Effects of drought stress on the seedling growth,development, and metabolic activity in different cultivars of canola

ABSTRACT

The comparative effects of drought stress on seed performance, growth parameters, free proline content, lipid peroxidation, and several antioxidative enzymes activities were studied in both cultivars of Brassica napus L. Drought stress increased mean germination rate and mean of day germination in both cultivars, and its effect was more pronounced in RGS003. The length and dry weight of root increased significantly in both cultivars under drought. RGS003 was more tolerant and obtained more biomass under drought than that of Sarigol. Proline content and pyrroline-5-carboxylate synthetase expression increased in Sarigol under drought. Measurement of malondialdehyde content in seedlings showed that lipid peroxidation was lower in RGS003 than in Sarigol. Antioxidant enzyme activities showed different trends in the two cultivars under drought stress but were higher in RGS003 than in Sarigol. These results suggest that RGS003 is better protected against drought-induced oxidative damage. Lipoxygenase activity only induced under water deficit condition in RGS003. Changes of respiratory enzymes activities of RGS003 subjected to drought stress showed a pattern different with Sarigol. Drought stress induced aconitase activity in RGS003, but it reduced fumarase and succinate dehydrogenase activity in Sarigol. This study showed that RGS003 exhibits a better protection mechanism against oxidative damage and RGS003 is more drought-tolerant than Sarigol possibly by maintaining and/or increasing growth parameters, antioxidant enzyme activities, and respiratory enzymes activities.     

比较研究苏北沿海滩涂盐土上不同油菜品种生物学特征和产量构成

以实验室自育的5个油菜品种(系)及其他6份油菜品种(系)为试验材料,研究了这11份油菜品种(系)在轻(中)度盐化土中的越冬性状、生物学特性、产量构成特性,得出如下结论:南盐油系列品系(种)在盐土上植株生长势强,从基部开始分枝,分枝多;南盐油系列品种(系)茎粗与宁油16、三北98、秦油66和秦油9号差异不明显,但高于宝杂油1号和秦油33;各品种(系)株高差异不大;荚长与荚宽差异也不大。南盐油系列品系(种)产量显著高于对比的宝杂油1号、秦油66、秦油9和秦油33,一次与二次分枝数与菜籽产量的回归分析显示其R2均达极显著水平。     

Beneficial effects of silicon nutrition in alleviating salinity stress in hydroponically grown canola,Brassica napus L., plants

Abstract

Silicon (Si) is the second most abundant element in soil and effectively counteracts the effects of various abiotic stresses, such as drought, heavy metal toxicity and salinity, on plants. In the present study the ameliorating effects of Si nutrition supplied as 2?mmol?L^?1 sodium silicate were investigated on hydroponically grown canola (Brassica napus L.) plants under salinity stress (i.e. 150?mmol?L^?1 sodium chloride). Salinity decreased plant growth parameters such as tissue fresh and dry weights. These decreases were accompanied by increased lignin contents, Na⁺ ion accumulation, increased lipid peroxidation and decreased chlorophyll contents in plants. Silicon nutrition, however, enhanced plant growth parameters and led to the prevention of lignin and the Na⁺ accumulation in shoots, reduced levels of lipid peroxidation in the roots and higher levels of chlorophyll. As a result of salinity, catalase activity in the whole plant and both soluble and cell wall peroxidase activities in the shoots decreased. Silicon nutrition, however, increased the reactive oxygen species scavenging capacity of salt-stressed plants through increased catalase and cell wall peroxidase activities. Thus, silicon nutrition ameliorated the deleterious effects of salinity on the growth of canola plants through lower tissue Na⁺ contents, maintaining the membrane integrity of root cells as evidenced by reduced lipid peroxidation, increased reactive oxygen species scavenging capacity and reduced lignification.     

