Ca2+ Signal Transduction Related to Neutral Lipid Synthesis in an Oil-Producing Green Alga Chlorella sp C2

Changes in the cytosolic Ca2+ levels and the role of Ca2+ signal transduction in neutral lipid synthesis in Chlorella sp. C2 under nitrogen starvation conditions were investigated. The results detected by using the scanning ion-selective electrode technique demonstrate that nitrogen starvation induced significant Ca2+ influx across the plasma membrane into cells. Ca2+ fluorescence imaging and flow cytometry were used to estimate the effect of this Ca2+ influx on the generation of the Ca2+ signal, and the results showed that the cytosolic Ca2+ concentration increased transiently and then remained at a stable, high level when the cells were exposed to nitrogen starvation. However, the increase could be inhibited by pre-treatment with the Ca2+ channel blockers ruthenium red, verapamil and GdCl3, indicating that both the influx of Ca2+ from the extracellular space via Ca2+ channels that are localized in the plasma membrane and the release of Ca2+ from intracellular calcium storage via the internal calcium store were required for the generation and transduction of the Ca2+ signal. During nitrogen starvation, neutral lipid synthesis in Chlorella sp. C2 in response to stress conditions was also inhibited to differing degrees by pre-treatment with the three Ca2+ channel blockers, demonstrating the regulation of Ca2+ via these Ca2+ channels in neutral lipid synthesis. The results suggested that by transduction of extracellular stress signals into the cell and the regulation of the Ca2+ signal in neutral lipid synthesis, Ca2+ signal transduction played important roles in the response mechanism of Chlorella sp. C2 to nitrogen starvation.