 and 5, respectively. The cDNA clones for SBEIIa and SBEIIb were isolated and sequenced. The amino acid sequences of SBEIIa and SBEIIb were almost 80% identical. The major structural difference between the two enzymes was the presence of a 94-amino acid N-terminal extension in the SBEIIb precursor. The (β/α)8-barrel topology of the α-amylase superfamily and the catalytic residues implicated in branching enzymes are conserved in both barley enzymes.
Expression Studies of the Zeaxanthin Epoxidase Gene inNicotiana plumbaginifolia
Authors: Audran Corinne , Borel Charlotte , Frey Anne , Sotta Bruno , Meyer Christian , Simonneau Thierry , Marion-Poll Annie 
Published: July 2002

Abstract
Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C40) via the C15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes zeaxanthin epoxidase, which catalyzes the conversion of zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leavesABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds theABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of zeaxanthin epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors.
NPH4, a Conditional Modulator of Auxin-Dependent Differential Growth Responses in Arabidopsis
Authors: Stowe-Evans Emily L. , Harper Reneé M. , Motchoulski Andrei V. , Liscum Emmanuel 
Published: July 2002

Abstract
Although sessile in nature, plants are able to use a number of mechanisms to modify their morphology in response to changing environmental conditions. Differential growth is one such mechanism. Despite its importance in plant development, little is known about the molecular events regulating the establishment of differential growth. Here we report analyses of the nph4(nonphototropic hypocotyl) mutants of Arabidopsis that suggest that the NPH4 protein plays a central role in the modulation of auxin-dependent differential growth. Results from physiological studies demonstrate that NPH4 activity is conditionally required for a number of differential growth responses, including phototropism, gravitropism, phytochrome-dependent hypocotyl curvature, apical hook maintenance, and abaxial/adaxial leaf-blade expansion. The nph4 mutants exhibited auxin resistance and severely impaired auxin-dependent gene expression, indicating that the defects associated with differential growth likely arise because of altered auxin responsiveness. Moreover, the auxin signaling events mediating phototropism are genetically correlated with the abundance of the NPH4 protein.
Changes in Hexokinase Activity inEchinochloa phyllopogon and Echinochloa crus-pavonis in Response to Abiotic Stress
Authors: Fox Theodore C. , Green Brian J. , Kennedy Robert A. , Rumpho Mary E. 
Published: July 2002

Abstract
Hexokinase (HXK; EC 2.7.1.1) regulates carbohydrate entry into glycolysis and is known to be a sensor for sugar-responsive gene expression. The effect of abiotic stresses on HXK activity was determined in seedlings of the flood-tolerant plant Echinochloa phyllopogon (Stev.) Koss and the flood-intolerant plant Echinochloa crus-pavonis (H.B.K.) Schult grown aerobically for 5 d before being subjected to anaerobic, chilling, heat, or salt stress. HXK activity was stimulated in shoots of E. phyllopogononly by anaerobic stress. HXK activity was only transiently elevated inE. crus-pavonis shoots during anaerobiosis. In roots of both species, anoxia and chilling stimulated HXK activity. Thus, HXK is not a general stress protein but is specifically induced by anoxia and chilling in E. phyllopogon and E. crus-pavonis. In both species HXK exhibited an optimum pH between 8.5 and 9.0, but the range was extended to pH 7.0 in air-grownE. phyllopogon to 6.5 in N2-grown E. phyllopogon. At physiologically relevant pHs (6.8 and 7.3, N2 and O2 conditions, respectively), N2-grown seedlings retained greater HXK activity at the lower pH. The pH response suggests that in N2-grown seedlings HXK can function in a more acidic environment and that a specific isozyme may be important for regulating glycolytic activity during anaerobic metabolism in E. phyllopogon.
Modification of Carbon Partitioning, Photosynthetic Capacity, and O2 Sensitivity in Arabidopsis Plants with Low ADP-Glucose Pyrophosphorylase Activity1
Authors: Sun Jindong , Okita Thomas W. , Edwards Gerald E. 
Published: July 2002

