Low oxygen inhibition of photosynthesis is caused by inhibition of starch synthesis.

Photosynthesis of C(3) plants is occasionally inhibited upon switching from normal to low partial pressure of O(2). Leaves of Solanum tuberosum exhibited this effect reproducibly under saturating light and 700 microbars of CO(2). We determined the partitioning of recent photosynthate between starch and sucrose and measured the concentration of hexose monophosphates in the stroma and cytosol after nonaqueous fractionation. The reduction in the rate of photosynthesis upon switching to low partial pressure of O(2) was caused by reduced starch synthesis. The concentration of hexose monophosphates in the stroma fell and the glucose 6-phosphate to fructose 6-phosphate to fructose 6-phosphate ratio fell from 2.7 to 1.3, indicating an inhibition of phosphoglucoisomerase as described by K-J Dietz ([1985] Biochim Biophys Acta 839: 240-248). The concentration of hexose monophosphates in the cytosol increased, ruling out a sucrose synthesis limitation by reduced transport from the chloroplast as the explanation for low O(2) inhibition of photosynthesis.