Properties of polyphenol oxidase from tubers of the yam Dioscorea bulbifera

The subunit MW of Dioscorea bulbifera polyphenol oxidase (MW 115 000 ± 2000) determined by SDS-PAGE is ca. 31 000 indicating that the enzyme is an oligomeric protein with four subunits. K_i values of various inhibitors and their modes of inhibition have been determined with catechol and pyrogallol as substrates. p-Nitrophenol, p-cresol, quinoline and resorcinol are competitive inhibitors of catechol binding while only orcinol and p-nitrophenol behave in the same way towards pyrogallol as substrate. From the effect of pH on V_max, groups with pK values ca. 4.7 and 6.8 have been identified to be involved in catalytic activity. The Arrhenius activation energy (E_a) at pH 4.0 is 8.9 kcal/mol between 40–65°. At pH 7.0, the value is 22.1 kcal/mol between 40 and 60°. The enthalpies (ΔH) at pH 4.0 and pH 7.0 are 2.3 kcal/mol and 32.4 kcal/mol respectively. The results are discussed considering the conformational changes of the enzyme during substrate binding.     

Purification and some properties of polyphenol oxidase from the yam tubers, Dioscorea bulbifera

In a comparison of the polyphenol oxidase activity of various species of yam tubers the greatest enzyme activity was found in D. bulbifera. The enzyme was purified from acetone powder extracts of this plant. Ammonium sulphate fractionation, followed by ion exchange chromatography and gel filtration gave 22-fold purification. The final product gave a single band on polyacrylamide disc gel electrophoresis. The purified enzyme showed activity towards catechol, pyrogallol and dl-β-3,4-dihydroxyphenylalanine (dl-DOPA) and had a MW 115000 ± 2000. It was characterized by response to various inhibitors. β-Mercaptoethanol, dithioerythritol, l-cysteine, sodium metabisulphite and KCN inhibited strongly.     

Effect of storage under nitrogen on ethanol,lactate, malate and their dehydrogenases in yam tubers

Under anaerobiosis in white yam tubers, lactate and malate increase and decrease in opposing directions for the first 4 days. Ethanol appears in yams after 7 days under nitrogen, coinciding with the simultaneous rise of both lactate and malate. However ethanol does not occur in white yam tubers on storage in air.     

Spirostanic diosgenin precursors from Dioscorea composita tubers

The main saponin from the fresh tuber of Dioscorea composita was dioscin and from the fermented material 3-O-[α-l-rhamnopyranosyl(1→4)-β-d-glucopyranosyl]diosgenin. The ¹³C NMR chemical shifts of saponins were used in the determination of their structure. No free sapogenin was isolated from the fresh tuber.     

Natural phenanthrenes and their biological activity

The aim of this review is to survey the various naturally occurring phenanthrene compounds that have been isolated from different plants. Only one review has previously been published on this topic. Gorham (1989) reviewed the structures, biosynthesis, separations and spectroscopy of stilbenes and phenanthrenes. The present study furnishes an overview of the hydroxy or/and methoxy-substituted 9,10-dihydro/phenanthrenes, methylated, prenylated and other monomeric derivatives, dimeric and trimeric phenanthrenes and their biological activities. A fairly large number of phenanthrenes have been reported from higher plants, mainly in the Orchidaceae family, in the species Dendrobium, Bulbophyllum, Eria, Maxillaria, Bletilla, Coelogyna, Cymbidium, Ephemerantha and Epidendrum. A few phenanthrenes have been found in the Hepaticae class and Dioscoreaceae, Combretaceae and Betulaceae families. Their distribution correlates strongly with the taxonomic divisions. These plants have often been used in traditional medicine, and phenanthrenes have therefore been studied for their cytotoxicity, antimicrobial, spasmolytic, anti-inflammatory, antiplatelet aggregation, antiallergic activities and phytotoxicity. On the basis of 120 references, this review covers the phytochemistry and pharmacology of phenanthrenes, describing 252 compounds. This contribution stems from our work on the medicinal plant Tamus communis.     

Transformation associated with catecholase in Dioscorea alata during storage

The Michaelis constant of catecholase in 3 cultivars of Dioscorea alata was determined. Oxidative browning was related to the activity of the enzyme in the yams. Inhibition by cysteine was competitive, while 2-mercaptoethanol caused an uncompetitive type of inhibition. On DEAE column chromatography a minor peak preceded the major peak in the fresh yam while a minor peak was eluted after the major peak in the stored yam.     

Structure and synthesis of the growth inhibitor batatasin I from Dioscorea batatas

The synthesis of 6-hydroxy-2,4,7-trimethoxyphenanthrene is described and its identity with the growth inhibitor, batatasin I, is confirmed.     

Effects of orchinol and related phenanthrenes on the enzymic degradation of indole-3-acetic acid

Orchinol, hircinol, loroglossol and certain related phenanthrenes inhibited horseradish peroxidase-catalysed IAA degradation to a varied degree. Among     

The occurrence of batatasins in the dioscoreaceae

The tubers and/or aerial bulbils of 13 species of Dioscorea, mostly of tropical origin, and one species each of Rajania and Tamus, were examined for the presence of batatasins. These phenolics have previously been reported in the temperate species D. opposite. One or more batatasins were found in either tubers or bulbils of most species examined, including taxa from both Old and New Worlds, and with annual or perennial tubers. Batatasin I was the most widespread in occurrence, followed by B-II, while B-III, B-IV and B-V were comparatively rare. Only the buibils of D. opposite contained all five batatasins.     

