Elucidating the effect of salinity stress in enhancing the phenolic acid content in Rauwolfia Serpentina in vitro

Rauwolfia serpentina (Apocynaceae) is a woody perennial shrub and important medicinal plant. Due to increased interest by both the scientific community regarding the medicinal uses of this plant species, a protocol for in vitro callus induction of Rauwolfia has been developed due to low germination rate (15%-20%). The leaf and stem explants were transferred to MS medium containing different combinations of plant growth hormones; 2,4-dichlorophenoxyacetic acid (2,4-D) + 2-benzyl amino purine (BAP).The concentration of 2,4-D (2.0mg/l) + BAP (1.0 mg/l) produced better results for callus induction in both leaf and stem explants. The least results were recorded in callus induced from leaf explants under the influence of 2, 4-D (2.0 mg/l) and BAP (1.5 mg/l). The present investigation aims to increase the phenolic content in vitro responsible for the antioxidant activity of Rauwolfia. Thus salinity stress has been applied in vitro to increase the phenolic acid content and various enzymes such as SOD (superoxide dismutase) and PAL (Phenyl alanine ammonia lyase) has been studied. The phenolics content was more in leaf callus at moderate salinity level of 15 ppm compared to control and other treatments at 10ppm and 20 ppm. There was increase in total phenolic acid content and antioxidant activity of Rauwolfia under moderate salinity. Result of the experiment showed that the SOD activity was highest at 20ppm followed by 15 ppm and 10 ppm salt treatment. Activities of PAL in the callus increased progressively with the increasing salt concentrations. Increased PAL activity in the leaf callus was linearly and positively correlated with increasing NaCl concentrations and the peak activity in the leaf callus was observed at NaCl concentration of 20 ppm.