Solubilization, Reconstitution and Characterization of Vanadate-sensitive, ATP-driven H+ -transport from cotyledons of Ricinus communis

Several treatments were investigated in an attempt to increasethe proportion of vanadate-sensitive proton pumping activityderived from membrane fractions of Ricinus cotyledons. The mostsuccessful procedure involved KI treatment of the microsomalfraction followed by solubilization with 1.25% (w/v) octylglucosideand reconstitution into phosopholipid liposomes. KI treatmentof the microsomal fraction resulted in an increase in the ATPasesensitivity to vanadate. Reconstitution was carried out by adilution method and the existence of ATP-driven H⁺-transportacross the proteoliposomes was demonstrated by quinacrine fluorescencequenching. The quenching was gramicidin reversible and stronglyinhibited by vanadate, ER B and PCMBS. Less inhibition was observedin the presence of NEM. Fusicoccin and sucrose did not havemarked effects on H⁺ -transport. Key words: ATPase, proton pumping, KI-treatment, solubilization, reconstitution, Ricinus communis     

ATPase and Proton Pumping Activities in Cotyledons and other Phloem-Containing Tissues2Ricinus communis

ATPase activity was investigated in phloem-containing tissuesof Ricinus communis in relation to its proposed role in phloemloading. Cytochemical staining of cotyledons revealed an ATP-hydrolysingactivity on the plasma membrane of the sieve tube/companioncell complex. Microsomal fractions prepared from cotyledonsand main veins contained a Mg²⁺-dependent ATPase activity whichshowed low stimulation by KC1 particularly at pH 6.5. The pHoptimum was at pH 8.5 to 90, although the effect of azide indicatedthe presence of mitochondrial ATPase. At pH 6.5, the cited optimumfor plasma membrane ATPase, the activity showed strong inhibitionby PCMBS, vanadate and DCCD. A high pyrophosphatase activitywas observed at pH 8.5. Acidification of the medium by intactcotyledons was increased by fusicoccin and inhibited by PCMBS,NEM and vanadate. Proton pumping by microsomal vesicles as measuredby quinacrine fluorescence was also inhibited by PCMBS, NEMand vanadate. Sucrose uptake by cotyledon discs showed stronginhibition by PCMBS, NEM and CCCP but was little affected byvanadate. Sucrose uptake varied with the developmental stageof the cotyledons and this correlated with microsomal ATPaseactivity measured at pH 6.5, although the precise cellular originof this activity is not certain. The results are discussed inrelation to the role of ATPase activity and proton pumping inphloem loading. Key words: ATPase, phlocm loading, proton pumping, Ricinus communis, sucrose     

Effect of high external NaCl concentration on ion transport within the shoot of Lupinus albus. II. Ions in phloem sap

Abstract. Phloem sap was collected from petioles of growing and fully expanded leaves of lupins exposed to 0–150 mol m⁻³ [NaCl]_ext, for various periods of time. Sap bled from growing leaves only after the turgor of the shoot was raised by applying pneumatic pressure to the root. Increased pressure was also needed to obtain sap from fully expanded leaves of plants at high [NaCl]_ext. Exposure to NaCl caused a rapid rise in the Na⁺ concentration in phloem sap to high levels. The Na⁺ concentration reached 20 mol m⁻³ within a day of exposure and reached a plateau of about 60 mol m⁻³ in plants at 50–150 mol m⁻³ [NaCl]_ext, after a week. There was a slower, smaller increase in the Cl⁻ concentration. K⁺ concentrations in phloem sap were not affected by [NaCl]_ext. Cl⁻ concentrations in phloem sap collected from growing leaves were similar to those from old leaves while Na⁺ concentrations were somewhat increased, suggesting that there was no reduction in the salt content of the phloem sap while it flowed within the shoot to the apex. Calculations of ion fluxes in xylem and phloem sap indicated that Na⁺ and Cl⁻ fluxes in the phloem from leaves of plants at high NaCl could be equal to those in the xylem. This prediction was borne out by observations that Na⁺ and Cl⁻ concentrations in recently expanded leaves remained constant.     

THE SYNTHESIS OF 5S RIBOSOMAL RNA DURING POLLEN DEVELOPMENT

Tradescantia paludosa 5S ribosomal RNA (rRNA) has been characterized with respect to its base composition and relative electrophoretic mobility in comparison with that of E. coli . The period of 5S rRNA synthesis during pollen grain development was determined by pulse labeling the RNA synthesized during a 24 hr period of development with ³²P and then chasing in cold medium until pollen maturity. The period of highest 5S rRNA synthesis was found to occur prior to microspore mitosis. During and following mitosis over a period of 4 days there was a sharp decrease in the amount of 5S RNA synthesized and during the last 48 hr of pollen maturation, no 5S rRNA was synthesized.     

