bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of light interception in research environments: a joint approach using directional light sensors and 3D virtual plants applied to sunflower (Helianthus annuus) and Arabidopsis thaliana in natural and artificial conditions
Authors: Chenu Karine , Rey Hervé , Dauzat Jean , Lydie Guilioni , Lecœur Jérémie
Published: November 2008

Light interception is a major factor influencing plant development and biomass production. Several methods have been proposed to determine this variable, but its calculation remains difficult in artificial environments with heterogeneous light. We propose a method that uses 3D virtual plant modelling and directional light characterisation to estimate light interception in highly heterogeneous light environments such as growth chambers and glasshouses. Intercepted light was estimated by coupling an architectural model and a light model for different genotypes of the rosette species Arabidopsis thaliana (L.) Heynh and a sunflower crop. The model was applied to plants of contrasting architectures, cultivated in isolation or in canopy, in natural or artificial environments, and under contrasting light conditions. The model gave satisfactory results when compared with observed data and enabled calculation of light interception in situations where direct measurements or classical methods were inefficient, such as young crops, isolated plants or artificial conditions. Furthermore, the model revealed that A. thaliana increased its light interception efficiency when shaded. To conclude, the method can be used to calculate intercepted light at organ, plant and plot levels, in natural and artificial environments, and should be useful in the investigation of genotype–environment interactions for plant architecture and light interception efficiency.
fw2.2 Directly Affects the Size of Developing Tomato Fruit, with Secondary Effects on Fruit Number and Photosynthate Distribution
Authors: Nesbitt T. Clint , Tanksley Steven D.
Published: November 2008

fw2.2 is a quantitative trait locus responsible for approximately 30% of the difference in fruit size between large, domesticated tomatoes (Lycopersicon esculentum Mill.) and their small-fruited wild relatives. The gene underlying this quantitative trait locus was cloned recently and shown to be associated with altered cell division in ovaries (Frary et al., 2000). However, it was not known whether the change in fruit size is associated with other changes in plant morphology or overall fruit yield—changes that could potentially cause the fruit weight phenotype. To shed light on this issue, a detailed comparison was made between nearly isogenic lines differing for alleles at this locus to search for pleiotropic effects associated with fw2.2. Field observations show that although the small-fruited nearly isogenic line produced smaller ovaries and fruit as expected, this was compensated by a larger number of fruit—due mainly to a significantly greater number of inflorescences—but with no net change in total fruit mass yield. This strongly suggests that fw2.2 may have a pleiotropic effect on how the plant distributes photosynthate among fruit. In a flower removal experiment to control for differences in inflorescence size and number, fruit size remained significantly different between the nearly isogenic lines. These observations indicate that the primary effect of fw2.2 is in controlling ovary and fruit size, and that other associated phenotypic effects are secondary.
Increasing the Glutathione Content in a Chilling-Sensitive Maize Genotype Using Safeners Increased Protection against Chilling-Induced Injury
Authors: Kocsy Gábor , von Ballmoos Peter , Rüegsegger Adrian , Szalai Gabriella , Galiba Gábor , Brunold Christian
Published: November 2008

With the aim of analyzing their protective function against chilling-induced injury, the pools of glutathione and its precursors, cysteine (Cys) and γ-glutamyl-Cys, were increased in the chilling-sensitive maize (Zea mays) inbred line Penjalinan using a combination of two herbicide safeners. Compared with the controls, the greatest increase in the pool size of the three thiols was detected in the shoots and roots when both safeners were applied at a concentration of 5 μm. This combination increased the relative protection from chilling from 50% to 75%. It is interesting that this increase in the total glutathione (TG) level was accompanied by a rise in glutathione reductase (GR; EC 1.6.4.2) activity. When the most effective safener combination was applied simultaneously with increasing concentrations of buthionine sulfoximine, a specific inhibitor of glutathione synthesis, the total γ-glutamyl-Cys and TG contents and GR activity were decreased to very low levels and relative protection was lowered from 75% to 44%. During chilling, the ratio of reduced to oxidized thiols first decreased independently of the treatments, but increased again to the initial value in safener-treated seedlings after 7 d at 5°C. Taking all results together resulted in a linear relationship between TG and GR and a biphasic relationship between relative protection and GR or TG, thus demonstrating the relevance of the glutathione levels in protecting maize against chilling-induced injury.
Biochemical and Genetic Analysis of the Effects ofAmylose-Extender Mutation in Rice Endosperm
Authors: Nishi Aiko , Nakamura Yasunori , Tanaka Naoki , Satoh Hikaru
Published: November 2008

Biochemical analysis of amylose-extender(ae) mutant of rice (Oryza sativa) revealed that the mutation in the gene for starch-branching enzyme IIb (BEIIb) specifically altered the structure of amylopectin in the endosperm by reducing short chains with degree of polymerization of 17 or less, with the greatest decrease in chains with degree of polymerization of 8 to 12. The extent of such change was correlated with the gelatinization properties of the starch granules, as determined in terms of solubility in urea solution. Theae mutation caused a dramatic reduction in the activity of BEIIb. The activity of soluble starch synthase I (SSI) in theae mutant was significantly lower than in the wild type, suggesting that the mutation had a pleiotropic effect on the SSI activity. In contrast, the activities of BEI, BEIIa, ADP-Glc pyrophosphorylase, isoamylase, isoamylase, pullulanase, and Suc synthase were not affected by the mutation. Therefore, it is stressed that the function of BEIIb cannot be complemented by BEIIa and BEI. These results strongly suggest that BEIIb plays a specific role in the transfer of short chains, which might then be extended by SS to form the A and B1 chains of amylopectin cluster in rice endosperm.
Chloroplast Transcription at Different Light Intensities. Glutathione-Mediated Phosphorylation of the Major RNA Polymerase Involved in Redox-Regulated Organellar Gene Expression
Authors: Baena-González Elena , Baginsky Sacha , Mulo Paula , Summer Holger , Aro Eva-Mari , Link Gerhard
Published: November 2008

