A light-enhanced metabolism of sulfite in cells of Cucumis sativus L. cotyledons

The effects of light and several photosynthetic inhibitors on the rate of sulfite metabolism in cells obtained from Cucumis sativus L. cotyledons was studied. The cells were treated with 200 M Na₂SO₃ and the disappearance of sulfite was monitored using either dithiobisnitrobenzoic acid or fuchsin. The rate of sulfite disappearance in light was double the dark rate. Disalicylidene propanediamine at 1 mM increased this light-enhanced metabolism approx. 50%; neither 1 M 3,4-dichlorophenyl-N,N-dimethylurea nor 0.1 mM cyanazine, which completely inhibited CO₂-dependent oxygen evolution, affected the rate of sulfite metabolism. Addition of 200 M Na₂SO₃ to the cells partially inhibited ¹⁴CO₂ fixation. The rate of sulfite consumption by the cells did not affect this inhibition. We conclude that light-dependent sulfite metabolism is cucumber cells may utilize reduced ferredoxin generated as a result of photosynthetic electron transport. An injurious interaction between CO₂ fixation and sulfite appears to occur independently of the sulfite-metabolism process.Abbreviations DCMU 3,4-dichlorophenyl-N,N-dimethylurea - DSPD disalicylidene propanediamine - DTNB 5,5-dithiobis-(2-nitrobenzoic acid)     

Plastid changes during the conversion of chloroplasts to chromoplasts in ripening tomatoes

Methods were developed for the isolation of plastids from mature green and ripening tomatoes (Lycopersicon esculentum Mill.) and purification by sucrose or Percoll density-gradient centrifugation. Assessment of the purity of preparations involved phase-contrast and electron microscopy, assays for marker enzymes and RNA extraction and analysis. Proteins were extracted from isolated plastids at different ripening stages and separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The profiles obtained from chloroplasts and chromoplasts showed many qualitative and quantitative differences. Labelling of proteins with [³⁵S]methionine in vivo showed that there was active protein synthesis throughout ripening, but there was a change in the plastid proteins made as ripening proceeded. The cellular location of synthesis of specific proteins has yet to be established.Abbreviations CS citrate synthase - EDTA ethylenediaminetetraacetic acid,-acetate - GAPDH NADP⁺-glyceraldehyde-3-phosphate dehydrogenase - rRNA ribosomal RNA - SDS sodium dodecyl sulphate - SDS-PAGE SDS-polyacrylamide gel electrophoresis - Tris 2-amino-2(hydroxymethyl)-1,3-propanediol     

Modulation of carrier-mediated uptake of abscisic acid by methyl jasmonate in Phaseolus coccineus L

The effects of methyl jasmonate and jasmonic acid on uptake of abscisic acid (ABA) by suspension-cultured runner-bean cells and subapical runner-bean root segments have been investigated. Increasing concentrations of methyl jasmonate inhibit ABA uptake by the cultured cells with a K _i of 22±3 M. This is not due to cytoplasmic acidification or to effects on metabolism of ABA, and is not additive with inhibition of radioactive ABA uptake by nonradioactive ABA. Uptake of indol-3-yl acetic acid (IAA) is unaffected by methyl jasmonate. The maximum effect of nonradioactive ABA in inhibiting uptake of radioactive ABA, previously shown to reflect saturation of an ABA carrier, is generally greater than the effect of maximally inhibitory concentrations of methyl jasmonate. Similar results were obtained with root segments, but longer incubation times were necessary to observe inhibitory effects of methyl jasmonate. Demethylation of methyl jasmonate to jasmonic acid does not appear to be required since similar concentrations of jasmonic acid had no observable direct effect on ABA uptake other than that attributable to cytoplasmic acidification. Histidine reagents, a proton ionophore and acidic external pH all affect in parallel the inhibition by methyl jasmonate and nonradioactive ABA of uptake of radioactive ABA by the cultured cells. There is no effect of ABA or nonradioactive methyl jasmonate on uptake of radioactive methyl jasmonate by the cultured cells. It is proposed that methyl jasmonate interacts with the ABA carrier. Various models for this interaction are discussed.Abbreviations ABA abscisic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - IAA indol-3-yl acetic acid     

Glutamate synthase in greening callus of Bouvardia ternifolia Schlecht

The distribution of the two glutamate-synthase (GOGAT) activities known to exist in higher plants (NADH dependent, EC 2.6.1.53; and ferredoxin dependent, EC 1.4.7.1) was studied in non-chlorophyllous and chlorophyllous cultured tissue as well as in young leaves of Bouvardia ternifolia. The NADH-GOGAT was present in all three tissues. Using a sucrose gradient we found it in both the soluble and the plastid fraction of non-chlorophyllous and chlorophyllous tissue, but exclusively in the chloroplast fraction of the leaves. Ferredoxin-GOGAT was found only in green tissues and was confined to the chloroplasts. Ferredoxin-GOGAT activity increased in parallel with the chlorophyll content of the callus during the greening process in Murashige-Skoog medium (nitrate and ammonium as the nitrogen sources), while NADH-GOGAT was not affected by the greening process in this medium. Furthermore, both activities were differentially affected by either nitrate or ammonium as the sole nitrogen source in the medium during this process. It is suggested that each GOGAT activity is a different entity or is differently regulated.Abbreviations GOGAT glutamate synthase - MS Murashige-Skoog (1962) medium - PMSF phenylmethylsulfonyl fluoride     

Establishment and maintenance of friable,embryogenic maize callus and the involvement of L-proline

