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81.
This study was designed to investigate the strength of attachment of plant seedling roots to the soil in which they were grown.
The study also assessed the effects of differing soil textures and differing soil matric potentials upon the strength of the
root:soil attachment. A device for growing roots upon a soil surface was designed, and was used to produce roots which were
attached to the soil. In order to quantify root:soil adhesion, roots of maize seedlings, grown on the soil surface, were subsequently
peeled off using a universal test machine, in conjunction with simultaneous time-lapse video observation. To clarify the partitioning
of energy in the root:soil peeling test, separate mechanical tests on roots, and on two adherent remoulded topsoil balls were
also carried out. The seedling root was characterised by a low bending stiffness. The energy stored in bending was negligible,
compared to the root:soil adhesion energy. The mechanical properties of two adherent remoulded topsoil balls were a decrease
of the soil:soil adhesion energy as the soil:soil plastic energy increased. These two parameters were therefore interdependent.
Using a video-camera system, it was possible to separate the different processes occurring during the root:soil peeling test,
in particular, the seed:soil adhesion and the root:soil soil adhesion. An interpretation of the complex and variable force:displacement
curves was thus possible, enabling calculation of the root:soil interfacial rupture energy. At a given suction (10 kPa), the
results of the peeling test showed a clear soil texture effect on the value of the root:soil interfacial rupture energy. In
contrast, for the same silty topsoil, the effect of the soil water suction on the value of the interfacial rupture energy
was very moderate. The root:soil interfacial rupture energy was controlled mainly by a product of microscopic soil specific
surface area and the macroscopic contact surface area between the root and the soil. Biological and physical interactions
contributing to root:soil adhesion such as root:soil interlocking mechanics were also analysed and discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
82.
83.
The yeast KAR1 gene is essential for mitotic growth and important for nuclear fusion. Mutations in KAR1 prevent duplication of the spindle pole body (SPB), and affect functions associated with both the nuclear and cytoplasmic microtubules. The localization of hybrid Kar1-lacZ proteins, described elsewhere (Vallen, E. A., T. Y. Scherson, T. Roberts, K. van Zee, and M. D. Rose. 1992. Cell. In press), suggest that the protein is associated with the SPB. In this paper, we report a deletion analysis demonstrating that the mitotic and karyogamy functions of KAR1 are separate and independent, residing in discrete functional domains. One region, here shown to be essential for mitosis, coincided with a part of the protein that is both necessary and sufficient to target Karl-lacZ hybrid proteins to the SPB (Vallen, E. A., T. Y. Scherson, T. Roberts, K. van Zee, and M. D. Rose. 1992. Cell. In press). Complementation testing demonstrated that deletions in this interval did not affect nuclear fusion. A second region, required only for karyogamy, was necessary for the localization of a Kar3-lacZ hybrid protein to the SPB. These data suggest a model for the roles of Kar1p and Kar3p, a kinesin-like protein, in nuclear fusion. Finally, a third region of KAR1 was found to be important for both mitosis and karyogamy. This domain included the hydrophobic carboxy terminus and is sufficient to target a lacZ-Kar1 hybrid protein to the nuclear envelope (Vallen E. A., T. Y. Scherson, T. Roberts, K. van Zee, and M. D. Rose. 1992. Cell. In press). Altogether, the essential mitotic regions of KAR1 comprised 20% of the coding sequence. We propose a model for Kar1p in which the protein is composed of several protein-binding domains tethered to the nuclear envelope via its hydrophobic tail. 相似文献
84.
We examine basic asymptotic properties of relative risk for two families of generalized Erlang processes (where each one is based off of a simplified Armitage and Doll multistage model) in order to predict relative risk data from cancer. The main theorems that we are able to prove are all corroborated by large clinical studies involving relative risk for former smokers and transplant recipients. We then show that at least some of these theorems do not extend to other Armitage and Doll multistage models. We conclude with suggestions for lifelong increased cancer screening for both former smoker and transplant recipient subpopulations of individuals and possible future directions of research. 相似文献
85.
