Effects of light and Suc on the CO₂ fixation and the PSII quantum yield in leaves of wild-type (A) and abi4/sun6 mutants (B). Two-week-old Arabidopsis plants and abi4/sun6 mutants grown under 16 h of light at 100 μmol m⁻² s⁻¹ and 8 h of darkness were transferred into a medium without Suc (Suc⁻) or with 0.5% Suc (Suc⁺), and then moved into the dark. After 48 h of darkness, the plants were exposed to continuous light at 100 μmol m⁻² s⁻¹ for 48 h. Net CO₂ fixation rates in leaves at the indicated times were measured with a photosynthesis measuring system under the following conditions: 100 μmol m⁻² s⁻¹, 360 ppm CO₂, 60% relative humidity at 25 °C. Chlorophyll fluorescence parameters of leaves at the indicated times were measured with a chlorophyll fluorometer under the same conditions. Data are the mean values ±SD of five individual experiments (n=5). Values without a common letter are significantly different according to t-test (P <0.05).