Identification and quality evaluation of Lepidium meyenii. (Maca) based on gas chromatographic analysis of its essential oils from roots

Lepidium meyeniiWalp. （Maca）, a perennial herbaceous plant with narrow distdbution in the Andean region, was cultivated by local residents as early as 1600 B.C. It has high nutritional values and multiple medicinal effects. In recent years the plant source of Maca has been greatly scarce since Maca products are increasingly becoming popular in the world. This makes the study urgent on the identification and quality evaluation of Maca materials. In present work, four Mace samples of different origins or handlings and three other natural plants, including radish, odental ginseng and American ginseng, were investigated. Their essential oils （steam distillates） of the hypogeal parts were weighed and analyzed by GC/MS. Through comparison of the characteristics of their chromatograms, it was found that the essential oil of Maca had unique GC/MS behaviors, and the characteristic peaks produced by the major essential oil components （Phenylacetonitrile, Benzaldehyde, 3-Methoxyphenylacetonitrile, etc） were distinct. Furthermore, the chromatograms of several Maca samples showed a similar qualitative pattern except for some differences in the quantitative composition, and the percentage of total essential oils in the samples varied from 0.88 % to 1.59 %. These behaviors and technologies can be applied to the identification of Maca materials in the markets and be a supplement to assess the quality of Maca matedals.

玛咖(Lepidium meyenii.)干粉的营养成分及抗疲劳作用研究

本文对南美药食两用植物玛咖(LepidiummeyeniiWalp.)干粉的营养成分进行了分析,其中蛋白质含量达到8.87%,并发现含有大量的支链氨基酸和一定量的牛磺酸、矿物质锌等多种具有抗疲劳作用的营养成分,且通过动物试验证明了玛咖干粉具有显著抗疲劳功效。

Effect of Lepidium meyenii(maca)roots on spermatogenesis of male rats

Aim:To determine the effect of oral administration of an aqueous extract from the roots of Lepidium meyenii(maca)on spermatogenesis in adult male rats.Methods;Male rats received an aqueous extract of the root(66.7 mg in onemL)twice a day for 14 consecutive days.Results:Treatment with Lepidium meyenii resulted in an increase in theweights of testis and epididymis but not the seminal vesicle weight.The length and frequency of stages IX-XIV seminif-erous tubules,where mitosis occurred,were increased and stages I-VI were reduced in rats treated with Lepidiummeyenii.Conclusion;The Lepidium meyenii root invigorates spermatogenesis in male rats by acting on its initialstages(IX-XIV).

Lepidium meyenii (Maca) improved semen parameters in adult men

Aim:The present study was designed to determine the effect of a 4-month oral treatment with tablets of Lepidiwnmeyenii(Maca)on seminal analysis in nine adult normal men aged 24-44 years old.Methods:Nine men receivedtablets of Maca(1500 or 3000 mg/day)for 4 months.Seminal analysis was performed according to guidelines of theWorld Health Organization(WHO).Serum luteinizing hormone(LH),follicle stimulating hormone(FSH),prolactin(PRL),testosterone(T)and estradiol(E_(2))were measured before and after treatment.Results;Treatment withMaca resulted in increased seminal volume,sperm count per ejaculum,motile sperm count,and sperm motility.Serumhormone levels were not modified with Maca treatment.Increase of sperm count was not related to dose of Maca.Conclusion:Maca improved sperm production and sperm motility by mechanisms not related to LH,FSH,PRL,Tand E_(2).

Effect of alcoholic extract of Lepidium meyenii (Maca) on testicular function in male rats

Aim: To evaluate the effect of the alcoholic extract of Lepidium meyenii (Maca) on the spermatogenesis in male rats. Methods: In Holtzman rats, Maca alcoholic extract (5%) was given by oral route at doses of 48 mg/day or 96 mg/day for 7 days, 14 days and 21 days. Testicular function was assessed by measurements of lengths of different stages of seminiferous epithelia and by epididymal sperm count. Results: Ethanolic extract of Maca increased the length of stages IX-XI of seminiferous epithelium at treatment day 7, day 14 and day 21. Progression of spermatogenesis was evident only after day 21 when lengths of stages XII-XIV of seminiferous epithelium were increased; at day 7 and day 14, no important change in spermatogenesis was observed. Epididymal sperm count was increased with 48 mg/day at all times. With 96 mg/day an increase in sperm count was observed at day 7, but it was reduced at day 14 and day 21 of treatment. Serum testosterone levels were not affected. Conclusion: The alcoholic extract of Maca activates onset ant progression of spermatogenesis at 48 mg/day or 96 mg/day in rats.

