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排序方式: 共有108条查询结果,搜索用时 15 毫秒
21.
Humaira Ashraf Amjad M. Husaini M. Ashraf Bhat GA Parray Salim Khan Nazir A. Ganai 《Physiology and Molecular Biology of Plants》2016,22(4):547-555
A set of 24 of SSR markers were used to estimate the genetic diversity in 16 rice genotypes found in Western Himalayas of Kashmir and Himachal Pradesh, India. The level of polymorphism among the genotypes of rice was evaluated from the number of alleles and PIC value for each of the 24 SSR loci. A total of 68 alleles were detected across the 16 genotypes through the use of these 24 SSR markers The number of alleles per locus generated varied from 2 (RM 338, RM 452, RM 171) to 6 (RM 585, RM 249, RM 481, RM 162). The PIC values varied from 0.36 (RM 1) to 0.86 (RM 249) with an average of 0.62 per locus. Based on information generated, the genotypes got separated in six different clusters. Cluster 1 comprised of 4 genotypes viz; Zag 1, Zag 13, Pusa sugandh 3, and Zag 14, separated from each other at a similarity value of 0.40. Cluster second comprised of 3 landraces viz; Zag 2. Zag 4 and Zag10 separated from each other at a similarity value of 0.45. Cluster third comprised of 3 genotypes viz; Grey rice, Mushk budji and Kamad separated from each other at a similarity value of 0.46. Cluster fourth had 2 landraces viz; Kawa kreed and Loual anzul, and was not sub clustered. Fifth cluster had 3 genotypes viz; Zag 12, Purple rice and Jhelum separated from each other at a similarity value of 0.28. Cluster 6 comprised of a single popular variety i.e. Shalimar rice 1 with independent lineage. 相似文献
22.
Slipped-strand mispairing: a major mechanism for DNA sequence evolution 总被引:141,自引:13,他引:128
Simple repetitive DNA sequences are a widespread and abundant feature of
genomic DNA. The following several features characterize such sequences:
(1) they typically consist of a variety of repeated motifs of 1-10
bases--but may include much larger repeats as well; (2) larger repeat units
often include shorter ones within them; (3) long polypyrimidine and poly-CA
tracts are often found; and (4) tandem arrangements of closely related
motifs are often found. We propose that slipped-strand mispairing events,
in concert with unequal crossing- over, can readily account for all of
these features. The frequent occurrence of long tandem repeats of
particular motifs (polypyrimidine and poly-CA tracts) appears to result
from nonrandom patterns of nucleotide substitution. We argue that the
intrahelical process of slipped-strand mispairing is much more likely to be
the major factor in the initial expansion of short repeated motifs and
that, after initial expansion, simple tandem repeats may be predisposed to
further expansion by unequal crossing-over or other interhelical events
because of their propensity to mispair. Evidence is presented that
single-base repeats (the shortest possible motifs) are represented by
longer runs in mammalian introns than would be expected on a random basis,
supporting the idea that SSM may be a ubiquitous force in the evolution of
the eukaryotic genome. Simple repetitive sequences may therefore represent
a natural ground state of DNA unselected for coding functions.
相似文献
23.
Complete sequences of the rRNA genes of Drosophila melanogaster 总被引:19,自引:0,他引:19
In this, the first of three papers, we present the sequence of the
ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of
D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S
(123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat
of D. melanogaster is AT rich (65.9% overall), with the spacers being
particularly AT rich. Analysis of DNA simplicity reveals that, in contrast
to the intergenic spacer (IGS) and the external transcribed spacer (ETS),
most of the rRNA gene regions have been refractory to the action of
slippage-like events, with the exception of the 28S rRNA gene expansion
segments. It would seem that the 28S rRNA can accommodate the products of
slippage-like events without loss of activity. In the following two papers
we analyze the effects of sequence divergence on the evolution of (1) the
28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary
structures among eukaryotic species, respectively. Our detailed analyses
reveal, in addition to unequal crossing-over, (1) the involvement of
slippage and biased mutation in the evolution of the rDNA multigene family
and (2) the molecular coevolution of both expansion segments and the
nucleotides involved with compensatory changes required to maintain
secondary structures of RNA.
相似文献
24.
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26.
An overview of models of stomatal conductance at the leaf level 总被引:4,自引:0,他引:4
GAËLLE DAMOUR THIERRY SIMONNEAU HERVÉ COCHARD LAURENT URBAN 《Plant, cell & environment》2010,33(9):1419-1438
Stomata play a key role in plant adaptation to changing environmental conditions as they control both water losses and CO2 uptake. Particularly, in the context of global change, simulations of the consequences of drought on crop plants are needed to design more efficient and water‐saving cropping systems. However, most of the models of stomatal conductance (gs) developed at the leaf level link gs to environmental factors or net photosynthesis (Anet), but do not include satisfactorily the effects of drought, impairing our capacity to simulate plant functioning in conditions of limited water supply. The objective of this review was to draw an up‐to‐date picture of the gs models, from the empirical to the process‐based ones, along with their mechanistic or deterministic bases. It focuses on models capable to account for multiple environmental influences with emphasis on drought conditions. We examine how models that have been proposed for well‐watered conditions can be combined with those specifically designed to deal with drought conditions. Ideas for future improvements of gs models are discussed: the issue of co‐regulation of gs and Anet; the roles of CO2, absissic acid and H2O2; and finally, how to better address the new challenges arising from the issue of global change. 相似文献
27.
