Plant Physiology

Pierce, John

doi: 10.1104/pp.81.4.943pmid: 16664961

Abstract Recent studies have provided a fairly detailed view of the various intermediates involved in the reactions of ribulosebisphosphate carboxylase and the manner in which the catalytically essential metal atom might catalyze their interconversions. A better understanding of how the enzyme distinguishes between its alternate substrates, CO2 and O2, has also emerged. The results of these studies should prove useful in anticipating possible ways in which the enzyme's substrate specificity might be manipulated. Together, the techniques that are described constitute a powerful methodology for more refined experimentation aimed at understanding the curious reactivities of ribulosebisphosphate carboxylase. This content is only available as a PDF. © 1986 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)

Kenrick, Janette R.; Bishop, David G.

doi: 10.1104/pp.81.4.946pmid: 16664962

Abstract The fatty acid composition of phosphatidylglycerol and sulfoquinovosyldiacylglycerol has been measured in the leaves of 27 species of higher plants from six families whose members differed in their degrees of chilling sensitivity. The content of high melting point fatty acids (represented by the sum of hexadecanoic, trans-3-hexadecenoic and octadecanoic acids) in phosphatidylglycerols varied little between members of the same plant family and was not obviously related to the relative chilling sensitivity of members of that family. The saturated fatty acid content (hexadecanoic + octadecanoic acids) of sulfoquinovosyldiacylglycerols also appeared to be characteristic of a plant family, although some exceptions were found. In one case, (Carica papaya) the content of saturated fatty acids in sulfoquinovosyldiacylglycerol was sufficiently high to suggest that this lipid could undergo phase separations above 0°C. It is concluded that the content of high melting point fatty acids in leaf phosphatidylglycerol is not a direct indication of the chilling sensitivity of a plant, but rather may be a reflection of the genetic origin of that plant. This content is only available as a PDF. © 1986 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)

Saini, Hargurdeep S.; Consolacion, Evangeline D.; Bassi, Pawan K.; Spencer, Mary S.

doi: 10.1104/pp.81.4.950pmid: 16664963

Abstract Application of exogenous ethylene in combination with gibberellic acid (GA3), kinetin (KIN), and/or CO2 has been reported to induce germination of lettuce seeds at supraoptimal temperatures. However, it is not clear whether endogenous ethylene also plays a mediatory role when germination under these conditions is induced by treatment regimes that do not include ethylene. Therefore, possible involvement of endogenous ethylene during the relief of thermoinhibition of lettuce (Lactuca sativa L. cv Grand Rapids) seed germination at 32°C was investigated. Combinations of GA3 (0.5 millimolar), KIN (0.05 millimolar), and CO2 (10%) were used to induce germination. Little germination occurred in controls or upon treatment with ethylene, KIN, or CO2. Neither KIN nor CO2 affected the rate of ethylene production by seeds. Both germination and ethylene production were slightly promoted by GA3. Treatments with GA3+CO2, GA3+KIN, or GA3+CO2+KIN resulted in approximately 10-to 40-fold increases in ethylene production and 50 to 100% promotion of germination as compared to controls. Initial ethylene evolution from the treated seeds was greater than from the controls and a major surge in ethylene evolution occurred at the time of visible germination. Application of 1 millimolar 2-aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene synthesis, in combination with any of above three treatments inhibited the ethylene production to below control levels. This was accompanied by a marked decline in germination percentage. Germination was also inhibited by 2,5-norbornadiene (0.25-2 milliliters per liter), a competitive inhibitor of ethylene action. Application of exogenous ethylene (1-100 microliters per liter) overcame the inhibitory effects of AVG and 2,5-norbornadiene on germination. The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA3, KIN, and CO2. It also appears that these treatment combinations do not act exclusively via promotion of ethylene evolution as the application of exogenous ethylene alone did not promote germination. 2 Present address: Chevron Chemical Co., 940 Hensley St., Richmond, CA 94804. 1 This work was supported by the National Science and Engineering Research Council of Canada, grant A-1451 to M. S. S. This content is only available as a PDF. © 1986 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)

Legge, Raymond L.; Cheng, Kwan-Hon; Lepock, James R.; Thompson, John E.

