Abstract
The DNA fragmentation is a characteristic phenomenon associated with PCD in animal cells (apoptosis), but the precise mechanisms and roles of plant PCD remain to be clarified. To investigate these points, we established the conditions that induced PCD and non-PCD that accompanied DNA fragmentation, and conducted a comparative analysis. Both cryptogein (proteinatious elicitor) and high concentration of nicotinamide (NA) induced cell death in cultured tobacco BY-2 cells. The cryptogein-induced cell death was PCD whereas NA-induced cell death was non-PCD, because de novo protein synthesis was necessary in the former but was not in the latter. However, the DNA fragmentation, resulting in DNA ladders with ca.180-bp intervals, was detected in both cell death processes. The nucleases involved in the cryptogein- and NA-induced DNA fragmentation exhibited different requirements for divalent cations; while nuclease activated during cryptogein-induced cell-death was Ca2+/Mg2+-dependent, the enzyme activated during NA-induced cell-death was Zn2+-dependent. Our results suggest that the DNA fragmentation is not specific to PCD, but the precise mechanisms are different between PCD and non-PCD.
