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61.
In temperate zones, the potential grain yield of wheat has increased during the twentieth century owing to progressive increases in the harvest index of new varieties, which are principally associated with reduction in plant stature. Crop biomass has not increased substantially. In contrast, the potential grain yield of maize in the USA has increased owing to progressive increases in biomass, principally associated with selection for grain yield at higher population density. Harvest index was already around 0.5 for recommended varieties in 1930, and has not increased significantly since. However, for both crops, the harvest index of a given variety has proved to be a highly‐heritable character, except under severe stress. Less is known about the physiology of tropical maize. This paper reviews evidence from Mexico and Malawi that tropical maize can respond to selection for reduced stature following the same pattern as temperate wheat, but, under other circumstances, the magnitude of harvest index is not highly heritable, varying inconsistently with season, management and environment. It is proposed that these differences arise out of the unique vulnerability of the grain‐setting process around flowering. The plasticity of harvest index under long, favourable conditions, however, remains to be explained, although it is probably also related to the events around grain setting. Nevertheless, to the subsistence farmer, higher harvest index may not be a high priority in crop improvement, because of the need for large quantities of high‐quality stover. 相似文献
62.
Distribution and conservation of mobile elements in the genus Drosophila 总被引:12,自引:1,他引:12
Essentially nothing is known of the origin, mode of transmission, and
evolution of mobile elements within the genus Drosophila. To better
understand the evolutionary history of these mobile elements, we examined
the distribution and conservation of homologues to the P, I, gypsy, copia,
and F elements in 34 Drosophila species from three subgenera. Probes
specific for each element were prepared from D. melanogaster and hybridized
to genomic DNA. Filters were washed under conditions of increasing
stringency to estimate the similarity between D. melanogaster sequences and
their homologues in other species. The I element homologues show the most
limited distribution of all elements tested, being restricted to the
melanogaster species group. The P elements are found in many members of the
subgenus Sophophora but, with the notable exception of D. nasuta, are not
found in the other two subgenera. Copia-, gypsy-, and F-element homologues
are widespread in the genus, but their similarity to the D. melanogaster
probe differs markedly between species. The distribution of copia and P
elements and the conservation of the gypsy and P elements is inconsistent
with a model that postulates a single ancient origin for each type of
element followed by mating-dependent transmission. The data can be
explained by horizontal transmission of mobile elements between
reproductively isolated species.
相似文献
63.
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65.
Background
Ran GTPase has multiple functions during the cell division cycle, including nucleocytoplasmic transport, mitotic spindle assembly and nuclear envelope formation. The activity of Ran is determined by both its guanine nucleotide-bound state and its subcellular localization. 相似文献66.
Yvonne Welte James Adjaye Hans R Lehrach Christian RA Regenbrecht 《Cell communication and signaling : CCS》2010,8(1):1-10
Background
The fibroblast growth factor receptor (FGFR) interprets concentration gradients of FGF ligands and structural changes in the heparan sulfate (HS) co-receptor to generate different cellular responses. However, whether the FGFR generates different signals is not known.Results
We have previously shown in rat mammary fibroblasts that in cells deficient in sulfation, and so in HS co-receptor, FGF-2 can only stimulate a transient phosphorylation of p42/44MAPK and so cannot stimulate DNA synthesis. Here we demonstrate that this is because in the absence of HS, FGF-2 fails to stimulate the phosphorylation of the adaptor FGFR substrate 2 (FRS2). In cells possessing the HS co-receptor, FGF-2 elicits a bell-shaped dose response: optimal concentrations stimulate DNA synthesis, but supramaximal concentrations (≥ 100 ng/mL) have little effect. At optimal concentrations (300 pg/mL) FGF-2 stimulates a sustained dual phosphorylation of p42/44MAPK and tyrosine phosphorylation of FRS2. In contrast, 100 ng/mL FGF-2 only stimulates a transient early peak of p42/44MAPK phosphorylation and fails to stimulate appreciably the phosphorylation of FRS2 on tyrosine.Conclusions
These results suggest that the nature of the FGFR signal produced is determined by a combination of the HS co-receptor and the concentration of FGF ligand. Both the phosphorylation of the adaptor FRS2, the kinetics (sustained or transient) of phosphorylation of p42/44(MAPK) are varied, and so differing cellular responses are produced. 相似文献67.
