Extrato aquoso de folhas de alface roxa: indução de tolerância ao estresse salino em alface

Abstract

Salt stress negatively affects the manifestation of physiological potential for germination, seed vigor and reduced seedling development. Moreover, the salinity can affect cell division by inhibiting the mitotic index and causing chromosomal abnormalities, as well as increase the production of reactive oxygen species. Plants, in turn, can react to this stress with morphological adjustments, biochemical, physiologic, cellular and molecular, and some of these adjustments can be induced by a wide variety of secondary metabolites that is produced for the plant's natural defense. Substances such as β-carotene, vitamins C and E and phenolic compounds are related to the antioxidant capacity of various vegetables and help to reduce the effects caused by salinity. In this scope, plant extracts have been studied, since the mechanism of action of antioxidants present in plant extracts, it has an important role in reducing lipid oxidation in plant and animal tissues, under stress conditions. Lettuce is the hardwoods vegetable more important in Brazil, beyond of vitamins and minerals, has carotenoids and a high content of phenolic compounds. Purple varieties have also a lot of anthocyanins, which gives them greater antioxidant activity. The aim of this study was to characterize the effect of purple lettuce leaf extract on the physiological quality, cytogenetics and antioxidant activity during germination and initial growth of lettuce seedlings, under different salt concentrations, to elucidate possible mechanisms of tolerance which may serve as a basis for future studies with other cultures. Experiments were performed in the laboratory and greenhouse, where lettuce seedlings, cultivar Regina, were submitted during the initial stages of development, a different concentrations of purple lettuce leaf extract combined or not with salt solutions, being evaluated parameters related to germination, biomass production, cell division and antioxidant activity. The use of purple lettuce extract provides increases in seed germination, assists the early development of seedlings, as well as decreases the oxidative stress caused by the salt, justified by the increase in the chlorophyll and nitrogen index and by the lower concentration of sodium in the leaves. The purple lettuce extract does not affect the mitotic index, reduces the cell index in prophase and increases the incidence of cells in telophase of lettuce roots. Salt stress negatively affects the development of lettuce seedlings.