摘要
Seeds from Tabebuia roseo-alba lose viability very fast. Moreover, the seed germination rate is very low, reaching approximately 40%. This study aimed at the in vitro induction of embryogenic callus. This technology allows subsequent plant regeneration as an alternative for the production of T. roseo-alba seedlings. Seeds were germinated in vitro and after 20 days, cotyledonary leaves, hypocotyls and root segments excised from these seedlings were used as explants. They were inoculated on MS medium supplemented with sucrose （30 g/L）, agar （5.0 g/L） and different auxins. The effect of 2,4-D, picloram and NAA at concentrations 0.0, 0.5, 1.0, 2.0 and 4.0 mg/L was evaluated. For the analysis of callus with embryogenic characteristics, ultra-structural study by scanning electron microscopy and cytochemical test with carmine were performed. The results showed that the culture medium supplemented with 4 mg/L NAA presented induction of callus with embryogenic characteristics in all explants used, with cotyledonary leaves showing the highest percentage （70% of explants with embryogenic characteristics）. The use of 2, 4-D and picloram was efficient for callus formation in different explants, but no embryogenic characteristics were observed. From the ultra-structural analysis of callus with embryogenic characteristics, it was found that cells from different explant sources had isodiametric format. This format is similar to somatic embryos in globular stage. The cytochemical analysis confirmed the presence of pro-embryogenic cells in callus mass. Callus induced from cotyledonary leaves presented 46% positive reaction to carmine acetic.
