Temporal Regulation of Somatic Embryogenesis by Adjusting Cellular Polyamine Content in Eggplant1

Abstract

Four critical stages of embryogenesis, including callus induction, cellular acquisition of morphogenetic competence, expression of embryogenic program, and development and maturation of somatic embryos during somatic embryogenesis from leaf discs of eggplant (Solanum melongena L.), were identified by scanning electron microscopy. Temporal changes in arginine decarboxylase (ADC) activity and polyamines (PAs) during critical stages of embryogenesis revealed that high levels of PAs (especially putrescine [PUT]), due to higher ADC activity in discs from the apical region (with high embryogenic capacity) than from the basal region of the leaf (with poor embryogenic capacity), were correlated with differential embryogenesis response. Kinetic studies of the up-and downregulation of embryogenesis revealed that PUT and difluoromethylarginine pretreatments were most effective before the onset of embryogenesis. Basal discs pretreated with PUT for 4 to 7 d showed improved embryogenesis that was comparable to apical discs. PA content at various critical steps in embryogenesis from basal discs were found to be comparable to that of apical discs following adjustments of cellular PA content by PUT. In contrast, pretreatment of apical discs with difluoromethylarginine for 3 d significantly reduced ADC activity, cellular PA content, and embryogenesis to levels that were comparable to basal discs. Discs from the basal region of leaves treated with PUT for 3 d during the identified stages of embryogenesis improved their embryogenic potential.

Effect of exogenous arginine on sugarcane (Saccharum sp.) somatic embryogenesis, free polyamines and the contents of the soluble proteins and proline

“…Results shown here are a new evidence of the crucial role that free polyamines play in somatic embryogenesis in various plant systems, as previously reported (Minocha and Minocha 1995;Yadav and Rajam 1998;Silveira et al 2006). Nevertheless, recent studies have shown the involvement of conjugated (Santa-Catarina et al 2007) and bound (De-la-Peña et al 2008) PAs in early stages of somatic embryo development in Ocotea catharinensis and Coffea canephora, respectively.…”

“…In addition, polyamines have been studied in relation to somatic embryogenesis in many plant systems (Nieves et al 2003;Minocha et al 2004;Bertoldi et al 2004, Silveira et al 2006Santa-Catarina et al 2007) and some reports show PAs involvement in this process, particularly in their free form (Minocha and Minocha 1995;Yadav and Rajam 1998).…”

Effect of polyamines on in vitro somatic embryogenesis in Momordica charantia L.

“…Bertoldi et al (2004) in Vitis vinifera and Bastola and Minocha (1995) in carrot have shown that a positive correlation exists between SE and enhanced ODC activity. Yadav and Rajam (1998) have reported that on account of high activity of ADC (the other enzyme involved in Put synthesis) during induction of embryogenic callus of leaf discs of eggplant, there were high titers of free Put as compared to Spd and Spm. But, immunoassays using antibodies have shown increased ADC levels corresponding to embryo maturation and not embryo induction (Amarasinghe et al 1996).…”

“…Very little is known about the underlying mechanisms that may regulate morphogenesis in addition to plant growth regulator effects (Yadav and Rajam 1998). PAs have been shown to be important for cellular differentiation to SE (Chi et al 1994;Bajaj and Rajam 1996;Rajam 1997) and have been suggested as regulators of SE (Montague et al 1979).…”

“…For example, a strong positive correlation between SE and increased cellular PA content has been clearly demonstrated in Daucus carota cell cultures where the inhibition of PA biosynthesis completely inhibited SE. Several reports have shown the involvement of PAs particularly in free forms in SE (Yadav and Rajam 1998). In fact combined PAs (conjugated and bound forms) are important for plant developmental processes such as flower development (Tiburcio et al 1988;Evans and Malmberg 1989;Kaur-Sawhney and Applewhite 1993) and moreover there may be interconversion between free and conjugated forms to maintain appropriate levels of free PAs during developmental processes (Torrigiani et al 1989).…”