Plant Physiology

Altman, Arie; Gülsen, Yücel; Goren, Raphael

doi: 10.1104/pp.69.1.1pmid: 16662136

Abstract Actively growing juice-vesicle explants, established from small lemon (Citrus limon L. Burm. f. var. `Eureka') fruits, were cultured in vitro on defined media. The juice vesicles continued to enlarge in culture for several months, without callus proliferation, and their initial growth was promoted by indoleacetic acid, gibberellic acid, and N6-benzyladenine. The metabolic competence of the explants, and its relevance to whole fruit development, was further investigated. Juice vesicles continued to accumulate protein on all media, for at least 16 days, but sugars did not change much during culture. Acid invertase increased dramatically during the first days of culture, and its specific activity was markedly promoted by indoleacetic acid, and to a lesser degree by gibberellic acid. Total peroxidase of juice vesicles increased progressively up to the 11th day of culture, and its specific activity was promoted by all three hormones, especially by N6-benzyladenine. Explant growth was accompanied by appearance of several cathodic and anodic isoperoxidases. The results suggest that the study of this unique juice vesicle system may contribute to a better understanding of fruit development. 2 Permanent address: Department of Fruit Growing and Breeding, Faculty of Agriculture, University of Ankara, Turkey. 1 Supported by a grant from the United States-Israel Binational Science Foundation, Jerusalem, Israel, to A. A. and R. G. This content is only available as a PDF. © 1982 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)

Meyer, Alejandro O.; Kelly, Grahame J.; Latzko, Erwin

doi: 10.1104/pp.69.1.7pmid: 16662187

Abstract Pyruvate orthophosphate dikinase has been identified in the green grains of eight cereal grasses, most of which are classified as C3 plants. The wheat (Triticum aestivum L. cv. Lerma Rojo) grain enzyme was further investigated: activity was low in very young grains, increased to a maximum at about 25 days after anthesis, then returned to a low level as the grain matured. It appeared to be located in the aleurone layer. A procedure was developed for obtaining partially purified preparations of pyruvate orthophosphate dikinase from the ears of wheat, oat (Avena sativa L.), barley (Hordeum distichum L.), and rye (Secale cereale L.). These preparations were suitable for measuring activities in both the forward and reverse reaction directions. The affinities of these enzymes for the six substrates (pyruvate, orthophosphate, and ATP in the forward reaction; phosphoenolpyruvate, pyrophosphate, and AMP in the reverse reaction) were determined and found to be similar to the reported affinities of the enzyme from the leaves of the C4 plant Zea mays. A possible role for pyruvate orthophosphate dikinase in cereal grains is considered briefly. 2 Present address: Department of Biochemistry and Nutrition, University of New England, Armidale, New South Wales 2351, Australia. 1 Support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. This content is only available as a PDF. © 1982 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, Desirazu Narasimha; Rao, N. Appaji

