Oxygen Stimulation of Apparent Photosynthesis in Flaveria linearis

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Abstract
A plant was found in the C3-C4 intermediate species, Flaveria linearis, in which apparent photosynthesis is stimulated by atmospheric O2 concentrations. A survey of 44 selfed progeny of the plant showed that the O2 stimulation of apparent photosynthesis was passed on to the progeny. When leaves equilibrated at 210 milliliters per liter O2 were transferred to 20 milliliter per liter O2 apparent photosynthesis was initially stimulated, but gradually declined so that at 30 to 40 minutes the rate was only about 80 to 85% of that at 210 milliliters per liter O2. Switching from 20 to 210 milliliters per liter caused the opposite transition in apparent photosynthesis. All other plants of F. linearis reached steady rates with 5 minutes after switching O2 that were 20 to 24% lower in 210 than in 20 milliliters per liter O2. At low intercellular CO2 concentrations and low irradiances, O2 inhibition of apparent phostosynthesis of the aberrant plant was similar to that in normal plants, but at an irradiance of 2 millimoles quanta per square meter per second and near 300 microliters per liter CO2 apparent photosynthesis was consistently higher at 210 than at 20 milliliters per liter O2. In morphology and leaf anatomy, the aberrant plant is like the normal plants of F. linearis. The stimulation of apparent photosynthesis at air levels of O2 in the aberrant plant is similar to other literature reports on observations with C3 plants at high CO2 concentrations, high irradiance and/or low temperatures, and may be related to limitation of photosynthesis by triose phosphate utilization.