Using of chlorophyll a fluorescence OJIP transients for sensing salt stress in the leaves and fruits of tomato

- OJIP curves and parameter values of leaves decreased under increased salt stress.
- O-step was a sensitive indicator of salt stress in leaves.
- OJIP curve and parameter values of fruit increased in 100 mM NaCl.
- Energy fluxes can show photosynthetic changes in salt-stressed fruit.
- Transient OJIP can be a non-destructive indicator of salt stress.

Salt is a major environmental stress to plant growth and productivity in tomato. Sensing salt stress is important to evaluate the degree of damage and the change in physiological condition in tomato plants. The aim of this study was to evaluate the salt stress in leaves and fruits in tomato using the chlorophyll a fluorescence OJIP transients (OJIP transients). Tomato plants were grown under various levels of salt stress (25, 50, 75, and 100 mM NaCl), following which we measured leaf stress indicators and OJIP transients in leaves and green fruits. In leaf stress indicators, the water potential decreased with increasing levels of salt stress, whereas the chlorophyll content (SPAD value) and the electrolyte leakage were not affected, except in 100 mM NaCl. The overall OJIP curves and each OJIP step in leaves decreased with increasing levels of salt stress, but were unaffected at the lowest level of salt stress (25 mM NaCl). Therefore, the OJIP curves were more sensitive indicators of salt stress in leaves than SPAD and electrolyte leakage. Conversely, in fruit, the OJIP curve was only significantly different in 100 mM NaCl compared with the control, and energy fluxes described by energy pipeline models were higher in 100 mM NaCl than in the control. These results indicate that, in severe salt stress such as 100 mM NaCl of fruit, JIP parameters and energy fluxes can show photosynthetic changes due to the increase in energy absorption efficiency of photosystem II against severe salt stress. Therefore, we conclude that OJIP transient analysis can be used as a non-destructive, simple, and rapid technique for sensing salt stress in tomato.