Estefania Mulvihill Lorenzo Sborgi Stefania A Mari Moritz Pfreundschuh Sebastian Hiller Daniel J Müller 《The EMBO journal》2018,37(14)
Gasdermin‐D (GSDMD), a member of the gasdermin protein family, mediates pyroptosis in human and murine cells. Cleaved by inflammatory caspases, GSDMD inserts its N‐terminal domain (GSDMDNterm) into cellular membranes and assembles large oligomeric complexes permeabilizing the membrane. So far, the mechanisms of GSDMDNterm insertion, oligomerization, and pore formation are poorly understood. Here, we apply high‐resolution (≤ 2 nm) atomic force microscopy (AFM) to describe how GSDMDNterm inserts and assembles in membranes. We observe GSDMDNterm inserting into a variety of lipid compositions, among which phosphatidylinositide (PI(4,5)P2) increases and cholesterol reduces insertion. Once inserted, GSDMDNterm assembles arc‐, slit‐, and ring‐shaped oligomers, each of which being able to form transmembrane pores. This assembly and pore formation process is independent on whether GSDMD has been cleaved by caspase‐1, caspase‐4, or caspase‐5. Using time‐lapse AFM, we monitor how GSDMDNterm assembles into arc‐shaped oligomers that can transform into larger slit‐shaped and finally into stable ring‐shaped oligomers. Our observations translate into a mechanistic model of GSDMDNterm transmembrane pore assembly, which is likely shared within the gasdermin protein family. 相似文献
86.
87.
88.
R Schulz K Steinmüller M Klaas C Forreiter S Rasmussen C Hiller K Apel 《Molecular & general genetics : MGG》1989,217(2-3):355-361
Summary The primary structure of the NADPH-protochlorophyllide oxidoreductase of barley has been deduced from the nucleotide sequence
of a cloned full-length cDNA. This cDNA hybridizes to a 1.7 kb RNA whose steady-state level in dark-grown seedlings is drastically
reduced upon illumination. The predicted amino acid sequence (388 residues in length) includes a transit peptide of 74 amino
acids whose end point has been delimited by sequencing the N-terminus of the mature protein. Expression of the cDNA inEscherichia coli leads to the synthesis of an enzymatically active precursor of the NADPH-protochlorophyllide oxidoreductase. Activity of
this protein in bacterial lysates is completely dependent on the presence of NADPH and protochlorophyllide and requires light. 相似文献
89.
CM Ward AP Wilkinson S Bramham HA Lee HW-S Chan GW Butcher A Hutchings MRA Morgan 《Mycotoxin Research》1990,6(2):73-83
From a single aflatoxin B1 oxime — bovine serum albumin conjugate, polyclonal and monoclonal antibody preparations were produced. The four rabbit polyclonal antisera were specific for aflatoxin Bi in a microtitration plate enzyme — linked immunosorbent assay. The monoclonal antibodies showed a wide range of differing specificities, recognizing, for example, aflatoxins B1, B2, G1 and G2; B1 and B2; B1 and G1; and G1 alone. No antibody preparations reacted with aflatoxin M1. The significance of these results to the strategy of anti-aflatoxin antibody production for use in quantitative enzyme immunoassays is discussed. 相似文献
90.
Iodinated human beta-endorphin was affinity-cross-linked to opioid receptors present in membrane preparations from bovine frontal cortex, bovine striatum, guinea pig whole brain, and rat thalamus. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography revealed covalently labeled peptides of 65, 53, 41, and 38 kilodaltons (kDa). The 65- and 38-kDa peptides were present in all four tissues. The 41-kDa peptide was seen only in bovine caudate and guinea pig whole brain while the 53-kDa peptide was absent in rat thalamus. All four labeled peptides were constituents of opioid receptors since their labeling was fully suppressed by the presence of excess opiates, such as bremazocine, during binding. The distribution and levels of the labeled species in the brain tissues examined and, in earlier work, in the neuroblastoma X glioma NG 108-15 cell line suggested that the 65-kDa peptide is a binding component of mu receptors while the 53-kDa peptide is a binding subunit of delta receptors. This result was strongly supported by the finding that the labeling of the 65-kDa peptide is selectively reduced by the presence of the highly mu-selective ligand Tyr-D-Ala-Gly-(N-Me)Phe-Gly-ol (DAMGE) during binding, while while the labeling of the 53-kDa peptide is selectively reduced or eliminated by the highly mu-selective ligand [D-Pen2, D-Pen5]enkephalin (DPDPE). The labeling of the 41- and 38-kDa bands was reduced by either DAMGE or DPDPE. The relationship of these lower molecular weight opioid-binding peptides to mu and delta receptors is not understood. Several possible explanations are presented. 相似文献