The protective role of Piriformospora indica colonization in Centella asiatica (L.) in vitro under phosphate stress

The core of present study was to determine potential role of Piriformospora indica, mutualistic Basidiomycete endosymbiont on co-cultivation with Centella asiatica (L.) Urb., a neutraceutical plant. The analysis of major secondary metabolite asiaticoside and differential expression of key genes involved in pathway under varying phosphate (P) concentrations maintained in vitro were carried out. Maximum asiaticoside content was documented in plants maintained in MS medium containing lowest level (62.5 mu M) tried (p < 0.001). At phosphate concentration of 125 mu M (10% of normal P), significant stimulation of plant growth and asiaticoside production were observed in colonized plants. P levels at 125 mu M however favored maximum fresh weight, root and shoot length, root and leaf number of plants. The transcript accumulation of beta Amyrin Synthase, the key gene in asiaticoside pathway was recorded at the P level of 62.5 mu M, which is significantly higher (p < 0.001) than those at other P concentrations tried which was evidenced by overproduction of auxin, Indole-3-Acetic Acid (IAA). A significantly higher level of IAA was recorded in P. indica colonized plants maintained in low (125 mu M) P medium. The presence of P. indica under low phosphate concentrations has protective role in mitigating effects of stress, as evidenced by non-significant hydrogen peroxide production, acid/alkaline phosphatase activity, total phenolics and increased super oxide dismutase (SOD) activity in colonized plants. The study clarifies positive correlation of the asiaticoside production in P. indica colonized plants under low P conditions with significant up regulation of asiaticoside pathway gene transcripts with less stress.