Stomatal Opening in Light of Different Wavelengths: Effects of Blue Light Independent of Carbon Dioxide Concentration

Abstract

Stomatal opening in Xanthium pennsylvanicum was found to be significantly greater in blue light than in red. Experiments in which leaves were placed in a closed system and allowed to establish their own steady-state carbon dioxide concentration showed that when the CO₂ concentration was about the same as that in red, opening was much greater in blue light. Blue light of low intensity could cause as great an opening as red of higher intensity, even though the CO₂ concentration was much higher in blue. Stomatal opening in light is considered as involving at least two reactions: (1) a response to the removal of CO₂ by photosynthesis; (2) a response to blue light not dependent on the removal of CO₂. Blue light became increasingly effective, relative to red, as the length of night was increased over the range 2 to 14 hours. This might, in part, explain previously observed effects of night length on rate of opening in light. The initial very rapid phase of closure in darkness appeared to be independent of CO₂ accumulation, for it was not prevented by flushing the intercellular spaces with air free of CO₂. It is suggested that closure in darkness, like opening in light, should be considered as involving components both dependent upon, and independent of, CO₂ concentration.