Diacylglycerol acyltransferase (EC 2.3.1.20) activity was assayed during the maturation of seeds of oilseed rape (Brassica napus 1.) and safflower (Carthamus tinctorius 1.). Developmental studies were also conducted with microspore-derived embryos of oilseed rape (6. napus 1. cv Topas) and an embryogenic microsporederived cell-suspension culture of winter oilseed rape (B. napus 1.cv Jet Neuf), In the maturing seeds, diacylglycerol acyltransferase activity increased to a maximum during rapid accumulation of lipid and declined, thereafter, with seed maturity. In microspore-derived embryos of oilseed rape (cv Topas), high levels of diacylglycerol acyltransferase activity were found throughout the early torpedo to late cotyledonary developmental stages with maximum enzyme specific activity associated with the mid-cotyledonary developmental stage. The cell-suspension culture of winter oilseed rape (cv Jet Neuf) contained 3 to 4% triacylglycerol on a dry weight basis and represented about half of the total lipid. The fatty acid profile of total lipid and triacylglycerol in the cell-suspension culture was similar in samples taken during a 1-year period. The Jet Neuf culture contained diacylglycerol acyltransferase with specific activity similar to that of Topas microspore-derived embryos. Jet Neuf diacylglycerol acyltransferase also displayed an enhanced specificity for erucoyl-COA over oleoyl-COA when assayed with 14 p~ acyl-coenzyme A in the readion mixture. The specific activity of diacylglycerol acyltransferase in homogenates prepared from the Jet Neuf culture ranged from 5 to 15 pmol of triacylglycerol min-' mg-' of protein when assayed at intervals during a period of 1 year. Thus, the cell-suspension culture may represent an attractive tissue source for purification and characterization of triacylglycerol biosynthetic enzymes.The determination of the quantity and composition of storage lipid during seed maturation in various oilseed crops has been reported in numerous studies such as those of Sims ' Supported by the following grants to R
The geographical distribution of chloroplast DNA (cpDNA) variation in 39 populations of two hybridizing Mexican red oaks, Quercus affinis and Q. laurina, was investigated using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Six haplotypes were identified. Of these, two (H1 and H4), separated by four mutations, had high frequencies (58 and 23% of the individuals, respectively) and were present across the whole geographical range of both species, often co occurring in the same populations. The other four haplotypes were rare, geographically restricted, and are probably derived from the two frequent haplotypes. Latitudinal or other clinal patterns in diversity levels or haplotype composition of populations were not apparent. The pattern of haplotype distribution was characterized by some mosaicism, with contrasting populations often situated in proximity. Average within-population diversity (hS=0.299) and population differentiation (GST=0.499) were, respectively, higher and lower than values reported in previous studies of oak species. There was evidence for phylogeographical structure, as indicated by NST (0.566) being significantly higher than GST. Haplotypic variation was largely species-independent, although some very weak associations were detected between haplotypes H1 and H4 and morphological and nuclear molecular variation correspondingly characterizing Q. affinis and Q. laurina. These oaks probably did not experience a marked restriction to one or a few particular subregions of their present range during the last glacial cycle. It is more likely that substantial populations persisted throughout several episodes of climatic change, but experienced recurrent latitudinal and altitudinal migrations which may have caused the widespread distribution of haplotypes H1 and H4 and frequent intermixing of populations.
Abstract. Chloroplast DNA (cpDNA) haplotype variation is compared among alpine and prairie/montane species of Packera from a region in southwestern Alberta that straddles the boundary of Pleistocene glaciation. The phylogeny of the 15 haplotypes identified reveals the presence of two groups: one generally found in coastal and northern species and the other from species in drier habitats. The presence of both groups in all four species and most populations from southwestern Alberta is evidence of past hybridization involving species or lineages that may no longer be present in the region. With the exception of the alpine P. subnuda (⌽ ST ϭ 1.0), interpopulational subdivision of haplotype variation is low (⌽ ST Ͻ 0.350), suggesting that interpopulational gene flow is high. However, based on haplotype distribution patterns, we propose that Pleistocene hybridization and incomplete lineage sorting have resulted in reduced subdivision of interpopulational variation so that gene flow may not be as high as indicated. Drift has been more important in the alpine species populations, especially P. subnuda.
Packera pseudaurea (Rydb.) Weber & Löve has previously been identified as a species containing an unusually high level of chloroplast DNA (cpDNA) polymorphism. Proposed sources of this intrapopulational variation have included hybridization and introgression, either ongoing or resulting from migrations associated with past glacial events. Restriction site analysis was performed on individuals from seven populations of P. pseudaurea from southern Alberta and adjacent Montana to assess variation more precisely. High levels of intrapopulational polymorphisms comprising a total of nine different haplotypes, only one apparently unique to the species, were detected in all but one southern population. The haplotypes separate into two groups upon phylogenetic analysis, a separation that corresponds to that detected in a wider sampling of Packera species. With one or two exceptions, the haplotypes of one group are also found in species based west of the Rocky Mountains. Those of the other are found in species based all over North America. These results lend support to the hypothesis that the variation in P. pseudaurea originated when the ranges of different Packera species were brought together by glaciation.Key words: Packera, cpDNA, phytogeography, haplotype variation, glaciation.
Packera sanguisorboides is endemic to the Sangre de Cristo and Sacramento Mountains of New Mexico, USA. As such, its distribution spans the boundary between two major floristic regions: the southern Rocky Mountain region and the Madrean region. Chloroplast DNA haplotype polymorphism patterns in populations from both regions show that most of the molecular variance exists among populations rather than between mountain ranges and that hybridization with at least one other Packera species containing distinct cpDNA haplotypes has contributed to the cpDNA diversity within P. sanguisorboides. Based on morphological and cpDNA data, the closest relatives to P. sanguisorboides are thought to be mesic species similar to P. glabella and P. sanguisorbae.
Packera pauciflora (Pursh) Löve & Löve is a wide ranging alpine or subalpine species that is disjunct in three regions of North America: the northern Rocky mountains, Quebec-Labrador, and the Sierra Nevada of California. It is one of two Packera species known to be self-fertile. We assessed intrapopulational chloroplast haplotype diversity (n) and haplotype nucleotide diversity ($ π) and found it was lower and population structure (Φ st ), higher than all but one of the five other Packera species examined to date. In addition, distinct differences exist between populations from California and those from the Rocky mountains and eastern Canada. Our results suggest that geographical isolation, hybridization, and breeding system have all played a role in the formation of haplotype diversity patterns, and that, in spite of the wide disjunctions, the species is monophyletic.
Résumé :Le Packera pauciflora (Pursh) Löve & Löve est une espèce alpine ou subalpine à large distribution, dont l'aire est disjointe en trois régions de l'Amérique du Nord : le nord des Montagnes Rocheuses, le Québec-Labrador, et la Sierra Nevada en Californie. Il s'agit d'une des deux espèces de Packera connues comme autofertiles. Les auteurs ont évalué la diversité des haplotypes chloroplastiques (n) et des haplotypes nucléiques ($ π) à l'intérieur des populations, et ils ont constaté qu'elle est plus faible, et que la structure de population (M st ) est plus élevée, que chez toutes les espèces de Packera examinées à date, sauf une. De plus, on observe des différences entre les populations de la Californie, des Montagnes Rocheuses et de l'est du Canada. Les résultats suggèrent que l'isolement géographique, les croisements ainsi que les systèmes de croisement, ont tous joué un rôle dans la formation des patrons de diversité des haplotypes, et que, en dépit de larges disjonctions d'aires, l'espèce demeure monophylétique.
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