AsPac J. Mol. Biol. Biotechnol. 2019 Vol. 27 (1) : 56-65 Acute gamma irradiated Stevia rebaudiana Bertoni enhanced particular types of steviol glycosides Miao Si Chiew a , Kok Song Lai a , Sobri Hussein b , Janna Ong Abdullah a* a Department of Cell and Molecular Biology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b Agrotechnology and Biosciences Division, Malaysia Nuclear Agency, 43000 Bangi, Selangor, Malaysia Received 17th November 2018 / Accepted 17th January 2019 Abstract. Stevia rebaudiana Bertoni from Asteraceae family is commercially valuable for its steviol glycosides (SGs) contents, which is 300 times sweeter than commercial sugar. The bottleneck in Malaysia is the lack of suitable stevia varieties that are able to thrive well under her climatic conditions and still produce high SGs. Mutation induction including gamma irradiation is effective in generating genetic variations and developing new plant varieties with desired traits. This study was aimed to determine the effects of acute gamma irradiation on phenotypic changes and enhancement of SGs contents of Stevia rebaudiana Bertoni variety AKH L1 (herein after will be designated as AKH L1). In vitro shoot tip explants of AKH L1 were subjected to a gamma doses regime of 10Gy to 50Gy, following which phenotypic changes of the irradiated explants and subsequent regenerated plantlets were observed. All irradiated explants exhibited different survival rates, with the lowest at 9.33±8.33% when subjected to 50Gy, while all the control (non-irradiated explants) survived. The LD 50 was found to be at 23Gy. Subsequent irradiation of 900 shoot tip explants at 23Gy, produced 468 surviving shoot tips, which were all capable to develop and successfully sub-cultured until the fourth generation, M 4 . These M 4 in vitro mutant plantlets exhibited significant increase in the numbers of leaf (16.07±5.19) and average leaf size (1.12±0.26cm x 0.54±0.15cm). HPLC analysis performed in parallel further revealed the mutant plants contained higher concentrations of stevioside (387.04ppm), rebaudioside A (670.18ppm) and rebaudioside D (106.26ppm) compared to the non-irradiated plantlets, which exhibited 96.87, 194.42 and 28.25ppm, respectively. Keywords: stevioside, rebaudioside A, rebaudioside D, HPLC, LD 50 irradiation INTRODUCTION Stevia rebaudiana Bertoni, a perennial sweet herb belongs to the family Asteraceae, is one of the 154 members of the genus Stevia. This plant is the most important source of non-caloric natural sweeteners, and is mainly known as “Sweet Weed’, “Sweet Leaf”, “Sweet Herbs” and “Honey Leaf”. The property of the species that called attention to the plant is the intense sweet taste of the leaves and aqueous extracts (Uddin et al., * Author for correspondence: Dr. Janna Ong Abdullah, Department of Cell and Molecular Biology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. Email – janna@upm.edu.my 2006). The extract of the stevia plant contains mixture of various sweet steviol glycosides, designated as SGs, such as stevioside, rebaudioside A, B, C, D, E and F, dulcoside A, steviolbioside, steviolmonoside, and rubusoside, which accumulate in the leaves and is 300 times sweeter than sugar (Ahmad et al., 2011; Reis et al., 2011; Mathur & Shekhawat, 2012). The compounds that made up the majority