Plant Physiology

Heber, Ulrich; Walker, David

doi: 10.1104/pp.100.4.1621pmid: 16653176

Abstract Coupled cyclic electron transport is assigned a role in the protection of leaves against photoinhibition in addition to its role in ATP synthesis. In leaves, as in reconstituted thylakoid systems, cyclic electron transport requires “poising,” i.e. availability of electrons at the reducing side of photosystem I (PSI) and the presence of some oxidized plastoquinone between photosystem II (PSII) and PSI. Under self-regulatory poising conditions that are established when carbon dioxide limits photosynthesis at high light intensities, and particularly when stomata are partially or fully closed as a result of water stress, coupled cyclic electron transport controls linear electron transport by helping to establish a proton gradient large enough to decrease PSII activity and electron flow to PSI. This brings electron donation by PSII, and electron consumption by available electron acceptors, into a balance in which PSI becomes more oxidized than it is during fast carbon assimilation. Avoidance of overreduction of the electron transport chain is a prerequisite for the efficient protection of the photosynthetic apparatus against photoinactivation. 2 This work was completed while U.H. was a Royal Society Guest Research Fellow at the Biddlestone Field Laboratory. 3 Leverhulme Emeritus Fellow. 1 Work performed in the authors' laboratories was supported by the Royal Society, the Agricultural Research Council, the Alexander von Humboldt Foundation, the Stiftung Volkswagenwerk, and the Sonderforschungsbereich 251 of the University of Würzburg. This content is only available as a PDF. © 1992 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)

Raikhel, Natasha

doi: 10.1104/pp.100.4.1627pmid: 16653177

1 Support was from the United States Department of Energy, Washington, DC. Article PDF first page preview Close This content is only available as a PDF. © 1992 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)

Ludevid, Dolors; Höfte, Herman; Himelblau, Edward; Chrispeels, Maarten J.

doi: 10.1104/pp.100.4.1633pmid: 16653178

Abstract The vacuolar membrane (tonoplast) contains an abundant intrinsic protein with six membrane-spanning domains that is encoded by a small gene family. Different isoforms of tonoplast intrinsic protein (TIP) are expressed in different tissues or as a result of specific signals. Using promoter-β-glucuronidase (GUS) fusions and in situ hybridization, we have examined the expression of γ-TIP in Arabidopsis thaliana. GUS staining of plants transformed with promoter-GUS fusions showed that γ-TIP gene expression is high in recently formed tissues of young roots. In the shoot, γ-TIP gene expression was highest in the vascular bundles of stems and petioles, as well as in the stipules and in the receptacle of the flower. No GUS activity was detected in root or shoot meristems or in older tissues, suggesting temporal control of γ-TIP gene expression associated with cell elongation and/or differentiation. In situ hybridization carried out with whole seedlings confirmed that in root tips, γ-TIP mRNA was present only in the zone of cell elongation just behind the apical meristem. In seedling shoots, mRNA abundance was also found to be correlated with cell expansion. These results indicate that γ-TIP may be expressed primarily at the time when the large central vacuoles are being formed during cell enlargement. 2 Present address: Departamento de Genetica Molecular, CID-CSIC, Jordi Girano 18, 08034 Barcelona, Spain. 3 Present address: Laboratoire de Biologie Cellulaire, INRA, Route de Saint-Cyr F-78026 Versailles, France. 1 Supported by a grant from the United States Department of Agriculture (to M.J.C.), a European Molecular Biology Organization fellowship (to H.H.), and a fellowship from the Provincial Government of Catalonia (to D.L.). This content is only available as a PDF. © 1992 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)

