Response of Photosynthetic Apparatus to Different Irradiance in Flag Leaves of High-Yielding Winter Wheat PH01-35 Grown under Low Light Conditions

Abstract

To further explain the mechanism of photoinhibition and light damage in wheat(Triticum aestivum L.) leaves when it was suddenly transferred from low light to high light conditions,the responses of photosynthetic apparatus in shaded leaves of the high-yielding winter wheat line,PH01-35,were examined using chlorophyll fluorescence and gas exchange techniques.After 15-day shading,the chlorophyll content increased greatly,but the net photosynthetic rate(Pn),light compensation point(LCP),light saturation point(LSP),apparent quantum yield(AQY),and carboxylation efficiency(CE) all decreased.Compared with leaves grown in full sunlight,the initial slope(α),decline slope(β),maximum relative electron transport rate(rETRmax),and minimum saturating irradiance(Ek) of rapid light curves in leaves grown in low light were lower when the plant was transferred from low light intensity of 250 μmol m-2 s-1 to high light intensity of 1 200 μmol m-2 s-1.Non photochemical quenching(NPQ) in leaves grown in low light was significantly lower than that in leaves grown in full sunlight,indicating that the ability of light use and thermal energy dissipation was limited in leaves grown in low light.The wheat leaves grown in low light were more suscepti-ble to photoinhibition due to low CO2 assimilation and photoprotective ability,such as xanthophylls cycle-dependent dissipation of excessive energy,despite the better energy absorbability in low light conditions.