Plant Physiology

Ray, Thomas B.; Black, Clanton C.

doi: 10.1104/pp.58.5.603pmid: 16659727

Abstract Phosphoenolpyruvate carboxykinase, EC 4.1.1.32 (PEPCK), was purified 43-fold from the grass Panicum maximum. Michaelis constants (Km) were determined for the exchange reaction, the carboxylation reaction, and the decarboxylation reaction. The Km values for oxaloacetate and ATP in the decarboxylation reaction were found to be lower than the Km values for the substrates used in the exchange reaction and in the carboxylation reaction. Phosphoenolpyruvate carboxylase was not detectable in the purified PEPCK preparation. Studies on the nucleotide specificity of the oxaloacetate decarboxylation reaction indicate that ATP serves as the best nucleotide for this reaction and that ADP is about 60% as effective as ATP. The pH optimum for decarboxylase activity is near 6.8. The decarboxylation reaction has a divalent cation requirement with both Mn2+ and Mg2+ needed for full activity. Temperature curves of the three PEPCK reactions indicate optimum activities between 38 and 45 C. There is a pronounced drop in the decarboxylation and carboxylation activities as the temperature is decreased from these optima. Below 30 C the energy of activation was 8.2 kcal/mol for the decarboxylation reaction. These studies are consistent with the proposal that under physiological conditions PEPCK catalyzes the decarboxylation of oxaloacetate in the bundle sheath cells of Panicum maximum leaves during C4 dicarboxylic acid photosynthesis. 1 This research was supported in part by National Science Foundation Grant BMS 74-24230 and by a co-operative agreement with Cotton, Inc. This content is only available as a PDF. © 1976 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)

Zimmermann, Ulrich; Steudle, Ernst; Lelkes, Peter I.

doi: 10.1104/pp.58.5.608pmid: 16659728

Abstract The electrical membrane resistance ρ0 of the marine alga Valonia utricularis shows a marked maximum in dependence on the turgor pressure. The critical pressure, Pc, at which the maximum occurs, as well as its absolute value, ρ0max, are strongly volume-dependent. Both Pc and ρ0max, increase with decreasing cell volume. It seems likely, that these relationships reflect the elastic properties of the cell wall, because the volumetric elastic modulus, ε, is also volume-dependent, increasing hyperbolically with cell volume. Both Pc and ρ0max can be affected by external application of indole-3-acetic acid at concentrations of 2·10−7m to 2 ·10−5m. The critical pressure is shifted by 1.2 to 6 bars toward higher pressures and the maximum membrane resistance increased up to 5.6-fold. During the course of the experiments (up to 4 hours), however, IAA had no effect on the volumetric elastic modulus, ε. The maximum in membrane resistance is discussed in terms of a pressure-dependent change of potassium fluxes. The volume dependence of P c and ρ0max suggests that not only turgor pressure but also ε must be considered as a regulating parameter during turgor pressure regulation. On this basis a hypothesis is presented for the transformation of both, a pressure signal and of changes in the elastic properties of the cell wall into alterations of ion fluxes. It is assumed that the combined effects of tension and compression of the membranes as well as the interaction between membrane and cell wall opposingly change the number of transport sites for K+ providing a turgor-sensing mechanism that regulates ion fluxes. The IAA effects demonstrated are consistent with this view, suggesting that the basic mechanisms for turgor pressure regulation and growth regulation are similar. Any relation connecting growth rate with turgor pressure should be governed by two parameters, i.e. by a yielding pressure, at which cell growth starts, and by the critical pressure, at which it ceases again. 1 This research was supported by a grant from the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 160. This content is only available as a PDF. © 1976 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)

Lin, Chu-Yung; Chen, Yih-Ming; Guilfoyle, Tom J.; Key, Joe L.

doi: 10.1104/pp.58.5.614pmid: 16659729

Abstract RNA polymerase I and II activities were measured in tissues of the soybean (Glycina max, var. Wayne) hypocotyl where dramatic changes in the relative level of RNA synthesis are associated with normal and auxin-induced growth transitions. When assayed in isolated nuclei, the activity of RNA polymerase I changed much more than the activity of RNA polymerase II during these growth transitions. The activity of RNA polymerase I expressed in the nuclei generally showed a positive correlation with the relative level of RNA synthesis (i.e. accumulation) of that tissue. Following solubilization of the RNA polymerases from these isolated nuclei and fractionation of them on DEAE-cellulose, the activity of RNA polymerase I relative to that of RNA polymerase II showed smaller changes during these growth transitions than when assayed in the nuclei. Thus, these data indicate that the activity of RNA polymerase I is significantly modulated in the nucleus, up or down depending upon the growth state, during growth transitions in the soybean in addition to lesser changes which occur in the apparent level of the enzyme. 1 Present address: Department of Botany, National Taiwan University, Taipei, Taiwan. This content is only available as a PDF. © 1976 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)

