The derivation and use of this NPQ parameter are described in greater detail in the Appendix A and in Ahn et al.(2009), Baker (2008), Brooks and Niyogi (2011), and Holzwarth et al. (2013). To separate qE from qT, qZ, and qI, \(F_\rm m^\prime\prime,\) the maximum fluorescence yield after qE has relaxed, is often measured (Ahn et al. 2009; Johnson and Ruban 2011) and used instead of \(F_\rm m^\prime\) in Eq. 2. PAM traces also

allow researchers to quickly assay the qE response with different check details mutants, light conditions, and 17DMAG chemical treatments. These measurements are often correlated with biochemical measurements that quantify parameters such as the protein or pigment content (for example, Betterle et al. 2009; Nilkens et al. 2010; Niyogi et al. 1998) to investigate the

relationship between these components and qE. Chemical inhibitors Chemical inhibitors have been used in in vitro measurements to perturb a plant’s qE response, often by inhibiting particular steps of photosynthetic electron transport (see Table 1). DCMU is commonly used to close RCs (Murata and Sugahara 1969) by blocking the electron flow from PSII to plastoquinone pool, effectively closing the RCs without using saturating light, as is done in PAM fluorimetry (Clayton et al. 1972). In this way, DCMU allows researchers to take measurements without photochemical quenching present. This allows for the isolation of NPQ processes without the complications of photochemical processes. Table 1 BI 10773 concentration Chemical treatments used to study qE Names Effects N,N′-dicyclohexylcarbodiimide (DCCD) Binds to protonatable protein carboxylate groups (Ruban et al. 1992) 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) Blocks electron flow from PSII to plastoquinone, closes

PSII reaction centers (Murata and Sugahara 1969) Nigericin Eliminates \(\Updelta\hboxpH\) (Heldt et al. 1973) Carbonylcyanide m-chlorophenylhydrazone (DCCP) Dissipates \(\Updelta\hboxpH\) and \(\Updelta \varPsi\) Phosphatidylethanolamine N-methyltransferase (Nishio and Whitmarsh 1993) Dithiothreitol (DTT) Inhibits violaxanthin de-epoxidase (Yamamoto and Kamite 1972) Gramicidin Eliminates \(\Updelta\hboxpH\) and \(\Updelta \varPsi\) (Nishio and Whitmarsh 1993) Dibromothymoquinone (DBMIB) Blocks electron flow from plastoquinone to cytochrome b 6 f (Nishio and Whitmarsh 1993) Methyl viologen Electron acceptor (Nishio and Whitmarsh 1993) Diaminodurene (DAD) Mediator of cyclic electron flow (Wraight and Crofts 1970) Phenazine methosulfate (PMS) Mediator of cyclic electron flow (Murata and Sugahara 1969) Valinomycin Eliminates \(\Updelta \varPsi\) (Wraight and Crofts 1970) Ionophores are used in qE studies to alter the \(\Updelta\hboxpH\) and/or \(\Updelta \psi.\) Nigericin is a commonly used chemical inhibitor in qE studies (Heldt et al. 1973).