Plant Physiology

Jones, Richard A.; Larkins, Brian A.; Tsai, C. Y.

doi: 10.1104/pp.59.4.525pmid: 16659886

Abstract Two zein proteins (Z1 and Z2) represent the majority of the protein synthesized during maize endosperm development. Undegraded membrane-bound polysomes isolated from normal maize synthesized these proteins when incubated in a cell-free protein-synthesizing system from wheat germ. The proteins synthesized in vitro were similar to authentic zein in ethanol solubility and electrophoretic mobility. Zein synthesis was associated with large size classes of membrane bound polysomes in normal maize. Membrane-bound polysomes isolated from developing kernels of opaque-2 mutant synthesized less total zein in vitro, and dramatically reduced incorporation into the Z1 component. The reduction in total zein corresponded to a 50% reduction in the level of membrane-bound polysomes in opaque-2, and the near absence of the large polysome size classes, which synthesized zein in normal maize. We concluded that the opaque-2 mutation results in a decreased “availability” of the zein mRNAs, reflected in a reduced level of membrane-bound polysomes. 3 Present address: Department of Vegetable Crops, University of California, Davis, Calif. 95616. 1 This work was supported by a grant from the Lilly Endowment and a David Ross Grant to C. Y. T. 2 Journal Paper No. 6374 of the Purdue University Agricultural Experiment Station. 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)

Robinson, J. Michael; Gibbs, Martin; Cotler, Donald N.

doi: 10.1104/pp.59.4.530pmid: 16659887

Abstract The influence of pH upon the O2 inhibition of 14CO2 photoassimilation (Warburg effect) was examined in intact spinach (Spinacia oleracea) chloroplasts. With conditions which favored the Warburg effect, i.e. rate-limiting CO2 and 100% O2, O2 inhibition was greater at pH 8.4 to 8.5 than at pH 7.5 to 7.8. At pH 8.5, as compared with 7.8, there was an enhanced 14C-labeling of glycolate, and a decrease of isotope in some phosphorylated Calvin cycle intermediates, particularly triose-phosphate. The 14C-labeling of starch was also more inhibited by O2 at higher pH. The enhanced synthesis of glycolate during 14CO2 assimilation at higher pH resulted in a diminution in the level of phosphorylated intermediates of the Calvin cycle, and this was apparently a causal factor of the increased severity of the Warburg effect. The 14C-labeling profiles have been interpreted in terms of a “CO2”-sensitive as well as a “CO2”-insensitive mechanism for glycolate synthesis. Both mechanisms functioned optimally at the higher pH and both responded to O2. 2 Postdoctoral trainee of National Institute of Health Grant BM-1586-09. 3 Present address: Immunological Research Laboratories, Harvard Medical School, Robert Brigham Hospital, Roxbury, Mass. 1 This research was generously supported by National Science Foundation Grant BMS71-00978 and United States Energy Research and Development Administration Grant ET(11-1)3231. 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)

Jones, Richard Wyn; Sheard, Robert W.

doi: 10.1104/pp.59.4.535pmid: 16659888

Abstract Growth at increasing continuous irradiance (at high nutrient nitrate) and nutrient nitrate concentrations (at high continuous irradiance) furnished increases in the in vivo and in vitro nitrate reductase activities of corn (Zea mays L.), field peas (Pisum arvense L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and globe amaranth (Gomphrena globosa L.) leaves and of marrow (Cucurbita pepo L.) cotyledons. Ratios of in vivo to in vitro activity declined exponentially in all species with increasing nitrate reductase levels promoted by nutrient nitrate. The ratios were more nearly independent of nitrate reductase levels generated by adjusting the irradiance; major exceptions were marrow and wheat at low (1.5 klux and less) irradiances and peas throughout the irradiance range, where decreases in the ratio were accompanied by increases in in situ nitrate concentration. The ratio also increased at the highest irradiance (39.2 klux) in wheat and barley, associated with a decline of in vitro nitrate reductase. These differences in response to irradiance and nutrient nitrate indicate that the in vivo assay does not provide a simple measure of nitrate reductase but rather yields a more composite measure of nitrate reduction, possibly related both to nitrate reductase level and to the supply of reductant for in vivo activity. 1 Research supported by National Research Council of Canada Grant A1989. 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)

Bednarski, Mary Ann; Izawa, Seikichi; Scheffer, Robert P.

