4. A model for the role of lumenal redox regulation in photoprotection
In the previous sections, we discussed redox regulation in the stroma, the trans-membrane mediators and the unique redox environments in the lumen, which are all affected by pH changes. In this section, we will explore the implications of the thylakoid pmf , not only on the canonical NPQ mechanisms, but on interactions with lumenal redox regulation, as summarized in Fig. 5.
There are several forms of NPQ, defined by their rates of activation and deactivation (Pinnola & Bassi 2018). These forms include the most rapid form, energy-dependent quenching (qE) (Liet al. 2004; Niyogi et al. 2005; Niyogiet al. 1998, 2005; Li et al. 2004), state-transition quenching (qT) (Quick & Stitt 1989), Z-dependent quenching (qZ) (Demmig-Adams & Adams 1996; Müller et al. 2001; Li et al. 2004; Nilkenset al. 2010), sustained quenching (qH) (Malnoëet al. 2018), and photoinhibitory quenching (qI) (Andersson & Aro 2004; Murata et al. 2007; Nawrocki et al. 2021a). In the following subsections, we will discuss the essential role of redox regulation on each NPQ form.