The Influence of Atrazine, Benzyladenine, and the Embryonic Axis on Chlorophyll Synthesis in Cucumber and Squash Cotyledons

Excision of the embryonic axis prior to 3 1/2 days of germination in the dark followed by 8-h of light decreased the total chlorophyll content of cucumber cotyledons but not squash cotyledons. Benzyladenine stimulated the accumulation of chlorophyll in the cotyledons of intact embryos and excised cotyledons in both cucumber and squash. Gibberellic acid had no effect. Atrazine inhibited chlorophyll formation in excised squash cotyledons. Benzyladenine also increased the carotenoid and xanthophyll content in the cotyledons from intact squash seedlings. The results suggest that pigment synthesis in cotyledons may be controlled by a number of substances produced in the embryonic axis and that cytokinin-like benzyladenine can simulate the action of one of them.     

Specific Labeling of Intracellular Toxoplasma gondii with Uracil*

SYNOPSIS Radioactive uracil was not significantly incorporated into the nucleic acids of human fibroblast cells. Infection of these cells with Toxoplasma gondii resulted in an exponential increase in the rate of uracil incorporation that paralleled the exponential growth of the parasite. One day after infection the rate of uracil incorporation was increased 100-fold. It was established by autoradiography that all of the [³H] uracil was incorporated into the intracellular parasites. A possible explanation for this difference in ability to use uracil is our observation that the specific activity of uridine phosphorylase was 100-fold greater in partially purified parasites than in the host cell.     

Growth, Fine Structure and Cyst Formation of a Microbial Mat Ciliate: Pseudocohnilembus pusillus (Ciliophora, Scuticociliatida)

ABSTRACT Pseudocohnilembus species exhibit a polymorphic life cycle consisting of trophic cells, theronts, and cysts. Pseudocohnilembus pusillus isolated from the intertidal mats of Laguna Figueroa, Baja California Norte, Mexico, forms desiccation-resistant cysts in response to bacterial food depletion. This isolate is a euryhaline organism, able to grow at salinities from freshwater to 96 ppt total salinity and from pH 6–9. Electron micrographs show that oral and somatic cilia and kinetids are retained inside young cysts. Cyst walls are composed of a single layer (0.1 μm) of granular material. Under all conditions, as bacterial food was depleted, P. pusillus cells formed cysts, except for a small proportion (1–5%) that continued to swim. Changes in pH and salinity did not directly induce cyst formation. Salinity did greatly affect growth rate. Doubling times were shortest at 16 ppt salinity and at pH 7–8. Cyst formation occurred later in the growth cycle as more food bacteria were added. Additionally, ciliates grown in small culture volumes (10 ml) formed cysts sooner than cultures in larger volumes (100 ml), suggesting that crowding may influence cyst formation. Mature cysts may survive desiccation at least as long as one month at 37° C and for as long as one year at 20 ± 3° C. Although trophic cells did not survive desiccation or anoxia, encysted ciliates from liquid stationary phase cultures kept in anoxic seawater for one month excysted into swimming cells within 2.5 h after exposure to air. The adaptability of P. pusillus to extremes of salinity, pH, desiccation, and anoxia permits survival in its environmentally variable, microbial mat habitat.     

The unique challenges of managing depression in mid-life women

Throughout most of their lives, women are at a greater risk of becoming depressed than men. Some evidence suggests that this heightened risk is associated with increased sensitivity to the hormonal changes that occur across the female reproductive lifecycle. For some women, the peri-menopause and early post-menopausal years may constitute a “window of vulnerability” during which challenging physical and emotional discomforts could result in significant impairment in functioning and poorer quality of life. A number of biological and environmental factors are independent predictors for depression in this population, including the presence of hot flashes, sleep disturbance, history of severe premenstrual syndrome or postpartum blues, ethnicity, history of stressful live events, past history of depression, body mass index and socioeconomic status. This paper explores the current knowledge on the complex associations between mood changes and aging in women. More specifically, the biological aspects of reproductive aging and their impact on mood, psychosocial factors, lifestyle, and overall health are reviewed. In addition, evidence-based hormonal and non-hormonal therapies for the management of depression and other complaints in midlife women are discussed. Ultimately, this article should help clinicians and health professionals to address a challenging clinical scenario: a preventive and effective strategy for the management of depression in the context of the menopausal transition and beyond.     

Shonto Revisited: Measures of Social and Economic Change in a Navajo Community, 1955–1971

Between 1954 and 1956 the senior author of this article carried out a detailed social and economic study of the community of Shonto, situated in what was then a particularly remote corner of the Navajo Indian Reservation in northeastern Arizona. In 1972 the junior author returned to do a restudy of the same community. A comparison of the data obtained in the two studies provides unique measures of social and economic change, and also of social and economic persistence, during a period of unprecedented growth and modernization of the Navajo Reservation . [social change, economic change, Navajo]