Drought usually kills the precious roots of Panax ginseng, but this study reveals a surprising twist: spraying a specific hormone not only saves the plant but actually increases its medicinal value. Drought stress is known to severely hurt the production of the perennial medicinal herb Panax ginseng.

While the phytohormone abscisic acid regulates many plant processes, it was previously unknown if it controls drought resistance in this specific species. This study characterizes how drought resistance responds to abscisic acid in Panax ginseng to fill that knowledge gap.

Panax ginseng faces various environmental challenges during its long four to six year growth period. Although abscisic acid regulates drought resistance in other plants, its effect on ginsenoside biosynthesis in ginseng remained a mystery until now.

The researchers found that both drought resistance and ginsenoside biosynthesis were significantly enhanced by abscisic acid treatment. Figure 1 demonstrates the protective effect of ABA treatment on Panax ginseng seedlings subjected to severe drought stress for 35 days. Panel A visually contrasts the significant wilting observed in untreated drought conditions against the turgid, healthy leaves maintained by plants sprayed with 15 micromolar ABA every two days.

This morphological resilience is further supported by root preservation shown in Panel B and soil moisture data in Panel C, which indicates that while water content dropped significantly across all groups, the ABA-treated plants retained better physiological integrity under identical dry conditions.

To ensure the results were due to the hormone and not soil moisture differences, the researchers measured soil water content. The data showed no obvious difference in soil water content between the drought and drought plus abscisic acid groups. This evidence suggests that exogenous abscisic acid application significantly enhanced drought resistance in Panax ginseng.

Figure 2 demonstrates that drought stress induces stomatal closure in *Panax ginseng* leaves, a process significantly enhanced by the application of ABA. Panel A provides microscopic evidence showing that while drought alone reduces pore size compared to the control, the combined treatment results in the tightest closure.

These results confirm that exogenous ABA effectively promotes stomatal closure under water-deficit conditions. Drought treatment significantly reduced chlorophyll content in the leaves, indicating damage to the photosynthesis system. But spraying with abscisic acid had no negative effect on chlorophyll content, suggesting it protects the photosynthesis system.

Furthermore, root activity was stronger in the drought plus abscisic acid group compared to the drought treatment alone. Figure 3 presents a comprehensive physiological profile of *Panax ginseng* subjected to drought stress, comparing the effects of water deprivation alone against treatment with exogenous abscisic acid (ABA).

The authors measured six distinct parameters, including chlorophyll content, root activity, and antioxidant enzyme levels like superoxide dismutase. By tracking these metrics over a 35-day period, the data illustrates how ABA application influences the plant's photosynthetic capacity and cellular defense mechanisms under severe dehydration.

Ginsenosides are the most valuable active components found in Panax ginseng roots. Both monomer and total ginsenoside levels were greatly increased under drought and drought plus abscisic acid treatments. Interestingly, the ginsenoside content was even higher in the drought plus abscisic acid group than in the drought group without abscisic acid.

Figure 4 displays the ginsenoside content in Panax ginseng roots across three conditions: Control, Drought, and Drought plus ABA treatment. The authors used high-performance liquid chromatography to measure these levels after thirty-five days, breaking down the results into specific monomers like Rd, Rb1, Re, and Rg1 alongside other types.

Visually, the stacked bars indicate that the total accumulation of these valuable active components is visibly higher in the drought-stressed plants, with the tallest bar appearing in the group treated with both drought stress and ABA. Three-hydroxy-three-methylglutaryl CoA reductase is known as a rate-controlling enzyme of ginsenoside biosynthesis in Panax ginseng.

The expression of PgHMGR1 and PgHMGR2 was induced by abscisic acid treatment according to qRT-PCR analysis. This suggests that upregulation of these genes might contribute to the enhanced ginsenoside accumulation seen with abscisic acid. Figure 5 displays a bar chart comparing the relative gene expression of PgHMGR1 and PgHMGR2 in Panax ginseng leaves between a control group and those treated with abscisic acid.

The authors observed that after three hours of exposure to thirty micromolar ABA, the expression levels for both genes increased significantly compared to the untreated samples. This induction is crucial because HMGR is a rate-controlling enzyme in ginsenoside biosynthesis, suggesting that ABA treatment may stimulate the production of these valuable compounds.

The study demonstrated that growth retardation and root shrinking caused by drought were compromised by abscisic acid treatment. Exogenous abscisic acid also protected the photosynthesis system, enhanced root activity, and improved the antioxidant protection system.

These results clearly support that both drought resistance and ginsenoside biosynthesis in Panax ginseng were promoted by abscisic acid. This study showed that the accumulation of ginsenosides was significantly enhanced by abscisic acid treatment in Panax ginseng.

Expression of the key regulatory enzymes PgHMGR1 and PgHMGR2 was significantly enhanced by abscisic acid treatment. Therefore, abscisic acid might govern ginsenoside biosynthesis by directly regulating the expression of PgHMGR1 and PgHMGR2. The authors prove that abscisic acid treatment simultaneously boosts drought resistance and triggers higher production of valuable ginsenosides, offering a practical solution for farmers.