Hajime Mizukami

Pigment formation in callus cultures of Lithospermum erythrorhizon

Abstract Undifferentiated callus tissues of Lithospermum erythrorhizon are capable of synthesizing shikonin derivatives, which are normally formed in the cork cells of the roots. Their biosynthesis in cultured cells is controlled by auxin and light. The pigment content increased linearly with time after a lag phase when callus tissues were grown on culture medium containing IAA in the dark, whereas it markedly decreased when 2,4-D was substituted for IAA or when cultures were irradiated with blue light.

Effect of nutritional factors on shikonin derivative formation in Lithospermum callus cultures

Abstract Some nutritional factors affecting the biosynthesis of shikonin derivatives in callus cultures of Lithospermum erythrorhizon were examined. High sucrose concentrations increased the content of shikonin derivatives, but neither glucose nor fructose was effective for shikonin derivative formation. High concentrations of nitrogen sources inhibited or retarded shikonin derivative formation and streptomycin sulphate stimulated their biosynthesis. Addition of ascorbic acid increased the content of shikonin derivatives. Among some precursors tested only l -phenylalanine had a positive effect. At high concentrations, Ca 2+ and Fe 2+ inhibited the biosynthesis of shikonin derivatives.

Variation in pigment production in Lithospermum erythrorhizon callus cultures

Abstract Different strains of callus cultures of Lithospermum erythrorhizon showed wide variations in the production of shikonin derivatives. From these cultures, two high pigment-producing strains, whose content of shikonin derivatives are stable and similar to that of intact plant root, have been established by repeated selection.

Formation of stereoisomeric mixtures of naphthoquinone derivatives in Echium lycopsis callus cultures

Abstract Callus cultures of Echium lycopsis were shown to produce a large amount of a mixture of red pigments consisting of five esterified derivatives of 5,8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentenyl)-1,4-naphthoquinone. Examination of the absolute configuration of these compounds revealed that the cultures produced both the R -form (shikonin) and the S -form (alkannin) in various ratios depending upon the esterified derivative, although the overall ratio for the total derivatives was ca 1:1. On the other hand, all the corresponding derivatives produced by Lithospermum cultures were primarily of the R -form. It was also demonstrated that pigment formation in Echium cultures was inhibited by either white or blue light as well as by the synthetic auxin 2,4-D as in the case of Lithospermum cultures.

Sugar Chain Construction of Functional Natural Products Using Plant Glucosyltransferases

Plant secondary product glycosyltransferases belong to family 1 of the glycosyltransferase superfamily and mediate the transfer of a glycosyl residue from activated nucleotide sugars to lipophilic small molecules, thus affecting the solubility, stability and pharmacological activities of the sugar-accepting compounds. The biotechnological application of plant glycosyltransferases in glycoside synthesis has attracted attention because enzymatic glycosylation offers several advantages over chemical methods, including (1) avoiding the use of harsh conditions and toxic catalysts, (2) providing strict control of regio-and stereo-selectivity and (3) high efficiency. This review describes the in vivo and in vitro glycosylation of natural organic compounds using glycosyltransferases, focusing on our investigation of enzymatic synthesis of curcumin glycosides. Our current efforts toward functional characterization of some glycosyltransferases involved in the biosynthesis of iridoids and crocin, as well as in the sugar chain elongation of quercetin glucosides, are described. Finally, I describe the relationship of the structure of sugar chains and the intestinal absorption which was investigated using chemoenzymatically synthesized quercetin glycosides.