Measurements of photosynthetic parameters
Gas-exchange measurements were performed with an open-flow infrared gas-exchange analyzer system (Li-Cor 6400XT) with a portable photosynthesis system. Light was supplied from a series of light-emitting diodes located above the cuvette, providing an irradiance of 150 μmol photons m-2 s-1, similar to the growth conditions aforementioned. The reference CO2 concentration was set at 400 mmol CO2 mol-1 air. All measurements were performed at 25°C, and the vapor pressure deficit was maintained at 0.2 kPa, while the amount of blue light was set to 10% of photon flux density to optimize stomatal aperture. The determination of the photosynthetic parameters was performed in 4-week-old plants.F v/F m, which corresponds to the potential quantum yield of the photochemical reactions of PSII and represents a measure of photochemical efficiency, was measured as described previously (Oh et al., 1996).