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PubMed1996

Antifungal properties of yam (Dioscorea alata) peel extract.

The extraction of natural antifungal compounds from the peels of yam (Dioscorea alata) and the effect of these compounds on both the vegetative and reproductive structures of some yam not pathogens were studied. Four prominent antifungal components were obtained; one of the components was fully characterized and identified as beta-sitosterol. The antifungal activity of the compounds toward the germination of spores of two yam pathogens showed an inhibition of less than 57% at a concentration of 50 mg/L while inhibition on the elongation of germ-tubes of Fusarium moniliforme was as high as 82% at the same concentration. However, the ED50 for inhibition of germ-tube elongation in the yam compounds for the same organism was below 32 mg/L. The role of the yam compounds at high concentrations in disease resistance is discussed.

Antifungal Agents↗

PubMed2002

A genetic linkage map of Guinea yam ( Dioscorea rotundata Poir.) based on AFLP markers.

A genetic linkage map of the tetraploid white yam ( Dioscorea rotundata Poir.) was constructed based on 341 co-dominantly scored amplified fragment length polymorphism (AFLP) markers segregating in an intraspecific F(1) cross. The F(1) mapping population was produced by crossing a landrace cultivar TDr 93-1 as female parent to a breeding line TDr 87/00211 as the male parent. The marker segregation data were split into maternal and paternal data sets, and separate genetic linkage maps were constructed since the mapping population was an F(1) cross between two presumed heterozygous parents. The markers segregated like a diploid cross-pollinator population suggesting that the D. rotundata genome is an allo-tetraploid (2n = 4 x = 40). The maternal map comprised 155 markers mapped on 12 linkage groups with a total map length of 891 cM. Three linkage groups consisted of maternal parent markers only. The paternal map consisted of 157 markers mapped on 13 linkage groups with a total map length of 852 cM. Three and one quantitative trait loci (QTLs) with effects on resistance to Yam Mosaic Virus (YMV) were identified on the maternal and paternal linkage maps, respectively. Prospects for detecting more QTLs and using marker-assisted selection in white yam breeding appear good, but this is subject to the identification of additional molecular markers to cover more of the genome.

Journal Article↗

PubMed2002

A genetic linkage map of water yam ( Dioscorea alata L.) based on AFLP markers and QTL analysis for anthracnose resistance.

A genetic linkage map of the tetraploid water yam ( Dioscorea alata L.) genome was constructed based on 469 co-dominantly scored amplified fragment length polymorphism (AFLP) markers segregating in an intraspecific F(1) cross. The F(1) was obtained by crossing two improved breeding lines, TDa 95/00328 as female parent and TDa 87/01091 as male parent. Since the mapping population was an F(1) cross between presumed heterozygous parents, marker segregation data from both parents were initially split into maternal and paternal data sets, and separate genetic linkage maps were constructed. Later, data analysis showed that this was not necessary and thus the combined markers from both parents were used to construct a genetic linkage map. The 469 markers were mapped on 20 linkage groups with a total map length of 1,233 cM and a mean marker spacing of 2.62 cM. The markers segregated like a diploid cross-pollinator population suggesting that the water yam genome is allo-tetraploid (2n = 4 x = 40). QTL mapping revealed one AFLP marker E-14/M52-307 located on linkage group 2 that was associated with anthracnose resistance, explaining 10% of the total phenotypic variance. This map covers 65% of the yam genome and is the first linkage map reported for D. alata. The map provides a tool for further genetic analysis of traits of agronomic importance and for using marker-assisted selection in D. alata breeding programmes. QTL mapping opens new avenues for accumulating anthracnose resistance genes in preferred D. alata cultivars.

Journal Article↗

PubMed2000

Rapid isolation of promoter sequences by TAIL-PCR: the 5'-flanking regions of Pal and Pgi genes from yams (Dioscorea).

Using a modified TAIL-PCR technique, the 5'-flanking regions of the phenylalanine ammonia lyase (Pal) genes of a yam species, Dioscorea bulbifera, and the phosphoglucose isomerase (Pgi) gene of D. tokoro were successfully isolated. Two novel modifications of the TAIL-PCR procedure introduced here, namely (1) the use of a battery of random 10-mers (RAPD primers) as short arbitrary primers, and (2) the use of a total of five nested, gene-specific primers, allow the rapid isolation of the 5'-flanking region of any gene from organisms with large genomes. Isolated 5'-flanking regions were fused to the gus gene, and tested for transient expression in tobacco BY2 cells. All the isolated 5'-flanking regions were shown to drive reporter gene expression. Three Pal promoters responded to salicylic acid, presumably as a result of the binding of a MYB transcriptional activator to the multiple MREs (Myb Recognition Elements) present in these regions.

