Histological analysis and transcription profiles on somatic embryogenesis in interspecific hybrids of Elaeis guineensis × E. oleifera

Abstract

Elaeis guineensis (African oil palm) and E. oleifera (American oil palm) are bred to attain high oil yields, disease resistances, and decelerated shoot elongation. We cultivated immature zygotic embryos from backcrossed and F1 interspecific progenies on media containing 110, 150, or 200 mg∙l−1 2,4-diclorophenoxyacetic acid (2,4-D) to obtain embryogenic cultures. These were set to multiply on medium containing 8 mg∙l−1 2,4-D or lower concentrations of auxins and finally we induced plantlets regeneration, from each zygotic embryo, independently, in order to have the clones organized according to their respective origins. Reductions in auxins induced cultures to revert from highly embryogenic into competent for embryogenesis and finally to organogenic degenerated callus lines. Histology and the expression of SOMATIC EMBRYOGENESIS RECEPTOR KINASE, DEHYDRIN, DEFENSIN, TRANSPOSASE, and LIPID TRANSFER PROTEIN were analyzed on four callus lines representative of morphological aspects consistently observed. The highest number of embryogenic cultures was obtained on 150 mg∙l−1 2,4-D. Maturation and multiplication of somatic embryos through secondary embryogenesis occurred simultaneously on 8 mg∙l−1 2,4-D. LIPID TRANSFER PROTEIN expression was detected in one of the embryogenic cultures and correlated with protoderm onset. Three six-week cycles on induction medium yielded 1.5 shoots above 6 cm per poly-embryogenic complex, which performed better than embryoids individualized mechanically. Rooting was observed for 77% and 82% of shoots from these two types of explants, respectively. Rooted plantlets ready for acclimatization were obtained nine months after shoot induction had started.