Modulation of phospholipase D and lipoxygenase activities during chilling. Relation to chilling tolerance of maize seedlings

Phospholipase D (phosphatidylcholine choline hydrolase, EC 3.1.4.4) and lipoxygenase activities (linoleate: oxygen oxidoreductase, EC 1.13.11.12) were analysed in chilling-susceptible and chilling-tolerant maize (Zea mays L.) seedlings in relation to their chilling tolerance. Before chilling, phospholipase D activity in the leaf microsomal fraction was 2-fold higher in the chilling-susceptible CO 316 when compared to that of paclobutrazol-treated, chilling-tolerant CO 316. Phospholipase D activity in the heavy membrane fraction comprising chloroplast and mitochondria showed a 3 to 4-fold increase during chilling and post-chilling periods, albeit with temporal variations. An increase in cytosolic phospholipase D activity was observed only in CO 316 and CO 328. Also, phospholipase D activity in the heavy membrane and cytosolic fractions of roots increased in CO 316 during chilling and post-chilling periods. Lipoxygenase activity was low in both leaves and roots of CO 328. Paclobutrazol treatment of CO 316 did not appear to affect the level of cytosolic lipoxygenase activity in roots during the early part of chilling and post-chilling, but increased the activity in leaves. The results suggest that during chilling and post-chilling periods, temporal variations in phospholipase D and lipoxygenase activities in both leaves and roots of CO 316, CO 316P and CO 328 could result in differential metabolism of phospholipids. Enhanced degradation coupled with low levels of turnover could lead to development of chilling injury in the tissue.