Breeding and selection of Buxus for resistance to Calonectria pseudonaviculata

Box blight is a widespread disease of Buxus caused by the pathogen Calonectria pseudonaviculata. It is responsible for significant losses in nurseries, gardens and wild boxwood populations. Our goal was to maximize the efficiency of a breeding programme towards increased disease resistance. The use of artificial inoculation of young F1 seedlings with C. pseudonaviculata spores under greenhouse conditions appeared to be a reliable tool for early selection of interesting prebreeding material. Overall, the four hybrid populations screened showed a segregating behaviour between their parents when determining the percentage of diseased leaves and lesion diameter. Genotypes were also found with an increased tolerance as compared to the parental species. Approximately 50% of the seedlings had the same score for both parameters after artificial inoculation in the greenhouse and in the field. Of the seedlings that showed severe symptoms in the greenhouse, <15% showed no disease symptoms in the field. Therefore, for larger breeding programmes, we propose a two‐step selection procedure: first artificial inoculation at seedling level to eliminate all genotypes with severe symptoms and then evaluation of the remaining seedlings in the field. Using this strategy, we were able to select several genotypes in our four hybrid populations with improved resistance to C. pseudonaviculata.     

利用低温水浴鉴定水稻苗期耐寒性

高效准确鉴定苗期耐寒性是水稻(Oryza sativa)耐寒研究的前提。基于流动水浴温度均一这一特性, 建立了一种恒温水浴鉴定水稻幼苗耐寒性方法。该方法中环境温度设定为20°C, 水浴温度设定为4°C。根据对2个水稻亚种不同材料的处理结果, 总结出几种常见品种的低温处理时间与存活率参考值, 并对操作过程中的一些注意事项进行了说明。     

黄土高原马栏林区优势种幼苗与其种群径级结构的演替研究

对黄土高原马栏林区几种典型群落类型中优势种辽东栎(Quercus liaotungensis)、油松(Pinus tabulaefor-mis)、白桦(Betula platyphylla)和山杨(Populus davidiana)的幼苗和种群径级结构进行了研究。结果表明:(1)辽东栎幼苗在马栏林区7种典型群落类型中均有分布,且数量充足,实生苗更新良好,辽东栎在不同的群落类型中表现出不同的种群径级结构。在油松 辽东栎混交林和辽东栎林中趋于稳定型;在油松林、油松 白桦混交林、白桦林、山杨林和白桦 山杨混交林中则为增长型;(2)油松幼苗在油松 白桦混交林、油松林和油松 辽东栎混交林中分布较多,但均少于辽东栎幼苗。在这些群落类型中油松种群的径级结构属于稳定型;(3)白桦和山杨幼苗数量较少,无正常更新能力,种群径级结构趋于衰退,以白桦和山杨为主的群落类型将逐渐被以油松和辽东栎为主的群落类型所取代;(4)马栏林区优势种幼苗分布的广度和丰度受到光照、水和灌草层等非生物和生物因素及其相互作用的影响。表明在黄土高原马栏林区以天然恢复为主的辽东栎种群,将在该地植被的自然恢复过程中产生重要作用;油松种群不仅过去而且将来也同样会在该地区的植被恢复中发挥重要作用。     

铅胁迫对黄瓜幼苗抗氧化酶活性及同工酶的影响

采用水培法和聚丙烯酰胺凝胶电泳法,研究铅胁迫对黄瓜幼苗过氧化物酶(POD)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性及同工酶的影响.结果表明,铅胁迫下黄瓜幼苗地上部POD活性除第5天外均随铅浓度的增加而逐渐降低,POD同工酶谱带和表达量减少.在0～500 mg·L^-1铅浓度范围内,SOD活性随铅浓度的增加而增加,第7天达到最大值后急剧下降,低于同期对照值,900 mg·L^-1铅处理SOD活性随时间的延长逐步降低,SOD酶谱带和表达量与铅浓度呈负相关.CAT酶谱带无明显变化,而表达量存在差异.     

莲幼苗的胚根发育及其筛分子研究

报道了莲无初生根型幼苗的胚根发育过程,其胚根由分生组织转化成贮藏组织,致使胚根不突破种皮;莲幼苗初生维管系统中的筛分子为筛管分子。莲的子叶和胚根连为一体的特殊结构与其生活环境和系统演化密切相关。     

盐度和温度对北美海蓬子在厦门海区引种以及生长特性的影响

研究了厦门海区盐度和温度对北美海蓬子（Salicornia bigelovii）种子萌发和幼苗生长的影响。结果显示,海蓬子种子对温度变化反应非常敏感,在15°C时发芽率最高（94%）,但萌发指数最低,而在20°C时萌发指数最大;在盐度5g·L^-1时种子具有最高的发芽率和萌发指数,在盐度50g·L^-1时仍有13.3%的发芽率,并且各种盐度处理下逐日萌发指数均能在2天内达到最大。盐度10-20g·L^-1最适宜幼苗生长,高盐（〉30g·L^-1）具有一定的抑制作用,主要表现为生长缓慢,含水量和根系活力下降,并且根的盐敏感程度大于茎。在不同盐度处理下,北美海蓬子适应一种新的耐盐机制,在无盐（0g·L^-1）和高盐（40g·L^-1）胁迫下,过氧化氢酶（catalase,CAT）和过氧化物酶（peroxide,POD）这2种酶蛋白对盐离子效应敏感,起主要的抗氧化作用;相反,生长在适宜盐度范围（10-30g·L^-1）内,超氧化物歧化酶（superoxide dismutase,SOD）维持较高活性。研究结果表明,北美海蓬子适宜在沿海滩涂环境条件下生长,有望作为一种抗盐耐海水蔬菜加以开发和利用,并进一步在污染海水净化修复中发挥可能的生态功能。     

