Differential biosynthesis and accumulation of picrosides in an endangered medicinal herb Picrorhiza kurroa

Picrorhiza kurroa Royle ex Benth (Family: Scrophulariaceae) is a medicinal herb, mainly found in the North-Western Himalayas. Extensive harvesting for pharmaceutical purposes, lack of organized cultivation and unorganized methods of uprooting the plants because of unawareness has brought an endangered status to this important herb in nature. The medicinal property of this plant is attributed to monoterpenoid picrosides. The influence of developmental status of different growth stages on picrosides content is poorly understood in Picrorhiza kurroa. Picroside-I (P-I) content increased from 0.05 % to 0.76 % in different growth stages of shoots. Significant increase in the contents of P-I (0.15–0.50 %) and Picroside-II (P-II) (0.1–0.45 %) was observed in rhizomes of different developmental stages. Highest amounts of P-I (8.7 %) and P-II (5.3 %) was detected in uppermost part of mature dried rhizomes compared to bottom part with 2.9 % and 2.2 % of P-I and P-II, respectively. P. kurroa grown at high altitude (Sairopa, 4,500 amsl) showed 1.75-folds increase in P-I in leaves whereas exponential increase in the P-I content was detected (0.05–1.7 %) in the leaves of different developmental stages (L1-L5) of P. kurroa grown at lower altitude (Jagatsukh, 1,900 m). Variable amounts of P-I and P-II in different growth and developmental stages of P. kurroa imply importance of selection of plant material (rhizomes and roots). The study undertaken explored the status of metabolites accumulation and biosynthesis in the field grown plants of P. kurroa where not only environmental parameters but different morphogenetic stages of its developmental cycles, different age groups and different parts of plantlets were extensively analysed and estimated for medicinally important picrosides.