Formosan sweetgum (Liquidambar formosana L.), the counterpart to sweetgum (L. styraciflua L.) grown in America, is distributed in most of temperate and subtropical China. Formosan sweetgum is popular in forestry and has been employed in urban landscaping in recent years, but its spiny fruits disintegrate very slowly and create a nuisance on lawns and walks (Brunner et al., 1998). Therefore, breeding for sterility would greatly improve the usefulness of Formosan sweetgum as a landscape tree.
The long generation time of many perennial woody species results in an extended period for traditional breeding programs. Genetic transformation based on tissue culture technology provides a way to speed up the breeding of Formosan sweetgum for simply inherited traits. In L. styraciflua, plants have been regenerated via adventitious shoots from mature leaf and petiole segments (Brand and Lineberger, 1988) and hypocotyl segments (Kim et al., 1997), and via somatic embryogenesis from hypocotyl-derived callus (Sommer and Brown, 1980), immature seeds (Merkle et al., 1998), and staminate and pistillate inflorescences (Merkle et al., 1998; Merkle and Battle, 2000). In addition, Sullivan and Lagrimini (1993) transformed L. styraciflua using Agrobacterium tumefaciens (Smith et. Townsend) Conn. In Formosan sweetgum, however, data on tissue culture, especially for plant regeneration, is very limited. Vendrame et al. (2001) used thidiazuron (TDZ) to regenerate hybrid sweetgum (L. styraciflua × L. formosana) by somatic embryogenesis. Durkovic et al. (2005) reported the micropropagation of Formosan sweetgum with a novel pattern of adventitious rooting.
To genetically modify Formosan sweetgum for sterility, an excellent plant regeneration system is essential. We had adopted the regeneration method described by Brand and Lineberger (1988) for shoot regeneration from leaves of Formosan sweetgum using woody plant medium (WPM; Lloyd and McCown, 1980) containing 11.1 μm 6-benzyladenine (BA) and 0.54 μm 1-naphthalene acetic acid (NAA). However, results were not satisfactory. Therefore, our objective was to develop a regeneration system from leaf explants of L. formosana via organogenesis induced by TDZ, which could be applicable for Agrobacterium-mediated transformation.
Brand, M.H. & Lineberger, R.D. 1988 In vitro adventitious shoot formation on mature-phase leaves and petioles of Liquidambar styraciflua L Plant Sci. 57 173 179
Brunner, A.M., Mohamed, R., Meilan, R., Sheppard, L.A., Pottman, W.H. & Strauss, S.H. 1998 Genetic engineering of sexual sterility in shade trees J. Arboricult. 24 263 272
Caboni, E., Tonelli, M.G., Lauri, P., Angeli, S.D. & Damiano, C. 1999 In vitro shoot regeneration from leaves of wild pear Plant Cell Tissue Org. Cult. 59 1 7
Durkovic, J., Pichler, V. & Lux, A. 2005 Micropropagation with a novel pattern of adventitious rooting in Formosan sweetgum Can. J. For. Res. 35 2775 2780
Huetteman, C.A. & Preece, J.E. 1993 Thidiazuron: a potent cytokinin for woody plant tissue culture Plant Cell Tissue Org. Cult. 33 105 119
Kim, M.K., Sommer, H.E., Bongarten, B.C. & Merkle, S.A. 1997 High-frequency induction of adventitious shoots from hypocotyl segments of Liquidambar styraciflua L. by thidiazuron Plant Cell Rpt. 16 536 540
Liu, G.F. & Bao, M.Z. 2003 Adventitious shoot regeneration from in vitro cultured leaves of London plane tree (Platanus acerifolia Willd.) Plant Cell Rpt. 21 640 644
Lloyd, G.B. & McCown, B.H. 1980 Commercially feasible micropropagation of mountain laurel, Kalmia latifolia, by use of shoot-tip culture Proc. Int. Plant Prop. Soc. 30 421 427
Merkle, S.A. & Battle, P.J. 2000 Enhancement of embryogenic culture initiation from tissues of mature sweetgum trees Plant Cell Rpt. 19 268 273
Merkle, S.A., Neu, K.A., Battle, P.J. & Bailey, R.L. 1998 Somatic embryogenesis from immature and mature tissues of sweetgum (Liquidambar styraciflua) Plant Sci. 132 169 178
Preece, J.E., Huetteman, C.A., Ashby, W.C. & Roth, P.L. 1991 Micro- and cutting propagation of silver maple. I. Results with adult and juvenile propagules J. Amer. Soc. Hort. Sci. 116 142 148
Sullivan, J. & Lagrimini, L.M. 1993 Transformation of Liquidambar styraciflua using Agrobacterium tumefaciens Plant Cell Rpt. 12 303 306
Vendrame, W.A., Holliday, C.P. & Merkle, S.A. 2001 Clonal propagation of hybrid sweetgum (Liquidambar styraciflua × L. formosana) by somatic embryogenesis Plant Cell Rpt. 20 691 695