Fluorescence spectrophotometry
A MINI Imaging PAM instrument (Heinz Walz GmbH, Effeltrich, Germany) was used to measure the Fv/Fm and △F/Fm′ of pepper and N. benthamiana leaves. The plants were adapted to darkness for 15 min and then placed directly into the instrument for testing according to the method of Schreiber and Klughammer(U & C, 2013).