钼磷配合施用对甘蓝型油菜产量和子粒品质的影响

利用酸性黄棕壤进行连续2年的盆栽试验,研究了钼肥和磷肥配合施用对甘蓝型油菜产量和子粒含油量、油产量、蛋白质含量、硫甙和芥酸含量以及脂肪酸组分等品质指标的影响。钼肥和磷肥各设置3个水平,分别为Mo 0、0.15、0.30 mg /kg土和P2O5 0、0.20、0.40 g /kg土,共9个处理。结果表明:施钼能够显著（P0.05）提高油菜子粒产量和生物学产量,显著增加油菜子粒含油量、油产量及油酸、亚油酸含量,降低子粒硫甙、亚麻酸和硬脂酸的含量;施磷则能够极显著提高子粒产量和子粒油产量,显著增加生物学产量和亚油酸含量,降低芥酸、硫甙及二十碳烯酸的含量;钼肥和磷肥对提高油菜子粒产量、油产量和油酸含量,降低芥酸含量存在显著（P0.05）的协同效应。因此,钼肥和磷肥在提高油菜产量、改善油菜子粒品质方面均具有良好的作用,且两者配合施用效果更好。     

Impact of arbuscular mycorrhizal fungi on the growth and expression of gene encoding stress protein – metallothionein BnMT2 in the non‐host crop Brassica napus L.

Arbuscular mycorrhizal (AM) fungi are an important component of the soil biota in most agroecosystems, and their association can directly or indirectly affect the diversity of soil microorganisms, nutrient cycling, and growth of host plants. Since not all crops are symbiotic, we hypothesized that the presence of AM fungi can: (1) inhibit the growth of non‐host plants by resulting in biotic stress, or (2) promote their growth indirectly by increased nutrient mobilization. These hypotheses were tested in the present study on the non‐mycorrhizal crop canola (Brassica napus L.) in the presence and absence of other autochthonous soil microorganisms. The soil was inoculated with a mixture of AM fungi (Acaulospora longula, Glomus geosporum, G. mosseae, Scutellospora calospora) and as a control, a non‐inoculated soil was used. The impact of inoculation on plant growth (biomass production, nutrient concentrations) and expression of the stress protein metallothionein gene BnMT2 was investigated in the shoots. B. napus L. did not form mycorrhizal associations on its roots, but its growth was promoted after inoculation with AM fungi. In the soil with autochthonic microorganisms, growth inhibition after inoculation was observed compared to the control. The concentrations of N, P, K, and S in the shoot were always significantly increased after inoculation with AM fungi. However, this was partly combined with reduced growth and thereby decreased total uptake of nutrients. Expression of BnMT2 in the leaves was increased after inoculation with AM spores at the soil devoid of indigenous microorganisms, but decreased in their presence. The expression of stress proteins (BnMT2) significantly increased with increasing length and biomass of shoots. In conclusion, the inhibition of the non‐host plant B. napus L. following inoculation with AM fungi was confirmed, however, only in combination with autochthonous microorganisms. Growth promotion of B. napus L. in the presence of AM fungi in the absence of autochthonous soil microorganisms suggest that plant growth depression in the presence of AM fungi was based on interactive effects of AM fungi with the autochthonous microorganisms in the soil rather than on a direct impact of the AM fungi.     

甘蓝型油菜5个重要性状QTL分析*

利用种皮色泽差异显著的甘蓝型油菜(Brassica napus)黄籽GH06和黑籽P174为亲本以及由它们构建的132个F2：3家系群体，对饼粕蛋白质含量、皮壳率、皮壳含油量、千粒重及种子含油量5个性状进行考察及QTL分析，5个性状均表现为连续分布，有的甚至表现出单向或双向超亲优势，表明5个性状均为多基因控制的数量性状。5个性状共检测到13个QTL，其中千粒重1个QTL，对表型变异贡献率为18.7%；饼粕蛋白质含量5个QTL，解释表型变异在7.8% ~14.4%之间；皮壳率3个QTL，解释表型变异在26.5%~32.8% 之间；皮壳含油量3个QTL及种子含油量1个QTL，解释表型变异在8.3% ~12.1%之间。在第20连锁群上，发现有饼粕蛋白质含量QTL与皮壳含油量和千粒重QTL重叠的区段。     

Regulatory effects of sulfur on oilseed rape (Brassica napus L.) response to selenite

