Molecular and Physiological Responses of Larix olgensis Seedlings to Drought and Exogenous ABA

With the intensification of global climate change and the frequent occurrence of extreme drought events, forest production is facing severe challenges. This study imposed drought stress and exogenous abscisic acid (ABA) treatment on Larix gmelini seedlings, evaluated their physiological characteristics, and analyzed the transcriptional response mechanism using transcriptome sequencing. The results showed that drought stress induced organ-specific changes in superoxide dismutase (SOD) and peroxidase (POD) activities, malondialdehyde (MDA) accumulation, and soluble protein content. SOD activity in leaves significantly increased, while POD activity, MDA content, and soluble protein levels in roots exhibited more dynamic changes. After ABA application, SOD activity in leaves reached its peak at 24 h, which was opposite to the situation in roots and stems, where POD activity was highest at 24 h. At 48 h, MDA accumulation was most significant in roots, while the early response in leaves was minimal. At 24 h, the soluble protein increase was most significant in stems. In addition, at this time point, ABA application significantly increased the soluble protein content in all three organs. Transcriptome sequencing analysis further identified core response genes involved in the MAPK signaling pathway, plant hormone signal transduction, starch and sucrose metabolism, and flavonoid biosynthesis pathways, including SNRK2, MAPKKK17, PYL, PP2C, XRN4, TMEM, TIR1, and TGA. In summary, Larix gmelini seedlings alleviate the inhibitory effect of drought stress on growth through a synergistic mechanism, specifically by activating the antioxidant system, initiating the MAPK signaling pathway, regulating plant hormone signal transduction, and reshaping carbon metabolism pathways, thereby enhancing stress resistance.