bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress Responses in Alfalfa (XXI. Activation of Caffeic Acid 3-O-Methyltransferase and Caffeoyl Coenzyme A 3-O-Methyltransferase Genes Does Not Contribute to Changes in Metabolite Accumulation in Elicitor-Treated Cell-Suspension Cultures)
Authors: Ni W. , Sewalt VJH. , Korth K. L. , Blount J. W. , Ballance G. M. , Dixon R. A. 
Published: October 2016

Abstract
Transcription of genes encoding L-phenylalanine ammonia-lyase (PAL), the first enzyme of the phenylpropanoid pathway, and caffeic acid 3-O-methyltransferase (COMT) and caffeoyl CoA 3-O-methyltransferase (CCOMT), enzymes involved in the synthesis of lignin and wall-esterified phenolic compounds, was strongly activated in elicitor-treated cell-suspension cultures of alfalfa (Medicago sativa L.). However, consequent changes in the extractable activities of COMT and CCOMT were small to nonexistent compared with a 15- to 16-fold increase in PAL activity. Only low levels of COMT and CCOMT transcripts were reflected in the total and polysomal RNA fractions compared with PAL transcripts. Elicited cell cultures did not accumulate lignin or the products of COMT and CCOMT in the soluble and wall-esterified phenolic fractions. In one alfalfa cell line in which elicitation resulted in very high PAL activity and increased deposition of methoxyl groups in the insoluble wall fraction, there was still no change in COMT and CCOMT activities. Overall, these results indicate that the initial gene transcription events in elicited cells may be less selective than the subsequent metabolic changes, highlighting the importance of posttranscriptional events in the control of phenylpropanoid biosynthesis.
Interactions between Photosynthesis and Respiration in the Green Alga Chlamydomonas reinhardtii (Characterization of Light-Enhanced Dark Respiration)
Authors: Xue X. , Gauthier D. A. , Turpin D. H. , Weger H. G. 
Published: October 2016

Abstract
The rate of respiratory O2 consumption by Chlamydomonas reinhardtii cell suspensions was greater after a period of photosynthesis than in the preceding dark period. This “light-enhanced dark respiration” (LEDR) was a function of both the duration of illumination and the photon fluence rate. Mass spectrometric measurements of gas exchange indicated that the rate of gross respiratory O2 consumption increased during photosynthesis, whereas gross respiratory CO2 production decreased in a photon fluence rate-dependent manner. The rate of postillumination O2 consumption provided a good measure of the O2 consumption rate in the light. LEDR was substantially decreased by the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or glycolaldehyde, suggesting that LEDR was photosynthesis-dependent. The onset of photosynthesis resulted in an increase in the cellular levels of phosphoglycerate, malate, and phosphoenolpyruvate, and a decrease in whole-cell ATP and citrate levels; all of these changes were rapidly reversed upon darkening. These results are consistent with a decrease in the rate of respiratory carbon flow during photosynthesis, whereas the increase in respiratory O2 consumption during photosynthesis may be mediated by the export of photogenerated reductant from the chloroplast. We suggest that photosynthesis interacts with respiration at more than one level, simultaneously decreasing the rate of respiratory carbon flow while increasing the rate of respiratory O2 consumption.
Characterization of Hypoxically Inducible Lactate Dehydrogenase in Maize
Authors: Christopher M. E. , Good A. G. 
Published: October 2016

Abstract
Oxygen deprivation induces a wide variety of genes, but the most extensively studied are those encoding enzymes of the glycolytic pathway. Lactate dehydrogenase (LDH, EC 1.1.1.27) activity increases up to 3.5-fold in maize (Zea mays L.) roots during several days of hypoxic induction. This increase in activity is accompanied by a decrease in in vitro enzyme stability. LDH activity in aerobic root extracts has an in vitro half-life of 240 min, decreasing to 100 min in 72-h hypoxically induced plant root extracts. The increase in enzyme activity during hypoxic induction is the result of increased protein levels, which correlate with increased transcript levels. Two ldh transcripts of 1.3 and 1.7 kb are induced, with maximum levels reached by 8 and 24 h, respectively. This suggests that the two ldh genes are differentially regulated. Treatment with the protein synthesis inhibitor cycloheximide does not preclude ldh induction during the first few hours of hypoxic stress, suggesting that new protein synthesis may not be essential for elevation of ldh transcript levels under hypoxic conditions. The rapid and substantial increase in ldh mRNA levels under hypoxic conditions and in the presence of cycloheximide suggests that the ldh gene may be valuable in analyzing the hypoxic signal transduction pathway.
Role of Apoplastic and Cell-Wall Peroxidases on the Stimulation of Root Elongation by Ascorbate
Authors: Cordoba-Pedregosa MdC. , Gonzalez-Reyes J. A. , Canadillas MdS. , Navas P. , Cordoba F. 
Published: October 2016

