Regulation of calcium influx, free radical production and alternative pathway activity is associated with abscisic acid-improved chilling tolerance in maize (Zea mays L.) cultured cells

Using an antimonate precipitation technique, fluorescence dye staining, and a 45Ca2+ uptake assay, it was demonstrated that abscisic acid (ABA) treatment at 26°C for 24 h prevented maize ( Zea mays L. Black Mexican Sweet) suspension-cultured cells from the chilling (4°C)-induced Ca2+ influx and overload. Typical ultrastructural characteristics of programmed cell death were observed in the untreated cultured cells during a 10-d chilling exposure. Ultrastructural changes occurred in maize cultured cells after ABA treatment at 26°C were similar to those observed in plants during cold acclimation.; Chilling enhanced both active oxygen species (AOS) production and lipid peroxidation in the control. However, such enhancements were significantly reduced in the ABA-treated cultured cells. Mitochondria served as a major site of AOS production under chilling in maize cultured cells. The improved chilling tolerance in the ABA-treated maize cultured cells is likely due, in part, to the cell's ability to avoid the chilling-induced Ca2+ influx and overload, which in turn protects cells from the Ca2+-mediated oxidative stress and injury.; The improved chilling tolerance by ABA was also associated with a higher activity of the cyanide-resistant alternative pathway. A positive correlation was found between the higher activity and an increased amount of alternative oxidase in mitochondria of the ABA-treated cells. Results indicated that the alternative pathway plays a significant role in lowering AOS production at warm temperatures, but not at severe chilling temperatures, e.g., 4°C. It is suggested that the higher alternative pathway activity in ABA-treated cells provides a better protection strategy against chilling-induced injurious oxidative stress at the beginning of a chilling stress and/or during recovery from chilling, and thus resulting in improved chilling tolerance.