Effects of various glutamine concentrations on gene expression and steviol glycosides accumulation in Stevia rebaudiana Bertoni.

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.

Effects of life cycle and leaves location on gene expression and glycoside biosynthesis pathway in Stevia rebaudiana Bertoni.

Stevia rebaudiana Bertoni is One of the most important biologically sourced and low-calorie sweeteners that known as "Sweet Weed". It contains steviol glycosides that they are about 200-300 times sweeter than sucrose. Tissue culture is the best method with high efficiency that can overcome to problems of traditional methods, and it is the most useful tools for studying stress tolerance mechanisms under in vitro conditions to obtain drought tolerance. In the present research, we investigated the impact of life cycle, leaves location and the harvesting time on expression of UGT74G1 and UGT76G1 as well as steviol glycosides accumulation. The highest gene expression of both UGT74G1 and UGT76G1 (207.677 and 208.396 Total Lab unit, respectively) was observed in young leaves in the second vegetative year. Also, the highest amount of stevioside accumulation (13.04) was due to the old leaves in vegetative stage which had significant differences with other effects whereas the lowest accumulation (7.47) was seen at young leaves at vegetative stage. Interestingly, the highest level of rebaudioside a production (15.74) was occurred at the young leaves at vegetative stage. There was significant differences between life cycle and leaves location on steviol glycoside production in stevia.

Effects of different concentrations of mannitol on gene expression in Stevia rebaudiana Bertoni.

Stevia rebaudiana Bertoni is one of the most important herbal sweetener plants from Asteracea family that have a lot of Steviol glycosides. Among different methods, tissue culture is the best way with high efficiency that is useful for studying stress tolerance mechanisms to obtain drought tolerance of stevia. For this purpose, different concentrations of mannitol (0, 10, 20, 30, 40, 50 mg/l) were used as various treatments in the culture medium of stevia. According to the results, the highest level of UGT85C2 gene expression (1.181 Total lab unit) was seen in plants grown under 30 mg/l mannitol treatment and the lowest level of this gene expression (0.603 Total lab unit) was observed under 40 mg/l mannitol treatment. However, the highest level of KO gene expression (1.323 Total lab unit) was observed under 20 mg/l mannitol. It shows stevia growth is affected by osmotic stress. Water deficiency has a negative impact on Stevia. However, the expression of genes had increased by particular mannitol concentrations. Actually, stevia can survive under various abiotic stresses.