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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 dm3 for shoot [shoot induction medium (SIM) medium] and 350 mmol dm3 [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 explantsproducing 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.
The Arabidopsis CDKG;2 gene encodes a putative cyclin-dependent Ser/Thr protein kinase of unknown biological function. This gene shows structural similarity to animal and human cyclin-dependent (PITSLRE) kinases. This study used the homozygous knockout cdkg;2 mutant based on T-DNA insertional line SALK_090262 to study the effect of mutation of the CDKG;2 gene on explant response and in vitro plant regeneration. For callus induction and proliferation, hypocotyls and cotyledons of 3-day-old seedlings of cdkg;2 and A. thaliana ecotype Col-0 were cultured on solid MS medium supplemented with 2,4-D (2 mg l-1). Organogenesis was induced after callus transfer on MS + TDZ (0.5 mg l-1). The initiation time of callus and shoot induction differed between the mutant and control cultures. Shoot regeneration after callus transfer on MS + TDZ was delayed in cdkg;2 (31 days versus 7 days in Col- 0). Shoots formed on callus derived from Col-0 hypocotyls but not on cotyledon-derived callus; in cdkg;2, shoots developed on both callus types. Mutant shoots did not form roots, regenerants were dwarfed, and inflorescences had small bud-like flowers with a reduced corolla and generative organs. Abnormalities observed during cdkg;2 organogenesis suggest a role of CDKG;2 as a regulator of adventitious root initiation.
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