Effects of heavy metals on plants and resistance mechanisms

Goal, Scope and Background. As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. Methods. The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. Results and Discussion. Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. Conclusions. There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. Recommendations and Outlook. To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.

小麦WHM基因的抗性分析

植物抗病研究一直是科学领域的一个热点，它不仅能从形态结构到分子基础对植物抗病进行机理的阐释，而且能够直接应用于农业生产，提高农业产值。 玉米基因组中Hm基因是编码一种依赖NADPH的HC-toxin 还原酶。Hm基因的序列和玉米，矮牵牛及金鱼草中的二氢黄酮醇-4-还原酶(Dihydroflavonol -4- reductase，DFR)基因的序列具有较高的同源性；对水稻中Hm同源基因YK1的研究表明，过表达YK1后植物抗胁迫能力增强。本实验室从小麦中克隆得到了Hm同源基因WHM，由于在双子叶植物中不含有Hm的同源基因，为了检测WHM在双子叶植物中是否具有生物学功能，我们选取了烟草为模式植物进行了相关研究。 WHM基因cDNA全长1255bp，编码361个氨基酸，WHM基因序列与Hm基因序列具有78%的同源性。为分析此基因在双子叶植物中的功能，我们构建了WHM基因的pBI121植物表达载体，并通过农杆菌介导叶圆片法转化烟草，成功获得了转基因植株。同时我们还构建了WHM基因的原核表达载体并成功诱导了WHM蛋白的表达。对转基因烟草进行抗病与抗盐实验，实验结果表明，对烟草叶片接种烟草黑胫病菌后，转基因烟草的抗病能力显著性的高于对照烟草；烟草叶片接种黑胫病菌后，与对照烟草相比，转基因烟草积累了更多的H2O2，具有更高的POD活性。烟草种子在含不同浓度NaCl的培养基上萌发一定时间后，发现对照烟草的根长变化倍数高于转基因烟草的根长变化倍数，说明转基因烟草对NaCl浓度变化不敏感，尤其是在高浓度时，转基因烟草的生长状态明显好于对照烟草。我们还对IPTG诱导的WHM基因的原核表达载体表达的总蛋白进行了DFR活性的检测，结果表明WHM蛋白在总蛋白中能够竞争性的结合NADPH，但是由于蛋白没有进行纯化，其是否具有DFR的活性还不能确定。

