Involvement of ethylene in somatic embryogenesis in Scots pine (Pinus sylvestris L.)

The involvement of the plant growth regulator ethylene in somatic embryo maturation of Pinus sylvestris (L.) was investigated. Genes that encoded 1-aminocyclopropane-1-carboxylate synthase (ACS), the rate-limiting enzyme in the ethylene biosynthesis pathway, were isolated and characterized. Two novel complementary DNAs (cDNAs) of PsACS1 and PsACS2 that encode ACS were isolated from embryogenic cultures (ECs) along with their polymerase chain reaction (PCR) products. The two sequences shared 69% similarity at amino acid level. PsACS1 was expressed in ECs at the proliferation and maturation stages, whereas the PsACS2 transcript was expressed in embryos only at the maturation stage. These expression levels varied among the five P. sylvestris genotypes studied. Moreover, the high levels of PsACS2 transcript abundance correlated with higher numbers of embryos at stage 3 of development. Ethylene production reached the highest levels at stage 3, and subsequently dropped. Hence, expression of PsACS2 corresponded to ethylene production during embryo development and could thus serve as a genetic marker for the early maturation stage. Both gene expression and ethylene production varied among the different genotypes. Investigating expression of ACC synthase genes further enhanced our understanding of the role of ethylene in embryo development and maturation and improved the efficiency of somatic embryogenesis of P. sylvestris.