Enhancement of peroxidase activity by stress-related chemicals in sweet potato

Stress-related plant hormones, abscisic acid (ABA, 0.5 mg l-1) or ethephon (0.5 ml l-1, an ethylene generating compound), enhanced peroxidase (POD) activity by ca 50% in suspension cultures of sweet potato (Ipomoea batatas), depending on the time after treatment when added to medium at the late logarithmic growth phase. Calcium chloride (50 mM) also increased POD activity by ca 20%, whereas paraquat (1 mg l-1) slightly stimulated it soon after treatment, but inhibited it after 13 days. ABA was the most effective in causing increased POD activity, i.e. 11 247 units g-1 dry cell wt (substrate, pyrogallol) 18 days after treatment, which was 1.78 times higher than a normal culture. However, the four chemicals used had no effect on the level of extracellular POD, which was maintained at 5-10% of total POD activity regardless of chemical treatment.ope