Rustificação in vitro de Lippia grata Schauer : Iluminação de lâmpadas LED x ventilação natural

Abstract

Lippia grata Schauer is an aromatic species, endemic to the Brazilian Northeast and of recognized medicinal importance due to the anti-inflammatory, antioxidant and antimicrobial activity present in its essential oils, making it a promising natural resource in the treatment of diseases. In vitro cultivation could make the use of its medicinal potential more efficient without the need to affect its natural habitat by anthropogenic actions. In this sense, the present research aimed to evaluate, with a morphophysiological and biochemical focus, L. grata plants grown in vitro under the use of LED lamps associated with natural ventilation in the flasks. The experimental units were constituted by nodal segments of L. grata, 1 cm long, removed below the apical bud and inoculated in flasks containing 10 mL of MS nutrient medium supplemented with 30 g L-1 of sucrose, gelled with 2.5 g L-1 phytagel and pH adjusted to 5.7. The natural ventilation of the flasks was controlled by two types of partial (ventilation) and total (non-ventilation) seals, distributed randomly in four different lighting systems, LVA 5: 1 = Red and Blue LEDs (5: 1) ; LVA 1: 1 = Red and Blue LEDs (1: 1); LB = White LED and FL = Fluorescent Lamp, calibrated at 60 μmol m - 2 s - 1 of luminous intensity inside a growth room with photoperiod of 16 hours, 80 ± 5% relative humidity and temperature of 25 ± 2 ° C , for 45 days, under a completely randomized design (DIC), with a 4x2 factorial arrangement, with 3 replicates, each replicate being 15 experimental units. On the 45th day, the plants were analyzed according to their biometric, biochemical and histological parameters. In this sense, we show that the natural ventilation of the flasks reduces the incidence of hyperhydric leaves in all lighting systems by 62%, presenting larger plants and more expanded leaves, and in these conditions the plants reduced their fresh mass by 27% indirectly evidencing the effect of gaseous exchange. The biochemical parameters of the plants were also positively influenced by the natural ventilation of the weak ones, since the contents of chloroplastídicos pigments and total soluble carbohydrates contents increased by 46% and 115%, respectively. In addition, under a histological approach we observed that there was a greater cellular organization of the epidermis and cortical parenchyma of the main leaf vein, a situation that was not observed in plants with conditions without ventilation. The influence of the lighting systems was also remarkable, especially the White LED, since it presented plants with less number of hyperhydric leaves even in non-ventilated bottles, which translates into a larger number of normal leaves, in addition to showing a greater number of shoots and roots. Also, the White LED associated with natural ventilation conditions was the only lighting system that promoted significant increases in chlorophyll a; chlorophyll b; total chlorophyll (a + b); carotenoids; total soluble carbohydrates; and sucrose in 87%; 143%; 102%; 76%; 223% and 116%, respectively, compared to that obtained under non-ventilated conditions. In view of this, we concluded that there is a synergistic effect in the use of White LED lamps associated with natural ventilation conditions of the weaker ones in the in vitro culture of L. grata as they contribute to the reduction of hyperhydric symptoms and stimulate a greater metabolic activity expressed through increase in their biochemical parameters.