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.     

Understanding the germination of bulbils from an ecological perspective: a case study on Chinese yam (Dioscorea polystachya)

Background and Aims

Bulbils serve as a means of vegetative reproduction and of dispersal for many plants; this latter aspect making them analogous to seeds. However, germination of bulbils may differ considerably from seeds due to dissimilar anatomical structures and perhaps environmental cue perception. The few laboratory studies done on bulbils suggest that their germination is similar to that of seeds in the same habitats and to vegetative buds of winter-dormant plants. The present study is the first to examine how bulbil germination is controlled in nature in relation to dispersal (before vs. after winter of the same cohort) and to ambient temperatures.

Methods

Under laboratory conditions, temperature and light requirements for root and shoot emergences from bulbils of Dioscorea polystachya collected in September, 2005, February, 2006 (produced in 2005) and July, 2006 were determined. Effects of cold stratification and dry storage for releasing dormancy were tested on September and July bulbils. The phenology of dormancy release and of root and shoot emergences and the persistence of bulbils in soil were followed over time under field conditions.

Key Results

Although a low percentage of bulbils collected in July or in September produced roots, but no shoots, in the laboratory and field, these roots died within approx. 1 month. Regardless of collection date, cold stratification markedly increased root and shoot emergences. Bulbils sown outdoors in October produced roots and shoots the following March and April, respectively. The soil bulbil bank is short lived.

Conclusions

Bulbils of D. polystachya are similar to seeds of many temperate plants being mostly dormant when dispersed in summer or autumn and overcoming dormancy with cold stratification during winter. Adaptively, bulbil germination primarily occurs in spring at the beginning of a favourable period for survivorship and growth.     

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.     

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.     

Bacterial leaf symbiosis in Dioscorea sansibarensis: morphology and ultrastructure of the acuminate leaf glands*

Abstract The symbiosis between a bacterium and the West African rain forest yam Dioscorea sansibarensis is described for the first time at the ultrastructural level. The bacteria are harboured in glands which run the entire length of the pronounced ‘drip-tip’ leaf acumenae of the host plant. Each acumen, which may be up to 12 cm long in very large mature leaves, contains from two to six bacterial glands. The glands are kidney-shaped in cross section and contain numerous multicellular simple trichomes which arise from the epidermis of the gland floor and project into the lumen of the gland. The bacteria are Gram-negative and variously rod, ovoid, and coccoid in shape. The bacterial cells contain mesosomes, polyhydroxybutyrate granules and large electron-dense bodies. Bacteria-free plants grow more slowly and produce one yellowish-green leaf per node in contrast to the vigorous growth habit of infected plants, with two deep green leaves per node. Infected plants exposed to a variety of atmospheres containing acetylene, both in the light and in the dark, failed to reduce acetylene to ethylene, indicating that nitrogen fixation is not a function of this symbiosis.     

Antifungal phenanthrenes in yam tubers

An extract from the peel of yams (Dioscorea rotundata) showed anti-fungal activity towards both Cladosporium cladoporioides and a variety of ya     

Hormonal effects on diosgenin biosynthesis and growth in Dioscorea deltoidea tissue cultures

Analysis of Dioscorea deltoidea tissue cultures grown in the presence of 2,4-D, indole-3-butyric acid, isopentenyladenine, benzyladenine and GA singly and in combination showed that the medium with 2,4-D most consistently favored diosgenin production. GA and high benzyladenine concentrations were toxic.     

Cyclic AMP phosphodiesterase from dormant tubers of Jerusalem artichoke

An enzyme, which hydrolyzes 3′,5′-cyclic AMP to 3′-AMP and 5′-AMP, has been isolated from dormant tubers of Jerusalem artichoke and purified 850 × with a recovery of 15% of total activity. The partially purified enzyme differs greatly from both animal and bacterial phosphodiesterases in terms of pH optimum, substrate specificity, cation dependence and sensitivity to methylxanthines. The plant hormones are without effect, whereas ATP, 5′-AMP, 3′-AMP, inorganic phosphate and pyrophophosphate are inhibitors. The enzyme seems to be greatly inhibited in vivo by inorganic phosphate during dormancy.     

