H₂O₂ Significantly Affects Larix kaempferi × Larix olgensis Somatic Embryogenesis

Larch is widely distributed throughout the world and is an important species for timber supply and the extraction of industrial raw materials. In recent years, the hybrid breeding of Larix kaempferi and Larix olgensis has shown obvious heterosis in quick-growth, stress resistance and wood properties. However, its growth and development cycle is too long to meet general production needs. In order to shorten the breeding cycle, we have for the first time successfully established and optimized a somatic embryogenesis system for Larix kaempferi × Larix olgensis. We found that the highest rate of embryonal-suspensor mass (ESM) induction was observed when late cotyledonary embryos were used as explants. The induced ESMs were subjected to stable proliferation, after which abscisic acid (ABA) and polyethylene glycol (PEG) were added to successfully induce somatic embryos. Treatment with PEG and ABA was of great importance to somatic embryo formation and complemented each other's effect. ABA assisted embryo growth, whereas PEG facilitated the formation of proembryo-like structures. On top of this, we studied in more detail the relationship between redox homeostasis and the efficiency of somatic embryogenesis (frequency of ESM induction). During subculture, we observed the gradual formation of three distinct types of ESM. The Type I ESM is readily able to form somatic embryos. In contrast to type I, the type III ESM suffers from severe browning, contains a higher level of hydrogen peroxide (H₂O₂) and demonstrates a decreased ability to form somatic embryos. External treatment with H₂O₂ decreased the somatic embryogenesis efficiency of Type I and type III ESMs, or the higher the exogenous H₂O₂ content, the lower the resulting somatic embryogenesis efficiency. We found that treatment with the H₂O₂ scavenger DMTU (dimethylthiourea) could significantly increase the somatic embryogenesis efficiency of the type III ESM, as a result of a decline in endogenous H₂O₂ content. Overall, these findings have contributed to setting up a successful somatic embryogenesis system for larch production.