Influence of light conditions on development, apoplastic peroxidase activities and peroxidase isoenzymes in chicory root explants

Cichorium intybus L. (cv. Bea) root explants grown in continuous light had a higher fresh weight, lignin and chlorophyll content than explants grown i n darkness, Intermediary values were found when the light conditions were s witched after 6 days. Peroxidase activities (EC 1.11.1.7) were measured in the apoplastic fluid with guaiacol, indoleacetic acid (IAA) and syringaldaz ine as substrates. There was an inverse relationship between specific IAA o xidase activity acid explant growth. Specific syringaldazine oxidase activi ty (SSO) correlated with the lignin content. Analysis by isoelectric focusi ng (IEF) showed that the apoplastic fluid contained both cationic and anion ic peroxidase isoforms, whose expression differed according to culture cond itions. Isoform isoelectric point (pI) 7.0 was only detectable when the exp lants were cultured for 12 days in darkness. When explants were grown for t he first 6 days in light, SSO and lignin content were high and the isoforms pI 4.0, 6.6, 7.6 and 8.1 were highly expressed. Conversely, when the first 6 days were in darkness, specific IAA oxidase activity was high and the is oforms pI 4.5, 6.7 and 6.8, were most strongly expressed. The isoperoxidase s pI 7.8 and 7.9 were strongly expressed when the explants were cultured fo r at least 6 days in darkness.