Previous studies using purified RNA polymerase from mustard (Sinapis alba) chloroplasts showed control of transcription by an associated protein kinase. This kinase was found to respond to reversible thiol/disulfide formation mediated by glutathione (GSH), although at concentrations exceeding those thought to exist in vivo. In the present study, several lines of evidence are presented to substantiate the functioning of this regulation mechanism, also in vivo: (a) Studies on the polymerase-associated transcription kinase revealed that at appropriate ATP levels, GSH concentrations similar to those in vivo are sufficient to modulate the kinase activity; (b) GSH measurements from isolated mustard chloroplasts showed considerable differences in response to light intensity; (c) this was reflected by run-on transcription rates in isolated chloroplasts that were generally higher if organelles were prepared from seedlings incubated under high-light as compared with growth-light conditions; (d) the notion of a general transcriptional switch was strengthened by in vitro experiments showing that the kinase not only affects the transcription of a photosynthetic gene (psbA) but also that of a non-photosynthetic gene (trnQ); and (e) the polymerase-kinase complex revealed specific differences in the phosphorylation state of polypeptides depending on the light intensity to which the seedlings had been exposed prior to chloroplast isolation. Taken together, these data are consistent with GSH and phosphorylation-dependent regulation of chloroplast transcription in vivo.
Antioxidant Systems and O2
.−/H2O2 Production in the Apoplast of Pea Leaves. Its Relation with Salt-Induced Necrotic Lesions in Minor Veins
Authors: Hernández José A. , Ferrer Maria Angeles , Jiménez Ana , Barceló Alfonso Ros , Sevilla Francisca
Published: November 2008

The present work describes, for the first time, the changes that take place in the leaf apoplastic antioxidant defenses in response to NaCl stress in two pea (Pisum sativum) cultivars (cv Lincoln and cv Puget) showing different degrees of sensitivity to high NaCl concentrations. The results showed that only superoxide dismutase, and probably dehydroascorbate reductase (DHAR), were present in the leaf apoplastic space, whereas ascorbate (ASC) peroxidase, monodehydroascorbate reductase (MDHAR), and glutathione (GSH) reductase (GR) seemed to be absent. Both ASC and GSH were detected in the leaf apoplastic space and although their absolute levels did not change in response to salt stress, the ASC/dehydroascorbate and GSH to GSH oxidized form ratios decreased progressively with the severity of the stress. Apoplastic superoxide dismutase activity was induced in NaCl-treated pea cv Puget but decreased in NaCl-treated pea cv Lincoln. An increase in DHAR and GR and a decrease in ASC peroxidase, MDHAR, ASC, and GSH levels was observed in the symplast from NaCl-treated pea cv Lincoln, whereas in pea cv Puget an increase in DHAR, GR, and MDHAR occurred. The results suggest a strong interaction between both cell compartments in the control of the apoplastic ASC content in pea leaves. However, this anti-oxidative response does not seem to be sufficient to remove the harmful effects of high salinity. This finding is more evident in pea cv Lincoln, which is characterized by a greater inhibition of the growth response and by a higher rise in the apoplastic hydrogen peroxide content, O2  .−production and thiobarbituric acid-reactive substances, and CO protein levels. This NaCl-induced oxidative stress in the apoplasts might be related to the appearance of highly localized O2  .−/H2O2-induced necrotic lesions in the minor veins in NaCl-treated pea plants. It is possible that both the different anti-oxidative capacity and the NaCl-induced response in the apoplast and in the symplast from pea cv Puget in comparison with pea cv Lincoln contributes to a better protection of pea cv Puget against salt stress.
Environmental and Developmental Regulation of the Wound-Induced Cell Wall Protein WI12 in the Halophyte Ice Plant
Authors: Yen Shyi-Kae , Chung Mei-Chu , Chen Pei-Chung , Yen Hungchen E.
Published: November 2008

A wounded gene WI12 was used as a marker to examine the interaction between biotic stress (wounding) and abiotic stress (high salt) in the facultative halophyte ice plant (Mesembryanthemum crystallinum). The deduced WI12 amino acid sequence has 68% similarity to WUN1, a known potato (Solanum tuberosum) wound-induced protein. Wounding, methyl jasmonate, and pathogen infection induced localWI12 expression. Upon wounding, the expression ofWI12 reached a maximum level after 3 h in 4-week-old juvenile leaves, whereas the maximum expression was after 24 h in 8-week-old adult leaves. The temporal expression ofWI12 in salt-stressed juvenile leaves was similar to that of adult leaves. The result suggests that a salt-induced switch from C3 to Crassulacean acid metabolism has a great influence on the ice plant's response to wounding. The expression ofWI12 and the accumulation of WI12 protein were constitutively found in phloem and in wounded mesophyll cells. At the reproductive stage, WI12 was constitutively found in petals and styles, and developmentally regulated in the placenta and developing seeds. The histochemical analysis showed that the appearance of WI12 is controlled by both environmental and developmental factors. Immunogold labeling showed WI12 preferentially accumulates in the cell wall, suggesting its role in the reinforcement of cell wall composition after wounding and during plant development.
Effects of PSAG12-IPT Gene Expression on Development and Senescence in Transgenic Lettuce
Authors: McCabe Matthew S. , Garratt Lee C. , Schepers Frank , Jordi Wilco J.R.M. , Stoopen Geert M. , Davelaar Evert , van Rhijn J. Hans A. , Power J. Brian , Davey Michael R.
Published: November 2008

