Role of thermal dissipation in the photoprotection in cucumber plants after exposure to a chill stress

Abstract

Experiments were carried out to investigate the changes in CO2 assimilation, photon allocation, and photosynthetic electron flux in leaves of cucumber (Cucumis sativus L.) plants after chilling stress. Chilling significantly decreased CO2 assimilation, the energy flux via linear electron transport (JPS2) and non-constitutive thermal dissipation (JNPQ) but increased fluorescence and constitutive thermal dissipation (Jf,D) in chilling-sensitive genotype Jinyan No. 4. In contrast, chilling had little effects on JNPQ and Jf,D although CO2 assimilation and JPS2 were inhibited in chilling-tolerant genotype Jinchun No. 3. In parallel with the reduction in JPS2, electron flux to oxygenation and carboxylation by ribulose-1,5-bisphosphate carboxylase/oxygenase all significantly decreased while electron flux to O2 significantly increased, especially in chilling-sensitive genotype. Thermal and fluorescence dissipation were the main energy dissipation pathways whilst water-water cycle was an important electron sink when photosynthetic carbon reduction was suppressed after chilling. Chilling sensitivity of the photosynthetic apparatus was related to the operation of different photoprotection mechanisms.