Relações da irradiância com o crescimento e compostos fenólicos em plantas de Moringa oleifera

Abstract

Solar radiation is an important factor for the growth and development of plants, not only because it is a primary source of energy, but also because it acts as a stimulus that modulates development. However, when available in high intensity can be a factor stressing the vegetable. In these conditions the excess of photochemical energy causes damage, mainly to the photosynthetic apparatus. To minimize effects such as these, the plants developed defense mechanisms such as the action of enzymatic and non-enzymatic agents. Secondary metabolites, especially flavonoids, act as filters against UV radiation, as well as being an important source of pharmacologically active products, often found in leaves. Moringa oleifera, commonly known as moringa or acácia-branca, is a rustic, medicinal and ornamental plant, rich in bioactive molecules with high nutritional value that has been widely used in the pharmaceutical, cosmetics, food and biodiesel industries. Studies that relate the effects of the intensity and quality of the solar radiation on the growth and accumulation of secondary compounds in moringa plants are inexistent. Thus, the objective of this study was to evaluate the physiological performance, growth and accumulation of phenolic compounds in moringa plants due to the alteration in the quality and intensity of solar radiation. Plants of M. oleifera were cultivated for five months at different levels of shading: full sun (FS), black (BLN), blue (BN) and red (RN) nets. Differences were observed in all analyzed variables: growth, gas exchange and phenolic compounds content. Plants cultivated in FS presented inferior shoot growth compared to the other treatments, differing also in gas exchange and foliar anatomy. At all levels of shading, the leaves presented higher protein and total amino acids content in relation to the roots. The leaves of plants cultivated under RN and BN presented, respectively, higher content of phenolics and total flavonoids. The use of nets contributed to the greater growth and partition of dry biomass between leaves and roots, in addition to minimizing the damages caused by high levels of irradiance. The present study, besides providing an understanding of the effects of the alteration in the quality and intensity of solar radiation on the ecophysiological behavior of M. oleifera plants, may provide support in future research on optimization of the production of secondary metabolites for this species.