Japanese Yam Research Articles

Biosynthetic Gene Expression and Tissue Distribution of Diosgenin in Dioscorea japonica.

Diosgenin is an aglycone of dioscin, a major bioactive steroidal saponin found in plants, including Himalayan Paris (Paris polyphylla), fenugreek (Trigonella foenum-graecum), and yam (Dioscorea spp.). We have previously demonstrated that a species of natural yam, Dioscorea japonica, contains a promising bioactive compound diosgenin, which induces anti-carcinogenic and anti-hypertriacylglycerolemic activities. Here, we found for the first time that Japanese yam (D. japonica) bulbils are richer in diosgenin than the edible tubers (rhizomes) and leaves. LC-MS and imaging-MS analyses revealed that diosgenin accumulated in the peripheral region of D. japonica bulbils. Additionally, we performed RNA-seq analysis of D. japonica, and multiple sequence alignment identified D. japonica CYP90 (DjCYP90), the orthologous gene of CYP90G4 in P. polyphylla, CYP90B50 in T. foenum-graecum, CYP90G6 in Dioscorea zingiberensis, and CYP90G in Dioscorea villosa, which encodes a diosgenin biosynthetic rate-limiting enzyme. The expression levels of DjCYP90 were significantly upregulated in D. japonica bulbils than in its rhizomes and leaves. Since diosgenin is one of the most promising functional food factors executing several favorable bioactivities, D. japonica bulbils rich in diosgenin would be a beneficial natural resource.

Japanese yam mosaic virus

This datasheet on Japanese yam mosaic virus covers Identity, Hosts/Species Affected, Further Information.

Effects of time and weeding method on the regeneration and growth of Japanese yam (Dioscorea japonica) vines and tubers in tea gardens

For the weed control of Japanese yams, farmers pull out the vines by hand because the chemical control of Japanese yams in tea plantations is difficult as the vines grow from the area below the tea trees, where the herbicides have limited reach. This study compared the regeneration and growth of vines after controlling weeds using the following methods: 1) cutting the vine at 30 cm height, 2) cutting the vine at ground level, and 3) pulling out the vine from the base (at the node of the tuber and vine). All three treatments were performed during three weeding seasons to determine the most effective method and time to control Japanese yams in tea gardens. In addition, we investigated the deterioration of old tubers and the formation of new tubers by studying their weight changes because each old tuber disappears and forms a new tuber each year. However, our results indicated that new tubers were formed before the disappearance of old tubers, and there were no border time periods where both old and new tubers were absent. Furthermore, the new tubers grew in a short period from July to August. Therefore, we recommend repeatedly pulling out Japanese yam vines during July for effective weed control. Moreover, when vines of Japanese yam were not pulled out completely or were cut in May or July, branches grew rapidly and reached the canopy of tea trees after 2–4 weeks. Furthermore, when vines were pulled out at the ground level, 40 % of vines reached the canopy after one month. Therefore, it is difficult to control Japanese yam completely by pulling out vines alone.

Vine length determines the propagation strategy of Japanese yam (Dioscorea japonica) in tea gardens

Vine length determines the propagation strategy of Japanese yam (Dioscorea japonica) in tea gardens

Propagule Powder of Japanese Yam (Dioscorea Japonica) Reduces High-Fat Diet-Induced Metabolic Stress in Mice through the Regulation of Hepatic Gene Expression.

Japanese yam propagules are supposed to have high potential as a functional food. However, there are almost no studies examining their physiological function. This study aims to elucidate the physiological function of Japanese yam propagules that are heated, freeze-dried, and powdered. A high-fat diet with Japanese yam propagules is administered to mice for 4 weeks. High-fat loading induces a decline in respiratory quotient, and a high-fat diet with propagules reduces it more. This result suggests that propagules increase fat oxidation, indicating fat utilization. The hepatic transcriptome is analyzed using a DNA microarray. Some of the genes affected by high-fat loading are reversed by simultaneous ingestion of propagules. Such genes are mainly involved in the immune system and fat metabolism. High-fat loading induces hepatic inflammation, which is repressed by simultaneous ingestion of propagules. For lipid metabolism, propagules repress an increase in cholesterol biosynthesis and catabolism by high-fat loading. Regarding carbohydrate metabolism, propagules decrease glycolysis and glycogen synthesis and increase gluconeogenesis. Moreover, amino acids are converted into pyruvate and then used for gluconeogenesis. Propagules act to delay the occurrence of hepatic disease by suppressing carbohydrate and fat metabolism disorders in high-fat loaded mice.

