Mitigation of Water-Deficit Stress, Physio-morphological Adaptation, and Elevation of Andrographolide in Andrographis paniculata using Foliar Glycine Betaine

Glycine betaine (GlyBet) is a low-molecular-weight organic metabolite, which plays a crucial role in ameliorating the adverse effects of various abiotic stresses including drought stress. The aim of this investigation was to evaluate the physio-biochemical adaptations and the production of bioactive andrographolide compounds upon exogenous foliar application of GlyBet (50 and 100 mM) in Andrographis paniculata (Green Chiretta, king of bitters; Acanthaceae) grown under water-deficit (WD) conditions. Soluble sugars in GlyBet-treated plants under WD conditions were better in controlling leaf osmotic potential (r = −0.65) than free proline (r = −0.50). Leaf temperature (Tleaf; + 2.14 °C) and crop water stress index (CWSI; > 0.8) were significantly increased in plants under WD without GlyBet application, leading to reduced stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (Pn). In contrast, these parameters were unchanged upon the treatment of exogenous GlyBet even when subjected to WD. A positive relation between Pn and leaf dry weight was demonstrated (r =  0.40). The highest amount of andrographolide (51.71 mg g−1 DW), neoandrographolide (3.95 mg g−1 DW), total andrographolide (68.01 mg g−1 DW), and andrographolide (360.66 mg plant−1) yield per plant were observed in 100 mM GlyBet-treated plants under WD. The key results of this investigation imply the use of GlyBet to alleviate drought stress and regulate the production of andrographolide.