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991.
麦类作物遗传转化(英) 总被引:2,自引:0,他引:2
麦类作物包括小麦 (TriticumaestivumL .)、硬粒小麦 (Triticumturgidumconv .durumDest.e.m)、大麦 (HordeumvulgareL .)、黑麦 (SecalecerealL .)、燕麦 (AvenasativaL .)及小大麦 (×TritordeumAschersonetGraebuer.)。自从基因枪被发明以来 ,科学家们已经利用来自麦类作物的幼胚、盾片、成熟种子胚、花粉粒、花药、幼穗、叶基组织、发芽种子幼苗的顶端分生组织及其愈伤组织或培养物作为外植体 ,通过基因枪、农杆菌介导、PEG法、电激法、微注射法、硅化纤维素介导、幼穗注射法等技术先后将一些选择标记基因、报告基因和有用的目的基因如抗真菌、抗虫、籽粒品质、抗干旱基因等转化到麦类作物中。转基因植物表现为抗性增强或籽粒的加工品质提高和营养成份增加。被转化的基因通常以单位点多拷贝的形式随机整合到受体细胞的基因组中 ,并以孟德尔规律遗传。整合位点一般分布在染色体的近端粒区域 ,整合的拷贝数大多为 5~ 10个拷贝 ,最高可达到 5 0个拷贝。在转化过程中 ,被转化的质粒上的片段包括选择标记基因、目标基因、甚至质粒的抗生素基因和其他无关序列 ,随机地连接并形成多个分子量大小不等 ,组成成分不同的分子簇 ,或首先由其中一个分子簇整合到植物基因组中 ,这会导致在整合位点附近产生“热点 相似文献
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993.
During the past decade, there have been many optimistic claims concerning the potential of novel oil-based products from genetically engineered crops, particularly for the manufacture of a new generation of renewable, carbon-neutral, industrial materials. Such claims have been underpinned by an impressive series of scientific advances that have resulted in the isolation of genes encoding most of the enzymes directly involved in oil biosynthesis. In some cases, these enzymes have even been re-engineered by site-directed or random mutagenesis to allow production of new fatty acid profiles that are not present in any existing organism. This has opened up the prospect of engineering `designer oil crops' to produce novel fatty acids with chain lengths from C8 to C24 and with a wide range of industrially useful functionalities, including hydroxylation, epoxidation, and conjugated and non-conjugated double or triple bonds. However, there remain significant technical challenges before this promise of designer transgenic crops is likely to be translated into large-scale commercial reality. For example, it has proved surprisingly difficult to engineer high levels of novel fatty acids in genetically engineered transgenic plants, although many wild type seeds can readily accumulate 90–95% of a single fatty acid in their storage oil. Another complication is the recent discovery of multiple pathways of triacylglycerol biosynthesis and the difficulty in ensuring that novel fatty acids are only channelled towards storage triacylglycerols and not to membrane or signalling lipids in major target crops like rapeseed. New findings from our lab have suggested that there may also be problems with the tissue specificity of some of the `seed-specific' gene promoters that are commonly used in transgenic crops. There are also considerable and often underestimated challenges associated with the economics, management and public acceptability of all transgenic crops, even for non-food use. In most cases the projections of petroleum reserves over the next few decades make it unlikely that crop-derived commodity products that substitute for petroleum will be competitive. Also the scale of crop production required to generate millions of tonnes of commodity oils, e.g., for biodegradable plastics, is likely to seriously impinge on food production at a time of increasing global populations, and is therefore unlikely to be acceptable. An alternative strategy to transgenic oil crops is to use molecular breeding techniques in order to develop new crops that already synthesise high levels of novel fatty acids of interest. Finally, the most promising market sectors and product ranges for the future development of oil crop biotechnology will be discussed. 相似文献
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996.
浙江千岛湖桡足类的群落结构 总被引:9,自引:1,他引:8
1999年1-12月,研究了贫-中营养型的大型深水湖泊-浙江千岛湖浮游桡足类的群落结构,包括其种类组成、现存量动态及群落多样性。在一年的研究中,共观察到16种桡足类(5种哲水蚤、1种猛水蚤和10种剑水蚤)。根据各种桡足类(桡足幼体+成体)的年平均密度,哲水蚤的优势种为右突新镖水蚤(Neodiaptomus schmack-eri)和球状许水蚤(Schmackeria forbesi);剑水蚤的优势种为一种中剑水蚤(Mesocyclops notius)和近邻剑水蚤(Cyclops vicinus)。桡足类群落平均密度46.81个/L,生物量0.126mg/L,物种多样性指数1.54。桡足类现存量的季节变化为夏>秋>冬>春,8月份密度达98.50个/L,生物量0.333mg/L;5月份密度仅10.70个/L,生物量0.017mg/L。水平变化以Ⅱ号站现存量为最高,密度达80.10个/L,生物量0.289mg/L;V号站的密度最低,仅29.80个/L;Ⅳ号站生物量最低,0.066mg/L。多样性指数以I站为最高3.21,Ⅸ站最低,仅0.85。桡足类群落多样性随着水体透明度的增大呈下降的趋势。 相似文献
997.
