Abstract
Leaves of some Gesneriaceae species often become brown when they are exposed to a rapid decrease in temperature by irrigation of cold water. In a damaged leaf, its epidermal and spongy cells do not change, while palisade cells shrink and die at last under microscopic observation. We previously reported that, in palisade cells of African violet (Saintpaulia) leaf, the pH in cytoplasm decreased and the pH in vacuole increased soon after the temperature decrease. In this study, we revealed that cellular pH also changed in palisade cells of Gesneriaceae leaves as observed in Saintpaulia after the temperature decrease. These changes of pH in palisade cells suggested possible changes of vacuolar membrane. We visualized the vacuolar membrane with a fluorescence dye to estimate the changes of vacuole directly. The vacuolar structure in palisade cells was dynamically changed after the temperature decrease. These results suggest that the changes in cellular pH are resulted from changes in permeability of the vacuolar membrane. Temperature-dependent structural change in the vacuolar membrane might be a general mechanism that triggers the cell injury in Gesneriaceae leaves.