Selenite is a form of selenium (Se) commonly found in Se-excessive soils. To regulate the Se content in plants in high-Se areas, a potted soil experiment was performed on oilseed rape (Brassica napus L.) to evaluate the effects of varied amounts of sulfur (S) on the biomass, accumulation and distribution of Se in B. napus under the conditions of different amounts of Se in the soil. The results showed that the seedlings of B. napus were more sensitive to Se than the mature plants were. The addition of S significantly alleviated the growth inhibition in seedlings and facilitated the growth of mature plants under higher Se (15 mg kg^?1) conditions. S treatment significantly decreased soil pH within the range of 0.22–0.60. An appropriate moderate amount (150 mg kg^?1) of S exerted the strongest inhibition on Se concentration and accumulation in B. napus at the seedling stage, but a higher amount (300 mg kg^?1) of S led to a more significant decrease in the mature plants under higher Se conditions, with the maximum reduction in various parts of B. napus reaching 51.3–60.9% and 42.5–53.4%, respectively. The application of S only affected the uptake of Se, and not the translocation of Se; the accumulation of Se in B. napus follows the sequence of pod ≈ stem > rapeseed > root, and the distribution ratio is approximately 1.00:0.97:0.69:0.49. Overall, the application of S alleviated the inhibitory effect on growth caused by excessive Se by reducing the Se concentration in B. napus and facilitating its growth, suggesting that S treatment is a suitable and highly cost-effective method to regulate the content of Se in B. napus.     

甘蓝型油菜正季与反季材料小孢子的培养

本文以甘蓝型油菜Westar的F1代为供试材料,通过对8个正季和同样的8个反季材料进行小孢子培养对比实验。结果表明,相同材料（基因型）正季能获得胚状体的反季一样能获得胚状体,但是相同材料的出胚数反季要比正季少50%,并且出胚时间要晚5～8d。正季与反季材料的成苗百分率相同,平均达到93%,加倍率基本一样,达到80%。由此可见,用反季节材料培养小孢子同样能获得成功,对特殊材料可以利用此法进一步加速育种进程。     

铝胁迫对油菜根系形态和生理指标的影响

为探讨油菜幼苗在不同浓度铝胁迫下的生理响应,以2个耐铝毒差异显著的油菜品种(耐铝品种R178和铝敏感品种S169)为试验材料,在营养液培养条件下,共设置0(对照)、50、100、150、200和 300 μmol·L^-1 6个铝(pH值4.5)处理,研究铝胁迫对油菜根系形态及生理指标的影响。结果表明,50 μmol·L^-1铝处理下R178各根系形态指标与对照相比均无显著差异,而S169根系各形态指标与对照均差异显著,其中总根尖数随着铝处理浓度的增加呈先升高后降低的趋势,其他根系指标均随着铝处理浓度的增加呈逐渐减少的趋势,300 μmol·L^-1铝处理下,2个品种的主根相对伸长率较对照分别减少65.7%和79.7%。随着铝处理浓度的增加,2个品种幼苗根系中可溶性蛋白和脯氨酸含量均呈先升高后降低的趋势,叶片中可溶性蛋白含量呈降低趋势,而脯氨酸含量则呈升高的趋势。铝胁迫导致2个品种幼苗根系和叶片的质膜透性显著增加,300 μmol·L^-1铝处理下R178和S169根系相对电解质外渗率较对照分别增加54%和59%,叶片中分别增加82%和90%,同一处理下R178根系和叶片电解质外渗率均小于S169。随着铝处理浓度的增加,2个品种根系中的超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性均呈先增加后降低的趋势;R178叶片中SOD活性呈增加趋势,而S169则呈先增加后降低的趋势,且在200 μmol·L^-1时达到最大值;2个品种叶片中的POD、CAT和抗坏血酸过氧化物酶(APX)活性均呈先增加后降低的趋势。综上,铝胁迫显著抑制了油菜根系生长,破坏了细胞质膜的完整性,油菜幼苗通过蛋白质和脯氨酸含量的积累以及保护酶活性的增高抵抗铝胁迫。本研究结果为耐铝油菜资源筛选和新品种选育提供了理论依据。     