Chemodifferentiation of diosgenin in Dioscorea composita

Diosgenin was isolated from different parts of a three-year-old plant of Dioscorea composite. The amounts (% on a dry wt basis) present were: tubers, 3.6; vine internodes and nodes with their leaves from first 20 nodes from the tubers, 1.6; similarly from intermediate 20 nodes, 0.039 and from upper 20 nodes, 0.03. The amounts (% on a dry wt basis) from tissue culture of nodal explants were: 30-day-old callus, 0.89; 90-day-old callus, 1.61; emergent shoots, 2.5; regenerated roots, 0.08.     

Sterol biosynthesis by a cell free extract of Dioscorea floribunda

The biosynthesis of sterols from mevalonate by a cell free extract prepared from actively growing tuber portions and leader shoots with young leaves of Dioscorea floribunda has been demonstrated. The preparation was capable of synthesizing 86.4 μg and 34.0 1£g of sterols from leader shoots with young leaves and actively growing tuber portions respectively. The cofactor requirement for the above system was also studied.     

Gibberellic acid-induced prolongation of the dormancy in tubers or rhizomes of several species of East Asian Dioscorea

Effects of the application of gibberellic acid on sprouting of tubers or rhizomes were tested in seven species of the genus Dioscorea that are native to the temperate regions of East Asia. The lowest concentrations for significant inhibition of sprouting in these species varied from 0.1–1 µM Application of gibberellic acid at 100 µM inhibited sprouting for more than 500 days at 20 °C. Some responses to the application of gibberellic acid differed between species and between sections of the genus. In D. japonica, the application of gibberellic acid inhibited sprouting of tubers and bulbils while it promoted seed germination.     

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.     

Inhibition of photosynthesis and respiration by batatasins

Effects of batatasins I, III and V, phenolic growth inhibitors occuring in dormant bulbils of Dioscorea batatas Decne., on photosynthetic reactions of chloroplasts from spinach (Spinacia oleracea L.) and on respiration of mitochondria from potatoes (Solanum tuberosum L.) were investigated. In chloroplasts, the batatasins effectively inhibited CO₂-dependent oxygen evolution and electron flow from water to acceptors such as dichlorophenolindophenol, ferricyanide and methylviologen. Photosystem-I dependent electron transport from ascorbate to oxygen was stimulated. The proton conductivity of thylakoid membranes was increased and phosphorylation was uncoupled from electron transport. Inhibition of electron transport with water as electron donor appeared to precede uncoupling. In mitochondrial, batatasin I did not much inhibit succinate-dependent O₂ uptake in the absence of ADP, but caused strong inhibition in the presence of ADP. Batatasins III and V inhibited oxygen uptake irrespective of the presence or absence of ADP. Inhibition of chloroplast and mitochondrial reactions by batatasins was shown to be reversible.Abbrevations B-I batatasin I, 6-hydroxy-2,4,7-trimethoxyphenanthrene - B-III batatasin III, 3,3-dihydroxy-5-methoxybibenzyl - B-V batatasin V, 2-hydroxy-3,4,5-trimethoxybibenzyl - Chl chlorophyll - MV methylviologen - DCPIP 2,6-dichlorophenol-indophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PVP polyvinylpyrrolidone     

Induction of in vitro tubers in a broad range of potato genotypes

This paper describes a reproducible method for the induction of in vitro potato tubers in a wide range of genotypes. These in vitro tubers could be induced in all genotypes tested and show striking similarity to field produced tubers. In vitro tubers may prove most useful as material for International germplasm distribution.     

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.     

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.     

The occurrence of acylated flavonol glycosides in the cruciferae

Nine acylated glycosides of kaempferol or quercetin were identified in Sisymbrium gilliesii, and in three Crambe spp. They were usually present together with the related unacylated glycosides. Acylation is a very common characteristic of the four crucifer species studied.