the identification of physiological and biochemical changes in leave and shoot of stevia under low temperature

Low temperature is one of the important limiting factors of growth, development and distribution of plants. Stevia (Stevia rebaudiana) is a sweet medicinal herb that is cultivated in many parts of world and may experiences low temperature in winter. In this study, we aimed to identify physiological and biochemical changes that occur in Stevia exposed to low temperature and enable the plants to survive at low temperature. Stevia grown in vitro and incubated under controlled conditions at 5, 10 and 25 ºC for one month and then physiological and biochemical indicators in leave and shoot were measured. Low temperature decreased the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids in the leaves. In addition, we observed increased accumulation of hydrogen peroxide and malondialdehyde in leaves and shoot of Stevia exposed to low temperature. Low temperature increased the activities of Superoxide dismutase, catalase, ascorbate peroxidase, polyphenol oxidase and guaiacol peroxidase in leaves and shoot of Stevia. Low temperature lead to increased accumulation of secondary metabolites (phenoloc compounds, flavonoids and anthocyanins) and also increased activities of the enzymes of their biosynthesis pathway (phenylalanine ammonia lyase and Tyrosine ammonia lyase) in leaves and shot of Stevia plants. In response to low temperature, Stevia plant increased the accumulation of total soluble sugar, reducing sugar, total amino acids and proline in their leaves and shoot. In general, to cope with low temperature, Stevia evolved a variety of physiological and biochemical mechanisms that can be suggested to use for identifying cold-tolerant stevia cultivars.