Plant Physiology

Streeter, John G.

doi: 10.1104/pp.90.3.779pmid: 16666876

Abstract Analysis of ammonium concentration in the cytosol of soybean (Glycine max [L.] Merr.) root nodules gave high levels of error variation. When the separation of cytosol and bacteroids was deliberately delayed following nodule maceration, a large increase in ammonium concentration was found in the cytosol. When a series of samples was subjected to delay intervals of 0 to 60 minutes, extrapolation of the regression line to time zero indicated that the ammonium concentration in cytosol at the time of nodule maceration was essentially nil. The source of ammonium buildup following maceration was not found, but hydrolysis of free amino acids or ureides was ruled out. An extremely low concentration of ammonium in the cytosol is consistent with a model for movement of ammonia (or ammonium) from bacteroids to host cytoplasm by diffusion. 1 Supported in part by the U.S. Department of Agriculture under agreement No. 84-CRCR-1-1426. Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center. Journal article 324-88. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Garbow, Joel R.; Ferrantello, Lisa M.; Stark, Ruth E.

doi: 10.1104/pp.90.3.783pmid: 16666877

Abstract High-resolution, solid-state 13C nuclear magnetic resonance (NMR) spectra are reported for suberized cell wall from potatoes (Solanum tuberosum L.). Through experiments combining the techniques of cross polarization and magic-angle spinning, we verified that suberin, like cutin, is a polyester and demonstrated that it also has phenylpropanoid groups characteristic of lignin. Roughly 50% of the suberized material consists of cell-wall polymers; aromatics and other unsaturated linkages outnumber methylene groups 2:1. In conjunction with traditional direct-polarization NMR results, these experiments provide support for prior suggestions that suberin and cell-wall components are chemically bonded via aromatic groups. 1 Supported, in part, by grant DMR-8617595 from the National Science Foundation and grant 667147 from The City University of New York PSC-CUNY Research Award Program. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Willeford, Kenneth O.; Gibbs, Martin

doi: 10.1104/pp.90.3.788pmid: 16666878

Abstract The localization of a series of enzymes involved in the anaerobic photodissimilation of acetate in Chlamydomonas reinhardtii F-60 adapted to a hydrogen metabolism was determined through the enzymic analyses of the chloroplastic, cytoplasmic, and mitochondrial fractions obtained with a cellular fractionation procedure that incorporated cell wall removal by treatment with autolysine, digestion of the plasmalemma with the detergent digitonin, and fractionation by differential centrifugation on a Percoll step gradient. The sequence of events leading to the photoevolution of H2 from acetate includes the conversion of acetate into succinate via the extraplastidic glyoxylate cycle, the oxidation of succinate to fumarate by chloroplastic succinate dehydrogenase, and the oxidation of malate to oxaloacetate in the chloroplast by NAD dependent malate dehydrogenase. The level of potential activity for the enzymes assayed were sufficient to accommodate the observed rate of the photoanaerobic dissimilation of acetate and the photoevolution of H2. 1 Supported by the U.S. Department of Energy DE-ACO2-76-ERO 3231. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Gowri, G.; Campbell, Wilbur H.

doi: 10.1104/pp.90.3.792pmid: 16666879

Abstract cDNA clones were selected from a corn (Zea mays L.) leaf lambda gt11 expression library using polyclonal antibodies for corn leaf NADH:nitrate reductase. One clone, Zmnrl, had a 2.1 kilobase insert, which hybridized to a 3.2 kilobase mRNA. The deduced amino acid sequence of Zmnrl was nearly identical to peptide sequences of corn leaf NADH:nitrate reductase. Another clone, Zm6, had an insert of 1.4 kilobase, which hybridized to a 1.4 kilobase mRNA, and its sequence coded for chloroplastic NAD(P)+:glyceraldehyde-3-phosphate dehydrogenase based on comparisons to sequences of this enzyme from tobacco and corn. When nitrate was supplied to N-starved, etiolated corn plants, nitrate reductase, and glyceraldehyde-3-phosphate dehydrogenase mRNA levels in leaves increased in parallel. When green leaves were treated with nitrate, only nitrate reductase mRNA levels were increased. Nitrate is a specific inducer of nitrate reductase in green leaves, but appears to have a more general effect in etiolated leaves. In the dark, nitrate induced nitrate reductase expression in both etiolated and green leaves, indicating light and functional chloroplast were not required for enzyme expression. 1 Supported by grants 86-CRCR-11289 and 88-37262-3896 from the Competitive Research Grants Office of the U.S. Department of Agriculture and grants DMB 85-02672 and 88-03998 from the National Science Foundation. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Gross, Wolfgang; Beevers, Harry

