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

Abstract:

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 (μ^−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 (ϕP₀ and ϕE₀) 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 (ψ₀). 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.

Key Words::

• Chlorophyll a fluorescence transients kinetics
• Cylindrospermopsis raciborskii
• N-phenyl-2-naphthylamine
• Rapid light curves

ACKNOWLEDGEMENTS

The study was supported by the National Natural Science Foundation of China (31170372), the Fundamental Research Funds for the Central Universities (XDJK2014D015) and the Natural Science Foundation Project of China SWU (SWNUB2011).