Lepidium meyenii (Maca) reduces spermatogenic damage induced by a single dose of malathion in mice

Aim: To observe the effect of the aqueous extract of hypocotyls of the plant Lepidium meyenii (Maca) on spermato-genic damage induced by the organophosphate insecticide malathion in mice. Methods: Mice were treated with 80 mg kg^(-1) of malathion in the presence or absence of an aqueous extract of Maca, which was orally administered 7, 14 or 21 days after injection of the malathion. Stages of the seminiferous epithelium were assessed by transillumination on days 0, 7, 14 and 21. Results: The administration of Maca increased significantly the length of stage 鈪?on days 7, 14 and 21 of treatment compared with the controls. An increase in the length of stage 鈪?occurred on day 14 of treatment. Malathion affected spermatogenesis by reducing the lengths of stage 鈪?on day 7, stages 鈪?and 鈪?鈪?on day 14 and a recovery of stages 鈪?鈪?on day 21. The magnitude of alteration in the length of stage 鈪?produced by malathion was significantly reduced by Maca on days 7 and 14. The length of stage 鈪?was increased when Maca was administered to mice treated with malathion. Assessment of the relative length of stages of the seminiferous epithelium showed that Maca treatment resulted in rapid recovery of the effect of malathion. Conclusion: Maca enhances spermatogenesis following spermatogenic damage caused by the organophosphorous pesticide.

Progress on the Chemical Constituents Derived from Glucosinolates in Maca(Lepidium meyenii)

Maca(Lepidium meyenii Walp.),a famous food supplement,has drawn an unprecedented international interest over the last two decades.It was assumed that glucosinolates,macamides,macaenes,and alkaloids are the main bioactive components of Maca before.Recently,a series of novel thiohydantoins which generally exhibit a variety of activities have been isolated from Maca.This review focuses on the progress on the main bioactive components of Maca and their biosynthetic pathway,which indicates that macamides,thiohydantoins,and some alkaloids may originate from glucosinolates.Interestingly,thiohydantoins from Maca are the first type of thiohydantoin derivatives to be found from a natural source and may contribute to some significant effects of Maca.

Effects of Lepidium sativum supplementation on growth and gonadotropins secretion in ovariectomized, estrogen-implanted rabbits

Objective: To test the effects of dietary supplementation of Lepidium sativum (LS) seed powder on growth performance and gonadotropins secretion in ovariectomized, estradiol-implanted rabbits. Methods: Ovariectomized, estradiol-implanted Chinchilla rabbits were assigned into four experimental groups: LS seed powder was included into normal rabbit chow at 0% (control), 5% (low), 7% (mid) and 10% (high) w/w. Experimental feed and water were given ad-libitum for 3 weeks. Weekly body weights and daily feed intake of rabbits were recorded. Twenty-one days post-feeding, blood samples were collected at 15-minute interval for 3 h (PeriodⅠ) after which 2.5 μg gonadotropin-releasing hormone (GnRH) was injected intravenously and the sampling continued for another hour (PeriodⅡ). Plasma was harvested and analyzed for luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by radioimmunoassay. Results: Feed intake was significantly (P<0.05) increased in LS-supplemented rabbits. However, the increase in feed intake did not result in significant body weight gain. LS seed supplementation significantly (P<0.001) increased mean plasma LH dose-dependently from the low- to the mid-LS level and then decreased LH at the high-LS level. LS supplementation increased (P<0.001) plasma FSH secretion. Injection of GnRH had no effect on plasma LH, however significantly (P<0.05) decreased overall plasma FSH secretion. Conclusions: LS seed supplementation stimulates feed intake and gonadotropins secretion in rabbits. Gonadotropins effect may be mediated through LS seeds phytosterols through the activation of estrogen receptors thereby producing agonistic effects resulting in LH and FSH secretion. The differential responses of gonadotropins to GnRH in LS-supplemented rabbits suggest differential regulation of the synthesis and secretion of these gonadotropins.