Tárrago, Jorge Fernández; Nicolás, Gregorio

doi: 10.1104/pp.58.5.618pmid: 16659730

Abstract Starch, total amylolytic and phosphorylase activities were determined in lentil cotyledons during the first days of germination. Several independent criteria show that the amylolytic activity is due mainly to an amylase of the α type. Starch is degraded slowly in the first days; during this time, α- and β-amylase activity are very low, while phosphorylase increases and reach a peak on the 3rd day. On the 4th day, there is a more rapid depletion of starch which coincides with an increase in α-amylase activity. By polyacrylamide gel electrophoresis of the crude starch-degrading enzyme, five bands were obtained: one phosphorylase, three α-amylases, and one β-amylase. Based on their heat lability or heat stability, two sets of α-amylase seem to exist in lentil cotyledons. 1 Present address: Departamento de Fisiología Vegetal, Universidad de Salamanca, Facultad de Ciencias, Spain. This content is only available as a PDF. © 1976 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)

Criswell, Jerome G.; Havelka, Ulysses D.; Quebedeaux, Bruno; Hardy, Ralph W. F.

doi: 10.1104/pp.58.5.622pmid: 16659731

Abstract The N2-fixing legume nodule requires O2 for ATP production; however, the O2 sensitivity of nitrogenase dictates a requirement for a low pO2 inside the nodule. The effects of long term exposures to various pO2s on N2[C 2 H 2] fixation were evaluated with intact soybean (Glycine max [L.] Merr., var. Wye) plants. Continuous exposure of their rhizosphere to a pO2 of 0.06 atmospheres initially reduced nitrogenase activity by 37 to 45% with restoration of original activity in 4 to 24 hours and with no further change in tests up to 95 hours; continuous exposure to 0.02 atmosphere of O2 initially reduced nitrogenase activity 72%, with only partial recovery by 95 hours. Similar exposures to a pO2 of 0.32 atmospheres had little effect on N2[C 2 H 2] fixation; a pO2 of 0.89 atmospheres initially reduced nitrogenase activity by 98% with restoration to only 14 to 24% of that of the ambient O2 controls by 95 hours. Re-exposure to ambient pO2 of plants adapted to nonambient pO2s reduced N2[C 2 H 2] fixation to similar magnitudes as the reductions which occurred upon initial exposure to variant pO2 conditions, and a time period was required to readapt to ambient O2. It is concluded that the N2[C 2 H 2]-fixing system of intact soybean plants is able to adapt to a wide range of external pO2s as probably occur in soil. We postulate that this occurs through an undefined mechanism which enables the nodule to maintain an internal pO2 optimal for nitrogenase activity. 1 Contribution No. 2382, Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours & Co. Inc., Wilmington, Del. 19898. This content is only available as a PDF. © 1976 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)

Edwards, Miriam

doi: 10.1104/pp.58.5.626pmid: 16659732

Abstract Charlock (Sinapis arvensis L.) seeds were imbibed with 10 mm GA3 for 24 hours at 0 C. After equilibration at 25 C, a 5-fold increase in radioactivity in the amino acids labeled from 2-14C-acetate was observed within 2 hours. The total amount of amino acids was reduced to half, and the specific radioactivity increased approximately 10-fold, indicating a diversion of metabolites for amino acid and protein synthesis in GA3-treated seeds. The rate of incorporation of l-14 C-leucine into protein was doubled. Autoradiographs showed that enhancement of protein synthesis was localized in the shoot and root meristems, the developing vascular tissues, and in the endosperm cells inside the testa. 1 This research was carried out at Michigan State University, Atomic Energy Commission Plant Research Laboratory under Contract No. AT (11-1)-1338, and supported by Science Research Council Grant No. B/ SR/5659. This content is only available as a PDF. © 1976 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)

