The changes of Ca2+ levels in young leaf cells of bromegrass under different controlled chilling temperatures were inves-tigated by an antimonite precipitation cytochemical method. The main results were as follows: under 25/20°C (day/night) tempera-ture and 14 h photoperiod, electron-dense Ca2+ antimonite precipitates, indicators of Ca2+ localization, were mainly localized in the vacuoles, cell walls and intercellular spaces; few Ca2+ deposits were observed in the cytosol and nuclei. After a 3°C chilling treatment for 3 h, many Ca2+ precipitates appeared in the cytosol and nuclei, indicating that Ca2+ influx had occurred in the cytosol and nuclei. When the 3°C treatment was prolonged to 8 h, more Ca2+ deposits appeared in the nuclei and cytosol, but the amount of Ca2+ depos-its in both the cytosol and nuclei decreased markedly after a 24 h treatment and most Ca2+ deposits were returned to the vacuoles and intercellular spaces after an 8 d treatment. When bromegrass was exposed to 7°C for 3 h, the Ca2+ distribution in the cells had no visible changes, compared with that of the 25/20°C grown control plants. However, when the chilling treatment of 7°C was pro- longed to 8 h, a Ca2+ influx occurred, where many Ca2+ deposits were observed in the nuclei and cytosol. More Ca2+ deposits ap- peared in the nuclei and cytosol after a 24 h treatment, but the amount of Ca2+ deposits in the cytosol and nuclei was reduced mark-edly after an 8 d treatment. After a 14 d treatment, the remaining low level of Ca2+ was recovered in both the cytosol and nuclei and the Ca2+ deposits were again located in the vacuoles and the intercellular spaces. The dynamics of subcellular Ca2+ localization in young leaf cells of bromegrass during a 12°C chilling treatment were similar to those of the 7°C treatment. Besides, the results showed that the frost tolerance of bromegrass exposed to 3°C for 8 d increased by 6°C, for 7°C and 8 d by 4°C and for 12°C and 14 d by 3°C, compared with the controls. Finally, the relationship between d
