Aspectos fisiológicos da cana-de-açúcar sob o cultivo in vitro em diferentes microambientes

Abstract

The objective of this study was to evaluate the in vitro development and antioxidative response of cane sugar, micropropagated in different conditions of gas exchange, sucrose and light. Plants were grown in multiplication and rooting medium, composed of: MS salts and vitamins, supplemented with 30 g L-1 sucrose, 100 g L-1 of inositol, 8 g L-1 of agar and 0.3 of mg L-1 kinetin, 0.2 mg.L-1 BAP (multiplication) or 1 mg.L-1 NAA (rooting). To evaluate the effect of gas exchange, we used 4 different caps, which allow different schemes of gas exchange (0.0787 ml d-1; 0.3446 ml d-1; 0.7330 ml d-1; 1.1970 ml d-1) in a growth room at 27 ± 2 °C with 16 hours photoperiod under a light intensity of 47.6 μmol m-2 s-1. In the experiment that evaluated the interaction effect between gas exchange and sucrose concentration in the culture medium, we used three concentrations of sucrose (0, 30 and 15 g L-1) and three regimes of gas exchange (0.0787 ml d-1, 0.3446 ml d-1 and 0.7330 ml d-1). In the experiment that evaluated the interaction between gas exchange, sucrose and light intensity, plants were grown at a temperature of 30 ± 1 ° C with a photoperiod of 16 hours in three different light intensities (55.2 μmol m-2 s-1, 100.8 μmol m-2 s-1, 147.9 μmol m-2 s-1), two concentrations of sucrose (30 to 15 g L-1) and two gas exchange systems (0.11 and 0.59 ml.d-1). Biometric parameters and the antioxidant enzymes activity of peroxidase, catalase, ascorbate peroxidase and polyphenol oxidase were evaluated in the late phase of multiplication and rooting. In the experiment that evaluated the four regimes of gas exchange, the plants showed high mortality in 1.1970 ml.d-1 gas exchange. However, the conditions of 0.3446 ml d-1 until 0.7330 ml d-1 gas exchange, showed the highest values of fresh weight and leaves number, promoting a decrease in activity of antioxidant enzymes when compared with the control treatment (0.0787 ml.d-1). In the experiments evaluating that evaluated the interaction between the gas exchange and sucrose showed that the reduction in sucrose of 30 to 15 g.L-1 promoting a reduction in dry weight, and the absence of sugar in the culture medium led to the death all plants at the end of the multiplication phase. There was an increase in biomass and number of leaves with the increase in gas exchange. In the rooting phase the increasing of gas exchange stimulated the production of roots. The enzyme activity in the rooting phase, for all enzymes showed significant differences in gas exchange and sucrose factor. What was observed is that the treatments with 0.3446 ml d-1 (with 15 and 30g L-1 sucrose) in all the enzymes analyzed, showed significantly lower mean of enzymatic activity. The effect of the interaction between gas exchange, sucrose and light intensity showed better growth and reduction of enzyme activity with 30g L-1 sucrose, 100.8 μmol m-2 s-1 light and evaporation rate of 0.59 ml d-1 treatments. The results suggested a reduction in oxidative stress and improved development of the plants under conditions that increased light intensity and gas exchange as compared to the cultivation system with sealed caps and low light.