Côté, Richard; Gerrath, Jean M.; Peterson, Carol A.; Grodzinski, Bernard

doi: 10.1104/pp.100.4.1640pmid: 16653179

Abstract Sink to source transition parallels loss of thigmotropic capacity in tendrils of a semileafless mutant, Pisum sativum cv Curly. Macroscopic tendril development is subdivided based on thigmotropic capacity. Stage I is the elongation stage and, although the rate of photosynthesis is similar to that of stage II and III tendrils, dark respiration rates are higher in stage I. During stage II, tendrils are thigmotropic and act as a sink. Even though stage II tendrils have CO2 exchange characteristics similar to those of stage III tendrils, which are coiled, our fluorescein, 14C-partitioning, and 11C-translocation experiments suggest that stage I and II tendrils do not export carbon. Only stage III tendrils act as sources of newly fixed carbon. Export from them is blocked by cold, heat girdling of the petiole, or anoxia treatment of the tendrils. A late stage II tendril complex, in which coiling is occurring, may be exporting photoassimilates; however, this phenomenon can be attributed to the fact that the pea leaf is a compound structure and there may be one or more stage III tendrils, no longer thigmotropic, within the tendril complex. Photosynthetic maturity in pea tendrils occurs at stage III and is characterized by the ability of these tendrils to export photoassimilates. 2 Present address: Laboratoire de Microbiologie Forestière, Institut National de la Recherche Agronomique, Centre de Recherches Forestières de Nancy, 54280 Champenoux, France. 1 Research was funded by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to B.G. and C.A.P. B.G. also received support from the Ontario Ministry of Agriculture and Food and an Ontario-Quebec Travel Fellowship. J.M.G. and R.C. were recipients of NSERC Postdoctoral and Postgraduate Fellowships, respectively. This content is only available as a PDF. © 1992 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)

Scheres, Ben; McKhann, Heather I.; Zalensky, Andrei; Löbler, Marian; Bisseling, Ton; Hirsch, Ann M.

doi: 10.1104/pp.100.4.1649pmid: 16653180

Abstract A number of early nodulin genes are expressed in specific cell types as pea (Pisum sativum) root nodules develop. The Pisum sativum early nodulin PsENOD2 is detected only in the uninfected cells of the nodule parenchyma, whereas PsENOD12 is expressed at two spatially removed sites: in root hairs and adjacent cortical cells, both of which can be invaded by Rhizobium entering through infection threads, and in derivatives of newly divided root inner cortical cells that establish the nodule primordium. We tested whether Rhizobium infection is required for triggering PsENOD12 gene expression by inducing nodule-like structures on Afghanistan pea roots with the auxin transport inhibitor N-(1-naphthyl)phthalamic acid (NPA). These nodule-like structures lack infection threads but resemble Rhizobium-induced nodules in other aspects. For one, both PsENOD2 and PsENOD12 transcripts were detected in these structures. PsENOD2 mRNA was localized by in situ hybridization to a zone equivalent to the nodule parenchyma of Rhizobium-induced nodules, whereas PsENOD12 transcripts were detected in a group of cells comparable to the nodule primordium of developing nodules. In addition, PsENOD12 mRNA was detected in uninfected root hairs 48 h after NPA treatment. These results indicate that infection is not a trigger for PsENOD12 gene expression in Afghanistan pea and rather suggest that the expression of the PsENOD2 and PsENOD12 genes is correlated with the differentiation of specific cell types in the developing nodule. 2 Present address: Department of Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands. 3 Present address: 4303 Medical Sciences IA, University of California, Davis, CA 95616. 4 Present address: Institute of Plant Biochemistry, O-4010 Halle, Germany. 1 Supported by National Science Foundation Grants DCB 87-03297 and DCB 90-21597. This content is only available as a PDF. © 1992 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)

