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981.
LAI FERN OW DAVID WHITEHEAD† ADRIAN S. WALCROFT‡ MATTHEW H. TURNBULL 《Global Change Biology》2010,16(1):288-302
We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C ( R 10 ) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature ( Q 10 ) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity ( R d / A sat ) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer. 相似文献
982.
We have investigated the usefulness of hypocotyl (cultured on N1B2 medium) and cotyledon explants (on CR medium: Murashige
and Skoog (MS) medium, 3% sucrose, 20 μm benzylaminopurine, pH 5.8) for the regeneration of shoots of the Korean radish ‘Jin
Ju Dae Pyong’. The importance of ethylene (indirectly), polyamines and gelling agent were studied in both media. Although
the addition of ethylene-inhibitors and silver nitrate to the culture media were beneficial towards shoot regeneration and
agar-based treatments (0.8% w/v) being superior in shoot production compared to agarose treatments (0.4% w/v), both explants
responded differently in culture. Hypocotyls cultured in the presence of silver nitrate or aminoethoxyvinylglycine (AVG) regenerated
significantly (p < 0.05) more shoots compared to N1B2 medium alone; supplementation of 20 μM AVG to N1B2 medium gave optimal shoot production
(40% of explants regenerating shoots). The addition of 10 μM AVG to CR medium produced maximum shoot regeneration from cotyledon
explants (60% producing shoots). Plants derived from 3-month-old cultures produced greater seed weights, larger leaves and
greater genetic variability (50–80% of cells having 20–40 chromosomes) compared to seed-derived (85–90% diploid) and plants
from 1-month-old cultures (78–88% diploid). Our results show, that if prolonged culture of explants is avoided, a large number
of phenotypically-normal plants can be produced, which in turn, could be utilized in the genetic improvement of radish. 相似文献
983.
984.
Variation is the raw material for evolution. Evolutionary potential is determined by the amount of genetic variation, but evolution can also alter the visibility of genetic variation to natural selection. Fluctuating environments are suggested to maintain genetic variation but they can also affect environmental variance, and thus, the visibility of genetic variation to natural selection. However, experimental studies testing these ideas are relatively scarce. In order to determine differences in evolutionary potential we quantified variance attributable to population, genotype and environment for populations of the bacterium Serratia marcescens. These populations had been experimentally evolved in constant and two fluctuating environments. We found that strains that evolved in fluctuating environments exhibited larger environmental variation suggesting that adaptation to fluctuations has decreased the visibility of genetic variation to selection. 相似文献
985.
Gupta PK Sharma PK Balyan HS Roy JK Sharma S Beharav A Nevo E 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2002,104(2-3):473-481
The variation in length of the intergenic spacer (IGS) region of the ribosomal DNA repeat unit was examined in 63 accessions
of wild barley, Hordeum spontaneum, and seven accessions of cultivated barley, Hordeum vulgare. The accessions of wild barley were collected from ecologically diverse climatic and edaphic microsites in Israel, and the
barley cultivars were those grown in India. Sixteen spacer-length variants (slvs) observed in the present study presumably
belonged to two known rDNA loci (Rrn1 and Rrn2). Each accession had one or more variants, which together represented the rDNA phenotype. The rDNA phenotypes of wild barley
accessions were widely diverse and differed substantially from those of cultivated barley. The slv phenotypes and the corresponding
alleles were shown to be largely correlated with different climatic, edaphic and ecogeographical microsites and niches (the
”Evolution Canyon” at Lower Nahal Oren, Mount Carmel; and Tabigha, Eastern Upper Galilee Mountains), so that a particular
rDNA phenotype of an accession could be used to predict the climate and soil to which the accession belonged. This sharp microsite
ecogeographic variation in ribosomal DNA appears adaptive in nature, and is presumably driven by climatic and edaphic natural
selection.
Received: 1 March 2001 / Accepted: 21 May 2001 相似文献
986.
Selection at linked sites has important consequences for the properties of neutral variation and for tests of the predictions
of the neutral theory of molecular evolution. We review the theory of the effect of adaptive gene substitutions on neutral
variability at linked sites (hitchhiking or selective sweeps) and discuss theoretical results on the effect of selection against
deleterious alleles on variation at linked sites (background selection). InDrosophila melanogaster there is a clear relation between the frequency of recombination in a given region of the chromosome and the amount of natural
variability in that region. Attempts to predict this relation have given rise to models of selective sweeps and background
selection. We describe possible methods of discriminating between these models, and also discuss the probable strong influence
of selective sweeps on variation in largely nonrecombining genomes, with particular reference toEscherichia coll. Finally we present some unresolved questions and possible directions for future research. 相似文献
987.
