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The Rate of Photorespiration as Measured by Means of Oxygen Uptake and Its Respiratory Quotient

^a Department of Botany, The Hebrew University of Jerusalem, and Department of Agronomy, The Volcani Instutute of Agricultural Research, Israel

Oxygen recycling inside photosynthesizing leaves was found to amount to less than 0.3% of the oxygen consumed by photorespiration under natural conditions, provided the influence of buildup of oxygen released by photosynthesis into the external air was taken into consideration. When this is related to the amounts of photorespired CO₂, which had been previously found to be reabsorbed by photosynthesis, it appears that previous respiratory quotients reported for photorespiration were underestimated. For the same reason the photosynthetic quotient was overestimated. Actually, quotients of photorespiration and of photosynthesis approach the more normal range of respiratory quotients int the dark. The oxygen recycling was calculated according to an electrical analogue to oxygen flow.

The determination of photorespiration, when measured by oxygen uptake, can be more accurate than that by CO₂ measurement. However, recycling of oxygen occurs in larger amounts at lower oxygen and higher CO₂ concentrations, as well as under conditions of high resistance to transpiration.