Résumé:
In this study, the effect of abscisic acid (ABA; 150 mu mol) or epibrassinolide (EBL, 3 mu mol) in mitigating the adverse drought conditions was evaluated in tomato plants (Solanum lycopersicum L. cv. Vilma). Potted plants were subjected to two 6-day periods separated by a one-time rehydration. Results showed that water deficit increased the content of superoxide radical (O2 center dot-), malondialdehyde (MDA), proline, ABA and its metabolites. On the other hand, the studied cytokinins showed a rather opposite trend. ABA application maintained and later reduced the O2 center dot- content. At the same time, the MDA level was lower but later increased, while the proline content was reduced compared to untreated plants. This indicates that ABA helps the plants cope with the initial stress phase. In addition, ABA-activated signalling pathways showed increased levels of ABA, auxins, salicylic acid or jasmonic acid. EBL even more increased O2 center dot- and proline content. At the same time, EBL increased the content of auxins, jasmonic acid and later ABA. In contrast, a decrease in salicylic acid and cytokinins was monitored. These findings indicate that ABA contributed to improved stress responses through early phytohormone-mediated signalling and reduction of stress markers, whereas EBL appeared less effective under our experimental conditions.
