Abstract: Wheat lines Xiaoyan 41 (XY41) and Xiaoyan 81 (XY81) are hybrid progenies of Xiaoyan 54 (XY54) and 8602, which show distinct differences from their parents in photosynthesis characteristics. In this study, the gas exchange, chlorophyll fluorescence, and 820 nm transmission in flag leaves after anthesis were compared between hybrids XY41 and XY81 and parents XY54 and 8602. At anthesis, contents of chlorophyll a, chlorophyll b, and carotenoids were higher in the hybrids than in the parents, especially in XY81. Photosynthetic rate (P_n) and carboxylation efficiency (CE) were the highest in 8602, whereas stomatal conductance (Gs) was the lowest in XY54, followed by XY41. The four cultivars had similar values of intercellular CO₂ concentration (C_i), ratio of variable F_K to the amplitude F_J–F_O (W_k), maximum quantum yield of PSII (F_v/F_m), efficiency that an electron moves to Q_A downstream (Ψo), efficiency with which an electron from the intersystem electron carriers moves to electron acceptors in reduced end at the PSI acceptor side (δ_Ro), relative variable transmission at 820 nm (ΔI/I_o), actually photochemical efficiency of PSII (Φ_PSII), and nonphotochemical quenching (NPQ). After anthesis, the decreases of pigment contents, P_n, CE, G_s, F_v/F_m, δ_Ro, and ΔI/I_o and the increase of W_k were larger in XY54 than in other cultivars. No differences were detected in C_i, Ψ_o, Φ_PSII, and NPQ among cultivars, and these parameters varied similarly in 8602 and the hybrids during the whole developmental period tested. Compared with XY 54, XY41, and XY81 had slower decrease in P_n, and this resulted from the difference in dark reaction capacity rather than chlorophyll contents, stomatal conductance, and photosynthetic light reaction capacity. XY41 and XY81 might inherit the high dark reaction capacity from parent 8602.

Key words: Wheat, Photosynthetic rate, Pigments, Stomatal conductance, Light reaction, Dark reaction