doi: 10.1104/pp.90.3.799pmid: 16666880

Abstract The intracellular distribution of enzymes capable of catalyzing the reactions from phosphoglycolate to glycerate in the bluegreen colored eucaryotic alga Cyanidium caldarium has been studied. After separating the organelles from a crude homogenate on a linear flotation gradient, the enzymes glycolate oxidase and glutamate-glyoxylate aminotransferase along with catalase were present in the peroxisomal fraction (density: 1.23 grams per cubic centimeter). Serine hydroxymethyltransferase was found in the mitochondrial fraction (density: 1.18 grams per cubic centimeter). In contrast to the observations in green leaves of higher plants, the enzymes for the conversion of serine to glycerate (serine-glyoxylate aminotransferase and hydroxypyruvate reductase) were found only in the soluble fraction of the gradient. The partial characterization of enzymes from Cyanidium participating in glycolate metabolism revealed only slight differences from the corresponding enzymes from higher plants. The phylogenetic implications of the observed similarities between the enigmatic alga Cyanidium and higher plants are discussed. 2 Present address: Department of Botany, North Carolina State University, Raleigh, NC 27695. 1 This work was supported by National Science Foundation (grant PCM 84-03542) and a postdoctoral fellowship (Feodor-Lynen-Program) from the Alexander-von-Humboldt foundation (Federal Republic of Germany) to W. G. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Siddiqi, M. Yaeesh; Glass, Anthony D. M.; Ruth, Thomas J.; Fernando, Mala

doi: 10.1104/pp.90.3.806pmid: 16666881

Abstract Using 13NO3−, effects of various NO3− pretreatments upon NO3− influx were studied in intact roots of barley (Hordeum vulgare L. cv Klondike). Prior exposure of roots to NO3− increased NO3− influx and net NO3− uptake. This `induction' of NO3− uptake was dependent both on time and external NO3− concentration ([NO3−]). During induction influx was positively correlated with root [NO3−]. In the postinduction period, however, NO3− influx declined as root [NO3−] increased. It is suggested that induction and negative feedback regulation are independent processes: Induction appears to depend upon some critical cytoplasmic [NO3−]; removal of external NO3− caused a reduction of 13NO3− influx even though mean root [NO3−] remained high. It is proposed that cytoplasmic [NO3−] is depleted rapidly under these conditions resulting in `deinduction' of the NO3− transport system. Beyond 50 micromoles per gram [NO3−], 13NO3− influx was negatively correlated with root [NO3−]. However, it is unclear whether root [NO3−] per se or some product(s) of NO3− assimilation are responsible for the negative feedback effects. 1 Supported by the Natural Sciences and Engineering Research Council of Canada. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Rao, I. Madhusudana; Terry, Norman

doi: 10.1104/pp.90.3.814pmid: 16666882

Abstract Sugar beets (Beta vulgaris L. cv F58-554H1) were cultured hydroponically for 2 weeks in growth chambers with two levels of orthophosphate (Pi) supplied in half strength Hoagland solution. Low-P plants were supplied with 1/20th of the Pi supplied to control plants. With low-P treatment, the acid soluble leaf phosphate and total leaf P decreased by about 88%. Low-P treatment had a much greater effect on leaf area than on photosynthesis. Low-P decreased total leaf area by 76%, dry weight per plant by 60%, and the rate of photosynthesis per area at light saturation by 35%. Low-P treatment significantly decreased the total extractable activity of phosphoglycerate kinase (by 18%) and NADP-glyceraldehyde-3-phosphate dehydrogenase (by 16%), but did not decrease the total activities of ribulose-1,5-bisphosphate (RuBP) carboxylase (RuBPCase) and ribulose-5-phosphate kinase. Low-P treatment decreased the initial activities of three rate-limiting Calvin cycle enzymes, but had no effect on the initial activity of RuBPCase. Furthermore, low-P treatment significantly increased the total extractable activities of fructose-1,6-bisphosphatase (by 61%), fructose-1,6-bisphosphate aldolase (by 53%), and transketolase (by 46%). The results suggest that low-P treatment affected photosynthetic rate through an effect on RuBP regeneration rather than through RuBPCase activity and that the changes in Calvin cycle enzymes with low-P resulted in an increased flow of carbon to starch. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Rao, I. Madhusudana; Arulanantham, A. Raviraj; Terry, Norman

