Journal
JOURNAL OF PLANT PHYSIOLOGY
Volume 165, Issue 11, Pages 1134-1141Publisher
ELSEVIER GMBH, URBAN & FISCHER VERLAG
DOI: 10.1016/j.jplph.2007.12.008
Keywords
DNA laddering; endonuclease; Oryza sativa; programmed cell death; salt stress
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death (PCD) both in animals and plants. However, the mechanism of DNA laddering varies in different species, even in different tissues of one organism. In the present study, we used root tip cells of rice, which have been induced by NaCl stress to undergo PCD, to analyze the endonuclease activities of cytoplasmic and nuclear extracts. Two endonucleases, a cytoplasmic of 20 kDa (OsCyt20) and a nuclear of 37 kDa (OsNuc37), were identified as PCD related. Our results indicated that OsCyt20 is a Ca(2+)/Mg(2+)-dependent nuclease, which is most active at neutral pH, and that OsNuc37 is Zn(2+)-dependent, with a pH optimum of 4.5-6. Both nucleases were induced at the early stage of PCD (2h salt treatment) and exhibited the highest activity approximately 4 h after exposure to NaCl, paralleling with the occurrence of DNA laddering. In vitro assays of endonuclease activities further revealed that OsNuc37, a gtycoprotein localized in the nucleus, is the executor for DNA laddering. The different effects of both endonucleases on DNA degradation during salt-induced PCD are discussed. (c) 2008 Elsevier GrnbH. All rights reserved.
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