Flavonoid Function and Activity to Plants and Other Organisms
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Biological Sciences in Space, Vol.17 No.1 (2003):Flavonoid 24-44 function and activity © 2003 Jpn. Soc. Biol. Sci. Space Flavonoid Function and Activity to Plants and Other Organisms Tsukasa Iwashina Tsukuba Botanical Garden, National Science Museum, 4-1-1 Amakubo, Tsukuba-shi, Ibaraki, 305-0005, Japan Abstract Flavonoid compounds distribute widely in vascular plants and Bryophytes, and ca. 5,000 kinds have been reported as naturally occurring substances. Many biological activities of the flavonoids were found until now. They include pollinator attractants, oviposition stimulants, feeding attractants and deterrents, allelopathy and phytoalexins. This paper reviews function and activity of flavonoids against plants and other organisms. Key words: flavonoids, pollinator attractants, feeding attractants and deterrents, allelopathy, phytoalexins Introduction di-P-coumaroylglucoside) and quercetin 3-O-(3´´,6´´-di- Pinus sylvestris Flavonoid is the general name of compounds that have P-coumaroylglucoside) in (Pinaceae) (Jungblut et al., 1995), quercetin 3-O-galactoside, myricetin a fifteen-carbon skeleton, which consists of two phenyl O O rings (A- and B-rings) connected by a three-carbon bridge 3- -rutinoside and two P-coumaroyl kaempferol 3- - Quercus ilex et al., (C-ring). In general, vascular plants and Bryophytes alone glucoside in (Fagaceae) (Skaltsa 1994), and glycosides of quercetin, apigenin and luteolin in Olea possess the biosynthetic ability of the flavonoids, except europea et al green algae, Nitella hookeri (Characeae) (Markham & (Oleaceae) (Karabourniotis ., 1992) act as UV- Porter, 1969), fungi, Aspergillus candidus and Phallus absorbing substances. More recently, it was proved that the major UV shield in the translucent bracts and leaves of impudicus (Marchelli & Vining, 1973; Bohm, 1975), and Rheum nobile marine coral, Echinophora lamellosa (Sanduja et al., 1984). the Himalayan alpine plant, (Polygonaceae), O The flavonoids are divided into several classes, i.e., are five quercetin glycosides, quercetin 3- -glucoside, 3- O-galactoside, 3-O-rutinoside, 3-O-arabinopyranoside and anthocyanins, flavones, flavonols, flavanones, dihydro- O et al flavonols, chalcones, aurones, flavan and proantho- new acylated 3- -glucoside (Iwashina ., unpublished cyanidins, isoflavonoids etc. (Iwashina, 2000). Moreover, data). The occurrence of anthocyanins as pollinator attractants numerous sorts of flavonoid occur in plants with additional hydroxyl, methoxyl, methyl and/or glycosyl substitution is well-known as a function of the flavonoids in plants. Additionally, it is known that flavones and flavonols, which patterns. Additionally, aromatic and aliphatic acids, sulfate, prenyl or methylenedioxyl groups also attach to flavonoid can hardly see by human eyes, also act as pollinator nucleus and their glycosides. Thus, ca. 5,000 kinds of attractants in addition to visible anthocyanins. Recently, other functions, oviposition stimulants, feeding attractants, flavonoids have been reported as naturally occurring compounds (Harborne & Baxter, 1999). The isolation and feeding deterrents, allelopathy and phytoalexins of naturally identification, structures, distribution and biosynthesis of occurring flavonoids, were found by many authors. In this paper, the flavonoid function and activity to the flavonoids in plants were reviewed by many authors (e.g., Geissman, 1962; Markham, 1982; Stafford, 1990; plants and other organisms are reviewed. Mabry et al., 1970; Harborne et al., 1975; Harborne & Mabry, 1982; Harborne, 1988, 1994; Iwashina, 2000). The Pollinator attractants flavonoids as medicinal resources were also reviewed (e.g., Majority of the entomophilous flowers in plants Cody et al., 1986, 1988). Especially, the pigments, kingdom were colored by various pigments. For example, anthocyanins were recently noticed as antioxidant, carotenoids are found as major pigments in many yellow antitumol, astoringents etc. (Ohba et al., 2000). However, flowers, such as Helianthus annuus, Taraxacum officinale the secondary metabolites involving the flavonoids were (Compositae) and Potentilla spp. (Rosaceae). On the other considered to be waste products of plant metabolism in the hand, anthochlor pigments are reported from Cosmos, early days of 20th century. One of the most important Anthirrhinum, Dahlia and Dianthus species and so on. function of flavonoids may be to serve as ultraviolet filter Betaxanthin pigments occur in yellow flowers of the order in land plants. It was shown by survey of some plants that Caryophyllales except Caryophyllaceae and the flavonoids act as UV shield. Indeed, it was shown that Molluginaceae. Almost orange, red, purple and blue two acylated flavonol