Oxygen Effect on Photosynthetic and Glycolate Pathways in Young Maize Leaves

AUTOR(ES)

Morot-Gaudry, Jean F.

RESUMO

To study the effect of O2 on the photosynthetic and glycolate pathways, maize leaves were exposed to 14CO2 during steady-state photosynthesis in 21 or 1% O2. At the two O2 concentrations after a 14CO2 pulse (4 seconds) followed by a 12CO2 chase, there was a slight difference in CO2 uptake and in the total amount of 14C fixed, but there were marked changes in 14C distribution especially in phosphoglycerate, ribulose bisphosphate, glycine, and serine. The kinetics of 14C incorporation into glycine and serine indicated that the glycolate pathway is inhibited at low O2 concentrations. In 1% O2, labeling of glycine was reduced by 90% and that of serine was reduced by 70%, relative to the control in 21% O2. A similar effect has been observed in C3 plants, except that, in maize leaves, only 5 to 6% of the total 14C fixed under 21% O2 was found in glycolate pathway intermediates after 60 seconds chase. This figure is 20% in C3 plants. Isonicotinyl hydrazide did not completely block the conversion of glycine to serine in 21% O2, and the first carbon atom of serine was preferentially labeled during the first seconds of the chase. These results supported the hypothesis that the labeled serine not only derives from glycine but also could be formed from phosphoglycerate, labeled in the first carbon atom during the first seconds of photosynthesis.

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