Possible involvement of reactive oxygen species scavenging enzymes in desiccation sensitivity of Antiaris toxicaria seeds and axes.

The relationships among desiccation sensitivities of Antiaris toxicaria seeds and axes, changes in activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase, (DHAR), production rate of superoxide radical (.O(2) (-)), and the contents of hydrogen peroxide (H(2)O(2)) and thiobarbituric acid (TBA)-reactive substance were studied. Desiccation tolerance of seeds and axes decreased with dehydration. Desiccation tolerance of axes was higher than that of seeds, and that of epicotyls was higher than radicles. Activities of SOD, CAT and DHAR of seeds increased during the initial phase of dehydration, and then decreased with further dehydration, whereas activities of APX and GR decreased with dehydration. These five enzyme activities of axes, however, increased during the initial phase of dehydration, and then decreased with further dehydration. The rate of superoxide radical production, and the contents of H(2)O(2) and TBA-reactive products of seeds and axes gradually increased with dehydration. These results show that the A. toxicaria seed is a typical recalcitrant seed. Loss of desiccation tolerance in seeds and axes was correlated with the increase in .O(2) (-) production rate, content of H(2)O(2) and TBA-reactive products, and the decline of antioxidant enzyme activities of seeds and axes.