Evidence of a key role for photosynthetic oxygen release in oil storage in developing soybean seeds

Based on the topographical analysis of photosynthesis and oil storage, we propose in a companion paper that photosynthetic oxygen release plays a key role in the local energy state, storage metabolism and flux toward lipid biosynthesis in developing soybean seeds. To test this hypothesis, we combined topographical analysis of ATP gradients across tissues, microsensor quantifications of internal O-2 levels, assays of energy balance, metabolite profiles and isotope-labelling studies. Seeds show a marked degree of oxygen starvation in vivo (minimum O-2 levels 0.1 kPa, approximate to 1.3 mu m), affecting ATP gradients, overall energy state, metabolite pools and storage activity. Despite the low light availability, photosynthesis supplies significant amounts of oxygen to the hypoxic seed tissue. This is followed by an increase in local ATP levels, most prominently within the lipid-synthesizing (inner) regions of the embryo. Concomitantly, partitioning of C-14-sucrose to lipids is increased, suggesting higher rates of lipid biosynthesis. It is concluded that both respiratory and biosynthetic fluxes are dynamically adjusted to photosynthetic oxygen supply.