Research and Development of Proteins and Peptides with Therapeutic Potential from Yam Tubers.

We discuss the diverse biological activities, therapeutic potential, and clinical applications of peptides and proteins isolated from various yams species including Dioscorea opposita Thunb (Chinese yam), D alata, D japonica (Japanese yam), D pseudojaponica, D batatas (Korea yam), and D cayenensis. Yam peptides and proteins have many pharmacological activities including immunomodulatory, antioxidant, estrogen-stimulating, osteogenic, angiotensin I-converting enzyme inhibiting, carbonic anhydrase and trypsin inhibiting, chitinase, anti-insect, anti-dust mite, lectin, and anti-proliferative activities. Yam peptides and proteins have therapeutic potential for treating cardiovascular diseases, inflammatory diseases, cancers, aging disorders, menopause, and osteoporosis.

ダイジョ、ジネンジョの褐変および冷凍・解凍によるレオロジーの変化

ダイジョ、ジネンジョの褐変および冷凍・解凍によるレオロジーの変化

Rapid and low-cost diagnosis of Japanese yam mosaic virus infection in Chinese yam (Dioscorea polystachya) leaves by a print-capture RT-PCR

A rapid diagnostic method for Japanese yam mosaic virus (JYMV) infection in Chinese yam (Dioscorea polystachya) by a print-capture RT-PCR was developed. The cut surface of a rolled leaf of a JYMV-infected Chinese yam was stamped onto a nitrocellulose membrane. The clipped membrane was boiled in eluting solution to elute the RNA for use as the template in RT-nested PCR. Although JYMV RNA was detectable in most infected plants in the first PCR of the print-capture RT-PCR, it was detected from all samples in the nested PCR. The tissue-printed membranes could be preserved for at least 3 months at 4 °C for JYMV detection.

마(Dioscorea opposita)에 발생한 Japanese yam mosaic virus 진단 및 염기서열 분석

마(Dioscorea opposita)에 발생한 Japanese yam mosaic virus 진단 및 염기서열 분석

Taiwanese and Japanese yam (Dioscorea spp.) extracts attenuate doxorubicin-induced cardiotoxicity in mice

The present study was designed to explore whether yam could protect the heart from doxorubicin (DOX)-induced oxidative stress leading to cardiotoxicity in vivo. In this study, the protective effects of water and ethanol extracts of three varieties of yam, including water extracts of Dioscorea japonica Thunb., ethanol extracts of D. japonica Thunb., water extracts of Dioscorea alata, ethanol extracts of D. alata, water extracts of Dioscorea purpurea, and ethanol extracts of D. purpurea, against DOX-induced cardiotoxicity in experimental mice were evaluated. DOX treatment led to significant decreases in the ratio of heart weight to body weight and heart rate, and increases in blood pressure and the serum level of lactate dehydrogenase, a marker of cardiotoxicity, were recovered by yam extracts, especially in water extracts of D. alata. Yam extracts also decreased the cardiac levels of thiobarbituric acid relative substances, reactive oxygen species, and inflammatory factors, as well as the expression of nuclear factor kappa B, while ethanol extracts of D. japonica Thunb. and D. purpurea were shown to be more potent. Moreover, yam extracts had a role in increasing the activities of glutathione peroxidase and superoxide dismutase, thus improving the DOX-induced alterations in oxidative status in the heart tissue of DOX-treated mice. All ethanol extracts of yam exhibited their antiapoptotic abilities on caspase-3 activation and mitochondrial dysfunction, and ethanol extracts of D. alata still exerted a superior effect. Based on these findings, it can be concluded that yam has significant cardioprotective properties against DOX-induced damage via its multiple effects on antioxidant, anti-inflammatory, or antiapoptotic activities.

Consumption of Japanese Yam Improves Lipid Metabolism in High-Cholesterol Diet-Fed Rats.

