Plant Physiology

van Staden, Johannes; Papaphilippou, Alexander P.

doi: 10.1104/pp.60.5.649pmid: 16660156

Abstract Concentrations of 10−8 to 10−5m O-β-d-glucopyranosylzeatin are less active than zeatin and zeatin riboside in the soybean (Glycine max L.) callus bioassay. At a concentration of 10−4m the glucoside was, however, more active or alternatively less toxic than similar concentrations of zeatin and zeatin riboside. Applied zeatin-O-glucoside is readily metabolized by soybean callus and both zeatin and zeatin riboside could be extracted from callus grown on basal medium containing the O-glucoside. 1 The C.S.I.R., Pretoria provided financial assistance. This content is only available as a PDF. © 1977 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)

Schubert, Karel R.; Engelke, Jean A.; Russell, Sterling A.; Evans, Harold J.

doi: 10.1104/pp.60.5.651pmid: 16660157

Abstract The ATP-dependent evolution of H2 catalyzed by nitrogenase and the hydrogenase-catalyzed oxidation of H2 have been implicated as factors influencing the efficiency of energy utilization in the N2 fixation process. The effects of rhizobial strain and plant age on the H2-evolving and H2-utilizing activity of leguminous root nodules are described in this manuscript. Two classes of legume-Rhizobium combinations were observed in studies with soybeans (Glycine max L. Merr.) and cowpeas (Vigna unguiculata L. Walp.). One group evolved H2 in air; the other group did not exhibit net evolution of H2. The latter group metabolized H2 formed within the nodule through the action of a hydrogenase. The capacity to oxidize H2 was strongly linked to the strain of Rhizobium used to inoculate cowpeas and soybeans. Although the magnitude of H2 evolution in air changed during vegetative growth of a given symbiont, the ratio of H2 evolved in air to total nitrogenase activity was not appreciably altered during this period. No consistent difference in nitrogenase activity as measured by the C2H2 reduction assay was observed between symbionts with an active hydrogenase and those that apparently lack the enzyme and evolve H2. The effects of the two reactions of H2 on total N2 fixation and yield must now be established. 2 Present address: Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824. 1 This research was funded by grants to H. J. E. from the National Science Foundation (PCM-74-17812-A02) and the Rockefeller Foundation (GA-AS 7628). Support was also provided by the Oregon Agricultural Experiment Station (Technical Paper No. 4537). This content is only available as a PDF. © 1977 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)

Higgins, Thomas J. V.; Spencer, Donald

doi: 10.1104/pp.60.5.655pmid: 16660158

Abstract Both polysomes and polysomal RNA, isolated from cotyledons of ripening pea (Pisum sativum) seeds and supplemented respectively with wheat germ S-100 and S-30 fractions, were used to program the cell-free synthesis of polypeptides. The relationship of these polypeptide products to seed storage proteins has been investigated. When fractionated on sucrose density gradients the translation products did not coincide with native storage proteins, nor were they exactly coincident with the subunits of storage proteins on dissociating gels. Treatment with antiserum prepared against storage proteins precipitated only a very small proportion of these products. Nonetheless, tryptic peptide mapping showed that a significant proportion (up to 65%) of the in vitro products from cell-free systems were related to the storage proteins. Alternative interpretations of these results are that either the translatable mRNAs for storage proteins make up a small proportion of the total template isolated from pea cotyledon polysomes, or that storage protein polypeptides are made in significant amounts in vitro but lack major antigenic determinants which in vivo may be acquired during chain completion or post-translational modification. This content is only available as a PDF. © 1977 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)

Ferrier, Jack M.; Dainty, Jack

doi: 10.1104/pp.60.5.662pmid: 16660159

Abstract The relative magnitudes of the hydraulic resistances, water capacities, and water potential equilibration time constants for the single cell, for the apoplast, and for the symplast in higher plant tissue are assessed. Swelling of beetroot (Beta vulgaris, var. `Detroit Red') storage tissue sections in pure water is measured using a displacement transducer. This method of measurement avoids the difficulty of solute diffusion in the apoplast. Theoretical analysis of the experimental results shows that the main path of water flow into the tissue is the apoplast rather than the symplast, that the main resistance to water flow into the cells is usually the cell membrane rather than the apoplast, but that in some cases the apoplast resistance and water capacity can contribute significantly to the water potential equilibration time constant of the tissue. 1 This work was supported by a grant to J. D. from the Connaught Fund (University of Toronto). This content is only available as a PDF. © 1977 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)

Turner, John F.; Harrison, Dorothy D.; Copeland, Les

doi: 10.1104/pp.60.5.666pmid: 16660160

Abstract A fructokinase (EC 2.7.1.4) was obtained from pea (Pisum sativum L.) seeds. This enzyme, termed fructokinase (fraction IV), was specific for fructose as substrate and had little activity with glucose or mannose. Excess fructose inhibited the enzyme at the optimum pH (8.2) but not at pH 6.6. MgATP was inhibitory at pH 6.6. The apparent Michaelis-Menten constants at pH 8.2 were 0.057 mm for fructose and 0.10 mm for MgATP. Mg2+ ions were essential for activity; Mn2+ could partially replace Mg2+. Fructokinase (fraction IV) had a requirement for K+ ions which could be substantially replaced by Rb+ or NH4+ but not by Na+. The enzyme was inhibited by MgADP. The possible significance of fructokinase (fraction IV) in plant carbohydrate metabolism is discussed. 1 This investigation was supported by the University of Sydney Research Grant. This content is only available as a PDF. © 1977 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)

