Regulation of photosynthesis during the light period in CAM plants -evaluation by a gas-phase O2 electrode and a compensating infrared C02 analysis system

Abstract

The CO2 dependent 02 evolution during the light period, at which the exogenous CO2 uptake was suspended, in 12 CAM plants (including pineapple (Ananas comosus)) was evaluated with a gas-phase oxygen electrode. At 5% CO2, the rate of photosynthetic 02 evolution in pineapple was saturated at 1 500 µmol m-2 s-1 PPFD and the maximum rate was 60 µmol m-2 s-1, which was 10 times those obtained at ambient CO2 conditions with the CO2 exchange system and significantly higher than the other CAM plants. At the saturated PPFD, the 02 evolution in pineapple substantially increased with increasing CO2 concentration up to 3% and decreased above 4%. However, in the other CAM plants, such increment was small. By the use of a novel compensating CO2 gas exchange system, the rate of CO2 exchange in pineapple at very high CO2 was measured and found the enhancement of CO2 uptake in both light (Phases III and IV) and dark (Phase I) periods. Based on the results obtained, possibilities of the further increases in CO2 uptake in CAM plants, especially of pineapple, are discussed in terms of stomatal functions and malate storage capacities