a, a parameter that describes how effectively photoinactivated PS II units protect their functional neighbours; Car, carotenoids; pH, transthylakoid pH difference; D1 protein, psbA gene product in the PS II reaction centre; f, functional fraction of PS II; Fv/Fm, the ratio of variable to maximum chlorophyll a fluorescence; kd, rate coefficient for degradation of D1 protein; ki and kr, rate coefficient for photoinactivation and repair of PS II, respectively; NADP+, oxidized nicotinamide adenine dinucleotide phosphate; P680, the primary electron donor in the PS II reaction centre; Ph, pheophytin; PS, photosystem; QA, first quinone acceptor of an electron in PS II; Rs, the gross rate of D1 protein synthesis.