Moderate drought followed by re-watering initiates beneficial changes in the photosynthesis, biomass production and Rubiaceae-type cyclopeptides (RAs) accumulation of Rubia yunnanensis

Abstract Roots and rhizomes of Rubia yunnanensis are important Chinese medicine materials with significant anti-tumor activity, which is mainly obtained from wild resources. There is an urgent need to develop the production practice for the cultivation of R. yunnanensis. The current study was performed to investigate the changes in the photosynthetic pigment content, photosynthetic characteristics, chlorophyll fluorescence parameters, biomass production, and secondary metabolites Rubiaceae-type cyclopeptides (RAs) contents in roots and rhizomes by drought and re-watering in R. yunnanensis grown in four water conditions: well-watered control (C), moderate drought (MD), severe drought (SD), and re-watering after moderate drought (RMD). The results indicated that compared with the control, drought stresses (MD and SD) significantly decreased photosynthetic pigments and impaired photochemical efficiency, as revealed by the reductions of maximum potential PSII efficiency (Fv/Fm), effective quantum yield of photochemical energy conversion (Yield) and electron transport rate (ETR), etc., resulting in limited photosynthetic capacity, and hence reduced biomass accumulation and RAs contents and yields in roots and rhizomes. The RMD plants could produce compensation effect and their photosynthetic ability recovered to control level; they showed the comparable dry biomass of roots and rhizomes and higher contents and yields of RAs compared with the control. This implied that moderate drought-induced injury in R. yunnanensis was reversible. These results reinforce the importance of water management and recommend the re-water operation for the cultivation of R. yunnanensis.