AbstractWild-type Arabidopsis plants, the starch-deficient mutant TL46, and the near-starchless mutant TL25 were evaluated by noninvasive in situ methods for their capacity for net CO2 assimilation, true rates of photosynthetic O2 evolution (determined from chlorophyll fluorescence measurements of photosystem II), partitioning of photosynthate into sucrose and starch, and plant growth. Compared with wild-type plants, the starch mutants showed reduced photosynthetic capacity, with the largest reduction occurring in mutant TL25 subjected to high light and increased CO2 partial pressure. The extent of stimulation of CO2 assimilation by increasing CO2 or by reducing O2 partial pressure was significantly less for the starch mutants than for wild-type plants. Under high light and moderate to high levels of CO2, the rates of CO2assimilation and O2 evolution and the percentage inhibition of photosynthesis by low O2 were higher for the wild type than for the mutants. The relative rates of14CO2 incorporation into starch under high light and high CO2 followed the patterns of photosynthetic capacity, with TL46 showing 31% to 40% of the starch-labeling rates of the wild type and TL25 showing less than 14% incorporation. Overall, there were significant correlations between the rates of starch synthesis and CO2 assimilation and between the rates of starch synthesis and cumulative leaf area. These results indicate that leaf starch plays an important role as a transient reserve, the synthesis of which can ameliorate any potential reduction in photosynthesis caused by feedback regulation.
A Computer-Assisted Personalized Approach in an Undergraduate Plant Physiology Class1
Authors: Artus Nancy N. , Nadler Kenneth D. 
Published: July 2002

Abstract
We used Computer-Assisted Personalized Approach (CAPA), a networked teaching and learning tool that generates computer individualized homework problem sets, in our large-enrollment introductory plant physiology course. We saw significant improvement in student examination performance with regular homework assignments, with CAPA being an effective and efficient substitute for hand-graded homework. Using CAPA, each student received a printed set of similar but individualized problems of a conceptual (qualitative) and/or quantitative nature with quality graphics. Because each set of problems is unique, students were encouraged to work together to clarify concepts but were required to do their own work for credit. Students could enter answers multiple times without penalty, and they were able to obtain immediate feedback and hints until the due date. These features increased student time on task, allowing higher course standards and student achievement in a diverse student population. CAPA handles routine tasks such as grading, recording, summarizing, and posting grades. In anonymous surveys, students indicated an overwhelming preference for homework in CAPA format, citing several features such as immediate feedback, multiple tries, and on-line accessibility as reasons for their preference. We wrote and used more than 170 problems on 17 topics in introductory plant physiology, cataloging them in a computer library for general access. Representative problems are compared and discussed.
A Selaginella lepidophyllaTrehalose-6-Phosphate Synthase Complements Growth and Stress-Tolerance Defects in a Yeasttps1Mutant1
Authors: Zentella Rodolfo , Mascorro-Gallardo José O. , Van Dijck Patrick , Folch-Mallol Jorge , Bonini Beatriz , Van Vaeck Christophe , Gaxiola Roberto , Covarrubias Alejandra A. , Nieto-Sotelo Jorge , Thevelein Johan M. , Iturriaga Gabriel 
Published: July 2002

Abstract
The accumulation of the disaccharide trehalose in anhydrobiotic organisms allows them to survive severe environmental stress. A plant cDNA,SlTPS1, encoding a 109-kD protein, was isolated from the resurrection plant Selaginella lepidophylla, which accumulates high levels of trehalose. Protein-sequence comparison showed that SlTPS1 shares high similarity to trehalose-6-phosphate synthase genes from prokaryotes and eukaryotes. SlTPS1mRNA was constitutively expressed in S. lepidophylla. DNA gel-blot analysis indicated that SlTPS1 is present as a single-copy gene. Transformation of a Saccharomyces cerevisiae tps1Δ mutant disrupted in theScTPS1 gene with S. lepidophylla SlTPS1restored growth on fermentable sugars and the synthesis of trehalose at high levels. Moreover, the SlTPS1 gene introduced into the tps1Δ mutant was able to complement both deficiencies: sensitivity to sublethal heat treatment at 39°C and induced thermotolerance at 50°C. The osmosensitive phenotype of the yeast tps1Δ mutant grown in NaCl and sorbitol was also restored by the SlTPS1 gene. Thus, SlTPS1 protein is a functional plant homolog capable of sustaining trehalose biosynthesis and could play a major role in stress tolerance in S. lepidophylla.
Starch and the Control of Kernel Number in Maize at Low Water Potentials
Authors: Zinselmeier Christopher , Jeong Byeong-Ryong , Boyer John S. 
Published: July 2002

Abstract
After reproduction is initiated in plants, subsequent reproductive development is sometimes interrupted, which decreases the final number of seeds and fruits. We subjected maize (Zea mays L.) to low water potentials (ψw) that frequently cause this kind of failure. We observed metabolite pools and enzyme activities in the developing ovaries while we manipulated the sugar stream by feeding sucrose (Suc) to the stems. Low ψw imposed for 5 d around pollination allowed embryos to form, but abortion occurred and kernel number decreased markedly. The ovary contained starch that nearly disappeared during this abortion. Analyses showed that all of the intermediates in starch synthesis were depleted. However, when labeled Suc was fed to the stems, label arrived at the ovaries. Solute accumulated and caused osmotic adjustment. Suc accumulated, but other intermediates did not, showing that a partial block in starch synthesis occurred at the first step in Suc utilization. This step was mediated by invertase, which had low activity. Because of the block, Suc feeding only partially prevented starch disappearance and abortion. These results indicate that young embryos abort when the sugar stream is interrupted sufficiently to deplete starch during early ovary development, and this abortion results in a loss of mature seeds and fruits. At low ψw, maintaining the sugar stream partially prevented the abortion, but invertase regulated the synthesis of ovary starch and partially prevented full recovery.
Chloroplast Acclimation in Leaves of Guzmania monostachia in Response to High Light
Authors: Maxwell Kate , Marrison Joanne L. , Leech Rachel M. , Griffiths Howard , Horton Peter 
Published: July 2002

