Induction and characterization of oil palm (Elaeis guineensis Jacq.) pro-embryogenic masses.
Oil palm is one of the most economically valuable oil seed plants, but the expansion of plantations has been limited by availability of seedlings, as the conventional propagation is through seeds, which have low germination rates. One possible solution for the large-scale production is the use of somatic embryogenesis. The aim of this study was evaluate the effects auxins 2,4-D and picloram on the induction of pro-embryogenic masses in E.guineenesis hybrid leaf explants and characterize, regarding embryogenic characteristics, with cytochemical and ultrastructural analysis. Specifically, in vitro plantlets leaves fragments were inoculated in Y3 culture medium supplemented by 2.4-D or picloram at different concentrations (0.0, 1.0, 3.0, 6.0 and 9.0 mg l⁻¹). After 90 days the presence/ absence of cell masses were evaluated. Both growth regulators efficiently induced cellular masses regardless of the concentrations applied. As the cell masses were not homogeneously formed, they were classified according to color and shape into four types: TYPE 1--elongated and translucent, TYPE 2--uneven and translucent, TYPE 3--globular and beige, TYPE 4--globular and white. Based on the anatomical and ultrastructural features, TYPE 2, 3 and 4 cell masses were considered to have the highest embryogenic potential and therefore may be most suited to large-scale vegetative propagation of oil palm.
The Origin and Development of Embryoids in Oil Palm (Elaeis guineensis Jacq) Embryo Culture
Mature zygotic embryos of Elaeis guineensis Jacq var tenera were excised and cultured on Eeuwens (1976, 1978) medium containing 2 mg/l 2,4-D. Callus was initiated from these embryos within 8 weeks. Embryoids were induced from the primary callus cultured on Murashige and Skoog (1962, MS) medium supplemented with 0.5 mg/l 2,4-D. For embryoid differentiation and plantlet regeneration, two successive media were employed. The first medium was MS-CAP devoid of 2,4-D but containing 0.05% activated charcoal . The second medium was MS-CAP containing 0.1 mg/l 2,4-D and 2.5 mg/l BA. The embryoids were harvested at various time, fixed, sectioned, stained and examined microscopically. The histological origin of embryoids was from single cells in the subepidermis along the surface of callus clumps. Embryoids proceeded in a standard development pattern to the globular-, heart- and finally to the cotyledon stage. Secondary embryoids occurred on the cotyledon of primary embryoids and originated from single, densely staining cells of the epidermis.
Somatic embryogenesis from immature peach palm inflorescence explants: towards development of an efficient protocol
Various factors affect the induction of somatic embryogenesis in peach palm (Bactris gasipaes Kunth). Among these, both the type and level of auxins had the greatest influence on in vitro responses, although the genotype and the developmental stage of the explants also influenced results. Younger inflorescences were more competent to respond to SE induction than more mature inflorescences and the use of a pre-treatment with 2,4-D (200 μM) in liquid MS culture medium also increased the embryogenic capacity, and diminished the development of flower buds. Higher oxidation rates were observed in explants maintained on 2,4-D-supplemented culture medium, while on 300 μM or 600 μM Picloram and Dicamba lower oxidation rates were observed. The progression from floral meristem to flower bud occurred at high frequency when low concentrations of auxins were used, independent of the type. Higher concentrations of Picloram or Dicamba reduced or even inhibited flower bud development. Picloram also enhanced the embryogenic induction rate more than 2,4-D and Dicamba, and among the concentrations evaluated 300 μM Picloram enhanced induction for both genotypes, with significant differences between genotypes. The best combination of variables used the least mature inflorescence (Infl1) from genotype I with the 2,4-D pre-treatment and 300 μM Picloram to generate 5 embryogenic calli from 18 explants; 26 embryos were obtained on average from each embryogenic callus. From these, eighteen embryos converted to plantlets and six of these survived transfer to the greenhouse.