Effects of Desiccation, Medium Osmolarity and Abscisic acid on the Maturation of Hevea brasiliensis Somatic Embryos

The effects of desiccation of Hevea somatic embryos and of sucrose and ABA concentrations in the maturation medium on their germinability were investigated. Conversion into plant, water and histochemical status of somatic embryos were compared systematically to those of the zygotic embryos used as reference. Slow desiccation or maturation on 351 mol m−3 sucrose supplemented with 1 mmol m−3 ABA strongly improved germinability and conversion of embryos into plants. The combination of the two treatments was the most effective, increasing the germination frequency by 3·7 and plant conversion by 6·6 in clone PR 107. Each of these two treatments increased the vigour of somatic embryos, stimulated the formation of root and shoot meristems and the synthesis and accumulation of starch and protein reserves. At the end of maturation, the Hevea somatic embryos bore an anatomical and histochemical resemblance to mature zygotic embryos. Likewise, the two treatments brought the water status of somatic embryos closer to that of the mature zygotic embryos, but without achieving a perfect match. Optimization of the successful conversion into plants may require full acquisition of this water status.