We investigated the effects of dietary Japanese yam (Dioscorea japonica Thunb.) on lipid metabolism. Male Wistar rats (6 wk old) were fed a high-cholesterol diet for 6 wk and then supplemented with 26% of Japanese yam or 0.5% of its constituent diosgenin for a further 4 wk of high-cholesterol feeding (C6-J4 and C6-D4 groups, respectively). In the C6-J4 group, body weight gains significantly decreased, but skeletal muscle fiber sizes in quadriceps significantly increased compared with the other groups. Furthermore, Japanese yam supplementation resulted in the reduction of triglyceride contents in their liver, quadriceps, and intra-abdominal visceral fat. Diosgenin supplementation resulted in an increase in the numbers of skeletal muscle fibers and decrease in the fat accumulations in liver and of the lipid contents in quadriceps. Although quadriceps cholesterol contents decreased concomitantly with increased serum HDL-cholesterol in both the groups, fecal bile acid, fecal cholesterol contents, and fecal weight were higher in the C6-J4 group than in the C6-D4 group. Meanwhile, we demonstrated that Japanese yam inhibited micellar cholesterol solubility in vitro in a concentration-dependent manner. These results suggest that Japanese yam is more effective than diosgenin in reducing fat accumulation and improving cholesterol metabolism during chronic consumption of a high-cholesterol diet.

Complete genome sequence of a divergent strain of Japanese yam mosaic virus from China.

A novel strain of Japanese yam mosaic virus (JYMV-CN) was identified in a yam plant with foliar mottle symptoms in China. The complete genomic sequence of JYMV-CN was determined. Its genomic sequence of 9701 nucleotides encodes a polyprotein of 3247 amino acids. Its organization is virtually identical to that of two JYMV isolates from Japan. With the latter, it shares nucleotide sequence identities of only 74.7-74.8%, indicating it might be a member of a new species. However, sequence analysis of the polyprotein and individual proteins suggested that the Chinese isolate is a divergent JYMV strain in the process of speciation.

Antioxidant and trypsin inhibition activity of dioscorin influenced by yam cultivars and eluent pH

SummaryThe total antioxidant activity (TAA) and trypsin inhibition activity (TIA) of storage protein dioscorin from six yam cultivars (Dashan, Hualien No. 3, Keelung, Mingchien, Tainong No. 2, and Japanese yam) were demonstrated. Japanese yam had the highest TAA and the lowest calculated EC50 at any purification stage. Following gel permeation, dioscorins purified from Hualien No. 3 and Japanese yam showed the highest TIA and lowest calculated IC50. Dioscorin with higher TIA apparently possesses better TAA. The pIs of dioscorin from all yam species were in the range of 5.94–4.33 indicating acidic protein in nature. Results from isoelectric focusing chromatography showed regardless of species higher TIA for dioscorin eluted at lower pH.

Natto and viscous vegetables in a Japanese-style breakfast improved insulin sensitivity, lipid metabolism and oxidative stress in overweight subjects with impaired glucose tolerance

We previously suggested that the consumption of natto and viscous vegetables as part of a Japanese-style meal based on white rice (WR) reduced postprandial glucose and insulin levels in healthy subjects. The aim of the present study was to assess whether a single breakfast of natto and viscous vegetables or the same breakfast consumed for 2 weeks could improve glucose control, insulin sensitivity, lipid metabolism and oxidative stress in overweight subjects with impaired glucose tolerance (IGT). A total of eleven free-living subjects with IGT followed a randomised, crossover breakfast intervention for 2 weeks. The test meal included boiled WR with natto (viscous fermented soyabeans), Japanese yam and okra. The control meal included WR with non-viscous boiled soyabeans, potatoes and broccoli. Both meals contained comparable amounts of carbohydrate, fat, protein and fibre. The test meal reduced acute glucose and insulin responses compared to the control meal in the study participants. Insulin sensitivity was assessed using the composite insulin sensitivity index (CISI) after both the test and control meal periods. The test meal resulted in improvements in CISI compared to the baseline, whereas no significant changes were observed after the control meal period. Serum levels of both total and LDL-cholesterol were assessed before and after the test meal period and found to decrease significantly. There was also a tendency towards reduced serum malondialdehyde-modified LDL and N(ɛ)-carboxymethyllysine. No differences were observed in the measures of chronic glycaemic control. Thus, we conclude that a breakfast of natto and viscous vegetables consumed for 2 weeks improves insulin sensitivity, serum lipid and oxidative stress.

