Pyrogallic acid triggers a cascade from suppression of photosynthesis and proliferation to PCD‑like in Microcystis aeruginosa.

Pyrogallic acid (PA) is an effective allelochemical against Microcystis aeruginosa. However, it remains unclear whether its inhibitory specificity is derived from a regulated programmed cell death (PCD)-like cascade. A time-resolved analysis (8-96 h) of M. aeruginosa responses confirmed that 2.0 mg·L-1 PA induced sequential photosynthetic inhibition and proliferative arrest. These early physiological dysfunctions initiated a coherent, time-ordered ROS-NO-Ca2+ signaling cascade, subsequently activating caspase‑3‑like protease and triggering typical PCD‑like events, including DNA fragmentation and cell vacuolization. Collectively, this study delineates a coherent pathway from the initial physiological suppression to a ROS-NO-Ca2+ signaling relay and ultimate PCD‑like execution, which is further supported by structural equation modeling (SEM) and TEM cell ultrastructural observations. This work identifies PA as a precise trigger for the algal cell suicide mechanism. Furthermore, the PA-initiated signaling cascade shows potential for controlling harmful cyanobacteria, offering a novel perspective for the ecological management of cyanobacterial blooms.