Propagação in vitro de serralha (Sonchusoleraceus L.) sob diferentes comprimentos de onda, intensidades luminosas e ventilação natural

Abstract

Sowthistle (Sonchus oleraceus L.) is a plant well known for its medicinal properties, being part of human food, important due to its nutritional characteristics and for presenting phenolic compounds in its composition. Physical factors, such as light intensity, light quality and the growing environment, directly influence the growth and secondary metabolism of the medicinal plants. This work aimed to evaluate the in vitro plantlets production of Sonchus oleraceus under the effect of photon flux intensities, wavelengths and natural ventilation systems on growth, photosynthetic pigments and accumulation of phenolic compounds. In the light intensity experiment, nodal segments were grown in MS culture medium under intensity of 26, 70, 100, 113 and 144 μmol m-2 s-1. In the light quality experiment, nodal segment seedlings were inoculated on MS medium under seven LED light spectra: red; blue; green; white; 70% red: 30% blue; 50% red: 50% blue; 30% red: 70% blue. In the natural ventilation systems (SVN) experiment, nodal segments with one pair of leaves were grown in four ventilation systems: conventional system (SC), ventilation system with microporous membrane in the lid with one hole (SVN1), with two holes (SVN2) and four holes (SVN4), in the absence of sucrose. The experiments were evaluated after 40 days of cultivation regarding: number of leaves, leaf, stem and root dry matter, photosynthetic pigments and total phenolic compounds contents. Sowthistle seedlings grown under high light intensities produced greater number of leaves (> 0.6 cm) and low light intensities produced greater number of leaves (< 0.3 cm). Higher light intensities provided greater dry matter accumulation for all variables analyzed. Intensities above 70 μmol m-2 s-¹ promoted higher photosynthetic rates. The light spectra affected the dry matter gain of Sonchus oleraceus seedlings in vitro. Plantlets under white LED light indicated the highest leaf, stem, root and total dry matter accumulations followed by the 70%V:30%A spectrum. In the monochromatic red and green spectra the seedlings showed a tendency to stiolate. Green light induced higher chlorophyll a, b, and carotenoid contents followed by the 70%V:30%A combination. Plantlets grown under white LED light showed the highest values for phenolic compounds. The natural ventilation system with more porous membranes influences the growth of saw palmetto in vitro. In the ventilation system with four porous membranes (SVN4), the seedlings achieved the highest values for leaf number and dry matter (SFM, SCM, SRM and TSS) and also for photosynthetic pigments (chlorophyll a, b and carotenoids). The contents of phenolic compounds were higher in the four-membrane ventilation system (SVN4). Therefore, the results indicated that the Sonchus oleraceus plantlets had a better development at intensities between 70 and 144 μmol m-2s-1, in the white light spectra and in the four-membrane ventilation system (SVN4).