Induction of somatic embryogenesis from different explants of shoot cultures derived from young Quercus alba trees

Abstract

The induction of somatic embryogenesis from shoot apices and leaf explants of shoot cultures derived from 6-to 7-year-old white oak (Quercus alba L.) trees is reported in this study. Embryogenic response was obtained in two out of the three genotypes evaluated with embryo induction frequencies up to 50.7% for WOQ-1 and 3.4% for WOQ-5 genotypes. The embryogenic explants formed translucent nodular structures and cotyledonary-stage somatic embryos, which developed from callus tissue, indicating an indirect embryogenesis process. An efficient procedure was developed for WOQ-1 material on the basis of the most appropriate leaf developmental stage. Growing leaves excised from two nodes below the shoot apex showed the highest embryogenic induction index. These leaves contain cells in an undifferentiated state, as shown by the presence of precursor cells of stomata, absence of intercellular spaces and low starch content in the mesophyll cells. Nodular structures and/or somatic embryos began to arise 7-8 weeks after culture initiation, although most emerged after 9-12 weeks in culture. The sequence of application of media for somatic embryo induction was optimized with a two-step procedure consisting of culturing the explants in medium supplemented with 21.48 lM NAA and 2.22 lM BA for 8 weeks and transfer of explants into plant growth regulator-free medium for another 12 weeks. Clonal embryogenic lines were established and maintained by secondary embryogenesis. Embryo germination (30%) and plantlet conversion (16.6%) were achieved after cold storage for 2 months.

Improved secondary embryo production in Quercus alba and Q. rubra by activated charcoal, silver thiosulphate and sucrose: influence of embryogenic explant used for subculture

“…This consisted of Murashige and Skoog (1962;MS) mineral salts and vitamins, 500 mg/l casein hydrolysate, 3 % (w/v) sucrose and 6 g/l Vitroagar (Pronadisa, Spain) (basal proliferation medium, BM) supplemented with 0.44 lM 6-benzyladenine (BA) with or without 0.27 lM 1-naphthaleneacetic acid (NAA) (Corredoira et al 2012;Mallón et al 2012). A Q. rubra embryogenic line named ROQ-8, previously initiated from leaf explants excised from axillary shoot cultures of a 7-year-old Q. rubra tree (Online Resource 1) has also been maintained on the same proliferation medium above defined for Q. alba material.…”

“…An embryogenic line named WOQ-5, previously initiated from leaf explants of shoot cultures derived from a 7-yearold Q. alba tree (Corredoira et al 2012) has been maintained for 2 years by secondary embryogenesis with sequential subculture at 5-week intervals on embryo proliferation medium. This consisted of Murashige and Skoog (1962;MS) mineral salts and vitamins, 500 mg/l casein hydrolysate, 3 % (w/v) sucrose and 6 g/l Vitroagar (Pronadisa, Spain) (basal proliferation medium, BM) supplemented with 0.44 lM 6-benzyladenine (BA) with or without 0.27 lM 1-naphthaleneacetic acid (NAA) (Corredoira et al 2012;Mallón et al 2012).…”

“…Acceptable proliferation rates with the presence of singularised cotyledonary-shaped embryos were reported for Q. suber lines cultured on medium devoid of plant growth regulators (PGRs) (Toribio et al 2005), whereas medium supplemented with 0.44 lM benzyladenine (BA) has been used for embryo proliferation in Q. robur (Mallón et al 2012) and Q. bicolor (Mallón et al 2013), although the presence of fused embryos represents a serious problem for the efficiency of these embryogenic systems. Conversely, embryogenic lines of other oak species, including Q. rubra (Gingas and Lineberger 1989), Q. alba (Corredoira et al 2012) and Q. ilex (Blasco et al 2013) proliferate through generation of a creamy granular embryogenic callus or nodular proembryogenic structures as a form of repetitive embryogenesis, giving rise to cultures of nodular and compact appearance with a low proportion of bipolar embryo differentiation. Thus, the continued proliferation of proembryogenic nodules and the arrest of embryo differentiation may even compromise the maintenance of the lines because embryogenic competence may be lost (BarraJiménez et al 2014).…”

“…Among North American oak species, Q. alba L. (white oak) and Q. rubra L. (red oak) are widely distributed and are also of significant importance (Steiner 1993). In Q. alba, we have induced SE from leaf explants derived from young trees (Corredoira et al 2012), but the method for proliferation of embryogenic lines has not been studied in detail. In particular, in Q. rubra, induction of SE has been obtained from immature zygotic embryos (Gingas and Lineberger 1989;Vengadesan and Pijut 2009) and leaf explants of young seedlings (Rancillac et al 1996), but no clear patterns of development for repetitive embryogenesis have been described.…”

Somatic Embryogenesis and Plant Regeneration in Sapindus mukorossi Gaertn. from Leaf-Derived Callus Induced with 6-Benzylaminopurine

“…Approximately 25 % of explants produced callus when were cultured adaxial side down. The higher percent response for callus induction and somatic embryo formation on the adaxial-side-up treatment may be attributed to the natural facility of conduction of nutritional and growth factors from the adaxial to the abaxial surface [29]. Adaxial-side-up orientation of leaf explants significantly promoted embryogenesis in comparison with abaxial-side-up orientation [30].…”