Plant Physiology

Manos, Peter J.; Goldthwaite, Jonathan

doi: 10.1104/pp.55.6.951pmid: 16659225

Abstract During winter, excised leaf tissue from Rumex obtusifolius degrades chlorophyll at twice the summer rate but the plant hormones, gibberellic acid and zeatin, inhibit the senescence rate by a constant percentage, regardless of season. 2 Present address: Department of Biology, Boston College, Chestnut Hill, Mass. 02167. 1 This work was supported in part by a National Institutes of Health Grant HD 06851, and by a National Institutes of Health Grant T 01 GM 00036 to P.J.M. This content is only available as a PDF. © 1975 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)

Jones, Richard W.; Sheard, Robert W.

doi: 10.1104/pp.55.6.954pmid: 16659226

Abstract The role of phytochrome in the induction of nitrate reductase of etiolated field peas (Pisum arvense L.) was examined. Terminal bud nitrate concentration increased in darkness, and the increase correlated with induction of nitrate reductase following brief exposure of intact plants to red, blue, far red, and white lights. Brief light exposure of intact plants stimulated nitrate uptake and induction of nitrate reductase by terminal buds subsequently excised and incubated on nitrate solution in darkness; exposure of excised buds in contact with nitrate led to less uptake but more induction. Nitrate and nitrate reductase activity both declined during incubation with water, irrespective of light treatment. Nitrate enrichment of intact terminal buds and uptake into excised buds and increases in nitrate reductase activity were all red/far red reversible. Dimethyl sulfoxide (1%, v/v) and sugars (sucrose 0.5%, glucose 1, w/v), although stimulating nitrate uptake into excised tissue in darkness, failed to enhance nitrate reductase activity over dark controls. Phytochrome may regulate nitrate reductase via both nitrate movement and a general mechanism such as enhancement of protein synthesis. 1 Research was supported by National Research Council of Canada A-1989. This content is only available as a PDF. © 1975 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)

Morris, Clayton J.; Thompson, John F.

doi: 10.1104/pp.55.6.960pmid: 16659227

Abstract The enzymic formation of acetylglutamate has been studied in Chlorella vulgaris extracts. Acetyl CoA and N2-acetyl-l-ornithine served as substrates for glutamate acetylation whereas acetylphosphate, N5-acetyl-l-ornithine, and N2-acetyl-2,4-diamino butyrate were ineffective. Acetyl CoA-glutamate transacetylase and acetylornithine-glutamate transacetylase activities have been purified over 180-fold with no indication of any separation of activities. The acetyl CoA activity was more labile than acetylornithine activity so that preparations having acetylornithine-glutamate transacetylase activity but no acetyl CoA-glutamate transacetylase activity were obtained. The two acetylating activities appear to be properties of one enzyme with one portion more easily denatured. Both acetylating activities had pH optima between 8 and 8.5. The Km value for glutamate was 3 mm for both activities. The Km values were 0.2 mm for acetylornithine and 3.2 mm for acetyl CoA. Arginine inhibited acetyl CoA-glutamate transacetylase (Ki = 0.94 mm) and acetylglutamate phosphokinase (Ki = 0.5 mm) but had no effect on acetylornithine-glutamate transacetylase. The lack of an inhibitory effect of proline on any of the three enzymic activities indicates that acetylglutamate is not a normal intermediate in proline biosynthesis. Growth of Chlorella with arginine as a nitrogen source had no effect on enzyme levels, showing that end-product repression is not a control factor in arginine biosynthesis in Chlorella. In Chlorella, arginine controls its own biosynthesis by inhibiting acetylglutamate phosphokinase and controls the level of acetylated intermediates by inhibiting acetyl CoA-glutamate transacetylase. This content is only available as a PDF. © 1975 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)

O'Neal, Thomas Denny; Joy, Kenneth W.

