biostudies-literatureSun YNational Natural Science foundation of Chinathe Project of Intergovernmental International Cooperation in Science and Technology Innovation3537https://www.ebi.ac.uk/biostudies/studies/S-EPMC9788621biostudies-literatureUnknown11(24)Photosystem II (PSII) of grapevine leaves is easily damaged under heat stress, but no such injury is observed when the leaves are heated in low light. To elucidate the mechanisms, we compared the photosynthetic characteristics of grapevine seedlings under heat treatments (42 °C) for 4 h in the dark or low light (200 μmol m^-2 s^-1). At 42 °C in the dark, the PSII maximum quantum yield (<i>Fv</i>/<i>Fm</i>) decreased significantly with the increase in time but did not change much in low light. The JIP (chlorophyll a fluorescence rise kinetics) test results showed that low light significantly alleviated the damage to the oxygen evolving complexes (OECs; the K-step was less visible) by heat stress. Further, in the presence of de novo D1 protein synthesis inhibitor chlorampPlants (Basel, Switzerland)Low Light Facilitates Cyclic Electron Flows around PSI to Assist PSII against High Temperature Stress.PMC9788621320013482019YFE0116500Wang QXiao HSun YCheng JfalseLow Light Facilitates Cyclic Electron Flows around PSI to Assist PSII against High Temperature Stress.Photosystem II (PSII) of grapevine leaves is easily damaged under heat stress, but no such injury is observed when the leaves are heated in low light. To elucidate the mechanisms, we compared the photosynthetic characteristics of grapevine seedlings under heat treatments (42 °C) for 4 h in the dark or low light (200 μmol m^-2 s^-1). At 42 °C in the dark, the PSII maximum quantum yield (<i>Fv</i>/<i>Fm</i>) decreased significantly with the increase in time but did not change much in low light. The JIP (chlorophyll a fluorescence rise kinetics) test results showed that low light significantly alleviated the damage to the oxygen evolving complexes (OECs; the K-step was less visible) by heat stress. Further, in the presence of de novo D1 protein synthesis inhibitor chloramp2022-01-01T00:00:00Z2022 Dec2025-04-04T07:58:59.075Z2025-04-04T07:58:59.075ZS-EPMC97886213655965010.3390/plants11243537