Exogenous Foliar Application of Methyl Jasmonate Alleviates Water-Deficit Stress in Andrographis paniculata

Andrographis paniculata has been widely used as a medicinal herb due to its enriched total andrographolide contents. Methyl jasmonate (MeJA), a natural plant signal-transducer molecule, is a potential elicitor in regulating secondary metabolites and alleviating drought stress. The objective of the present study was to assess the impacts of exogenously-applied foliar MeJA on morphological, physiological, and biochemical traits as well as total andrographolide contents of A. paniculata under water-deficit stress. The experiment consisted of four different foliar MeJA doses [0 (distilled water or control), 125, 250, and 500 μM] exogenously-applied at the pre-flowering stage (100 days after sowing) on uniform plants and two soil moisture regimes [well-watered (WW; 100% field capacity) and water-deficit (WD; 67.6% field capacity)]. Leaf osmotic potential of the WD plants was significantly declined by 25.43% over the WW plants, leading to chlorophyll degradation (SPAD value), diminution of photon yield of photosystem II (ΦPSII), and reduction in net photosynthetic rate (Pn) and plant biomass. Foliar application of 250 μM MeJA alleviated the negative effects of water-deficit stress by improving leaf osmotic potential, SPAD value, ΦPSII, Pn, and transpiration rate. Leaf biomass of A. paniculata was retained under MeJA treatments even in water-deficit conditions. An increase in neoandrographolide, 14-deoxyandrographolide, total andrographolide, and andrographolide yield per plant was observed when 125 μM MeJA was applied under water-deficit stress. Exogenous foliar application of MeJA at 250 μM alleviates water-deficit stress in A. paniculata and may provide an important tool to minimize the economic loss caused by dry conditions during the vegetative growth stage.