glycosides, kaempferol 3-O-(3´´,6´´- flowers, e.g., Rosa, Tulipa, Commerina, Delphinium, Viola etc. are due to the anthocyanin pigments, except those of Received: May 29, 2003 the order Caryophyllales including betalain pigments. The Address for correspondence: Tsukasa Iwashina so-called “black flowers” such as Fritillaria Tsukuba Botanical Garden, National Science Museum, camtschatcensis (Liliaceae) are also due to the 4-1-1 Amakubo, Tsukuba-shi, Ibaraki, 305-0005, Japan anthocyanins. These visible pigments act as pollinator E-mail: [email protected] attractants. In addition, it was proved that flavones and － 24 － Iwashina, T. flavonols are also the pollinator attractants (Table 1). (Harborne & Smith, 1978). Though a major pigment of Flavones and flavonols have two absorbing bands in UV Crocosmia × crocosmiiflora orange-yellow flowers range (250-280 and 310-380 nm), but not in visible range. (Iridaceae) is a water-soluble carotenoid, crocin (Ootani However, since some insects, especially bee, can & Hayashi, 1982), kaempferol 3-O-rhamnosylglucoside discriminate UV light (UV-A), flavones and flavonols also and quercetin 3-O-glucoside are accompanied (Ootani et act as attractants. Indeed, flavone and flavonol glycosides al., 1986). are detected from flowers of many plants, with visible Flower color of Strongylodon macrobotrys (Legumi- pigments, anthocyanins, carotenoids and/or anthochlors, nosae) is bluish-green, in other words, jade color, and a and sometimes betalains. An acylated flavone, apigenin major visible pigment is anthocyanin, malvidin 3,5-di-O- 7-O-glucuronide-4´-O-(6´´-malonylglucoside) was isolated glucoside accompanied with C-glycosylflavones, isovitexin from the deep purple flowers of Centaurea cyanus 7-O-glucoside and isovitexin (Iwashina et al., 1984b). (Compositae), with an acylated anthocyanin, cyanidin 3- The visible pigments in the flowers of cactaceous O-(6´´-succinylglucoside)-5-O-glucoside (Kondo et al., species are exclusively red purple betacyanins and yellow 1994). In this case, the flavone also acts as a copigment betaxanthins, and never synthesize the anthocyanins substance. On the other hand, isoflavonoids, flavanones, (Iwashina et al., 1985). However, other flavonoids occur dihydroflavonols, and flavan and proanthocyanidins do not in “betalain plant families”. Thus, quercetin 3-methyl ether seem to act as pollinator attractants, since absorption 7-O-glucoside and 4´-O-glucoside are present in the red maxima of those flavonoids are in 250-290 nm range alone, purple flowers of cactaceous plants, Neoporteria clavata which insects can not discriminate these UV range. and related species together with betacyanins (Iwashina et In case of Iris tectorum (Iridaceae), though iso- al., 1986). In another cactus, Astrophytum myriostigma, flavonoids, such as tectorigenin and its 7-O-glucoside, the yellow flowers are due to flavonol aglycone, quercetin irigenin 7-O-glucoside and iristectorigenins are abundantly itself, which is contained in cells as the crystal form, without contained in rhizomes, they were not detected from the betalain pigments (Iwashina et al., 1988). flowers (Iwashina & Ootani, 1998). Insteadly, the Similar situation was investigated in the genus Aloe anthocyanins, delphinidin 3-O-(P-coumaroylrutinoside)-5- (Liliaceae) and related genera. Aloe species can not O-glucoside and 3-O-rutinoside-5-O-glucoside (Ishikura, apparently synthesize the anthocyanins (Iwashina, 1980) and a C-glycosylflavone, embigenin 2´´-O- unpublished data). Their yellow and yellow orange flowers rhamnoside (Hirose et al., 1962) are present in the flowers are due to anthraquinone pigments such as barbaloin and as pollinator attractants. aloe-emodin (Iwashina et al., 1986). C-Glycosylflavones, Two rare flavonol allosides, kaempferol 3-O-alloside e.g., orientin (Fig. 1-1) and isoorientin (Fig. 1-2) coexist and rhamnocitrin 3-O-alloside, are found from the reddish with the anthraquinones, and may be function as pollinator purple flowers of Glaucidium palmatum (Glaucidiaceae), attractants (Iwashina et al., 1986). endemic to Japan (Iwashina & Ootani, 1990). Flavones and flavonols are present not only in yellow, In the flowers of Iris species, C-glycosylflavones and red, purple and blue flowers but also in almost wild white their O-glycosides, isovitexin (Fig. 1-12), vitexin (Fig. 1- ones. Thus, the insects, especially bee, can visit to white 13), swertisin (Fig. 1-14) and isovitexin 2´´-O-rhamnoside flowers. and 2´´-O-xyloside are present as pollinator attractants, with anthocyanins, malvidin and petunidin 3-O-(P- Oviposition stimulants coumaroylrutinoside)-5-O-glucosides (Hayashi et al., 1978, One of the most complex aspects of plant-insect et al 1980, 1989; Iwashina ., 1996; Iwashina & Ootani, interactions involves the oviposition response of insects to C 1996; Yabuya,