Stevia rebaudiana Bertoni is a famous medicinal plant for its low calorific value compounds which are named steviol glycosides (SGs) and they are 150-300 times sweeter than sugar. Among various SGs, stevioside and rebaudioside A considered to be the main sweetening compounds. Soil salinity is one of the most essential stress in the world. Salinity affects the survival and yield of crops. In current study the effects of salinity and osmotic stress caused by different concentration of NaCl (0, 20, 40, 60 and 80 mM) on morphological traits, genes expressionand amount of both stevioside and rebaudioside Aunder in vitro conditions has been investigated. The morphological traits such as bud numbers, root numbers, shoot length (after 15 and 30 days) were evaluated. With increasing salinity, the values of all studied morphological traits decreased. To investigation of UGT74G1 and UGT76G1 genes expression that are involved in the synthesis of SGs, RT-PCR was done and there were significant differences between all media. The highest expression of both genes was observed in plantlets grown on MS media (with NaCl-free). Also, the lowest amounts of gene expression of the both genes were seen in MS+ 60 mM NaCl. Based on HPLC results, the highest amount of both stevioside and rebaudioside A were observed in plantlets grown in MS media (with NaCl-free). Finally, it can be concluded that stevia can survive under salt stress, but it has the best performance in the lower salinity.
Stevia rebaudiana Bertoni is one of the most important biologically sourced and low-calorie sweeteners that contains a lots of Steviol glycosides. Tissue culture is the best method for propagation of stevia and micro nutrients can affect both morphological traits and steviol glycosides production. In the present study, we investigated the effect of different concentrations of glutamine (10, 20, 30 and 40 g/l) on expression of UGT74G1 and UGT76G1 genes and stevioside and rebaudioside A accumulation in the leaves of stevia under in vitro conditions. The highest level of expression for UGT74G1 (1.000 Total lab unit) was seen at plants grown in MS media without glutamine and the highest gene expression level for UGT76G1 (1.321 Total lab unit) was observed at plants grown in 2% glutamine. Based on HPLC results, the highest amount of stevioside (22.74) was accumulated in plants which were under 3% glutamine treatment and the lowest production level of stevioside (16.19) was resulted under MS (0 glutamine) medium. The highest rebaudioside A (12.19) accumulation was observed under 2% glutamine treatment and the lowest accumulation of rebaudioside A (8.41) was seen at plants grown in MS medium.
Stevia rebaudiana (Bertoni) is a non-caloric sweetener belonging to Asteraceae family. Stevia compounds such as steviol glycosides (SGs) are 200 times sweeter than sugar. Stevioside and rebaudioside A are the two major steviol glycosides. Nitrogen is an essential element for plant growth and development. In this study the effects of nitrogen influenced by different concentrations of NH4NO3 (0, 825 and 1650 mg/l) and KNO3 (0, 950 and 1900 mg/l) is examined in MS medium. To analysis the UGT74G1 and UGT76G1 genes expression, involved in the synthesis of SGs, RT-qPCR technique was performed. Data showed that there were significant differences between all media. The shoot length, seedlings dry weight and leaf fresh weight of stevia increased with applying NH4NO3 along with KNO3. The highest expression of UGT74G1 gene, was observed in plantlets grown on MS medium with 0 mg/l NH4NO3 and 950 mg/l KNO3 (1.291 total lab unit) but the highest expression of UGT76G1 gene, was observed in plantlets grown on MS medium added by 1650 mg/l NH4NO3 +950 mg/l KNO3 (1.08 total lab unit). Moreover, the lowest value of UGT74G1 gene expression were revealed in MS medium added by 1650 mg/l NH4NO3 +0 mg/l KNO3 (0.80 total lab unit) and the lowest values of UGT76G1 gene expression seen in MS medium with 0 mg/l NH4NO3 +950 mg/l KNO3 (0.85 total lab unit) concentrations. The results of this study could be valuable in stevia breeding programs through glycosides biosynthesis pathways.
Stevia rebaudiana Bertoni is one of two species that contains steviol glycosides. Among steviol glycosides that extracted from leaves, stevioside and rebaudioside A are the two major and the sweetest glycosides that are about 200-300 times sweeter than sucrose with zero calories. The best method for stevia propagation is tissue culture. So, for investigation of nutrients in medium, we studied the effect of different concentrations of MS media (MS, 0.5 MS, 0.25 MS, 0 MS) on morphological traits, UGT74G1 and UGT76G1 genes expression and accumulation of steviol glycosides in stevia leaves. The best growth rate (0.472 mm/d) has occurred in plants grown in MS media. Also, the highest gene expression of UGT74G1 gene (1.000 Total lab unit) was seen under MS treatment. However, the highest expression level of UGT76G1 gene (1.701 Total lab unit) was observed at plants grown in 0 MS. The highest amount of both Stevioside and Rebaudioside A (14.23 and 8.12, respectively) were accumulated in plants under MS treatment. Obviously, dilution of MS media associated with decreasing in both expression of the intended genes and accumulation of steviol glycosides.
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