Plant Physiology

Oaks, Ann; Jones, Karen; Misra, Santosh

doi: 10.1104/pp.63.5.793pmid: 16660814

Abstract Glutamate synthase (EC 2.6.1.53) has been examined in developing endosperms and roots of maize. KCl is required for maximum activity in each tissue. The effect with KCl is seen with buffer strength of 25 to 100 millimolar in the assay. The optimum concentration for the enzyme from endosperm is 20 millimolar and for the enzyme from root tissue the saturating concentration is about 20 millimolar. In root material the enzyme is labile but activity can be restored if KCl is added to the assay. Divalent cations such as Mg2+ or Mn2+ also activate the enzyme to some extent. In each case NADH or NADPH can serve as reductant. The reaction is insensitive to α-aminooxyacetate, but is inhibited by glutamate, the glutamate analogs methionine sulfoximine and methionine sulfone, and by the glutamine analogs azaserine and albizziin. 2 To whom reprint requests should be addressed. 1 This work was supported by grants from the National Research Council of Canada (A-2818) and Agriculture Canada (AC-7040). This content is only available as a PDF. © 1979 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)

Smillie, Robert M.; Nott, Robyn

doi: 10.1104/pp.63.5.796pmid: 16660815

Abstract Tomato leaves were detached and stored at 0 C for various periods of time. Chloroplasts were isolated from the leaves and their photoreductive activities were determined. Comparisons were made between two altitudinal forms of the wild tomato Lycopersicon hirsutum Humb. and Bonpl. (a tropical lowlands form and a highlands form adapted to growth at 3,100 meters), and two cultivars of the domestic tomato L. esculentum Mill. In each case the capacity of the isolated chloroplasts to photoreduce ferricyanide declined linearly with time of storage of the leaves at 0 C, but not at 10 C. This injury developed more slowly in the high altitudinal form of the wild tomato compared with the low altitudinal form and the two domestic cultivars indicating an enhanced resistance toward chilling injury in the tomato from 3,100 meters. Chloroplast activity declined in green tomato fruit held at 0 C, at about the same rate as in the chilled leaves. Measurements of photochemical activities in the isolated chloroplasts and in vivo measurements of cytochrome-554 photooxidation in chilled leaves showed that the site of action of the chilling effect was water donation to photosystem II. The chilling-induced impairment of photoreductive activity in chloroplasts provides a useful assay for detecting and measuring differences in the susceptibility of plants to chilling injury. This content is only available as a PDF. © 1979 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)

McKersie, Bryan D.; Thompson, John E.

doi: 10.1104/pp.63.5.802pmid: 16660816

Abstract The effects of stigmasterol, sitosterol, campesterol, and cholesterol on the phase properties of dipalmitoylphosphatidylcholine bilayers have been compared by differential scanning calorimetry and x-ray diffraction. The sterols were equally effective at progressively reducing the cooperativity and the enthalpy of the dipalmitoylphosphatidylcholine phase transition as their concentrations in the bilayer were increased. Moreover, both differential scanning calorimetry and x-ray diffraction indicated that the dipalmitoylphosphatidylcholine transition was eliminated by each of the sterols when they were present at a concentration of 33 mole%. This indicates that the interaction between phospholipid and both plant and animal sterols is stoichiometric, each sterol associating with two phospholipid molecules. At concentrations above 33 mole% the sterols were no longer completely solvated by the phospholipid, and sterol-sterol interaction resulted. Cholesterol, even at concentrations as high as 50 mole%, did not disrupt the lamellar structure of the bilayer. When these high concentrations of plant sterols were intercalated into the phospholipid, crystallinity, which presumably derives from sterol-sterol interaction, was detectable in the bilayer by x-ray diffraction. This observation is consistent with previous reports to the effect that the C17 chains of the plant sterols render them less soluble in phospholipid than is cholesterol. It is clear that this solvation difference is of insufficient magnitude to affect the stoichiometry of dipalmitoylphosphatidylcholine-sterol interaction, but it could well account for the less effective modulation of lipid bilayer permeability exhibited by plant sterols in comparison with cholesterol. 2 Present address: Department of Crop Science, University of Guelph, Ontario, Canada. 1 This research was supported by the National Research Council of Canada. This content is only available as a PDF. © 1979 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)

Walton, Jonathan D.; Earle, Elizabeth D.; Yoder, Olen C.; Spanswick, Roger M.

