Programmed cell death of Chlamydomonas reinhardtii induced by three cyanobacterial volatiles β-ionone, limonene and longifolene.

β-Ionone, limonene and longifolene are 3 main components in cyanobacterial volatile organic compounds, which are formed through different pathways and can poison and even kill other algae. To uncover their toxic mechanism from programmed cell death (PCD), the photosynthetic pigments, chlorophyll fluorescence, caspase-like activities, cell size, nuclear variations and DNA ladders were investigated in Chlamydomonas reinhardtii treated with β-ionone (0.2 mM), limonene (0.2 mM) and longifolene (0.4 mM) at lethal concentration during 24 h. In the treatments with the 3 compounds, the photosynthetic pigments in C. reinhardtii cells gradually degraded, and Fv/Fm gradually decreased and disappeared at 24 h, suggesting that the cell death might be a PCD, due to the physiological activities gradually disappearing. During the cell death, the activities of caspase-9-like and caspase-3-like significantly increased, with the highest at 1 h. With prolonging the treatment time, C. reinhardtii cells gradually shrank, and the nuclei concentrated firstly following by a broken process, with moving to the cell edge. For DNA, obvious ladders were detected at 1 h, and then they gradually degraded to fragments of 100-250 bp at 24 h. These hallmarks suggested that β-ionone, limonene and longifolene may poison other algae by inducing PCD.