Fig. 4

Cytosolic Ca²⁺ levels increase after Sr²⁺ addition. a Cytosolic Ca²⁺ levels were detected using the specific fluorescent probe Fluo-4 AM. Trichoderma reesei RUT-C30 strain was cultured in MM for 2 days with or without supplementation of the Ca²⁺ channel inhibitor LaCl₃ and 0 or 70 mM Sr²⁺. To treat hyphae, 4 μM Fluo-4 AM was used. For detection, automatic inverted fluorescence microscopy was used to monitor the fluorescence intensity. Stronger green fluorescence indicated a higher intracellular Ca²⁺ content. b Comparative fluorescence ratios demonstrating the effects of LaCl₃ on the cytosolic Ca²⁺ burst induced by Sr²⁺. The y-axis represents the Ca²⁺ fluorescence ratio measured by CLSM, and the x-axis represents different treatments with Sr²⁺ and LaCl₃. c Transcriptional levels of crz1 after treatment with 0 or 70 mM Sr²⁺ for 48, 60, or 72 h were also detected. The final values are presented as the mean ± standard deviation (SD) from three independent experimental results. Asterisks indicate significant differences compared to the strain without Sr²⁺ treatment (p < 0.05, according to Student’s t-test). DIC, differential interference contrast; MM, minimal medium