Endogenous Diurnal and Nocturnal Activity of Guard Cells as Indicated by Stomatal Aperture and Protoplasmic Streaming

The hourly stomatal apertures on epidermal strips of Antirrhinum majus, Rheum rhaponticum, Vicia faba, and Zebrina pendula fixed by Lloyd's technique were compared with the number of stomata found to contain streaming at the same time. With all four species there was an indication of an endogenously controlled rhythm in stomatal opening with both increases and decreases in aperture and streaming during daytime hours in either the light or dark. A similar endogenously activated rhythm was also found at night in Rheum and Vicia. Some relationships exist between changes in stomatal aperture and streaming. Streaming in guard cells may only be a byproduct of metabolism, but as such, it serves the useful purpose as a mixer of chemical activity.