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Effects of -Hydroxy-2-Pyridinemethanesulfonic Acid on Photosynthetic Carbon Dioxide Uptake and Stomatal Movements in Excised Tomato Leaves

Department of Biology, University of Isfahan, Isfahan, Iran

The effects of 10^–2M -hydroxy-2-pyridinemethanesulfonic acid (HPMS) on the CO₂ compensation point, photosynthetic CO₂ uptake, CO₂ evolution into CO₂-free air in light, and stomatal movement, in excised tomato leaves (Lycopersicon esculentum Mill. Eurocross BB-F₁ Hybrid) were studied. It was found that -HPMS had a transient lowering effect on the CO₂ compensation point of treated leaves within the first 5 minutes of application. The net photosynthetic CO₂ uptake was inhibited by -HPMS treatment. The inhibition increased with time and was enhanced in an O₂-free atmosphere. The CO₂ evolution into CO₂-free air in light was inhibited by -HPMS. The inhibition was O₂-dependent because the effect was observed only in 21% O₂ but not in O₂-free N₂. Stomatal apertures were affected by -HPMS, but the effect was transient and was observed 15 to 30 minutes after the application. The time course of this closure did not account for the observed inhibition of net CO₂ uptake.