The extensin multigene family responds differentially to superoxide or hydrogen peroxide in tomato cell cultures

Changes in extensin gene expression were examined in cultured tomato cells following treatments leading to the production of activated oxygen species. Digitonin, a steroid glycoalkaloid compound, has been shown to trigger a r apid and transient production of superoxide anion, O-2(-.). 6 h after appli cation of 50 or 100 mu M Of digitonin, the accumulation of four extensin tr anscripts (1.5, 2.6, 4.0 and 6.1 lib) was observed. Superoxide dismutase st rongly inhibited the digitonin-mediated response, suggesting a key role of O-2(-.) in the signalling cascade. Furthermore, cells treated with enzymati cally produced O-2(-.) generated by xanthine oxidase (0.015 U/ml) gave a si milar extensin response and again, SOD exerted a strong inhibitory effect o n the response. On the other hand, H2O2 (2 mM) or the enzymatic H2O2 genera tor, glucose oxidase (0.34 U/ml), elicited the accumulation of only three o f the four transcripts (1.5, 2.6 and 4.0 kb), indicating that the correspon ding genes could be regulated either by H2O2 or O-2(-.) but that the gene e ncoding the 6.1 kb transcript was exclusively expressed in response to O-2( -.) Finally, it was shown that lipid peroxidation, which was only induced w hen cells were exposed to H2O2, did not participate in the AOS-mediated gen e expression for extensin, It can be concluded from these results that toma to cells are able to discriminate H2O2 from O-2(-.) and they probably sense the latter by the specific oxidation of an extracellular component. (C) 19 99 Federation of European Biochemical Societies.