Induction of shikimate dehydrogenase and peroxidase in pepper (Capsicum annuum L.) seedlings in response to copper stress and its relation to lignification

Pepper (Capsicum annuum L.) plants growing in a nutrient solution with excess copper, showed an increase in shikimate dehydrogenase (SKDH, EC 1.1.1.25) and peroxidase (EC 1.11.1.7) activities in the hypocotyl. In the roots, peroxidase was also induced, but SKDH activity per organ was depleted rather than enhanced. Copper stress caused stunting in the plants, reflected by a decrease in the fresh weight of all the organs. In the hypocotyl, the induction of both enzymatic activities was associated with the accumulation of soluble phenolics and lignin. The two SKDH isozymes present in the control hypocotyls (SKDH-3 and SKDH-4) increased in a similar proportion after copper stress. In the case of peroxidases, two new isozymes (PRX-A2 and PRX-A4) were detected in copper-stressed hypocotyls, and the other two isoperoxidases, PRX-B and PRX-A3, were enhanced c. 10 and three times, respectively, with respect to the control. The application of the chelator EDTA was able to counteract all the stress effects of the metal cited above. The role of these enzymes in phenolic metabolism under heavy metal stress is discussed. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.