Programmed cell death occurs in browning explants of Fraxinus mandshurica during somatic embryo-genesis, but the underlying mechanism is unclear. In this study, single cotyledons of zygotic embryos of F. mand-shurica were used as explants. Mitochondrial structure and function, caspase-3-like protease activity, hydrogen perox-ide metabolism, and nitric oxide accumulation induced by high concentrations of sucrose and plant growth regulators were studied. The results show that plant growth regulators induced somatic embryogenesis and also promoted explant browning. High sucrose concentrations had similar effects. High concentrations of sucrose and plant growth regulators led to the accumulation of hydrogen peroxide and nitric oxide which induced changes in mitochondrial structure and function such as modifications in mitochondrial mor-phology, increased membrane permeability, decreased mem-brane potential, and the release of cytochrome c into the cytoplasm. An increase in caspase-3-like protease activity triggered programmed cell death in some browning explant cells. During somatic embryogenesis there were increased activities of superoxide dismutase, peroxidase, and catalase, which are associated with hydrogen peroxide metabolism and jointly maintain reactive oxygen species levels. Intracel-lular nitric oxide synthase and nitrate reductase activities were not significantly correlated with nitric oxide content. Instead, intracellular nitric oxide may be derived from non-enzymatic reactions. Our results indicate that hydrogen peroxide and nitric oxide may function as signals, playing key roles in somatic embryogenesis and programmed cell death of explant cells of F. mandshurica . The interaction between nitric oxide and reactive oxygen species determines the occurrence of programmed cell death in explant cells; somatic embryogenesis and programmed cell death are posi-tively regulated by hydrogen peroxide. However, the regula-tion of nitric oxide is complex.

Hao Wang;Dongyan Zhang;Juan Luis Fernández-Lorenzo;Hailong Shen;Ling Yang

State Key Laboratory of Tree Genetics and Breeding,School of Forestry,Northeast Forestry University,Harbin 150040,People's Republic of China;Crop Production Department,High Polytechnique School of Engineering,Santiago de Compostela University,Lugo,Spain

林业研究（英文版）

[1]Hao Wang;Dongyan Zhang;Juan Luis Fernández-Lorenzo;Hailong Shen;Ling Yang-.Reactive oxygen species, nitric oxide and plant cell death associated with caspase-like protease activity during somatic embryogenesis in Fraxinus mandshurica)[J].林业研究（英文版）,2022(03):1005-1017

cotyledons,shurica,Intracel

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