Caracterização dos mecanismos morfofisiológicos e teor de óleo essencial de espécies de Piper em resposta a intensidades de radiação

Abstract

Species of the genus Piper have economic importance, being used in the food, pharmaceutical and agriculture industries. As a highlight in this genus the black pepper (Piper nigrum L.), which produces the most consumed condiment in the world. Among the environmental factors that influence the development and production of plants, solar radiation stands out, as it induces highly plastic adaptive responses providing adjustment in the growth and in the photosynthetic apparatus and in the metabolism of essential oils. Thus, in order to understand the plasticity of the species of the genus Piper due to different environments of incident solar radiation, the objective of this study was to evaluate changes in growth, essential oil content, photosynthetic pigments, anatomy, in the transient fluorescence of chlorophyll “ a ”and gas exchange in wild species of medicinal importance, found in different environments in the natural condition (Piper tuberculatum Jacq. and Piper arboreum) and the best known pepper cultivar in the world, 'Bragantina' ('Panniyur 1 '). The experiment was carried out with two native species (Piper tuberculatum Jacq. And Piper arboreum Aubl.) And black pepper. Seedlings of native species were obtained via seminal and black pepper, by cutting, being transplanted into 5- liter pots and acclimatized for 30 days in a nursery with 50% of incident solar radiation. After this period, the plants were exposed to different light environments (100% solar radiation or full sun, 50% and 20% radiation, using a black Sombrit® shade screen). After six months, growth, biomass allocation, essential oil content, chlorophyll fluorescence were evaluated using the Handy PEA fluorometer, quantification of photosynthetic pigments, point gas exchange with 1200 μmol photons, and light response curves, in addition to leaf, stem and root anatomy. The data were submitted to analysis of variance and the means grouped by the Scott Knott test (p <0.05). Principal component analysis (PCA) was performed and for the similarity calculation a matrix was obtained using the Euclidean distance and the grouping performed based on the UPGMA method (unweighted pair-group method with arithmetic means). The three species when grown at 100% of incident solar radiation showed greater investment in the root system, increasing the length, volume, number of roots and dry mass. However, those that were grown with low incident solar radiation invested in aerial parts, increasing the leaf area, the length of the stem and the number of leaves. The highest content of essential oil was obtained in the roots of P. nigrum grown at 50% radiation (1.59 g g-1 MS). The cultivation of species with 100% of incident solar radiation caused a reduction in the number of open reduction centers, thus causing an increase in F0, this increase being more evident in P. nigrum. The oxygen evolution complex and the energy connectivity of the components of photosystem II were affected when P. arboreum and P. nigrum grew under high incidence of solar radiation. P. tuberculatum showed higher A / E, Amax, LSP, LCP, collenchyma thickness, number of xylemic vessels in the leaves when cultivated with 100% solar radiation. The 20% and 50% environments influenced the quantum yield (i), xylem length, gs. P. nigrum showed an increase in φ (Io) Amax, in the environment of 20% of incident solar radiation. However, gs, E, RD, stem epidermis thickness and root xylem length and leaf water potential (Ѱw), showed better performance when the plants were kept at 100% radiation. The results of this experiment prove the loss of plasticity of the cultivated species, and improvement studies are recommended to develop more tolerant genotypes for shaded cultivation and establishes that P. tuberculatum can be used as a model of plasticity.