Abstract
Elongation of onion (Allium cepa L.) roots was highly stimulated by ascorbate (ASC) and its natural precursor I-galactone-[gamma]-lactone (GL). When incubation media were supplemented with lycorine (Lyc), an inhibitor of the ASC biosynthesis, root growth was negligible even in the presence of ASC or GL. ASC completely inhibited in vitro guaiacol peroxidase activities that were isolated from both the apoplast and the cell wall. However, ferulic-acid-dependent peroxidase from the cell wall was partially inhibited by ASC, whereas ferulic acid peroxidase activity from the apoplastic fluid was completely inhibited by ASC as long as ASC was present in the assay medium. ASC content in cells was increased by preincubations with ASC or GL, whereas Lyc reduced it. On the other hand, ASC or GL treatments decreased both apoplast and cell-wall-bound peroxidase activities, whereas Lyc had a slight stimulating effect. These results are discussed on the basis of a possible control of root elongation by ASC via its action on peroxidases that are involved in the regulation of cell-wall extensibility.
Evidence for Substrate Induction of a Nitrate Efflux System in Barley Roots
Authors: Aslam M. , Travis R. L. , Rains D. W. 
Published: October 2016

Abstract
Induction of an NO3- efflux system in intact barley (Hordeum vulgare L.) roots was demonstrated. Since the measurement of NO3- efflux is dependent on its accumulation, experiments were devised to facilitate accumulation under noninducing conditions. This was accomplished by incubating seedlings in 10 mM NO3- in the presence of RNA and protein synthesis inhibitors. Under these conditions NO3- uptake is mediated by constitutive high- and low-affinity transport systems. Control roots were incubated with 1.0 mM NO3-. This resulted in the accumulation of similar levels of NO3- in both treated and control roots; however, cytoplasmic NO3- efflux from inhibitor-treated roots was much lower than from control roots. Following a brief lag period, efflux rates increased rapidly in the presence of NO3- for 8 to 12 h. The NO3- efflux system was also induced by ambient NO2-. After induction the efflux system was relatively stable in the presence of RNA and protein synthesis inhibitors as long as NO3- or NO2- was present. These results suggest that NO3- efflux may be an inducible system requiring both RNA and protein synthesis, as does induction of the uptake system. The efflux system, however, has a much slower turnover rate than the uptake system.
Characterization of the Endoproteases Appearing during Wheat Grain Development
Authors: Dominguez F. , Cejudo F. J. 
Published: October 2016

Abstract
The pattern of endoproteolytic activities occurring during wheat (Triticum aestivum, cultivar Chinese Spring) grain development was investigated. Total endoprotease activity, assayed in solution with azocasein as a substrate, increased during the early stages of grain development to reach a maximum at 15 d postanthesis that was maintained until the grain was mature. Endoprotease activity was also assayed in gradient polyacrylamide gels co-polymerized with gelatin. The increase in endoproteolytic activity was due to the appearance of up to 18 endoproteolytic bands that were arbitrarily classified into five groups (A, B, C, D, and E). The presence of serine, aspartic, metallo, and, to a lesser extent, thiol proteases in developing wheat grains was demonstrated by the use of class-specific protease inhibitors. The appearance of the different classes of endoproteases during seed development was subject to temporal control; serine proteases were more abundant at early stages and aspartic and metallo proteases were more abundant at later stages. At intermediate stages of development (15–20 d postanthesis), most of the endoproteases were localized in the aleurone, testa, and embryo. The content of acidic thiol proteases was low in the developing starchy endosperm.
Nitrite Transport in Chloroplast Inner Envelope Vesicles (I. Direct Measurement of Proton-Linked Transport)
Authors: Shingles R. , Roh M. H. , McCarty R. E. 
Published: October 2016

