Plant Physiology

Flügge, U. Ingo; Freisl, Martha; Heldt, Hans W.

doi: 10.1104/pp.65.4.574pmid: 16661240

Abstract The relationship between the rate of orthophosphate (Pi) transport into the stroma and the rate of CO2 fixation by intact chloroplasts was investigated. High Pi concentrations in the medium lead to a depletion of stromal metabolites, due to excessive Pi transport into the stroma, resulting in the inhibition of CO2 fixation. This inhibitory effect of Pi is released by inhibitors of Pi transport, such as pyrophosphate, citrate or pyridoxal-5-phosphate. The latter compound appeared to be specially valuable in inhibiting Pi transport without affecting stromal reactions. The Pi optima of CO2 fixation were studied when the rate of CO2 fixation or the rate of Pi transport was varied by the application of specific inhibitors. For optimal performance the rates of CO2 fixation and Pi transport have to be matched in such a way, that transport neither limits nor exceeds CO2 fixation. This accounts for the large variation in the Pi optima for CO2 fixation by different chloroplast preparations. 2 Present address: Lehrstuhl für Biochemie der Pflanze der Universität Göttingen, Untere Karspüle 2, 3400 Göttingen, Federal Republic of Germany. 1 This work has been supported by the Deutsche Forschungsgemeinschaft. This content is only available as a PDF. © 1980 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)

Rauser, Wilfried E.; Samarakoon, Ananda B.

doi: 10.1104/pp.65.4.578pmid: 16661241

Abstract Vein loading in unifoliate leaves of white bean seedlings exposed to excess Co2+, Ni2+, or Zn2+ for 1 to 4 days was studied by incubating leaf discs in [14C]sucrose. The discs from plants exposed to metal exhibited an increased total uptake of radiosucrose but reduced vein loading. Differences between treatments due to infiltration of disc margins were eliminated by analyzing 7-millimeter discs cut from the center of incubated 14-millimeter discs. Uptake of radiosucrose was greater particularly in discs from seedlings exposed to excess Ni2+ and Zn2+. The effect increased as exposure of the seedlings to metal increased up to 4 days. Autoradiographs showed vein loading in control leaf tissues with most of the radiosucrose accumulating in minor veins and little remaining in the mesophyll. In discs from metal-treated plants, most of the sucrose remained in the mesophyll without accumulating preferentially in the minor veins. This effect was evident within 24 hours of exposure to excess metal and intensified with longer exposures to metal. The inhibition of vein loading was also evident in situ. Both the preferential accumulation of sucrose into the minor veins of control tissues and the accumulation into mesophyll of metal exposed tissues were sensitive to 2,4-dinitrophenol and the blockage of sulfhydryl groups. It is concluded that the inhibition of vein loading contributes markedly to the observed toxicological effects of reduced photoassimilate export and of accumulation of carbohydrates in fully expanded leaves of bean seedlings exposed to excess metal ions. 1 This study was supported by grant A4921 to W. E. R. from the Natural Sciences and Engineering Research Council of Canada. This content is only available as a PDF. © 1980 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)

Hagar, William G.; Freeberg, John A.

doi: 10.1104/pp.65.4.584pmid: 16661242

Abstract The photosynthetic rates of intact sporophytes or gametophytes of the fern Todea barbara grown in sterile culture were measured using an infrared gas analyzer. Sporophytes consisted of single whole plants with roots and leaves grown in tubes of agar. Gametophytes were grown as several plants covering the surface of the agar. Sporophytes had photosynthetic rates at light saturation of 8.50 microliters CO2 per hour per milligram dry weight and 1,300 microliters CO2 per hour per milligram chlorophyll, whereas rates for gametophytes were lower, 2.36 microliters CO2 per hour per milligram dry weight and 236 microliters CO2 per hour per milligram chlorophyll. O2 inhibited the photosynthetic rates of both plants to a degree typical of C-3 plants. The light-saturated photosynthetic rates of sporophytes increased 42% and gametophytes increased 27% when the O2 concentration was changed from 21 to 1%. This content is only available as a PDF. © 1980 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)

Brown, Daniel C. W.; Thorpe, Trevor A.

