Sodium nitroprusside and salicylic acid facilitated post-stress recovery in birch seedlings under cadmium stress by modulating ROS/RNS and lupeol levels

Abstract Nitric oxide (NO) and salicylic acid (SA) are recognized for their ability to mitigate cadmium (Cd) stress, yet their roles in facilitating plant post-stress recovery after Cd exposure remain poorly understood. This study showed that birch seedlings exposed to 8 and 40 mg kg⁻ 1 Cd for 15 and 30 days displayed significant dry weight reduction, elevated reactive nitrogen species (RNS) and reactive oxygen species (ROS) levels, and increased lupeol accumulation compared to controls. After 15 days of 40 mg kg⁻ 1 Cd treatment, the exogenous supplement of the NO donor sodium nitroprusside (SNP) or SA effectively alleviated growth inhibition while reducing ROS levels and ROS/RNS ratios by 35.82–149.31% (SNP) and 33.12–147.53% (SA), concurrently enhancing lupeol content by 28.33–54.29% (SNP) and 19.59–80.01% (SA) and upregulating BpLUS2 (lupeol synthase) expression in the leaves, stems, and roots of the seedlings. Yeast expressing BpLUS2 (pYES2-BpLUS2) exhibited 32.89% higher lupeol production and 660.00% greater growth under Cd stress than controls. Furthermore, 1 and 3 μmol L⁻ 1 exogenous lupeol increased fresh weight by 62.45% and 101.20% in Cd-stressed birch calli. Collectively, these findings demonstrate that SNP or SA supplementation promotes post-stress recovery in birch seedlings under Cd stress, highlighting the potential role of lupeol in mitigating Cd-induced stress. Graphical Abstract