Structural characterizations andα-glucosidase inhibitory activities of four Lepidium meyenii polysaccharides with different molecular weights

Four polysaccharides(MCPa,MCPb,MCPc,MCPd)were obtained from Lepidium meyenii Walp.Their structures were characterized by chemical and instrumental methods including total sugar,uronic acid and protein content determi-nation,UV,IR and NMR spectroscopy,as well as monosaccharide composition determination and methylation analy-ses.Four polysaccharides were a group of glucans with different molecular weights ranging from 3.12 to 14.4 kDa,and shared a similar backbone chain consisting of(1→4)-glucose linkages with branches attached to C-3 and C-6.Furthermore,bioactivity assay showed that MCPs had concentration-dependent inhibitory activity onα-glucosidase.MCPb(Mw=10.1 kDa)and MCPc(Mw=5.62 kDa)with moderate molecular weights exhibited higher inhibitory activ-ity compared with MCPa and MCPd.

独行菜属植物玛咖(Lepidium meyenii)的微形态研究

利用光学显微镜和环境扫描电子显微镜,对不同颜色、不同产地玛咖(Lepidium meyenii)的叶表皮、花粉粒以及种皮进行了微形态学研究。结果表明:(1)不同颜色玛珈的叶表皮、花粉粒微形态具有高度的一致性,但与我国部分独行菜属植物有着明显的差异;(2)不同产地、不同颜色玛珈的种皮微形态有明显的差异。该研究为新植物资源玛咖的种质鉴定、分类提供了一些新的依据。

Qualitative Identification and Semi-Quantitative Comparison of Sucrose in Maca (<i>Lepidium meyenii</i>) by Infrared Spectrum Analysis

Objective: In order to establish a method for qualitative identification and semi-quantitative comparison of sucrose in Macas by infrared spectral analysis. Methods: Six Maca samples with three color types and from two producing areas in Yunnan province (China) were collected. Fourier trans-form infrared spectroscopy (FTIR) of raw Maca, ethyl acetate extracts (EtOAc-E), alcohol extracts (EtOH-E) and extracted residues were recorded selectively. Comparative analysis and analysis-through-separation strategies were used to explore the FTIR analytical method for sucrose in Maca. Results: Sucrose was proved to be a component in the Lijiang purple Maca (LPM) sample by comparative analysis of FTIR and second derivative in-frared spectroscopy (SDIR) with sucrose as a reference substance. Relative higher content of sucrose might be responsible for the distinctive absorption character of FTIR from LPM. With the aid of comparative analysis and analysis-through-separation strategies, conclusions could be drawn that all of the six Maca samples in this research contained some sucrose more or less. Furthermore, relative content of sucrose in the LM was higher than those in HM in general. Conclusion: An infrared spectrum analysis method for qualitative identification and semi-quantitative comparison of sucrose in different Maca samples was developed. Compared with other analytical methods, the developed method shows unparalleled charm for its inherent merits of convenient, fast, low cost, visual, efficient et al.

Genetic diversity analysis of Lepidium sativum(Chandrasur) using inter simple sequence repeat(ISSR) markers

Lepidium sativum（commonly known as garden cress） belongs to the family Brassicaceae. It is a fastgrowing erect, annual herbaceous plant. Its seeds possess significant fracture healing, anti-asthmatic, anti-diabetic,hypoglycemic, nephrocurative and nephroprotective activities. In the present study, we assessed the genetic diversity of various genotypes of L. sativum using inter-simple sequence repeat（ISSR） markers. Out of 41 ISSR primers screened, 32 primers showed significant, clear and reproducible bands. A total of 510 amplified bands were obtained using 32 ISSR primers, out of which 422 bands were polymorphic and 88 bands were monomorphic. The percentage of polymorphism was found to be 82. A total of 35 unique alleles ranging insize from 200 to 2,900 bp were observed.Cluster analysis based on unweighted pair-group method,arithmetic mean divided the 18 genotypes into two main clusters, with the first having only HCS-08 genotype of L.sativum and other having all of the other 17 genotypes. The Jaccard similarity coefficient revealed a broad range32–72 % genetic relatedness among the 18 genotypes.