Infection with the fungal endophyte Epichloë festucae may alter the allelopathic potential of red fescue

Red fescue (Festuca rubra) is a perennial grass used as both forage and turfgrass. Asymptomatic plants of this species are systemically infected by the fungal endophyte Epichloë festucae, which has a beneficial effect on the infected plants. The aim of this study was to determine the effect of the endophyte Epichloë festucae on the allelopathic potential of F. rubra against four associated pasture species that are also considered as weeds in lawns, Trifolium pratense, Trifolium repens, Lotus corniculatus and Plantago lanceolata. Two experiments were designed to evaluate the allelopathic effect of extracts from the roots and leaves of endophyte‐infected (E+) and non‐infected (E?) plants on the germination and seedling growth of the four target species. Regardless of the endophyte status of the host plant, leaf extracts elicited a stronger reduction in germination and seedling growth than root extracts. Extracts from E+ plants reduced the speed of germination index of Trifolium spp. to a greater extent than those from E? plants. Radicle length of the target species was the parameter most affected by the presence of the endophyte in F. rubra. Root extracts from E+ plants had a greater inhibitory effect on the radicle growth of the target species than did root extracts from E? plants. A greater concentration in total phenolic compounds was found in the roots of E+ plants than of E?; however, this difference was not observed in the leaves. Thus, the allelopathic potential of F. rubra is altered in infected plants.     

盐胁迫下豌豆幼苗的超弱发光

通过钠盐对豌豆 (pisumsativum)萌发时超弱发光影响的比较研究表明 ,在等渗条件下豌豆幼苗受激发光强度顺序为Na2 CO3 >NaCl>Na2 SO4 ;Na2 CO3 盐胁迫对植物的伤害程度高于其他盐类 ;多盐比单盐存在时的毒害小 ,受激发光作用降低。利用超弱发光方法 ,可以分析盐害对植物的作用 ,进一步搞清胁迫条件下植物生理反应的变化规律。     

高CO2浓度下豆科4种乔木幼苗的生理生化反应

本文对４种豆科乔木幼苗在高ＣＯ２浓度（５５０×１０－６±５０×１０－６）和在对照ＣＯ２浓度（约为３５０×１０－６）下生长的幼苗的一些生理生化指标进行了比较研究。初步结果显示：高ＣＯ２浓度能缩短幼苗子叶的存活时间。高ＣＯ２环境下生长的４种幼苗叶片中的可溶性蛋白、可溶性糖、纤维素、Ｎ、Ｐ、Ｋ、Ｍｇ的含量（均为全量）较对照ＣＯ２环境下生长的幼苗的相应值低,而淀粉含量则较高。其中以全氮、可溶性糖差异较显著。以单位鲜重表示的幼苗叶片叶绿素（Ｃｈｌ）和类胡萝卜素（Ｃａｒ）含量降低。高ＣＯ２浓度下生长的４种幼苗（３０天龄）叶片中硝酸还原酶活性比对照ＣＯ２浓度下生长的幼苗的值低。高ＣＯ２浓度下生长的４种幼苗叶片的平均蒸腾速率有不同程度的降低,而气孔阻力升高。幼苗对高ＣＯ２环境的反应与种的生态特性有关。喜光的大叶合欢幼苗对高ＣＯ２环境的反应较大,喜光而具一定耐荫性的猴耳环幼苗次之,而耐荫的光叶红豆和茸荚红豆幼苗则较小     

Overproduction of d-xylose isomerase in Escherichia coli by cloning the d-xylose isomerase gene

The Escherichia coli d-xylose isomerase (d-xylose ketol-isomerase, EC 5.3.1.5) gene, xylA, has been cloned on various E. coli plasmids. However, it has been found that high levels of overproduction of the d-xylose isomerase, the protein product of the xylA gene, cannot be accomplished by cloning the intact gene on high copy-number plasmids alone. This is believed to be due to the fact that the expression of the gene through its natural promoter is highly regulated in E. coli. In order to overcome this, the xylA structural gene has been fused with other strong promoters such as tac and lac, resulting in the construction of a number of fused genes. Analysis of the E. coli transformants containing the fused genes, cloned on high copy-number plasmids, indicated that a 20-fold overproduction of the enzyme can now be obtained. It is expected that overproduction of the enzyme in E. coli can still be substantially improved through additional manipulation with recombinant DNA techniques.