An ipt gene under control of the senescence-specific SAG12 promoter from Arabidopsis (PSAG12-IPT) significantly delayed developmental and postharvest leaf senescence in mature heads of transgenic lettuce (Lactuca sativa L. cv Evola) homozygous for the transgene. Apart from retardation of leaf senescence, mature, 60-d-old plants exhibited normal morphology with no significant differences in head diameter or fresh weight of leaves and roots. Induction of senescence by nitrogen starvation rapidly reduced total nitrogen, nitrate, and growth of transgenic and azygous (control) plants, but chlorophyll was retained in the lower (outer) leaves of transgenic plants. Harvested PSAG12-IPTheads also retained chlorophyll in their lower leaves. During later development (bolting and preflowering) of transgenic plants, the decrease in chlorophyll, total protein, and Rubisco content in leaves was abolished, resulting in a uniform distribution of these components throughout the plants. Homozygous PSAG12-IPTlettuce plants showed a slight delay in bolting (4–6 d), a severe delay in flowering (4–8 weeks), and premature senescence of their upper leaves. These changes correlated with significantly elevated concentrations of cytokinin and hexoses in the upper leaves of transgenic plants during later stages of development, implicating a relationship between cytokinin and hexose concentrations in senescence.
The Organization of Cytoplasmic Ribosomal Protein Genes in the Arabidopsis Genome
Authors: Barakat Abdelali , Szick-Miranda Kathleen , Chang Ing-Feng , Guyot Romain , Blanc Guillaume , Cooke Richard , Delseny Michel , Bailey-Serres Julia
Published: November 2008

Eukaryotic ribosomes are made of two components, four ribosomal RNAs, and approximately 80 ribosomal proteins (r-proteins). The exact number of r-proteins and r-protein genes in higher plants is not known. The strong conservation in eukaryotic r-protein primary sequence allowed us to use the well-characterized rat (Rattus norvegicus) r-protein set to identify orthologues on the five haploid chromosomes of Arabidopsis. By use of the numerous expressed sequence tag (EST) accessions and the complete genomic sequence of this species, we identified 249 genes (including some pseudogenes) corresponding to 80 (32 small subunit and 48 large subunit) cytoplasmic r-protein types. None of the r-protein genes are single copy and most are encoded by three or four expressed genes, indicative of the internal duplication of the Arabidopsis genome. The r-proteins are distributed throughout the genome. Inspection of genes in the vicinity of r-protein gene family members confirms extensive duplications of large chromosome fragments and sheds light on the evolutionary history of the Arabidopsis genome. Examination of large duplicated regions indicated that a significant fraction of the r-protein genes have been either lost from one of the duplicated fragments or inserted after the initial duplication event. Only 52 r-protein genes lack a matching EST accession, and 19 of these contain incomplete open reading frames, confirming that most genes are expressed. Assessment of cognate EST numbers suggests that r-protein gene family members are differentially expressed.
Characterization of a Functional Soluble Form of a Brassica napus Membrane-Anchored Endo-1,4-β-Glucanase Heterologously Expressed in Pichia pastoris
Authors: Mølhøj Michael , Ulvskov Peter , Dal Degan Florence
Published: November 2008

The Brassica napus gene,Cel16, encodes a membrane-anchored endo-1,4-β-glucanase with a deduced molecular mass of 69 kD. As for other membrane-anchored endo-1,4-β-glucanases, Cel16 consists of a predicted intracellular, charged N terminus (methionine1-lysine70), a hydrophobic transmembrane domain (isoleucine71-valine93), and a periplasmic catalytic core (lysine94-proline621). Here, we report the functional analysis of Δ1-90Cel16, the N terminally truncated Cel16, missing residues 1 through 90 and comprising the catalytic domain of Cel16 expressed recombinantly in the methylotrophic yeast Pichia pastoris as a soluble protein. A two-step purification protocol yielded Δ1-90Cel16 in a pure form. The molecular mass of Δ1-90Cel16, when determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was about 130 kD and about 60 kD after enzymatic removal of N-glycans, fitting the expected molecular mass of 59 kD. Δ1-90Cel16 was highly N glycosylated as compared with the native B. napus Cel16 protein. Δ1-90Cel16 had a pH optimum of 6.0. The activity of Δ1-90Cel16 was inhibited by EDTA and exhibited a strong dependence on calcium. Δ1-90Cel16 showed substrate specificity for low substituted carboxymethyl-cellulose and amorphous cellulose. It did not hydrolyze crystalline cellulose, xyloglycan, xylan, (1→3),(1→4)-β-d-glucan, the highly substituted hydroxyethylcellulose, or the oligosaccharides cellotriose, cellotetraose, cellopentaose, or xylopentaose. Size exclusion analysis of Δ1-90Cel16-hydrolyzed carboxymethylcellulose showed that Δ1-90Cel16 is a true endo-acting glucanase.
Responses of Photosynthetic Electron Transport in Stomatal Guard Cells and Mesophyll Cells in Intact Leaves to Light, CO2, and Humidity
Authors: Lawson Tracy , Oxborough Kevin , Morison James I.L. , Baker Neil R.
Published: November 2008

