Advances in Breeding Apomictic Brachiaria in Tropical America

Prior to 1988 Brachiaria improvement was based exclusively on the collection, introduction, and evaluation of natural germplasm from Africa. Breeding programs in Brachiaria have been possible only in the past 10 years with the creation of a sexual, tetraploid B. ruziziensis cross-compatible with B. decumbens and B. brizantha. Applied Brachiaria breeding projects are underway both in Colombia (International Center for Tropical Agriculture, CIAT) and Brazil (National Centre for Beef Cattle Research - Brazilian Corporation for Agricultural Research, CNPGC/EMBRAPA). These seek to combine the broad edaphic adaptation and other desirable agronomic attributes of B. decumbens cv. Basilisk with spittlebug resistance. An accumulation of basic biological knowledge of the plant has facilitated genetic manipulation. Significant genetic progress has been achieved. Major constraints to further progress in breeding Brachiaria include the cost and imprecision of evaluation methodologies

Programmed buckling by controlled lateral swelling in a thin elastic sheet

Recent experiments have imposed controlled swelling patterns on thin polymer films, which subsequently buckle into three-dimensional shapes. We develop a solution to the design problem suggested by such systems, namely, if and how one can generate particular three-dimensional shapes from thin elastic sheets by mere imposition of a two-dimensional pattern of locally isotropic growth. Not every shape is possible. Several types of obstruction can arise, some of which depend on the sheet thickness. We provide some examples using the axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 figure

A Spitzer Study of the Mass Loss Histories of Three Bipolar Pre-Planetary Nebulae

We present the results of far-infrared imaging of extended regions around three bipolar pre-planetary nebulae, AFGL 2688, OH 231.8+4.2, and IRAS 16342$-$3814, at 70 and 160 $\mu$m with the MIPS instrument on the Spitzer Space Telescope. After a careful subtraction of the point spread function of the central star from these images, we place constraints on the existence of extended shells and thus on the mass outflow rates as a function of radial distance from these stars. We find no apparent extended emission in AFGL 2688 and OH 231.8+4.2 beyond 100 arcseconds from the central source. In the case of AFGL 2688, this result is inconsistent with a previous report of two extended dust shells made on the basis of ISO observations. We derive an upper limit of $2.1\times10^{-7}$ M$_\odot$ yr$^{-1}$ and $1.0\times10^{-7}$ M$_\odot$ yr$^{-1}$ for the dust mass loss rate of AFGL 2688 and OH 231.8, respectively, at 200 arcseconds from each source. In contrast to these two sources, IRAS 16342$-$3814 does show extended emission at both wavelengths, which can be interpreted as a very large dust shell with a radius of $\sim$ 400 arcseconds and a thickness of $\sim$ 100 arcseconds, corresponding to 4 pc and 1 pc, respectively, at a distance of 2 kpc. However, this enhanced emission may also be galactic cirrus; better azimuthal coverage is necessary for confirmation of a shell. If the extended emission is a shell, it can be modeled as enhanced mass outflow at a dust mass outflow rate of $1.5\times10^{-6}$ M$_\odot$ yr$^{-1}$ superimposed on a steady outflow with a dust mass outflow rate of $1.5\times10^{-7}$ M$_\odot$ yr$^{-1}$. It is likely that this shell has swept up a substantial mass of interstellar gas during its expansion, so these estimates are upper limits to the stellar mass loss rate.Comment: 31 pages, 12 figures, accepted to A

Absorção e distribuição de cádmio e micronutrientes em cultivares de feijoeiro expostas a doses de cádmio.

Visando avaliar os efeitos de doses crescentes de cádmio em solução nutritiva sobre a absorção e a translocação de Cd, Zn, Fe, Mn e Cu por plantas de feijoeiro (Phaseolus vulgaris L.), foi montado um ensaio em casa de vegetação utilizando-se as cultivares Ouro Negro e Carioca. As doses de Cd utilizadas foram: 0,0; 0,025; 0,05; 0,10 e 0,50 ?g/mL, aplicadas em vasos de 4,8 L contendo solução nutritiva de Clark com metade da força iônica original a pH 6,0. Verificou-se aumento na absorção de Cd com o aumento das doses do elemento em solução. As raízes acumularam maiores quantidades do metal que a parte aérea. As doses de Cd diminuíram os conteúdos de Zn e de Mn nas raízes de ambas as cultivares, sem afetar, na mesma proporção, a quantidade desses cátions na parte aérea das plantas. O conteúdo de Cu das plantas aparentemente não foi alterado pelas doses de Cd, com exceção de um pequeno aumento no conteúdo na raiz da cultivar Carioca, enquanto que o conteúdo de Fe foi significativamente alterado na raiz da cultivar Ouro Negro

Accurate determination of elastic parameters for multi-component membranes

Heterogeneities in the cell membrane due to coexisting lipid phases have been conjectured to play a major functional role in cell signaling and membrane trafficking. Thereby the material properties of multiphase systems, such as the line tension and the bending moduli, are crucially involved in the kinetics and the asymptotic behavior of phase separation. In this Letter we present a combined analytical and experimental approach to determine the properties of phase-separated vesicle systems. First we develop an analytical model for the vesicle shape of weakly budded biphasic vesicles. Subsequently experimental data on vesicle shape and membrane fluctuations are taken and compared to the model. The combined approach allows for a reproducible and reliable determination of the physical parameters of complex vesicle systems. The parameters obtained set limits for the size and stability of nanodomains in the plasma membrane of living cells.Comment: (*) authors contributed equally, 6 pages, 3 figures, 1 table; added insets to figure