Rizogênese em brotações micropropagadas de casaqueira (Campomanesia rufa)

Abstract

Campomanesia rufa (O. Berg.) Nied. also known as casaqueira is a native fruit plant from Brazilian Savannah and stands out for its medicinal potential. However, there is a difficulty on Campomanesia genus propagation due to its recalcitrant seeds and natural habitat degradation. Thereby, the micropropagation of these species rises as an promising alternative. The rooting stage is a critical phase on micropropagation, being essential to obtain viable seedlings. The goal for this project was to study and evaluate the role of auxin on the in vitro and ex vitro adventitious rooting process, which is extremely important to multiplicate and maintain C. rufa conservation, helping to understand the biochemical and histological alterations of its rhizogenesis. IAA and IBA were the auxins evaluated on this project, the concentrations used in vitro were 0, 1, 5 and 10 μM along with the MS medium supplementation. The concentrations used ex vitro were 0, 500 and 1000 μM by the rapid immersion method. For the histological analysis, the samples were embedded in Historesin® and stained with 0,5% Toluidine Blue, and analyzed in light optic microscopic. The biochemical analysis of Peroxidase (POD), Catalase (CAT) and Superoxide dismutase (SOD) activities, hydrogen peroxide (H2O2) and lipid peroxidation content for the optimum treatment of the ex vitro group were evaluated, alongside with the control group. The application of 10 μM of IBA in vitro presented the best results through indirect organogenesis. This indirect pathway was confirmed through histological analysis, with which the primordium formation was observed from the callus, without any vascular connection with the stem tissue. The immersion with 500 and 1000 μM of IAA showed the best results ex vitro, therefore the 500 μM is recommended due to its lower cost. On the ex vitro rooting, the direct pathway was confirmed through histological analysis, with the primordium being formed from the vascular tissue cells, probably from the cambium. The exogenous application of IAA increased the POD activity in the induction phase, by rising the cell wall rigidness and modulating the IAA levels at shoots. In this stage, there is also an increase in CAT activity, which along with SOD operates upon ROS scavenging, mitigating the lipid peroxidation. In the initiation phase, SOD and CAT continue to modulate the ROS levels in order to maintain lipid peroxidation at base levels. The cell wall became thinner due to POD activity decline, which allowed the begging of cell division, forming root primordium. In the expression stage, CAT and POD activities decreased, promoting a rise on the H2O2 content and lipid peroxidation causing the plasma membrane softening, which alongside with cell wall thickness reduction enables cell elongation required to emerge the root primordium.