Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse

Poleward Tubulin Flux in Spindles: Regulation and Function in Mitotic Cells

The poleward flux of tubulin subunits through spindle microtubules is a striking and conserved phenomenon whose function and molecular components remain poorly understood. To screen for novel components of the flux machinery, we utilized RNA interference to deplete regulators of microtubule dynamics, individually and in various combinations, from S2 cells and examined the resulting impact on flux rate. This led to the identification of two previously unknown flux inhibitors, KLP59C and KLP67A, and a flux promoter, Mini-spindles. Furthermore, we find that flux rate is regulated by functional antagonism among microtubule stabilizers and destabilizers specifically at plus ends. Finally, by examining mitosis on spindles in which flux has been up- or down-regulated or restored after the codepletion of antagonistic flux regulators, we show that flux is an integral contributor to anaphase A but is not responsible for chromosome congression, interkinetochore tension, or the establishment of normal spindle length during prometaphase/metaphase

Közösségfejlesztés a Magyarországi Baptista Egyházban

Szakdolgozatom témájaként a Baptista Egyházban folyó közösségfejlesztés elemzését választottam. A közösségfejlesztés napjainkban a szociológiának egyre nagyobb teret hódító kutatási területe. Manapság különböző közösségek fejlesztésére van lehetőség. Hallhatunk iskolák, szervezetek, vállalatok, egyházak vagy éppen települések különféle közösségeinek fejlesztéséről. Ezen tevékenységek fontosak a társadalmi csoportok kohéziójának az elősegítéséhez és fenntartásához. Dolgozatom célja, hogy képet adjak a Baptista Egyház közösségéinek működéséről, összetételéről, kialakulásáról és értékrendszeréről. A kutatásom célja az interjú alanyok válaszain keresztül bemutatni a baptista gyülekezeteken belüli közösségek kapcsolatainak rendszerét, összetettségét, valamint azt, hogy a válaszadók miként vállalnak szerepet a gyülekezetük közösségének építésében. Kutatási módszerként az interjút választottam és használtam. Félig strukturált interjúkkal dolgoztam. Szakdolgozatomban három hipotézist fogalmaztam meg, amelyekre a válaszokat a feltett kutatási kérdéseim alapján kaptam meg. Hipotéziseim részben igaznak bizonyultak. A gyülekezetbe járó tagok szeretnék, ha közösségük folyamatosan fejlődne, kapcsolataik erősödne.BSc/BASzociológi

Microtubule Plus-End Conformations and Dynamics in the Periphery of Interphase Mouse Fibroblasts

The plus ends of microtubules (MTs) alternate between phases of growth, pause, and shrinkage, a process called “dynamic instability.” Cryo-EM of in vitro–assembled MTs indicates that the dynamic state of the plus end corresponds with a particular MT plus-end conformation. Frayed (“ram's horn like”), blunt, and sheet conformations are associated with shrinking, pausing, and elongating plus ends, respectively. A number of new conformations have recently been found in situ but their dynamic states remained to be confirmed. Here, we investigated the dynamics of MT plus ends in the peripheral area of interphase mouse fibroblasts (3T3s) using electron microscopical and tomographical analysis of cryo-fixed, freeze-substituted, and flat-embedded sections. We identified nine morphologically distinct plus-end conformations. The frequency of these conformations correlates with their proximity to the cell border, indicating that the dynamic status of a plus end is influenced by features present in the periphery. Shifting dynamic instability toward depolymerization with nocodazole enabled us to address the dynamic status of these conformations. We suggest a new transition path from growth to shrinkage via the so-called sheet-frayed and flared ends, and we present a kinetic model that describes the chronology of events taking place in nocodazole-induced MT depolymerization

The Kinesin-13 Proteins Kif2a, Kif2b, and Kif2c/MCAK Have Distinct Roles during Mitosis in Human Cells

The human genome has three unique genes coding for kinesin-13 proteins called Kif2a, Kif2b, and MCAK (Kif2c). Kif2a and MCAK have documented roles in mitosis, but the function of Kif2b has not been defined. Here, we show that Kif2b is expressed at very low levels in cultured cells and that GFP-Kif2b localizes predominately to centrosomes and midbodies, but also to spindle microtubules and transiently to kinetochores. Kif2b-deficient cells assemble monopolar or disorganized spindles. Chromosomes in Kif2b-deficient cells show typical kinetochore-microtubule attachments, but the velocity of movement is reduced ∼80% compared with control cells. Some Kif2b-deficient cells attempt anaphase, but the cleavage furrow regresses and cytokinesis fails. Like Kif2a-deficient cells, bipolar spindle assembly can be restored to Kif2b-deficient cells by simultaneous deficiency of MCAK or Nuf2 or treatment with low doses of nocodazole. However, Kif2b-deficient cells are unique in that they assemble bipolar spindles when the pole focusing activities of NuMA and HSET are perturbed. These data demonstrate that Kif2b function is required for spindle assembly and chromosome movement and that the microtubule depolymerase activities of Kif2a, Kif2b, and MCAK fulfill distinct functions during mitosis in human cells

The coupling between sister kinetochore directional instability and oscillations in centromere stretch in metaphase PtK1 cells

High-resolution kinetochore tracking reveals that oscillations in centromere stretch occur at twice the frequency of kinetochore oscillations because of the nonlinear kinetics of kinetochore directional instability, which produce poleward and away-from-the-pole kinetochore oscillations