2.5 Photosynthetic pigment content, photosynthesis, and chlorophyll fluorescence
Photosynthetic pigments were extracted with 80% acetone for 48 h and observed by spectrophotometry based on Arnon (1949). Net photosynthesis (Pn) and stomatal conductance (GS) were assessed with a CIRAS-3 portable photosynthesis system (CIRAS, Amesbury, MA, USA).
The apple plants were kept in darkness for 30 min before measuring their chlorophyll fluorescence. The FV/Fm ratio was measured by placing fully expanded leaves on an Imaging-Pam Chl fluorimeter (Walz, Effeltrich, Germany), then determining chlorophyll fluorescence parameters with Imaging WinGegE software.