Heterogeneous behavior of PSII in soybean (Glycine max) leaves with identical PSII photochemistry efficiency under different high temperature treatments

Summary: The purpose of this study is to demonstrate the heterogeneous behavior of PSII in soybean (Glycine max) leaves and identical maximum PSII photochemistry efficiency (F V/F M) under different high temperature treatments. We observed that, with an identical decrease in F V/F M in soybean leaves caused by different high temperature treatments, chlorophyll a fluorescence differed significantly, indicating different behaviors in the photosynthetic apparatus. The quantitative analysis showed that, with an identical F V/F M, leaves treated at 48°C showed a higher W K, an indicator of damage to the oxygen-evolving complex along with a lower O2 evolution rate compared with leaves treated at 45°C. This demonstrated that the donor side of PSII was damaged more severely at 48°C than at 45°C despite the same decrease in F V/F M in the two heat-treated leaves. The ratios of Q A- and Q B-reducing PSII reaction centers to total PSII reaction centers were both lower in leaves treated at 48°C than in leaves treated at 45°C with an identical F V/F M, indicating that the acceptor side of PSII was also more damaged by heat treatment at 48°C than at 45°C. However, when damage to the donor side of PSII was similar in leaves treated at two different temperatures, the acceptor side of PSII was damaged less severely at 48°C, which accounted for higher electron transport rate at the acceptor side of PSII in leaves treated at 48°C than in leaves treated at 45°C. [Copyright &y& Elsevier]