Drought stress in Andrographis paniculata: impact on physiological parameters and andrographolide content as mediated by growth stages

Andrographis paniculata, commonly known as kalmegh is a highly valued medicinal plant. Pot-grown plants were subjected to water stress at vegetative, flowering, and fruiting stage by withholding water supply, followed by rewatering to facilitate recovery. Plants at the flowering and fruiting stage were particularly sensitive to drought stress compared to those at the vegetative stage. The plants were analysed for four diterpenoid compounds, namely andrographolide, 14-deoxyandrographolide, neoandrographolide, and andrograpanin. In plants subjected to stress at the vegetative and flowering stage, total andrographolide content increased significantly (P ≤ 0.05), by as much as 37% and 44%, respectively, over the levels in the control following 6 or more days of exposure, but remained unaffected in plants subjected to stress at the fruiting stage. Across all three stages, a significant decrease was observed in dry weight, relative water content (RWC), photosynthesis, conductance, and transpiration. Total andrographolide content was negatively correlated to dry weight, RWC, and rate of photosynthesis. These findings are useful in (1) identifying the ideal harvesting stage to achieve peak levels of bioactive compounds, (2) scheduling irrigation more efficiently to minimise yield loss due to water stress and maximise the content of bioactive compounds, and (3) developing stress-tolerant genotypes.