Uso de citocininas não convencionais (meta-topolinas) no controle de anomalias em plantas micropropagadas : redução de perdas na micropropagação

Abstract

This paper has analyzed the morphophysiological and biochemical responses in sugarcane plants (Saccharum spp) and cactus pear (Opuntia stricta Haw) in function of exposition to various kinds and concentrations of cytokinins during these species’ micropropagations. The cytokinins are growth regulators which are largely used in the multiplication phase to induce breaking of the apical dominance, stimulating cell division and budding of lateral buds. The 6-benzylaminopurine (BAP) is the most used cytokinin in the micropropagation industry due to its effectiveness and accessibility; however it may incur abnormal growth in some plants. A kind of aromatic, non-conventional cytokinin, the meta-topolin (mT), has been an alternative to BAP for the purpose of reducing occurrence of morphophysiological disorders. Morphophysiological anomalies like fasciation in sugarcane and hyperhydricity in cactus pear, are problems caused by excessive exposure to BAP. The work was done in the Laboratório de Cultura de Tecidos Vegetais/UFRPE with collaboration of the Biofábrica Governador Miguel Arraes/CETENE. Sugarcane plants of the RB98710 variety were grown in static liquid system in various cytokinin concentrations (6,66 μmol L-1 of BAP; 5 μmol L-1 of BAP or mT). Buddings of cactus pear from variety Orelha de Elefante Mexicana, growth in vitro were used in the experiment. The treatments consisted in two kinds of cytokinins, BAP and mT in concentrations of 2,22 μmol L-1 of BAP, 1,11 μmol L-1 of BAP or 1,11 μmol L-1 of mT in static system in liquid or solid medium. Analysis were realized for multiplication ratio, fresh matter, height, analysis for enzymatic activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT), as well as quantification in hydrogen peroxidase (H2O2) and malondialdehyde (MDA). In sugarcane it was observed that the mT promoted the higher rate on multiplication and higher height of plants and tillers. The role of hydrogen peroxyde in plant growth and development was observed. The plants submitted to higher BAP concentration displayed a higher MDA content. In the cactus pear growth it was observed that high concentrations of BAP favored the reduction of fresh matter, as well as buddings’ height. Formation of buds in liquid medium happened, in low amounts compared to solid medium. The hyperhydricity characteristics were more intense in buds grown with BAP. The hyperhydric buddings displayed a purple coloring, primarily in the podaries. From this paper it was verified that the sugarcane variety RB98710 responded positively to mT addition. The use of mT in cactus pear micropropagation in MS solid medium leads to promising results for bud production.