Abstract
Chloroplast inner envelope membrane vesicles that are loaded with the pH-sensitive fluorophore, pyranine, show rapid internal acidification when nitrite is added. Acidification is dependent upon [delta]pH, with the inside of vesicles being alkaline with respect to the outside. The rate of vesicle acidification was directly proportional to the concentration of nitrite that was added and the imposed pH difference across the membrane. In contrast, added nitrate had no effect on vesicle acidification. Nitrite also caused acidification of asolectin vesicles. The extent of vesicle acidification is dependent on the internal volume of vesicles. Inner envelope and asolectin vesicles that were prepared by extrusion were approximately the same size, allowing them to be compared when the final extent of acidification, measured after the pH gradient had collapsed, was similar. The rate of nitrite-dependent acidification was similar in these two preparations at any single nitrite concentration. These results indicate that nitrite movement occurs by rapid diffusion across membranes as nitrous acid, and this movement is dependent on a proton gradient across the lipid bilayer. Under conditions approximating those in vivo, the rate of diffusion of nitrous acid far exceeds that of nitrite reduction within chloroplasts.
Effects of Epidermal Cell Shape and Pigmentation on Optical Properties of Antirrhinum Petals at Visible and Ultraviolet Wavelengths
Authors: Gorton H. L. , Vogelmann T. C. 
Published: October 2016

Abstract
We used the Mixta+ and mixta- lines of Antirrhinum majus as a model system to investigate the effects of epidermal cell shape and pigmentation on tissue optical properties in the visible and ultraviolet (UV) spectral regions. Adaxial epidermal cells of Mixta+ flowers have a conical-papillate shape; in the mixta- line the cells are slightly domed. Mixta+ cells contained significantly more anthocyanin and other flavonoids than mixta- cells when plants were grown under either high- or low-UV conditions. Mixta+ cells focused light (3.5–4.7 times incident) within their pigmented interiors, whereas mixta- cells focused light (2.1–2.7 times incident) in the unpigmented mesophyll. UV light penetrated the epidermis (commonly 20–50% transmittance at 312 nm) mainly through the unpigmented peripheral regions of the cells that were similar for the two lines, so that overall penetration through Mixta+ and mixta- epidermises was equal. However, maximum UV absorption in the central region of epidermal cells was slightly greater in Mixta+ than mixta-, and intact Mixta+ flowers reflected less light in the spectral regions with intermediate flavonoid absorbance. In both cases, about 50 to 75% of the difference could be attributed to cell shape and resulting changes in the optical pathlength or focusing.
Lhcb Transcription Is Coordinated with Cell Size and Chlorophyll Accumulation (Studies on Fluorescence-Activated, Cell-Sorter-Purified Single Cells from Wild-Type and immutans Arabidopsis thaliana)
Authors: Meehan L. , Harkins K. , Chory J. , Rodermel S. 
Published: October 2016

Abstract
To study the mechanisms that integrate pigment and chlorophyll a/b-binding apoprotein biosynthesis during light-harvesting complex II assembly, we have examined β-glucuronidase (GUS) enzyme activities, chlorophyll contents, and cell sizes in fluorescence-activated, cell-sorting-separated single cells from transgenic Arabidopsis thaliana wild-type and immutans variegation mutant plants that express an Lhcb (photosystem II chlorophyll a/b-binding polypeptide gene)/GUS promoter fusion. We found that GUS activities are positively correlated with chlorophyll content and cell size in green cells from the control and immutans plants, indicating that Lhcb gene transcription is coordinated with cell size in this species. Compared with the control plants, however, chlorophyll production is enhanced in the green cells of immutans; this may represent part of a strategy to maximize photosynthesis in the green sectors to compensate for a lack of photosynthesis in the white sectors of the mutant. Lhcb transcription is significantly higher in pure-white cells of the transgenic immutans plants than in pure-white cells from norflurazon-treated, photooxidized A. thaliana leaves. This suggests that immutans partially uncouples Lhcb transcription from its normal dependence on chlorophyll accumulation and chloroplast development. We conclude that immutans may play a role in regulating Lhcb transcription, and may be a key component in the signal transduction pathways that control chloroplast biogenesis.
Stimulation of Photophosphorylation by Ascorbate as a Function of Light Intensity
Authors: Forti G. , Elli G. 
Published: October 2016