Abstract
Acclimation of leaves to high light (HL; 650 μmol m−2 s−1) was investigated in the long-lived epiphytic bromeliad Guzmania monostachiaand compared with plants maintained under low light (LL; 50 μmol m−2 s−1). Despite a 60% decrease in total chlorophyll in HL-grown plants, the chlorophyll a/bratio remained stable. Additionally, chloroplasts from HL-grown plants had a much lower thylakoid content and reduced granal stacking. Immunofluorescent labeling techniques were used to quantify the level of photosynthetic polypeptides. HL-grown plants had 30% to 40% of the content observed in LL-grown plants for the light-harvesting complex associated with photosystems I and II, the 33-kD photosystem II polypeptide, and Rubisco. These results were verified using conventional biochemical techniques, which revealed a comparable 60% decrease in Rubisco and total soluble protein. When expressed on a chlorophyll basis, the amount of protein and Rubisco was constant for HL- and LL-grown plants. Acclimation to HL involves a tightly coordinated adjustment of photosynthesis, indicating a highly regulated decrease in the number of photosynthetic units manifested at the level of the content of light-harvesting and electron transport components, the amount of Rubisco, and the induction of Crassulacean acid metabolism. This response occurs in mature leaves and may represent a strategy that is optimal for the resource-limited epiphytic niche.
An Imperfect Heat Shock Element and Different Upstream Sequences Are Required for the Seed-Specific Expression of a Small Heat Shock Protein Gene
Authors: Carranco Raúl , Almoguera Concepción , Jordano Juan 
Published: July 2002

Abstract
Chimeric constructs containing the promoter and upstream sequences of Ha hsp17.6 G1, a small heat shock protein gene, reproduced in transgenic tobacco (Nicotiana tabacum) its unique seed-specific expression patterns previously reported in sunflower. These constructs did not respond to heat shock, but were expressed without exogenous stress during late zygotic embryogenesis coincident with seed desiccation. Site-directed mutagenesis of its distal and imperfect heat shock element strongly impaired in vitro heat shock transcription factor binding and transgene expression in seeds. Deletion analyses of upstream sequences indicated the contribution of additional cis-acting elements with either positive or negative effects on transgene expression. These results show differences in the transcriptional activation through the heat shock element of small heat shock protein gene promoters in seeds compared with the heat shock response. In addition, they suggest that heat shock transcription factors and other distinct trans-acting factors cooperate in the regulation of Ha hsp17.6 G1 during seed desiccation.
Cloning and Functional Characterization of a Constitutively Expressed Nitrate Transporter Gene,OsNRT1, from Rice
Authors: Lin Chung-Ming , Koh Serry , Stacey Gary , Yu Su-May , Lin Tsai-Yun , Tsay Yi-Fang 
Published: July 2002

AbstractElucidating how rice (Oryza sativa) takes up nitrate at the molecular level could help improve the low recovery rate (&lt;50%) of nitrogen fertilizer in rice paddies. As a first step toward that goal, we have cloned a nitrate transporter gene from rice called OsNRT1. OsNRT1 is a new member of a growing transporter family called PTR, which consists not only of nitrate transporters from higher plants that are homologs of the Arabidopsis CHL1 (AtNRT1) protein, but also peptide transporters from a wide variety of genera including animals, plants, fungi, and bacteria. However, despite the fact that OsNRT1 shares a higher degree of sequence identity with the two peptide transporters from plants (approximately 50%) than with the nitrate transporters (approximately 40%) of the PTR family, no peptide transport activity was observed when OsNRT1 was expressed in either Xenopus oocytes or yeast. Furthermore, contrasting the dual-affinity nitrate transport activity of CHL1, OsNRT1 displayed only low-affinity nitrate transport activity in Xenopus oocytes, with aK m value of approximately 9 mm. Northern-blot and in situ hybridization analysis indicated that OsNRT1 is constitutively expressed in the most external layer of the root, epidermis and root hair. These data strongly indicate thatOsNRT1 encodes a constitutive component of a low-affinity nitrate uptake system for rice.
Calcium-Calmodulin Suppresses the Filamentous Actin-Binding Activity of a 135-Kilodalton Actin-Bundling Protein Isolated from Lily Pollen Tubes
Authors: Yokota Etsuo , Muto Shoshi , Shimmen Teruo 
Published: July 2002

