The effect of putrescine and calcium nanoparticle on photosynthetic pigments and antioxidant enzymes activities in stevia (Stevia rebaudiana Bertoni) under salt stress

The objective of this study was to evaluate the effect of different concentrations of calcium nanoparticle and putrescine on some physiological traits of the medicinal plant, stevia, under salt stress. In this regard, the experiment was performed based on a factorial completely randomized design with three replications. The experimental treatments contained three levels of calcium nanoparticle (0, 75, and 150 ppm), two levels of putrescine (0 and 1 mM), and three levels of salt (0, 75, 150 mM). Based on analysis of variance results, the simple effect of each treatment as salt stress, calcium nanoparticle, and putrescine was significant at P≤0.05; however, their interaction effect was not significant. Results also showed that salt stress (150 mM) resulted in the reduction of chlorophyll a (0.21), chlorophyll b (0.47), and total chlorophyll (0.68 mg/g dry weight) compared to the control while, an increase in carotenoid content (0.10) was observed under 150 mM salinity. Also, the photosynthetic pigments content increased under 150 ppm calcium nanoparticle and 1 mM of putrescine. Considering antioxidant enzymes, the treatment with 150 mM salt increased catalase enzyme as 1.69 and as 5.02 g/wet weight. In addition, the effect of putrescine led to the increase of catalase and peroxidase by 2.18 and 4.46 g/wet weight of leaves, respectively. Moreover, the treatment with 150 ppm calcium nanoparticles resulted in increases in catalase and peroxidase contents by 1.87 and 4.84 g/wet weight of leaves, respectively. The most appropriate concentrations of putrescine and calcium nanoparticles were 1 mM and 150 ppm, respectively which are recommended for assessment of other physiological and biochemical properties of stevia.