The genus Iris L., belonging to the family Iridaceae, encompasses more than 300 species of herbaceous perennials. These plants are commonly used as ornamental plants in gardens and heavy metal phytoremediation (Han et al., 2013; Huang et al., 2003a, 2011; Kim et al., 2009). I. germanica L., which is regarded as one of the most horticulturally important tall bearded irises, has been cultivated ever since ancient time with hundreds of commercially valuable cultivars (Huang et al., 2003b; Jeknic et al., 1999). In addition, the rhizomes of some I. germanica cultivars contained an essential oil composed partly of irones (Jehan et al., 1994). These violet-scented ketonic compounds have been frequently used in cosmetics and perfumes (Gozu et al., 1993).
The cultivation of I. germanica is limited, thus failing to meet the ever increasing demand of the raw materials. Although I. germinica is traditionally propagated through splitting the rhizomes or by seeds, these methods are not efficient in producing sufficient seedlings (Jehan et al., 1994; Simonet, 1932). Besides, conventional breeding for iris’s genetic improvement is hampered by the high degree of incompatibility between species (Jeknic et al., 1999).
Somatic embryogenesis is the fastest system of plant regeneration and generally considered to be prerequisite for genetic transformation (Jeknic et al., 1999; Karami et al., 2006). Therefore, several protocols for iris regeneration via somatic embryogenesis from a variety of explant types have been developed (Jevremović and Radojević, 2006; Kim et al., 2009; Laublin et al., 1991; Radojević et al., 1987; Radojević and Subotić, 1992; Shibli and Ajlouni, 2000), including I. germanica regenerated from leaf bases, apices, sepals, petals, and ovaries (Jehan et al., 1994). Jehan et al. (1994) found that the optimal medium for obtaining embryogenic callus was MS medium supplemented with 2.9 g/L proline. The frequency of embryogenic callus induction was 10% and 95% of embryos coverted into the plantlets. Therefore, the low efficiency of proline to improve embryogenic callus in I. germanica and that of plant regeneration in other Iris species has hindered the establishment of a suitable transformation system (Jeknic et al., 1999). To date, genetic transformation based on regeneration system via somatic embryogenesis is not available in any kind of Iris species. Therefore, the search for a method to improve embryogenic callus production and plant regeneration is imperative.
Somatic embryogenesis also provides a model system for the study of early events in plant embryo development (Zimmerman, 1993). In monocotyledonous plants, the morphology of embryos varies depending on the species, especially of the cotyledon which is also called scutellum (Hartmann et al., 1997). However, detailed information concerning morphological or histological changes in SEs of I. germanica has not been reported yet.
The primary objective of this study is to establish an efficient plant regeneration system via somatic embryogenesis of I. germanica from shoot apexes and study morphological and histological changes of the SEs.
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