Showing papers on "Isovitexin published in 1986"
TL;DR: Primary leaves of oats (Avena sativa L.) have been used to study the integration of secondary phenolic metabolism into organ differentiation and development and it is suggested that these latter enzymes participate mainly in the biosynthesis of non-flavonoid phenolic products, such as lignin in the xylem tissue and wall-bound hydroxycinnamic acid-esters in epidermal, phloem, and sclerenchyma tissues.
Abstract: Primary leaves of oats (Avena sativa L.) have been used to study the integration of secondary phenolic metabolism into organ differentiation and development. In particular, the tissue-specific distribution of products and enzymes involved in their biosynthesis has been investigated. C-Glucosylflavones along with minor amounts of hydroxycinnamic-acid esters constitute the soluble phenolic compounds in these leaves. In addition, considerable amounts of insoluble products such as lignin and wall-bound ferulic-acid esters are formed. The tissue-specific activities of seven enzymes were determined in different stages of leaf growth. The rate-limiting enzyme of flavonoid biosynthesis in this system, chalcone synthase, together with chalcone isomerase (EC 5.5.1.6) and the terminal enzymes of the vitexin and isovitexin branches of the pathway (a flavonoid O-methyltransferase and an isovitexin arabinosyltransferase) are located in the leaf mesophyll. Since the flavonoids accumulate predominantly (up to 70%) in both epidermal layers, an intercellular transport of products is postulated. In contrast to the flavonoid enzymes, L-phenylalanine ammonia-lyase (EC 4.3.1.5), 4-coumarate: CoA ligase (EC 6.2.1.12), and S-adenosyl-L-methionine: caffeate 3-O-methyltransferase (EC 2.1.1.-), all involved in general phenylpropanoid metabolism, showed highest activities in the basal leaf region as well as in the epidermis and the vascular bundles. We suggest that these latter enzymes participate mainly in the biosynthesis of non-flavonoid phenolic products, such as lignin in the xylem tissue and wall-bound hydroxycinnamic acid-esters in epidermal, phloem, and sclerenchyma tissues.
77 citations
TL;DR: It is shown that at least two different forms of gG exist and the distribution of the two alleles over chemical races of Silene pratensis in Europe is described; possible evolutionary relations between the various glycosyltransferases in Silene are discussed.
Abstract: The 7-O- and 2″-O-glycosylation of the flavone isovitexin (6-C-glucosylapigenin) in the petals of Silene plants is accomplished by allozymes which differ in their specificity toward the sugar to be transferred. The g locus controls the 7-O-glycosylation; allele gG controls the binding of glucose, and allele gX that of xylose. In the present paper it is shown that at least two different forms of gG exist. The enzyme activities encoded by these two different alleles differ with respect to the flavone acceptor to which glucose is transferred. Allele gGm encodes a 7-O-glucosyltransferase that transfers glucose to isovitexin but that is not able to glycosylate isovitexin 2″-O-rhamnoside. The 7-O-glucosyltransferase encoded by allele gGd preferentially transfers glucose to isovitexin 2″-O-rhamnoside and not to isovitexin. The allozymes encoded by gGm and gGd were partly purified. Linearity of incorporation, pH optimum, effect of divalent cations and EDTA, apparent molecular weight, substrate specificity, and Michaelis enzyme kinetic parameters were determined for both enzyme activities. The simultaneous presence within a plant of gene glR, which controls the biosynthesis of isovitexin 2″-O-rhamnoside, with either gGm or gGd leads to different glycosylation types. In gGm/glR plants two monoglycosides accumulate in the petals, isovitexin 7-O-glucoside and isovitexin 2″-O-rhamnoside, respectively, whereas in gGd/glR plants the corresponding diglycoside, isovitexin 7-O-glucose 2″-O-rhamnoside, is synthesized. The distribution of the two alleles over chemical races of Silene pratensis in Europe is described; possible evolutionary relations between the various glycosyltransferases in Silene are discussed.
7 citations
5 citations
TL;DR: It is shown that there are two different enzymes catalyzing the biosynthesis of isovitexin 7-O-galactoside, which differ with respect to heat inactivation, pH optimum, flavone acceptor specificity and Michaelis-Menten enzyme kinetic parameters.
Abstract: Abstract The expression of the allelic isovitexin 7-O-glycosylation genes gG (transfer of glucose) and gX (transfer of xylose) was studied in cotyledons, rosette leaves, stem leaves and petals of Silene plants. These studies revealed that gG is expressed in all ontogenetic stages, whereas its allele gX is only expressed in the petals. In the vegetative parts of gX individuals 7-O -xylosylation is replaced by 7-O-galactosylation. The possibility that gX encodes an enzyme activity that catalyzes different reactions in the petals and the vegetative parts resulting in the accumulation of the 7-O-xyloside and the 7-O-galactoside respectively, has been disproved. It is shown that there are two different enzymes catalyzing the biosynthesis of isovitexin 7-O-galactoside. These 7-O -galactosyl-transferase activities differ with respect to heat inactivation, pH optimum , flavone acceptor specificity and Michaelis-Menten enzyme kinetic parameters. The genes controlling these enzyme activities are regulated differentially, with gene O7g (described previously by Steyns et al. [11]), expressed in the cotyledons and the rosette leaves and Xgal in the stem leaves and petals.
3 citations
TL;DR: It is argued that the absence of 7-O-xylosylation in the leaves is not due to post-translational inactivation of the gX controlled enzyme, and the regulation of the expression of gene gX throughout ontogeny differs markedly from that of two allelic g locus variants, controlling the 7- O-glucosylations of isovitexin.
Abstract: The isovitexin-O-glycosylation patterns of rosette leaves, stem leaves and petals of Silene dioica plants were investigated. The 7-O -xylosylation of isovitexin, controlled by gene gX, only occurs in the petals. In the leaves isovitexin is 7-O -galactosylated, which is controlled by gene Xgal. Acyl groups may be linked to either the 7-O- or the 2″-O-substituted sugar; the former only occurs in the leaves, whereas the latter takes place both in leaves and petals. The restriction of the gX controlled enzyme activity and its product to the petals of Silene dioica plants is in complete agreement with previously obtained results (reference [2]) on the expression of g X in the genetic background of the closely related Silene pratensis, into which gX can be introduced by introgressive hybridization. On the basis of serological enzym e inhibition studies, it is argued that the absence of 7-O-xylosylation in the leaves is not due to post-translational inactivation of the gX controlled enzyme. The regulation of the expression of gene gX throughout ontogeny therefore differs markedly from that of two allelic g locus variants, controlling the 7-O-glucosylation of isovitexin.
1 citations