Heat stress is a critical environmental factor affecting crop productivity by impairing photosynthetic efficiency. This study evaluated the impact of high-temperature stress on Photosystem II (PSII) functionality in 24 tomato (Solanum lycopersicum) genotypes using chlorophyll fluorescence parameters, including maximum quantum efficiency (Fv/Fm), effective quantum yield of PSII photochemistry (Y(II)), regulated non-photochemical quenching (Y(NPQ)), non-regulated energy dissipation (Y(NO)), and electron transport rate (ETR). Measurements were conducted at three developmental stages: early (ES), mid (MS), and final (FS). Under control conditions, Fv/Fm values ranged from 0.593 to 0.76 (ES), 0.654 to 0.887 (MS), and 0.533 to 0.694 (FS), with a significant decline under heat stress across all genotypes. Similarly, Y(II) and ETR decreased under stress, indicating reduced photochemical efficiency and electron transport activity. In contrast, Y(NO) increased, suggesting enhanced non-regulated energy dissipation, while Y(NPQ) exhibited genotype-specific variations in photoprotective energy dissipation. Genotypes SG3, SG4, SG6, SG10, SG17, SG18, and SG24 demonstrated relatively higher PSII efficiency and ETR under stress, suggesting superior heat tolerance. Conversely, SG1, SG11, SG19, and SG21 exhibited the most pronounced reductions, indicating susceptibility. Correlation analysis revealed strong positive relationships between Fv/Fm, Y(II), and ETR, while Y(NO) showed a negative association with these parameters, highlighting its detrimental effect on PSII efficiency. Principal component analysis (PCA) confirmed a shift in trait associations under stress, emphasizing increased reliance on photoprotective mechanisms. Overall, this study underscores the variability in PSII functionality among tomato genotypes under heat stress, identifying promising candidates for breeding programs aimed at enhancing thermotolerance and improving crop resilience in high-temperature environments.

Photosystem II, Heat Stress, Tomato, Electron Transport Chain, Chlorophyll

These findings underscore the importance of PSII efficiency and energy dissipation balance in determining heat tolerance in tomato. The identification of tolerant genotypes provides a valuable resource for breeding programs aimed at developing climate-resilient cultivars capable of maintaining productivity under rising global temperatures.

Sandeep Kumar, Deepak Dubey, Priyanka Dubey and Syed Kulsoom Fatima Jafri (2025). Photosystem II Performance and Heat Stress Tolerance in Tomato (Solanum lycopersicum L.): Insights from Chlorophyll Fluorescence and Electron Transport Analysis. Biological Forum, 17(9): 19-26.