Chéour, Foued; Arul, Joseph; Makhlouf, Joseph; Willemot, Claude

doi: 10.1104/pp.100.4.1656pmid: 16653181

Abstract Cabbage leaf discs (Brassica oleracea L., Capitata group) were floated adaxial side up in 0, 0.05, or 0.25 m CaCl2 solutions at 15°C for 14 d in the dark. To assess whether the delay of senescence by calcium treatment involved protection of membrane lipids, chlorophyll and protein content and the lipid composition of the membranes were determined during incubation. Chlorophyll and protein content decreased with time, in correlation with a reduction in the amount of phospholipids. The degree of unsaturation of phospholipids and free fatty acids decreased, whereas the ratio of sterol to phospholipid increased. The proportions of phospholipid classes did not change during senescence. The catabolism of phospholipids was delayed by 0.05 m calcium, but accelerated by 0.25 m, as compared to the untreated control. Based on the levels of the lipid intermediates, phospholipase D, phosphatidic acid phosphatase, lipolytic acyl hydrolase, and lipoxygenase appeared to be involved in the breakdown of phospholipids during senescence. Phospholipase D and phosphatidic acid phosphatase may be directly influenced by calcium. The calcium treatment apparently did not affect the activity of acyl hydrolase. Lipoxygenase, responsible for the peroxidation of the polyunsaturated fatty acids, was probably indirectly influenced by calcium. We conclude that the delay of senescence of cabbage leaf discs by calcium treatment involved protection of membrane lipids from degradation. 2 Present address: École Supérieure d'Industrie Alimentaire, 56 Rue Alain Savary, Tunis, Tunisia. 1 This research was supported by the Conseil des Recherches en Pêche et Agro-alimentaire du Québec and the Natural Sciences and Engineering Research Council of Canada. Contribution No. 263 from the Centre de Recherches et de Développement sur les Aliments, Agriculture Canada, Saint-Hyacinthe. Contribution No. 61 from the Centre de Recherches en Horticulture, Université Laval. This content is only available as a PDF. © 1992 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)

King, Graeme A.; Davies, Kevin M.

doi: 10.1104/pp.100.4.1661pmid: 16653182

Abstract Changes in mRNA activity in tips of harvested asparagus spears (Asparagus officinalis L.) held in light or dark for up to 48 h at 20°C were investigated as an initial step in elucidating the genetic response of asparagus spears to harvest. Total RNA was isolated from 30-mm tips of spears 180 mm in length at 0, 6, 12, 24, and 48 h after spear harvest and translated in vitro, and translation products were separated using both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional polyacrylamide gel electrophoresis. We detected 25 consistent changes in translatable mRNAs, involving both increase and decrease in mRNA abundance. The majority of the changes occurred within 12 h of harvest. Most of the changes were not light regulated. cDNA libraries were constructed from polyadenylated mRNA extracted from tips of spears at harvest (0 h) and after 12 h in the dark at 20°C. Differential hybridization screening of the cDNA libraries isolated nine cDNA clones whose corresponding transcripts had altered expression after harvest. Investigations of mRNA activity during spear development demonstrated that the changes detected were harvest related. Possible roles for the mRNAs corresponding to the isolated clones in tips of harvested spears are discussed. 1 Supported by a grant in aid from the Scientific Research Committee of the New Zealand Asparagus Council. This is Levin Horticultural Research Center paper No. 92/002. This content is only available as a PDF. © 1992 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)

Askerlund, Per; Evans, David E.

doi: 10.1104/pp.100.4.1670pmid: 16653183

Abstract Purification and functional reconstitution of a calmodulin-stimulated Ca2+-ATPase from cauliflower (Brassica oleracea L.) is described. Activity was purified about 120-fold from a microsomal fraction using calmodulin-affinity chromatography. The purified fraction showed a polypeptide at 115 kD, which formed a phosphorylated intermediate in the presence of Ca2+, together with a few polypeptides with lower molecular masses that were not phosphorylated. The ATPase was reconstituted into liposomes by 3-([cholamidopropyl]-dimethylammonio-)1-propanesulfonate (CHAPS) dialysis. The proteoliposomes showed ATP-dependent Ca2+ uptake and ATPase activity, both of which were stimulated about 4-fold by calmodulin. Specific ATPase activity was about 5 μmol min−1 (mg protein)−1, and the Ca2+/ATP ratio was 0.1 to 0.5 when the ATPase was reconstituted with entrapped oxalate. The purified, reconstituted Ca2+-ATPase was inhibited by vanadate and erythrosin B, but not by cyclopiazonic acid and thapsigargin. Activity was supported by ATP (100%) and GTP (50%) and had a pH optimum of about 7.0. The effect of monovalent and divalent cations (including Ca2+) on activity is described. Assay of membranes purified by two-phase partitioning indicated that approximately 95% of the activity was associated with intracellular membranes, but only about 5% with plasma membranes. Sucrose gradient centrifugation suggests that the endoplasmic reticulum is the major cellular location of calmodulin-stimulated Ca2+-pumping ATPase in Brassica oleracea inflorescences. 2 Present address: Department of Plant Biochemistry, University of Lund, P.O. Box 7007, S-220 07 Lund, Sweden. P.A. was supported by a Swedish Natural Science Research Council (NFR) postdoctoral fellowship, a Royal Society/Swedish Royal Academy of Sciences exchange fellowship, and a grant from the Swedish Institute. 3 Royal Society 1983 University Research Fellow. 1 Supported by a grant from the United Kingdom Agricultural and Food Research Council (AFRC) under its Plant Molecular Biology initiative. This content is only available as a PDF. © 1992 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)