Withanolides from the Rhizomes of Dioscorea japonica and Their Cytotoxicity

Edible yams are tropical crops that serve as important staple foods in many parts of the world. The rhizome of Dioscorea japonica , well-known as "Japanese yam", is a food and medicinal source known as "San Yak" in Korea. Bioassay-guided fractionation and chemical investigation of the extract of this yam resulted in the identification of two new withanolides, named dioscorolide A (1) and dioscorolide B (2). The structures of these new compounds were determined by spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) techniques, high-resolution mass spectrometry (HRMS), and chemical methods. The cytotoxic activities of the isolates (1 and 2) were evaluated by determining their inhibitory effects on four human tumor cell lines (A549, SK-OV-3, SK-MEL-2, and HCT15) and a human normal cell line (HUVEC) using a sulforhodamine B (SRB) bioassay. Compounds 1 and 2 showed cytotoxicity against tumor cell lines (A549, SK-OV-3, SK-MEL-2, and HCT15) with IC(50) values ranging from 6.3 to 26.9 μM and exhibited lower activity against the normal cell line (HUVEC) with IC(50) values ranging from 27.1 to 28.8 μM, suggesting selective toxicity among tumor and normal cells.

Yam Storage Protein Dioscorins from Dioscorea alata and Dioscorea japonica Exhibit Distinct Immunomodulatory Activities in Mice

The aim of this study was to elucidate the effect of the major storage protein dioscorin isolated from two different yam species, Tainong No. 1 (TN1-dioscorins) and Japanese yam (Dj-dioscorins), on the immune activities of mice. Dj-dioscorins, like TN1-dioscorins, could induce expression of the pro-inflammatory cytokines and stimulate phagocytosis of RAW 264.7. Intraperitoneal injection of the TN1-dioscorins into mice stimulated phagocytosis of bone marrow, spleen, and thymic cells. In contrast, the T and B cells in bone marrow, spleen, and thymus isolated from mice injected with Dj-dioscorins had higher proliferative responses to mitogens. Furthermore, Dj-dioscorins enhanced proliferation of CD4(+), CD8(+), and Tim3(+) (Th1) cells in spleen and CD19(+) cells in both spleen and thymus. Supplement of Dj-dioscorins in the lymphoid cells isolated from Dj-dioscorins primed mice induced cell proliferation of both spleen and thymic cells. These findings indicated that TN1-dioscorins have a higher ability to stimulate the phagocytic activity of the lymphoid cells than Dj-dioscorins, whereas Dj-dioscorins possess more abilities than TN1-dioscorins to enhance the proliferation of the lymphoid cells.

Simultaneous detection of Japanese yam mosaic virus and Yam mild mosaic virus from yam leaves using a tube capture reverse transcription-polymerase chain reaction assay

To detect Japanese yam mosaic virus (JYMV) and Yam mild mosaic virus (YMMV) in yam plants in Japan, we developed a duplex RT-PCR assay consisting of a tube-capture procedure followed by one-step RT-PCR with two primer pairs. A 241-bp fragment of the coat protein region of JYMV and a 174-bp fragment of the nuclear inclusion protein b region of YMMV were amplified, thus identifying the two viruses from yam plants cultivated in Yamaguchi Prefecture in 2007. All water yam plants examined were infected with YMMV alone. All the Japanese yam and Chinese yam plants were infected with either JYMV alone or both JYMV and YMMV, suggesting that YMMV and JYMV are prevalent among field-grown yam plants.

Molecular evidence for a new potyvirus species in yam (Dioscorea spp.) on the island of Guadeloupe