Genome of Plant Maca （Lepidium meyenil） Illuminates Genomic Basis for High-Altitude Adaptation in the Central Andes

Maca （Lepidium meyenii Walp, 2n = 8x = 64）, belonging to the Brassicaceae family, is an economic plant cultivated in the central Andes sierra in Peru （4000-4500 m）. Considering that the rapid uplift of the central Andes occurred 5-10 million years ago （Ma）, an evolutionary question arises regarding how plants such as maca acquire high-altitude adaptation within a short geological period. Here, we report the high-quality genome assembly of maca, in which two closely spaced maca-specific whole-genome duplications （WGDs; ~6.7 Ma） were identified. Comparative genomic analysis between maca and closely related Brassicaceae species revealed expansions of maca genes and gene families involved in abiotic stress response, hormone signaling pathway, and secondary metabolite biosynthesis via WGDs. The retention and subsequent functional divergence of many duplicated genes may account for the morphological and physiological changes （i.e., small leaf shape and self-fertility） in maca in a high-altitude environment. In addition, some duplicated maca genes were identified with functions in morphological adaptation （i.e., LEAF CURLING RESPONSIVENESS） and abiotic stress response （i.e., GL YClNE-RICH RNA-BINDING PROTEINS and DNA-DAMAGE-REPAIR/TOLERATION2） under positive selection. Collectively, the maca genome provides use- ful information to understand the important roles of WGDs in the high-altitude adaptation of plants in the Andes.

Lepidium sativum Linn.种子的脱脂乙醇提取物体外自由基清除活性(英文)

AIM:The objective of the present study was to evaluate the antioxidant potential of the defatted ethanolic extract of the seeds of Lepidium Sativum Linn.METHODS:Different in vitro chemical assays viz.DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging,ABTS (2,2-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical scavenging,iron chelation,lipid peroxidation,super-oxide scavenging and non-enzymatic haemoglobin glycosylation assay were used.The total antioxidant capacity of the extract was determined spectrophotometrically by phosphomolybdic acid method.RESULT & CONCLUSION:The defatted lepidium seed extract showed significant free radical scavenging activity in ABTS and non-enzymatic glycosylation assays,and a moderate activity in all the other assays.IC50 of the extract in the DPPH,ABTS,iron chelation,lipid peroxidation and super oxide scavenging assays were found to be 171.13,38.64,128.94,71.39 and 206.09 μg·mL-1 respectively.The haemoglobin glycosylation assay of the extract showed a percentage scavenging of 46.60% and 74.88%,at 0.5 and 1.0 μg·mL-1,concentrations,respectively.Total antioxidant capacity of ethanolic extract of L.sativum (10 mg·mL-1) was found to be equivalent to 58.38 μg·mL-1 of ascorbic acid.

Identification of maca(Lepidium meyenii Walp.) and its adulterants by a DNA-barcoding approach based on the ITS sequence

Maca(Lepidium meyenii) is an herbaceous plant that grows in high plateaus and has been used as both food and folk medicine for centuries because of its benefits to human health. In the present study, ITS(internal transcribed spacer) sequences of forty-three maca samples, collected from different regions or vendors, were amplified and analyzed. The ITS sequences of nineteen potential adulterants of maca were also collected and analyzed. The results indicated that the ITS sequence of maca was consistent in all samples and unique when compared with its adulterants. Therefore, this DNA-barcoding approach based on the ITS sequence can be used for the molecular identification of maca and its adulterants.

Induction of apoptosis in leukemic cells by the alkaloid extract of garden cress(Lepidium sativum L.)