doi: 10.1104/pp.81.4.954pmid: 16664964

Abstract Changes in the molecular organization of membranes in pericarp cells of ripening tomato fruit were examined by fluorescence depolarization after labeling with fluorescent lipid-soluble probes. The fluorescent labels were partitioned into isolated protoplasts and purified plastids from fruit at various stages of senescence. Values for steady-state anisotropy (rss) of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labeled protoplasts rose progressively during the early stages of ripening over a time frame that overlapped the climacteric rise in ethylene production. This can be interpreted as reflecting a decrease in the lipid fluidity of primarily plasma membrane. By contrast, there was no significant change during ripening in rss for plastid membranes labeled with DPH, 1-[4-trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), and cis- or trans-parinaric acid. Nor was there any change during ripening in the limiting fluorescence anisotropy (roo) and order parameter (S) for plastids labeled with DPH or TMA-DPH, parameters that are corrected for any differences in lifetime. Some degree of lifetime heterogeneity, possibly reflecting structurally distinct domains, was discerned in both young and senescent plastids that had been labeled with DPH or TMA-DPH, but this also did not change as ripening progressed. Thus membranes of the pericarp cells sustain different fates as the tomato fruit ripens, implying that there are distinguishable mechanisms of membrane deterioration in senescing tissues. 2 Present address: Electron Optics Laboratory, Roswell Park Memorial Institute, Buffalo, NY 14263 1 Supported by grants from the Natural Sciences and Engineering Research Council of Canada to J. E. T. and J. R. L. This content is only available as a PDF. © 1986 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)

Bhaya, Devaki; Castelfranco, Paul A.

doi: 10.1104/pp.81.4.960pmid: 16664965

Abstract In addition to chlorophyll-protein complexes, other proteins were labeled when isolated developing pea (Pisum sativum L.) chloroplasts were incubated with [14C]-5-aminolevulinic acid. The major labeled band (M r = 43 kilodaltons by lithium dodecyl sulfate-polyacrylamide gel electrophoresis) was labeled even in the presence of chloramphenicol. Heme-dependent peroxidase activity (as detected by the tetramethyl benzidine-H2O2 stain) was not visibly associated with this band. The radioactive band was stable to heat, 5% HCl in acetone, and was absent if the incubation with [14C]-5-aminolevulinic acid was carried out in the presence of N-methyl protoporphyrin IX dimethyl ester (a specific inhibitor of ferrochelatase). Organic solvent extraction procedures for the enrichment of cytochrome f from chloroplast membranes also extracted this unknown labeled product. It was concluded that this labeled product was probably a c-type cytochrome; however, the possibility that it might be a protein containing a covalently linked linear tetrapyrrole was not ruled out. 2 Present address: 9 Thygaraj Marg, New Delhi—110011, India. 1 Supported by National Science Foundation Grants PCM 81-08538 and DMB-8415321. This content is only available as a PDF. © 1986 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)

Schneegurt, Mark A.; Beale, Samuel I.

doi: 10.1104/pp.81.4.965pmid: 16664966

Abstract The heme and chlorophyll precursor δ-aminolevulinic acid (ALA) can be formed by two biosynthetic routes: from the intact carbon skeleton of glutamate via a five-carbon pathway, which occurs in chloroplasts and bluegreen algae, and by ALA synthase-catalyzed condensation of succinyl-CoA and glycine, which occurs in bacteria and animal mitochondria. The biosynthetic route of plant mitochondrial heme a was determined by incubating terminal epicotyl sections of 8-day-old etiolated Zea mays seedlings in the dark with l-1-[14C]glutamate (which can be incorporated into ALA only via the five-carbon route) or 2-[14C]glycine (which would be incorporated via ALA synthase). Label incorporation was measured in highly purified protoheme and heme a. In 12-hour incubations, label uptake was greater than 70%. Total cellular protoheme was labeled 29.7 times more effectively by glutamate than glycine. Heme a was labeled 4.1 times more effectively by glutamate than by glycine. To assess the relative ability of the two amino acids to contribute label to the farnesyl moiety of heme a, label incorporation into total cellular nonsaponifiable lipids was measured. Glycine labeled this fraction 11.3 times more effectively than glutamate. Thus, a contribution by glycine to the farnesyl moiety may account for the small amount of label appearing in heme a. Our results indicate that in etiolated maize, noncovalently bound hemes, including mitochondrial heme a, are made mostly, and possibly entirely, from ALA synthesized via the five-carbon pathway. There is little or no contribution from ALA formed via ALA synthase, and no evidence was found for the operation of this enzyme in maize. 1 Supported by National Science Foundation Grants DMB-8213948 and DMB-8518580. This content is only available as a PDF. © 1986 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)

Sasakawa, Hideo; Larue, Thomas A.