doi: 10.1104/pp.55.6.968pmid: 16659228

Abstract Of a variety of purine and pyrimidine nucleotides tested, only ADP and 5′AMP significantly inhibited the Mg2+-dependent activity of pea leaf glutamine synthetase. They were less effective inhibitors where Mn2+ replaced Mg2+. They were competitive inhibitors with respect to ATP, with inhibition constant (Ki) values of 1.2 and 1.8 mm, respectively. The energy charge significantly affects the activity of glutamine synthetase, especially with Mg2+. Of a variety of amino acids tested, l-histidine and l-ornithine were the most inhibitory, but significant inhibition was seen only where Mn2+ was present. Both amino acids appeared to compete with l-glutamate, and the Ki values were 1.9 mm for l-histidine (pH 6.2) and 7.8 mm for l-ornithine (pH 6.2). l-Alanine, glycine, and l-serine caused slight inhibition (Mn2+-dependent activity) and were not competitive with ATP or l-glutamate. Carbamyl phosphate was an effective inhibitor only when Mn2+ was present, and did not compete with substrates. Inorganic phosphate and pyrophosphate caused significant inhibition of the Mg2+-dependent activity. 2 Present address: Department of Biology, Carleton University, Colonel By Drive, Ottawa, Ontario, Canada. 1 This work was supported by a grant from the National Research Council of Canada. This content is only available as a PDF. © 1975 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)

O'Neal, Thomas Denny

doi: 10.1104/pp.55.6.975pmid: 16659229

Abstract An enzyme was extensively purified from jack bean leaves (Canavalia ensiformis L.) which produced o-ureidohomoserine from l-canaline and carbamyl phosphate. The most highly purified preparations catalyzed both this reaction and citrulline synthesis from ornithine and carbamyl phosphate, and the ratio of the two activities remained nearly constant during purification. When hydrated jack bean seeds were the enzyme source, ornithine carbamyltransferase (EC 2.1.3.3) activity was high but synthesis of ureidohomoserine was barely detectable. Both ornithine carbamyltransferase and the ureidohomoserine synthesizing enzyme had similar Km values for carbamyl phosphate. The purification data suggest that one enzyme may catalyze both reactions in jack bean leaves. This content is only available as a PDF. © 1975 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)

Jacoby, Benjamin

doi: 10.1104/pp.55.6.978pmid: 16659230

Abstract Autoradiographs of 22Na-loaded bean (Phaseolus vulgaris L. cv. `Brittle Wax') leaf slices showed that most of the tracer was concentrated in vascular tissue. Rubidium-86 was uniformly distributed in slices that had been incubated in darkness; after incubation in the light many small dark spots appeared on the autoradiographs, apparently corresponding with the stomata. Autoradiographs of 42K-loaded slices showed a rather uniform distribution of the tracer, whether the slices had been incubated in light or in darkness. 1 Supported by a grant from the Central Research Fund of The Hebrew University of Jerusalem. This content is only available as a PDF. © 1975 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)

Jones, C. Allan; Rasmussen, Reinhold A.

doi: 10.1104/pp.55.6.982pmid: 16659231

Abstract Isoprene production by Hamamelis virginiana L. and Quercus borealis Michx. leaves was studied. When ambient CO2 concentrations were maintained with bicarbonate buffers, the rate of isoprene production at 125 microliters per liter of CO2 was approximately four times that at 250 microliters per liter of CO2. Isoprene production was drastically inhibited by 97% O2. Dichlorodimethylphenylurea (0.1 mm), NaHSO3 (10 mm), and α-hydroxy-2-pyridinemethanesulfonic acid (10 mm) inhibited isoprene production but increased the compensation point of the tissue. Isonicotinic acid hydrazide neither inhibited isoprene emission nor increased the compensation point of the tissue significantly. Inhibition of isoprene production does not seem to correlate with stomatal resistance. Isoprene was labeled by intermediates of the glycolate pathway, and similarities are noted between the biosynthesis of isoprene and that of β-carotene. 2 Present address: Department of Agronomy, University of Arkansas, Fayetteville, Ark. 72701. 1 This research was supported in part by a National Defense Education Act Title IV Fellowship 71-002943 awarded to C. A. J. and in part by the Environmental Protection Agency Grant AP 01115 awarded to R. A. R. This content is only available as a PDF. © 1975 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)

Neumann, Peter M.; Prinz, Rivka

doi: 10.1104/pp.55.6.988pmid: 16659232

Abstract Growth of bean (Phaseolus vulgaris cv. `Brittle Wax') seedlings in iron-free media caused large reductions in root size and dye reduction capacity. Shoot growth was also severely retarded and the classical symptoms of chlorosis were observed. A single prophylactic spray of FeSO4, applied to the primary leaves of 7-day seedlings, enabled subsequent growth to equal that obtained when iron was continuously supplied to the roots over a 12-day period, although chlorophyll levels were lower. By adding a silicone-based surfactant to FeSO4 spray solutions, the burn damage normally caused to seedlings by such sprays was largely eliminated and the irreversible adsorption of iron increased. Foliar spray of an iron chelate (ferric ethylenediaminedi (o-hydroxyphenylacetic acid)) were less effective than those of FeSO4. This content is only available as a PDF. © 1975 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)

