**2. Somatic embryogenesis**

Somatic embryogenesis is defined as a process in which a zygotic embryo-like bipolar structure develops from a nonzygotic cell with no vascular connection to the original tissue [8, 11–14]. This process is based on the concept of cellular totipotency, where all the somatic cells of plant tissue contain the genetic information necessary to produce a complete and functional plant (Haberlandt 1902 *apud* [15–17]). In somatic embryogenesis there is no gamete fusion, only somatic cells of explant tissue that will be responsible for the formation of somatic embryos. These embryos undergo the same developmental stages as the zygotic embryo (**Figure 1**) that will develop into a plant with a genetic pattern identical to the explant donor plant [18].

The occurrence of somatic embryogenesis is associated with the induction of differentiated explant tissue cells that acquire the embryogenic characteristic, followed by the expression of the somatic embryo [19–22]. Thus, this process consists in the termination of the gene expression model present in the explant differentiated tissue cells that will be replaced by the expression of embryogenic genes [23, 24]. But embryogenic program does not occur in all cells at the same time, only in some of them [14, 17, 25, 26]. Several changes may occur to reprogram a somatic cell to the competent embryogenic stage.

Embryogenic cells have different characteristics, they are unique, small, superficially they are similar to meristematic cells, with isodiametric forms, small vacuoles, stained nuclei, with abundance of organelles, thick cell wall and starch accumulation [22, 26–28]. The formation of somatic embryos is strongly associated with the embryogenic competence of the explant cells. Possibly, the acquisition of embryogenic competence is related to the endogenous level of plant hormones, which favor tissue sensitivity to plant growth regulators present in the culture medium, which modulates events leading to the formation of the somatic embryo [21, 28, 29].

Somatic embryogenesis can be applied to most plant species [30], but adequate conditions must be available for this, such as explant type, culture medium and growing environment condition [28].

**5**

genotypes.

*Observations on Somatic Embryogenesis in* Coffea arabica *L.*

*DOI: http://dx.doi.org/10.5772/intechopen.90853*

**3. Somatic embryogenesis in** *Coffea*

**Figure 1.**

Somatic embryogenesis is applied to *C. arabica* and *C. canephora* species for the purpose of vegetative multiplication of elite cultivars, large-scale clonal cultivar, Arabica F1 hybrid [4], to obtain transgenic plants and also as plant differentiation study model [31]. In addition, cloning allows the *in vitro* stock of germplasm cultivars for exchange between research institutions and the preservation of materials

In *C. arabica* the formation of somatic embryos can be obtained either by indirect [34], direct [35] or both somatic embryogenesis (**Figure 2**). Indirect somatic embryogenesis occurs in two phases, callogenesis followed by embryogenesis. On the other hand, direct somatic embryogenesis occurs in one phase without callogenesis. Comparison between these two forms of embryogenesis shows that the direct pathway is more advantageous than the indirect pathway. The direct pathway that occurs in a single phase ends up reducing inputs, labor and cultivation time while the indirect pathway occurs in two phases with higher costs of producing somatic embryos [6, 36, 37]. But although the direct pathway is more advantageous, most studies show that vegetative multiplication of *C. arabica* genotypes is mainly achieved by indirect somatic embryogenesis [6]. In the indirect pathway, explants of this species produce embryos more easily and in high quantity while in the direct pathway the number of formed embryos is smaller and this process occurs in a long time. Studies have indicated that the difficulty of direct pathway occurrence in *C. arabica* genotypes seems to be related to the presence of substances produced by the explant tissue itself [38]. This was demonstrated in explants of *C. canephora* and *Daucos carota* that showed inhibition of direct route when they were cultivated in culture medium with addition of substances secreted by explants of *C. arabica*. This result is possibly related to the difficulty of direct pathway occurrence in *C. arabica*

*Coffee* regeneration via somatic embryogenesis can be obtained from different types of explants (**Figure 3**), such as anthers [39, 40], leaves [34, 41–46] and roots [47, 48]. However, leaf explant is the most used type for the application of direct or indirect somatic embryogenesis in *C. arabica* genotypes, this has been occurring since the pioneering work of Sondhal and Sharp [34]. Normally, these explants are

.

used in rectangular shape with dimensions close to 1.5 × 2 cm2

since seeds of this species have some degree of recalcitrance [32, 33].