Objective: Garden cress(Lepidium sativum L.) is an important herb in traditional medicine used to improve production of breast milk in women and semen in men. In the present research the authors evaluated its ability to destroy leukemic cancer(Jurkat E6-1) cells, using the alkaloid extract of this plant.Methods: Constituents of the alkaloid extract were analyzed by gas chromatography–mass spectrometry(GC–MS) and their cytotoxicity in leukemic cancer cells and healthy peripheral blood mononuclear cells(PBMCs) was assessed. Cell death via apoptosis was confirmed by DNA laddering, caspase-3 activity,annexin V-fluorescein isothiocyanate and mitochondrial toxicity assays. The specific course of gene activation in treated cells was determined through quantitative polymerase chain reaction(qPCR).Results: GC–MS analysis identified six alkaloids and proto-alkaloids, namely, benzyl isothiocyanate(1),2-ethoxy-4 H-3,1-benzoxazin-4-one(2),(4 R)-2-(2-aminophenyl)-4-phenyloxazoline(3), 5-acetyl-1,2-di hydro-6-methyl-2-oxo-4-phenyl-3-pyridinecarbonitrile(4), benzo[b][1,8]-naphthyridin-5(10 H)-on e,2,4,7-trimethyl(5) and 1,4-diaminoanthraquinone(6), in the alkaloid extract of L. sativum. Of these,compound 1 was previously identified in the seeds of L. sativum. Exposure to the alkaloid extract caused death of Jurkat E6-1 cells, with median lethal concentration(LC50) of 75.25 mg/mL. However, the alkaloid extract also showed a nontoxic and proliferative(1.6-fold) effect in healthy PBMCs. Further experiments performed with Jurkat cells at LC50 and sub-LC50 doses demonstrated DNA fragmentation, activation of caspase-3 and time-dependant phosphatidylserine translocation(apoptosis) from inner to outer cell membranes. Cell toxicity and assessment of adenosine triphosphate level, together with using qPCR to evaluate expression profile of major apoptosis genes, revealed that apoptosis may be induced by disruption in the mitochondrial outer membrane potential, through activation of extrinsic and intrinsic apoptosis pathways in Jurkat cells.Conclusion: The ability of the alkaloid extract of L. sativum seeds to induce apoptosis indicates a potential pharmacological use in cancer chemotherapy. The separation of individual active compounds and further in-depth exploration of the molecular mechanism of apoptosis may lead to novel chemotherapeutic compounds in our future antineoplastic research.

Lepithiohydimerins A-D:Four Pairs of Neuroprotective Thiohydantoin Dimers Bearing a Disulfide Bond from Maca(Lepidium meyenii Walp.)

Main observation and conclusion An HPLC-UV-guided separation was performed and four pairs of unprecedented macathiohydantoin dimers,lepithiohydimerins A—D(1—4)bearing a rare disulfide bond were isolated from the tubers of Maca.Their structures were unambiguously confirmed by NMR spectroscopic,X-ray crystallographic and electronic circular dichroism(ECD)analyses.At the concentration of 20μmol/L,compounds 2-1,2-2,and 4-1 increased the viability of PC12 cells with the cell viability at(72.06±1.14)%,(72.64±1.49)%,and(70.93±1.22)%,respectively.Furthermore,the serial concentration experiment showed that they can protect PC12 cells in a dose-dependent manner.

用反相高效液相色谱法测定Lepidium meyenii

十字花科独行菜属Lepidium meyenii是一种分布在秘鲁高海拔地区的植物，其梨形块茎胚轴具有很高的营养价值。当地印第安人用其治疗贫血、肺结核、不育以及疲劳等病症。本次首次采用高效液相色谱法，以从中分离到的5个化合物为主要指标，对L.meyenii进行了定性和定量研究。

宽叶独行菜提取物微胶囊的制备与表征

利用微胶囊技术,以宽叶独行菜提取物为芯材、海藻酸钠为壁材,制备宽叶独行菜提取物微胶囊,设计响应面实验并对其性能进行表征.结果表明,宽叶独行菜提取物微胶囊最佳制备方案为:海藻酸钠质量浓度为2.0%,氯化钙质量浓度2.0%,芯壁体积比1∶3.从扫描电子显微镜成像图片可以看出,微胶囊整体呈球状,形状规则,结构紧致,成形性好.FTIR和TG图谱显示宽叶独行菜提取物被很好地包裹在壁材里,且具有良好的热稳定性.最后对微胶囊进行体外胃肠液模拟消化实验,12h后肠液和胃液累积释放量分别达到80.21%和24.32%.微胶囊在胃肠液中的释放动力学拟合结果表明,零级拟合方程更能反映体外释放行为.

