Cytochemical Localization of Calcium and Ca2+-ATPase Activity in Plant Cells under Chilling Stress: a Comparative Study between the Chilling-Sensitive Maize and the Chilling-Insensitive Winter Wheat

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Abstract
Electron microscopic observations revealed that electron-dense antimonate Ca2+ deposits were mostly localized in the vacuole and the intercellular space in both maize and winter wheat when their seedlings were grown at 25°C. The reaction products—cerium phosphate deposits of Ca2+- ATPase activity were mainly seen at the cytoplasmic side of the plasma membrane. Few cerium phosphate deposits also were observed on the nuclear envelope. In both species, after 1 or 3 h 2°C chilling, antimonate Ca2+ deposits increased in the cytosol and the nucleus, but cerium phosphate deposits showed no visible difference compared to their corresponding 25°C seedlings. After 12, 24, or 72 h chilling, maize seedlings still maintained a high level of antimonate Ca2+ deposits in the cytosol and the nucleus. During these periods, maize Ca2+-ATPase, as indicated by the number of cerium phosphate deposits, became less and less active as chilling proceeded. In winter wheat, the increased cytosolic and nuclear antimonate Ca2+ deposits were restored to a low resting level after 12, 24, or 72 h chilling, while the Ca2+-ATPase was maintained active, contrary to maize scenario. The transient cytosolic and nuclear Ca2+ increase and the activities of Ca2+-ATPase during chilling are discussed in relation to plant chilling injury and cold acclimation.

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