biologia plantarum

Biologia plantarum 64:591-597, 2020 | DOI: 10.32615/bp.2020.091

The toxicity of BDE-47 to the photosystem of Lemna minor fronds

N.W. QIU¹, W.R. ZHANG¹, X.H. YAN¹, R.J. WANG¹, L. TIAN^1,*, G.L. HAN², F. ZHOU^3,*

¹ College of Life Sciences, Qufu Normal University, Qufu, Shandong 273165, P.R. China

² Shandong Provincial Key Laboratory of Plant Stress, Shandong Normal University, Jinan 250014, P.R. China

³ School of Food Science, Nanjing Xiaozhuang University, Nanjing 211171, P.R. China

To elucidate the toxicity of 2,2ʹ,4,4ʹ-tetrabromodiphenyl ether (BDE-47) on photosynthetic primary processes, in vivo and in vitro treatments of BDE-47 were performed. The 20-d treatment in vivo (5 - 20 μg dm^-3) suppressed the reproduction of duckweed (Lemna minor) and led to decline in chlorophyll (Chl) content of fronds. The most obvious features of BDE-47-treated fronds included a Chl a fluorescence rise at the J phase and a depression at the G phase, whereas significant fluorescence rises at the L, K, and J phases were found on the ΔV_t curve of thylakoid membranes treated with 10 - 15 mg dm^-3 BDE-47 for 4 h (in vitro). In both in vivo and in vitro experiments, the BDE-47 treatments significantly reduced the density of the active reaction centers (RC/CS_o), affected the efficiency and speed of photosynthetic electron transfer [the maximum quantum yield of photosystem (PS) II photochemistry - F_v/F_m, quantum yield for electron transport (at t = 0) - φ_Eo, electron transport flux per excited cross section - ET_o/CS_o, and net rate of reaction centers closure at 300 and 100 μs - dV/dt_o and dVG/dt_o, respectively], and increased energy dissipation [quantum yield for energy dissipation (at t = 0) - φ_Do, dissipated energy flux per reaction center - DI_o/RC, and issipated energy flux per excited cross section - DI_o/CS_o]. The BDE-47 at 5 - 15 mg dm^-3 had no impact on the minimum (initial) fluorescence (F_o) and total electron carriers per reaction center (S_m) of the thylakoid membranes, but PS II units were less tightly grouped (a positive L-band). On the contrary, there was no positive L-band on the difference between relative fluorescence intensities of the normalized induction curves from 50 μs to 300 μs (W_K) of each BDE-47 treatment and control (ΔW_K), and F_o and S_m increased after the treatment with BDE-47. The above results indicate that BDE-47 not only affected the permeability of thylakoid membranes, but also relaxed the structure of PS II, thereby affecting the function of PS II. In addition, BDE-47 could induce secondary damage to the PSs in duckweed fronds.

Keywords: chlorophyll a fluorescence, duckweed, energy dissipation, photosynthetic electron transfer, thylakoids.

Received: April 14, 2020; Revised: June 9, 2020; Accepted: June 10, 2020; Published online: August 31, 2020  Show citation