Pfeffer, Philip E.; Rolin, Dominique B.; Kumosinski, Thomas F.; MacFall, Janet S.; Schmidt, Julian H.

doi: 10.1104/pp.100.4.1682pmid: 16653184

Abstract N2-fixing Bradyrhizobium japonicum nodules and cortical tissue derived from these nodules were examined in vivo by 31P nuclear magnetic resonance (NMR) spectroscopy. Perfusion of the viable nodules and excised cortical tissue with O2 followed by N2 or Ar caused a loss of orthophosphate (Pi) resonance magnetization associated with the major portion of acidic Pi (δ 0.9 ppm, pH 5.5) residing in the cortical cells. Resumption of O2 perfusion restored approximately 80% of the intensity of this peak. Detailed examination of the nuclear relaxation processes, spin-lattice relaxation time (T1), and spin-spin relaxation time (T2), under perfusion with N2 or Ar as opposed to O2, indicated that loss of signal was due to T1 saturation of the acidic Pi signal under the rapid-pulsed NMR recycling conditions. In excised cortical tissue, Pi T1, values derived from biexponential relaxation processes under perfusing O2 were 59% 3.72 ± 0.93 s and 41% 0.2 ± 0.08 s, whereas under N2 these values were 85% 7.07 ± 1.36 s and 15% 0.39 ± 0.07 s. The T1 relaxation behavior of whole nodule vacuolar Pi showed the same trend, but the overall values were somewhat shorter. T2 values for cortical tissue were also biexponential but were essentially the same under O2 (38% 0.066 ± 0.01 s and 63% 0.41 ± 0.08 s) and N2 (39% 0.07 ± 0.01 s and 61% 0.37 ± 0.01 s) perfusion. Soybean (Glycine max) root tissue as well as Pi solutions exhibited single exponential T1 decay values that were not altered by changes in the perfusing gas. These data indicate that oxygen induces a change in the physical environment of phosphate in the cortical cell tissue. Although under certain conditions oxygen has been observed to act as a paramagnetic relaxation agent, model T1 experiments demonstrate that O2 does not significantly influence Pi relaxation in this manner. Alternatively, we suggest that an increase in solution viscosity brought on by the production of an occlusion glycoprotein (under O2 perfusion) is responsible for the observed relaxation changes. This content is only available as a PDF. © 1992 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)

MacFall, Janet S.; Pfeffer, Philip E.; Rolin, Dominique B.; MacFall, James R.; Johnson, G. Allan

doi: 10.1104/pp.100.4.1691pmid: 16653185

Abstract The effects of selected gas perfusion treatments on the spinlattice relaxation times (T1) of the soybean (Glycine max) nodule cortex and inner nodule tissue were studied with 1H high resolution magnetic resonance microscopy. Three gas treatments were used: (a) perfusion with O2 followed by N2; (b) O2 followed by O2; and (c) air followed by N2. Soybean plants with intact attached nodules were placed into the bore of a superconducting magnet and a selected root with nodules was perfused with the gas of interest. Magnetic resonance images were acquired with repetition times from 50 to 3200 ms. The method of partial saturation was used to calculate T1 times on selected regions of the image. Calculated images based on T1 showed longer T1 values in the cortex than in the inner nodule during all of the gas perfusions. When nodules were perfused with O2-O2, there was no significant change in the T1 of the nodule between the two gas treatments. When the nodule was perfused with O2-N2 or air-N2, however, the T1 of both the cortex and inner nodule increased. In these experiments, the increase in T1 of the cortex was 2- to 3-fold greater than the increase observed in the inner nodule. A similar change in T1 was found in detached live nodules, but there was no change in T1 with selective gas perfusion of detached dead nodules. These observations suggest that cortical cells respond differently to selected gas perfusion than the inner nodule, with the boundary of T1 change sharply delineated at the interface of the inner nodule and the inner cortex. This content is only available as a PDF. © 1992 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)