钠-葡萄糖协同转运蛋白2抑制剂联合葶苈子治疗慢性心力衰竭合并肺部感染的临床疗效分析

目的探讨钠-葡萄糖协同转运蛋白2抑制剂联合葶苈子治疗对心力衰竭(心衰)合并肺部感染患者心功能、消化功能及肺功能的影响。方法选取秭归县中医院2017年8月至2019年3月收治的168例心衰合并肺部感染患者作为研究对象。根据治疗方法不同将患者分为观察组和对照组,每组84例。对照组接受钠-葡萄糖协同转运蛋白2抑制剂联合头孢他啶治疗,观察组在对照组基础上接受葶苈子治疗,共治疗30 d。比较两组治疗前后营养状态指标〔血清前白蛋白(PA)、白蛋白(ALB)、红细胞计数(RBC)、体质量指数(BMI)〕、免疫功能指标〔分化簇抗原(CD3、CD4、CD8)、免疫球蛋白(IgG、IgM)〕、血清炎症因子〔白细胞介素(IL-8、IL-10、IL-17)及肿瘤坏死因子(TNF-α)〕、肠道菌群(肠球菌、大肠埃希菌、乳杆菌、双歧杆菌、酵母菌、消化球菌)、心肺功能指标〔动脉血氧饱和度(PaO_(2))、动脉血二氧化碳分压(PaCO_(2))、心率、最大摄氧量(VO_(2)max)、最大运动负荷(Wmax)、最大氧脉搏、无氧阈值(AT)、第1秒用力呼气容积/用力肺活量比值(FEV1/FVC)、FEV1和每分最大通气量(MVV)〕。结果两组治疗后PA、ALB、RBC、BMI、CD3、CD4、CD8、IgG、IgM、乳杆菌、双歧杆菌、PaO_(2)、VO_(2)max、Wmax、最大氧脉搏、AT、FEV1/FVC、FEV1、MVV均较治疗前明显升高,IL-8、IL-17、TNF-α、肠球菌、大肠埃希菌、PaCO_(2)、心率水平均较治疗前明显降低,且观察组治疗后PA、ALB、RBC、BMI、CD3、IgG、IgM、IL-10、双歧杆菌、乳酸菌、PaO_(2)、VO_(2)max、Wmax、最大氧脉搏、AT、FEV1/FVC、FEV1、MVV水平均明显高于对照组〔PA(mg/L):259.69±20.73比217.69±20.73,ALB(g/L):41.46±4.58比36.56±3.73,RBC(×1012/L):4.52±0.24比4.21±0.31,BMI(kg/m^(2)):22.37±2.73比19.66±2.24,CD3:0.63±0.08比0.56±0.08,IgG(g/L):21.85±3.68比15.72±4.36,IgM(g/L):4.68±1.68比3.73±1.67,IL-10(ng/L):65.28±7.23比50.23±6.14,双歧杆菌(CFU/kg):83.5±8.6比78.5±8.3,乳酸菌(CFU/kg):62.1±6.5比53.5±6.0,PaO_(2)(mmHg,1 mmHg≈0.133 kPa):98.36±1.75比91.95±2.95,VO_(2)max(L/min):1.71±0.35比1.22±0.39,Wmax(W):127.49±19.54比97.49±15.37,最大氧脉搏(L/次):11.27±2.42比9.46±2.79,AT:(50.49±7.48)%比(41.35±6.67)%,FEV1/FVC:(75.68±5.86)%比(65.48±8.54)%,FEV1:(82.44±5.73)%比(73.57±7.75)%,MVV(L/min):74.86±10.64比64.63±9.68,均P<0.05〕,CD4、CD8、IL-8、IL-17、TNF-α、肠球菌、大肠埃希菌、PaCO_(2)、心率水平均显著低于对照组〔CD4:0.32±0.06比0.39±0.05,CD8:0.28±0.06比0.34±0.05,IL-8(ng/L):16.64±2.63比26.35±4.13,IL-17(ng/L):112.38±30.16比207.75±42.23,TNF-α(ng/L):45.27±10.23比61.26±14.29,肠球菌(CFU/kg):63.6±5.6比69.5±6.8,大肠埃希菌(CFU/kg):65.8±6.4比70.5±7.0,PaCO_(2)(mmHg):41.84±4.45比56.18±5.37,心率(次/min):75.96±11.57比91.75±12.68,均P<0.05〕。结论葶苈子联合钠-葡萄糖协同转运蛋白2抑制剂治疗心衰合并肺部感染,可有效改善患者心肺功能,降低炎症指标水平,提升患者的营养状态,纠正肠道菌群情况,对临床治疗有一定指导意义。