Abstract: Aimed to understand the effects of exogenous Ca²⁺ on the D₁ protein phosphorylation and PSⅡ performances of wheat leaf chloroplasts under high temperature and illumination stress, wheat leaves at grain-filling stage were sprayed with 10 mmol·L^-1 of CaCl₂ or water (as control), and then subjected to high temperature and illumination stress (35 ℃ and 1600 μmol·m^-2·s^-1) for various hours,  with the changes in photosynthetic electron transport rate (ETR), net photosynthetic rate, chlorophyll fluorescence parameters, and relative amount of phosphorylated and nonphosphorylated D₁ protein in thylakoid membranes determined. After spraying with Ca²⁺, the PSⅡ reaction center under the stress was reversibly inactivated, the net degradation of D-protein was effectively restrained, the D₁ protein phosphorylation was maintained at a higher level, and the ETR of whole chain and PSⅡ, the maximal photochemical efficiency of PSⅡ (F_v/F_m),  the actual photochemical efficiency of PSⅡ (Ф_PSⅡ),  the photochemical quenching coefficient (q_P ), and  net photosynthetic rate (P_n) were all higher, suggesting that exogenous Ca²⁺ could improve the PSⅡ performances and mitigate its damage under high temperature and illumination stress via regulating the turnover of D₁ protein in wheat leaf chloroplasts.

Key words: Ca²⁺, wheat, high temperature and illumination stresses, D₁ protein phosphorylation, photosystemⅡperformance, unmanned aerial vehicle imagery (UAV), crown closure, geometric-optical model, linear spectral mixture analysis (SMA).