CONSEQUENCES OF HIGH CO2-CONCENTRATIONS IN AIR ON GROWTH AND GAS-EXCHANGE RATES IN TOBACCO MUTANTS

Wild type tobacco N. tabacum var. John William's Broadleaf and the tob acco aurea mutant Su/su were permanently grown under 700 ppm CO2 in ai r. In comparison to plants grown under 350 ppm CO2 in air but under ot herwise identical conditions growth was substantially enhanced. Gas ex change measurements carried out by mass spectrometry show that the rat e of photosynthesis in the wild type and in the mutant is increased by more than 100%. The photorespiratory rate in the wild type measured;a s O-18(2)-uptake in the light in the ''700 ppm CO2-plants'' is not red uced to the extent expected or deduced from experiments in which the 3 50 ppm system responds under in vitro conditions to 700 ppm CO2. An an alysis of the induction kinetics of room temperature fluorescence kine tics of the adapted (700 ppm CO2) system and the control system (350 p pm CO2) under various CO2-partial pressures shows that permanent growt h under the elevated CO2-partial pressure leads to a structural modifi cation of the photosynthetic apparatus.