Abstract
Leaves of Flaveria brownii exhibited slightly higher amounts of oxygen inhibition of photosynthesis than the C4 species, Flaveria trinervia, but considerably less than the C3 species, Flaveria cronquistii. The photosynthetic responses to intercellular CO2, light and leaf temperature were much more C4-like than C3-like, although 21% oxygen inhibited the photosynthetic rate, depending on conditions, up to 17% of the photosynthesis rate observed in 2% O2. The quantum yield for CO2 uptake in F. brownii was slightly higher than that for the C4 species F. trinervia in 2% O2, but not significantly different in 21% O2. The quantum yield was inhibited 10% in the presence of 21% O2 in F. brownii, yet no significant inhibition was observed in F. trinervia. An inhibition of 27% was observed for the quantum yield of F. cronquistii in the presence of 21% O2. The photosynthetic response to very low intercellular CO2 partial pressures exhibited a unique pattern in F. brownii, with a break in the linear slope observed at intercellular CO2 partial pressure values between 15 and 20 μbar when analyzed in 21% O2. No significant break was observed when analyzed in 2% O2. When taken collectively, the gas-exchange results reported here are consistent with previous biochemical studies that report incomplete intercellular compartmentation of the C3 and C4 enzymes in this species, and suggest that F. brownii is an advanced, C4-like C3-C4 intermediate.
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