Burnell, James N.; Shrift, Alex

doi: 10.1104/pp.60.5.670pmid: 16660161

Abstract l-Cysteinyl-tRNA synthetase (EC 6.1.1.16) from Phaseolus aureus was purified approximately 300-fold and was free of contaminating aminoacyl-tRNA synthetases. Optimum assay conditions were determined and substrate specificity and inhibitor properties were investigated using the ATP-PPi exchange reaction. The Km values for l-cysteine, ATP, and PPi were 6.20 × 10−5m, 1.15 × 10−3m, and 1 × 10−3m, respectively. Both l-selenocysteine (Km = 5 × 10−5m) and α-l-aminobutyric acid (Km = 1 × 10−2m) acted as alternative substrates of the purified cysteinyl-tRNA synthetase. The enzyme was sensitive to sulfhydryl group reagents; it was inhibited by sulfide, 0-acetylserine, and reduced glutathione. 1 This research was supported by National Institutes of Health Grant ES 00807 to A. S. This content is only available as a PDF. © 1977 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)

Bligny, Richard; Douce, Roland

doi: 10.1104/pp.60.5.675pmid: 16660162

Abstract The effects of copper deficiency on cell culture growth, cell respiration, mitochondrial oxidative properties, and electron transport chain have been studied with suspension-cultured sycamore cells (Acer pseudoplatanus L.). Within the range of the copper concentration studied (0.1-25 μg/1 of culture medium), the mean rate of cell division is independent of copper concentration. An initial copper concentration lower than 2 μg/1 limited the maximum density of population reached at the stationary phase of growth. On a protein basis, the uncoupled O2 uptake rates were about the same for normal and copper-deficient cells. In contrast, the half-maximal inhibition of O2 uptake rate was obtained at greater KCN concentration in the normal cells (20 μM) compared to copper-deficient cells (2 μM). Similar results were obtained with the normal and copper-deficient sycamore cell mitochondria. In the copper-deficient mitochondria, the concentration of the cytochrome aa 3 was less than 0.02 nmol/mg mitochondrial protein or 1/20 of the normal rate. The b- and c-type cytochrome content was invariant with copper depletion. It appeared that cytochrome aa 3 is present in large excess in normal cells. This work also indicated that cytochrome c is a very mobile molecule. This content is only available as a PDF. © 1977 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)

Stulen, Ineke; Oaks, Ann

doi: 10.1104/pp.60.5.680pmid: 16660163

Abstract The level of asparagine synthetase is low in 10-mm root tips from corn seedings (Zea mays W64 × W182F) but relatively high in mature root sections taken 20 to 35 mm from the tip. When root tips are excised there is a marked increase in asparagine synthetase over a 5-hour period. In mature root sections, on the other hand, the asparagine synthetase activity declines over the same 5-hour period. The increase in the root tip is sensitive to cordycepin, 6-methylpurine, and cycloheximide, which indicates that both RNA and protein synthesis are involved in the formation of asparagine synthetase in the root tip sections. The glutamine analogue azaserine also inhibits formation of the enzyme in root tips, as does glucose. The increase in the root tip is not sensitive to asparagine. Additions of glucose or asparagine have no effect on enzyme activity in extracts. When cycloheximide, azaserine, or glucose is added to the mature root sections there is no effect on recovered enzyme activity. 2 Present address: State University of Groningen, Department of Plant Physiology, Postbox 14, Haren (Gr), The Netherlands. 3 To whom correspondence should be addressed. 1 This research was supported by Grant A-2818 from the National Research Council of Canada and by a travel grant from the Dutch organization for Basic Research (ZWO) for I. S. This content is only available as a PDF. © 1977 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)

Etherton, Bud; Keifer, David W.; Spanswick, Roger M.

doi: 10.1104/pp.60.5.684pmid: 16660164

Abstract The reliability of two different membrane resistance-measuring methods that use a single intracellular microelectrode was tested against a conventional method that uses two intracellular microelectrodes. The first single-electrode method used a single square current pulse and required a constant microelectrode resistance. This method was unreliable because the electrode resistance changed markedly on cell penetration and changed with time within the cell. The second method used a high frequency square wave for injecting current into the cell and depended upon the membrane having a much longer RC (resistance × capacitance)-time constant than the microelectrode. The resistance values obtained by this latter method were usually different from membrane resistances obtained at the same time on the same cells using two intracellular microelectrodes. Therefore, neither single intracellular microelectrode method was as reliable as the conventional method. All tests were with coleoptile cells of Avena sativa var. Victory. 1 Research supported by funds from the Vermont Agricultural Experiment Station and by funds from National Science Foundation Grant GB 28124X to R. M. S. Vermont Agricultural Experiment Station Journal Series No. 369. This content is only available as a PDF. © 1977 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)

Anderson, James D.

doi: 10.1104/pp.60.5.689pmid: 16660165

Abstract The ATP content of soybean (Glycine max [L.] Merr. cv. Kent) axes incubated for 3 hours in 1 mm solutions of adenine and adenosine increased over 100% and 75%, respectively, over axes incubated in water. The increase in ATP was primarily due to the conversion of these purines to nucleotides via the nucleotide salvage pathway. The ATP formed was in a metabolically active pool because label from adenine was incorporated into acid-insoluble material. Adenine also increased the levels of GTP, UTP, and CTP, but not to the extent of the ATP level. This content is only available as a PDF. © 1977 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)