*2.6. Chlorophyll Fluorescence Imaging*

Intact leaflets from TE plants were dark-adapted using aluminum foil for 10 min. After the dark adaptation period, leaflets were detached and immediately used for chlorophyll imaging using a closed FluorCam model FC 800-C with FluorCam v.7.0 software (FluorCam,

Photon System Instruments, Brno, Czech Republic). The minimum fluorescence in a darkadapted state (Fo) was acquired during a dark period of 5 s, after which an 800 ms saturating light pulse (2400 µmol m−<sup>2</sup> s −1 ) from a blue LED (peak emission of 449 nm) was used to measure maximum fluorescence in a dark-adapted state (Fm). From F<sup>o</sup> and Fm, the variable fluorescence in a dark-adapted state (Fv) was calculated (F<sup>v</sup> = F<sup>m</sup> − Fo), which was used to determine the maximum photosystem II (PSII) quantum yield (Fv/Fm). In general, the lower the value of Fv/F<sup>m</sup> is, the more severe the photoinhibition and thus the leaf injury [33]. By calculating Fv/F<sup>m</sup> using chlorophyll fluorescence imaging, we were able to assess not only the prevalence of injury but also the spatial heterogeneity of Fv/F<sup>m</sup> from a leaflet. Eight leaflets from the 5th leaf were used for each lighting treatment when plants were 23, 62, and 138 DIT, corresponding with 8 December 2018, 16 January 2019, and 2 April 2019, respectively.