Background
The cell shape and morphology of plant tissues are intimately related to structural modifications in the primary cell wall that are associated with key processes in the regulation of cell growth and differentiation. The primary cell wall is composed mainly of cellulose immersed in a matrix of hemicellulose, pectin, lignin and some structural proteins. Xyloglucan is a hemicellulose polysaccharide present in the cell walls of all land plants (Embryophyta) and is the main hemicellulose in non-graminaceous angiosperms. 相似文献28.
A systematic lab-scale experimental investigation is reported for the external nitrification (EN) biological nutrient removal (BNR) activated sludge (ENBNRAS) system, which is a combined fixed and suspended medium system. The ENBNRAS system was proposed to intensify the treatment capacity of BNR-activated sludge (BNRAS) systems by addressing two difficulties often encountered in practice: (a) the long sludge age for nitrification requirement; and (b) sludge bulking. In the ENBNRAS system, nitrification is transferred from the aerobic reactor in the suspended medium activated sludge system to a fixed medium nitrification system. Thus, the sludge age of the suspended medium activated sludge system can be reduced from 20 to 25 days to 8 to 10 days, resulting in a decrease in reactor volume per ML wastewater treated of about 30%. Furthermore, the aerobic mass fraction can also be reduced from 50% to 60% to <30% and concommitantly the anoxic mass fraction can be increased from 25% to 35% to >55% (if the anaerobic mass fraction is 15%), and thus complete denitrification in the anoxic reactors becomes possible. Research indicates that both the short sludge age and complete denitrification could ameliorate anoxic aerobic (AA) or low food/microorganism (F/M) ratio filamentous bulking, and hence reduce the surface area of secondary settling tanks or increase the treatment capacity of existing systems. The lab-scale experimental investigations indicate that the ENBNRAS system can obtain: (i) very good chemical oxygen demand (COD) removal, even with an aerobic mass fraction as low as 20%; (ii) high nitrogen removal, even for a wastewater with a high total kjeldahl nitrogen (TKN)/COD ratio, up to 0.14; (iii) adequate settling sludge (diluted sludge volume index [DSVI] <100 mL/g); and (iv) a significant reduction in oxygen demand. 相似文献
29.
迁徙水鸟保护对生物多样性保护具有重要意义。开展水鸟种群数量和幼鸟比例监测,对科学评估其种群变化趋势、制定长期保护策略具有重要价值。长江中下游湿地是东亚-澳大利西亚迁徙路线上重要的水鸟越冬区之一。本研究采用野外同步调查等方法对该区域87个湿地的亟需保护和具有代表性的10种大型越冬水鸟,其中雁形目6种,分别是鸿雁Anser cygnoides、豆雁A.fabalis、灰雁A.grus、白额雁A.albifrons、小白额雁A.erythropus和小天鹅Cygnus columbianus;鹤形目4种,分别是白鹤Leucogeranus leucogeranus、白枕鹤Antigone vipio、灰鹤Grus grus和白头鹤G.monacha,进行了长期监测(2003—2019年冬季),并结合相关文献,评估其种群变化趋势、幼鸟比例和死亡率。研究结果如下:(1)2005—2019年3种水鸟(豆雁、灰雁和灰鹤)的种群数量呈上升趋势,7种水鸟(鸿雁、白额雁、小白额雁、小天鹅、白鹤、白枕鹤和白头鹤)种群数量呈下降趋势;(2)种群趋势下降组(N=7)和上升组(N=3)的幼鸟比例均值在2016—2... 相似文献
30.
Ramphao M Wentzel MC Merritt R Ekama GA Young T Buckley CA 《Biotechnology and bioengineering》2005,89(6):630-646
Installing membranes for solid-liquid separation into biological nutrient removal (BNR) activated sludge (AS) systems makes a profound difference not only in the design of the BNR system itself, but also in the design approach for the whole wastewater treatment plant (WWTP). In multizone BNR systems with membranes in the aerobic reactor and fixed volumes for the anaerobic, anoxic, and aerobic zones (i.e., fixed volume fractions), the mass fractions can be controlled (within a range) with the interreactor recycle ratios. This zone mass fraction flexibility is a significant advantage in membrane BNR systems over conventional BNR systems with SSTs, because it allows for changing of the mass fractions to optimize biological N and P removal in conformity with influent wastewater characteristics and the effluent N and P concentrations required. For PWWF/ADWF ratios in the upper range (f(q) approximately 2.0), aerobic mass fractions in the lower range (f(maer) < 0.60), and high (usually raw) wastewater strengths, the indicated mode of operation of MBR BNR systems is as extended aeration WWTPs. Although the volume reduction compared with equivalent conventional BNR systems with secondary settling tanks is not as large (40% to 60%), the cost of the membranes can be offset against sludge thickening and stabilization costs. Moving from a flow-unbalanced raw wastewater system to a flow-balanced (f(q) = 1), low (usually settled) wastewater strength system can double the ADWF capacity of the biological reactor, but the design approach of the WWTP changes from extended aeration to include primary sludge stabilization. The cost of primary sludge treatment then has to be paid from the savings from the increased WWTP capacity. 相似文献