Changes in phenolic metabolism in salicylic acid-treated shoots of Cistus heterophyllus

The exogenous application of salicylic acid (SA) not only protects plants against stress, but also enhances their growth and productivity. In this study, proliferating shoots of Cistus heterophyllus subsp. carthaginensis, an endangered plant species, were incubated in the presence of 0, 10, 100, and 1,000 ¿M SA for a period of 2 months. Overall growth, phenylpropanoid metabolism and antioxidant capacity were then determined. At low SA concentration, the efficiency of photosystem II (PSII) and shoot growth remained stable, while chlorophyll and carotenoid levels increased. Furthermore, there were no major changes in the levels of H2O2 in the different treatments (less than 10 % compared with the control), but an increase in lipid peroxidation, proline content and free and bound SA concentrations was observed in 100 ¿M SA-treated shoots. SA treatments resulted in increased activities of phenylalanine ammonia lyase (EC 4.3.1.24) and soluble peroxidases (EC 1.11.1.7), which strongly correlated with the decrease in soluble flavanols and the increase of proanthocyanidins, whereas cell wall-bound peroxidases exhibited a SA-concentration-dependent down-regulation. The results provided evidence that the differences in SA-induced changes in phenolic metabolism, especially the oxidation of flavanols by soluble peroxidases, could serve as a backup defence system contributing to a reduction in oxidative cellular damage, as suggested by the high anti-lipid oxidation activity displayed by Cistus extracts. © 2013 Springer Science+Business Media Dordrecht.