SEPARATION OF DIRECT AND INDIRECT RESPONSES OF STOMATA TO LIGHT - RESULTS FROM A LEAF INVERSION EXPERIMENT AT CONSTANT INTERCELLULAR CO2 MOLAR FRACTION

Previous work has shown that stomata respond directly to light, but it was not clear whether the only additional response is through CO2, or whether some other metabolite is involved in this response. Gas excha nge experiments were done with normally positioned and inverted leaves of Hedera helix to investigate this problem. The macroscopic optical properties of the leaves and their anatomical structure were also stud ied. These experiments showed that there is no need to postulate the e xistence of a messenger other than CO2 to explain the indirect respons e of stomata to light. The experiments also showed that leaf inversion affects both stomatal conductance and photosynthesis, and highlight t he difficulties involved in the interpretation of the effect of leaf i nversion on stomata when stomatal conductance measurements are not don e concurrently with measurements Of CO2 flux density and intercellular CO2 molar fraction.