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101.
102.
Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in KwaZulu-Natal failed to yield a single seed, only empty panicles. Laboratory experiments showed that vernalisation had no consistent effect on seed production. Field- and laboratory-grown plants produced seeds in the 2010/2011 season, because of having sufficient time at optimum temperatures required for seed production (1 491 and 1 585 hours, respectively), compared to a shorter period (1 352 hours) of suitable temperatures during the 2009/2010 growing season. An inadequate period of optimum temperatures (15–25°C) during seed production resulted in the lack of seeds in the field in the 2009/2010 growing season. This study showed that temperature and duration of exposure thereto during the seed-production period play vital roles in G. maxima sexual reproduction. 相似文献
103.
Marmoset phylogenetics, conservation perspectives, and evolution of the mtDNA control region 总被引:3,自引:1,他引:2
Tagliaro CH; Schneider MP; Schneider H; Sampaio IC; Stanhope MJ 《Molecular biology and evolution》1997,14(6):674-684
Marmosets (genus Callithrix) are a diverse group of platyrrhine primates
with 13-15 purported taxa, many of them considered endangered.
Morphological analyses constitute most of the basis for recognition of
these forms as distinct taxa. The purpose of this study was to provide a
molecular view, based on mitochondrial control region sequences, of the
evolutionary history of the marmosets, concomitant with a molecular
phylogenetic perspective on species diversity within the group. An
additional purpose was to provide the first comparative examination of a
complete New World monkey control region sequence with those of other
mammals. The phylogenetic analyses provide convincing support for a split
between the Atlantic forest and Amazonian marmosets, with the inclusion of
the pygmy marmoset (Cebuella pygmaea) at the base of the Amazonian clade.
The earliest branch of the Atlantic forest group was C. aurita. In the
Amazonian group, the analyses do not support the recognition of C.
humeralifer and the recently described C mauesi as distinct taxa. They do,
however, support a clear distinction between C. argentata and a strongly
supported mixed clade of C. humeralifer and C. mauesi. In the Atlantic
forest group, the phylogenetic tree suggests mixing between C. penicillata,
C. kuhli, and possibly C. jacchus. Most of the sequence features
characteristic of other mammal control regions were also evident in
marmosets, with the exception that conserved sequence blocks (CSBs) 2 and 3
were not clearly identifiable. Tandem repeat units often associated with
heteroplasmy in a variety of other mammals were not evident in the marmoset
sequences.
相似文献
104.
Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae) 总被引:5,自引:0,他引:5
Campbell CS; Wojciechowski MF; Baldwin BG; Alice LA; Donoghue MJ 《Molecular biology and evolution》1997,14(1):81-90
Individual plants of several Amelanchier taxa contain many polymorphic
nucleotide sites in the internal transcribed spacers (ITS) of nuclear
ribosomal DNA (nrDNA). This polymorphism is unusual because it is not
recent in origin and thus has resisted homogenization by concerted
evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the
result of gene flow between two major North American clades resolved by
phylogenetic analysis of ITS sequences. Western North American species plus
A. humilis and A. sanguinea of eastern North America form one clade (A),
and the remaining eastern North American Amelanchier make up clade B. Five
eastern North American taxa are polymorphic at many of the nucleotide sites
where clades A and B have diverged and are thought to be of hybrid origin,
with A. humilis or A. sanguinea as one parent and various members of clade
B as the other parent. Morphological evidence suggests that A. humilis is
one of the parents of one of the polymorphic taxa, a microspecies that we
refer to informally as A. "erecta." Sequences of 21 cloned copies of the
ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical
to A. humilis sequence or to the clade B consensus sequence, or they are
apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier
"erecta" and another polymorphic taxon are suspected to be relatively old
because both grow several hundred kilometers beyond the range of one of
their parents. ITS sequence polymorphisms have apparently persisted in
these two taxa perhaps because of polyploidy and/or agamospermy (asexual
seed production), which are prevalent in the genus.
相似文献
105.
