2.6 Determination of photosynthetic parameters
The CIRAS-3 portable photosynthesis system (CIRAS, Amesbury, MA, USA) was used to determine the Pn and Gs. For each measurement, data were collected from six fully mature leaves of different seedlings. Before measuring chlorophyll fluorescence, the apple plants were kept in darkness for 30 minutes. To measure FV/FM ratio, fully expanded leaves were placed on a modulated chlorophyll fluorescence imaging system from Walz (Effeltrich, Germany).