RESUMEN
Understanding the physiological and biochemical regulations in a medicinal plant under stress environments is essential. Here, the effect of water stress such as flooding and water deficit [80% (control), 60%, 40%, 20% field capacity (FC)] conditions on Valeriana jatamansi was studied. Both types of water stresses retarded the plant growth and biomass. Photosynthetic pigments were reduced with maximum reduction under flood stress. Chlorophyll fluorescence study revealed distinct attributes under applied stresses. Better performance index (PI) of flood-grown plants (than 20% and 40% FC) and higher relative fluorescence decrease ratio (Rfd) in 40% FC and flood-grown plants than that of control plants, indicated the adaptation ability of plants under water deficit (40% FC) and flood stress. Reduction in net photosynthetic rate was lesser in flood stress (40.92%) compared to drought stress (73.92% at 20% FC). Accumulation of starch was also decreased (61.1% at 20% FC) under drought stress, while it was increased (24.59%) in flood stress. The effect of water stress was also evident with modulation in H2O2 content and membrane damage. Differential modulation of biosynthesis of secondary metabolites (valtrate, acevaltrate and hydroxyl valerenic acid) and expression of iridoid biosynthetic genes under water stress was also revealed. The present study demonstrated the distinct effect of drought and flood stress on V. jatamansi plants, and drought [20% FC] caused severe loss and more damage than flood stress. Therefore, severe drought should be avoided during cultivation of V. jatamansi and regulated water stress-applications have potential for modulation of biosynthesis of specific secondary metabolites.