High-resolution images of the chlorophyll fluorescence parameterF  q  ′/F  m  ′from attached leaves of commelina (Commelina communis) and tradescantia (Tradescantia albiflora) were used to compare the responses of photosynthetic electron transport in stomatal guard cell chloroplasts and underlying mesophyll cells to key environmental variables.F  q  ′/F  m  ′estimates the quantum efficiency of photosystem II photochemistry and provides a relative measure of the quantum efficiency of non-cyclic photosynthetic electron transport. Over a range of light intensities, values ofF  q  ′/F  m  ′were 20% to 30% lower in guard cell chloroplasts than in mesophyll cells, and there was a close linear relationship between the values for the two cell types. The responses ofF  q  ′/F  m  ′of guard and mesophyll cells to changes of CO2 and O2 concentration were very similar. There were similar reductions ofF  q  ′/F  m  ′of guard and mesophyll cells over a wide range of CO2concentrations when the ambient oxygen concentration was decreased from 21% to 2%, suggesting that both cell types have similar proportions of photosynthetic electron transport used by Rubisco activity. When stomata closed after a pulse of dry air,F  q  ′/F  m  ′of both guard cell and mesophyll showed the same response; with a marked decline when ambient CO2 was low, but no change when ambient CO2 was high. This indicates that photosynthetic electron transport in guard cell chloroplasts responds to internal, not ambient, CO2 concentration.
Protection against Heat Stress-Induced Oxidative Damage in Arabidopsis Involves Calcium, Abscisic Acid, Ethylene, and Salicylic Acid
Authors: Larkindale Jane , Knight Marc R.
Published: November 2008

Plants, in common with all organisms, have evolved mechanisms to cope with the problems caused by high temperatures. We examined specifically the involvement of calcium, abscisic acid (ABA), ethylene, and salicylic acid (SA) in the protection against heat-induced oxidative damage in Arabidopsis. Heat caused increased thiobarbituric acid reactive substance levels (an indicator of oxidative damage to membranes) and reduced survival. Both effects required light and were reduced in plants that had acquired thermotolerance through a mild heat pretreatment. Calcium channel blockers and calmodulin inhibitors increased these effects of heating and added calcium reversed them, implying that protection against heat-induced oxidative damage in Arabidopsis requires calcium and calmodulin. Similar to calcium, SA, 1-aminocyclopropane-1-carboxylic acid (a precursor to ethylene), and ABA added to plants protected them from heat-induced oxidative damage. In addition, the ethylene-insensitive mutant etr-1, the ABA-insensitive mutant abi-1, and a transgenic line expressingnahG (consequently inhibited in SA production) showed increased susceptibility to heat. These data suggest that protection against heat-induced oxidative damage in Arabidopsis also involves ethylene, ABA, and SA. Real time measurements of cytosolic calcium levels during heating in Arabidopsis detected no increases in response to heat per se, but showed transient elevations in response to recovery from heating. The magnitude of these calcium peaks was greater in thermotolerant plants, implying that these calcium signals might play a role in mediating the effects of acquired thermotolerance. Calcium channel blockers and calmodulin inhibitors added solely during the recovery phase suggest that this role for calcium is in protecting against oxidative damage specifically during/after recovery.
AtREM1, a Member of a New Family of B3 Domain-Containing Genes, Is Preferentially Expressed in Reproductive Meristems
Authors: Franco-Zorrilla José M. , Cubas Pilar , Jarillo José A. , Fernández-Calvı́n Begoña , Salinas Julio , Martı́nez-Zapater José M.
Published: November 2008

We have isolated and characterized AtREM1, the Arabidopsis ortholog of the cauliflower (Brassica oleracea) BoREM1. AtREM1 belongs to a large gene family of more than 20 members in Arabidopsis. The deduced AtREM1 protein contains several repeats of a B3-related domain, and it could represent a new class of regulatory proteins only found in plants. Expression of AtREM1 is developmentally regulated, being first localized in a few central cells of vegetative apical meristems, and later expanding to the whole inflorescence meristem, as well as primordia and organs of third and fourth floral whorls. This specific expression pattern suggests a role in the organization of reproductive meristems, as well as during flower organ development.
Insertional Mutants of Chlamydomonas reinhardtii That Require Elevated CO2 for Survival
Authors: Van Kyujung , Wang Yingjun , Nakamura Yoshiko , Spalding Martin H.
Published: November 2008

Aquatic photosynthetic organisms live in quite variable conditions of CO2 availability. To survive in limiting CO2conditions, Chlamydomonas reinhardtii and other microalgae show adaptive changes, such as induction of a CO2-concentrating mechanism, changes in cell organization, increased photorespiratory enzyme activity, induction of periplasmic carbonic anhydrase and specific polypeptides (mitochondrial carbonic anhydrases and putative chloroplast carrier proteins), and transient down-regulation in the synthesis of Rubisco. The signal for acclimation to limiting CO2 in C. reinhardtii is unidentified, and it is not known how they sense a change of CO2 level. The limiting CO2 signals must be transduced into the changes in gene expression observed during acclimation, so mutational analyses should be helpful for investigating the signal transduction pathway for low CO2 acclimation. Eight independently isolated mutants of C. reinhardtiithat require high CO2 for photoautotrophic growth were tested by complementation group analysis. These mutants are likely to be defective in some aspects of the acclimation to low CO2because they differ from wild type in their growth and in the expression patterns of five low CO2-inducible genes (Cah1, Mca1, Mca2,Ccp1, and Ccp2). Two of the new mutants formed a single complementation group along with the previously described mutant cia-5, which appears to be defective in the signal transduction pathway for low CO2 acclimation. The other mutations represent six additional, independent complementation groups.
Exceptional Sensitivity of Rubisco Activase to Thermal Denaturation in Vitro and in Vivo
Authors: Salvucci Michael E. , Osteryoung Katherine W. , Crafts-Brandner Steven J. , Vierling Elizabeth
Published: November 2008

