Effect of two different strains of Agrobacterium rhizogenes on hairy root induction in Stevia rebaudiana L.Bertoni

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Date
2012
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Birsa Agricultural University, Kanke, Ranchi, Jharkhand
Abstract
The present work has been conceived to establish the protocol for Agrobacterium rhizogenes Conn mediated hairy root induction on Stevia rebaudiana L.Bertoni, a valuable medicinal plant as well as calorie free natural sweetener. The work focused on the induction of hairy roots using two different strains of A. rhizogenes ATCC 15834 and MTCC 532. The transformed roots were highly differentiated. To obtain aseptic explants for transformation, micropropagation was carried out by inoculating shoot tip of S. rebaudiana on MS media supplemented with 2mg/l BAP, 50 mg/l AdSO4 and 1mg/l citric acid. Two different Agrobacterium rhizogenes strains (ATCC 15834 and MTCC 532) were tested to investigate the ability for transformation and production of secondary metabolites. Both bacterial strains ATCC 15834 and MTCC 532 were maintained at 28°C & 25°C respectively for 48h on solid medium. The optimum growth of A. rhizogenes (OD 0.6) was observed after 48h of incubation in rotary shaker in dark. In case of ATCC 15834, the media was supplemented with 50mg/l rifampicin. Bacterial suspension was prepared by inoculating single colony in liquid medium followed by incubation for 48 h (ATCC 15834) and 24 h (MTCC 532). The selected explants were wounded and dipped in the thick bacterial suspension. Co-cultivation was done for different time periods. In case of ATCC 15834 the highest transformation frequency was found to be 91.60% at 48 h co-culture after 24 days with the highest number of hairy roots (20.66) per explants. While MTCC 532 showed the highest infection frequency (94.33%) along with the highest number of hairy roots (24.33) per explants for 3 h co-culture after 24 days. A. rhizogenes strain MTCC 532 was found to be better than ATCC 15834 both for transformation frequency as well as number of hairy roots/ explants. A comparative account of HPLC study using C18 separating column with isocratic mobile phase revealed presence of active component stevioside at 210nm in in vitro roots of both strains as well as in vivo roots of Stevia rebaudiana. The identification of stevioside in sample was done by comparing the retention time.
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Effect of two different strains of Agrobacterium rhizogenes on hairy root induction in Stevia rebaudiana L.Bertoni
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