Figure 3 The Yin and Yang of photoinhibition. Depending on genotype, irradiance and time the extent of photoinhibition (indicated by decline in ϕ_PSII) proceeds through engagement of internal mechanisms of photoprotection (indicated by the extent of NPQ). Rapidly reversible (seconds to minutes) NPQ_ΔpH potentiates the more slowly reversible (minutes to hours) de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin (NPQ_ΔAZ) in light harvesting antennae of PSII in thylakoid membranes. In some plants, such as avocado, this photoprotection is augmented by a second de-epoxidation of lutein epoxide to lutein (NPQ_ΔLAZ) that may persist for days. If still inadequate it will be followed by similarly slowly recoverable PSII reaction centre photoinactivation (NPQ_PI). (Reproduced from Jia et al. 2013. Plant Physiology 161, 836-852; Copyright American Society of Plant Biologists)