Abstract
The presence of enzymes and substrates participating in H2O2-decomposing system (NADPH→glutathione→ascorbate→H2O2) found in chloroplasts, and superoxide dismutase (SOD) (EC 1.15.1.1) was confirmed in cultured tobacco cells. The specific activities of ascorbate peroxidase (AP), glutathione reductase (GR) (EC 1.6.4.2) and SOD were much higher in callus than in leaves, but catalase (EC 1.11.1.6) was not detected. Tobacco callus also had activities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and isocitrate reductase (EC 1.1.1.42), which supplied NADPH. When tobacco callus was illuminated, they became green. The contents of GR, glutathione, and ascorbate were higher in the light than in the dark, but no difference in AP and SOD could be detected between in the light and dark. By the test of Ouchterlony double immunodiffusion using anti-spinach AP and anti-spinach GR, it was confirmed that callus AP and GR had different structures from the leaf enzymes. These results show that callus has developed an active oxygen-decomposing system for overcoming the oxidative stress brought about by becoming callus.
