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Changes in polyamine content during in vivo maturation and in vitro culture of maize (Zea mays L.) pollen were studied. The endogenous content of free, conjugated and bound polyamines was analyzed during 30 days of pollen evolution, in both developmental pathways (microsporogenesis and androgenesis). The induction of androgenesis from cold-pretreated uninucleate pollen results, in most of cases, in a lower total polyamine content than that of the in vivo uninucleate pollen. These differences indicate that polyamine metabolism is altered during the induction of androgenesis, and this could be a consequence of increased polyamine assimilation. In general, pollen stages that involve cell division (tetrades, pre-anthesis pollen and four-day cultured pollen) are characterized by a predominance of free Spd. The increase of Spd and Spm in 15-day cultured pollen, when the first embryoids are formed, outline the possible implication of these polyamines in embryogenetic processes. Furthermore, these findings may contribute to the improvement of maize androgenesis yield, especially in recalcitrant genotypes, by the exogenous application of polyamines or polyamine-inhibitors to the culture medium.Abbreviations PAs
polyamines
- Put
putrescine
- Spd
spermidine
- Spm
spermine
- S
free polyamine fraction
- SH
conjugated polyamine fraction
- PH
bound polyamine fraction 相似文献
44.
Regulation of hepatic cholesterol and lipoprotein metabolism in ethinyl estradiol-treated rats 总被引:2,自引:0,他引:2
S K Erickson S Jaeckle S R Lear S M Brady R J Havel 《Journal of lipid research》1989,30(11):1763-1771
The regulation of hepatic cholesterol and lipoprotein metabolism was studied in the ethinyl estradiol-treated rat in which low density lipoprotein (LDL) receptors are increased many fold. Cholesterol synthesis was reduced at both its diurnal peak and trough by ethinyl estradiol. The diurnal variation in 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was abolished, whereas that for acyl coenzyme A: cholesterol acyltransferase (ACAT) was retained. LDL receptor number did not vary diurnally. Feeding these animals a cholesterol-rich diet for 48 h suppressed cholesterol synthesis and reductase activities to levels similar to those found in cholesterol-fed control animals, but ACAT activity was unaffected. LDL receptors were reduced about 50%. Intravenously administered cholesterol-rich lipoproteins suppressed HMG-CoA reductase and LDL receptors in 2 h but had a variable effect on ACAT activity. Intragastric administration of mevalonolactone reduced reductase and increased acyltransferase activity but had little effect on LDL receptors when given 2 or 4 h before death. Although animals fed a cholesterol-rich diet before and during ethinyl estradiol treatment became hypocholesterolemic, free and esterified cholesterol concentrations in liver were high as was ACAT activity. HMG-CoA reductase was inhibited to levels found in control animals fed the cholesterol-rich diet. LDL receptors were increased to a level about 50% of that reached in animals receiving a control diet and ethinyl estradiol. These data demonstrate that key enzymes of hepatic cholesterol metabolism and hepatic LDL receptors respond rapidly to cholesterol in the ethinyl estradiol-treated rat. Furthermore, estradiol increases LDL receptor activity several fold in cholesterol-loaded livers. 相似文献
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Marcelo dos Santos Guerra 《Plant Systematics and Evolution》1989,168(1-2):83-86
Azima tetracantha has an asymmetrical karyotype with large chromosomes and a large amount of heterochromatin. The haploid number (n = 11) may represent the base number of the family. However, a possible secondary origin of this base number is also considered. 相似文献
49.
O Lider L M Santos C S Lee P J Higgins H L Weiner 《Journal of immunology (Baltimore, Md. : 1950)》1989,142(3):748-752
We have previously demonstrated that the oral administration of guinea pig myelin basic protein (MBP) protects Lewis rats against the induction of experimental autoimmune encephalomyelitis (EAE) when subsequently immunized with guinea pig MBP in CFA. In addition, animals made orally tolerant to MBP also have diminished proliferative and antibody responses to MBP, but not to other Ag. Nonetheless, the mechanism of oral tolerance to MBP in the EAE model remains undefined. In the present study, we report that T cells isolated from the spleen and mesenteric lymph nodes of MBP orally tolerized animals can adoptively transfer protection against EAE. Furthermore, these T cells are of the CD8+ subclass. In addition, CD8+ T cells from MBP orally tolerized animals also suppress in vitro proliferative responses and antibody responses to MBP in an Ag-specific fashion. These results demonstrate that active cellular mechanisms are initiated after oral administration of an autoantigen that can down-regulate an experimental autoimmune disease and provide the basis for the isolation and characterization of the cells mediating both in vivo and in vitro suppression. 相似文献
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A Alvarez U Hidalgo M E Kawada A Munizaga A Zú?iga L Ibánez C S Koenig M J Santos 《Analytical biochemistry》1992,206(1):147-154
This paper shows the successful isolation of peroxisomes from human liver samples that were kept frozen at -70 degrees C. Purification of these peroxisomes was obtained by a combination of two subcellular fractionation techniques: differential centrifugation and isopycnic fractionation in Nycodenz density gradients. Peroxisome integrity was evaluated by latency measurements and by ultrastructural observation. The procedure described here may be useful for the isolation of other subcellular organelles from frozen human samples. 相似文献