Chlorophyll a fluorescence OJIP transient as a tool to characterize and evaluate response to heat and chilling stress in tomato leaf and fruit

In tomato production, extreme temperatures such as heat and chilling are major factors limiting growth and productivity. Recently, the chlorophyll a fluorescence OJIP transient (OJIP transient) has been used as an effective tool for studying damage to and activity of the electron transport chain in the photosynthetic apparatus under various environmental stresses. The aim of this study was to evaluate the validity of the OJIP transient as a stress indicator and to characterize the effect of heat and chilling stress on the photosynthetic apparatus in tomato leaf and fruit. Detached leaves and fruits were incubated at 25 °C (control), 40 °C (heat stress), and 4 °C (chilling stress); OJIP transients were measured after exposure to stress for 1 h and 24 h, and several parameters were calculated according to the JIP-test. After exposure to stress for 1 h and 24 h, the OJIP curves and the JIP parameters clearly revealed differences between stress types and between tissue types. In addition, the JIP parameters and the energy pipeline model indicated that heat stress had a greater influence on the photosystem (PS) II electron transport chain than chilling stress, and that changes were greater in the fruit than in the leaf. Furthermore, the PS I electron transport chains of leaf and fruit appeared to be more heat resistant than those in PS II. Our results indicate that, in tomato leaf and fruit, OJIP transients and calculated JIP parameters can be used as sensitive methods for measuring the heat and chilling stress damage to the photosynthetic apparatus, and to identify the action sites of temperature stress.

► OJIP transients are effective tools for measuring heat and chilling stress damage in tomato plants.
► Changes in OJIP transients and action site induced by temperature stress shows tissue- and stress-specific differences.
► PS II electron transport chain is more influenced by heat stress than by chilling stress.
► PS I electron transport chains in leaf and fruit are more heat-resistant than those in PS II.
► JIP parameter of PS I is sensitivity to chilling stress.