Somatic embryogenesis in Norway spruce: Anatomical study of embryo development and influence of polyethylene glycol on maturation process

Abstract

The sequence of the developmental stages during somatic embryo maturation in Norway spruce (Picea abies (L.) Karst.) was described for a maturation medium (containing abscisic acid) and for the same medium supplemented with 3.75 and 7.5 % polyethylene glycol (PEG-4000). Embryo maturation was accomplished after six weeks of cultivation on the PEG-free medium, and prolonged cultivation resulted in a higher frequency of irregularly developing embryos. The addition of 3.75 % PEG increased the speed of the maturation process by two weeks and caused changes in the morphometric characteristics, e.g. an increase in embryo length (approx. 30-40 %). PEG at a concentration of 7.5 % did not further speed up the process. In addition, the size of the embryos remained approximately the same, and only the root cap length increased by approx. 40 % as compared to the 3.75 % PEG variant. On the other hand, some morphological abnormalities occurred (e.g. rows of dead cells and ruptures in the center of embryos), which are unambiguously negative for further germination. As the developmental process improved, the number of subcultivations needed was lowered and thus the probability of damage due to mechanical irritation also decreased. This has been attributed to the undoubtedly positive effect of the presence of 3.75 % PEG in the medium. Based on all of the obtained results, we concluded that, of all the treatments tested, the medium supplied with 3.75 % PEG proved to be the most beneficial for embryo development of the studied genotype of Norway spruce.