Changes in enzyme activity of white yam tubers after prolonged storage

There is a substantial increase in the activities of phosphorylase, hexokinase, glucose-6-phosphate dehydrogenase and alcohol dehydrogenase in white yam tubers as they age. The high glucose-6-phosphate dehydrogenase activities suggest that the pentose phosphate pathway is important in yam tuber tissue.     

Isolation of high quality RNA from seeds and tubers of the Mexican yam bean (Pachyrhizus erosus)

Pachyrhizus erosus is a tuberous legume native to Central America that has great potential for development as a food crop. It produces both protein rich grain and starch filled tubers. There are two major limitations to its dietary use, the high levels of rotenone found in the grains and the low starch content of the tubers, both of which must be addressed, for development of the crop. The low variability of the existing gene pool of the genus limits the use of conventional plant breeding to address these problems. Genetic engineering technology is, therefore, being adopted. For this purpose, an efficient means of RNA isolation from yam bean tissues was developed. The quality of RNA obtained by this method was tested byin vitro translation and was sufficient for use in RT-PCR.     

Structures and synthesis of the growth inhibitors batatasins IV and V,and their physiological activities

Two new compounds, batatasins IV and V were isolated from dormant bulbils of Chinese yam (Dioscorea batatas) and shown to be 2′,3-dihydroxy-5-methoxybibenzyl and 2′-hydroxy-3,4,5-trimethoxybibenzyl, respectively. An analogue, 3,4′-dihydroxy-5-methoxybibenzyl was synthesized. Inhibitory activities of these three compounds as well as batatasin I (6-hydroxy-2,4,7-trimethoxyphenanthrene) and batatasin III (3,3′-dihydroxy-5-methoxy-bibenzyl) in lettuce seed germination, lettuce hypocotyl elongation and wheat coleoptile section elongation tests are described.     

间作豆科作物对山药田土壤化学和生物学性质的影响

采用田间小区试验方法,探讨了山药与苜蓿和三叶草两种豆科绿肥作物间作对土壤化学性质和生物学性质以及土壤综合肥力的影响.结果表明: 与山药单作相比,间作苜蓿和三叶草提高了0～20 cm和20～40 cm土层硝态氮、速效磷和速效钾含量,降低了山药根茎膨大初期和膨大盛期土壤pH和电导率.间作有助于提高山药整个生育期0～20 cm和20～40 cm土层土壤脲酶、碱性磷酸酶和过氧化氢酶活性以及土壤呼吸,但对蔗糖酶和脱氢酶活性影响不明显.采用隶属函数模型和主成分分析相结合的方法对间作山药收获期的土壤肥力进行综合分析,结果表明,间作两种豆科作物均具有显著提高山药田0～20 cm和20～40 cm土层土壤综合肥力的效果.通过间作豆科绿肥作物增加山药田的生物多样性是培肥山药田土壤、改善山药田土壤生态环境、缓解连作障碍的有效途径.     

Structure and synthesis of batatasins,dormancy-inducing substances of yam bulbils

Batatasin, which occurs in dormant bulbils of yams (Dioscorea batatas Decne.) and induces dormancy in this organ has been shown by spectrometric analysis and synthesis to be 3,3′-dihydroxy-5-methoxy-bibenzyl.     

In vitro micro-tuber initiation and dormancy in yam

Dormancy is a mechanism that regulates the timing of sprouting (germination) of affected plant parts as well as ensures that the food quality of edible parts is maintained in storage until the following growing season. In yam, however, little is known about the control of tuber initiation or tuber dormancy. The objective of this study was to determine the effects of selected plant growth regulators (PGRs) on tuber initiation and dormancy, using an in vitro system. In two replicated experiments, 2-chloroethylphosphonic acid (ethephon, an ethylene source), abscisic acid (ABA) and gibberellin (GA₃) – and their inhibitors silver nitrate, fluridone and 2-chloroethyl-trimethylammonium chloride, respectively – were added at two concentrations to the culture medium prior to explant culture. Dates of micro-tuber initiation and sprouting (end of dormancy) and tuber number were recorded. In the control (no PGR) in Experiment 1, micro-tubers were initiated at the base of the stem after 176 days and sprouted 235 days later, that is 411 days after culturing. Most PGR treatments had only small effects (±30 days) on the duration of dormancy and the time of micro-tuber initiation. However, in GA₃ micro-tuber initiation occurred after 76 days, about 100 days earlier than in the control, whereas fluridone affected the position of micro-tubers and duration of dormancy. With fluridone treatments, tubers were found at the base of the stem (normal position) and on lower and upper nodes. Lower node tubers sprouted within 225 days of culturing compared with about 420 days after culturing at other nodal positions and in other PGR treatments. These data suggest an important role for ABA and gibberellic acid in yam micro-tuber initiation and the induction of dormancy.     

Diosbulbin d and 8-epidiosbulbin e acetate,norclerodane diterpenoids from dioscorea bulbifera tubers

From tubers of Dioscorea buibifera L. var sativa a new 18-norclerodane diterpenoid, 8-epidiosbulbin E acetate, has been isolated, besides the previously known norditerpenoid, diosbulbin D, and its structure established by spectroscopic means.     

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

An 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.     

Phenolics of five yam (dioscorea) species

Cyanidin-3-glucoside, (+)-catechin and the procyanidin dimers ‘B-1’ and ‘B-3’ were identified as phenolic constituents of Dioscorea alata tubers, and strong evidence for the presence of a procyanidin trimer and a tetramer was found. The quantity of (+)-catechin and relative proportions of the procyanidin dimers were determined in 10 cultivars of five of the main edible yam species.