小麦—偏凸山羊草6Mv/6B代换系的研究

小麦条锈病（Puccinia striiformis f. sp. tritici）是世界性小麦病害，可导致受害小麦减产30%以上，甚至绝收。小麦条锈病在我国西南、华北麦区危害严重，四川麦区是小麦条锈病发病最重的地区之一，每年因条锈病流行造成小麦产量损失巨大。利用抗条锈病品种是控制该病害最安全、经济的有效途径，因此挖掘利用抗病新基因，开展抗病遗传基础研究是当前育种工作中面临的重要任务。 偏凸山羊草（Aegilops ventricosa，DDMvMv，2n=28）是一年生草本植物，起源于地中海西部沿岸地区，具有对小麦白粉病、锈病等高抗或免疫、耐盐、抗寒、蛋白质含量高等优良性状，是小麦遗传育种很好的种质资源。本研究以高抗条锈病的小麦—偏凸山羊草6Mv/6B代换系（Moisson 6Mv/6B）为材料，对其含有的带条锈病抗性基因的偏凸山羊草6Mv染色体在四川小麦背景中的传递情况、与小麦—簇毛麦双端体附加系所具有的白粉病抗性的聚合以及对Moisson 6Mv/6B进行电离辐射诱变筛选抗条锈病的小麦—偏凸山羊草易位系三个方面进行了研究。取得的主要研究结果如下： 1. Moisson 6Mv/6B与高感条锈病的四川地区普通小麦品种绵阳26、绵阳93-124和SW3243的杂种F1与其普通小麦亲本分别作为父、母本回交，通过对其BC1和F2的结实率、根尖细胞有丝分裂中期染色体的观察以及对条锈病抗性的鉴定，发现含6Mv染色体的F1植株作母本时的回交结实率（83.10%）普遍高于含6Mv染色体的F1植株作父本（48.61%），结实率与普通小麦基因型密切相关（χ2=34.15>>χ20.05=5.99（df=2））；6Mv染色体在三种四川小麦中通过雌、雄配子传递的传递方式与其传递率间没有显著相关性，其传递率与普通小麦基因型呈显著相关性（χ2=6.42>χ20.05=5.99（df=2））。 2. Moisson 6Mv/6B与高抗白粉病的小麦—簇毛麦双端体附加系Pana（2n=42+2t）正反杂交，希望在聚合两者抗性的同时观察不同受体背景下的抗性反应。对Moisson 6Mv/6B和Pana正反杂交的结实率、杂交后代的农艺性状进行观察，并对杂交后代进行基因组荧光原位杂交（GISH）分析及条锈病和白粉病的抗性鉴定。结果表明Moisson 6Mv/6B作母本时杂交结实率（80.56%）高于Pana作母本时（58.33%），结实率与杂交方式间紧密相关（χ2=4.96>χ20.05=3.84（df=1））；Moisson 6Mv/6B和Pana杂交后代株高比最高亲本高约10cm，成熟期也较两亲本提前两个星期左右；正反杂交后代中具有偏凸山羊草6Mv染色体的植株具有条锈病抗性，具有簇毛麦端体的植株具有白粉病抗性，同时筛选到4株含有偏凸山羊草和簇毛麦遗传物质并对条锈病和白粉病兼抗的材料，证明来自偏凸山羊草6Mv染色体的条锈病抗性与来自簇毛麦端体的白粉病抗性已经聚合在一起，且没有产生相互抑制的作用，暗示通过这两个抗性基因的聚合是完全能获得兼抗条锈病和白粉病的小麦新种质。 3. 对Moisson 6Mv/6B在减数分裂时期的成株进行总剂量为6Gy、辐射频率为120rad/min的60Co-γ射线辐射，对辐射植株自交后代进行农艺性状及根尖细胞有丝分裂中期染色体形态观察和条锈病抗性鉴定。结果为辐射植株自交结实率为2.22%，根尖细胞有丝分裂中期的染色体存在明显碎片，辐射自交后代植株对条锈病具有成株期抗性。 小麦—偏凸山羊草6Mv/6B代换系对条锈病抗性稳定，是培育条锈病抗性品种的良好供体。本研究证明在四川小麦背景中要利用该品种抗性，在结实数满足需要时，可将其作父本，亦可作母本，但关键是要选择好一个优良的受体基因型；同时其条锈病抗性与来自簇毛麦的白粉病抗性没有相互抑制作用，可将两者抗性有效聚合用于小麦育种中。 Wheat stripe rust (Puccinia striiformis f. sp. Tritici) is a worldwide disease of wheat, and could lead to victims of 30 percent or even total destruction of wheat production. Wheat stripe rust harms badly in China's southwest and North China. Sichuan province is one of the regions damaged by wheat stripe rust heavily. The use of resistant varieties is the most secure and economical way to control the wheat stripe rust. Therefore, it is essential to identify new disease-resistant genes and genetically research of disease resistance. Aegilops ventricosa (DDMvMv, 2n = 28) is an annual herbaceous plant, originating in the coastal areas of the western Mediterranean, with good characters such as resistance of wheat powdery, rust, salt, cold and high protein content. It is a good germplasm resource. In this study, the wheat- Aegilops ventricosa 6Mv/6B substitution line Moisson 6Mv/6B (highly resistant to the wheat stripe rust) was used to study on the transmission of chromosome 6Mv of Aegilops ventricosa in different genetic background of Sichuan wheat varieties, hybridization with wheat- Haynaldia villosa ditelosomic addition line Pana (highly resistant to the powdery mildew) and screening of wheat- Aegilops ventricosa translocation line by exposuring Moisson 6Mv/6B under ionizing radiation. The main results are as following: 1. Moisson 6Mv/6B was crossed with Sichuan wheat varieties mianyang26, mianyang93-124 and SW3243 (highly susceptible to stripe rust), respectively. Their F1 hybrids were further backcrossed as male and female to corresponding wheat varieties. The seed-setting rate, chromosomes confirmation in the mitotic metaphase of root tip cells, and resistance to stripe rust of the subsequent BC1 and F2 plants were investigated. The average seed-setting rate of backcross via 6Mv as female donor (83.10%) was higher than that of backcross via 6Mv as male donor (48.61%), suggesting that the seed-setting rate was associated with the wheat genotypes（χ2=34.15>>χ20.05=5.99（df=2））. In all analyzed populations, transmission frequencies of chromosome 6Mv were not correlated with the ways of 6Mv through male or through female. However, transmission frequencies of chromosome 6Mv were significantly correlated with Sichuan wheat genotypes（χ2=6.42>χ20.05=5.99（df=2））. 2. To aggregating the resistances to stripe rust and powdery mildew, as well as research on the resistance reactions in different genetic background, Moisson 6Mv/6B was reciprocally hybrided with the wheat- Haynaldia villosa ditelosomic addition line Pana (highly resistant to the powdery mildew). The seed-setting rate, agronomic characters, genomic in situ hybridization (GISH) of hybrid progenies，and resistances to stripe rust and powdery mildew were investigated. The results showed that the seed-setting rate of hybridization via Moisson 6Mv/6B as female donor (80.56%) was significant higher than that via Pana as female donor (58.33%). The seed-setting rate was associated with the hybrid methods (χ2 = 4.96> χ20.05 = 3.84 (df = 1)). The plant height of hybrid progenies was about 10 cm higher than Pana, the parent with maximum height. And the maturity of hybrid progenies was about two weeks earlier than that of the parents. In the hybrid progenies, the plants with the 6Mv chromosome have the resistance to stripe rust and the plants with the telosome from Haynaldia villosa have the resistance to powdery mildew. It was found that four plants with both the 6Mv chromosome and the telosome from Haynaldia villosa were resistant to stripe rust and powdery mildew. It indicated that the resistance to stripe rust and powdery mildew aggregated, and no mutual inhibition was found. It implied that the aggregation of the two resistance genes was able to provide the new wheat germplasm with the resistances to stripe rust and powdery mildew. 3. Moisson 6Mv/6B was irradiated with 60Co-γ rays of 6Gy (120rad/min) during meiosis. The agronomic characters and chromosomes confirmation in the mitotic metaphase of root tip cells，as well as resistance to stripe rust were investigated. The seed-setting rate of irradiated plants was only 2.22%. The chromosomes in mitotic metaphase had clear fragments. The resistance to stripe rust of progeny of irradiated plants was the adult-plant resistance. The wheat- Aegilops ventricosa 6Mv/6B substitution line is a good stripe rust resistance donor for its stabile resistance. Our study demonstrated that the key for use the resistance is to choose a good receptor. There is no difference between Moisson 6Mv/6B be the female and be the male if the seed number meets the requirement. At the same time, the stripe rust resistance of Moisson 6Mv/6B did not have the mutual inhibition with the powdery mildew resistance from Haynaldia villosa. It is able to aggregate the two resistances for wheat breeding.