Friable, embryogenic maize (Zea mays L.), inbred line A188, callus was established and maintained for more than one year without apparent loss of friability or embryogenic potential. Embryoid development was abundant in these cultures and plants were easily regenerated. Frequencies of friable-callus initiation and somatic-embryoid formation increased linearly with addition to N6 medium (C.C. Chu et al. 1975, Sci. Sin. [Peking] 18, 659–668) of up to 25 mM L-proline. Proline additions up to 9 mM to MS medium (inorganic elements of T. Murashige and F. Skoog 1962, Physiol. Plant. 15, 473–497, plus 0.5 mg 1^-1 thiamine hydrochloride and 150 mg 1^-1 L-asparagine monohydrate) did not stimulate embryoid formation. A major part of the difference between MS and N6 media could be attributed to their respective inorganic nitrogen components. L-Glutamine was not a satisfactory substitute for L-proline. Of 111 regenerated plants grown to maturity from three independent friable, embryogenic cell lines ranging in age from three to seven months, only four plants were abnormal based on morphology and pollen sterility. Seed was produced by 77% of the regenerated plants.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - MS medium containing inorganic elements of Murashige and Skoog (1962), plus 0.5 ml 1^-1 thiamine hydrochloride and 150 mg 1^-1 L-asparagine monohydrate - N6 medium of Chu et al. (1975) Paper No. 13,904, Scientific Journal Series Minnesota Agricultural Experiment Station     

Mechanics of circadian pulvini movements in Phaseolus coccineus L.

The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, , were estimated from these diagrams. Under physiological conditions the values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.Symbols volumetric elastic modulus - _i instantaneous volumetric elastic modulus - _i stationary volumetric elastic modulus - weight-averaged stationary bulk modulus of extensibility - ₀ osmotic pressure of the vacuole of a cell at the point of incipient plasmolysis - weight-averaged osmotic pressure of the vacuoles of the tissue at 50% incipient plasmolysis - water potential     

Larger adenylate energy charge and ATP/ADP ratios in aerenchymatous roots of Zea mays in anaerobic media as a consequence of improved internal oxygen transport

Internal transport of O₂ from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O₂ transport) in non-aerenchymatous roots.Abbreviation AEC adenylate energy charge     

Chloroplast movement in Mougeotia induced by blue light pulses

The profile-to-face chloroplast movement in the green alga Mougeotia has been induced by strong blue and near-ultraviolet light pulses (6 J m^-2). Simultaneously, strong red or far-red light (10 W m^-2) was applied perpendicularly to the inducing beam. The response was measured photometrically. Against the far-red background the reciprocity law was found to hold for pulse durations varying two orders of magnitude. The action spectrum exhibited a maximum near 450 nm and a distinct increase in near-ultraviolet. The time-course and the spectral dependence of pulse responses of chloroplasts in Mougeotia were similar to those recorded for other plants which are sensitive only to blue. This points to an alternative sensor system active in the short-wavelength region in addition to the phytochrome system.Abbreviations FR far-red light - Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome - R red light This paper is dedicated to the memory of Professor Jan Zurzycki     

Membrane potentials as an indication for plant cell penetration by aphid stylets

Electrical penetration graphs (EPGs) of aphids on plants demonstrate distinct periods of lowered potential level: the potential drop (pd). Such pds are produced frequently during the stylet pathway to the phloem. Experimental evidence supports the hypothesis that the pd corresponds with a stylet puncture of a (epidermal or mesophyll) cell membrane. The intracellular potentials of-100 to-180 mV are thought to be measured thereby with the stylets acting as microelectrodes. The short pd of 5–15 s can be described as a sequence of three distinct phases. Besides the short pd, occurring during pattern B and C, long pds are produced during the complete pattern D+E. Pattern D+E may occur on the potential level of the pd (abbr.: D+E (pd)) and on the potential level of the preceding pattern C (abbr.: D+E(c)). Pattern D+E(pd) seems to be related to sieve element penetration, at least in a number of cases. Both pds, short and long, are produced on host and non-host plants, on susceptible and resistant cultivars, using several aphid species.

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Potentiels membraneux comme indication pour des pénétrations intracellulaires des plantes par les stylets des aphides

Résumé L'enrégistrement électrique de la pénétration du stylet des aphides dans les tissus de la plante se caracterise par des périodes distinctes de chute de potentiel (c.p.). Ces c.p. existent fréquemment au cours du trajet du stylet vers le phloème. Une évidence expérimentale soutient l'hypothèse de la correspondance entre la c.p. et la piqûre de la membrane des cellules épidermales et parenchymateuses. Les potentiels intracellulaires de-100 à-180 mV pourraient être mesurés par l'intermédiaire des stylets comme microélectrodes. Les. c.p. brèves, de 5 à 15 s peuvent être décrites comme des séquences composées de 3 phases distinctes. Outre les c.p. brèves pendant les ondes B et C, les pucerons produisent des c.p. durables qui se maintiennent au cours des ondes D+E. Ou bien l'onde D+E peuve apparaite au niveau de potentiel de c.p. (D+E(cp)), ou au niveau de potentiel de l'onde C précédente (D+E(c)). L'onde D+E(cp) semble être reliée à la pénétration des vaisseaux conducteurs, du moins dans certain cas. Les c.p. brêves et durables sont produits sur les plantes hôtes et non-hôtes chez plusiers espèces d'aphids.

     

Inhibitory effect of molecular hydrogen on C2H2-reducing activity in Anabaena 7120 preilluminated in red or blue light

Molecular hydrogen inhibits nitrogenase activity in Anabaena pre-illuminated with red or blue light. The inhibitory effect of molecular hydrogen decreased in the presence of oxygen and several electron acceptors. When NH₄Cl and urea were added simultaneously with molecular hydrogen, marked synergistic inhibitory effects took place. The inhibitory effect of molecular hydrogen disappeared or was weakened after the suppression of hydrogenase activity. The addition of O₂ and electron acceptors to systems showed no enhancing effect on the C₂H₂-reducing activity.