Influence of Growth Regulators on Callogenesis and Somatic Embryo Development in Date Palm (Phoenix dactylifera L.) Sahelian Cultivars

This study provides a physiological analysis of somatic embryogenesis in four elite cultivars of date palms: Ahmar, Amsekhsi, Tijib, and Amaside, from the initial callogenesis to establishment and proliferation of embryogenic suspension cultures. Somatic embryos development and in vitro plants rooting were also studied. For each step, auxins and cytokinins concentrations were optimised. The primary callogenesis from leaf explants of seedlings appeared highly dependent on genotype. Ahmar (80%) and Amsekhsi (76%) appeared highly callogenic, whereas Tijib (10%) and Amaside (2%) produced low amounts of calluses. 2,4-Dichlorophenoxyacetic acid appeared favorable to the induction of primary callogenesis and its effect was enhanced by the addition of benzyl adenine or adenine sulfate. Secondary friable calli obtained from chopped granular calli were used to initiate embryogenic cell suspensions in media supplied with 2,4-dichlorophenoxyacetic acid. Suspension cultures showed a growth rate of fourfold after four subcultures in presence of 2,4-dichlorophenoxyacetic acid 2 mg/L. Our results showed that a seven-day transitory treatment with benzyl adenine 0,5 mg/L was necessary to optimize embryos development. Naphthalene acetic acid induced the development of primary orthogravitropic roots during embryos germination. The comparison with cytofluorometry of nuclear DNA amounts showed no significant difference in ploidy level between regenerated plants and seedlings

Abstracts

In order to better understand the developmental processes that govern the formation of somatic embryos in oil palm (Elaeis guineensis Jacq.), we investigated the transcription factor genes expressed during embryogenesis in this species. The AP2/EREBP transcription factor family includes the AP2 subgroup, which contains several proteins that play important roles in plant development. We identified and characterized EgAP2-1, which codes for a protein that contains two AP2 domains similar to those of the transcription factor BABYBOOM (BBM) and more generally AINTEGUMENTA-like (AIL) proteins of the AP2 subgroup. In a similar way to related genes from eudicots, ectopic expression of EgAP2-1 in transgenic Arabidopsis plants alters leaf morphology and enhances regeneration capacity. In oil palm, EgAP2-1 transcripts accumulate to the greatest extent in zygotic embryos. This expression pattern was investigated in more detail by in-situ hybridization, revealing that in both zygotic and somatic embryos, EgAP2-1 expression is concentrated in proliferating tissues associated with the early development of leaf primordia, root initials and provascular tissues. (Résumé d'auteur

Biotechnologies du palmier dattier

Le palmier dattier est une plante d'intérêt écologique, économique et social majeur pour de nombreux pays des zones arides qui comptent parmi les plus pauvres du globe. En effet, en créant au milieu du désert un microclimat favorable au développement de cultures sous-jacentes, le palmier dattier constitue l'axe principal de l'agriculture dans les régions désertiques et représente la principale ressource vivrière et financière des populations oasiennes. Pour traiter les problématiques liées à la culture du palmier au Maghreb, en Afrique et en Europe du Sud, 60 chercheurs font ici un bilan de leurs recherches sur l'évaluation, la conservation et la valorisation des ressources génétiques du palmier dattier, ouvrant ainsi de nouvelles perspectives pluridisciplinaires. L'ouvrage présente les dernières avancées scientifiques sur la production à grande échelle, les variations somaclonales et l'amélioration génétique. Enfin, il pose les bases de nouveaux projets internationaux sur la conservation des ressources génétiques du palmier dattier, un enjeu important pour développer l'agriculture oasienne

BA enhances the germination of oil palm somatic embryos derived from embryogenic suspension cultures

Embryogenic suspension cultures of oil palm (#Elaeis guineensis$ Jacq.) allow mass propagation of somatic embryos ; however regeneration rates are low. Histological observations have revealed that shoot development might be limited by the absence of a caulinary meristem. The addition of 6-benzyladenine during development was found to induce shoot apex differentiation and thus increased germination rates, by up to 70%. However, multiple shoot formation was a consequence of a longer period of cytokinin supply during the development of the embryo. In contrast, a short period of culture on medium with 6-benzyladenine at the beginning of embryo development was found to result in single shoot production. (Résumé d'auteur