Photosystem II of Ligustrum lucidum in response to different levels of manganese exposure

The toxic effect of excessive manganese (Mn) on photosystem II (PSII) of woody species remains largely unexplored. In this study, five Mn concentrations (0, 12, 24, 36, and 48 mM) were used, and the toxicity of Mn on PSII behavior in leaves of Ligustrum lucidum was investigated using in vivo chlorophyll fluorescence transients. Results showed that excessive Mn levels induced positive L- and K- bands. Variable fluorescence at 2 ms (V(J)) and 30 ms (V(I)), absorption flux (ABS/RC), trapped energy flux (TR(o)/RC), and dissipated energy flux (DI(o)/RC) increased in Mn-treated leaves, whereas the performance index (PI(ABS)), electron transport flux (ET(o)/RC), maximum quantum yield (φ(Po)), quantum yield of electron transport (φ(Eo)), and probability that an electron moves further than Q(A)(−) (ψ(o)) decreased. Also, excessive Mn significantly decreased the net photosynthesis rate and increased intercellular CO(2) concentration. The results indicated that Mn blocked the electron transfer from the donor side to the acceptor side in PSII, which might be associated with the accumulation of Q(A)(−), hence limiting the net photosynthetic rate.