Effect of elevated CO₂ on photosynthetic CO₂ fixation and chlorophyll fluoresence with two different cultivars of radish with or without big storage root.

Abstract

Down regulation of gene expression by accumulated sugar and/or accelerated senescence by accelerated ontogeny are suggested for the mechanisms for down regulation of photosynthesis by elevated CO₂ (see PCP. 39, 1-7, '98). Photosynthetic CO₂ fixation and utilization of light energy were monitored simultaneously using Li-6400-40 (LI-COR) with the first leaf of ambient CO₂ (350 ppm) and elevated CO₂ (750 ppm) grown two different cultivars of radish with (White Cherrish) or without (Kosena) storage root every two days during development. Maximum values of the rate of photosynthetic CO₂ fixation, initial slope of A-Ci curve, Φ_PSII, were almost similar with two treatments. But these values decreased faster with elevated CO₂ grown plant than those of control. These results suggest that down regulation of photosynthesis by elevated CO₂ is due to accelerated ontogenesis and with Kosena developing leaves become big sink and absorb photosynthate very actively.