Heavy metal accumulation efficiency, growth and centelloside production in the medicinal herb Centella asiatica (L.) urban under different soil concentrations of cadmium and lead

The present study explores the effect of varying concentrations of soil cadmium (50-200 mg/kg soil) and lead (200-800 mg/kg soil) on glasshouse grown plantlets of Centella asiatica. The plantlets were fairly tolerant to soil cadmium and lower concentrations of lead in terms of biomass accumulation. Application of 200 mg/kg soil cadmium concentration, led to enhanced biomass/two-fold increase in shoot length and a significant accumulation of cadmium in shoots and roots. Specific activities of anti-oxidant enzyme systems such as superoxide dismutase, ascorbate pemxidase, and guaicol pemxidase were also found to be elevated under treated conditions. Interestingly, the ratio of cadmium concentration in roots: soil (bioaccumulation coefficient factor) was more than 1, Centella asiatica could be a potential bioaccumulator of cadmium. Also since translocation of cadmium from roots to shoots was less than 40 %, the leaves, accumulating more than twenty five fold more centellosides (in 200 mg/kg soil cadmium v/s control conditions) could also be potentially exploited for phytochemicals with minimum post-harvest processing. Real time PCR analysis also revealed higher population of centelloside biosynthetic gene transcripts such as squalene synthase, farnesyl pyrophosphate synthase, beta amyrin synthase, as compared to control conditions. Plant growth, although tolerant to lower concentrations of soil lead could not effectively accumulate lead in roots, and centelloside contents was also found to be only marginally higher than control. This study reports the possibility of exploiting C. asiatica as potential plant systems that may be cultivated on cadmium contaminated soils to reap phyto-pharmaceutical benefits.