Studies on the mechanisms of ozone tolerance: Cytokinin-like activity of N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N'-phenylurea, a compound protecting against ozone injury

The cytokinin-like activity of the growth regulating chemical EDU, N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N′-phenylurea, was determined and compared with the actitivity of kinetin using the tobacco callus bioassay. EDU has a pronounced stimulatory effect on callus growth at concentrations of 5 × 10−4 and 1 × 10−3M but was 5 000 times less potent than the synthetic cytokinin, kinetin. Senescence regulation and oxidant resistance induced by EDU and kinetin were also studied. EDU retarded the breakdown of chlorophyll, protein and RNA in 03-sensitive tobacco leaf discs during senescence. EDU was much more effective in arresting senescence and in protecting against 03 injury than kinetin. Results indicate the EDU-induced plant tolerance to 03 phytotoxicity may be indirect through enzyme induction regulation.