Micropropagação de Phyla betulifolia sob a intervenção de luz e ventilação: crescimento vegetativo, anatomia, defesa antioxidante e fração volátil

Abstract

Environmental factors are important parameters that influence the growth and in vitro metabolism of plants. Phyla betulifolia (Kunth) Greene (Verbenaceae) is a medicinal plant that presents a potential therapeutic use. The objective of this study was to evaluate the effects of the natural ventilation system (SVN) and of different intensities and light qualities on vegetative growth, anatomy, antioxidant defense, photosynthetic pigment accumulation and volatile chemical composition of P. betulifolia. Electronic and light microscopy techniques were used for anatomical evaluations. The antioxidant defense was evaluated by classic non - enzymatic antioxidant defense methods (free radical capture - DPPH, total antioxidant capacity - CAT, chelating power and reducing power). Dosing analysis of photosynthetic pigments and phenolic composition were performed by spectrophotometric methods and volatile fraction by headspace-GC/MS. Nodal segments of P. betufolia were inoculated in flasks with 45 mL of MS medium and sealed with caps containing 0, 1, 2 and 4 holes, respectively named by SM (without membranes), SVN 1, 2 and 4. The flasks were kept under light intensity of 32 μmol m-2 s-1 , for 45 days. The SVN4 treatment provided better conditions for the accumulation of leaves, stem, root and total dry matter. SVN4 also accumulated greater amount of photosynthetic pigments and presented the best results of antioxidant defense regarding CAT, DPPH, chelating power and reducing power assays. The light intensity was evaluated from nodal segments pre-established in MS medium, which were inoculated in culture tubes with 15 mL of MS medium and submitted to different light intensities 20, 57, 78, 102, 139 μmol m-2 s-1 , being evaluated after 45 days. The light intensity

of 139 m-2

s-1 provided a higher accumulation of dry matter (MSF, MSR and MST). However, this treatment was responsible for the lower contents of chlorophyll a, b and carotenoids, as well as lower antioxidant defense by DPPH radical capture method. 25 volatile compounds were detected, without qualitative and quantitative differences between the treatments. Regarding light quality, nodal segments were inoculated in culture tubes with 15 mL of MS medium and cultured under different spectra: red (V); blue (A); combinations of blue and red A:V (1:2.5; 2.5:1; 1:1); white LED (BR); green (VD); and yellow (AM), obtained by Light Emitting Diodes (LEDs) and cold white fluorescent (FL), for 45 days. The A:V light combinations (1: 2.5 and 1: 1) were responsible for the greater accumulation of dry matter. The accumulation of chlorophyll a and carotenoids was higher in VD, chlorophyll b and total in AM. The levels of CFT and antioxidant activities evaluated by CAT, DPPH and chelating power methods were higher in A treatment. The chromatographic profile obtained for the V samples indicated differences in the qualitative chemical composition of the samples, being the one that presented a smaller number of constituents. At the end of the experiments, it was observed that the best in vitro culture conditions for P. betulifolia were reached in the SVN4, at the highest light intensities (102 and 139 μmol m-2 s-1 ), under A light spectrum and combinations of A:V (2.5:1 and 1:2.5), being these treatments that presented more developed plantlets and with better conditions for the acclimatization phase.