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 & mu;M] 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 (& phi;(PSII)), and reduction in net photosynthetic rate (P-n) and plant biomass. Foliar application of 250 & mu;M MeJA alleviated the negative effects of water-deficit stress by improving leaf osmotic potential, SPAD value, & phi;(PSII), P-n, 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 & mu;M MeJA was applied under water-deficit stress. Exogenous foliar application of MeJA at 250 & mu;M 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.