Chilling-induced Ca2+ overload enhances production of active oxygen species in maize (Zea mays L.) cultured cells:: the effect of abscisic acid treatment

Chilling (4 degreesC) induced a prolonged high level of intracellular Ca2+ (Ca2+ overload) and lipid peroxidation in maize (Zea mays L. cv Black Mexican Sweet) cultured cells. However, such Ca2+ overload and enhanced lipid peroxidation were not seen in abscisic acid (ABA)-treated cells, which had an improved chilling tolerance. A Ca2+ ionophore, A23187, caused Ca2+ overload in both ABA-treated maize cells and the untreated control, whereas an enhanced lipid peroxidation was detected only in the control. The high level of active oxygen species (AOS) in the control during chilling at VC could be reduced by the presence of lanthanum (La3+), a Ca2+ channel blocker, in the medium. Moreover, both the A23187-induced lipid peroxidation and AOS production in the control could be reduced by extracellular EGTA, a Ca2+ chelator. Laser-scanning confocal microscopy revealed that mitochondria were one of the major AOS sources under chilling and during A23187 treatment. In vitro assays showed that superoxide production in isolated maize mitochondria was enhanced by the presence of Ca2+. Findings suggest that chilling-induced Ca2+ influx in the control triggers a marked generation of AOS, which in turn results in the enhanced lipid peroxidation. The ability of ABA-treated cells to avoid the chilling-induced Ca2+ influx may serve as a mechanism that prevents the chilling-induced oxidative stress and thus results in less chilling injury.