Effect of salt treatment on growth, isoenzymes and metabolites of Andrographis paniculata (Burm. f.) Nees

Andrographis paniculata is a well-known medicinal plant having vast therapeutic potentials. Efficient use of saline land for promoting the cultivation of medicinal plants is valuable for pharmaceutical and economic benefits. Relatively little is known about the physiological and biochemical basis of salt tolerance in this plant. Here, we studied the growth, isoenzymes, malondialdehyde, proline and secondary metabolites of A. paniculata in response to different salt treatments with NaCl (0, 41.1, 92.4, 143.7 and 193.4 mM). The results indicated that growth traits were decreased and all the expression level of superoxide dismutase (SOD), catalase (CAT), cytochrome oxidase (CYT), peroxidase (POD), polyphenol oxidase (PPO) and esterase (EST) isoenzyme in leaves and roots was enhanced with increasing salinity. Malondialdehyde was positively correlated to salt levels. Proline decreased at first and then dramatically increased at 193.4 mM. The content of key secondary metabolites was continuously increased under less than 143.7 mM NaCl concentrations. Results suggest that A. paniculata has relatively salt resistance by activating enzyme expressions both in roots and leaves, elicitation of secondary metabolites and osmoprotectant, but also reasonably regulating the allocation of resources. It is preferent to using resources for defense rather than for growth in A. paniculata and there is metabolic shift from growth to defense under salt conditions. Induction of isoenzyme activities and production of secondary metabolites are the primary defense strategies. Additionally, moderate salt treatment could promote the accumulation of bioactive phytocompounds, which is valuable for breeding plants with high quality. Thus, the cultivation of this medicinal herb in moderate saline areas could be considered as an agricultural option. Furthermore, our upshorts can provide a reference for screening better salt-tolerant cultivars of A. paniculata.