St John's wort ( Hypericum perforatum L.) is a medicinal plant, which produces pharmaceutically important metabolites with antidepressive, anticancer and antiviral activities ( Zanoli, 2004 Gartner et al, 2005 Kubin et al, 2005), and it is also regarded as a serious weed in many countries ( Buckley et al, 2003). Our observations suggest that the egg cell exists in an active metabolic state before pollination, and that its parthenogenetic activation leading to embryo formation may occur before fertilisation and endosperm initiation. Cyto-embryological analysis showed that meiotic and aposporic processes do initiate within the same ovule: the aposporic initial often appeared evident at the time of megaspore mother cell differentiation. The occurrence of both dihaploids and hexaploids indicates that apospory and parthenogenesis may be developmentally uncoupled and supports two distinct genetic factors controlling apospory and parthenogenesis in this species. Seeds set by haploid parthenogenesis and/or by fertilisation of aposporic egg cells were detected in most populations. Flow cytometric analysis of seeds indicated that all ecotypes were facultatively apomictic, with varying degrees of apomixis and sexuality. All ecotypes were polyclonal, being not dominated by a single genotype, and characterised by different levels of differentiation among multilocus genotypes. Molecular markers were used to determine levels of genetic variation within and relationship among ecotypes of the facultative apomict Hypericum perforatum L. A more profound knowledge of the mechanisms that regulate reproductive events in plants would contribute fundamentally to understanding the evolution and genetic control of apomixis. Thus, apomixis fixes successful gene combinations and propagates high fitness genotypes across generations. The essential feature of apomixis is that embryo sacs and embryos are produced in ovules without meiotic reduction or egg cell fertilisation. Progeny produced by apomixis are clonal replicas of a mother plant. Apomixis is a mode of asexual reproduction through seed.
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