Prevalence of yam potyviruses in the French Caribbean islands of Guadeloupe was evaluated in 142 samples collected from yams showing symptoms of mosaic and mottling and belonging to Dioscorea rotundata (52 samples), D. alata (52 samples) and D. trifida (38 samples). Samples were screened by enzyme-linked immunosorbent assay (ELISA) with universal potyvirus monoclonal antibodies (AGDIA) and by immunocapture reverse-transcriptase polymerase chain reaction (IC-RT-PCR) for the specific detection of Yam mosaic virus (YMV) (Bousalem et al., 2000a) and Yam mild mosaic virus (YMMV) (Bousalem et al., 2003). Fifteen percent of the samples were positive in the broad-spectrum ELISA used but negative in both the specific IC-RT-PCR tests used, suggesting one or more other potyviruses might be present in the ELISA-positive samples. The highest proportion was in D. rotundata (15/52; 29%), followed by D. trifida (5/38; 13%), and D. alata (2/52; 4%). In an attempt to characterize those potential yam potyviruses, total RNA was extracted from one D. trifida sample (TGwadE2) and universal potyvirus degenerate primers (Colinet et al., 1994) were used to amplify the core and C-terminal region of the coat protein (CP) and the 3′untranslated region (3′UTR) which are commonly used as markers of genetic relatedness of potyviruses. Sequence information generated (GenBank AY821494) from the cloned fragment was compared with sequences of other potyviruses by a BLAST search and by pairwise sequence comparison carried out on 209 potyviruses sequences aligned by the Clustal algorithm from the MegAlign software of DNASTAR package. The partial amino acid (aa) sequence available for the CP (152 aa) had the highest similarity with Zucchini yellow mosaic virus (66% identity) whereas the 3′UTR (126 nucleotides) had the highest similarity with Potato virus Y (35% identity). Sequence comparisons of the CP (aa) and 3′UTR with YMMV isolates (Bousalem et al., 2003), YMV isolates (Bousalem et al., 2000b) and Japanese yam mosaic virus isolate (JYMV, AB016500) showed the highest similarity at the amino acid level (62·5% identity) with the JYMV CP and highest similarity of the 3′UTR with the YMMV (32% identity). According to molecular taxonomy, TGawdE2 isolate should be regarded as a distinct member of the genus Potyvirus (family Potyviridae) and was tentatively named Dioscorea mosaic virus.

Field Studies on Cross‐protection against Japanese yam mosaic virus in Chinese yam (Dioscorea opposita) with an Attenuated Strain of the Virus

AbstractAn attenuated strain of Japanese yam mosaic virus (JYMV), designated T‐3, was evaluated for its cross‐protection efficacy against virulent (native) strains of JYMV in Chinese yam (Dioscorea opposita) grown in farmers’ fields in Japan. Native strains of JYMV were detected by a polymerase chain reaction‐based assay in all the Chinese yam plants grown from virus‐free tubers in the first growing season in the fields. In contrast, the virus was detected in only one of fifty plants grown from tubers preinoculated with T‐3 during the experiments for 6 years, suggesting that T‐3 consistently cross‐protected against native JYMV in Chinese yam in the field. Chinese yam plants preinoculated with T‐3 produced significantly greater yield of tubers per plant compared with non‐inoculated plants.

Effect of Seed Tuber Weights on the Development of Tubers and Flowering Spikes in Japanese Yams (Dioscorea japonica) Grown under Different Photoperiods and with Plant Growth Regulators

The effect of seed tuber (ST) weight on the development of main shoots, aerial tubers (bulbils, AT), new tubers (below ground, NT), and flowering spikes (inflorescences) was examined in Japanese yam plants (Dioscorea japonica) grown under different photoperiods and with plant growth regulators (PGRs). Within the same PGR and ST-weight group, the main shoot lengths of plants grown under a 24-h photoperiod (constant light, LD) were found to be longer than those grown under an 8-h photoperiod (SD) in all seasons. Furthermore, within the same photoperiod and ST-weight group, except for the plants grown from 25 g of ST (25gST plants) under SD conditions, the main shoot lengths of control and gibberellic acid (GA3)-treated plants were found to be longer than those of uniconazole-P (Uni)-treated plants. These tendencies were stronger in the 50gST plants than in the 25gST plants. In the 25gST plants, the final fresh weight (FW) of NT and the combined FW of AT and NT were greater in plants grown under LD conditions (LD plants) than those of SD plants; however, this was not observed in the case of the 50gST plants. This is because AT and NT development commenced earlier in the 25gST plants than in the 50gST plants. Furthermore, in the case of the 25gST-LD plants, the control plants also produced a few AT. Hence, we could confirm that the yield of NT was slightly increased by the inhibition of AT in the GA3-treated plants. The 25gST or 50gST-SD plants had only one peak of spike development from June through July, whereas the 25gST or 50gST-LD plants had two peaks of spike development, that is, in June and July and then again from September through October. In the season (June to July) of early spike development, the number of spikes per LD plant was greater than that in the SD plants, and the total number of spikes per plant was inhibited by GA3 treatment. These tendencies were stronger in the 50gST plants than in the 25gST plants.