Antisenescence Effect of 2-pyridylureas with Un- and Cyclic- Ureido Group

The potential antisenescence effect of eight synthetic urea compounds was investigated in excised barley (Hordeum vulgare L.) leaves which were induced to senesce by incubation in complete darkness. The compounds having uncyclic ureido group showed higher chlorophyll retention activity than those with cyclic ureido group. Compounds 1, 6 and 4PU had long-term protecting effects on chlorophyll degradation whereas the effects of compounds 2 and 5 were short-term. These effects were mediated by increased H 2 O 2-scavenging enzyme activities. The chlorophyll retention activity of the more active compounds (1, 2, 5, 6, 8) was lower compared to the standard 4PU at the end of the third aging day. Treatment of leaf segments with compounds 1 and 8 resulted in an increased carotenoids content after 48 h. In addition, it was higher compared to the 4PU-treated leaf tissues. Our results provide information about the relationship between the antisenescence effect of synthetic urea compounds and the activity of some antioxidative enzymes. We suggest that the activities of the antioxidative enzymes as well as the balance between H 2 O 2-generating and H 2 O 2-scavenging enzymes are important parameters that could provide evidence about the senescence-retarding effect of the tested compounds. The structure-activity relationships for the screened compounds was also studied. The presence of unsubstituted 2-pyridyl ring and of 5-chloro-or (3,5-dichloro)-2-pyridyl ring contributed to the higher activity of the tested compounds.