*Schematic representation of the comparison of somatic and zygotic embryogenesis from Ref. [18].*

*Observations on Somatic Embryogenesis in* Coffea arabica *L. DOI: http://dx.doi.org/10.5772/intechopen.90853*

#### **Figure 1.**

*Coffee - Production and Research*

involving genetic segregation [7].

**2. Somatic embryogenesis**

to the competent embryogenic stage.

growing environment condition [28].

In the selection phase, the progenies have the characteristic of heterosis that favors the occurrence of differentiated plants. Some of these plants may have special characteristics such as tolerance to biotic and abiotic factors or high productivity or excellent drink quality or all of these. To confirm if a progeny is special it must be multiplied and evaluated in relation to its agronomic performance in the field. Following this phase, the progeny may be released as a clonal cultivar. Cloning selected materials allows to capture all selection and improvement gains without

The multiplication of intermediate genotypes to breeding program is not indicated by seeds because plants resulting from the germination may have genetic segregation that leads to loss of the special features [8]. Thus, it is recommended that these genotypes be vegetatively multiplied to maintain their genetic pattern. The vegetative multiplication of coffee plants has been obtained by cutting, and the species *C. canephora* responds very well to this process [9] while arabica plants are

Usually *C. arabica* genotypes are vegetatively multiplied by in *vitro* cultivation. *In vitro* culture or plant tissue culture belongs to Plant Biotechnology which comprises culturing cells, tissues or organs under aseptic conditions and using artificial culture media containing different components such as water, minerals, vitamins, carbon source and plant growth regulators [11]. Plant tissue culture involves micro-

Somatic embryogenesis is defined as a process in which a zygotic embryo-like bipolar structure develops from a nonzygotic cell with no vascular connection to the original tissue [8, 11–14]. This process is based on the concept of cellular totipotency, where all the somatic cells of plant tissue contain the genetic information necessary to produce a complete and functional plant (Haberlandt 1902 *apud* [15–17]). In somatic embryogenesis there is no gamete fusion, only somatic cells of explant tissue that will be responsible for the formation of somatic embryos. These embryos undergo the same developmental stages as the zygotic embryo (**Figure 1**) that will develop into a plant with a genetic pattern identical to the explant donor plant [18]. The occurrence of somatic embryogenesis is associated with the induction of differentiated explant tissue cells that acquire the embryogenic characteristic, followed by the expression of the somatic embryo [19–22]. Thus, this process consists in the termination of the gene expression model present in the explant differentiated tissue cells that will be replaced by the expression of embryogenic genes [23, 24]. But embryogenic program does not occur in all cells at the same time, only in some of them [14, 17, 25, 26]. Several changes may occur to reprogram a somatic cell

Embryogenic cells have different characteristics, they are unique, small, superficially they are similar to meristematic cells, with isodiametric forms, small vacuoles, stained nuclei, with abundance of organelles, thick cell wall and starch accumulation [22, 26–28]. The formation of somatic embryos is strongly associated with the embryogenic competence of the explant cells. Possibly, the acquisition of embryogenic competence is related to the endogenous level of plant hormones, which favor tissue sensitivity to plant growth regulators present in the culture medium, which modulates events leading to the formation of the somatic embryo [21, 28, 29].

Somatic embryogenesis can be applied to most plant species [30], but adequate conditions must be available for this, such as explant type, culture medium and

less efficient by this way, having low multiplication rate [10].

propagation processes such as somatic embryogenesis.

**4**

*Schematic representation of the comparison of somatic and zygotic embryogenesis from Ref. [18].*
