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Figure 3 The Yin and Yang of photoinhibition. Depending on genotype, irradiance and time the extent of photoinhibition (indicated by decline in ϕPSII) proceeds through engagement of internal mechanisms of photoprotection (indicated by the extent of NPQ). Rapidly reversible (seconds to minutes) NPQΔpH potentiates the more slowly reversible (minutes to hours) de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin (NPQΔAZ) 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 (NPQΔLAZ) that may persist for days. If still inadequate it will be followed by similarly slowly recoverable PSII reaction centre photoinactivation (NPQPI). (Reproduced from Jia et al. 2013. Plant Physiology 161, 836-852; Copyright American Society of Plant Biologists)