doi: 10.1104/pp.69.1.11pmid: 16662139

Abstract Serine hydroxymethyltransferase, the first enzyme in the pathway for interconversion of C1 fragments, was purified to homogeneity for the first time from any plant source. The enzyme from 72-h mung bean (Vigna radiata L.) seedlings was isolated using Blue Sepharose CL-6B and folate-AH-Sepharose-4B affinity matrices and had the highest specific activity (1.33 micromoles of HCHO formed per minute per milligram protein) reported hitherto. The enzyme preparation was extremely stable in the presence of folate or l-serine. Pyridoxal 5′-phosphate, ethylenediaminetetraacetate and 2-mercaptoethanol prevented the inactivation of the enzyme during purification. The enzyme functioned optimally at pH 8.5 and had two temperature maxima at 35 and 55°C. The K m values for serine were 1.25 and 68 millimolar, corresponding to V max values of 1.8 and 5.4 micromoles of HCHO formed per minute per milligram protein, respectively. The K 0.5 value for l-tetrahydrofolate (H4folate) was 0.98 millimolar. Glycine, the product of the reaction and d-cycloserine, a structural analog of d-alanine, were linear competitive inhibitors with respect to l-serine with K i values of 2.30 and 2.02 millimolar, respectively. Dichloromethotrexate, a substrate analog of H4folate was a competitive inhibitor when H4folate was the varied substrate. Results presented in this paper suggested that pyridoxal 5′-phosphate may not be essential for catalysis. The sigmoid saturation pattern of H4folate (n H = 2.0), one of the substrates, the abolition of sigmoidicity by NADH, an allosteric positive effector (n H = 1.0) and the increase in sigmoidicity by NAD+ and adenine nucleotides, negative allosteric effectors (n H = 2.4) clearly established that this key enzyme in the folate metabolism was an allosteric protein. Further support for this conclusion were the observations that (a) serine saturation exhibited an intermediary plateau region; (b) partial inhibition by methotrexate, aminopterin, O-phosphoserine, dl-α-methylserine and dl-O-methylserine; (c) subunit nature of the enzyme; and (d) decrease in the n H value from 2.0 for H4folate to 1.5 in presence of l-serine. These results highlight the regulatory nature of mung bean serine hydroxymethyltransferase and its possible involvement in the modulation of the interconversion of folate coenzymes. 2 To whom requests for reprints should be addressed. Permanent address: Department of Biochemistry, Indian Institute of Science, Bangalore 560 012, India. 1 This investigation was supported from a research grant of the Department of Science and Technology, Government of India, India. D. N. R. is a recipient of the Senior Research Fellowship of the Department of Atomic Energy, Government of India, India. This content is only available as a PDF. © 1982 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)

Duggan, Jeffrey X.; Meller, Erna; Gassman, Merrill L.

doi: 10.1104/pp.69.1.19pmid: 16662156

Abstract The in vivo oxidation of the C4 and C5 of 5-aminolevulinic acid (ALA) to CO2 has been studied in etiolated barley (Hordeum vulgare L. var. Larker) leaves in darkness. The rate of 14CO2 evolution from leaves fed [4-14C]ALA is strongly inhibited by aminooxyacetate, anaerobiosis, and malonate. The rate of 14CO2 evolution from leaves fed [5-14C]ALA is also inhibited by these treatments but to a lesser extent. These results suggest that (a) one step in ALA catabolism is a transamination reaction and (b) the C4 is oxidized to CO2 via the tricarboxylic acid cycle to a greater extent than is the C5. 2 Present address: The Perkin-Elmer Corp., Oak Brook Instrument Division, 2000 York Road, Oak Brook, IL 60521. 3 To whom correspondence should be addressed. 1 Supported by National Science Foundation Grants PCM 76-02308 and PCM 79-01605 and a grant from the University of Illinois at Chicago Circle Research Board (to M. L. G.). These studies formed a part of a thesis submitted (by J. X. D.) to the Graduate College of the University of Illinois at Chicago Circle in partial fulfillment of the requirements for the PhD degree. This content is only available as a PDF. © 1982 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)

Barash, Isaac; Pupkin, Gila; Netzer, David; Kashman, Yoel

doi: 10.1104/pp.69.1.23pmid: 16662165

Abstract A new phytotoxin, stemphyloxin I, C21H32O5, was isolated from cultures of the pathogenic fungus Stemphylium botryosum f. sp. lycopersici. The toxin is a tricyclic compound possessing a most unusual β-ketoaldehyde group. Injection of stemphyloxin I into a tomato leaflet caused unlimited necrotic spots and a loss of turgor, which at higher toxin concentration wilted the whole compound leaf. Visible symptoms could be observed at a toxin concentration as low as 2.7 micromolar. Stemphyloxin I is a nonspecific toxin. It exhibits a differential toxicity towards various plants, tomato and eggplant being the most sensitive. Incorporation of [14C]amino acids into proteins of exponentially growing tomato cell suspension was completely suppressed in the presence of 1 micromolar toxin. The toxin showed no significant difference in its inhibitory activity against green and white tomato cell cultures. The methoxy derivative of stemphyloxin I, in which the β-ketoaldehyde group is exclusively modified, showed a reduction of approximately 50 times in its inhibitory activity as compared to the toxin. The diacetate derivative conferred the same activity as stemphyloxin I. 1 Supported by Grant I.31.79 from the United States—Israel Binational Agricultural Research and Development Fund. This content is only available as a PDF. © 1982 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)