AbstractWe have isolated a 135-kD actin-bundling protein (P-135-ABP) from lily (Lilium longiflorum) pollen tubes and have shown that this protein is responsible for bundling actin filaments in lily pollen tubes (E. Yokota, K. Takahara, T. Shimmen [1998] Plant Physiol 116: 1421–1429). However, only a few thin actin-filament bundles are present in random orientation in the tip region of pollen tubes, where high concentrations of Ca2+ have also been found. To elucidate the molecular mechanism for the temporal and spatial regulation of actin-filament organization in the tip region of pollen tubes, we explored the possible presence of factors modulating the filamentous actin (F-actin)-binding activity of P-135-ABP. The F-actin-binding activity of P-135-ABP in vitro was appreciably reduced by Ca2+ and calmodulin (CaM), although neither Ca2+ alone nor CaM in the presence of low concentrations of Ca2+ affects the activity of P-135-ABP. A micromolar order of Ca2+ and CaM were needed to induce the inhibition of the binding activity of P-135-ABP to F-actin. An antagonist for CaM, W-7, cancelled this inhibition. W-5 also alleviated the inhibition effect of Ca2+-CaM, however, more weakly than W-7. These results suggest the specific interaction of P-135-ABP with Ca2+-CaM. In the presence of both Ca2+ and CaM, P-135-ABP organized F-actin into thin bundles, instead of the thick bundles observed in the absence of CaM. These results suggest that the inhibition of the P-135-ABP activity by Ca2+-CaM is an important regulatory mechanism for organizing actin filaments in the tip region of lily pollen tubes.
Subcellular Localization of a High Affinity Binding Site ford-myo-Inositol 1,4,5-Trisphosphate fromChenopodium rubrum
Authors: Martinec Jan , Feltl Tomáš , Scanlon Chris H. , Lumsden Peter J. , Macháčková Ivana 
Published: July 2002

AbstractIt is now generally accepted that a phosphoinositide cycle is involved in the transduction of a variety of signals in plant cells. In animal cells, the binding of d-myo-inositol 1,4,5-trisphosphate (InsP3) to a receptor located on the endoplasmic reticulum (ER) triggers an efflux of calcium release from the ER. Sites that bind InsP3 with high affinity and specificity have also been described in plant cells, but their precise intracellular locations have not been conclusively identified. In contrast to animal cells, it has been suggested that in plants the vacuole is the major intracellular store of calcium involved in signal induced calcium release. The aim of this work was to determine the intracellular localization of InsP3-binding sites obtained from 3-week-old Chenopodium rubrum leaves. Microsomal membranes were fractionated by sucrose density gradient centrifugation in the presence and absence of Mg2+ and alternatively by free-flow electrophoresis. An ER-enriched fraction was also prepared. The following enzymes were employed as specific membrane markers: antimycin A-insensitive NADH-cytochrome c reductase for ER, cytochrome c oxidase for mitochondrial membrane, pyrophosphatase for tonoplast, and 1,3-β-d-glucansynthase for plasma membrane. In all membrane separations, InsP3-binding sites were concentrated in the fractions that were enriched with ER membranes. These data clearly demonstrate that the previously characterized InsP3-binding site from C. rubrum is localized on the ER. This finding supports previous suggestions of an alternative non-vacuolar InsP3-sensitive calcium store in plant cells.
Redox-Regulated RNA Helicase Expression
Authors: Kujat Sonya L. , Owttrim George W. 
Published: July 2002

Abstract
In photosynthetic organisms it is becoming increasingly evident that light-driven shifts in redox potential act as a sensor that initiates alterations in gene expression at both the level of transcription and translation. This report provides evidence that the expression of a cyanobacterial RNA helicase gene,crhR, is controlled at the level of transcription and mRNA stability by a complex series of interacting mechanisms that are redox regulated. Transcript accumulation correlates with reduction of the electron transport chain between QA in photosystem II and QO in cytb 6 f, whenSynechocystis sp. strain PCC 6803 is cultured photoautotrophically or photomixotrophically and subjected to darkness and/or electron transport inhibitors or illumination that preferentially excites photosystem II. crhR mRNA stability is also regulated by a redox responsive mechanism, which differs from that affecting accumulation and does not involve signaling initiated by photoreceptors. The data are most consistent with plastoquinol/cyt b 6 finteraction as the sensor initiating a signal transduction cascade resulting in accumulation of the crhR transcript. Functionally, CrhR RNA unwinding could act as a linker between redox regulated transcription and translation. The potential for translational regulation of redox-induced gene expression through RNA helicase-catalyzed modulation of RNA secondary structure is discussed.