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81.
Sea urchin Hox genes: insights into the ancestral Hox cluster 总被引:3,自引:0,他引:3
We describe the Hox cluster in the radially symmetric sea urchin and
compare our findings to what is known from clusters in bilaterally
symmetric animals. Several Hox genes from the direct-developing sea urchin
Heliocidaris erythrogramma are described. CHEF gel analysis shows that the
Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA,
and only a single cluster is present, as in lower chordates and other
nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus,
Drosophila, and selected vertebrate Hox genes confirm that the H.
erythrogramma genes, and others previously cloned from other sea urchins,
belong to anterior, central, and posterior groups. Despite their radial
body plan and lack of cephalization, echinoderms retain at least one of the
anterior group Hox genes, an orthologue of Hox3. The structure of the
echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox
cluster more similar to the current chordate cluster than was expected Sea
urchins have at least three Abd-B type genes, suggesting that Abd-B
expansion began before the radiation of deuterostomes.
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A dynamic leaf gas‐exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies 下载免费PDF全文
Steven L. Voelker J. Renée Brooks Frederick C. Meinzer Rebecca Anderson Martin K.‐F. Bader Giovanna Battipaglia Katie M. Becklin David Beerling Didier Bert Julio L. Betancourt Todd E. Dawson Jean‐Christophe Domec Richard P. Guyette Christian Körner Steven W. Leavitt Sune Linder John D. Marshall Manuel Mildner Jérôme Ogée Irina Panyushkina Heather J. Plumpton Kurt S. Pregitzer Matthias Saurer Andrew R. Smith Rolf T. W. Siegwolf Michael C. Stambaugh Alan F. Talhelm Jacques C. Tardif Peter K. Van de Water Joy K. Ward Lisa Wingate 《Global Change Biology》2016,22(2):889-902
Rising atmospheric [CO2], ca, is expected to affect stomatal regulation of leaf gas‐exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas‐exchange that include maintaining a constant leaf internal [CO2], ci, a constant drawdown in CO2 (ca ? ci), and a constant ci/ca. These strategies can result in drastically different consequences for leaf gas‐exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas‐exchange responses to varying ca. The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas‐exchange responses to ca. To assess leaf gas‐exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ13C) or photosynthetic discrimination (?) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca‐induced changes in ci/ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca ? ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant ci. Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca, when additional water loss is small for each unit of C gain, and increasingly water‐conservative at high ca, when photosystems are saturated and water loss is large for each unit C gain. 相似文献
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Long-term follow-up of patients subjected to mitral commissurotomy permits evaluation of the late efficacy of this operation and the causes of subsequent deterioration in some cases.Three hundred and eighty-nine patients operated upon for mitral stenosis from 1950 to 1957 were studied. Of these, 89 died, 38 were lost to follow-up and 262 were re-examined.Results for the postoperative period of five to 12 years were satisfactory in 204 patients (77%) and unsatisfactory in 58 (22%). The possible causes of deterioration were studied separately.A second commissurotomy was performed on 23 patients (8.7%), because of re-stenosis thought to be due to a rheumatic process in one and to fibrotic scarring in nine, and because of an inadequate opening in 13.Mitral commissurotomy is a palliative operation, but is definitely useful in cases of tight mitral stenosis.The duration of improvement in patients with a functionally adequate opening is related to the state of the myocardium and to the possibility of rheumatic fever recurrences. Because of the risk of fibrotic restenosis, the possibility that a second commissurotomy might be required should be considered in each patient subjected to this operation. 相似文献
87.
Influence of various mixtures of inhaled toluene and xylene on the biological monitoring of exposure to these solvents in rats. 总被引:1,自引:0,他引:1
The present study was undertaken to describe the influence of simultaneous exposure by inhalation to toluene and xylene on some aspects of their respective metabolic disposition. Adult male rats were exposed acutely (5 h) to 75, 150, and 225 ppm of toluene or xylene and to various mixtures of these solvents: toluene (75 ppm) and xylene (225 ppm), toluene (150 ppm) and xylene (150 ppm), toluene (225 ppm) and xylene (75 ppm). Compared with single exposure, simultaneous exposure resulted in lower amounts of excreted hippuric acid (20-30%) and methylhippuric acids (4-40%) in urine over a period of 24 h, even though significant differences were seen only with the toluene (150 ppm) and xylene (150 ppm) combination. In addition, increased concentrations of solvents in blood (toluene, 230%; xylene, 500%) and in brain (toluene, 230%; xylene, 320%) were found during the immediate post-exposure period. Simultaneous exposure also enhanced the pulmonary elimination of both solvents (toluene, 190-240%; xylene, 340-650%). Influence of repeated simultaneous exposure (9 days) was investigated for the toluene (150 ppm) and xylene (150 ppm) combination and the results compared with those of repeated exposure to each solvent administered singly. Under these conditions, repeated simultaneous exposure decreased the excretion of urinary metabolites, but only after the first exposure. On the other hand, simultaneous exposure resulted in significantly higher concentrations of toluene (210%) and xylene (240%) in blood throughout the entire 9-day exposure period. These results strongly suggest mutual metabolic interactions (inhibition) between toluene and xylene that affect the metabolic disposition of both solvents and ultimately the biological monitoring of data of exposure to a combination of solvents in rats. 相似文献
88.
The reproductive performance of three species of Callitrichidae housed under identical conditions, including relatively spacious caging and visual screening, was compared. The three species were Callithrix jacchus, Saguinus fuscicollis, and Saguinus oedipus. Callithrix jacchus was the most reliable breeder, with the lowest percentage of stillborn and the highest post-weaning survival. While the reproductive performance of S oedipus was better than that generally reported for other colonies, the reproductive performance of the Saguinus species was still poorer than that of C jacchus. The two Saguinus species did not differ significantly in either percentage of stillborn or post-weaning survival. None of the species showed infertility due to lactation, but the mean inter-birth interval was significantly longer for S oedipus than for either C jacchus or S fuscicollis. 相似文献
89.
Pseudomonas aeruginosa diaminopimelate decarboxylase: evolutionary relationship with other amino acid decarboxylases 总被引:1,自引:0,他引:1
Martin C; Cami B; Yeh P; Stragier P; Parsot C; Patte JC 《Molecular biology and evolution》1988,5(5):549-559
The lysA gene encodes meso-diaminopimelate (DAP) decarboxylase
(E.C.4.1.1.20), the last enzyme of the lysine biosynthetic pathway in
bacteria. We have determined the nucleotide sequence of the lysA gene from
Pseudomonas aeruginosa. Comparison of the deduced amino acid sequence of
the lysA gene product revealed extensive similarity with the sequences of
the functionally equivalent enzymes from Escherichia coli and
Corynebacterium glutamicum. Even though both P. aeruginosa and E. coli are
Gram-negative bacteria, sequence comparisons indicate a greater similarity
between enzymes of P. aeruginosa and the Gram- positive bacterium C.
glutamicum than between those of P. aeruginosa and E. coli enzymes.
Comparison of DAP decarboxylase with protein sequences present in data
bases revealed that bacterial DAP decarboxylases are homologous to mouse
(Mus musculus) ornithine decarboxylase (E.C.4.1.1.17), the key enzyme in
polyamine biosynthesis in mammals. On the other hand, no similarity was
detected between DAP decarboxylases and other bacterial amino acid
decarboxylases.
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90.