Effects of Oxygen on Metabolism by the Glycollate Pathway in Leaves

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Abstract
Segments of wheat leaves were supplied in the light with 14C-labelled serine or glucose in atmospheres containing different concentrations of O2 and zero or 350 parts/106 CO2. Some O2 was necessary for sucrose synthesis from either serine or glucose but sucrose synthesis from glucose depended on reactions with a high affinity for O2 whereas sucrose synthesis from serine depended both on reactions with high and low affinities for O2. In the presence of CO2 sucrose synthesis from serine was decreased when the O2 concentration was increased from 20 to 80% by volume and CO2 was liberated; sucrose synthesis from glucose was almost unaffected by the same change in conditions. Also, in an atmosphere containing 80% O2 and 350 parts/106 CO2, radioactivity from [14C]serine, was incorporated into glycine. This was not true for glucose feeding. Hence glucose provides a substrate for sucrose synthesis but not for photorespiration whereas serine is used for both processes in the presence of CO2; in the absence of CO2 glucose provides substrate for both sucrose synthesis and photorespiration and serine metabolism to sucrose is restricted.

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