Conroy, James M.; Borzelleca, David C.; McDonell, Leslie A.

doi: 10.1104/pp.69.1.28pmid: 16662176

Abstract Antisera specific for the basic peroxidase from horseradish (Amoracea rusticana) were used to examine homology among horseradish peroxidase isoenzymes and among basic peroxidases from root plants. The antisera cross-reacted with all tested isoperoxidases when measured by both agar diffusion and quantitative precipitin reactions. Precipitin analyses provided quantitative measurements of homology among these plant peroxidases. The basic radish (Raphanus sativus L. cv. Cherry Belle) peroxidase had a high degree of homology (73 to 81%) with the basic peroxidase from horseradish. Turnip (Brassica rapa L. cv. Purple White Top Globe) and carrot (Daucus carota L. cv. Danvers) basic peroxidases showed less cross-reaction (49 to 54% and 41 to 46%, respectively). However, the cross-reactions of antisera with basic peroxidases from different plants were greater than were those observed with acidic horseradish isoenzymes (30 to 35%). These experiments suggest that basic peroxidase isoenzymes are strongly conserved during evolution and may indicate that the basic peroxidases catalyze reactions involved in specialized cellular functions. Anticatalytic assays were poor indicators of homology. Even though homology among isoperoxidases was detected by other immunological methods, antibodies inhibited only the catalytic activity of the basic peroxidase from radish. This content is only available as a PDF. © 1982 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)

Pace, Gary M.; MacKown, Charles T.; Volk, Richard J.

doi: 10.1104/pp.69.1.32pmid: 16662179

Abstract From 10 to 60% of the nitrate present in plant tissue extracts and stem exudates of corn (Zea mays L.) was found to be reduced during Kjeldahl digestion, even in the absence of added reducing agents. This reduction is of particular concern in [15N]nitrate assimilation studies, because it results in an overestimate of nitrate reduction. To overcome this problem, a method was developed for removing nitrate prior to Kjeldahl digestion, thereby preventing nitrate reduction. The procedure utilizes hydrogen peroxide for partial oxidation of organic matter in order to minimize the nitration of organic compounds. The free nitrates are then volatilized as nitric acid from concentrated sulfuric acid at 95°C. When the proposed method was used as a pretreatment to Kjeldahl digestion, less than 0.5% of the applied nitrate was recovered in the reduced nitrogen fraction of plant tissue extracts and stem exudates. 2 Present address: Allied Chemical. Syracuse Research Laboratory, P.O. Box 6, Solvay, NY 13209. 3 Present address: Department of Agronomy, United States Department of Agriculture, Science and Education Administration, Agricultural Research, University of Kentucky, Lexington, KY 40506. 1 Supported by Grant PCM-7703152 from the National Science Foundation. Paper No. 6804 of the Journal Series of the North Carolina Agricultural Research Service at Raleigh. This content is only available as a PDF. © 1982 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)

Owens, Lowell D.

doi: 10.1104/pp.69.1.37pmid: 16662180

Abstract Crown galls induced by infection of tobacco plants with Agrobacterium tumefaciens strain C58-Cl(pTiB6S3) were excised and cultured in vitro. After about one year of culture on medium-lacking phytohormones, two noncloned lines spontaneously formed shoots. Leaf explants from shoots of tumor-line T5 were capable of growing on hormone-free medium, and the resulting mixture of organized and unorganized tissue synthesized octopine. Detached leaves from T5 shoots also synthesized octopine. These results establish that shoots from this octopine-type tumor contain transformed cells and are true crown-gall teratomas. This content is only available as a PDF. © 1982 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)