Mechanism for Giycinebetaine to Improve Plant Salt Resistance and Its Research Advances in Genetic Engineering

The paper systematically discusses the mechanism for glycinebetaine to improve plant salt resistance and its research advances in genetic engineering at home and abroad as well as summarizing the research progresses about the key enzymes and their genetic engineering in glycinebetaine biosynthesis. It suggests that on the basis of further understanding the mechanism for glycinebetaine to improve plant salt resistance,the transformation of the genes relating to glycinebetaine biosynthesis should be carried out in major crops so that new plant varieties resistant to salt can be obtained.

Defoliation, nitrogen, and competition: effects on plant growth and resource allocation of Cleistogenes squarrosa and Artemisia frigida

Two species, Artemisia frigida Willd. (C-3, semishrub, and dominant on overgrazed sites) and Cleistogenes squarrosa (Trin.) Keng (C-4, perennial bunchgrass, and dominant or codominant on moderately grazed sites) were studied to determine the effects of defoliation, nitrogen (N) availability, competition, and their interactions on growth, biomass, and N allocation in a greenhouse experiment. The main treatments were: two nitrogen levels (NO = 0 mg N pot(-1), N1 = 60 mg N pot(-1)), two defoliation intensities (removing 60% of total aboveground biomass and no defoliation), and three competitive replacement series (monocultures of each species and mixtures at 0.5:0.5). Our results were inconsistent with our hypothesis on the adaptive mechanisms of A. frigida regarding the interactive effects of herbivory, N, and competition in determining its dominant position on overgrazed sites. Cleistogenes squarrosa will be replaced by A. frigida on over-grazed sites, although C. squarrosa had higher tolerance to defoliation than did A. frigida. Total biomass and N yield and N-15 recovery of C. squarrosa in mixed culture were consistently lower than in monocultures, whereas those of A. frigida grown in mixtures were consistently higher than in monocultures, suggesting higher competitive ability of A. frigida. Our results suggest that interspecific competitive ability may be of equal or greater importance than herbivory tolerance in determining herbivore-induced species replacement in semi-arid Inner Mongolian steppe. In addition, the dominance of A. frigida on overgrazed sites has been attributed to its ability to shift plant-plant interactions through (lap colonization, root niche differentiation, and higher resistance to water stress.