doi: 10.1104/pp.63.5.806pmid: 16660817

Abstract Helminthosporium maydis race T (HMT) toxin caused a reduction in the steady-state ATP levels when leaf mesophyll protoplasts isolated from maize containing Texas male-sterile (T) but not male-fertile (N) cytoplasm were incubated in the dark. At a toxin concentration 10 times the mean effectived dose for inhibition of root growth, the ATP levels began to fall in 30 to 90 seconds, fell by 50% in about 4 minutes, and reached 23% of the original levels in 100 minutes. This is faster than any previously observed response of whole cells or tissues to HMT toxin. In protoplasts incubated in the light, ATP levels were 25% higher than in the dark and were either unaffected or only slightly diminished by toxin. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, overcame the effect of light on both toxin-treated and control protoplasts. Oligomycin, an inhibitor of mitochondrial ATP synthesis, mimicked the effects of toxin in the dark, in the light, and in the light plus DCMU, but it was not specific for T cytoplasm. During the first 24 hours of culture, ATP levels in control protoplasts increased in both the light and dark. In the dark, ATP was not detectable after 24-hour incubation in the presence of toxin, whereas in the light a substantial amount of ATP remained. Our results are compatible with the hypothesis that mitochondria in vivo are inhibited by HMT toxin. Other responses of cells and tissues to toxin can be explained in terms of reduced ATP levels. 2 National Science Foundation Graduate Fellow. Present address: Department of Biological Sciences, Stanford University, Stanford, California 94305. 1 Supported by Rockefeller Foundation Grant 75002 and National Science Foundation Grants PCM 75-15277 and PCM 77-04645. This content is only available as a PDF. © 1979 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)

Lieberman, Morris; Wang, Shiow Y.; Owens, Lowell D.

doi: 10.1104/pp.63.5.811pmid: 16660818

Abstract Cortex tissue from postclimacteric `Golden Delicious' apples (Malus domestica, Borkh.) stored at 0 C for 9 months after harvest were induced to form callus in vitro. Cell suspension cultures were subsequently formed from calli. Of five media tested, only the medium of Schenk and Hildebrandt (Can J Bot 1972, 50: 192) and that of Uchimiya and Murashige (Plant Physiol 1974, 54: 936) allowed callus formation. During growth both the callus and cell cultures produced ethylene in a pattern which showed a rapid rise and then a fall as the culture grew. 14C-Labeled methionine was converted to labeled ethylene by the cell suspension cultures, which also could be inhibited from producing ethylene by a rhizobitoxine analog or free radical scavengers. Ethylene production in these cultures, like that in intact fruit tissue slices, could be stimulated by IAA or suppressed by N6-(γ,γ-dimethylallyl) adenosine and GA3. This content is only available as a PDF. © 1979 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)

Bethlenfalvay, Gabor J.; Phillips, Donald A.

doi: 10.1104/pp.63.5.816pmid: 16660819

Abstract Hydrogenase activity of root nodules in the symbiotic association between Pisum sativum L. and Rhizobium leguminosarum was determined by incubating unexcised nodules with tritiated H2 and measuring tissue HTO. Hydrogenase activity saturated at 0.50 millimolar H2 and was not inhibited by the presence of 0.10 atmosphere C2H2, which prevented H2 evolution from nitrogenase. Total H2 production from nitogenase was estimated as net H2 evolution in air plus H2 exchange in 0.10 atmosphere C2H2. Although such an estimate of nitrogenase function may not be quantitatively exact, due to uncertain relationships between H2 exchange and H2 uptake activity of hydrogenase, differences observed in H2 exchange under various conditions represent an indication of changes in hydrogenase activity. Hydrogenase activity was lower in associations grown under higher photosynthetic photon flux densities and decreased relative to total H2 production by nitrogenase. Total H2 production and hydrogenase activity were maximum 28 days after planting. Thereafter, hydrogenase activity and H2 production declined, but the potential proportion of nitrogenase-produced H2 recovered by the uptake hydrogenase system increased. Of five R. leguminosarum strains tested two possessed hydrogenase activity. Strains which had the potential to reassimilate H2 had significantly higher rates of N2 reduction than those which did not exhibit hydrogenase activity. 2 Present address: Department of Plant Pathology and Crop Physiology, Louisiana State University, Baton Rouge, La. 70803. 1 This material is based on research supported by National Science Foundation Grants No. PRF 77-07301 A01 and PCM 78-01146. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the National Science Foundation. This content is only available as a PDF. © 1979 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, Gerald E.; Lilley, Ross McC.; Craig, Stewart; Hatch, Marshall D.

