Two Steps of Gas Exchange in Leaf Photosynthesis

Publisher Website
Google Scholar
Abstract
Photosynthesis and transpiration of excised leaves of Taraxacum officinale L. and a few other species of plants were measured, using an open gas analysis system. The rates of CO2 uptake and transpiration increased in two steps upon illumination of stomata‐bearing epidermis of these leaves at a light intensity of 50 mW × cm−2. Abscisic acid inhibited only the second step of gas exchange. Illumination of the astomatous epidermis of hypostomatous leaves caused only the first step of gas exchange. These data indicate that the first and second steps arise from cuticular and stomatal gas exchange, respectively. The rate of the cuticular photosynthesis in a Taraxacum leaf reached saturation at a light intensity of 5 mW × cm−2, and the rates of the stomatal photosynthesis and transpiration reached saturation at a higher intensity of 35 mW × cm−2. The cuticular photosynthesis of a Taraxacum leaf was 18% of the stomatal photosynthesis at 50 mW × cm−2 and 270% at 5 mW × cm−2. The other species of leaves showed the same trend. The importance of cuticular CO2 uptake in leaf photosynthesis, especially under low light intensity was stressed from these data.
Keywords