Abstract
The temperature is one of the key environmental factors surrounding the living organisms in nature. In plant cells, transient increase in cytosolic Ca^<2+> concentration ([Ca^<2+>]_c) occurs as a response to an acute temperature change. Such a rise in [Ca^<2+>]_c reportedly leads to cold acclimatization. Here, we examined the effect of the temperature- shifts from ambient to the lower or higher temperatures, on induction of [Ca^<2+>]_c increases, using suspension-cultured plant cell lines expressing aequorin, a luminescent [Ca^<2+>]_c-reporter. The cultures used here include three tobacco (Nicotiana tabacum L.) cell lines, namely BY-2, Bel-W3 (O_3-sensitive) and Bel-B (O_3-tolerant), and rice (Oryza sativa L., cv. Nipponbare) AQ7 cells. Generally, rice cells and tobacco cells behaved similarly. The levels of [Ca^<2+>]_c spikes induced by cold shock were much greater than those induced by heat shock in all cell lines tested. Effects of inhibitors suggested that the cold shock-induced [Ca^<2+>]_c spike requires the uptake of extracellular Ca^<2+> via plasma membrane Ca^<2+> channels, while the heat shock response might be due to channel-independent leakages of extracellular and organelle Ca^<2+> into cytoplasm.
