Maltose-driven carbohydrate status and early raffinose synthesis enhance maturation efficiency in hybrid fir somatic embryogenesis

Somatic embryogenesis (SE) is a critical biotechnological tool for the large-scale propagation of the Abies genus, which faces significant threats from climate change and high commercial demand. While sucrose is a first-choice energy source among conifers, firs often exhibit a dramatic preference for maltose. Using hybrid fir (Abies alba x numidica), we have shown an order-of-magnitude higher amount of mature cotyledonary embryos cultivated on maltose compared to sucrose. Determination of endogenous carbohydrate balance during maturation and post-maturation phases revealed fundamental difference in spectrum between sucrose (S) and maltose (M) variants, notably massive presence of hexoses in S variant and, remarkably, an earlier accumulation of raffinose in M variant, pointing to establishing a "mature" biochemical profile. After post-maturation desiccation treatment, though both variants accumulated raffinose family oligosaccharides (RFO), their proportion of in total carbohydrate content remained higher in M variant. Based on the results, we propose, that specific features of fir carbohydrate processing machinery (degradation and transport) resulted in slower but steady C and energy supply in M variant and represent the base of maltose superiority.