VARIATION AND LOCALIZATION OF FLAVONOID AGLYCONES IN HELIANTHUS ANNUUS (COMPOSITAE)

Flavonoid aglycone variation within Helianthus annuus, a species widely distributed throughout North America, was analyzed. Flavonoid aglycones of H. annuus consist of two types, flavones and chalcones. The flavone aglycones are sequestered in glandular trichomes that occur on both leaf surfaces, whereas the chalcone aglycones appear to be incorporated in the waxy leaf cuticle. Considerable variation in flavonoid profile was observed with some plants exhibiting as few as one, and others as many as seven of the eight aglycones detected. No definable phytogeographic patterns were observed for this flavonoid variation. Flavonoid aglycone variation also did not differentiate the infraspecific taxa within H. annuus. DURING THE PAST three decades, numerous studies have utilized interspecific flavonoid variation to assess phylogenetic relationships among species. In contrast, comparatively little effort has been made to document the extent of flavonoid variation within species or populations or to examine evolutionary problems existing at the intraspecific or population level (Harborne and Turner, 1984). Even fewer studies have determined the localization of the observed flavonoids in cells and tissues. Given the magnitude of adaptive functions ascribed to flavonoids (Thompson et al., 1972; McClure, 1975; Flint and Caldwell, 1983), flavonoid localization and infraspecific patterns of flavonoid variation may provide unique insights into the evolution of a species. Flavonoid studies in Helianthus have demonstrated the presence of four types of compounds: flavone and chalcone aglycones which appear to occur in external structures on the surface of leaves and flavonol glycosides and anthochlors that are present in leaf and floral tissue (Gershenzon, Mabry and Kreitner, 1981; Schilling and Mabry, 1981; Schilling, 1983). Because leaf flavonoid aglycones appear to occur externally, and can be easily and rapidly surveyed, we analyzed variation and localization of these compounds in H. annuus. ' Received for publication 3 April 1986; revision accepted 14 July 1986. We thank Drs. 0. Solbrig, A. J. Gilmartin, T. Duncan, B. Tumer and C. Heiser for permission to sample Helianthus leaves from herbarium specimens. Secial thanks to Ed Schilling for providing authentic compounds and for assistance in flavonoid identification, and to Jerry McClure for helpful comments on the manuscript. Support from an NSF dissertation im-provement'grant to LHR and DES, Sigma Xi award, Washington State Univ. travel award to LHR, and NSF grant BSR 8315098 to DES is gratefully acknowledged. Helianthus annuus L., an obligately outcrossing, annual sunflower, occurs throughout most of North America and comprises three subspecies, annuus, lenticularis, texanus, and one variety, macrocarpus. These taxa are distinguished primarily by length and width of the achenes, involucral bracts, discs, and ray flowers (Heiser, 1954). The ranges of the three subspecies are broadly overlapping; ssp. annuus occurs throughout the central and eastern U.S.; ssp. lenticularis occurs throughout western North America; ssp. texanus occurs in eastern Texas. Helianthus annuus var. macrocarpus is the cultivated sunflower. There is frequent intergradation between these taxa, often making delimitation difficult. In addition, frequent interand intraspecific hybridization further complicates the systematics of H. annuus (Heiser, 1954). We analyzed flavonoid aglycone profiles of numerous H. annuus specimens representing all three subspecies to: 1) aid in the delimitation of infraspecific taxa within this species, 2) determine whether any correlation exists between flavonoid profile variation and geographic location, and 3) determine the structure and localization ofthe flavonoid aglycones present in this species. MATERLIL AND METHODS-Two hundred and sixty-five individuals from throughout the range of H. annuus were analyzed for flavonoid aglycone variation, including 169 individuals of ssp. lenticularis, 46 individuals of ssp. texanus, 23 individuals of ssp. annuus, and 27 individuals morphologically intermediate between ssp. annuus and ssp. lenticularis. Leaf material utilized in this study was obtained from three sources: 1) field collections, 2) plants grown from seed under uniform conditions in