Heat stress inhibits photosynthesis by reducing the activation of Rubisco by Rubisco activase. To determine if loss of activase function is caused by protein denaturation, the thermal stability of activase was examined in vitro and in vivo and compared with the stabilities of two other soluble chloroplast proteins. Isolated activase exhibited a temperature optimum for ATP hydrolysis of 44°C compared with ≥60°C for carboxylation by Rubisco. Light scattering showed that unfolding/aggregation occurred at 45°C and 37°C for activase in the presence and absence of ATPγS, respectively, and at 65°C for Rubisco. Addition of chemically denatured rhodanese to heat-treated activase trapped partially folded activase in an insoluble complex at treatment temperatures that were similar to those that caused increased light scattering and loss of activity. To examine thermal stability in vivo, heat-treated tobacco (Nicotiana rustica cv Pulmila) protoplasts and chloroplasts were lysed with detergent in the presence of rhodanese and the amount of target protein that aggregated was determined by immunoblotting. The results of these experiments showed that thermal denaturation of activase in vivo occurred at temperatures similar to those that denatured isolated activase and far below those required to denature Rubisco or phosphoribulokinase. Edman degradation analysis of aggregated proteins from tobacco and pea (Pisum sativum cv “Little Marvel”) chloroplasts showed that activase was the major protein that denatured in response to heat stress. Thus, loss of activase activity during heat stress is caused by an exceptional sensitivity of the protein to thermal denaturation and is responsible, in part, for deactivation of Rubisco.
Differential Regulation of mRNA Levels of Acyl Carrier Protein Isoforms in Arabidopsis
Authors: Bonaventure Gustavo , Ohlrogge John B.
Published: November 2008

All higher plants express several different acyl carrier protein (ACP) isoforms in a tissue-specific manner. We provide evidence that expression of mRNA for the most abundant ACP isoform in Arabidopsis leaves (ACP4) is increased severalfold by light, whereas mRNA levels for ACP isoforms 2 and 3 are independent of light. The presence of GATA-like motifs in the upstream region of theAcl1.4 gene (encoding for ACP4) and the similarity in light-mediated induction to ferredoxin-A mRNA suggests a direct role of light in Acl1.4 gene activation. Polyribosomal analysis indicated that light also affects the association of ACP transcripts with polysomes, similarly to mRNAs encoding ferredoxin-A. ACP2, ACP3, and ACP4 mRNA levels were also examined in Arabidopsis cell suspension culture and were found to be differentially controlled by metabolic and/or growth derived signals. Comparison of 5′-untranslated regions (UTRs) of ACP mRNAs of diverse plant species revealed two motifs that have been conserved during evolution, a CTCCGCC box and C-T-rich sequences. Fusions of the 5′-UTR sequences of ACP1 and ACP2 to luciferase and expression in transgenic plants indicated that the ACP1 leader contributes to preferential expression in seeds, whereas the ACP2 5′-UTR favored expression in roots. The deletion of 58 bp containing the conserved motifs of the ACP1 5′-UTR resulted in 10- to 20-fold lower gene expression in leaf and seed tissues of transgenic Arabidopsis plants.
Unraveling the Effects of Plant Hydraulics on Stomatal Closure during Water Stress in Walnut
Authors: Cochard Hervé , Coll Lluis , Le Roux Xavier , Améglio Thierry
Published: November 2008

The objectives of the study were to identify the relevant hydraulic parameters associated with stomatal regulation during water stress and to test the hypothesis of a stomatal control of xylem embolism in walnut (Juglans regia× nigra) trees. The hydraulic characteristics of the sap pathway were experimentally altered with different methods to alter plant transpiration (E  plant) and stomatal conductance (g  s). Potted trees were exposed to a soil water depletion to alter soil water potential (Ψsoil), soil resistance (R  soil), and root hydraulic resistances (R  root). Soil temperature was changed to alter R  root alone. Embolism was created in the trunk to increase shoot resistance (R  shoot). Stomata closed in response to these stresses with the effect of maintaining the water pressure in the leaf rachis xylem (P  rachis) above −1.4 MPa and the leaf water potential (Ψleaf) above −1.6 MPa. The same dependence of E  plant andg  s on P  rachis or Ψleaf was always observed. This suggested that stomata were not responding to changes in Ψsoil,R  soil, R  root, orR  shoot per se but rather to their impact onP  rachis and/or Ψleaf. Leaf rachis was the most vulnerable organ, with a thresholdP  rachis for embolism induction of −1.4 MPa. The minimum Ψleaf values corresponded to leaf turgor loss point. This suggested that stomata are responding to leaf water status as determined by transpiration rate and plant hydraulics and thatP  rachis might be the physiological parameter regulated by stomatal closure during water stress, which would have the effect of preventing extensive developments of cavitation during water stress.
Environmental Regulation of Lateral Root Initiation in Arabidopsis
Authors: Malamy Jocelyn E. , Ryan Katherine S.
Published: November 2008

