Somatic embryogenesis in oak (Quercus spp.)

Abstract

The present review summarizes the factors involved in controlling the process of oak somatic embryogenesis as a method for vegetative plant propagation and includes also data on artificial seed production, cryopreservation and transformation. One major limitation, the inability to initiate embryogenic cultures from mature trees, has been recently overcome. Leaves from selected cork oak trees with an age of 50 yr and more have been used to initiate somatic embryogenesis (SE) with a frequency of up to 20%. These findings offer encouraging prospects for cloning proven superior plant material and to integrate this propagation system into tree improvement programs. Once the process of SE has been initiated, the multiplication cycle proceeds via secondary embryogenesis, which can be maintained indefinitely. Problems are reported by the formation of anomalous embryos. The mutability of somatic embryogenic cell lines of various oak species has been monitored by flow cytometry and molecular markers. No somaclonal variation was detected applying random amplified polymorphic DNA (RAPD) or amplified fragment length polymorphism (AFLP) markers, whereas DNAcontent measurements via flow cytometry revealed tetraploidy in some cell lines after several years of continuous subculture. Maturation and low germination frequencies are the main bottlenecks for a broader use of this technique. Recently attention has been on embryo quality and parameters for conversion capacity such as high endogenous cytokinin level and low abscisic acid (ABA) level. Although oak is probably the species that is the most well-developed system for a broadleaved forest tree, data on growth performances of somatic embryo-derived plants are rare.

An evaluation of a new approach to the regeneration of Helichrysum italicum (Roth) G. Don, and the molecular characterization of the variation among sets of differently derived regenerants

“…AFLP currently applied for molecular characterisation and genetic mapping strategies showed their potential in discovering tissue culture-induced variations in several species like Quercus spp. [8], Carya illinoiensis [9,48], Syngonium podophyllum [49], Agave fourcroydes Lem. [50], Elaeis guineensis [51] Actinidia deliciosa [52], and Phoenix dactylifera [53].…”

“…By contrast, the AFLP technique allows the performance of reproducible analyses with reduced amounts of DNA, combining the peculiarities of RFLPs and PCR-based protocols and revealing a greater number of polymorphisms. This has made AFLP a powerful tool that has been employed in several studies of somaclonal variation: in oak [8], pecan trees [9], sugarcane [10], sunflower [11], and Arabidopsis thaliana [4]. Some authors [12,13] compared the different types of molecular marker classes for discovering plant genetic variation, and all stated that AFLP consistently showed higher efficiency in detecting polymorphisms than RFLP, RAPD and SSR.…”

Somatic Embryogenesis and Subsequent Plant Regeneration from Zygotic Embryo Derived Callus of Rubber (Hevea brasiliensis Muell. Arg).

“…Hernandez et al (2003a) made similar observations for somatic embryo induction in Quercus suber. Wilhelm (2000) also reported that the frequency of initiating somatic embryos was associated with the developmental stages of the zygotic embryo explant.…”

Tree somatic embryogenesis in science and forestry

“…In contrast, attempts to achieve somatic embryogenesis of broad-leaved tree species, e.g., oak and beech (Olszewska, 2000;Hazubska-Przybył et al, 2015), have not yielded positive results, although there was recently new information concerning the initiation of somatic embryogenesis from leaves derived from in vitro cultures established from the shoots of thirty-year-old Quercus robur trees (Kotlarski et al, 2015). In some countries, selected species of oak trees have been successfully propagated using this method (Wilhelm, 2000;Vieitez et al, 2012); while in the case of beech, research on somatic embryogenesis has been rarely undertaken (Vieitez et al, 1992;Naujoks, 2003). The reason is most likely the general difficulty to achieve vegetative reproduction of this tree species (Hazubska-Przybył et al, 2015).…”