عنوان مقاله [English]
Introduction: Salinity is one of the most important environmental stresses that reduced the growth, development and production of plants around the world. Stevia is a perennial herbaceous plant of the Asteraceae family. Stevia has a strong sweetening effect due to stoviol glycosides. Since the germination of stevia is poor and the seedling growth rate is slow and slow in the early stages, its evaluation to salinity stress is of special importance. Due to the increasing demand for the use of cultivars with better relative tolerance to non-living environmental stresses is increasing day by day. Also, the desirable properties of stevia for the health of the community and its sweetening and antidiabetic properties were selected for study; due to the different roles of melatonin in the plant, this study was used to investigate its effect on the growth, physiological, morphological and biochemical traits of stevia under salinity stress.
Materials and Methods: In order to investigate effects of melatonin application on growth and physiology and biochemical in salinity stress in Stevia herb, a pot factorial experiment based on completely randomized design with three replications was conducted in the research greenhouse of Agriculture Faculty, Mohaghegh University of Ardebily in 2019. Treatments were consisted of salinity stress at three levels (0, 50 and 100 mM) as the first factor and the application melatonin of at three levels (0, 75, 150 µM) as the second factor. In this experiment, morphological traits including stem length, plant dry weight, stem dry weight and physiological characteristics such as photosynthetic pigment concentration, proline, ion leakage, relative water content, soluble sugar content, catalase, peroxidase and antioxidant activity were investigated.
Results and Discussion: Vegetative traits such as stem length, plant dry weight and stem dry weight, were significantly decreased with increasing salinity stress. Foliar spraying melatonin at high levels of salinity stress improved these traits compared to control plants. Also, the highest chlorophyll a, total chlorphyll and carotenoids content was obtained in control plants (non-salinity stress) with foliar spraying melatonin 150 µM which were 6.64 and 7.46 and 6.24 mg g-1 FW, respectively. The highest antioxidant activity (2.80%), total peroxidaz 0.419 U mg-1 protein min-1) and proline (0.49 mg g-1 DW) and Carbohidrat (92.65 mg g-1 FW) was observed in 100 mM salinity stress treatment and application 150 µM melatonin. But catalase (9.57 U mg-1 protein min-1) in 100 mM salinity stress treatment and application 75 µM melatonin was obtained. The highest relative water content (RWC) was obtained under non salinity stress conditions (control) and application of 150 µM melatonin, Then salinity stress cause decrease this quality but application melatonin cause improve this quality. Maximum level electrolyt leakage leaves also was observed in 100 mM salinity stress treatment and not application melatonin. Decreased vegetative growth due to salinity treatment is probably due to reduced photosynthetic levels as well as reduced photosynthetic pigments such as chlorophyll a and b, net carbon uptake, stomatal conduction and pore closure due to salinity stress salinity and melatonin stress significantly increased the antioxidant activity of stevia leaves. According to the results of this study, it can be said that stevia is a plant sensitive to salinity stress. As increasing salinity stress levels, a significant decrease in growth indices and photosynthetic pigments is seen. The use of melatonin improved these traits under salinity stress. Increasing the amount of melatonin compensated for the damage to the plant. As the biochemical and physiological properties of the plant such as antioxidant activity, the amount of proline, total carbohydrates improved and ultimately increased plant growth; therefore, it can be stated that melatonin consumption can increase the morphological, physiological and biochemical traits of stevia under salinity stress. The results of this study showed that salinity reduces and impairs plant growth and the use of melatonin can reduce the destructive effects of salinity to some extent and increase plant tolerance to salinity.
Conclusions: In general, it could be concluded that using of melatonin under salt stress conditions can increase plant growth and improve Stevia physiology and biochemical traits.