title: Analysis of Breeding Systems, Ploidy, and the Role of Hexaploids in Three Hypericum perforatum L. Populations.
abstract: Hexaploid seeds are produced by predominantly tetraploid populations of Hypericum perforatum, but the fate of hexaploid seedlings and their reproductive behavior have not been closely examined. We used flow cytometry to analyze single seeds and individual plant samples of three accessions of H. perforatum to determine ploidy levels and reproductive pathways. Seed samples of all three accessions were facultative apomicts, with tetraploid cytotype predominant (85-91%) and a lower frequency of hexaploids (9-14%), with diploids (5%) detected in only one population. Seedling populations consisted of tetraploids (87-97%) and hexaploids (3-13%). Hexaploid embryos are most likely generated by a 2n gamete of the tetraploid and fertilized by a normal, reduced tetraploid male gamete. These hexaploids are expected to produce unbalanced gametes because they possess chromosome complements that include two triploid sets originally derived from two different species. The observation that some tetraploid seeds had endosperm with high cellular DNA content indicates that some unbalanced male gametes produced by hexaploids were evidently viable and could effect fertilization. Whether this mechanism is also true for egg cells or whether the hexaploids are capable of producing unreduced embryo sacs is uncertain. Because of severe reproductive difficulties, hexaploid seedlings may play a very minor role in gene flow and the further evolution of H. perforatum. The likelihood that hexaploids will evolve to types with an increased frequency of bivalent paring in meiosis is relatively low. However, hexaploids may include novel chemotypes, which could be vegetatively propagated if valuable, medicinal types can be identified among them.
authors.affiliation: USDA-ARS, North Central Regional Plant Introduction Station, Iowa State University, Ames, IA 50011-1170.
authors.forename: Luping
authors.initials: L
authors.lastname: Qu
authors.forename: Mark P
authors.initials: MP
authors.lastname: Widrlechner
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Rigby
references.citation: Genome. 2003 Aug;46(4):573-9
references.pmid: 12897865
references.citation: Plant J. 2000 Jan;21(1):97-108
references.pmid: 10652155
references.citation: Chembiochem. 2005 Jan;6(1):171-7
references.pmid: 15593112
references.citation: CNS Drug Rev. 2004 Fall;10(3):203-18
references.pmid: 15492771
references.citation: Plant J. 2001 May;26(3):275-82
references.pmid: 11439116
references.citation: Philos Trans R Soc Lond B Biol Sci. 2003 Jun 29;358(1434):1095-103
references.pmid: 12831475
references.citation: Adv Genet. 1947;1:403-29
references.pmid: 20259289
references.citation: Heredity (Edinb). 2006 Apr;96(4):322-34
references.pmid: 16508660
references.citation: Molecules. 2009 Feb 11;14(2):682-725
references.pmid: 19214156
references.citation: Curr Pharm Des. 2005;11(2):233-53
references.pmid: 15638760
references.citation: Ann Bot. 2005 Jan;95(1):255-60
references.pmid: 15596473
references.citation: Pharm Biol. 2009;47(8):774-782
references.pmid: 19907671
references.citation: Planta Med. 2007 Dec;73(15):1614-21
references.pmid: 18072074
references.citation: Cytometry. 1983 Mar;3(5):328-31
references.pmid: 6839881
references.citation: J Nerv Ment Dis. 1999 Sep;187(9):532-8
references.pmid: 10496508
references.citation: Hereditas. 2004;140(1):34-41
references.pmid: 15032945