Senescence of rice leaves level and polyamine XXIX. Ethylene production, polyamine biosynthetic enzyme activity during senescence

Changes of ethylene production, polyamine level and activities of enzymes related to polyaminc biosynthesis during scncsccncc o1 intact leaves of rice (Oryza sativa L.) seedlings were investigated. Ethylene production decreased markedly at thc carly stagc of senescence, but increased slightly at the later stage. Putrescine. spermidine and spermine, but not cadavcrinc and diaminopropanc. were present in rice leaves throughout senescence. The sperminc level decreased progressivcly with incrcasing agc. Thc putrcscinc and spermidine levels as well as arginine decarboxylase activity decreased at the early stage of senescence and increased at the later stage. The increase of ornithine decarboxylase and S-adenosylmethionine decarboxylase activities occurred at the time when Icavcs wcrc fully expanded and at an advanced stage of senescence. These data seem to support the view that polyamincs play an important rolc in the regulation of rice senescence. Results also suggest that endogenous polyamine levels and ethylene production may not bc interrelated during senescence of rice leaves.