RELATIONSHIP BETWEEN PROLINE AND ABSCISIC-ACID IN THE INDUCTION OF CHILLING TOLERANCE IN MAIZE SUSPENSION-CULTURED CELLS

Both proline and abscisic acid (ABA) induce chilling tolerance in chil ling-sensitive plants. However, the relationship between proline and A BA in the induction of chilling tolerance in unclear. We compared the time course of the increase in chilling tolerance induced by proline a nd ABA, and the time course of the uptake of both into the cultured ce lls of maize (Zea mays L. cv Black Mexican Sweet) at 28-degrees-C. The plateau of proline-induced chilling tolerance preceded by 12 h the pl ateau of ABA-induced chilling tolerance. The uptake of exogenous ABA i nto the cells reached a plateau in 1 h, whereas the uptake of exogenou s proline gradually increased throughout the 24-h culture period. Alth ough the proline content in ABA-treated cells was 2-fold higher than i n untreated cells at the end of the 24-h ABA treatment at 28-degrees-C , the correlation between the endogenous free proline content and the chilling tolerance in the ABA-treated cells was insignificant. Isobuty ric acid treatment, which resulted in a larger accumulation of proline in the cells than ABA treatment, did not increase chilling tolerance. The induction of chilling tolerance by proline and ABA appeared to be additive. Cycloheximide inhibited ABA-induced chilling tolerance, but it did not inhibit proline-induced chilling tolerance. Newly synthesi zed proteins accumulate in ABA-treated cells at 28-degrees-C while the chilling tolerance is developing (Z. Xin and P.H. Li [1993] Plant Phy siol 101: 277-284), but none of these proteins were observed in the pr oline-treated cells. Results suggest that proline and ABA induce chill ing tolerance in maize cultured cells by different mechanisms.