Physiological Mechanism Of Ascorbic Acid Affecting Somatic Embryogenesis Of Fraxinus Mandshurica

Fraxinus mandshurica is a native broad-leaved tree species in north China and plays an important role in production ofbuilding materials,furniture and street virescence.For developing the resources of.mandshurica by using the improved materials,research into the somatic embryogenesis with the large scale propagation potential become urgent.Through adding exogenous antioxidant ascorbic acid(ASA)and the oxidant hydrogen peroxide(H2O2)into the medium,the physiological and biochemical effects of ASA during the somatic embryogenesis of E mandshurica by the mature embryo cotyledonary explants were tested,and the relationships among the explants ASA,ASA-GSH,H2O2 and NO during somatic embryogenesis of.mandshurica were revealed by combining with the metabolic changes of intracellular hydrogen peroxide(H2O2)and nitric oxide(NO),this could provide some physiological basis for optimizing the somatic embryogenesis of.mandshurica.The main results are as follows:(1)Somatic embryogenesis of F.mandshurica were conducted by using mature zygotic embryos as explants and adding ASA into the medium Low concentration ASA(10 mg*L-1 and 20 mg·L-1)inhibitd the browning of explants while the higher concentration of ASA(100 mg·L-1)promoted the browning of explants,increased the content of intracellular polyphenol,the activity of polyphenol oxidase(PPO)and phenylalanine ammonia lyase(PAL)significantly.The low concentration of ASA(10 mg·L-1)inhibited the somatic embryogenesis and significantly reduced the induction rate of somatic embryos from mature zygotic contyledonary explants of.mandshurica.Higher concentration ASA treatments(50 mg·L-1 and 100 mg·L-1)significantly increased the somatic embryo induction rate of mature zygotic cotyledon explants of.mandshurica.Among them,the high concentration ASA(100 mg·L-1)could significantly increase the somatic embryo induction rate of mature zygotic embryo explants from different provenances which indicates that ASA plays a key role as a two-way regulator in the somatic embryogenesis of.mandshurica.(2)In the early stage of somatic embryo induction(0-28d),the main function of ASA in explant is extracellular degradation.As a precursor oxide,it could release hydrogen peroxide(H2O2)and promote the browning and death of explant cells.During the somatic embryogenesis,the intracellular ASA-GSH cycle was dominant and the ASA could eliminate hydrogen peroxide(H2O2)even provide positive protection for somatic embryogenesis as an antioxidant.(3)In the process of somatic embryo induction of.mandshurica,the content of intracellular hydrogen peroxide increased first and then decreased and the enzymatic(SOD,CAT)and non-enzymatic(ASA-GSH cycle)reactions related to these reactions regulate the dynamic balance of intracellular hydrogen peroxide.The intracellular NO may play an important role in the regulation of somatic embryogenesis as the hydrogen peroxide(H2O2).