Winter, Harry C.; Powell, Gary K.; Dekker, Eugene E.

doi: 10.1104/pp.69.1.41pmid: 16662181

Abstract Glutamine synthetase activity, extracted from an acetone powder of 7-day germinated peanuts (Arachis hypogaea L.), was precipitated by ammonium sulfate (40-60% saturation) and further purified by gel filtration and calcium phosphate gel treatment. When it was adsorbed to and subsequently eluted from a column of diethylaminoethyl-cellulose, two peaks of activity (designated glutamine synthetase 1 and 2) were obtained which were enriched 150- and 20-fold, respectively, over the initial extract. Glutamine synthetase 1 was present in ungerminated seeds and in the cotyledons during germination; glutamine synthetase 2 appeared during germination and was found largely in the developing plant. Compared with glutamine synthetase 2, glutamine synthetase 1 appeared to have a slightly smaller molecular weight and was more stable to heat and storage. The catalytic properties of the two forms were essentially the same. Whereas neither form catalyzed γ-glutamyltransferase activity with 4-methyleneglutamine, both glutamine synthetases 1 and 2 catalyzed an ATP- and NH4+-dependent conversion of [14C]-4-methyleneglutamic acid to [14C]-4-methyleneglutamine, but the Km value for 4-methyleneglutamic acid was 10-fold greater and the Vmax only one-fourth that measured with l-glutamic acid. This is the first report of glutamine synthetase activity with 4-methyleneglutamic acid as substrate, although the level of this activity does not appear adequate to account for the rapid synthesis of 4-methyleneglutamine observed in germinating peanuts. 2 Predoctoral Trainee of the United States Public Health Service, National Institutes of Health Grant T32-GMO7767. 1 Supported by grant 5901-0410-8-0164-0 from the Competitive Research Grants Office of the United States Department of Agriculture, Science and Education Administration, by United States Public Health Service Grant AM-03718 from the National Institutes of Health, and by a Faculty Research Grant from the H. H. Rackham School of Graduate Studies, The University of Michigan. This content is only available as a PDF. © 1982 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)

Thorne, John H.

doi: 10.1104/pp.69.1.48pmid: 16662182

Abstract The environmental sensitivity of the processes associated with the import of photosynthate by developing soybean seeds was investigated within intact fruit and with excised, immature embryos. Intact pods of field-grown (Glycine max [L.] Merr.) Amsoy 71 soybeans were subjected to localized regimes of 0, 21, or 100% O2 and 15, 25, or 35°C during pulsechase translocation experiments and, 2.5 hours later, the uptake and distribution of 14C-photosynthate among dissected fruit tissues determined. In other experiments, excised embryos were incubated in [14C]sucrose solutions under various experimental conditions to separate the effects of these treatments on accumulation by the embryos from those which may operate on phloem unloading in the maternal seedcoat. Import of 14C-photosynthate by intact soybean fruit was both temperature- and O2-dependent. This dependency was shown to occur only within the seeds; import by the pod walls was essentially insensitive to fruit temperature or O2 treatments. The embryos of anaerobic fruit were completely unlabeled, regardless of fruit temperature. But under anaerobic in vitro incubation conditions, uptake of [14C]sucrose in excised embryos was only 30% less than that in aerobic in vitro conditions. The data suggest that, within intact fruit, anoxia prevented sucrose efflux from the seed coat phloem and any subsequent uptake by the embryo. The demonstrated energy dependence of phloem unloading may reflect requirements for membrane integrity or energy metabolism in the companion cell-sieve element complex, consistent with a facilitated unloading process. Collectively, these data characterize the environmental sensitivity of photosynthate import in developing soybean fruit. They imply that environmental regulation of import may occur at both the embryo level and at the phloem terminals within the seed coat. 1 Present address: Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours and Co., Wilmington, DE 19801. This content is only available as a PDF. © 1982 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)