Effects of Calcium Channel Blockers on Intracellular Calcium Distribution and Expression of Calcium Signaling-Related Genes in Sophora tonkinensis

To investigate the functional divergence and molecular mechanisms governing calcium homeostasis in leaves and root tips of Sophora tonkinensis under perturbation of distinct calcium signaling pathways, plants were treated with LaCl ₃ (a plasma membrane Ca ²⁺ channel blocker), Na ₃ VO ₄ (Ca ²⁺ -ATPase inhibitor), and EGTA (an extracellular Ca ²⁺ chelator). Subcellular calcium distribution and the expression of calcium signaling-related genes were analyzed at 20, 40, and 60 days post-treatment using potassium pyroantimonate precipitation combined with transmission electron microscopy and quantitative real-time PCR. LaCl ₃ treatment initially induced intracellular calcium accumulation, followed by activation of alternative efflux pathways in leaves and increased extracellular deposition in root tips. Na ₃ VO ₄ treatment exacerbated intracellular calcium overload, causing sustained calcium toxicity in leaves, while root tips exhibited coordinated calcium redistribution. EGTA treatment dampened overall calcium signaling, yet root tips preserved functionality by mobilizing internal calcium stores. Gene expression analysis revealed a significant upregulation of StCML9 in roots (up to 11.7-fold relative to the control), with its expression tightly synchronized with Ca ²⁺ fluctuations, suggesting its role as a central calcium sensor mediating adaptive responses. In contrast, StCDPKs were generally suppressed in leaves. These findings demonstrate that S. tonkinensis establishes a dynamic calcium homeostasis network through organ-specific calcium distribution and transcriptional reprogramming. This study offers mechanistic insights into the species' adaptation to high-calcium karst environments and provides new avenues for enhancing plant stress tolerance and medicinal quality through targeted modulation of calcium signaling pathways.