Cell samples of untreated algal culture and Exp. 4 algal cells after 48 h pretreatment were analysed using SEM. Algal cells without treatment appeared to have smooth and tight surfaces
(Fig. S1h), however when cells were treated with 2.19 mg HNO2– N/L FNA, cell surfaces shrank and some cells collapsed. The process of FNA pretreatment certainly led to a surface defection, but again, despite disruption of the cell membranes, lipid remained in the algae (Table 1).