Measurement of Photorespiratory Oxygen Exchange by Membrane Inlet Mass Spectrometry.

Photosynthesis and metabolism in plants involve oxygen as both a product and substrate. Oxygen is taken up during photorespiration and respiration and produced through water splitting during photosynthesis. To distinguish between processes that produce or consume O 2 in leaves, isotope mass separation and detection by mass spectrometry allows measurement of evolution and uptake of O 2 as well as CO 2 uptake. This chapter describes how to calculate the rate of Rubisco oxygenation and carboxylation from in vivo gas exchange of stable isotopes of 16 O 2 and 18 O 2 with a closed cuvette system for leaf discs and membrane inlet mass spectrometry.