Histological and Biochemical Studies of Zygotic Embryogenesis towards improvement of Somatic Embryogenesis in Date Palm (Phoenix dactylifera L.)

In Algeria, the culture of date palm is subjected to many threats of which most worrying are the ageing of date palm orchards and Bayoud, vascular mortal disease of the date palm, caused by Fusarium oxysporum F. sp. albedenis. The methods of in vitro culture are currently adapted for the improvement of the culture and the fight against these threats. Various techniques of micropropagation were largely developed on the date palm, of which somatic embryogenesis remains the most current. However, in the development of the somatic embryos, although relatively synchronous, a random remainder stays, in particular during the phase of germination. The objective of this paper falls under the comprehension of the embryonic zygotic development of the date palm, which has been studied very little, in order to better apprehend the problems relating to the process of somatic embryogenesis. Thus, our work was directed towards the deepening of knowledge of the stages of the formation and the maturation of zygotic embryogenesis towards the histological and biochemical plan. During the development of the ovule fertilized in young seed, the embryonic bag undergoes several transformations. The cell egg or zygote which appears at the 12th day after pollination suddenly shows the first transverse division leading to two superimposed and unequal cells. Successive divisions allow the formation of a globular embryo of form two months after fecundation. The development of the embryo, relatively slow, thus passes by a stage heart form to bilateral symmetry; two side territories being used for the installation of the cotyledon entirely sheathing. Continuous divisions of the cells of the embryo lead to an increase in size and embryonic complexity, in order to set up the embryonic axis and the cotyledonary limb. The embryonic axis then consists of a shoot meristem surrounded by the cotyledon and the first leaf post cotyledonary initiated during the embryogenesis which is traversed by procambial beams. The distinction between the hypocotyl axis and the very reduced root meristem is difficult. The electrophoretic study of mature proteins of zygotic embryos of two varieties, 'Deglet nour' and 'Ghars', highlights several bands whose majority have their counterparts in the profiles of the zygotic embryos of Washingtonia filifera Will and Elaeis guinneensis (Chandra and DeMason, 1988; Morcillo, 1998). These results suggest similarities in the composition out of proteins of reserve at these various species of palm trees. The germination and the viability of the somatic embryos thus depend on the installation of the proteinic reserves and especially of the conducting beams which connect the shoot part and the root part.