doi: 10.1104/pp.59.4.540pmid: 16659889

Abstract Host-selective toxin from Helminthosporium maydis race T inhibited oxidative phosphorylation (AT32P formation) and stimulated ATPase activity by mitochondria from male-sterile (T) but not from normal (N) cytoplasm maize (Zea mays L.). Toxin increased the rate of NADH oxidation, but succinate oxidation was slightly, and malate-pyruvate oxidation was strongly inhibited as the associated ATP formation was abolished. There was a 1-minute lag before toxin gave maximal stimulation of NADH oxidation; the responses to 2,4-dinitrophenol and valinomycin were immediate. There was also a delay in the effect of toxin on ATP formation. T mitochondria were more sensitive than were N mitochondria to uncoupling by nigericin plus K+; there was no evidence, however, that the action of toxin is related to that of nigericin or other ionophores. With NADH as the substrate, the degree of uncoupling increased with increases in toxin concentration up to a saturating level; kinetics of the response suggested reversibility. T mitochondria exposed to toxin for 5 minutes regained normal rates of respiration and of ATP formation when they were washed with toxin-free medium, showing that the uncoupling effect is reversible. Evidently HM-T toxin does not bind firmly to its site(s) of action, in contrast to reports for another hostselective toxin. 3 Present address: Charles F. Kettering Research Laboratory, 150 E. South College St., Yellow Springs, Ohio 45387. 4 Present address: Department of Biology, Wayne State University, 410 W. Warren St., Detroit, Mich. 48202. 1 Supported by National Science Foundation Grants GB-24962 and GB-37959. 2 Journal Article No. 7757, Michigan Agricultural Experiment Station. 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)

Wang, Chien Yi; Mellenthin, Walt M.

doi: 10.1104/pp.59.4.546pmid: 16659890

Abstract Ripening reactions in pears (Pyrus communis L.) were differentially affected by an aminoethoxy analog of rhizobitoxine (l-2-amino-4-[2-aminoethoxy]-trans-3-butenoic acid) (AAR). Ethylene production of both `Anjou' and `Bartlett' pears was inhibited by AAR. Decrease in firmness, increase in protein N and soluble pectin were delayed by AAR in `Anjou' but not in `Bartlett' pears. While loss in malic acid was retarded in `Anjou' pears, rates of citric acid accumulation and malic acid reduction were not affected by AAR in `Bartlett' pears. 2 Present address: Horticultural Crops Marketing Laboratory, Agricultural Marketing Research Institute, ARS, U.S. Dept. of Agriculture, Beltsville, Md. 20705. 1 Technical Paper No. 4357. Oregon Agricultural Experiment Station. This study was supported by the Winter Pear Control Committee, Washington State Tree Fruit Research Commission, and the Hood River Grower-Shipper Association. 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)

Berlin, Jochen; Widholm, Jack M.

doi: 10.1104/pp.59.4.550pmid: 16659891

Abstract Phenylalanine ammonia lyase (PAL) activity was measured in p-fluorophenylalanine (PFP)-sensitive and -resistant tobacco (Nicotiana tabacum L.) and carrot (Daucus carota L.) cell lines which are known to oversynthesize phenylalanine. A correlation between phenolic levels and PAL activities was detected. The phenylalanine analog-resistant and -sensitive carrot cells showed no differences in the accumulation of phenolic compounds and PAL activities. The PFP-resistant tobacco cells, however, had 10 times higher levels of phenolics and also 10 to 20 times higher PAL activities than the PFP-sensitive line. The PAL activity in the resistant tobacco line increased dramatically after inoculation of the cells into fresh medium. Conditions affecting this increase were characterized. A comparison of the responses of PAL activity to light treatment and changes in the 2,4-dichlorophenoxyacetic acid concentration in the medium revealed no differences for both tobacco lines. After inoculation of the cells into fresh medium, the rates of nitrate uptake from the medium were similar for both lines as were the rates of protein synthesis. The reason for the increased PAL levels in the resistant tobacco cells remains unknown. 2 Present address: Lehrstuhl für Biochemie der Pflanzen, D44 Münster, Hindenburgplaz 55, West Germany. 3 To whom reprint requests should be addressed. 1 This work was supported in part by funds from the Illinois Agricultural Experiment Station and a postdoctoral fellowship of Deutsche Forschungsgemeinschaft to J. B. 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)

Davenport, Thomas L.; Morgan, Page W.; Jordan, Wayne R.

