Further support for the involvement of phytoehrome in stomatal movement

The involvement of phytochrome in stomatal movement in Commelina communis L. is indicated by the following observations: 1) Short irradiation with red or blue light causes opening, of isolated stomata and swelling of guard cell protoplasts. This is reversed by subsequent far red irradiation. 2) In a similar way, stomatal response to prolonged irradiation with red or blue light is decreased by concomitant far red irradiation. 3) Pretreatment with filipin, which interferes with phytochrome binding to membranes, decreases stomatal opening in red and blue light. The stomatal responses to blue and red light are modified by DCMU, N₂, CO_2‐enriched atmosphere, and CO_2‐free air, which are known to affect, among other processes, chlorophyll fluorescence. Increased chlorophyll fluorescence by DCMU, N₂ and CO₂‐enriched atmosphere enhanced stomatal opening in blue light and inhibited it in red light. CO₂‐free air, which decreases chlorophyll fluorescence, had the opposite effect.