At the end of the first and second phases, plants were dark-adapted
for 20 min before measurement. Chlorophyll fluorescence of leaveswas
measured with a MINI-PAM fluorometer (Walz, Effeltrich, Germany).
Fluorescence was determined on the middle of the blades using a
dark-clip (DLC-8, modified to minimise boundary layer restrictions as
described by Beer et al. (1998))