Abstract
The extent of net photoinhibition of photosystem II (PSII) is determined by a balance between the rate of photodamage to D1 protein and the rate of D1 protein turnover cycle. The protein turnover requires much energy cost. The aims of this study are 1) to evaluate the energy cost of D1 repair and 2) to know whether acclimation of photosynthesis to growth light affects the rates of D1 photodamage and repair. We measured the rates of D1 photodamage and repair and compared these between the spinach leaves grown in high-light (HL) and low-light (LL). We determined the rate constants of photodamage (kpi) and repair (krec) on the basis of Kato et al. (2002). The HL leaves showed smaller kpi and greater krec than the LL leaves. The energy cost to repair the photodamaged D1 protein was calculated based on Kato & Sakamoto (2009). The cost at 1,600 μmol photon m-2 s-1 for 120 min was calculated to be 15,000 - 20,000 μmol ATP m-2. These values correspond to 10% or more of the ATP produced by the dark respiration for the same period. The cost was greater in the HL leaves than in the LL leaves. This may result from the HL leaf has more PSII per leaf area than the LL leaf.
