Abstract:The changes of Ca2+ localization in ceils of rice (Oryza sativa L. ) seedlings under chilling stress were investigated with calcium antimonate precipitate-electromicroscopic-cyto- chemical methods. When rice seedlings grew at the optimum temperature, it was shown that the deposits of calcium antimonate, being the indicator for Ca2+ localization, mainly concen-trated within the vacuoles and intercellular spaces, and that there was also some Caz+ deposits in plastid, mitochondria, cytoplasm and nucleus. This indicates that under the normal condition, the vacuoles are the main pool of Ca2+ in plant cells, and that there is quite an amount of Ca2+ in the intercellular spaces. On the contrary, the free Ca2+ in cytoplasm and nucleus is very low under the normal condition. When the rice seedlings were treated at the temperature of 1 ℃ for 24 h, there nearly appeared a ring of well arranged Ca2+ precipitates in the inner side of plasmalemma. Meanwhile, the level of Ca2+ in cytoplasm and nucleus increased considerably. When the chilling stress of 1 ℃ continued for 48 h, a great amount of Ca2+ distributed within the cytoplasm and nucleus, and there was also a large quantity of Ca2+ deposits on vacuolar membranes and envelope of plastid. However, the ultrastructures of the cells remained normal. Based on the above observations, the authors proposed that the increase of Ca2+ in cytoplasm and nucleus under chilling stress might be related to the ulterior changes of physiological-biochemical processes.