doi: 10.1104/pp.90.3.820pmid: 16666883

Abstract Sugar Beets (Beta vulgaris L. cv F58-554H1) were cultured hydroponically in growth chambers. Leaf orthophosphate (Pi) levels were varied nutritionally. The effect of decreased leaf phosphate (low-P) status was determined on the diurnal changes in the pool sizes of leaf ribulose 1,5-bisphosphate (RuBP), 3-phosphoglycerate (PGA), triose phosphate, fructose 1,6-bisphosphate, fructose-6-phosphate, glucose-6-phosphate, adenylates, nicotinamide nucleotides, and Pi. Except for triose phosphate, low-P treatment caused a marked reduction in the levels of leaf sugar phosphates (on a leaf area basis) throughout the diurnal cycle. Low-P treatment decreased the average leaf RuBP levels by 60 to 69% of control values during the light period. Low-P increased NADPH levels and NADPH/NADP+ ratio but decreased ATP; the ATP/ADP ratio was unaffected. Low P treatment caused a marked reduction in RuBP regeneration (RuBP levels were half the RuBP carboxylase binding site concentration) but did not depress PGA reduction to triose phosphate. These results indicate that photosynthesis in low-P leaves was limited by RuBP regeneration and that RuBP formation in low-P leaves was not limited by the supply of ATP and NADPH. We suggest that RuBP regeneration was limited by the supply of fixed carbon, an increased proportion of which was diverted to starch synthesis. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Larondelle, Yvan; Mertens, Emmanuel; Van Schaftingen, Emile; Hers, Henri-Géry

doi: 10.1104/pp.90.3.827pmid: 16666884

Abstract The phosphatases that hydrolyze fructose 2,6-bisphosphate in a crude spinach (Spinacia oleracea L.) leaf extract were separated by chromatography on blue Sepharose, into three fractions, referred to as phosphatases I, II, and III, which were further purified by various means. Phosphatase I hydrolyzed fructose 2,6-bisphosphate, with a K m value of 30 micromolar, to a mixture of fructose 2-phosphate (90%) and fructose 6-phosphate (10%). It acted on a wide range of substrates and had a maximal activity at acidic pH. Phosphatase II specifically recognized the osyl-link of phosphoric derivatives and had more affinity for the β-anomeric form. Its apparent K m for fructose 2,6-bisphosphate was 30 micromolar. It most likely corresponded to the fructose-2,6-bisphosphatase described by F. D. Macdonald, Q. Chou, and B. B. Buchanan ([1987] Plant Physiol 85: 13-16). Phosphatase III copurified with phosphofructokinase 2 and corresponded to the specific, low-K m (24 nanomolar) fructose-2,6-bisphosphatase purified and characterized by Y. Larondelle, E. Mertens, E. Van Schaftingen, and H. G. Hers ([1986] Eur J Biochem 161: 351-357). Three similar types of phosphatases were present in a crude extract of Jerusalem artichoke (Helianthus tuberosus) tuber. The concentration of fructose 2,6-bisphosphate decreased at a maximal rate of 30 picomoles per minute and per gram of fresh tissue in slices of Jerusalem artichoke tuber, upon incubation in 50 millimolar mannose. This rate could be accounted for by the maximal extractable activity of the low-K m fructose-2,6-bisphosphatase. A new enzymic method for the synthesis of β-glucose 1,6-bisphosphate from β-glucose 1-phosphate and ATP is described. 1 Supported by the U.S. Public Health Service (N.I.H. grant DK 9235), The Belgian State-Prime Minister's office-Science Policy Programming, and Belgian FRSM. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Battey, James F.; Ohlrogge, John B.

doi: 10.1104/pp.90.3.835pmid: 16666885

Abstract To determine if medium and long chain fatty acids can be appropriately metabolized by species that normally produce 16 and 18 carbon fatty acids, homogenates of developing Cuphea wrightii, Carthamus tinctorius, and Crambe abyssinica seeds were incubated with radiolabeled lauric, palmitic, oleic, and erucic acids. In all three species, acyl-CoA synthetase showed broad substrate specificity in synthesis of acyl-coenzyme A (CoA) from any of the fatty acids presented. In Carthamus, two- to fivefold less of the foreign FAs, lauric, and erucic acid was incorporated into acyl-CoAs than palmitic and oleic acid. Lauric and erucic acid also supported less glycerolipid synthesis in Carthamus than palmitic and oleic acid, but the rate of acyl-CoA synthesis did not control rate of glycerolipid synthesis. In all species examined, medium and long chain fatty acids were incorporated predominantly into triacylglycerols and were almost excluded from phospholipid synthesis, whereas palmitic and oleic acid were found predominantly in polar lipids. However, the rate of esterification of unusual fatty acids to triacylglycerol is slow in species that do not normally synthesize these acyl substrates. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)