998.
We document spatial changes in species diversity, composition, community structure, and mortality of trees across a gradient
of water availability in a tropical dry forest in western Mexico. This gradient occurs along the main stream of a small watershed
of less than 1 km in length. Four 30 × 80 m plots were established systematically to include the driest (ridge top of the
watershed) to the wettest sites (watershed bottom) within this watershed. All stems larger than 5 cm were identified, and
measured for diameter and height. Dead stems larger than 5 cm were measured and classified as: a) found on live or dead trees,
and b) standing (“snags”) or lying (“downlogs”) on the ground. The number of recorded species per plot declined from 73 to
44 species as water availability decreased. A decline in estimated total richness, and in Shannon-Wiener and Simpson diversity
indices was also observed in the drier plots. Species composition strongly changed along the gradient, with the two ends of
the gradient sharing only 11% of the species. Stem density and percentage of dead stems and trees increased in abundance and
basal area from the wetter to the drier sites. Tree and stem size (basal area, height and stem diameter) showed the opposite
trend. Nonetheless, total basal area of live trees was largest at the two end gradient locations and oscillated between 12.22
m2 ha−1 and 7.93 m2 ha−1. Proportion of snags increased towards the driest site (from 46 to 72%), while that of down logs decreased. Overall, our
results suggest that small-scale gradients of water availability play a paramount role in the spatial organization of tree
communities in seasonal tropical environments.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
999.
Bio‐safety evaluation of Cry1Ac,Cry2Ab,Cry1Ca,Cry1F and Vip3Aa on Harmonia axyridis larvae
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Dietary exposure studies are initial steps in environmental risk assessments of genetically engineered plants on non‐target organisms. These studies are conducted in the laboratory where surrogate species are exposed to purified and biologically active insecticidal compounds at higher concentrations than those expected to occur in transgenic crops foliage. Thus, dietary exposure (early tier) tests provide robust data needed to make general conclusions about the susceptibility of the surrogate species to the test substance. For this, we developed suitable artificial diet and used it to establish a dietary exposure test for assessing the toxicity of midgut‐active insecticidal compounds to the larvae of the Asian ladybird beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Using boric acid as a model compound, we validated the bioassay established for H. axyridis larvae. An artificial diet containing boric acid which negatively affected survival, development and adult weights was offered to larvae and indicated that the bioassay was able to detect toxic effects of insecticidal substances incorporated in diets. Using this dietary exposure test, environmental risk assessment of Cry1Ac, Cry2Ab, Cry1Ca, Cry1F and the non‐Cry protein Vip3Aa was evaluated by analysing pupation rates, adult emergence rates, 7‐day larval weights, and freshly emerged male and female weights among the toxin treatments and a pure artificial diet. These life‐table parameters did not vary among artificial diets containing 200 μg/g Bt proteins or pure artificial diet. In contrast, boric acid adversely affected all life‐table parameters. Thus on these bases, we concluded H. axyridis larvae are not sensitive to these Bt proteins expressed in genetically engineered crops. 相似文献
1000.
Jay Ram Lamichhane Yann Devos Hugh J. Beckie Micheal D. K. Owen Pascal Tillie Antoine Messéan 《Critical reviews in biotechnology》2017,37(4):459-475
Conventionally bred (CHT) and genetically modified herbicide-tolerant (GMHT) crops have changed weed management practices and made an important contribution to the global production of some commodity crops. However, a concern is that farm management practices associated with the cultivation of herbicide-tolerant (HT) crops further deplete farmland biodiversity and accelerate the evolution of herbicide-resistant (HR) weeds. Diversification in crop systems and weed management practices can enhance farmland biodiversity, and reduce the risk of weeds evolving herbicide resistance. Therefore, HT crops are most effective and sustainable as a component of an integrated weed management (IWM) system. IWM advocates the use of multiple effective strategies or tactics to manage weed populations in a manner that is economically and environmentally sound. In practice, however, the potential benefits of IWM with HT crops are seldom realized because a wide range of technical and socio-economic factors hamper the transition to IWM. Here, we discuss the major factors that limit the integration of HT crops and their associated farm management practices in IWM systems. Based on the experience gained in countries where CHT or GMHT crops are widely grown and the increased familiarity with their management, we propose five actions to facilitate the integration of HT crops in IWM systems within the European Union. 相似文献