Efeito do frio sobre os carboidratos solúveis em culturas embriogênicas de Acca sellowiana O. Berg (Myrtaceae)

Abstract

The pathway of somatic embryogenesis in Acca sellowiana, a fruit tree species with limitations concerning vegetative propagation, was well established but the number of embryos that restart growth after the cotyledonary phase is low. In this work, somatic embryos at different developmental stages obtained after treatments with 2,4-D were submitted to cold (4 °C) during 20 days to induce transformation of embryos into plantlets. High proportion (95%) of somatic embryogenesis was found from zygotic embryos treated with 2,4-D continuously (T1) when compared to transitory treatment with 2,4-D (T2 - 55%). However, T1 induced higher rates (82%) of deformation than T2 (62%). In both treatments, no plantlets were obtained from somatic embryos after cold. In T1, 50% of the embryos cultivated at the globular phase remained quiescent and only embryos at the cotyledonary phase (76%) showed positive responses indicating restart of growth. In T2, only 30% of embryos at cotyledonary phase turned greenish, and presented higher values of total sugars. The carbohydrate analyses showed myo-inositol, glucose, fructose and sucrose as the major components, present in different proportions, the latter decreasing during the culture period. The low levels of raffinose during the growth period and their reduction under cold treatment could be related to changes of the normal somatic embryo development, without accumulation of carbohydrates, thus inhibiting plantlet regeneration.