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

Abstract

Elaeis guineensis (African oil palm) and E . oleife ra (American oil palm) are bred to attain high oil yields, disease resistances, and decelerated shoot elongation. We cultivated immature zygotic embryos from backcrossed and F 1 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 EM BRYOGENESIS RECEPTOR KINASE , DEHYDRIN , DEFENSIN , TRANSPOSASE , and LIPID TRANSFER PROTEIN were analyzed on four callus lines representative of morphological aspects con sistently observed. The highest number of em bryogenic 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 corre lated with protoderm onset. Three six-week cy cles on induction medium yielded 1.5 shoots above 6 cm per poly-embryogenic complex, which performed better tha n embryoids indi vidualized mechanically. Root ing 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 induc