Effect of sucrose concentration, polyethylene glycol and activated charcoal on maturation and regeneration of Abies cephalonica somatic embryos

For promoting the maturation of two embryogenic cell lines of Abies cephalonica Loud., the effect of two sucrose concentrations (87.6 and 175.2 mM) applied alone (Control) or in combination with activated charcoal (AC) (1 week) or with polyethylene glycol (PEG1 and PEG4) (1 or 4 weeks) was studied. The effect of each maturation medium was tested with four concentrations of abscisic acid (4, 8, 16 and 32 μM ABA). AC supplement significantly increased the percentage of embryogenic cell masses (ECMs) with cotyledonary embryos but did not affect the average number of embryos per 1 g of ECMs fresh weight. The highest percentages of ECMs (77.5%) with cotyledonary somatic embryos and the highest average number of somatic embryos (36.5 ± 13.4) were found on media with PEG for 4 weeks. The maturation media with 87.6 mM sucrose significantly increased the number of ECMs able to form cotyledonary embryos (66.8%) when PEG was included in the maturation medium, but did not affect the average number of somatic embryos. Overall correlation between proliferation diameter during maturation phase and the number of ECMs with somatic embryos (r = −0.40) as well as all significant correlations within individual experimental variants were consistently negative after 8 weeks of maturation, meaning that proliferation growth hampers the formation of somatic embryos. The highest germination percentages 21.6% and 18.2% were obtained when somatic embryos were maturated on media with or without AC supplement, respectively. Lowest germination percentages, 9.1% and 4.4%, were obtained on maturation media with PEG4 and PEG1.