The Regulation of Stomatal Aperture in Tobacco Leaf Epidermal Strips III. The Effect of Atp

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Abstract
The addition of ATP in the light and dark and ADP in the light to bathing solutions containing K+ can stimulate stomatal opening in tobacco leaf epidermal strips. UTP or AMP do not stimulate opening in the light or dark. The presence of ouabain prevents ATP or ADP stimulating stomatal opening. The additions of Ca2+ and Mg2+, though they reduce stomatal aperture, do not prevent ATP stimulating stomatal opening. Increasing the concentration of ATP presented to the stomata in the dark increases the aperture. The rate of stomatal opening in the presence of ATP is increased in the light. In bathing solutions which contain Na+ as the only cation ATP neither initiates nor maintains stomatal opening. The results are discussed in relation to a postulated light-stimulated, ATPase-mediated accumulation ofK+ in the guard cells which is followed by an influx of water, osmotic swelling, and stomatal opening

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