Plant morphology is dramatically influenced by environmental signals. The growth and development of the root system is an excellent example of this developmental plasticity. Both the number and placement of lateral roots are highly responsive to nutritional cues. This indicates that there must be a signal transduction pathway that interprets complex environmental conditions and makes the “decision” to form a lateral root at a particular time and place. Lateral roots originate from differentiated cells in adult tissues. These cells must reenter the cell cycle, proliferate, and redifferentiate to produce all of the cell types that make up a new organ. Almost nothing is known about how lateral root initiation is regulated or coordinated with growth conditions. Here, we report a novel growth assay that allows this regulatory mechanism to be dissected in Arabidopsis. When Arabidopsis seedlings are grown on nutrient media with a high sucrose to nitrogen ratio, lateral root initiation is dramatically repressed. Auxin localization appears to be a key factor in this nutrient-mediated repression of lateral root initiation. We have isolated a mutant, lateral root initiation 1 (lin1), that overcomes the repressive conditions. This mutant produces a highly branched root system on media with high sucrose to nitrogen ratios. The lin1 phenotype is specific to these growth conditions, suggesting that thelin1 gene is involved in coordinating lateral root initiation with nutritional cues. Therefore, these studies provide novel insights into the mechanisms that regulate the earliest steps in lateral root initiation and that coordinate plant development with the environment.
Aluminum Toxicity Is Associated with Mitochondrial Dysfunction and the Production of Reactive Oxygen Species in Plant Cells
Authors: Yamamoto Yoko , Kobayashi Yukiko , Devi S. Rama , Rikiishi Sanae , Matsumoto Hideaki
Published: November 2008

Potential mechanisms of Al toxicity measured as Al-induced inhibition of growth in cultured tobacco cells (Nicotiana tabacum, nonchlorophyllic cell line SL) and pea (Pisum sativum) roots were investigated. Compared with the control treatment without Al, the accumulation of Al in tobacco cells caused instantaneously the repression of mitochondrial activities [monitored by the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and the uptake of Rhodamine 123] and, after a lag of about 12 h, triggered reactive oxygen species (ROS) production, respiration inhibition, ATP depletion, and the loss of growth capability almost simultaneously. The presence of an antioxidant, butylated hydroxyanisol, during Al treatment of SL cells prevented not only ROS production but also ATP depletion and the loss of growth capability, suggesting that the Al-triggered ROS production seems to be a cause of ATP depletion and the loss of growth capability. Furthermore, these three late events were similarly repressed in an Al-tolerant cell line (ALT301) isolated from SL cells, suggesting that the acquisition of antioxidant functions mimicking butylated hydroxyanisol can be a mechanism of Al tolerance. In the pea root, Al also triggered ROS production, respiration inhibition, and ATP depletion, which were all correlated with inhibition of root elongation. Taken together, we conclude that Al affects mitochondrial functions, which leads to ROS production, probably the key critical event in Al inhibition of cell growth.
Isolation and Functional Analysis of Homogentisate Phytyltransferase from Synechocystis sp. PCC 6803 and Arabidopsis
Authors: Collakova Eva , DellaPenna Dean
Published: November 2008

Tocopherols, collectively known as vitamin E, are lipid-soluble antioxidants synthesized exclusively by photosynthetic organisms and are required components of mammalian diets. The committed step in tocopherol biosynthesis involves condensation of homogentisic acid and phytyl diphosphate (PDP) catalyzed by a membrane-bound homogentisate phytyltransferase (HPT). HPTs were identified fromSynechocystis sp. PCC 6803 and Arabidopsis based on their sequence similarity to chlorophyll synthases, which utilize PDP in a similar prenylation reaction. HPTs from both organisms used homogentisic acid and PDP as their preferred substrates in vitro but only Synechocystis sp. PCC 6803 HPT was active with geranylgeranyl diphosphate as a substrate. Neither enzyme could utilize solanesyl diphosphate, the prenyl substrate for plastoquinone-9 synthesis. In addition, disruption of Synechocystis sp. PCC 6803 HPT function causes an absence of tocopherols without affecting plastoquinone-9 levels, indicating that separate polyprenyltransferases exist for tocopherol and plastoquinone synthesis in Synechocystis sp. PCC 6803. It is surprising that the absence of tocopherols in this mutant had no discernible effect on cell growth and photosynthesis.
Arabidopsis Seedling Growth, Storage Lipid Mobilization, and Photosynthetic Gene Expression Are Regulated by Carbon:Nitrogen Availability
Authors: Martin Thomas , Oswald Oliver , Graham Ian A.
Published: November 2008

The objective of the current work was to establish the degree to which the effects of carbon and nitrogen availability on Arabidopsis seedling growth and development are due to these nutrients acting independently or together. Growth of seedlings on low (0.1 mm) nitrogen results in a significant reduction of seedling and cotyledon size, fresh weight, chlorophyll, and anthocyanin content but a slight increase in endogenous sugars. The addition of 100 mm sucrose (Suc) to the nitrogen-depleted growth media results in a further reduction in cotyledon size and chlorophyll content and an overall increase in anthocyanins and endogenous sugars. Storage lipid breakdown is almost completely blocked in seedlings grown on low nitrogen and 100 mm Suc and is significantly inhibited when seedlings are grown on either low nitrogen or high Suc. Carbohydrate repression of photosynthetic gene expression can only be observed under low nitrogen conditions. Low (0.1 mm) nitrogen in the absence of exogenous carbohydrate results in a significant decrease in chlorophyll a/b-binding proteinand ribulose bisphosphate carboxylase small subunit gene transcript levels. Thus, carbon to nitrogen ratio rather than carbohydrate status alone appears to play the predominant role in regulating various aspects of seedling growth including storage reserve mobilization and photosynthetic gene expression.
A Slow Maturation of a Cysteine Protease with a Granulin Domain in the Vacuoles of Senescing Arabidopsis Leaves
Authors: Yamada Kenji , Matsushima Ryo , Nishimura Mikio , Hara-Nishimura Ikuko
Published: November 2008