Base Sequence↗

PubMed2002

Temperature dependence of seedling establishment of a perennial, Dioscorea tokoro.

The temperature dependence of seed germination and seedling growth was analyzed in Dioscorea tokoro, an East Asian summer-green perennial. Seeds were able to germinate fully only at 11-20 degrees C. At around 17-20 degrees C the first leaf petiole of the seedling elongated and quickly set the first leaf blade at a position enabling photosynthesis. At temperatures higher than 20 degrees C petiole elongation was retarded, and seedlings formed a rhizome and established as a perennial. The rhizome size increased with temperature up to 29 degrees C. Thus, during growth immediately after germination, temperature appears to be a key factor in determining whether the plant establishes as a perennial or grows rapidly without rhizome thickening.

Journal Article↗

PubMed1986

Pharmacological evaluation of Dioscorea dumetorum tuber used in traditional antidiabetic therapy.

This study was undertaken to confirm or otherwise disprove the alleged effectiveness of Dioscorea dumetorum tuber in the traditional treatment of clinical diabetes mellitus. Hydroalcoholic extracts of the tuber were fractionated by precipitation or solvent partition and the various extracts or fractions subjected to phytochemical and pharmacological tests. Whereas the alkaloid-containing fraction was hyperglycaemic in fasting normal mice, the whole extract and the fractions containing steroidal derivatives evinced significant hypoglycaemic activities in fasting normal mice or rabbits and in fasting alloxan-diabetic rabbits. The hypoglycaemic action of the glycosidic portion in particular was prompt and potent, in normal as well as in severely alloxan-diabetic rabbits suggesting thereby the possibility of obtaining an agent that could act in conditions of even severe insulin lack.

Animals↗

PubMed2000

Additional phosphate stabilises uninterrupted growth of a Dioscorea deltoidea cell culture.

Suspension cells of Dioscorea deltoidea Wall (strain D-1) were maintained in a semicontinuous culture (SCC) in shake flasks at a high growth rate. It was shown that continuous propagation growth of this culture is unstable on Murashige's and Skoog's (MS) medium due to P starvation. On a P-enriched MS-medium the SCC was stable even at mean specific growth rates >0.3 day(-1). Highest volumetric concentrations of furostanol glycosides were obtained, when a P-enriched SCC was not further subcultivated but fed with sucrose. The investigated culture is able to control phosphate uptake and to prevent toxicity on media with excess P. High concentrations of cellular P(i) did not effect the ratio of furostanol to starch.

Journal Article↗

PubMed2001

Study of two plants used in traditional medicine in Zimbabwe for skin problems and rheumatism: Dioscorea sylvatica and Urginea altissima.

Two plants used in Zimbabwean traditional medicine, Dioscorea sylvatica (Dioscoreaceae) and Urginea altissima (Liliaceae), produce mild inflammation and itching when rubbed on the skin. Investigations of the causes of these cutaneous reactions showed that raphides of calcium oxalate are, at least in part, responsible for the effects. Histamine could not be detected.

Histamine↗

PubMed1997

Aetiology of yam (Dioscorea rotundata) tuber rots held in traditional stores in Nigeria: importance of Fusarium spp. and yam beetle.

The extent and causes of yam (Dioscorea rotundata) tuber rots were investigated in Igalaland, Nigeria. Rots were found to be associated with prior physical damage in almost all cases. Numerous fungal species were isolated from the infected lesions of which Fusarium spp. predominated, not Botrydiplodia theobromae as previously reported in other studies. None of the fungi was able to infect undamaged yams in laboratory experiments. The damage was caused by both biotic and abiotic factors of which the yam beetle (Heteroligus meles) was the largest single cause. There were significant differences in the frequency with which different varieties of yam were attacked by H. meles and found to be infected with Fusarium spp. In an independent survey of farmers' experience of yam rots, varieties that scored well correlated with apparent resistance to the beetle and Fusarium spp. These studies highlight the importance of yam beetle infestation and the need to have independent methods for varietal authentication.

Animals↗

PubMed1999

Dioscorin, the major tuber storage protein of yam (Dioscorea batatas decne) with carbonic anhydrase and trypsin inhibitor activities.