Rowan A. Grayling Kathryn A. Bailey John N. Reeve 《Extremophiles : life under extreme conditions》1997,1(2):79-88
The DNA-binding and nuclease-protection properties of the HMf histones from the hyperthermophilic archaeon Methanothermus fervidus have been shown to be consistent with the formation of nucleosome-like structures (NLS). These proteins bind to DNA molecules
as short as 20 bp and form complexes that protect DNA fragments from micrococcal nuclease (MNase) digestion that are 30 bp,
∼ 60 bp and multiples of ∼ 60 bp in length. The sequences of 49 of the ∼ 60-bp DNA fragments protected from MNase digestion
by HMfA have been determined and their intrinsic curvatures calculated. A circular permutation gel mobility-shift assay was
used to determine directly the curvatures for five of these sequences. HMfA bound to intrinsically curved and noncurved DNAs,
but exhibited a slight preference for the model curved DNA in binding competitions with a model noncurved DNA. The results
obtained are consistent with the concept that the archaeal NLS is analogous, and possibly homologous, to the central core
of the eukaryal nucleosome formed by a histone (H3 + H4)2 tetramer.
Received: August 11, 1996 / Accepted: November 12, 1996 相似文献
106.
107.
The study of cellular “microexudates” by ellipsometry and their relationship to the cell coat 总被引:6,自引:0,他引:6
G. Poste L. W. Greenham L. Mallucci P. Reeve D. J. Alexander 《Experimental cell research》1973,78(2):303-313
The use of ellipsometry, an optical technique for the detection of very thin films, to measure the thickness of the ‘microexudate’ deposited by mammalian cells on glass and other solid surfaces is described. Significant differences were found in the thickness and the rate of formation of microexudates in different cell types. Cultivation of cells at low temperatures and in medium supplemented with actinomycin D and cycloheximide inhibited the production of cellular microexudates, indicating that these materials are actively synthesized by the cell and do not result merely from passive leakage of macromolecular material as suggested previously. Evidence is reviewed to show that cellular microexudates have a number of properties in common with the cell coat material. 相似文献
108.
Cell Division of Escherichia coli BUG-6: Effect of Varying the Length of Growth at the Nonpermissive Temperature 总被引:11,自引:7,他引:4
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When Escherichia coli BUG-6 is grown at 42 C and then returned to 30 C, the division kinetics during the recovery at 30 C are dependent on the length of time the cells were grown at 42 C. If chloramphenicol is added when the cells are shifted from 42 to 30 C, no division occurs if the period at 42 C is less than 4 min or more than 110 min. Maximum division occurs when the period at 42 C is 50 min. A discussion of these results with reference to a previously proposed model is presented. 相似文献
109.
Bacteriophage SP01, SP17, and phi29 rapidly absorb irreversibly to minicells of Bacillus subtilis but do not produce a lytic cycle in minicells. 相似文献
110.
Minicells of Bacillus subtilis 总被引:50,自引:28,他引:22
John N. Reeve Neil H. Mendelson Sheila I. Coyne Linda L. Hallock 《Journal of bacteriology》1973,114(2):860-873
After nitrosoguanidine (N-methyl-N'-nitro-N-nitrosoguanidine) mutagenesis, two Bacillus subtilis mutants (div IV-A1 and div IV-B1) were isolated that are defective in the location of division site along cell length. Both mutations were transferred into strain CU403 by transformation, and their properties were studied in the CU403 genetic background. Location of divisions in close proximity to cell pole regions in both mutants results in minicell production. Purified minicells contain a ratio of ribonucleic acid to protein comparable to that found in the parent cells. Autoradiographs of (3)H-thymine incorporation into deoxyribonucleic acid (DNA), thymine-2-(14)C incorporation into DNA, electron micrographs, and chemical analyses for DNA all fail to demonstrate DNA in the minicells. Minicells produced by both mutants are highly motile, an indication of functional energy metabolism. Electron micrographs reveal that minicells are produced by a structurally normal division mechanism and that minicells contain a normal cell surface. The div IV-A1 mutation has been mapped by PBS1 transduction linked to ura. The div IV-B1 mutation is closely linked to pheA by both PBS1 transduction and by co-transformation. 相似文献