ACC对不同氮效率油菜生长后期硝态氮再利用的调控机理

【目的】研究了进一步解析乙烯对油菜生长后期硝态氮 (NO₃–) 再利用的影响,揭示植株生长后期氮素再利用的生理机制。【方法】以氮高效油菜品种湘油15 (27号) 与氮低效油菜品种814 (6号) 为试验材料,在15 mmol/L氮水平下,每7天浇灌一次50 mL 100 μmol/L 1-氨基环丙烷-1-羧酸 (1-am-inocyclopropane-1-carboxylic acid,简称ACC),研究ACC对植物生长后期 (花期、收获期) 氮素再利用的影响及其与氮素利用效率 (NUE) 的关系。并用拟南芥野生型 (col.0) 和突变体 (nrt1.5) 材料作为验证,分别于玻璃顶网室和22℃恒温培养室进行砂培试验。【结果】ACC处理显著抑制了油菜BnNRT1.5的表达,且植株的衰老可以显著诱导BnNRT1.5的表达。相对于对照处理,ACC处理植株韧皮部汁液NO₃– 的再转运能力显著降低,导致下部叶NO₃– 含量显著升高,中部叶NO₃– 含量显著下降,上部叶NO₃– 含量无显著变化,进而导致植株含氮量和籽粒含氮量显著提高,以及以生物量和籽粒产量为基础的氮素利用效率 (NUE) 显著降低。由此推测,油菜生长后期氮素的再利用能力受到NRT1.5基因的显著调控。拟南芥野生型和突变体材料的验证结果表明,相对于拟南芥野生型 (col.0) 材料,拟南芥nrt1.5植株生长后期相对于col.0有更多的NO₃– 累积在植株衰老叶片中,更少的NO₃– 通过韧皮部转运到生长旺盛的新叶,植物生长后期氮素从老叶向新叶转运的再利用能力显著降低。【结论】油菜生长后期氮素的再利用能力受到ACC的显著调控,油菜和拟南芥NRT1.5基因表达量分别受到抑制或者发生基因突变时,会导致植株韧皮部汁液NO₃– 再转运量减少,更多NO₃– 累积在衰老叶片中而不能得以高效的再利用。因此,调控油菜生长后期NRT1.5的表达,提高油菜生长后期氮素的再转运和利用可以作为提高氮素利用效率的有效手段。     

不同施氮量下干旱胁迫对棉花生长及种内关系的影响

土壤水分和氮肥是影响荒漠绿洲区作物生长和种内关系的主要因素。为明确不同施氮量下干旱胁迫对棉花产量以及种内关系的影响,本研究以集群栽培(1穴3株)下棉花为研究对象,设置3种施氮量[300 kg(N)·hm~(-2)、225 kg(N)·hm~(-2)、150 kg(N)·hm~(-2)]和3种水分处理(正常水分、中度干旱胁迫、重度干旱胁迫),测定了不同处理下棉花的生长指标和棉花产量,分析了不同处理下棉花种内关系的变化。结果表明:1)同一施肥条件下,2016年和2017年棉花株高在重度干旱胁迫下显著降低,而茎粗随干旱胁迫加剧显著降低,但叶面积随干旱胁迫加剧却有所增加,且在中度干旱胁迫下的叶面积最大。2)同一施肥条件下,与正常水分相比,中度和重度干旱胁迫下棉花的茎秆生物量均显著下降;叶片生物量和籽棉产量在中度干旱胁迫下最高,在重度干旱胁迫下却降低。3)在当地施氮量300kg·hm~(-2)下,随着干旱胁迫的加剧,相对邻体效应(relativeneighbor effect, RNE)数值从正值变为负值;在氮肥减少处理(225 kg·hm~(-2))下,随着干旱胁迫的加剧, RNE数值先升高后降低,而在施氮量为150 kg·hm~(-2)处理下, RNE数值随着干旱的加剧逐渐降低,且均为负值。总之,在当地施氮量和中度干旱胁迫下棉花能够获得较高的籽棉产量,且在此处理下棉花的种内关系为助长关系;其他处理均降低了棉花的产量,并使得棉花的种内关系转变为竞争关系。     

铬胁迫对青菜（Brassica chinensis L.）植物螯合肽含量及抗氧化特性的影响

选用不同耐铬胁迫青菜品种春油1号和青伏令,采用不同浓度Cr3＋处理,测定青菜抗氧化酶活性及植物螯合肽含量等生理指标。结果表明,随着Cr3＋处理浓度升高,两种青菜叶片抗氧化酶活性、酸溶性SH、植物螯合肽（PCs）及谷胱甘肽（GSH）含量均呈增加趋势（P〈0.05）,高浓度Cr3（＋300 mg.L-1）处理下,耐铬胁迫较弱的青伏令叶片SOD、POD、CAT活性分别比对照增加了24.2%、41.7%、21.4%,耐铬胁迫较强的春油1号分别比对照增加了37.2%、70.7%、43.0%,并且PCs含量是对照的3.17倍,明显高于耐铬胁迫较弱品种青伏令（1.71倍）。Cr3＋处理下耐铬胁迫较强的青菜品种春油1号表现出相对较高的抗氧化酶活力及非酶物质含量,不同品种青菜对铬胁迫的生理差异较大。     

