Abstract
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 (VJ) and 30 ms (VI), absorption flux (ABS/RC), trapped energy flux (TRo/RC), and dissipated energy flux (DIo/RC) increased in Mn-treated leaves, whereas the performance index (PIABS), electron transport flux (ETo/RC), maximum quantum yield (φPo), quantum yield of electron transport (φEo), and probability that an electron moves further than QA− (ψo) decreased. Also, excessive Mn significantly decreased the net photosynthesis rate and increased intercellular CO2 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 QA−, hence limiting the net photosynthetic rate.
Highlights
It is well-known that manganese (Mn) is an essential micronutrient element required for the growth and development of plants
K, J, or I step was positively correlated with the Mn level or the stress time in the Mn-treated leaves
We found that L. lucidum leaves were more sensitive to the Mn levels compared with the stress time
Summary
It is well-known that manganese (Mn) is an essential micronutrient element required for the growth and development of plants. Kitao et al.[19] have suggested that excessive Mn affects the activity of CO2 reduction cycle rather than Fv/FM in white birch, while increased QA reduction and thermal energy dissipation, as well as decreased quantum yield of PSII, have been observed. The “JIP-test” analysis of the OJIP transients allows the calculation of structural, conformational, and functional parameters quantifying the PSII behavior under environmental stresses, including absorption flux, trapped energy flux, electron transport flux, and dissipated energy flux[21]. We aimed to investigate changes in the OJIP transient and related parameters in the leaves of L. lucidum in the presence of Mn. In addition, we evaluated the toxicity of Mn to PSII behavior when L. lucidum was cultured under Mn stress for up to 40 days
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