NÓRA BREZA JÁNOS PATÓ LÁSZLÓ ŐRFI BÁLINT HEGYMEGI-BARAKONYI PÉTER BÁNHEGYI EDIT VÁRKONDI 《Journal of receptor and signal transduction research》2013,33(4):361-373
The development of selective protein kinase inhibitors has become an important area of drug discovery for the treatment of different diseases. We report the synthesis and characterization of a series of novel quinazoline derivatives against three therapeutically important and pharmacologically related kinases: 1) epidermal growth factor receptor (EGFR; wild type and mutant) in the field of cancer, 2) receptor-interacting caspase-like apoptosis-regulatory kinase (RICK) in the field of inflammation, and 3) pUL97 of human cytomegalovirus (HCMV). For reference purpose we have synthesized the four clinically relevant quinazolines, including the lead compounds, which we previously identified for RICK and pUL97. A total of 52 quinazoline derivatives were synthesized and tested on the basis of these leads to specifically target the hydrophobic pocket of the ATP-binding site. Selected compounds were tested on wild-type and mutant forms of EGFR, RICK, and pUL97 kinases; their logP and logS values for assessing suitability as drugs were calculated and hit or lead compounds identified. 相似文献
68.
The phylogenetic origin of the bifunctional tyrosine-pathway protein in the enteric lineage of bacteria 总被引:5,自引:0,他引:5
Because bifunctional enzymes are distinctive and highly conserved products
of relatively infrequent gene-fusion events, they are particularly useful
markers to identify clusters of organisms at different hierarchical levels
of a phylogenetic tree. Within the subdivision of gram-negative bacteria
known as superfamily B, there are two distinctive types of tyrosine-pathway
dehydrogenases: (1) a broad- specificity dehydrogenase (recently termed
cyclohexadienyl dehydrogenase [CDH]) that can utilize either prephenate or
L-arogenate as alternative substrates and (2) a bifunctional CDH that also
posseses chorismate mutase activity. (T-proteins). The bifunctional
T-protein, thought to be encoded by fused ancestral genes for chorismate
mutase and CDH, was found to be present in enteric bacteria (Escherichia,
Shigella, Salmonella, Citrobacter, Klebsiella, Erwinia, Serratia,
Morganella, Cedecea, Kluyvera, Hafnia, Edwardsiella, Yersinia, and Proteus)
and in Aeromonas and Alteromonas. Outside of the latter "enteric lineage,"
the T-protein is absent in other major superfamily-B genera, such as
Pseudomonas (rRNA homology group I), Xanthomonas, Acinetobacter, and
Oceanospirillum. Hence, the T-protein must have evolved after the
divergence of the enteric and Oceanospirillum lineages.
3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase-phe, an early-pathway
isozyme sensitive to feedback inhibition by L- phenylalanine, has been
found in each member of the enteric lineage examined. The absence of both
the T-protein and DAHP synthase-phe elsewhere in superfamily B indicates
the emergence of these character states at approximately the same
evolutionary time.
相似文献
69.
70.
Fourteen native strains of Trichoderma spp. from wildand agricultural pathosystems in the state of Yucatan, Mexico, with growth-promoting ability of Capsicum chinense Jacq. seedlings were evaluated and antagonistic effect of their filtrate against second-stage juveniles (J2) of Meloidogyne incognita. The strains Th05-02 and Th27-08 showed the best significant effects on plant hight variable increments 55.57 and 47.62%, theTh07-04 with 29.48% more root length, theTh02-01 and Th07-04 isolates increased from 48.71 to 84.61% in volume radical and 53.40% of total dry biomass. Statistical analysis (p≤0.001) of Th43 and Th43-13-14 filtrates caused 100% mortality at 24 and 48h. In the test of reversibility to 24 h after replacing the filtrates Th43-13, Th43-14, TH09-06 and TH20-07 by sterile distilled water, the J2 did not recover their viability, so they were considered as the best potential strains of Trichoderma spp. with antagonistic capacity in J2 of M.incognita. 相似文献