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

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 degrees 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 3h 2 degrees 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 degrees 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.