Oxygen‐dependent stomatal opening in Zea mays leaves. Effect of Light and carbon dioxide

The oxygen requirement for stomatal opening in maize plants ( Zea mays L. hybrid INRA 508) was studied at different CO 2 concentrations and light intensities. In the absence of CO 2 , stomatal opening always required O 2 , but this requirement decreased with increasing light intensity. In darkness, the lowest O 2 partial pressure needed to obtain a weak stomatal movement was about 50 Pa. This value was lowered to ca 10 Pa in light (320 μmol m −2 s −1 ). On the other hand. in the absence of O 2 , CO 2 enabled stomatal opening to occur in the light, presumably due to the evolved photosynthetic O 2 . Thus, CO 2 , which generally reduced stomatal aperture, could induce stomatal movement in anoxia and light. The effect of CO 2 on stomatal opening was closely dependent on O 2 concentration and light intensity. Stomatal aperture appeared CO 2 ‐independent at an O 2 partial pressure which was dependent on light intensity and was about 25 Pa at 320 umol m −2 s −1 . The presence of a plasmalemma oxidase, in addition to mitochondrial oxidase, might explain the differences in the O 2 requirement at various light intensities. The possible involvement of such a system in relation to the effect of CO 2 is discussed.