Cloning and prokaryotic expression analysis of squalene synthase 2 (SQS2) from Salvia miltiorrhiza f. alba Effects of plant-derived smoke water on accumulation of biomass and active substance of Salvia miltiorrhiza f. alba Construction of plant expression vectors with PMI gene as selection marker and their utilization in transformation of Salvia miltiorrhiza f.alba Influence of naturaldecay of fibrousroots on growth and content of active compositions of Salvia miltiorrhiza f. alba Influence of continuous cropping years on yield and active compounds in Salvia miltiorrhiza f. alba