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Antioxidative response of Stevia leaves to low temperature treatment

Stevia (Stevia rebaudiana (Bert.)) leaves are a very good source of natural antioxidants, especially phenolics and flavonoids that protect the human body from free radicals and many chronic diseases. Moreover, antioxidants present the important link in the complex defence mechanisms against reactive oxygen species (ROS). Low temperatures adversely affect the detoxification of ROS and the resistance of certain varieties to low temperatures is laregly based on increased activity of antioxidant enzymes.Being a tropical plant, stevia does not tolerate low temperatures. Nevertheless, regarding its positive effects on human health, it would be useful to expand its breeding area to temperate regions. For that reason, it is necessary to investigate the biochemical mechanisms involved in antioxidative response to the low temperature treatment in stevia leaves. In the present study, plants were exposed to low temperature conditions (4°C)in the dark at different time points with subsequent 24 h recovery period. Biochemical analyses included spectrophotometric determination of total hydrogen peroxide concentration (HP), total phenols (PHE), guaiacol peroxidase (GPX) and catalase activity (CAT) and lipid peroxidation intensity (LP). HP concentration in stevia leaves decreased in low temperature treated plants after 24 h of treatment, followed by an increase to maximum value that did not change after the recovery period. Lowering of HP concentration coincided with 64% increase in CAT activity after 3 h treatment and GPX activity increase by 60% after 6 h of treatment. The significant increase in GPX activity after 36 h of treatment was likely due to the total PHE increase that may be a component of acclimation-induced chilling tolerance. Our results showed that short term low temperature treatment could induce better tolerance of stevia due to increased leaf antioxidative enzymes activities.

Stevia; antioxidant enzymes; total phenols; hydrogen peroxide

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