Abstract
When isolated, stroma-free thylakoids are illuminated in the presence of ADP and orthophosphate in the absence of any electron acceptor except O2, the addition of ascorbate stimulates electron transport through the formation of the radical monodehydroascorbate and the coupled synthesis of ATP (G. Forti and G. Elli [1995] Plant Physiol 109: 1207–1211). The stimulation is shown here to be higher at low light intensity. These observations are explained in terms of the increase of the electron transport rate by ascorbate, which established a higher value of the steady-state pH gradient, causing activation of ATP synthase, which is known to be dependent on the level of the H+-electrochemical potential difference, and a higher rate of proton flux across the membranes available for utilization by ATP synthesis.
Overexpression of L-Phenylalanine Ammonia-Lyase in Transgenic Tobacco Plants Reveals Control Points for Flux into Phenylpropanoid Biosynthesis
Authors: Howles P. A. , Sewalt VJH. , Paiva N. L. , Elkind Y. , Bate N. J. , Lamb C. , Dixon R. A. 
Published: October 2016

Abstract
Transgenic tobacco (Nicotiana tabacum L.) plants overexpressing the enzyme L-phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) were grown from seeds of a primary transformant containing the bean PAL2 gene, which had shown homology-dependent silencing of the endogenous tobacco PAL genes. Analysis of endogenous and transgene-encoded PAL transcripts and protein in the primary transformant (T0) and first-generation (T1) overexpressor plants indicated that the transgene-encoded PAL is the cause of the greater than wild-type levels of PAL activity (up to 5- and 2-fold greater in leaf and stem tissue, respectively) in the T1 plants. Leaves of PAL-overexpressing plants contained increased levels of the hydroxycinnamic acid ester chlorogenic acid but not of the flavonoid rutin, indicating that PAL is the key control point for flux into chlorogenic acid. In addition, levels of the glucoside of 4-coumaric acid increased in the overexpressing plants, suggesting that the 4-coumarate:coenzyme A ligase or coumarate hydroxylase reactions might have become limiting. These results help to define the regulatory architecture of the phenylpropanoid pathway and indicate the possibility of engineering-selective changes in this complex metabolic pathway by overexpression of a single early pathway gene.
Reexamination of the Intracellular Localization of de Novo Purine Synthesis in Cowpea Nodules
Authors: Atkins C. A. , Smith PMC. , Storer P. J. 
Published: October 2016

Abstract
Sucrose and Percoll density gradient centrifugation were used to separate organelles from the central zone tissue of cowpea (Vigna unguiculata L. Walp. cv Vita 3: Bradyrhizobium strain CB 756) nodules. Enzyme activity analysis has shown that both plastids and mitochondria have a full complement of enzymes for de novo purine synthesis. In vitro activities of individual component enzymes (glycinamide ribonucleotide synthetase, EC 6.3.4.13; glycinamide ribonucleotide transformylase, EC 2.1.2.2; aminoimidazole ribonucleotide synthetase, EC 6.3.3.1; aminoimidazole carboxamide ribonucleotide transformylase, EC 6.3.2.6; and adenylosuccinate-AMP lyase, EC 4.3.2.2) as well as of the whole purine pathway (from ribose-5-phosphate to inosine monophosphate) were similar in the two organelles. No significant cytosolic or bacteroidal activity of any of the purine pathway enzymes was detected on assay. These findings are contrary to earlier studies (M.J. Boland, K.R. Schubert [1983] Arch Biochem Biophys 220: 179–187; B.J. Shelp C.A. Atkins, P.J. Storer, D.T. Canvin [1983] Arch Biochem Biophys 224: 429–441) that concluded that enhanced expression of purine synthesis in nodules of ureide-forming species is localized to plastids. Significantly increased recovery of activity of key pathway enzymes (particularly of labile aminoimidazole ribonucleotide synthetase) coupled with improved assay methods and the use of Percoll in addition to sucrose for gradient centrifugation have together contributed to much higher reaction rates and more definitive analyses of particulate fractions.
Conversion of Chlorophyll b to Chlorophyll a and the Assembly of Chlorophyll with Apoproteins by Isolated Chloroplasts
Authors: Ohtsuka T. , Ito H. , Tanaka A. 
Published: October 2016

