Stomatal closure fully accounts for the inhibition of photosynthesis by abscisic acid.

The partial pressure of intercellular CO calculated from gas exchange data for abscisic acid-treated leaves of grapevine (Vitis vinifera L.) and sunflower (Helianthus annuus L.) does not indicate the average intercellular CO of the leaf. The latter can be determined from chlorophyll fluorescence quenching information and accurately modelled from gas exchange data. Stomatal closure can fully account for previously assumed non-stomatal inhibition of photosynthesis. Autoradiograms show that abscisic acid induces non-uniform gas exchange over small areas of the leaf.