Characterization of phospholipase D from Chorispora bungeana callus in response to freezing stress

The influence of freezing on phospholipase D (PLD) was studied in Chorispora bungeana Fisch. & C.A. Mey., which is a naturally cold-tolerant species. During the freezing treatment (-4 A degrees C), PLD activities in both microsomal and mitochondrial membranes increased at day 3, remained at a high level at day 6 and then declined to a moderate level. The RT-PCR analyses showed that PLD activity partially corresponded to the CbPLD gene transcript level. The freezing treatment resulted in increases in the K (m) and V (max) for microsomal and mitochondrial PLD, respectively. Freezing injury, as measured by electrolyte leakage and malondialdehyde content, peaked at day 6 and then gradually decreased. Alleviation of freezing injury was related to a decreased content of membrane-associated Ca2+. We suggest that the specific mechanism of cold resistance of C. bungeana is linked with PLD.