EARLY STAGES OF THE APOPTOTIC PATHWAY IN PLANT-CELLS ARE REVERSIBLE

Chromatin condensation and nDNA fragmentation, indicators of apoptosis in mammalian cells, occur in plant cells during senescence and follow ing induction by chemical agents. In Nicotiana plumbaginifolia cells, camptothecin, okadaic acid, salicylic acid, hydrogen peroxide, and the calcium ionophore A23187 induced chromatin condensation and nDNA frag mentation. Exposure of cells to low concentrations or removal of the c hemical agent resulted in an initial phase of chromatin condensation, followed by its reversal. A further feature of apoptosis in mammalian cells, annexin V binding, indicative of phosphotidylserine exposure, w as also confirmed in relation to the other events in the apoptotic pat hway. With respect to flow cytometric characteristics, apoptosis trigg ered by a variety of chemicals occurs in plant cells in a manner close ly related to that in mammalian cells. However, the extent of chromati n condensation is substantially greater, and in the early stages is re versible.