Catharanthus roseus cell suspension cultures converted exogenously supplied curcumin to a series of glucosides, none of which has been found in nature so far. The e⁄ciency of glucosylation was dependent on culture stage of the cells and medium sucrose concentration. Methyl jasmonate and salicylic acid enhanced the glucoside formation only when they were added to the cultures prior to the addition of curcumin. The glucoside yield was 2.5 W Wmol/g fresh weight of the cells at an optimal culture condition. The water solubility of curcumin-4P P,4Q Q-O-L L-D-digentiobioside was 0.65 mmol/ml, which was 20 million-fold higher than that of curcumin. ß

Major barriers to delivery of biomolecules are crossing the cellular membranes and achieving a high cytoplasmic concentration by circumventing entrapment into endosomes and other lytic organelles. Motivated by such aim, we have investigated the capability of multiwalled carbon nanotubes (MWCNTs) to penetrate the cell membrane of plant protoplasts (plant cells made devoid of their cell walls via enzymatic treatment) and studied their internalization mechanism via confocal imaging and TEM techniques. Our results indentified an endosome-escaping uptake mode of MWCNTs by plant protoplasts. Moreover, short MWCNTs (<100 nm) were observed to target specific cellular substructures including the nucleus, plastids, and vacuoles. These findings are expected to have a significant impact on plant cell biology and transformation technologies.

Quercetin (3,3Ј,4Ј,5,7-pentahydroxyflavone) is a widely distributed secondary metabolite in plants. Human beings regularly consume quercetin in various fruits, vegetables or herbal medicines; such as apple, onion, and sophora flower. Quercetin has been found to have various biological activities including antiproliferative effects on several cancer cells, [1][2][3] anti-inflammatory and anti-allergic effects, 4) anti-oxidative activity, 5) and atherosclerosis-preventing effect. 6) In clinical study, supplementation of quercetin in hypertensive patients for 28 d significantly reduced blood pressure. 7) However, orally administered quercetin is poorly absorbed, and the bioavailability of quercetin administered in capsule form to human beings was reported to be less than 1%. 8) Therefore, several trials have been conducted to increase the bioavailability of quercetin by optimizing its formulation. For example, a pharmacokinetic study in rats revealed that bioavailability of quercetin was increased 5.7-fold by administration using a solid lipid nanoparticle as an oral delivery carrier compared with that administered as a quercetin suspension. 9)Quercetin is generally accumulated in plants as glycosides such as glucosides, rutinosides and xylosides. These quercetin glycosides show higher solubility in water than quercetin due to the hydrophilicity of the sugar moieties. Indeed, quercetin-4Ј-O-b-D-glucopyranoside has higher bioavailability than its aglycone in human beings, suggesting that conjugation with glucose would enhance quercetin absorption in the small intestine. 10,11) Glucosyl conjugation of lipophilic small molecules leads to an increase in their water solubility.12) Several glucosides of quercetin have been prepared by enzymatic synthesis to enhance the water solubility, as exemplified by a-monoglucosyl rutin (aMR), 13) a-oligoglucosyl rutin (aOR), 14) and "enzymatically modified isoquercitrin" (EMIQ).15) In Japan, EMIQ has been approved as a food additive, 16) and in U.S.A., FDA declared EMIQ generally regarded as safe (GRAS) for use in multiple food categories. However, how glucosyl conjugation affects the pharmacokinetic behavior of quercetin remains unknown except that aMR exhibited 4.5-fold higher area under the plasma concentration-time curve (AUC ) value than quercetin after oral administration as a suspension in carboxymethylcellulose (CMC) solution in rats. 13) In the present investigation, we examined the intestinal absorption and bioavailability of quercetin after oral administration of various quercetin glucosides, and revealed that glucosyl conjugation of isoquercitrin (IQC) with a-glucosidic linkages is quite effective for improving the bioavailability. We also showed that hydrolysis of the glycosidic linkage prior to the absorption through small intestinal epithelium is essential. We further suggest that the collaborative action of two glucosidases, mucosal maltose-glucoamylase (MGAM) and lactase-phlorozin hydrolase (LPH), both anchoring in the mucosal membrane of the epithelial tissue, pla...

Iridoids form a broad and versatile class of biologically active molecules found in thousands of plant species. In addition to the many hundreds of iridoids occurring in plants, some iridoids, such as secologanin, serve as key building blocks in the biosynthesis of thousands of monoterpene indole alkaloids (MIAs) and many quinoline alkaloids. This study describes the molecular cloning and functional characterization of three iridoid glucosyltransfeases (UDP-SUGAR GLYCOSYLTRANSFERASE6 [UGT6], UGT7, and UGT8) from Madagascar periwinkle (Catharanthus roseus) with remarkably different catalytic efficiencies. Biochemical analyses reveal that UGT8 possessed a high catalytic efficiency toward its exclusive iridoid substrate, 7-deoxyloganetic acid, making it better suited for the biosynthesis of iridoids in periwinkle than the other two iridoid glucosyltransfeases. The role of UGT8 in the fourth to last step in secologanin biosynthesis was confirmed by virus-induced gene silencing in periwinkle plants, which reduced expression of this gene and resulted in a large decline in secologanin and MIA accumulation within silenced plants. Localization studies of UGT8 using a carborundum abrasion method for RNA extraction show that its expression occurs preferentially within periwinkle leaves rather than in epidermal cells, and in situ hybridization studies confirm that UGT8 is preferentially expressed in internal phloem associated parenchyma cells of periwinkle species.