Oxidative events during in vitro regeneration of sunflower

The changes in the activity of some antioxidant enzymes and endogenous H₂O₂ level in zygotic sunflower embryos during organogenesis and somatic embryogenesis were monitored. Pathways of regeneration were induced on media differing with sucrose concentration 87 mmol dm⁻³ for shoot [shoot induction medium (SIM) medium] and 350 mmol dm⁻³ [embryo induction medium (EIM) medium] for somatic embryo induction. Water potential of the explants cultured on SIM increased, while the embryos maintained on EIM showed middle water deficit stress. The pattern of superoxide dismutase (SOD) isoforms was similar in organogenic and embryogenic culture; however, the intensity of MnSOD bands was higher on SIM than on EIM. Differences in catalase activity were observed: high activity on SIM predominated, whereas on EIM it was reduced. The activity of guaiacol peroxidase in the explants producing shoots and somatic embryos differed at the beginning of culture, but became comparable at the time of shoot and somatic embryo formation (day 5). H₂O₂ content was unchanged in organogenic culture, but on EIM it increased on day 1 followed by significant decrease. The results indicate that sugar concentration per se, or via induction of different developmental pathways influences the activity of antioxidant enzymes and also H₂O₂ level in cultured sunflower embryos.