Matthews, Benjamin F.; Gurman, Andrew W.; Bryan, John K.

doi: 10.1104/pp.55.6.991pmid: 16659233

Abstract The sensitivity of homoserine dehydrogenase (EC 1.1.1.3) to inhibition by the feed-back modifier, l-threonine, was examined in preparations derived from etiolated shoots, roots, and lightgrown tissues of Zea mays L. var. earliking. A progressive decrease in enzyme sensitivity was observed during seedling growth. Enzyme derived from internode tissue retained a greater sensitivity to the effector than enzyme derived from apical portions of etiolated shoots, whereas enzyme from root tips was characteristically more sensitive than that prepared from mature cells of the root. Enzyme desensitization occurred rapidly during culture of excised shoots and the activities of both homoserine dehydrogenase and aspartokinase (EC 2.7.2.4) declined during shoot culture under a variety of conditions. The initial enzyme levels and the characteristic sensitivity of homoserine dehydrogenase were preserved during culture at 5 to 7 C, but desensitization was not prevented by inclusion of cycloheximide in the culture medium. Results of control experiments provide evidence that desensitization occurs in vivo. No alteration of the enzyme properties was detected during extraction or concentration of sensitive or insensitive enzyme or during coextraction of enzyme from mixed populations of different age shoots; nor was a differential distribution of inhibitors or activators indicated during assay of mixed preparations. The change in enzyme sensitivity was apparent under a variety of assay conditions and was not accompanied by changes in the apparent affinity of the enzyme for the substrate, homoserine. It is suggested that systematic changes in the regulatory characteristics of certain enzymes could be an important level of metabolic regulation during cellular differentiation. Three forms of maize homoserine dehydrogenaase were detected after acrylamide gel electrophoresis of samples derived from 72-hr shoots. Similar analysis of samples from older shoots revealed a broad asymmetric band of enzyme activity, suggesting that changes in the relative distribution of specific forms of the enzyme could be related to the growth-dependent changes in the sensitivity of maize homoserine dehydrogenase. 2 Present address: Department of Microbiology, The University of Rochester, School of Medicine and Dentistry, Rochester, N.Y. 14642. 1 This study was supported by National Science Foundation Grant 29599. This content is only available as a PDF. © 1975 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)

Dicamelli, Cynthia A.; Bryan, John K.

doi: 10.1104/pp.55.6.999pmid: 16659234

Abstract The relative contribution of each of several forms of homoserine dehydrogenase (EC 1.1.1.3) to the total enzyme population in etiolated shoots and in roots of Zea mays L. var. earliking was examined by the use of gel filtration chromatography and disc gel electrophoresis. In enzyme preparations derived from shoots of seedlings grown for 72, 120, or 168 hours, two molecular forms, II and III, which have the same apparent molecular weight but differ in net charge, contributed 75 to 80% of the total enzyme activity. A lower molecular weight species, form I, contributed 20 to 25% of the activity from 72-hour shoots, but was found to decrease concomitantly with a proportional increase in activity contributed by aggregated enzyme form(s) during shoot development. Form I contributed a comparatively larger fraction of the total enzyme activity in preparations of roots of 72-hour seedlings. The characteristic enzyme activity of different tissues was found to be the result of variations in both the amount and the properties of individual forms. Form I was consistently insensitive to inhibition by the feed-back modifier, l-threonine, but evidence is presented which indicates that the regulatory properties of form II and/or form III are systematically altered during shoot growth. The activity of the enzyme forms was also differentially stimulated by monovalent cations, K+ being the most effective activator; in all cases the potential for activation was correlated with the potential for inhibition. In contrast to these differences among the forms of the maize enzyme, all forms were shown to share a number of common characteristics. Potential factors which could influence the growth-associated changes in homoserine dehydrogenase are discussed briefly. 1 This study was supported by National Science Foundation Grant 29599. This content is only available as a PDF. © 1975 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)