doi: 10.1104/pp.65.4.587pmid: 16661243

Abstract Shoot-forming tobacco callus is found to have high levels of adenosine phosphates and NAD+, and a low energy charge during meristemoid and shoot primordium formation. NADH levels are low and show little change during this period. There is a decline in the content of NADPH to nondetectable levels during the process, and a transient increase of NADP+ is observed early in culture. These patterns are indicative of a shift to a more intensive rate of metabolism during meristemoid and shoot primordium formation and apparently reflect the requirement for energy and reducing power during organ initiation. 1 Supported by Natural Sciences and Engineering Research Council of Canada Grant A-6467 to T. A. T. This content is only available as a PDF. © 1980 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)

Arron, Geoffrey P.; Edwards, Gerald E.

doi: 10.1104/pp.65.4.591pmid: 16661244

Abstract Potato tuber mitochondria oxidized exogenous NADH and exogenous NADPH at similar rates; the electron transfer inhibitor rotenone did not inhibit the oxidation of either substrate. Submitochondrial particles, prepared from potato tuber mitochondria, exhibited a greater capacity to oxidize NADH than NADPH; rotenone inhibited the oxidation of NADH by 29% and the oxidation of NADPH by 16%. The oxidation of both NADH and NADPH by potato mitochondria exhibited pH optima of 6.8, and although substantial NADH oxidase activity was observed at pH 8.0, little NADPH oxidase activity was detected at that pH. The oxidation of NADPH by the mitochondria was more sensitive to inhibition by EDTA than was the oxidation of NADH. The sulfhydryl reagents N-ethylmaleimide, p-chloromercuribenzoate, p-chloromercuriphenyl sulfonic acid, and mersalyl inhibited the oxidation of exogenous NADPH by the mitochondria whereas NADH oxidation was unaffected at similar concentrations of inhibitor. The data suggest that exogenous NADPH is oxidized by potato mitochondria via a dehydrogenase primarily situated on the outer face of the inner mitochondrial membrane that is neither the dehydrogenase involved with endogenous NADH oxidation nor with exogenous NADH oxidation. 1 This work was supported by the College of Agriculture and Life Sciences, University of Wisconsin, Madison, and by National Science Foundation Grant PCM 77-09384 to G. E. E. This content is only available as a PDF. © 1980 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)

Orihuel-Iranzo, Benito; Campbell, Wilbur H.

doi: 10.1104/pp.65.4.595pmid: 16661245

Abstract The cotyledons of soybean begin to develop photosynthetic capacity shortly after emergence. The cotyledons develop nitrate reductase (NR) activity in parallel with an increase in chlorophyll and a decrease in protein. In crude extracts of 5- to 8-day-old cotyledons, NR activity is greatest with NADH as electron donor. In extracts of older cotyledons, NR activity is greatest with NADPH. Blue-Sepharose was used to purify and separate the NR activities into two fractions. When the blue-Sepharose was eluted with NADPH, NR activity was obtained which was most active with NADPH as electron donor. Assays of the NADPH-eluted NR with different concentrations of nitrate revealed that the highest activity was obtained in 80 millimolar KNO3. Thus, this fraction has properties similar to the low nitrate affinity NAD(P)H:NR of soybean leaves. When 5- to 8-day-old cotyledons were extracted and purified, further elution of the blue-Sepharose with KNO3, subsequent to the NADPH elution, yielded an NR fraction most active with NADH. Assays of this fraction with different nitrate concentrations revealed that this NR had a higher nitrate affinity and was similar to the NADH:NR of soybean leaves. The KNO3-eluted NR fraction which was purified from the extracts of 9- to 14-day-old cotyledons, was most active with NADPH. The analysis of these fractions prepared from the extracts of older cotyledons indicated that residual NAD(P)H:NR contaminated the NADH:NR. Despite this complication, the pattern of development of the purified NR fractions was consistent with the changes observed in the crude extract NR activities. It was concluded that NADH:NR was most active in young cotyledons and that as the cotyledons aged the NAD(P)H:NR became more active. 1 This work was supported by National Science Foundation Grant PCM 76-18803 and by a cooperative agreement with the Mobil Chemical Company. This content is only available as a PDF. © 1980 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)

Gilkes, Neil R.; Chrispeels, Maarten J.

