Characterization of a leaf-type catalase in sweet potato (Ipomoea batatas Lam. (L.))

In this report a major sweet potato catalase was detected and identified from fully-expanded mature leaves using an in-gel activity staining assay with native- and SDS-PAGEs. The catalase activity was optimal from pH 8 to 12, and was repressed by beta-mercaptoethanol and a catalase inhibitor 3-amino-1,2,4-triazole. However, catalase activity was much less affected by temperature within the range of 5 to 45 degrees C. Temporal and spatial expression demonstrated that it was specifically detected in leaves, but not in roots and stems. Its activity increased from the immature L2 leaves, reached the maximum in the fully-expanded mature L3 leaves, slightly decreased in the partly-yellowing senescent L4 leaves, and was almost undetectable in, the completely yellow L5 leaves, which were similar to the folded and unopened immature L1 leaves. The catalase levels approximately inversely correlated with the H2O2 amounts in leaves of different developmental stages. Dark and ethephon, an ethylene-releasing compound, also enhanced catalase activities from 6 h to 24 h, however, the enhanced activity decreased from 24 h to 48 h in detached leaves after treatment. The catalase levels also approximately inversely correlated with the H2O2 amounts in treated leaves. These data suggest a possible role for sweet potato catalase in coping with H2O2 scavenging in leaves. Based on these data we conclude that a major leaf-type catalase is identified in sweet potato leaves. Its activity level is maximal in mature leaves and becomes significantly lower in natural and in induced senescent leaves. The leaf-type sweet potato catalase likely functions in H2O2 removal in leaves.