Artificial miRNA调控甘蓝型油菜芥酸的研究

芥酸是重要的工业原料,主要来源是甘蓝型油菜种子,为调节甘蓝型油菜种子内芥酸含量,针对甘蓝型油菜芥酸合成过程中的关键酶基因Bnfad2设计特异性amiRNA,并构建种子特异表达载体,转化高芥酸甘蓝型油菜品种MY15和低芥酸甘蓝型油菜品种LEA01,并对转化植株T_0种子脂肪酸进行分析。结果表明,转化的高芥酸甘蓝型油菜芥酸的增加最高达到5.12%,最低2.11%;而转化的低芥酸品种,最高仅为0.45%,最低只有0.16%,而且所有转化低芥酸材料的芥酸含量都小于1%;同时转化种子内油酸的含量得到了明显的提高,最低为4.99%,最高达到了10.71%,亚油酸降低的幅度十分明显,最大降幅达到17%。表明amiRNA技术可以通过影响脂肪酸合成过程中特定基因的表达,有效改变种子内脂肪酸的组成,从而改变其营养结构,提高营养价值,进一步提高油菜种子的附加值。本研究为运用amiRNA技术调节油菜脂肪酸组成和改变其营养结构提供了一定理论依据。     

农杆菌介导的油菜遗传转化研究进展

综述油菜遗传转化中再生体系的建立、农杆菌侵染方法、适宜菌株及载体选择等方面的研究进展,并对转化中寄主基因型、目的基因及其启动子的选择、筛选方法、外源基因稳定性等方面存在的问题进行了分析与讨论,为优化油菜等芸薹属的遗传转化提出可行性建议.     

Phosphate-solubilizing rhizobacteria enhance the growth and yield but not phosphorus uptake of canola (Brassica napus L.)

The ability of phosphate-solubilizing rhizobacteria to enhance the growth and phosphorus uptake of canola (Brassica napus L., cv. Legend) was studied in potted soil experiments in the growth chamber. One hundred and eleven bacteria isolated from the rhizosphere of field-grown plants, and a collection of nine bacteria known to be effective plant growth-promoting rhizobacteria (PGPR), were screened for P-solubilization in vitro. All rhizobacteria were identified using whole-cell fatty acids methyl ester (FAME) profiles. The best P-solubilizing isolates were two Bacillus brevis strains, B. megaterium, B. polymyxa, B. sphaericus, B. thuringiensis, and Xanthomonas maltophilia (PGPR strain R85). The P-solubilizers were tested for their effects on growth and P-uptake of canola plants in a P-deficient soil amended with rock phosphate. Although some of the P-solubilizing rhizobacteria significantly increased plant height or pod yield, none increased P-uptake. The most effective inoculant was a B. thuringiensis isolate which significantly increased the number and weight of pods and seed yield without rock phosphate. Xanthomonas maltophilia increased plant height, whereas the other bacilli increased the number on weight of pods. These results demonstrate the potential use of these P-solubilizing rhizobacteria as inoculants for canola, but indicate that P-solubilization was not the main mechanism responsible for positive growth response. Received: 8 February 1996     

Improvement of Brassica napus growth under cadmium stress by cadmium-resistant rhizobacteria

