Dark Stomatal Movement in Sunflowers in Response to Illumination under Nitrogen

Experiments were performed on intact sunflowers (Helianthus annuus) placed in a specially designed experimental chamber which allows instantaneous modifications of the atmospheric composition without changing any other conditions. After one night in normal conditions, the plant was illuminated under pure nitrogen atmosphere; the opening stomatal movement, measured as a transpiration rate variation, was inhibited. After an anoxia time period not exceeding one hour, the light was turned off and normal air restored. The stomatal movement was no longer inhibited, and a transient increase in the transpiration rate, referred to here as the postillumination transpiration peak (PITP), was observed.