Dioscorin, the tuber storage protein of yam (Dioscorea batatas Decne), was purified successively by ammonium sulfate fractionation, DE-52 ion exchange chromatography, and Sephadex G-75 column. Two protein bands (82 and 28 kDa) were found under nonreducing conditions after SDS-PAGE; but only one band (32 kDa) was detected under reducing conditions. The first 21 amino acids in the N-terminal region of the 28 kDa form were VEDEFSYIEGNPNGPENWGNL, which was highly homologous to deductive sequence of dioscorin from cDNA of another yam species (Dioscoreacayenensis Lam) reported by Conlan et al. (Plant Mol. Biol. 1995, 28, 369-380). Hewett-Emmett and Tashian (Mol. Phylogenet. Evol. 1996, 5, 50 -77) mentioned that, according to DNA alignments, dioscorin from yam (D. cayenensis) was alpha-carbonic anhydrase (alpha-CA) related. In this report, we found that the purified dioscorin showed both CA dehydration activity using sodium bicarbonate as a substrate and CA activity staining after SDS-PAGE. A polyclonal antibody, which was raised against trypsin inhibitor (TI), a storage protein of sweet potato (Ipomoea batatas [L.] Lam var. Tainong 57), cross-reacted with dioscorin, which also showed TI activity determined by both activity staining after SDS-PAGE and trypsin inhibition determination.

Amino Acid Sequence↗

PubMed1999

A new pregnane glycoside from Dioscorea collettii var. hypoglauca.

During further bioactivity-guided fractionation, a new pregnane glycoside, hypoglaucin G (1), and a known compound, pregna-5, 16-dien-3beta-ol-20-one 3-O-alpha-L-rhamnopyranosyl-(1-->2)- [alpha-L-rhamnopyranosyl-(1-->4)] -beta-D-glucopyranoside (2), were isolated from the EtOH extract of Dioscorea collettii var. hypoglauca rhizomes, which induced morphological deformation of Pyricularia oryzae mycelia with minimum morphological deformation concentration values of 135 microM and 236 microM, respectively. The structure of 1 was established as 16beta-(4'-methyl-5'-O-beta-D-glucopyranosyl- pentanoxyl)-pre gn-5-en-3 beta-ol-20-one 3-O-alpha-L- rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-D- glucopyranoside on the basis of chemical evidence and spectral analysis, especially by 2D NMR techniques.

Antifungal Agents↗

PubMed2003

Dioscorealides and dioscoreanone, novel cytotoxic naphthofuranoxepins, and 1,4-phenanthraquinone from Dioscorea membranacea Pierre.

[structure: see text] Commonly used among ingredients in Thai traditional anticancer preparations, the rhizome of Dioscorea membranacea Pierre was found potently cytotoxic and possibly contributed to such a therapeutic effect. Bioassay-guided isolation resulted in two novel cytotoxic naphthofuranoxepins, dioscorealides A (1) and B (2), and a new 1,4-phenanthraquinone, dioscoreanone (3). The structure determination, achieved mainly by means of NMR and CD spectral and X-ray crystallographic analyses, and cytotoxicity are discussed here.

Journal Article↗

PubMed1999

Dioscorea alata (water yam) as a replacement for maize in diets for laying hens.

One hundred and twenty-six point-of-lay birds were randomly alloted into six groups of 21 birds each and fed six diets containing 0%, 10%, 20%, 30%, 40% or 50% of Dioscorea alata meal as a replacement for maize, corresponding to 0%, 20%, 40%, 60%, 80% and 100% maize replacement. There were no significant differences (p > 0.05) in feed intake, egg weight or feed efficiency between the control diet and the test diets. However, the daily egg production per 100 birds (hen day production), differed significantly (p < 0.05) among the treatments. The birds on the control diet and diets with substitution rates of up to 80% laid significantly (p < 0.05) more eggs than those on the 100% substitution rate. This shows that D. alata can replace up to 80% of maize or constitute 40% of a laying chicken diet, provided the rations are isocaloric and isonitrogenous. For this to be achieved, more soybean and/or more fish scraps, and more palm oil are needed in the diets containing D. alata than in diets based on maize.

Animal Feed↗

PubMed1999

Analysis of the sequence of dioscorea Alata bacilliform virus: comparison to others members of the badnavirus group.

The complete nucleotide sequence of the genome of Dioscorea alata bacilliform virus (DaBV) has been determined from cloned fragments. Features of the genome confirm DaBV to be a pararetrovirus of the genus Badnavirus which is more similar to other mealy-bug transmitted badnaviruses, in particular to cacao swollen shoot virus, than to rice tungro bacilliform virus. Sequence variability between cloned fragments suggests that the genetic variability of the virus may be quite high (up to 11% nucleotide sequence variation for some small regions of the genome) although the overall variability detected was 4.2% at the nucleotide level.