doi: 10.1104/pp.59.4.554pmid: 16659892

Abstract Plant water deficits reduced the basipetal transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of 14C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetally translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in well watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential sufficient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of well watered petioles tested under anaerobic conditions and acropetal transport tested under all conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maximally reduced is more critical than the degree of reduction. 2 Present address: University of Florida, IFAS, Agricultural Research and Education Center, 18905 S.W. 280th St., Homestead, Fla. 33031. 3 Present address: Texas A&M University, Blackland Research Center, Box 748, Temple, Tex. 76501. 1 This research was supported in part by a grant from Cotton Incorporated. A contribution of the Texas Agricultural Experiment Station. Preliminary reports appeared in Plant Physiol. 54: S-43 and Plant Physiol. 56: S-57. 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)

Swaminathan, Santhanam; Bock, Robert M.; Skoog, Folke

doi: 10.1104/pp.59.4.558pmid: 16659893

Abstract Evidence on the localization of cytokinins in chloroplast tRNA was obtained by comparison of Euglena gracilis var. bacillaris light-grown and dark-grown wild type cultures and chloroplast-bleached mutant strains. The several cytokinins characteristic of tRNA were separated by Sephadex LH-20 column chromatography of the hydrolysates and were quantitatively determined by tobacco bioassays of the eluates. The results indicate that 6-(3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine (i6 A) is formed in both the cytoplasmic and chloroplast tRNA, whereas 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-β-d- ribofurano-sylpurine (c-io6A) is produced mainly in the cytoplasmic tRNA and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-β-d- ribofurano-sylpurine (ms2io6A) is localized exclusively in chloroplast tRNA. The restriction of the methiolation reaction to the chloroplast is supported by results of radioisotope experiments showing that 35S-labeled MgSO4 is incorporated into ms2io6A in the wild type cultures, but not in the chloroplast-bleached mutant strains. 2 Present address: Department of Human Oncology, University of Wisconsin Medical School, Madison, Wisconsin 53706. 1 This work was supported by funds from the Wisconsin Alumni Research Foundation, and by National Science Foundation Research Grant BMS72-02226 to F. 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)

Reibach, Paul H.; Benedict, C. Roy

doi: 10.1104/pp.59.4.564pmid: 16659894

Abstract The active species of “CO2” and the amount of fractionation of stable carbon isotopes have been determined for a partially purified preparation of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) from corn (Zea mays) leaves. The rates of the enzyme reactions, using substrate amounts of HCO3−, CO2 or CO2 plus carbonic anhydrase, show that HCO3− is the active species of “CO2” utilized by PEP carboxylase. The Km values for CO2 and HCO3− are 1.25 mm and 0.11 mm, respectively, which further suggest the preferential utilization of HCO3− by PEP carboxylase. The amount of fractionation of stable carbon isotopes by PEP carboxylase from an infinite pool of H12CO3− and H13CO3− was −2.03‰. This enzyme fractionation (δ), together with the fractionation associated with absorption of CO2 into plant cells and the equilibrium fractionation associated with atmospheric CO2 and dissolved HCO3− are discussed in relation to the fractionation of stable carbon isotopes of atmospheric CO2 during photosynthesis in C4 plants. 1 This research was supported in part by the Texas Agricultural Experiment Station and The Robert A. Welch Research Foundation, Grant A-482. 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)

Rabino, Isaac; Mancinelli, Alberto L.; Kuzmanoff, Konrad M.

doi: 10.1104/pp.59.4.569pmid: 16659895

Abstract The spectral sensitivity and the irradiance dependence of anthocyanin synthesis, a “high irradiance response,” in cabbage (Brassica oleracea, cv. Red Acre) and tomato (Lycopersicon esculentum, cv. Beefsteak) seedlings exposed to continuous irradiation depend upon the length of the exposure. In cabbage, blue and red are more effective than far red when the irradiations are shorter than 12 hours and less effective than far red when the irradiations are longer than 12 hours. The irradiance dependence is negligible under red and becomes evident under blue and far red red only for exposures longer than 12 hours. Anthocyanin synthesis under intermittent light treatments, of efficiency comparable to that of continuous treatments, obeys the Bunsen-Roscoe reciprocity law and is a function of the dose (irradiance × time), rather than of the irradiance alone. The validity of the reciprocity relationships suggests that only one photoreceptor is responsible for the photocontrol of the response in the blue, red, and far red spectral regions. The characteristics of the response suggest that the photoreceptor is phytochrome, at least in cabbage. 1 Research partially supported by National Science Foundation Grant BMS-74-19976 to A. L. M. 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)