“…Hormetic responses of HAB-forming and toxin-producing cyanobacteria appear in the electron transport rate, fluorescence intensity, and photochemical quantum yield of PSII. ,,− ,,− ,, Chlorophylls and less frequently carotenoids also respond in a hormetic fashion. ,,,,,,− ,,,,, For example, tris(1,3-dichloro-2-propyl) phosphate (TDCPP), a Cl-OPFR, significantly increased chlorophyll a and carotenoid concentrations in M. aeruginosa by ∼27–32% at 0.1 and 1 mg L –1 , whereas the response returned to levels similar to the control or below at 5 and 10 mg L –1 . Increasing concentrations of reactive oxygen species (ROS) and decreasing ratios of high-potential to low-potential forms of cytochrome b 559 also occur, suggesting thermodynamic transformation of cytochrome b 559 , whose states are modulated by nitric oxide, to yield mild ROS and enhance stimulation. ,,,,, ROS such as hydrogen peroxide are key molecules and essential in cell signaling . This mild increase in ROS contributes to the overcompensation response of photosynthesis, while cytochrome P450 is also an important component of the stress response and contaminant biodegradation. , Low doses of contaminants can also activate clathrin-mediated endocytosis to facilitate a swift absorption of macro- (C, N, P) and micronutrients (Ca, K, Mg) to enhance chlorophylls, photosynthesis, growth, and microcystins production. , …”