Rhodes, Patsy R.; Matsuda, Kaoru

doi: 10.1104/pp.58.5.631pmid: 16659733

Abstract Measurements of the water status of various plant tissues exposed to differing levels of salts for 1 hour were made using the recently developed Campbell J-14 press (Logan, Utah). Values obtained with the press were found to correlate well with estimates of relative water content, and experiments with 3-day-old pumpkin seedlings showed that detectable changes in press values of cotyledon tissues could be obtained within 5 minutes following salt- or desiccation-induced stress. Polyribosome levels were measured in tissues from various plant species following short duration water stress. A small reduction in polyribosome percentage was obtained in cotyledons of 3-day-old pumpkin seedlings which were exposed to an osmotic potential (NaCl) of −4 bar for 10 minutes, but more pronounced changes were found after 30 minutes of stress. Shoot tissues of peas, barley, wheat, and safflower following 20- or 30-minute salt- or desiccation-induced stress yielded extracts with reduced polyribosome levels; however, 30 minutes of exposure of cotton and pumpkin seedlings to −6 bars did not result in altered polyribosome percentage of extracts from roots. Studies using shoot tissues from pumpkins and peas showed that polyribosome percentages and growth rates of both plants were reduced in proportion to loss of tissue water. These plants differed in their sensitivity to stress in that polyribosome content and growth rate reductions were both nearly twice as severe per unit of water loss in peas as in pumpkins. These data along with those obtained by others suggest that growth rate reductions may be directly proportional to reductions in polyribosome levels during water stress. 1 This work was supported by Western Regional Research Project W- 67. The University of Arizona Agriculture Experiment Station, Journal Paper No. 2602. This content is only available as a PDF. © 1976 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)

Coster, Hans G. L.; Steudle, Ernst; Zimmermann, Ulrich

doi: 10.1104/pp.58.5.636pmid: 16659734

Abstract Experimental evidence is reviewed which shows that the cell membrane is compressible by both mechanical and electrical forces. Calculations are given which show that significant changes in the thickness of cell membranes can occur as a result of (a) direct compression due to the turgor pressure; (b) indirect effects due to the stretching of the cell wall; and (c) the stresses induced by the electric field in the membrane. Such changes in the membrane thickness may provide the pressure-transducing mechanism required for osmoregulation and growth. An important feature of the model is that this pressure transduction can occur not only in the plasmalemma (where there is a pressure gradient), but also in the tonoplast. 1 This work was supported by a grant from the Deutsche Forschungs-gemeinschaft, Sonderforschungsbereich 160, to U. Z., and by a grant from the Australian Research Grants Committee to H. G. L. C. Part of this work was done while H. G. L. C. was on leave at the Kernforschungsanlage Jülich and when U. Z. was on leave at The University of New South Wales. This content is only available as a PDF. © 1976 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)

Baker, James Earl

doi: 10.1104/pp.58.5.644pmid: 16659735

Abstract The levels of superoxide dismutase (SOD) activity in extracts of preclimacteric apple, banana, avocado, and tomato fruits were not greatly different than in extracts of postclimacteric fruits. The results indicate that no major quantitative change in SOD occurs in fruits with or preceding the onset of senescence. Tomato fruit SOD was studied in more detail, and was found largely in the soluble fraction, and to a lesser extent in the mitochondrial and plastid fractions. The soluble fraction was purified by ammonium sulfate fractionation, column chromatography, and isoelectric focusing. Isoelectric focusing separated SOD from contaminating peroxidases. The purified tomato SOD showed an apparent molecular weight of 31,500 determined by gel filtration. Polyacrylamide gel electrophoresis of this preparation indicated two SOD components corresponding to two protein bands, one of which stained more intensely than the other. The purified tomato enzyme was inhibited 90% by 1 mm KCN. This content is only available as a PDF. © 1976 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)

Gonzalez, Alfredo; Brecht, Patrick E.; Rehkugler, Carole C.

doi: 10.1104/pp.58.5.648pmid: 16659736

Abstract Free methionine levels in rin and normal tomato fruits were determined microbiologically. Similar levels (1750 μg/100 g fresh weight) for mature green fruits of both rin and a normal isogenic line suggest that the lack of ripening of rin fruits is not due to low methionine levels. Methionine levels of mature green rin and normal fruits were 1750 μg/ 100 g fresh weight. Normal fruits ripened either on or off the vine were 2860 and 2500 μg/100 g fresh weight, respectively. The rin fruits which were left on the plant or held in air at 20 C until soft and yellow were significantly lower in methionine than C2H4-treated rin fruits or any normal fruits. Harvested rin and normal fruits held at 20 C in continuously applied ethylene (10 μl/l) had higher methionine levels than comparable air controls; levels in treated rin fruits were significantly higher than those in normal fruits. 2 Vegetable Crops Department. Paper No. 721. 3 Lab of Microbiology. 1 This study was supported in part by funds from CONACYT (Mexican Government). This content is only available as a PDF. © 1976 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)