Multi-level responses of Camellia reticulata to heat stress: insights from photosynthetic performance, antioxidant activity, lipidomics, and fatty acid profiling.

BACKGROUND: Climate change-induced heatwaves threaten the sustainable cultivation of Camellia reticulata, a valuable oil-producing species adapted to cool climates. Despite its economic importance, the mechanisms underlying its response to elevated temperatures are poorly understood. We hypothesized that C. reticulata activates distinct physiological and lipidomic adjustments to cope with different intensities of heat stress. To test this hypothesis, we subjected plants to three temperature regimes: 25 °C (control), 35 °C, and 40 °C, and conducted an integrated analysis of physiological traits and lipid metabolism.

RESULT: Our results revealed distinct response strategies in C. reticulata under moderate versus extreme heat stress. Both 35 °C and 40 °C treatments led to significant decreases in chlorophyll content compared with the control, with a much more drastic reduction under 40 °C. Exposure to 35 °C enhanced antioxidant systems and shifted membrane lipids toward a more thermostable composition, effectively preventing visible injury despite mild PSII photoinactivation. In contrast, plants exposed to 40 °C displayed severe PSII photodamage and progressive leaf browning during recovery, even with elevated flavonoid accumulation and enhanced antioxidant capacity. Buds, however, remained viable. This physiological disruption was closely linked to deleterious remodeling of membrane lipids that compromises membrane stability. Concomitantly, significant accumulation of unsaturated neutral glycerolipids was observed, suggesting a cellular protective mechanism that sequesters excess unsaturated fatty acids into storage pools. The preferential survival of buds over leaves indicates that plants prioritize meristem protection. This study identifies the adaptive mechanisms under moderate heat and characterizes the physiological breakdown under extreme heat, highlighting lipid metabolism as a key target for improving thermotolerance in C. reticulata.