Arabidopsis RD21 is a cysteine protease of the papain family. Unlike other members of the papain family, RD21 has a C-terminal extension sequence composed of two domains, a 2-kD proline-rich domain and a 10-kD domain homologous to animal epithelin/granulin family proteins. The RD21 protein was accumulated as 38- and 33-kD proteins in Arabidopsis leaves. An immunoblot showed that the 38-kD protein had the granulin domain, whereas the 33-kD protein did not. A pulse-chase experiment with Bright-Yellow 2 transformant cells expressing RD21 showed that RD21 was synthesized as a 57-kD precursor and was then slowly processed to make the 33-kD mature protein via the 38-kD intermediate. After a 12-h chase, the 38-kD intermediate was still detected in the cells. These results indicate that the N-terminal propeptide was first removed from the 57-kD precursor, and the C-terminal granulin domain was then slowly removed to yield the 33-kD mature protein. Subcellular fractionation of the Bright-Yellow 2 transformant showed that the intermediate and mature forms of RD21 were localized in the vacuoles. Under the acidic conditions of the vacuolar interior, the intermediate was found to be easily aggregated. The intermediate and the mature protein were accumulated in association with leaf senescence. Taken together, these results indicate that the intermediate of RD21 was accumulated in the vacuoles as an aggregate, and then slowly matured to make a soluble protease by removing the granulin domain during leaf senescence.
Cellulose in Cyanobacteria. Origin of Vascular Plant Cellulose Synthase?
Authors: Nobles David R. , Romanovicz Dwight K. , Brown R. Malcolm
Published: November 2008

Although cellulose biosynthesis among the cyanobacteria has been suggested previously, we present the first conclusive evidence, to our knowledge, of the presence of cellulose in these organisms. Based on the results of x-ray diffraction, electron microscopy of microfibrils, and cellobiohydrolase I-gold labeling, we report the occurrence of cellulose biosynthesis in nine species representing three of the five sections of cyanobacteria. Sequence analysis of the genomes of four cyanobacteria revealed the presence of multiple amino acid sequences bearing the DDD35QXXRW motif conserved in all cellulose synthases. Pairwise alignments demonstrated that CesAs from plants were more similar to putative cellulose synthases from Anabaena sp. Pasteur Culture Collection 7120 and Nostoc punctiforme American Type Culture Collection 29133 than any other cellulose synthases in the database. Multiple alignments of putative cellulose synthases from Anabaena sp. Pasteur Culture Collection 7120 and N. punctiforme American Type Culture Collection 29133 with the cellulose synthases of other prokaryotes, Arabidopsis, Gossypium hirsutum, Populus alba × Populus tremula, corn (Zea mays), and Dictyostelium discoideumshowed that cyanobacteria share an insertion between conserved regions U1 and U2 found previously only in eukaryotic sequences. Furthermore, phylogenetic analysis indicates that the cyanobacterial cellulose synthases share a common branch with CesAs of vascular plants in a manner similar to the relationship observed with cyanobacterial and chloroplast 16s rRNAs, implying endosymbiotic transfer of CesA from cyanobacteria to plants and an ancient origin for cellulose synthase in eukaryotes.
Isolation and Characterization of a New Peroxiredoxin from Poplar Sieve Tubes That Uses Either Glutaredoxin or Thioredoxin as a Proton Donor
Authors: Rouhier Nicolas , Gelhaye Eric , Sautiere Pierre-Eric , Brun Annick , Laurent Pascal , Tagu Denis , Gerard Joelle , de Faÿ Elisabeth , Meyer Yves , Jacquot Jean-Pierre
Published: November 2008

A sequence coding for a peroxiredoxin (Prx) was isolated from a xylem/phloem cDNA library from Populus trichocarpaand subsequently inserted into an expression plasmid yielding the construction pET-Prx. The recombinant protein was produced inEscherichia coli cells and purified to homogeneity with a high yield. The poplar Prx is composed of 162 residues, a property that makes it the shortest plant Prx sequence isolated so far. It was shown that the protein is monomeric and possesses two conserved cysteines (Cys). The Prx degrades hydrogen peroxide and alkyl hydroperoxides in the presence of an exogenous proton donor that can be either thioredoxin or glutaredoxin (Grx). Based on this finding, we propose that the poplar protein represents a new type of Prx that differs from the so-called 2-Cys and 1-Cys Prx, a suggestion supported by the existence of natural fusion sequences constituted of a Prx motif coupled to a Grx motif. The protein was shown to be highly expressed in sieve tubes where thioredoxin h and Grx are also major proteins.
Chlorophyll Biosynthesis. Expression of a SecondChl IGene of Magnesium Chelatase in Arabidopsis Supports Only Limited Chlorophyll Synthesis
Authors: Rissler Heather M. , Collakova Eva , DellaPenna Dean , Whelan James , Pogson Barry J.
Published: November 2008

