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     

The nutrition of stomachless phytoplanktivorous fish in comparison with Tilapia

The contents of alimentary tracts of stomachless phytoplanktivorous fish, including silvercarp (Hypophthalmichthys molitrix), Esomus danrica thermoicos, and Amblypharyngodon meletinus were investigated microscopically and compared with those of Tilapia (Oreochromis mossambicus, a fish with stomach).The predominance of detritus in the food and the low efficiency with which phytoplankton is utilized prove, that stomachless fish are not primarily herbivorous. The possibility of omnivorous feeding as an alternative is discussed. These results may contribute to our understanding of the role of filterfeeders in aquaculture and ecosystems.     

Life history,population dynamics and production of Pontoporeia hoyi (Crustacea,Amphipoda) in relation to the trophic gradient of Lake George,New York

The life history characteristics, population dynamics and production of Pontoporeia hoyi in Lake George, New York, were studied from May 1981 through October 1982. P. hoyi, in terms of both density and standing crop, is the most prevalent member of the deep water macrobenthos of Lake George. It reproduces in the winter, with young being released in the late winter-early spring. At the southernmost study site, young released in the spring grew to 6–7 mm in length and bred during their first winter. At the remaining sites, P. hoyi required two years to complete its life cycle. This difference in life history characteristics can be related to food availability and temperature differences. The open waters of the south end of Lake George are not only more productive but are also more closely associated with the littoral zone, providing a wealth of bacteria-rich detritus for benthic deposit feeders. The greater food availability in the south basin of Lake George is reflected in significantly larger brood sizes and smaller size at maturity for P. hoyi populations from the south end of the lake.The southernmost study site has significantly greater P. hoyi density and standing crop than all other sites. The cohort of the year dominated density and standing crop at the southern site while the cohort of the previous year dominated standing crop at the other sites. Peak abundance ranged from 600 · m^–2 at the north site to 2 900 · m^–2 at the south site. Cohort production ranged from 2g · m^–2 at the north site to 15g · m^–2 at the south site.     

Impact de l'échantillonnage sur la mésure des nucléotides adényliques (ATP,ADP, AMP) du microplancton

The influence of sampling and sample treatment upon adenylic nucleotide (ATP, ADP, AMP) content of microplankton is studied. Changes in light conditions during nigh-sampling and extracting do not induce significant variations, in the adenylic nucleotide content of microplankton or in energy charge values.The contribution of zooplankton (size up to 200 µm) to microplankton adenosine values can be neglected for inshore surface waters and traditional sample volumes (about one liter). This result can been explained by the low density of zooplankton in such a small sample volume and by differences in efficiency of the extracting method used.

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Impact de l'échantillonnage sur la mésure des nucléotides adényliques (ATP, ADP, AMP) du microplancton

     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.