Abstract
The photosynthetic apparatus is reorganized during acclimation to various light environments. During adaptation of plants grown under a low-light to high-light environment, the light-harvesting chlorophyll a/b-protein complexes decompose concomitantly with an increase in the core complex of photosystem II. To study the mechanisms for reorganization of photosystems, the assembly of chlorophyll with apoproteins was investigated using isolated chloroplasts. When [14C]chlorophyllide b was incubated with chloroplasts in the presence of phytyl pyrophosphate, it was esterified and some of the [14C]chlorophyll b was converted to [14C]chlorophyll a via 7-hydroxymethyl chlorophyll. [14C]Chlorophyll a and b were incorporated into chlorophyll-protein complexes. Light-harvesting chlorophyll a/b-protein complexes of PSII had a lower [14C]chlorophyll a to [14C]chlorophyll b ratio than P700-chlorophyll a-protein complexes, indicating the specific binding of chlorophyll to apoproteins in our systems. 7-Hydroxymethyl chlorophyll, an intermediate molecule from chlorophyll b to chlorophyll a, did not become assembled with any apoproteins. These results indicate that chlorophyll b is released from light-harvesting chlorophyll a/b-protein complexes of photosystem II and converted to chlorophyll a via 7-hydroxymethyl chlorophyll in the lipid bilayer and is then used for the formation of core complexes of photosystems. These mechanisms provide the fast, fine regulation of the photosynthetic apparatus during construction of photosystems.
Hormonal Regulation of Dormancy in Developing Sorghum Seeds
Authors: Steinbach H. S. , Benech-Arnold R. L. , Sanchez R. A. 
Published: October 2016

Abstract
The role of abscisic acid (ABA) and gibberellic acid (GA) in determining the dormancy level of developing sorghum (Sorghum bicolor [L.] Moench.) seeds from varieties presenting contrasting preharvest sprouting behavior (Redland B2, susceptible; IS 9530, resistant) was investigated. Panicles from both varieties were sprayed soon after pollination with fluridone or paclobutrazol to inhibit ABA and GA synthesis, respectively. Fluridone application to the panicles increased germinability of Redland B2 immature caryopses, whereas early treatment with paclobutrazol completely inhibited germination of this variety during most of the developmental period. Incubating caryopses in the presence of 100 [mu]M GA4+7 overcame the inhibitory effect of paclobutrazol, but also stimulated germination of seeds from other treatments. IS 9530 caryopses presented germination indices close to zero until physiological maturity (44 d after pollination) in control and paclobutrazol-treated particles. However, fluridone-treated caryopses were released from dormancy earlier than control and paclobutrazol-treated caryopses. Incubation in the presence of GA4+7 stimulated germination of caryopses from all treatments. Our results support the proposition that a low dormancy level (which is related to a high preharvest sprouting susceptibility) is determined not only by a low embryonic sensitivity to ABA, but also by a high GA content or sensitivity.
Activation of Plant Plasma Membrane Ca2+-Permeable Channels by Race-Specific Fungal Elicitors
Authors: Gelli A. , Higgins V. J. , Blumwald E. 
Published: October 2016

Abstract
The response of plant cells to invading pathogens is regulated by fluctuations in cytosolic Ca2+ levels that are mediated by Ca2+-permeable channels located at the plasma membrane of the host cell. The mechanisms by which fungal elicitors can induce Ca2+ uptake by the host cell were examined by the application of conventional patch-clamp techniques. Whole-cell and single-channel experiments on tomato (Lycopersicon esculentum L.) protoplasts revealed a race-specific fungal elicitor-induced activation of a plasma membrane Ca2+-permeable channel. The presence of the fungal elicitor resulted in a greater probability of channel opening. Guanosine 5[prime]-[β-thio]diphosphate, a GDP analog that locks heterotrimeric G-proteins into their inactivated state, abolished the channel activation induced by the fungal elicitor, whereas guanosine 5[prime][[gamma]-thio]triphosphate, a nonhydrolyzable GTP analog that locks heterotrimeric G-proteins into their activated state, produced an effect similar to that observed with the fungal elicitor. Mastoparan, which stimulates GTPase activity, mimicked the effect of GTP[[gamma]]S. The addition of HA1004 (a protein kinase inhibitor) in the presence of the elicitor totally abolished channel activity, whereas okadaic acid (a protein phosphatase inhibitor) moderately enhanced channel activity, suggesting that the activation of the channel by fungal elicitors is modulated by a heterotrimeric G-protein-dependent phosphorylation of the channel protein.