Magnesium (Mg) chelatase is a heterotrimeric enzyme complex that catalyzes a key regulatory and enzymatic reaction in chlorophyll biosynthesis, the insertion of Mg2+ into protoporphyrin IX. Studies of the enzyme complex reconstituted in vitro have shown that all three of its subunits, CHL I, CHL D, and CHL H, are required for enzymatic activity. However, a new T-DNA knockout mutant of the chlorina locus, ch42-3 (Chl I), in Arabidopsis is still able to accumulate some chlorophyll despite the absence of Chl I mRNA and protein. In barley (Hordeum vulgare), CHL I is encoded by a single gene. We have identified an open reading frame that apparently encodes a second Chl Igene, Chl I2. Chl I1 and Chl I2 mRNA accumulate to similar levels in wild type, yet CHL I2 protein is not detectable in wild type or ch42-3, although the protein is translated and stromally processed as shown by in vivo pulse labeling and in vitro chloroplast imports. It is surprising that CHL D accumulates to wild-type levels in ch42-3, which is in contrast to reports that CHL D is unstable in CHL I-deficient backgrounds of barley. Our results show that limited Mg chelatase activity and CHL D accumulation can occur without detectable CHL I, despite its obligate requirement in vitro and its proposed chaperone-like stabilization and activation of CHL D. Thus, the unusual post-translational regulation of the CHL I2 protein provides an opportunity to study the different steps involved in stabilization and activation of the heterotrimeric Mg chelatase in vivo.
The ram1 Mutant of Arabidopsis Exhibits Severely Decreased β-Amylase Activity
Authors: Laby Ron J. , Kim Donggiun , Gibson Susan I.
Published: November 2008

Despite extensive biochemical analyses, the biological function(s) of plant β-amylases remains unclear. The fact that β-amylases degrade starch in vitro suggests that they may play a role in starch metabolism in vivo. β-Amylases have also been suggested to prevent the accumulation of highly polymerized polysaccharides that might otherwise impede flux through phloem sieve pores. The identification and characterization of a mutant of Arabidopsis var. Columbia with greatly reduced levels of β-amylase activity is reported here. The reduced β-amylase 1 (ram1) mutation lies in the gene encoding the major form of β-amylase in Arabidopsis. Although the Arabidopsis genome contains nine known or putative β-amylase genes, the fact that the ram1 mutation results in almost complete loss of β-amylase activity in rosette leaves and inflorescences (stems) indicates that the gene affected by theram1 mutation is responsible for most of the β-amylase activity present in these tissues. The leaves of ram1plants accumulate wild-type levels of starch, soluble sugars, anthocyanin, and chlorophyll. Plants carrying the ram1mutation also exhibit wild-type rates of phloem exudation and of overall growth. These results suggest that little to no β-amylase activity is required to maintain normal starch levels, rates of phloem exudation, and overall plant growth.
Mutations in Two Independent Genes Lead to Suppression of the Shoot Apical Meristem in Maize
Authors: Pilu Roberto , Consonni Gabriella , Busti Elena , MacCabe Andrew P. , Giulini Anna , Dolfini Silvana , Gavazzi Giuseppe
Published: November 2008

The shoot apical meristem (SAM), initially formed during embryogenesis, gives rise to the aboveground portion of the maize (Zea mays) plant. The shootless phenotype (sml) described here is caused by disruption of SAM formation due to the synergistic interaction of mutations at two genetic loci. Seedlings must be homozygous for both sml (shootmeristemless), and the unlinked dgr (distorted growth) loci for a SAM-less phenotype to occur. Seedlings mutant only for sml are impaired in their morphogenesis to different extents, whereas thedgr mutation alone does not have a recognisable phenotype. Thus, dgr can be envisaged as being a dominant modifier of sml and the 12 (normal):3 (distorted growth):1 (shoot meristemless) segregation observed in the F2 of the double heterozygote is the result of the interaction between the sml and dgrgenes. Other segregation patterns were also observed in the F2, suggesting instability of the dgr gene. Efforts to rescue mutant embryos by growth on media enriched with hormones have been unsuccessful so far. However, mutant roots grow normally on medium supplemented with kinetin at a concentration that suppresses wild-type root elongation, suggesting possible involvement of the mutant in the reception or transduction of the kinetin signal or transport of the hormone. The shootless mutant appears to be a valuable tool with which to investigate the organization of the shoot meristem in monocots as well as a means to assay the origins and relationships between organs such as the scutellum, the coleoptile, and leaves that are initiated during the embryogenic process.
An Aquaglyceroporin Is Abundantly Expressed Early in the Development of the Suspensor and the Embryo Proper of Loblolly Pine
Authors: Ciavatta Vincent T. , Morillon Raphael , Pullman Gerald S. , Chrispeels Maarten J. , Cairney John
Published: November 2008

In contrast to angiosperms, pines and other gymnosperms form well-developed suspensors in somatic embryogenic cultures. This creates a useful system to study suspensor biology. In a study of gene expression during the early stages of conifer embryogenesis, we identified a transcript, PtNIP1;1, that is abundant in immature loblolly pine (Pinus taeda) zygotic and somatic embryos, but is undetectable in later-stage embryos, megagametophytes, and roots, stems, and needles from 1 year-old seedlings. Analysis ofPtNIP1;1 transcript in embryo proper and suspensor tissues by reverse transcription-polymerase chain reaction suggests preferential expression in the suspensor. Based on comparisons of derived amino acid sequences, PtNIP1;1 belongs to the nodulin-like members of the major intrinsic protein superfamily branch of the aquaporin (major intrinsic protein) superfamily. Through heterologous expression in Xenopus laevis oocytes and the yeast (Saccharomyces cerevisiae)fps1  − mutant, PtNIP1;1 has been shown to be an active aquaglyceroporin.