doi: 10.1104/pp.65.4.600pmid: 16661246

Abstract Homogenates of mung bean cotyledons were subjected to equilibrium density centrifugation on linear sucrose gradients and the positions of the various organelles determined by assay of marker enzymes. Measurement of phospholipid distribution on such gradients showed that the major peak of phospholipid at a density of 1.11 to 1.13 grams per cubic centimeter coincided with the position of the endoplasmic reticulum (ER), confirming ultrastructural evidence that storage parenchyma cells are rich in ER. Germination and seedling growth were accompanied by a rapid decline in ER-associated phospholipid but a marked increase in the ER marker enzyme NADH cytochrome c reductase. Similar experiments with developing seeds indicated that the amount of ER-associated phospholipid increases during cotyledon expansion reaching a maximum during seed maturation. There was no subsequent decline during seed desiccation, instead ER-associated phospholipid levels were maintained in the dry seed until germination when catabolism was initiated 12 to 24 hours after the start of imbibition. This timing indicates that the observed ER breakdown is not an expression of the overall senescence of the cotyledons, but may represent the dismantling of the extensive rough ER used for reserve protein synthesis during cotyledon development. 2 To whom requests for reprints should be addressed. 1 Supported by grants from the National Science Foundation (Metabolic Biology). This content is only available as a PDF. © 1980 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)

Emerich, David W.; Albrecht, Steve L.; Russell, Sterling A.; Ching, Temay; Evans, Harold J.

doi: 10.1104/pp.65.4.605pmid: 16661247

Abstract Oxyleghemoglobin was used to supply low concentrations of O2 to H2-oxidizing bacteroids from Rhizobium japonicum USDA 122 DES. The H2 oxidation system of these bacteroids was capable of effectively utilizing O2 at the low concentrations of O2 expected to be found in soybean nodules. Apparent Km values of approximately 10 nanomolar O2 have been calculated for the oxyhydrogen reaction. These values include the Km values for both H2 oxidation and endogenous substrate oxidation. Even in the presence of oxyleghemoglobin, H2 additions stimulated C2H2 reduction, reduced the rate of endogenous respiration and maintained the ATP contents of bacteroids. In our reconstituted oxyleghemoglobin and bacteriod system, we estimate that the H2 oxidation system is capable of recycling all of the H2 evolved during the N2 fixation process. 2 Present address: Plant Science Unit, ARS Southern Region, Department of Agronomy, 304 Newell Hall, University of Florida, Gainesville, Florida 32611. 3 Department of Agronomic Crop Science, Oregon State University. 1 This research was supported by the National Science Foundation Grant PCM 77-08784, postdoctoral fellowships to D. W. E. from the Rockefeller Foundation and the National Science Foundation (SP 178-15650), and also the research was supported by the Oregon Agricultural Experiment Station from which this is Technical Paper No. 5263. This content is only available as a PDF. © 1980 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)

Triplett, Eric W.; Barnett, Neal M.; Blevins, Dale G.

doi: 10.1104/pp.65.4.610pmid: 16661248

Abstract Experiments were designed to study the importance of organic acids as counterions for K+ translocation in the xylem during excess cation uptake. A comparison was made of xylem exudate from wheat seedlings treated 72 hours with either 1.0 millimolar KNO3 or 0.5 millimolar K2SO4, both in the presence of 0.2 millimolar CaSO4. Exudation from KNO3 plants had twice the volume and twice the K+ and Ca2+ fluxes or rate of delivery to shoots, as K2SO4 plants. Malate flux was 25% higher in K2SO4 than in KNO3 exudate. Malate was the principal anion accompanying K+ or Ca2+ in K2SO4 treatment, while in the KNO3 treatment, NO3− was the principal anion. The contribution of SO42− was negligible in both treatments. In a second experiment, exudate was collected every 4 hours during the daytime throughout a 72-hour treatment with KNO3. Malate was the only anion present in exudate at first, just after the CaSO4 pretreatment had ended. Malate concentration decreased and NO3− concentration increased with time and these concentrations were negatively correlated. By 62 hours, NO3− represented 80% of exudate anions. K+ and NO3− concentrations in exudate were strongly correlated with K+ and NO3− uptake, respectively. The first 36 hours of absorption from KNO3 solution resembled the continuous absorption of K2SO4, in that malate was the principal counterion for translocation of K+. 2 Present address: Agronomy Department, University of Missouri, Columbia, Mo. 65211. 3 To whom reprint requests should be addressed. 1 Scientific Article No. A2624, Contribution No. 5662 of the Maryland Agricultural Experiment Station, Department of Botany. This content is only available as a PDF. © 1980 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)