Key words: Linum austriacum, cotyledonary node, decapitation, direct regeneration.
Linaceae, one of the flowering plant families, consists of genera including Anisadenia, Cliococca, Hesperolinon, Linum, Radiola, Reinwardtia, Sclerolinon and Tirpitzia. The largest genus of the family Linaceae, Linum, contains about 230 species distributed in the worldwide (Heywood, 1985). According to classical taxonomy based on morphological characters, the genus Linum is divided into the sections Syllinum, Cathartolinum, Dasylinum, Linum and Linastrum (Ockendon and Walters, 1968).
Several species of the Linum genus are well known for their lignan content. Presence of lignans in the genus Linum has been proven from 1970 (Weiss et al., 1975). Lignans are dimers derived from monolignol (Hemmati et al., 2007). They constitute a large group of natural products, which display diverse biological effects. The dibenzylbutane group (e.g. secoisolariciresinol diglucoside, SDG), aryltetralin group (e.g. podophyllotoxin, PTOX) and arylnaphthalene group (e.g. justicidin B) are the main types of lignans in genus Linum (Bakke and Klosterman, 1956; Broomhrad and Dewick, 1990; Mohagheghzadeh et al., 2002). In 2002, Mohagheghzadeh and coworker demonstrated that justicidin B produced in Linum austriacum cell cultures, which was the first report on the occurrence of arylnaphthalene lignans in a species of the Linaceae. Hence, due to various pharmacological effects of justicidin B, such as anticancer, cytotoxic, antiviral (e.g. HIV), fungicidal, antiprotozoal, and antiplatelet properties (Joseph et al, 1988; Asano et al, 1996; MacRae et al, 1989; Gertschet al, 2003; Chen et al, 1996), bioproduction of this valuable lignan by biotechnological procedures would be a conceivable alternative to the supply from wild-grown plants as natural sources.
Development of efficient procedure for regeneration of plants from cultured cells, tissues and organs are a prerequisite for usage of in-vitro culture techniques to genetically manipulation of plants for enhances plants germplasm (Zhang et al. 2004). Often, regeneration methods depends on the tissue’s type used for operate cultures, so that this starting materials can potentially became limiting factors (Koroch et al. 2003). Cotyledons, hypocotyls, meristems and stem segments have been used as explants for culture initiation in Linum, but only efficiency of hypocotyl segments for plant regeneration has proven (Friedt 1990). However, regardless the easy regeneration of plants from hypocotyl segments, these explants has a potential drawback: after transformation, they develop a large number of chimeric shoots (Jordan et al, 1988). The cause is the incomparable ability of flax shoot hypocotyls to form adventitious buds in response to stress or decapitation (Mundhara et al, 2002; 2001). Development of adventitious buds on hypocotyl segments is occur in epidermal cells on the whole explant surface (Link et al, 1946; Murray et...