Histological changes and differences in activities of some antioxidant enzymes and hydrogen peroxide content during somatic embryogenesis of Musa AAA cv. Yueyoukang 1

Abstract

To determine the possible involvement of oxidative stress in somatic embryogenesis of banana (Musa spp.), and provide a means to overcome the recalcitrance in embryogenesis, changes in histology, hydrogen peroxide (H2O2) content and antioxidant enzyme activities during banana somatic embryogenesis were investigated. From embryogenic cells (ECs) to early globular embryos, nearly all cells showed typical meristematic characteristics with a high nucleus/cytoplasm ratio. Cells started to lose their meristematic characteristic during later globular stage. Starch granules in cells showed spatial and temporal changes during somatic embryogenesis. POD (E.C.1.11.1.7) activity decreased significantly after transfer of ECs to the embryo regeneration medium which was followed by a significant increase and peaked at the late stages of embryogenesis. CAT (E.C.1.11.1.6) activity showed similar pattern, however its highest activity appeared in the ECs instead of the later embryos. On the contrary, a gradual increase in SOD (E.C.1.15.1.1) activity was observed after inoculation of ECs on embryo regeneration medium until the globular stage. Similarly to SOD activity, the hydrogen peroxide (H2O2) content also increased after inoculation of ECs on embryo regeneration medium and it peaked in proembryos, followed by a significant decrease in later embryogenic stages. The H2O2 content as well as activities of all tested antioxidant enzymes were significantly higher in ECs than in non-embryogenic cells. These results suggested that high levels of antioxidant enzyme activity and high H2O2 content were necessary for embryogenic competence of ECs while high H2O2 content played an important role in early development of somatic embryogenesis of banana.