Genotype-specific antioxidant, reactive-carbonyl, and polyamine responses underlying heat tolerance in six winter wheat cultivars

Heat stress is a major constraint on wheat ( Triticum aestivum L.) production, intensifying with climate change. Tolerance differs widely among cultivars, yet how the antioxidant, reactive-carbonyl, and polyamine systems are jointly reconfigured as temperature increases is unclear. We profiled six winter wheat cultivars at 20 °C, 35 °C, and 40°C. We measured shoot biomass, pigments, and gas exchange; assayed the activities of the ascorbate–glutathione and reactive-carbonyl detoxification enzymes and phenylalanine ammonia-lyase; and quantified major polyamine pools. We then integrated these data using principal component analysis (PCA) and a stress-tolerance index (STI). Biomass, chlorophyll, and photosynthesis declined with temperature, whereas carotenoids and defensive enzymes were induced at 35°C and anthocyanins at 40 °C. Cultivars separated at 40 °C: tolerant genotypes maintained their defences, sensitive ones did not. Two signatures were most diagnostic: glyoxalase I and alkenal/alkenone oxidoreductase remained above control in every cultivar except Mv Tarsoly, the only genotype in which both carbonyl-detoxification arms declined below baseline. Cadaverine, a rarely reported diamine, also peaked in Mv Tarsoly, which ranked lowest in both PCA and STI. Spermine and spermidine decreased by up to 77% and 57%, against several-fold increases in putrescine, cadaverine, and 1,3-diaminopropane, with putrescine peaking in Mv Ikva. Polyamine remodelling thus acted as a marker of oxidative stress and, we propose, may also mediate it. PCA and STI supported this pattern, ranking Mv Lucilla, Mv Kolompos, and Mv Dandár above Mv Pirkadat, Mv Ikva, and Mv Tarsoly; the first three are candidate germplasm for climate-tolerant wheat breeding, pending field validation.