EFFECT OF SALINITY AND DROUGHT STRESS ON GROWTH PARAMETERS, GLYCOSIDE CONTENT AND EXPRESSION LEVEL OF VITAL GENES IN STEVIOL GLYCOSIDES BIOSYNTHESIS PATHWAY OF Stevia rebaudiana (BERTONI)

M. PANDEY¹*, S.K. CHIKARA^2
1Department of Biotechnology, Shri Venkateshwara University, Rajabpur Gajraula - 244 236, UP, India.
²Department of Biotechnology, Shri Venkateshwara University, Rajabpur Gajraula - 244 236, UP, India.
* Corresponding Author : mukesh02.max@gmail.com

Received : 07-06-2015     Accepted : 11-07-2015     Published : 01-09-2015
Volume : 7     Issue : 1       Pages : 153 - 160
Genetics 7.1 (2015):153-160

Keywords : Salinity stress, drought stress, S. rebaudiana, Steviol glycosides, Real-time quantitative PCR, HPLC
Academic Editor : Chandra Sheela, Sharma Sanjula, Gupta Moni
Conflict of Interest : None declared
Acknowledgements/Funding : The authors would like to thank to the Director of Xcelris Genomics for providing facilities and assistance.

Stevia [Stevia rebuaidana (Bertoni)], a family of Asteraceae is known to yield diterpenoid steviol glycosides (SGs) that is about 300 times sweeter than sugar. The present work examined the effects of different concentrations (25, 50, 75 and 100mM) of NaCl and mannitol on growth, physiological response, glycosides content and expression profile of four genes in steviol glycosides biosynthesis pathway after 30 days of culture. The results showed that NaCl and mannitol significantly (p < 0.05) affect the no. of shoot, shoot length, root no. and root length. As NaCl and mannitol concentration increases leaf DW, stem DW, root DW, shoot DW and leaf FW were decreased markedly by 30-70 % and 50-55 %, respectively at 100mM. In addition, transcript expression profiling of genes involved in steviol glycoside biosynthesis pathway showed an increased in expression genes; KAH, UGT85C2, UGT74G1 and UGT76G1 in 50, 75 and 100mM NaCl concentrations compared with control. Interestingly, expression ratio of UGT76G1 (Rebaudioside A) was significantly increased by 67% as compared to UGT74G1 (Stevioside), showing that salinity stress plants are sweeter than normal plant, whereas all four genes were down-regulated in drought stress conditions. These results were compared with the steviol glycoside contents measured in the leaves that was quantified by HPLC. Results showed that amount of Rebaudioside A was significantly increased to 45.83, 63.32 and 80.21 mg g-1 at 50, 75 and 100mM NaCl condition whereas significant decrease was found in all treatment condition of mannitol. Present work thus suggests that NaCl is acting as an enhancer and manitol acting as a repressor of transcription to genes of steviol glycoside biosynthesis pathway that could alter the production of steviol glycosides.