Use of chlorophyll a fluorescence to elucidate the toxicity target of N-phenyl-2-naphthylamine on photosynthetic system of Cylindrospermopsis raciborskii (Cyanobacteria)

In order to investigate the toxicity targets of the secondary metabolite from aquatic plants, N-phenyl-2-naphthylamine, on Cylindrospermopsis raciborskii photosynthetic system II (PSII), we determined chlorophyll a (Chl a), specific growth rate (mu(-d)), photosynthetic rapid light curves and polyphasic Chl a fluorescence transients following exposure to N-phenyl-2-naphthylamine. The results showed significant decreases in Chl a following 48 h at high concentration (0.50 mg l(-1)) exposure to N-phenyl-2-naphthylamine. The PSII electron transfer rate and Chl a fluorescence transients appeared to be affected after the cells were exposed to concentrations of 0.50, 1.00 and 2.00 mg l(-1). Exposure to higher concentration of N-phenyl-2-naphthylamine (> 0.50 mg l(-1)) mainly depressed the density of reaction centers (RC/CS0) and quantum energy flux ratios (phi P-0 and phi E-0) but increased the absorption flux per RC (ABS/RC), dissipated energy flux per RC (DI0/RC) and the average redox state of Q(A)(-)/Q(A) in the time span from 0 to t(Fmax) (S-m/ t(Fmax)). However, exposure to low concentration (<= 0.5 mg l(-1)) mainly inhibited the trapping energy fluxes per reaction center (TR0/RC), electron transport energy fluxes per reaction center (ET0/RC) and energy flux ratio (psi(0)). This suggested that the donor and the acceptor sides of PSII were targets of N-phenyl-2-naphthylamine in C. raciborskii. Additionally, our results indicated that the toxicity target at low concentrations of N-phenyl-2-naphthylamine was at each step of electron transport between Q(A)(-) and the Cyt b6/f complex; whereas, the reduction of Q(A) was the potential target at high concentrations. We suggest that N-phenyl-2-naphthylamine may be a potential allelochemical to control harmful cyanobacterial blooms.