• Stomata;
  • guard ceils;
  • CO2;
  • temperature;
  • Vicia faba


One of the least understood areas in guard cell movements remains the effect of CO2, particularly its effect on isolated guard cells. In this study the reactions of guard cells in both isolated epidermal strips and intact leaf sections from Vicia faba have been observed in a variety of temperatures and CO2 concentrations in both light and darkness. The results are consistent with the hypothesis that stomatal aperture in the isolated guard cell is the result of two temperature-dependent systems. A decrease in aperture consistently observed at 30 to 35°C in the light reflects the transition from one system to the other. The low temperature system appears consistent with the chemiosmotic hypothesis of phosphoenolpyruvate carboxylase regulation of malate. It demonstrates some sensitivity to CO2 between 25 and 35 °C, resulting in a shift in optimum aperture to slightly higher temperatures. The high temperature system shows no apparent sensitivity to CO2. Stomata from intact leaf sections showed a considerable decrease in aperture as the CO2 concentration increased from 0 to 60 μl 1−1. The stomatal response threshold to CO2 appears to be at least as low as 60μ1 1−1 and centred in the mesophyll tissue. All observable CO2 responses in both strips and leaf sections disappeared at temperatures in excess of 35 °C in the light.