Kua-Chun Ou Chih-Yang Wang Kuan-Ting Liu Yi-Ling Chen Yi-Chen Chen Ming-Derg Lai Meng-Chi Yen 《Biochemical and biophysical research communications》2014
Transfer RNA (tRNA) abundance is one of the critical factors for the enhancement of protein productivity in prokaryotic and eukaryotic hosts. Gene copy number of tRNA and tRNA codon usage bias are generally used to match tRNA abundance of protein-expressing hosts and to optimize the codons of recombinant proteins. Because sufficient concentration of intracellular tRNA and optimized codons of recombinant proteins enhanced translation efficiency, we hypothesized that sufficient supplement of host’s tRNA improved protein productivity in mammalian cells. First, the small tRNA sequencing results of CHO-K1 cells showed moderate positive correlation with gene copy number and codon usage bias. Modification of human interleukin-2 (IL-2) through codons with high gene copy number and high codon usage bias (IL-2 HH, modified on Leu, Thr, Glu) significantly increased protein productivity in CHO-K1 cells. In contrast, modification through codons with relatively high gene copy number and low codon usage bias (IL-2 HL, modified on Ala, Thr, Val), or relatively low gene copy number and low codon usage bias (IL-2 LH, modified on Ala, Thr, Val) did not increase IL-2 productivity significantly. Furthermore, supplement of the alanine tRNA or threonine tRNA increased IL-2 productivity of IL-2 HL. In summary, we revealed a potential strategy to enhance productivity of recombinant proteins, which may be applied in production of protein drug or design of DNA vaccine. 相似文献
988.
The trade‐off between offspring size and number can present a conflict between parents and their offspring. Because egg size is constrained by clutch size, the optimal egg size for offspring fitness may not always be equivalent to that which maximizes parental fitness. We evaluated selection on egg size in three turtle species (Apalone mutica, Chelydra serpentina and Chrysemys picta) to determine if optimal egg sizes differ between offspring and their mothers. Although hatching success was generally greater for larger eggs, the strength and form of selection varied. In most cases, the egg size that maximized offspring fitness was greater than that which maximized maternal fitness. Consistent with optimality theory, mean egg sizes in the populations were more similar to the egg sizes that maximized maternal fitness, rather than offspring fitness. These results provide evidence that selection has maximized maternal fitness to achieve an optimal balance between egg size and number. 相似文献
989.
Facultative paedomorphosis is the ability of a salamander to either metamorphose into a terrestrial, metamorphic adult or
retain a larval morphology to become a sexually mature paedomorphic adult. It has been hypothesized that density and initial
body size variation within populations are instrumental in cueing metamorphosis or paedomorphosis in salamanders, yet few
studies have adequately tested these hypotheses in long-term experiments. Beginning in the spring of 2004, 36 experimental
ponds were used to manipulate three body size variation levels (low, medium, high) and two density levels (low, high) of Ambystoma talpoideum larvae. Larvae were individually marked using visible implant elastomers and collected every 2 weeks in order to measure
snout–vent length and mass. Bi-nightly sampling was used to collect new metamorphs as they appeared. Analysis revealed significant
effects of density, size variation and morph on body size of individuals during the summer. Individuals that metamorphosed
during the fall and following spring were significantly larger as larvae than those becoming paedomorphic across all treatments.
These results support the Best-of-a-Bad-Lot hypothesis, which proposes that the largest larvae metamorphose in order to escape
unfavorable aquatic habitats. Large larvae may metamorphose to leave aquatic habitats, regardless of treatment, due to the
colder climate and lower productivity found in Kentucky, which is in the northern-most part of A. talpoideum’s range. By maintaining a long-term experiment, we have provided evidence for the transition of both larvae and paedomorphs
into metamorphs during fall and spring metamorphosis events. Furthermore, the production of similar morphs under different
environmental conditions observed in this research suggests that the ecological mechanisms maintaining polyphenisms may be
more diverse that first suspected.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
990.
K. Hancock D. E. Broughel I. N. S. Moura A. Khan N. J. Pieniazek A. E. Gonzalez H. H. Garcia R. H. Gilman V. C. W. Tsang 《International journal for parasitology》2001,31(14):1601-1607
We examined the genetic variability in the pig–human tapeworm, Taenia solium, by sequencing the genes for cytochrome oxidase I, internal transcribed spacer 1, and a diagnostic antigen, Ts14, from individual cysts isolated from Peru, Colombia, Mexico, India, China, and the Philippines. For these genes, the rate of nucleotide variation was minimal. Isolates from these countries can be distinguished based on one to eight nucleotide differences in the 396 nucleotide cytochrome oxidase I (COI) sequence. However, all of the 15 isolates from within Peru had identical COI sequences. The Ts14 sequences from India and China were identical and differed from the Peru sequence by three nucleotides in 333. These data indicate that there is minimal genetic variability within the species T. solium. Minimal variability was also seen in the ITS1 sequence, but this variation was observed within the individual. Twenty-two cloned sequences from six isolates sorted into 13 unique sequences. The variability observed within the sequences from individual cysts was as great as the variability between the isolates. 相似文献