Badnavirus↗

PubMed1984

Isolation and characterization of an intermediate steroid metabolite in diosgenin biosynthesis in suspension cultures of Dioscorea deltoidea cells.

The aglycon form of the steroidal sapogenin furost -5-ene-3 beta, 22,26-triol, 3 beta- chacotrioside 26 beta-D-glucopyranoside was isolated from cell suspension cultures of Dioscorea deltoidea and its molecular structure was determined by mass spectrometry and 1H and 13C n.m.r. spectroscopy. From kinetic studies and incorporation experiments with [1-14C]acetate it was concluded that the steroidal compound (in the glycoside form) is an intermediate in vivo in diosgenin biosynthesis. It accumulated in growing cells of D. deltoidea and was metabolized to diosgenin (in the glycoside form, i.e. dioscin ) in non-dividing cells.

Acetates↗

PubMed1996

Antineoplastic agents; I. Three spirostanol glycosides from rhizomes of Dioscorea collettii var. hypoglauca.

By activity-guided fractionation, three known steroidal saponins, prosapogenin A of dioscin, dioscin and gracillin, were isolated from the total saponin fraction of Dioscorea coiletti var. hypoglauca as active compounds causing morphological abnormality of Pyricularia oryzae mycelia. The compounds also exhibited cytotoxic activity against the cancer cell line K562 in vitro. The structures of the compounds were elucidated on the basis of chemical evidence and IR, FAB-MS, 1H-NMR, 13C-NMR, and two-dimensional NMR (2D-NMR) analysis.

Antineoplastic Agents↗

PubMed1990

Hypoglycaemic activity of dioscoretine from tubers of Dioscorea dumetorum in normal and alloxan diabetic rabbits.

Dioscoretine isolated from the aqueous fraction of the methanol extract of Dioscorea dumetorum tubers when administered intra-peritoneally to normal and alloxan diabetic rabbits produces significant hypoglycaemic effects at a dose of 20 mg/kg. The fasting blood sugar in normoglycaemic rabbits was reduced from 112 mg/100 ml to 55 mg/100 ml after 4 hours. In alloxan diabetic rabbits, the blood sugar was lowered from 520 mg/100 ml to 286 mg/100 ml at the same time interval. The aqueous fraction of the methanol extract produced comparable effects at 100 mg/kg. The chloroform fraction of the same extract raised the fasting blood sugar of normal rabbits to 196 mg/100 ml after 6 h. The acute toxicity studies gave LD50 values of 1.4 g/kg for the aqueous fraction and 0.58 g/kg for dioscoretine when tested on mice. The hypoglycaemic effects were compared to those of tolbutamide.

Alkaloids↗

PubMed2001

Effect of yam (Dioscorea cayenensis) and dasheen (Colocassia esculenta) extracts on the kidney of streptozotocin-induced diabetic rats.

Streptozotocin-induced diabetic wistar rats were maintained for 4 weeks on a supplement of extracts of yam (Dioscorea cayenensis) or dasheen (Colocassia esculenta). The activities of malic enzyme, NADP+ isocitrate dehydrogenase, Glucose 6-P-dehydrogenase and the transaminases were determined to assess any degree of metabolic alteration caused by diabetic nephropathy. Diabetic rats fed normal diet and those fed yam extract, dasheen extract and commercial linamarin respectively lost weight significantly compared to healthy controls. The diabetic rats fed dasheen extract, maintained near normoglycaemic values compared to diabetic rats on normal diet (P < 0.05). Malic enzyme activity was significantly reduced (P < 0.05) in diabetic rats on the normal diet compared to normal healthy controls. Feeding of yam or dasheen extract raised the activity of this enzyme towards normal. Feeding of dasheen extract or commercial linamarin significantly lowered (P < 0.05) the activity of NADP+ isocitrate dehydrogenase below that of healthy controls. Glucose 6-P-dehydrogenase activity was significantly increased (P < 0.05) in diabetic rats compared to healthy controls. Alanine transaminase in the kidney of diabetic rats fed yam extract was significantly higher than healthy controls (P < 0.05). These results demonstrate an overall aggravation of the diabetic nephropathy by yam and dasheen extracts in the diet. In the Caribbean region where these foods are dietary staples, there may be a correlation with the reported high prevalence of diabetes mellitus and the development of renal disease.

Alanine Transaminase↗