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Ultraviolet-Stimulated KHCO₃ Efflux from Rose Cells

Regulation of Cytoplasmic pH

Department of Botany, University of California, Davis, California 95616, Nuclear Magnetic Resonance Facility, University of California, Davis, California 95616, Plant Growth Laboratory, University of California, Davis, California 95616

Suspension-cultured cells of Rosa damascena that have been irradiated with ultraviolet light (254 nanometers, 2.1 x 10⁴ joules per square meter) rapidly lose K⁺ and HCO₃^– ions to the medium. If the HCO₃^– is derived from respiratory CO₂ inside the cell, then loss of HCO₃^– should be accompanied by an acidification of the cytoplasm. Estimates of the pH of control and ultraviolet-irradiated cells by ³¹P-nuclear magnetic resonance spectroscopy indicated that, following irradiation, the pH of both cytoplasm and vacuole dropped by 0.2 to 0.3 units. This change was not as great as was predicted from the observed HCO₃^– loss. Analysis of nitrogenous compounds in the cell suggested that reduction of nitrate and synthesis of -aminobutyric acid absorbed some of the protons formed by the synthesis and dissociation of bicarbonate.