doi: 10.1104/pp.81.4.972pmid: 16664967

Abstract Nitrate uptake by roots of cowpea (Vigna unguiculata) was measured using 15NO3−, and the energy cost to the root was estimated by respirometry. Roots of 8-day-old cowpea seedlings respired 0.6 to 0.8 milligram CO2 per plant per hour for growth and maintenance. Adding 10 millimolar NO3− to the root medium increased respiration by 20 to 30% during the following 6 hours. This increase was not observed if the shoots were in the dark. Removal of NO3− from the root medium slowed the increase of root respiration. The ratios of additional respiration to the total nitrogen uptake and reduced nitrogen content in roots were 0.4 gram C per gram N and 2.3 grams C per gram N, respectively. The latter value is close to theoretical estimates of nitrate assimilation, and is similar to estimates of 1 to 4 grams C per gram N for the respiratory cost of symbiotic N2 fixation. 2 Permanent address: Faculty of Agriculture, Nagoya University, Chikusa, Nagoya 464, Japan. 1 Supported by grant 05-0560 from the United Nations Development Program to the International Institute for Tropical Agriculture. This content is only available as a PDF. © 1986 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)

Hasegawa, Koji; Noguchi, H.; Iwagawa, T.; Hase, T.

doi: 10.1104/pp.81.4.976pmid: 16664968

Abstract Three growth inhibitors which might be involved in phototropism of Sakurajima radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls, were isolated as crystalline forms from light-exposed radish seedlings and identified as cis- and trans-raphanusanins and 6-methoxy-2,3,4,5-tetrahydro-1,3-oxazepin-2-one (designated raphanusamide). The cis- and trans-raphanusanins inhibited growth of etiolated radish hypocotyls at concentrations higher than 1.5 micromolar, raphanusamide at concentrations higher than 20 micromolar. 1 Partly supported by grants-in-aid for Scientific Research in 1983 to 1985 NO. 58540430 to K. H. from the Japanese Ministry of Education, Science and Culture. This content is only available as a PDF. © 1986 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)

Noguchi, H.; Nishitani, K.; Bruinsma, J.; Hasegawa, Koji

doi: 10.1104/pp.81.4.980pmid: 16664969

Abstract When etiolated radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls were subjected to a continuous unilateral illumination with white fluorescent light (0.1 watt per square meter), the growth rate at the lighted side was strongly inhibited for the first 2 hours, while that at the shaded side showed no change. After 2.5 hours growth on the lighted side recovered gradually, while that on the shaded side was slightly inhibited. The neutral growth inhibitors, cis- and trans-raphanusanins and raphanusamide, were determined in the lighted and shaded sides from 1 hour before until 2 hours after the start of unilateral illumination. In the lighted side, cis- and trans-raphanusanins increased by 0.5 hour after the start of illumination, reached 3 to 3.5-fold greater concentrations than in the shaded side after 1 hour, and then decreased gradually. Raphanusamide increased in the lighted side to a 3-fold greater concentration than that in the shaded one 2 hours after the start of the illumination. Unilateral applications of cis- and trans-raphanusanins and raphanusamide suppressed the growth of the hypocotyl on the applied side more than that on the opposite one, causing the hypocotyls to bend towards the site of application. The data suggest that phototropic curvature in radish is caused by the light-induced synthesis of growth-inhibiting cis- and trans-raphanusanins, and raphanusamide at the site of illumination. 1 Partly supported by grants-in-aid for Scientific Research in 1983-1985 No. 58540430 to K. H. from the Japanese Ministry of Education, Science and Culture. This content is only available as a PDF. © 1986 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)

Maki, Sonja L.; Brenner, Mark L.; Birnberg, Paul R.; Davies, Peter J.; Krick, Thomas P.

doi: 10.1104/pp.81.4.984pmid: 16664970

Abstract Experiments were designed to test the hypothesis that the labeled products recovered from plant tissue incubated with [14C]GA12-7-aldehyde ([14C]GA12ald) would serve as appropriate [14C]markers for the recovery of naturally-occurring gibberellins (GAs). The [14C]GA12ald (about 200 millicuries per millimole) was synthesized from pumpkin endosperm using [4,5-14C]mevalonic acid. It was added to the adaxial surface of isolated pea cotyledons at 22 days after flowering. Products recovered after 0.5 and 4.0 hour incubations yielded four major peaks which were separated by high performance liquid chromatography (HPLC). These products were purified by multiple-column HPLC using on-line radioactivity detection. They were then added as [14C]markers to two unlabeled pea extracts. In general, preparative HPLC followed by further HPLC purification resulted in a single UV-absorbing peak co-eluting with each [14C]marker. These [14C] and UV-absorbing peaks were shown to contain GA53, GA44, GA20, GA19, and GA17 by GC-MS. The finding of GA53 is novel; all others have previously been found in pea. Endogenous GAs of pea were thus readily detected using [14C]GA12ald metabolites as [14C]markers to recover naturally occurring GAs suggesting that the method may be applicable in detecting naturally occurring GAs in other species. 1 Supported in part by grants from the Herman Frasch Foundation and Monsanto Agricultural Products. Contribution from the University of Minnesota Agricultural Experiment Station, St. Paul, MN 55108. Paper No. 14,548, Scientific Journal Series. This content is only available as a PDF. © 1986 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)