Determination of fruit photosynthesis under different CO2and low PPFD levelsFruits 94 DAFB were used for determining in-vitro response to different CO2 concentrations, and fruits 114 DAFB were fordifferent low PPFD, respectively, because the mandarin fruitsshow active photosynthesis during these stages as reported pre-viously [5]. Photosynthesis and respiration rates were measuredby oxygen electrode apparatus (Rank Brothers, Cambridge, U.K.)supplemented with halogen lamps (Sumita Optical Glass, Saitama,Japan) as reported earlier [5]. Briefly, 10 rind discs (3 mm diameter)were prepared from equator zone of three fruits with the albedo tissue removed, soaked in 0.05 M phosphate buffer (pH 7.0) for30 s, and placed in an electrode tank with 3 ml of fresh phosphate buffer at 25◦C. The CO2 concentration, 50–1000 ppm, was adjustedby adding different amount of NaHCO3 solution into the tank andPPFD of 135 ?mol m−2s−1was supplied. The pH in the tank was7.0. Meanwhile, PPFD, from 2.7 to 270 ?mol m−2s−1, was regulatedby placing the lamp at various distances from the electrode tankcontaining 440 ppm CO2. The O2increase (net photosynthesis) inthe buffer was recorded under light conditions for 15 min, then O2decrease (respiration) was measured for 10 min under dark by cov-ering the tank with three layers of aluminum foil. Before use, thebuffer had been bubbled with N2gas for 1 h and stored in a des-iccator containing 2 M NaOH to remove CO2. Leaf photosynthesisand respiration rates were also measured as a control by using 10discs (3 mm diameter) from five leaves at the same sampling date.Experiments were repeated at least 3 times and mean value ± SEwas presented.