doi: 10.1104/pp.63.5.821pmid: 16660820

Abstract A procedure is described for isolating and purifying mesophyll protoplasts and bundle sheath protoplasts of the C4 plant Panicum miliaceum. Following enzymic digestion of leaf tissue, mesophyll protoplasts and bundle sheath protoplasts are released and purified by density centrifugation. The lower density of mesophyll protoplasts allowed rapid separation of the two protoplast types. Evidence for separation of mesophyll protoplasts and bundle sheath protoplasts (up to 95% purity) is provided from light microscopy (based on size difference in both chloroplasts and protoplasts), levels of marker enzymes in the preparations (i.e. pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase for mesophyll and ribulose-1,5-bisphosphate carboxylase for bundle sheath), and differences in substrate-dependent O2 evolution by chloroplasts isolated from protoplasts. Chloroplasts were isolated from protoplasts by several passages of the protoplasts through a 20-micrometer nylon mesh. Mesophyll chloroplasts were judged approximately 90 to 95% intact and bundle sheath chloroplasts 80 to 90% intact based on retention of chloroplast marker enzymes and the ferricyanide test for intactness. It was necessary to include 10 millimolar MgCl2 in media for osmotically shocking the chloroplasts in order to obtain maximum and linear rates of ferricyanide-dependent O2 evolution. Chloroplasts isolated from mesophyll protoplast preparations had low rates of light-dependent O2 evolution in the presence of 10 millimolar NaHCO3 (0.13 micromoles per milligram chlorophyll per minute) in comparison to bundle sheath chloroplasts (1 to 2.5 micromoles per milligram chlorophyll per minute). The mesophyll chloroplasts catalyze high rates of 3-phosphoglycerate-dependent O2 evolution (2 to 4 micromoles per milligram chlorophyll per minute). Orthophosphate but not phosphoenolpyruvate inhibited the 3-phosphoglycerate-dependent O2 evolution by the mesophyll chloroplasts. Rates of O2 evolution were much higher with mesophyll than with bundle sheath chloroplasts in the presence of pyruvate plus oxaloacetate. The results are discussed in relation to the proposed function of these chloroplasts during C4 photosynthesis. 1 Research was performed at Division of Plant Industry, CSIRO, Canberra City, Australia in part while G. E. Edwards was on study leave under a Guggenheim Fellowship. Partial support was provided by National Science Foundation Grant PCM 77-09384 to G. E. E. This content is only available as a PDF. © 1979 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)

Giaquinta, Robert T.

doi: 10.1104/pp.63.5.828pmid: 16660821

Abstract Several physiological processes were studied during sugar beet root development to determine the cellular events that are temporally correlated with sucrose storage. The prestorage stage was characterized by a marked increase in root fresh weight and a low sucrose to glucose ratio. Carbon derived from 14C-sucrose accumulation was partitioned into protein and structural carbohydrate fractions and their amino acid, organic acid, and hexose precursors. The immature root contained high soluble acid invertase activity (V max 20 micromoles per hour per milligram protein; K m 2 to 3 millimolar) which disappeared prior to sucrose storage. Sucrose storage was characterized by carbon derived from 14C-sucrose uptake being partitioned into the sucrose fraction with little evidence of further metabolism. The onset of storage was accompanied by the appearance of sucrose synthetase activity (V max 12 micromoles per hour per milligram protein; K m 7 millimolar). Neither sucrose phosphate synthetase nor alkaline invertase activities were detected during beet development. Intact sugar beet plants (containing a 100-gram beet) exported 70% of the translocate to the beet, greater than 90% of which was retained as sucrose with little subsequent conversions. 1 Contribution No. 2598 from Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898. This content is only available as a PDF. © 1979 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)

Elliott, William M.

doi: 10.1104/pp.63.5.833pmid: 16660822

Abstract The control exerted by light on leaf and stem growth in light-grown Alaska pea seedlings was studied during the main photoperiod. Two high irradiance responses were observed. The action spectrum for one had a single sharp peak at 600 nanometers. The action spectrum for the other showed a broad peak between 440 and 470 nanometers. These two light responses must be activated simultaneously for any inhibition of stem growth or promotion of leaf growth. Both action spectra may be explained in terms of the high irradiance response of phytochrome. 1 This research was supported by a Hartwick College faculty research grant. This content is only available as a PDF. © 1979 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)

Janes, Harry W.; Rychter, Anna; Frenkel, Chaim

doi: 10.1104/pp.63.5.837pmid: 16660823

Abstract Ethylene, cyanide gas, and volatalized ethanol, acetaldehyde, and acetic acid were applied in a continuous flow to whole potato tubers. Freshly cut slices were obtained periodically during the treatment, and showed a progressive development of a cyanide-resistant respiration. The application of the employed volatiles in 100% O2 accelerated the onset and the magnitude of the cyanide-resistant respiration. These results show that, similar to ethylene and cyanide, the application of ethanol, acetaldehyde, or acetic acid can also lead to the development of cyanide-resistant respiration in whole potato tubers, and that this type of respiration is retained in freshly cut slices. 1 Present address: Institute of Botany, University of Warszawa, Warsaw, Poland. This content is only available as a PDF. © 1979 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)