Embriogênese somática direta e indireta em cana-de-açúcar: busca de correlações com o estresse in vitro

Abstract

The somatic embryogenesis is a technique of in vitro culture applied in clonal propagation of plants and regeneration of genetically transformed cells, in addition to supporting basic studies related to morphological, molecular and biochemical events that happen during the embryogenic process. The initial stages of this morphogenic pathway are characterized by the induction of genes related to stress, which leads to the hypothesis that somatic embryogenesis is an extreme response to stress in plant cells cultivated in vitro. In this work, were induced embryogenic pathways direct and indirect in the RB 872552 variety of sugarcane and analyzed the activity of enzymes from antioxidant system in order to assess the correlation between somatic embryogenesis and regulation of oxidative stress. For the direct pathway (ESD), were applied four treatments (TS, TD, TG e TA) based on protocols previously described for sugarcane. These protocols differed as to the composition of the medium and incubation condition (dark or light period of 16 hours) in a completely randomized design with 10 replications per treatment. For the indirect pathway (ESI), were used by eight different treatments combinations of four concentrations of 2,4-D (2,4-dichlorophenoxyacetic acid) and two Fe-EDTA, in a factorial 4x2 and 20 replicates per treatment. Were calculated the indices of embryo formation (IFE) and callus (IFC) and evaluated the activity of catalase, peroxidase and polyphenoloxidase. Somatic embryos were visualized only in the treatment of ESD plus 2,4-D and BAP (6-benzylaminopurine), and treatment of ESI with 8 mg.L-1 2,4-D. The conversion of somatic embryos into plants was performed in culture medium without added phytoregulators. The activity of antioxidant enzymes was obtained by reading of a spectrophotometer, from the extract obtained from embryogenic and non-embryogenic tissues treatment of ESD. The polyphenoloxidase and catalase activity increased in non-embryogenic tissue, whereas peroxidase was less active in these tissues when compared to embryogenic. It was found that the induction of somatic embryogenesis in the variety studied is related to oxidative stress and that these antioxidant enzymes may become important as biochemical markers of this process.