Salt Toxicity Impacts Yields and Herbal Quality of Salvia Miltiorrhiza

Salt stress is one of the most destructive environmental threats to crop production, causing osmotic imbalance, ion toxicity, and oxidative damage that stunt growth and reduce yields. For medicinal plants like Salvia miltiorrhiza, the problem is twofold: stress not only hurts the plant but also disrupts the biosynthesis of the very compounds that give the herb its therapeutic value. Gibberellins are plant hormones that promote growth, but under stress, plants need to slow down and defend themselves.

The GA 2-oxidase (GA2ox) enzyme family helps plants fine-tune this trade-off by inactivating active gibberellins. Yet until now, no one had explored whether these enzymes could simultaneously enhance stress tolerance and secondary metabolism in medicinal plants. Based on these challenges, there is an urgent need to investigate how GA2ox genes function in Salvia miltiorrhiza and whether they can be harnessed to improve both stress resilience and medicinal compound yield.

A team led by researchers at Northwest A&F University in China reports (DOI: 10.1093/hr/uhag058) these findings in Horticulture Research, published online February 26, 2026. The study systematically identified 12 GA2ox genes in Salvia miltiorrhiza and focused on SmGA2ox4, a gene strongly induced by salt, gibberellin, and methyl jasmonate (MeJA)-a stress-related hormone. By overexpressing this gene in both Arabidopsis thaliana and Salvia miltiorrhiza hairy roots, the team demonstrated enhanced salt tolerance alongside increased accumulation of tanshinones, the plant's key lipophilic bioactive compounds.

The researchers conducted a genome-wide search and identified 12 GA2ox family genes in Salvia miltiorrhiza, with SmGA2ox4 standing out for its strong response to methyl jasmonate (MeJA), a stress signal. When they overexpressed SmGA2ox4 in transgenic Arabidopsis, the plants showed significantly higher germination rates and longer primary roots under salt stress compared to wild-type controls. Physiological measurements revealed that the transgenic lines accumulated more chlorophyll and proline-a protective osmolyte-while producing less malondialdehyde (MDA), a marker of oxidative damage. Antioxidant enzyme activities, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), were also substantially elevated. The transgenic plants maintained a lower sodium-to-potassium ratio, indicating better ion homeostasis-a key determinant of salt tolerance.

When the team tested SmGA2ox4 in its native host using transgenic hairy roots, the results were consistent: overexpression lines showed improved growth, lower MDA, higher proline, and enhanced antioxidant enzyme activity under salt stress. Strikingly, high-performance liquid chromatography (HPLC) analysis revealed that SmGA2ox4 overexpression promoted tanshinone accumulation but suppressed salvianolic acid biosynthesis, while RNA interference (RNAi)-mediated silencing did the opposite. This bidirectional regulation was traced to differential expression of key pathway genes: SmCYP76AH1 and SmKSL1 (tanshinone pathway) were upregulated, while SmRAS1 and SmCYP98A14 (salvianolic acid pathway) were downregulated.

"We were surprised to find that one gene could do two seemingly opposite things-help the plant survive salt stress and at the same time push it to produce more of its most valuable medicinal compounds," the authors said. "It's like the plant is reallocating its resources: instead of using energy for growth, it invests in defense and secondary metabolism. This dual function makes SmGA2ox4 a particularly attractive target for breeding. The fact that it also responds to multiple hormonal signals suggests it sits at a key intersection of stress and metabolic regulation in the plant."

The discovery has direct implications for cultivating Salvia miltiorrhiza in saline soils, which are expanding due to irrigation practices and climate change. By selecting or engineering varieties with enhanced SmGA2ox4 activity, growers could maintain-or even increase-tanshinone yields on marginal lands where the plant would otherwise struggle. The study also provides a blueprint for similar work in other medicinal plants facing environmental stress. Moreover, the finding that a single gene can positively regulate stress tolerance while negatively regulating another class of compounds (salvianolic acids) highlights the need for careful metabolic engineering-but also opens the door to fine-tuning the balance of multiple bioactive ingredients in a single plant.