LIPOXYGENASES IN DEVELOPING ZEA-MAYS KERNELS

In Zea mays kernels, lipoxygenase (LOX, linoleate: oxygen oxidoreductase, EC 1.13.11.12) activities exhibit three distinct optima at pH 6.8, 5.5, and 7. 75. Only the pH 6.8 LOX activity increases in the presence of 10 mM calcium ion and accounts for the majority of the LOX activity found in the embryo. Both pH 6.8 and 7. 75 activities are higher with linoleic acid than with linolenic acid, and both are inhibited > 75% with 10 mM monophenyl butazone (MPB). The pH 5.5 LOX activity is more active with linolenic acid than with linoleic acid and is stimulated by MPB. The separate LOX activities were followed through seed development by measuring LOX activity at each pH. The total and specific activities of LOX were generally higher in the embryo than endosperm tissues throughout kernel development. The increase in LOX activity in the embryo 14 days after pollination coincides with the developmental stage when abscisic acid is most effective in reversing vivipary.