This study focuses on the characterization of four bacterial isolates from heavy metal-polluted rhizosphere in order to examine their plant growth promoting (PGP) activity. The PGP activity on the canola (Brassica napus) of the strains which showed cadmium resistance and multiple PGP traits was assessed in the presence and in the absence of Cd²⁺. The strains, Pseudomonas tolaasii ACC23, Pseudomonas fluorescens ACC9, Alcaligenes sp. ZN4 and Mycobacterium sp. ACC14 showed 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity. They also synthesized ACCD enzyme in vitro when 0.4 mM Cd²⁺ was added to the growth medium. The presence of the metal, however, reduced the ACCD activity in Alcaligenes sp. ZN4 and Mycobacterium sp. ACC14, while it did not affect the ACCD activity of P. tolaasii ACC23 and P. fluorescens ACC9. ACC9 and ACC23 produced indole acetic acid (IAA) and siderophores, while ACC14 produced only IAA. IAA and siderophores were produced more actively under Cd-stress.Root elongation assays conducted on B. napus under gnotobiotic conditions demonstrated increases (from 34% up to 97%) in root elongation of inoculated canola seedlings compared to the control plants. Subsequently, the effect of inoculation with these strains on growth and uptake of Cd²⁺ in roots and shoots of canola was studied in pot experiments using Cd-free and Cd-treated (15 μg Cd²⁺ g^?1 dw) soil. Inoculation with P. tolaasii ACC23, P. fluorescens ACC9 and Mycobacterium sp. ACC14 promoted the growth of plants at concentrations of 0 and 15 μg Cd²⁺ g^?1 soil. The maximum growth was observed in the plants inoculated with P. tolaasii ACC23. The strains did not influence the specific accumulation of cadmium in the root and shoot systems, but all increased the plant biomass and consequently the total cadmium accumulation.The present observations showed that the bacterial strains used in this study protect the plants against the inhibitory effects of cadmium, probably due to the production of IAA, siderophores and ACCD activity.     

草除灵对甘蓝型油菜苗期生理生化及超微结构的影响

为探明草除灵作用的生理机制及其胁迫下不同甘蓝型油菜品种的耐性差异机制,以浙大619、浙大622为试验材料,对苗期油菜叶面喷施不同浓度的草除灵,采用生理生化分析方法、叶绿素荧光技术和超显微技术,探究草除灵对甘蓝型油菜苗期生理生化特性以及超微结构的影响。结果表明,低浓度(2.5 g·L~(-1))的草除灵对2个油菜品种的生长无显著影响,当草除灵浓度大于5.0 g·L~(-1)时,随着处理浓度的升高,油菜生长受抑制的程度逐渐增加,净光合速率、叶绿素含量和叶绿素荧光值显著下降,抗氧化酶系统的活性降低,膜脂过氧化加剧,活性氧积累增多,叶绿体、线粒体等叶肉细胞超微结构受损,且浙大619的抗草除灵胁迫能力高于较敏感品种浙大622。因此,本研究明确了草除灵对甘蓝型油菜安全性的影响,这对该除草剂的田间推广应用具有重要意义。     

Effect of regeneration procedures on genetic diversity in Brassica napus and B. rapa as estimated by isozyme analysis

This investigation was conducted to assess changes in the genetic structure of two varieties of two species of annual Brassica. Seeds of B. napus cv. Topas and B. rapa Broccoletto were sent to nine research institutes in different geographical areas of Europe for regeneration. The multiplied material was sent back after one year of regeneration and analysed electrophoretically. The original populations of each species and their multiplied samples were stained for 12 different enzymes, of which 4 were found to be polymorphic (DIA, SKD, GPI and PER). It was possible to detect considerable differences in isozyme patterns in B. napus and allelic frequencies in B. rapa, both within and between populations. When the original population was compared with the regenerated samples, the Chi-square homogeneity test for all pairwise comparisons revealed distinctness with a 99% probability for B. napus and 95% probability for B. rapa with one or more of the enzyme systems examined. Furthermore, the average of gene diversity analysis (Nei, 1973) revealed that some regenerated populations have less while others have increased genetic variation compared with the original population. These observations indicated that the frequencies were non-random and considerable shifts in genetic diversity have occurred during multiplication. In addition, different regeneration procedures have caused the fixation of certain alleles.     

甘蓝型油菜矮秆突变体的遗传及其矮秆基因的RAPD标记

甘蓝型油菜(BrassicanapusL.)矮秆突变体DS-1与中双四号配制正反交组合F1、F2、BC1和BC2,遗传分析表明,该突变体的矮秆性状受一对部分显性主效基因和微效基因控制,将这对显性主效基因命名为Ds1。同时随机选取147株F2植株作为Ds1的RAPD标记的筛选群体,最终从1041条随机引物中筛选到1条引物S470,其扩增的多态性片段S470.416与Ds1连锁,遗传距离为8.9cM。